Optical properties and electron transfer in novel bis salicylimine diamino metallo-Schiff-base
compounds
by Jeffrey Rockefeller Wilcox
A thesis submitted in partial fulfillment of the requirement for the degree of Masters of science in
Chemistry
Montana State University
© Copyright by Jeffrey Rockefeller Wilcox (2002)
Abstract:
A family of bis salicylamine diamino metallo-Schiff-base compounds synthesized by Warren Miller
was spectroscopically characterized. Excitation coefficients showed a strong dependence on metal
strength of donor substituted on the salicylamine, and presence of strong acceptors on the diamino
portion of the ligand. Fluorimetiy experiments were performed with an interferometer based
instrument.
[N, N ’, N”, N”’-tetra(4-diethylaminosalicylimine)-1,2,4,5 tetraaminobenzene]Zn(II) 2, a compound
containing both acceptor and donor moieties showed a bi-mechanistic electron transfer in solution with
C60. Photoinduced absorption through step-scan spectroscopy yields quantum efficiencies for the
solvated ions for both pathways of 21.6% and 21.5% respectively. A new kinetic treatment is shown
for separating these embedded signals of the two pathway s in order to obtain their efficiencies. OPTICAL PROPERTIES AND ELECTRON TRANSFER IN
NOVEL BIS SALICYLIMINE DIAMINO M ETALLO-SCHIFF-BASE
COM POUNDS
by
Jeffrey R ockefeller W ilcox
A th e s is su b m itte d in p a rtia l fu lfillm en t
o f th e r eq u ir em en t for th e d egree
of
M asters o f s c ie n c e
in
C h em istry
MONTANA STATE UNIVERSITY
B o zem a n , M o n ta n a
D e cem b er 2 0 0 2
f\J 3 - ^
yV If ^ ^
© COPYRIGHT
by
Jeffrey R ockefeller W ilcox
2002
All R igh ts R eserved
ii
APPROVAL
o f a th e s is s u b m itte d by
Jeffrey R ock efeller W ilcox
T h is t h e s is h a s b e e n read b y e a c h o f th e th e s is c o m m itte e a n d h a s
b e e n fo u n d to b e sa tisfa c to r y regard in g c o n te n t, E n g lish u s a g e , form at,
c ita tio n s, b ib lio g ra p h ic sty le, a n d c o n s is te n c y , a n d is rea d y for
s u b m is s io n to th e C ollege o f G ra d u a te S tu d ie s.
Dr. Lee S p a n g er
(Signature)
Dkte /
A pproved for Jdj.e D e p a r tm e n t o f C h em istry & B io c h e m istry
/?
Dr. P a u l G rieco
(SignattfZe)O T
D ate
A pproved for th e C ollege o f G rad u ate S tu d ie s
5
Dr. B ru ce M cLeo
(Signature)
D ate
iii
STATEMENT OF PERM ISSION TO U SE
In p r e se n tin g th is th e s is in P artial fu lfillm en t o f th e r eq u ir em en ts
for a m a s te r ’s d egree a t M o n ta n a S ta te U n iversity, I a g ree th a t th e
Library s h a ll m a k e it ava ila b le to borrow ers u n d e r r u le s o f th e library.
If I h a v e in d ic a te d m y in te n tio n to C opyright th is t h e s is by
in c lu d in g a co p y rig h t n o tice p age, co p y in g is allow ab le o n ly for sch o la rly
p u r p o s e s , c o n s is t e n t w ith “fair u s e ” a s p rescrib ed in th e U .S . C opyright
Law. R e q u e sts for p e r m issio n for e x te n d e d q u o ta tio n from or
r ep ro d u c tio n o f th is th e s is in w h o le or in p a rts m a y be g ra n ted o n ly by
th e co p y rig h t hold er.
S ig n a tu r e
D a te
[)SX *
‘
T h a n k s to m y fam ily for all th eir su p p o rt,
to J o n for s e e in g m e th ro u g h a tim e o f se p a ra tio n ,
a n d m y g ra n d m o th er for sh o w in g m e
h o w life s h o u ld be lived.
J effrey R ock efeller W ilcox w a s b o rn to p a r e n ts W en d y M ary W ilcox
a n d R ob ert W inn W ilcox in S e a ttle W a sh in g to n o n th e 8 # o f A u g u st in
th e y e a r 1 9 7 5 a lo n g w ith h is tw in b ro th er J o n R obert W ilcox. J e ff s p e n t
h is pre co lle g ia te y e a r s livin g w ith h is fam ily o n B a in b rid g e Isla n d in
W a sh in g to n . A fter co m p le tin g a h ig h sc h o o l e d u c a tio n h e follow ed th e
p a th o f h is old er sib lin g s, D a n n y W inn W ilcox a n d A m y C a th lee n W ilcox,
to h ig h er e d u c a tio n . In 1 9 9 0 , J e ff b e g a n h is fr e sh m a n y e a r th e U n iv ersity
o f O regon in h o p e s o f b e c o m in g a n h isto r ic a l p reserv a tio n a rch itect.
D u r in g h is so p h o m o re y e a r h e c h a n g e d h is m ajor to c h e m istr y . T he
follow in g y e a r h e tra n sferred to W a sh in g to n S ta te U n iv e r sity to c o n tin u e
h is p u r s u it o f C h em istry. H ere h e p a rticip a ted in p h y sic a l c h e m istr y
g r o u p s d irected by. Dr. St. J o h n D ixon -W arren a n d Dr. K evin B ray a n d
q u ick ly b e c a m e e n c h a n te d . U p o n e n te r in g M o n ta n a S ta te U n iv ersity J e ff
w a s g iv en th e o p p o rtu n ity to jo in th e Lee S p a n g ler r e s e a r c h group
w h e r e in h e p u r s u e d h is M a ster’s d egree
J e ff’s fa m ily is o n e o f th e c lo se su p p o rtiv e c o m p o n e n ts o f h is
life a n d th e y h a v e c o n tin u a lly e n c o u r a g e d h is e n d e a v o r s in ch em istry .
E v en tu a lly , J e ff h o p e s to rejoin h is fa m ily in sa ilin g th e w a te r s o f th e
N orth w est.
vi
I w o u ld lik e to a ck n o w led g e th e efforts o f Dr. Lee S p a n g le r a n d
th o s e p a r tic ip a n ts in h is grou p w h o h a v e g u id ed m e th r o u g h th eir
e x a m p le . A n a d d itio n a l a c k n o w le d g e m e n t g o e s to Mr. W arren M iller o f
th e G a lla tin R e se a rc h la b o ra to ries w h o s e in n o v a tin g c o m p o u n d s m ad e
o u r w ork a reality.
vii
TABLE OF CONTENTS
P age
1. INTRODUCTION................................................................................................................ I
2. GROUND STATE SPECTROSCOPY OF SC H IF F -B A SE S.............................. 9
A b so r p tio n ........................................................................................................................... 9
E x p e r im e n ta l................................................................................................................9
R e su lts a n d In te r p r eta tio n ..................................................................................11
M etal C en ter S u b s titu tio n ............................................................................12
L igand D on or S u b s titu tio n .......................................................................... 14
A ccep tor-M etal P roxim ity E ffe c ts............................................................. 15
D im eric M e ta llo -S c h iff-B a se ........................................................................17
F lu o rim etry ....................................................................................................................... 18
M ich elso n in terfero m eter.....................................................................................19
In terferom eter b a s e d flu o rim eter .................................................................... 2 2
E x cita tio n S p e c tr o sc o p y ...................................................................................... 2 2
E x c ita tio n -E m issio n S p e c tr o sc o p y .................................................................2 5
3. EXCITED STATE SPECTROSCOPY OF A SC H IFF -B A SE .......................... 31
E x tin c tio n C o efficien t.................................................................................................. 31
E x p erim en ta l, B le a c h in g M eth o d ....................................................................31
R e s u lts & In terp reta tio n ....................
35
4. ELECTRON TRANSFER INVOLVING A SC H IFF-B A SE COM POUND...38
S c h iff-b a se e lectro n tr a n sfe r ....................................................................................3 8
E x p erim en ta l, PIA M eth o d o lo g y ...................................................................... 3 8
D a ta A n a ly s is ........................................................................................................... 4 3
K in etic Im p ortan ce o f a B i-m e c h a n istic S y s te m ..................................... 4 9
A n a ly sis for B i-M ec h a n istic S y s te m ............................................................. 51
R e su lts & In terp reta tio n .....................................................................................5 5
5. CONCLUSION..................................................................................................................6 7
A b so r p tio n .............................................................................................. th...................... 6 7
E lectro n T ra n sfer..........................................................................................
68
viii
R E FE R E N C E S.............................................................................................................. 7 3
APPENDIX A: W arren M iller C o m p o u n d s .......................................................7 6
ix
LIST OF TABLES
T able
P age
1. 2 -1 G rou n d S ta te E x tin c tio n C o efficien ts for M iller
C o m p o u n d s ......................................................
2. 4 -1 K inetic v a lu e s
12
for b i-m e c h a n is tic s y s y te m .............................. 6 6
X
LIST OF SC H EM ES
Schem e
P age
I. 4 -1 E lectron tra n sfer m e c h a n ism ; (a) A ccep tor
e x cited c a s e , (b) D on o r e x cited c a s e ................................................5 0
xi
LIST OF FIGURES
I
F ig u res
P age
1. 2 -1
M eta llo -S c h iff-b a se s s y n th e s iz e d b y ............................................10
2. 2 -2 G rou n d sta te a b so r p tio n o f M iller...................................................13
3. 2 -3 G rou n d sta te a b so r p tio n o f M iller c o m p o u n d s .......... ;........... 15
4 . 2 -4 G rou n d sta te a b so r p tio n o f M iller c o m p o u n d s w ith ............16
5. 2 -5 G rou n d sta te a b so r p tio n o f G R B I - 19 a n d Ceo....................... 18
6 . 2 -6
M ich elso n in terfero m eter c h a m b e r ........................................... 2 0
7. 2 - 7 E x cita tio n sp e c tr u m o f Ptg( p o p ) P r o b e d a t ............................2 3
8. 2 -8
3D F lu orim eter d a ta u s in g PMT d e te c to r ................................. 2 6
9. 2 - 9 a F req u en cy v s. freq u en cy for E x c ita tio n .....................................2 7
10.
2 -9 b W avelen gth v s. freq u en cy for E x c ita tio n ............................ 2 7
11.
2 - 1 0 T otal e x c ita tio n -e m iss io n p lo t for G R B 1 - 1 1 - 1 ................ 2 9
12.
2 -1 1 T otal e x c ita tio n -e m iss io n sp e c tr u m o f................................ 3 0
13.
3 -1 P h o to -b lea c h in g e x p e rim en ta l la y o u t.....................................3 3
14.
3 -2 P h o to -e x c ita tio n from g ro u n d sta te to e x c ite d ................... 3 4
15.
3 -3 d a ta u s in g E q u a tio n 4 for G R B I - 19 PIA...............................3 6
16.
4 -1 3D p lo t o f raw F ou rier tra n sfo rm ed s ig n a l.......................... 4 0
17.
4 -2 PIA layou t; a) P u lse la s e r b) B ea m d u m p s ............................4 2
18.
4 -3 P h o to in d u c ed e lectro n tra n sfer free........................................ 4 4
xii
19.
4 -4 ) R aw d a ta o f io n c o n c e n tr a tio n a n d io n ................ ..............4 5
20.
4 -5 E n ergy level tra n sfer s c h e m e .......................................................4 8
21.
4 - 6 3D p lo t o f raw PIA d a ta for G 1 9 ................................................. 5 2
22.
4 - 7 S u b tr a c tio n d iag ra m o f sp e ctra l d a ta ....................
23.
4 -8 In tegration ratio co n tr ib u tio n d ia g r a m ..................................5 4
24.
4 -9 T im e d e c a y s for G 19* 8s 3Ceo* w ith o u t....................................5 6
25.
4 -1 0 R aw d a ta tim e d e c a y tr a c e s o f th e ......................................... 6 0
26.
4 -1 1 O ne over d on or io n c o n c e n tr a tio n v s. tim e .......................6 1
27.
4 -1 2 T im e d e c a y tr a c e s o f th e G 1 9 ................................................. 6 3
28.
4 -1 3 P lot o f d[D+]/ d t v s. [A*]. T he slo p e a t lo w e r ..................... 6 4
29.
4 - 1 4 P lot o f d[D+]/ dt v s. [A*] .............................................................. 6 5
54
xiii
A b stra ct
A fam ily o f b is sa lic y la m in e d ia m in o m e ta llo -S c h iff-b a se
c o m p o u n d s s y n th e s iz e d b y W arren M iller w a s sp e c tr o sc o p ic a lly
c h a r a cter iz ed . E x cita tio n co effic ien ts sh o w e d a stro n g d e p e n d e n c e o n
m e ta l str e n g th o f d on or s u b s titu te d o n th e sa lic y la m in e , a n d p r e se n c e o f
str o n g a c c e p to r s o n th e d ia m in o p o rtio n o f th e lig a n d . F lu o r im e tiy
e x p e r im e n ts w ere p erform ed w ith a n in terfero m eter b a s e d in str u m e n t.
[N,N N ”,N ”’-tetr a (4 -d ie th y la m in o sa lic y lim in e )- 1,2 ,4 ,5
tetraam in obenzen e]Z n (II) 2 , a c o m p o u n d c o n ta in in g b o th a c ce p to r a n d
d on or m o ie tie s s h o w e d a b i-m e c h a n is tic e lectro n tr a n sfe r in so lu tio n
w ith Ceo. P h o to in d u c e d a b so r p tio n th ro u g h s te p -s c a n sp e c tr o sc o p y y ie ld s
q u a n tu m e ffic ie n c ie s for th e so lv a te d io n s for b o th p a th w a y s o f 21.6%
a n d 2 1 .5 % resp ectiv ely . A n e w k in etic tr e a tm e n t is sh o w n for sep a ra tin g
th e s e e m b e d d e d s ig n a ls o f th e tw o p a th w a y s in order to o b ta in th eir
e ffic ie n c ies.
I
CHAPTER I
INTRODUCTION
F r a n k en d isco v ered in 196 1 th a t a q u artz cry sta l c o u ld d o u b le th e
fr e q u e n c y o f a ru b y la ser .
T h is p h e n o m e n o n , term ed s e c o n d h a rm o n ic
g e n e ra tio n (SHG), is a r e s u lt o f th e n o n lin e a r op tic (NLO) p ro p erties o f
th e q u a rtz cry sta l. A ny m e d iu m th a t c h a n g e s a n e lec tr o m a g n etic field a s
it p a s s e s th r o u g h it in te r m s o f p h a se , freq u en cy , a m p litu d e , or
p o la riza tio n is c o n sid e r e d a n NLO m a te r ia l.3 T he n o n lin e a r r e s p o n se o f a
c o m p o u n d is d e p ic te d in th e e q u a tio n ,
p —CilL + /7E ^ + yE/ ^ + •••
(i)
w h ere E is e lec tr o n ic field str en g th , a is th e lin ea r p olarizab ility, |3 is th e
first n o n lin e a r h yp erp olarizab ility a n d y is th e s e c o n d m o le c u la r
h yp erp olarizab ility. F ield c h a n g e o c c u r s d u e to c o m p o u n d s h a v in g a n
in s ta n ta n e o u s e lec tr o n d e n s ity d is p la c e m e n t (p olarization).3 T erm ed
h yp erp olarizab ility, th is d is p la c e m e n t is th e in d ic a tio n o f a c o m p o u n d ’s
r e a d in e s s to “sw itc h o n ” its s e c o n d order n o n lin e a r a b so r p tio n .4 S u c h
m a te r ia ls h a v e evolved v irtu a lly h a n d -in -h a n d w ith la s e r s s in c e th e
in tr o d u c tio n o f th e c o h e r e n t lig h t so u r c e in I 9 6 0 .1 T he d isc o v er y o f NLO
c o m p o u n d s c o rrela tes to th e in tro d u c tio n o f la se r s d u e to th e relatively
h ig h e lec tr ic field n e e d e d to c a u s e h y p erp o la riza tio n w ith in th e m aterial.
E x p lo ra tio n o f in o rg a n ic NLO m a te r ia ls a s th e o n ly c o m p o u n d s
e x h ib itin g n o n lin e a r b eh a v io r c o n tin u e d in to th e 7 0 ’s. W ith th e in te r e st
in NLO c o m p o u n d s e x p a n d in g for u s e w ith la se r d o u b lin g , m ix in g a n d
e v e n trip lin g, n e w in o rg a n ic cry sta llin e c o m p o u n d s w ere so u g h t. W hile
in o r g a n ic NLO c r y sta ls h a v e d e sira b le p ro p erties s u c h a s g o o d th erm a l
sta b ility a n d b e in g relatively e a s y to m a c h in e , th ey are e x p e n siv e a n d
h a v e a rela tiv ely low h yp erp olariza b ility p er fo rm u la u n it a n d th u s
req u ire str o n g field s to g e n era te a n o n lin e a r r e sp o n se . T h is r e s p o n se led
le a d to e x p lo ra tio n o f organ ic c o m p o u n d s in a q u e s t to g e n e ra te larger
h y p erp o la riza b ilities.
O rgan ic c o m p o u n d s relieve so m e o f th e d is a d v a n ta g e s a n d
sh o r tc o m in g s fo u n d in in o rg a n ic c r y sta ls b u t a lso in tro d u c e so m e
in h e r e n t n e w o n e s . O rganic NLO m a ter ia ls, first in v e stig a te d in 1 9 7 0 a n d
la te r r e in tr o d u c e d in a p olym er form in 1 9 7 6 , h a v e a su r p r isin g in c r e a se
for th e s e c o n d order h yp erp olariza b ility term over th a t o f th e tra d itio n a l
in o r g a n ic c r y s ta ls .1 O rgan ics sh o w a real s e n s e o f o p tica l “tr a d e o ff’ in
th e v isib le region , w ith th e d elo ca lized n e lec tr o n s h e lp in g b y in c r e a sin g
th e NLO r e s p o n se , b u t h in d erin g by in tro d u c in g str o n g lin ea r a b so rp tio n ,
s o m e tim e s in r eg io n s o f d e sire d tr a n sp a r e n c y .3 T he o rg a n ic c o m p o u n d s
te n d to h a v e low er m a n u fa c tu r in g c o st, e n h a n c e d NLO p ro p erties over a
b road fr e q u e n c y ran ge, sy n th e tic flexib ility, h ig h o p tica l d a m a g e
th r e s h o ld s , a n d in tr in sic ta ilo ra b ility .3 H ow ever, w ith th e s e a d v a n ta g e s
c o m e v olatility, lo w th erm a l sta b ility , m e c h a n ic a l w e a k n e s s , a n d a stro n g
a v e r sio n to form b u lk c r y s ta ls .2’3
S c ie n tis ts h o w ev er c o n tin u e to m a k e a d v a n c e m e n ts in th e organ ic
NLO field, in c r e a s in g th e p o ssib ility o f su ita b le c o m p o u n d s . To fu rther
im p rove o n o rgan ic NLO c o m p o u n d s , Frazier in 1 9 8 6 p r o d u ce d th e first
o r g a n o m e ta llic c o m p le x for NLO s tu d y .2-5 T h is in tro d u c ed a m arriage
b e tw e e n th e o rgan ic large s e c o n d order term a n d th a t o f th e in o rg a n ic
sta b ility . T he c o m b in ed effect is fu rth er in c r e a se d b y th e o p e n sh e ll
n a tu r e o f th e c o m p le x a n d th e ab ility to fin e tailor th e c o m p o u n d s
in v o lv in g d ifferen t tr a n sitio n m e ta ls or o rg a n ic m o ie tie s.
In 1 9 8 7 G reen in tro d u c ed th e first NLO u s e fu l o rg a n o m eta llic
c o m p le x .4-5’6 O rg a n o m eta llics, a n d S c h iff-b a se s in p a rticu la r, p o s s e s s
sev era l p ro p erties th a t in d ic a te p o te n tia l u tility for NLO a p p lic a tio n s a n d
o p tica l p ro p erties in gen eral. T ra n sitio n m e ta l c o m p le x e s are so m e o f th e
m o s t h ig h ly colored c o m p o u n d s k n o w n w h ic h in d ic a te s low en ergy, h ig h
d ip ole c h a n g e tr a n sitio n s. T h e se tr a n s itio n s often in volve sig n ific a n t
ch a rg e tr a n sfe r (CT) from th e m e ta l to th e lig a n d or v ice v e rsa . (O rganic
s y s te m s w ith low en ergy, h ig h CT c h a r a cter h a v e b e e n s h o w n to h a v e
str o n g n o n -lin e a r o p tica l p ro p erties s u g g e s tin g th e p o te n tia l for th e
o r g a n o m e ta llic s .) O rg a n o m eta llics a lso h a v e th e a d v a n ta g e o f h a v in g a
larger n u m b e r o f s tr u c tu r a l v a r ia tio n s availab le. T he o rg a n ic lig a n d c a n
be fu n c tio n a liz e d w ith stro n g e lectro n d o n o rs (D) a n d a c c e p to r s (A) to
4
c o n s tr u c t D- - - A, “p u s h -p u ll” s y s te m s a n a lo g o u s to o rg a n ic s y s te m s
w h ic h h a v e b e e n s u c c e s s fu lly e n g in e e re d for h ig h er P v a lu e s .7 In
a d d itio n , th e m e ta l c e n te r c a n be va ried a n d c a n p la y a role a s a n
e lec tr o n d o n o r (electron “r ich ” m eta ls) a n electro n a c ce p to r (electron
“p oor” m e ta ls) or a s p art o f th e h ig h ly p olarizab le, c o n ju g a te d bridge
b e tw e e n o th er d on or or a c cep to r g r o u p s.6 V ariation o f th e m e ta l a lso
p e r m its s y n th e s is o f c o m p o u n d s w ith a n o p e n sh e ll e lec tr o n ic
co n fig u ra tio n w h ic h o n e s tu d y in d ic a te d m a y e n h a n c e n o n lin e a r ity .8 T h is
o p e n s h e ll e n h a n c e m e n t o f th e h y p erp o la riza b ility w a s a ttrib u te d to a
larger n u m b e r o f a c c e s s ib le , low -ly in g CT s ta te s. T he S c h iff-b a se a lso
e x h ib its favorable th er m a l sta b ility , w ith d e c o m p o sitio n te m p e r a tu r e s o f
3 0 0 °C a n d a b ove in so m e o f th e NLO a ctiv e m a te r ia ls.9
T h e o r g a n o m e ta lic c o m p o u n d s d isp la y p ro p erties o f g en era l
in te r e st for o p tica l a p p lic a tio n s. T he str o n g a n d h ig h ly tu n a b le
a b so r p tio n b a n d s in d ic a te p o ssib le u tility a s s e n sitiz e r s for flu o r e sc e n c e
a n d d ye la s e r a p p lic a tio n s. H igh ly c o n ju g a te d organ ic s y s te m s
fu n c tio n a liz e d w ith m u ltip le electro n ic d o n a tin g g ro u p s th a t h a v e b e e n
fo u n d to b e good elec tr o n d o n o rs in p h o to in d u c e d e lec tr o n tra n sfer (PET)
w ere p r e v io u sly in v e stig a te d in th e Lee S p a n g ler r e se a r c h group. T he
a b ility to fu n c tio n a lize th e S c h iff-b a se lig a n d a n d c h a n g e th e p o ssib le
red o x a c tiv ity o f th e m e ta l c en te r m a k e th is c la s s o f c o m p o u n d s
in trig u in g for in ter m o le c u la r PET s tu d ie s . In d ilu te s o lu tio n , th e d iffu sio n
rate a n d th e lifetim e o f th e ex cited p h o to in itia to r lim it in ter m o le c u la r PET
s tu d ie s . T h e p r e se n c e o f th e h e a v y a to m m a y in c r e a se sp in orbit c o u p lin g
a n d e n h a n c e form ation o f lo n g-liv ed trip let s ta te s. T h e se s ta te s provide
tw o a d v a n ta g e s for in ter m o le c u la r PET in d ilu te so lu tio n s: th e y do n o t
a p p re c ia b ly d e c a y before d iffu sio n lim ited c o llisio n s o c cu r a n d a n
e lec tr o n tra n sferred from a trip let sta te r e s u lts in a s ta te for w h ic h
g e m in a te r ec o m b in a tio n is sp in -fo r b id d en w h ic h s h o u ld in c r e a s e io n
yield . T h e flu o r e sc e n c e p ro p erties o f th e s e c o m p o u n d s are relatively
u n e x p lo r e d a n d n o t d irectly m e n tio n e d in th e b u lk o f th e NLO literatu re
o n S c h iff-b a se s, a lth o u g h th e e x p e rim en ta l se c tio n o f o n e p a p er
m e n tio n s a red s o lu tio n y ie ld in g d ark b lu e c ry sta ls. 10 A nd fin a lly th e
e x is te n c e o f low -lyin g, stro n g ly a b so r b in g CT s ta te s in c o m b in a tio n w ith
h ig h h y p erp o la riza b ilies s u g g e s t th e p o ssib ility o f str o n g tw o p h o to n
a b so r p tio n a n d th e p o ssib ility o f s e q u e n tia l a b so r p tio n th a t c o u ld
p r o d u ce o p tica l lim itin g.
S c h iff-b a se c o m p o u n d s in tro d u c ed n e w flexib ility in g eo m etry d u e
to th e m e ta l c e n te r s a n d a h ig h order o f tu n in g w ith th e o rg a n ic m o itie s .5
T h e se h ig h ly c o n ju g a te d s y s te m s p o s s e s s ch irality d u e to th eir
n o n c e n tr o s y m a tic co n fig u ra tio n a llo w in g for th e grow th o f NLO active
c r y s ta ls .5-11 O rg an om etallic S c h iff-b a se c o m p le x e s are sp e c u la te d to
p r o d u ce a h ig h er n o n lin e a r r e s p o n se in c o m p a r iso n to a so le ly organ ic
ch r o m a p h o re , a n d a t th e p r e se n t tim e co m e c lo se to d o in g s o .2 T he m e ta l
lig a n d in te r a c tio n is th o u g h t to in c r e a s e th e co n ju g a tio n in th e ex cited
s ta te s b e tw e e n th e a c ce p to r a n d d o n o r m o ie tie s. T he o rg a n o m eta llic b o n d
c r e a te s a ca g e a t th e c e n te r o f th e o rg a n ic ch ro m a p h o re w h ic h im p ro v es
th e th e r m a l sta b ility o f th e c o m p o u n d b y sta b ilizin g th e c h e la te ring
s tr u c tu r e . T h is cen tr a l m e ta l a c ts a s a %co n ju g a te bridge b e tw e e n th e
e lec tr o n d o n a tin g a n d e lectro n a c c e p tin g m o ie tie s o f th e c o m p o u n d
(d o n o r -m e ta l-a c c ep to r ).4 A lth o u g h th e NLO effect is largely e n h a n c e d by
th e S c h iff-b a se c o n ju g a tio n , th e g ro u n d sta te a b so r p tio n is d o m in a te d b y
th e o rg a n ic c h r o m o p h o r e .10 M etal a lso im p ro v es th e th er m a l sta b ility o f
th e c o m p o u n d b y sta b ilizin g th e c h e la te ring str u c tu r e b y b o n d in g to th e
org a n ic lig a n d s th ro u g h a a-n in ter a c tio n . 4>12 W hen a lo w d m e ta l is u s e d
it a c ts a s a bridge for th e a c ce p to rs. H igh d m e ta ls bridge w ith th e
d o n o rs. 6 A h ig h d egree o f co n fig u ra b le geo m etry is d u e to th e in c r e a sin g
n u m b e r o f b o n d s b e tw e e n th e m e ta l a n d th e lig a n d s, w h ic h are flexible
th r o u g h th e tt d e lo c a liz a tio n .6 T h e se w e a k b o n d s b e tw e e n th e lig a n d s
a n d m e ta l c e n te r are w h a t in d u c e th e brid gin g p ro p erties e x h ib ite d by
th e m e ta l.5 A ny e lo n g a tio n o f th is d e lo c a liz ed sy ste m r e s u lt s in in c r e a se d
h y p erp o la riza b ility a n d so in c r e a s e s NLO r e sp o n se . 5
S c h iff-b a se c o m p le x e s a b so rb in te n s e ly in th e u ltr a v io le t d u e to th e
m e ta l d-d* a n d lig a n d n-n* tr a n s itio n s a r o u n d 3 0 0 - 4 0 0 n m .4 Longer
w a v e le n g th a b so r p tio n in te n s itie s ta k e o n th e c h a ra cter o f th e organ ic
lig a n d a n d s h o w e ffects o f so lv a to c h r o m ism d u e to in te r a c tio n s w ith th e
m e ta l.4 T he m e ta l-lig a n d bridge a lso in c r e a s e s th e overall in te n s ity o f th e
lig a n d b a n d s h a p e w ith m ore a p p a r e n t effect tow ard th e red sid e o f th e
v isib le ra n g e. T h e se low er tr a n sitio n s in n ea rly all p r g a n o m eta llic s o c cu r
in th e v isib le region r e d u c in g th e “tr a n sp a r e n c y w in d o w ”.3 T h is d e lica te
b a la n c e b e tw e e n str o n g s e c o n d order a b so r p tio n a n d o b ta in in g a large
tr a n sp a r e n c y w in d o w in th e v isib le reg io n o n c e a g a in r eite r a te s th e NLO
tradeoff. S c ie n tis ts n o w c a n p ro d u ce d o n o r a n d a c cep to r m o ie tie s w ith
v aried c o n ju g a tio n th a t w h e n a tta c h e d to v a rio u s tr a n sitio n m e ta ls c a n
p r o d u ce d is tin c t NLO p rop erties. P o ten tia lly , w ith k n o w n lig a n d s a n d
c o m p o u n d a r ra n g e m e n ts, s c ie n tis ts c a n p red ict S c h iff-b a se s tr u c tu r e s
th a t w ill y ie ld h ig h s e c o n d order r e s p o n s e s . O rg a n o m eta llics offer a
m u ltitu d e o f c o m p o u n d s , w h ic h h a v e a d iv ersity o f o x id a tio n s ta te s (e.g.
h yp erp olarizab ility), w ith low en erg y tr a n sitio n s ta te s (from m e ta l-lig a n d
b on d ), n d e lo c a liz ed s y s te m s , a n d e a s y cry sta l p a c k in g (d ue to chiral
c e n te r ).
B e c a u s e o f th e p o ten tia lly str o n g NLO r e s p o n se o f o rg a n o m e ta llics,
th e m e ta llo -S c h iff-b a s e s h a v e g e n e ra ted in ter e st. B u t a s id e from lin ea r
a b so r p tio n a n d electric field in d u c e d s e c o n d h a rm o n ic g e n e ra tio n (EFISH)
e x p e r im e n ts, very little o p tica l c h a r a cter iz a tio n h a s o c cu rr e d a n d for a
rela tiv ely sm a ll n u m b e r o f c o m p o u n d s. T he S p a n g ler g ro u p , in te r e ste d in
a s e r ie s o f n o v el B is sa lic y lim in e d ia m in o m e ta llo -S c h iff-b a se
c o m p o u n d s d e sig n e d b y W arren M iller for NLO p ro p erties, h a s d evoted
8
tim e to ch a r a cter iz e th e lin ea r o p tica l p ro p erties o f th e c o m p o u n d s w ith a
n o n lin e a r e x a m in a tio n to e n s u e . D e sig n a s p e c ts o f s u c h c o m p o u n d s for
th e u s e o f NLO m a ter ia ls correlate d irectly to s y s te m s r ich in a p p lic a tio n s
for e lec tr o n tr a n sfe r s in c e b o th a c ce p to r a n d /o r d o n o r m o ie tie s a p p ea r in
th eir co n fig u ra tio n . 13>10 W ith p rop er c h a r a cter iz a tio n o f th e lin ea r
a b so r p tio n , u s e fu l in fo rm a tio n o n th e S c h iff-b a se c o m p o u n d s a n d th eir
p o s s ib le d e s ig n a s p e c t s m a y be fo u n d o th er th a n b y sim p ly perform ing
n o n lin e a r ex p e rim en ts.
9
CHAPTER 2
GROUND STATE SPECTROSCOPY OF SC H IFF-B A SE S
A b so rp tio n
A b so rp tio n sp e c tr a o f th e M iller c o m p o u n d s y ield th e g ro u n d sta te
to e x c ite d s ta te tr a n sitio n s. T h e se in te r a c tio n s w ill in d ic a te th e b e s t
fr e q u e n c ie s for p u m p in g w h e n ex p lo rin g o th er a ttr ib u te s o f th e
c o m p o u n d s a n d c a n a lso b e u s e d to e x a m in e th e a n a ly te ’s o p tica l
p r o p e r tie s th r o u g h p u m p -p ro b e m e th o d s.
E x p e rim en ta l
W arren M iller d e sig n e d a n d s y n th e s iz e d th e B is sa lic y lim in e
d ia m in o m e ta llo -S c h iff-b a se c o m p o u n d s in v e stig a te d in th is th e s is . T he
a b so r p tio n e x p e r im e n ts w ere p erform ed w ith a S h im a d z u (U V -2401p c)
sp e ctro p h o to m e te r . T he c o m p o u n d s in v e stig a te d are s h o w n in Figure 2 1, a n d th e form al n a m e s are p rovid ed in a p p en d ix A. T h e se m eta llo S c h iff-b a se c o m p le x e s
10
GRB 1-11-1
GRB 1-11-2
GRB 1-11-3
GRB 1-11-4
GRB 1-15
GRB 1-17
GRB 1-19
(Figure 2-1) Bis salicylimine diamino metallo-Schiff-bases synthesized by Warren Miller
and investigated in this thesis. The formal names are provided in Appendix A.
c o n ta in m u ltip le d ie th y la m in o (stron g donor) a n d c y a n o (acceptor) g ro u p s
in a n o rgan ic lig a n d w h ic h e n c a s e s a tr a n sitio n m eta l.
R e s u lts a n d In terp retation
In order to in v e stig a te th e effects o f a n u m b e r o f s tr u c tu r a l
p a r a m e te r s o n th e g ro u n d sta te a b so r p tio n b eh avior, a v a riety o f B is
sa lic y lim in e d ia m in o m e ta llo -S c h iff-b a se s w ere s y n th e s iz e d (by Miller)
a n d m e a su r e d . T he c o m p o u n d s are sh o w n in Figure 2 -1 (form al n a m e s
are p rovid ed in a p p e n d ix A) a n d are d e sig n e d to exp lore e ffe cts o f varyin g
th e m e ta l, c o n ju g a tio n le n g th , a n d d o n o r /a c c e p to r s u b s titu tio n o n th e
ligan d .
T he s tr u c tu r e la b e le d G R B 1 -1 1 -1 se r v e s a s th e referen ce
c o m p o u n d for th e r e s t o f th e a n a lo g s. T h is co m p o u n d w a s p r e v io u sly
rep orted b y D i B ella a n d co -w o rk ers a s h a v in g a h ig h h y p erp o la riza b ility
(a lth o u g h th e a b so r p tio n sp e ctru m w a s n o t sh ow n ) a n d w a s id en tified by
M iller a s a flu o r e s c e n t s p e c ie s from a s ta te m e n t w ith in th e D i B ella p a p er
n o tin g th a t in p u rifyin g th e sa m p le b lu e c r y sta ls w ere o b ta in e d from a
red s o lu tio n .10 T he a b so r p tio n sp e c tr u m o b ta in ed in th is w o rk stro n g ly
r e s e m b le s th e litera tu re sp e c tr u m o f th e n ic k e l B is sa lic y lim in e d ia m in o
m e ta llo -S c h iff-b a se (NiL). T he sp e c tr u m o f th e lig a n d its e lf (HgL), a lso
rep orted b y D i B ella a n d co -w o rk ers c lo se ly r e se m b le s th a t o f th e m eta l
c o n ta in in g s p e c ie s w ith tw o e x c e p tio n s , I) NiL e x h ib its a n a d d itio n a l
p e a k a t ~ 2 5 0 n m a b s e n t in H2L th a t is p r e su m a b ly d u e to a m eta l-lig a n d
(M-L) ch a rg e tra n sfer b a n d a n d 2) th e ZnL sp e ctru m is r e d -sh ifte d by
~ 1 5 n m . T h e se lig a n d s c o n ta in stro n g d o n o r (diethylam ino) g r o u p s a t th e
e n d s o f th e m o le c u le s a s w ell a s str o n g c y a n o group e lec tr o n a c ce p to rs
n e a r th e c e n te r o f th e m o le c u le (and n e a r th e e th y le n e d ia m in e m eta l
c h e la tin g site). G rou n d sta te e x tin c tio n co effic ien ts for th e s e B is
sa lic y lim in e d ia m in o m e ta llo -S c h iff-b a se s are liste d in T ab le 2 -1 .
C om pound
W avelen g th (nm)
s (L m o h 1 c n r b
G R B l-1 1-1
590
G R B l-1 1-2
566
3 ,2 0 0
G R B l-1 1-3
6 0 2 .5
1 5 ,5 0 0
G R B l-1 1-4
554
2 9 ,3 0 0
G R B 1-15
528
1 1 ,7 0 0
G R B 1-17
512
1 ,4 0 0
G R B 1-19
440
4 7 ,4 0 0
G R B 1-21
587
7 ,7 0 0
G R B I -2 3
586
2 9 ,7 0 0
4 4 ,9 0 0
(Table 2-1) Ground state extinction coefficients for Miller compounds.
M etal C en ter S u b s titu tio n . T he effect o f m eta l s u b s titu tio n is
s h o w n in F igure 2 -2 , w h ic h s h o w s Z n2+, Ni2+ a n d C u2+ all c h e la te d by th e
s a m e “p u s h -p u ll” ligan d . T he sp e ctra l b a n d s d isp la y very sim ila r
w a v e le n g th a n d s h a p e s , b u t in te n s itie s vary d ram atically. T he ZnL
a b s o r b a n c e is 1.5 tim e s a s in te n s e a s NiL a n d a factor o f 6 larger th a n
CuL. T h e c lo se r e se m b la n c e o f th e b a n d s h a p e s a n d w a v e le n g th s
13
str o n g ly s u g g e s ts th a t th e tr a n s itio n s are d u e to th e o rg a n ic lig a n d . T h is
is s u p p o r te d by th e fa ct th a t all th e fe a tu r e s sh o w n (3 0 0 n m a n d above)
a ls o a p p e a r s in th e bare lig a n d sp e c tr u m rep orted by D i B ella a n d
cow ork ers. T h u s w e s e e th a t for th is lig a n d , w h ic h c o n ta in s stro n g
a c c e p to r s, th e m e ta l fu n c tio n s to sig n ific a n tly c h a n g e th e o scilla to r
str e n g th o f th e lo w -ly in g e lec tr o n ic tr a n s itio n s w ith o u t a p p recia b ly
c h a n g in g th eir e n e r g ie s. It is a lso in te r e stin g to n o te th a t th is effect is n o t
m o n o to n ic w ith d e lec tr o n p o p u la tio n a n d th a t th e o p e n s h e ll C u 2+ (d9) is
low er in in te n s ity th a n th e c lo se d s h e ll d 10 a n d d8 s p e c ie s (Zn2+ a n d N i2+,
resp ectiv ely ).
W avelength (nm)
300
400
500
600 700
GRBl-11-1
M=Zn
GRB1-23
M=Ni
0.5-
0.0
34000
+
- T
GRBI-2 1 M=Cu
-
29000
24000
19000
14000
Frequency (cm )
(Figure 2-2) Ground state absorption of Miller compounds with varying metals;
GRBl-11-1 (Zn), GRBI-23 (Ni), GRBI-2 1 (Cu).
L igand D o n o r S u b s titu tio n . T he p r e v io u s se r ie s o f c o m p o u n d s
in d ic a te d th a t lig a n d s c o n ta in in g str o n g d o n o rs a n d a c c e p to r s d o m in a te
th e lo w fr e q u e n c y sp e c tr u m o f th e m e ta llo -S c h iff-b a se s. W e n o w co m p a re
a s e r ie s o f m o le c u le s c o n ta in in g th e s a m e m eta l (Zn, w h ic h e x h ib its th e
h ig h e s t m o la r absorbtivity) b u t w ith v a ry in g don or g r o u p s o n th e sa m e
lig a n d str u c tu r e . G R B l- 1 1-1 (d iethylam ino) G R B l- 1 1 -4 (m eth oxy), a n d
G R B l- 1 1-2 (H) are a s e r ie s w ith d e c r e a s in g d on or str e n g th , a n d th eir
s p e c tr a s h o w a co rr e sp o n d in g d e c r e a se in in te n sity w ith th e H
s u b s titu te d c o m p o u n d b e in g d ra m a tica lly w ea k er (Figure 2 -3 ). The
d ie th y la m in o is r ed -sh ifted b y ~ 1 2 .5 n m from th e m e th o x y c o m p o u n d
in d ic a tin g s lig h t so lv o c h o m ism in th e o scilla to r str en g th . A lso sh o w n for
c o m p a r iso n is G R l- 1 1-3 w h ic h h a s a n a p th a l in s te a d o f p h e n o l
e x te n d in g th e c o n ju g a tio n in th e m o le c u le . Its sp e c tr u m s h o w s a red sh ift
slig h tly greater th a n th e d ie th y la m in o lik ely d u e to th e larger co n ju g a ted
s y s te m in th e ligan d . T he m olar e x tin c tio n is in ter m e d ia te to th e H a n d
m e th o x y s u b s titu te d c o m p o u n d s c o n s is t e n t w ith th e fu s e d rin g b ein g a
w e a k e lec tr o n d on or, b u t o b v io u sly stro n g er th a n h y d ro g en . T h is ser ie s
o f c o m p o u n d s illu str a te s th a t b o th a b so r p tio n fr e q u e n c ie s a n d in te n sitie s
c a n b e e n g in e e r e d in " p u sh -p u ll” m e ta llo -S c h iff-b a se s in th e sa m e w a y
c o n ju g a te d o rgan ic " p u sh -p u ll” s y s te m s are.
15
300
W avelength (nm)
400
500
600 700
G R B l-1 1-1
2.0 -
G R B l-1 1-4
S
G R B l-1 1-3
1.0-
G R B l-1 129000
24000
19000
14000
Frequency (cm )
(Figure 2-3) Ground state absorption of Miller compounds with varying substituents;
Structure (a) - GRBl-11-1 (R=diethylamino), GRBl-11-2 (R=hydrogen), GRBl-11-4
(R=methoxy), and structure (b) - GRBl-11-3.
A ccep tor-M etal P roxim ity E ffects. In order to p ro b e th e effect o f th e
a c ce p to r g r o u p s o n th e o p tica l p r o p e r tie s o f th e B is sa lic y lim in e d ia m in o
m e ta llo -S c h iff-b a s e s , a n a lo g s o f G R B l- 1 1-1 a n d G R B l- 1 1-3 w ith a
p y ra zin e rin g in se r te d b e tw e e n th e d ia m in e c h e la tin g g ro u p a n d th e
str o n g c y a n o g ro u p a c c e p to r s w ere sy n th e s iz e d . T he s p e c tr a o f th e n e w
c o m p o u n d s (Figure 2 -4 ) e x h ib it a n e a r ly fou r-fold d e c r e a s e in
16
W avelength (nm)
500
600 700
G R B l-Il-I
GRBl-11-3
GRB1-15
GRB1-17
G R B l-1 1-1
G R B l-1 1-3
GRB1-17
34000
GRB1-15
29000
24000
19000
14000
Frequency (cm'1)
(Figure 2-4) Ground state absorption of Miller compounds with varying conjugation
lengths between acceptor and donor.
Emax, a n d a c h a n g e in b a n d sh a p e . In a d d itio n , Xmax b lu e s h ifts in sp ite o f
a n in c r e a s e in th e overall siz e o f th e lig a n d Tt s y ste m . T h is in d ic a te s th a t
a c ce p to r gro u p p roxim ity to th e m e ta l a to m p la y s a n im p o rta n t role in
th e e lec tr o n ic str u c tu r e o f th e m o le c u le r eg a r d le ss o f th e p r e se n c e
(G R B 1 -1 1 -1 , G R B 1-15) or a b s e n c e (G R B 1 -1 1 -3 , G R B 1-17) o f a stro n g
d o n a tin g gro u p o n th e ligan d . T h is is su p p o r te d by w ork b y th e Di B ella
grou p o n a sim ila r S ch iff-b a s e w ith I) a d ia m in e bridge, 2) a n op h e n y le n e d ia m in e bridge a n d 3) a n itro s u b s titu te d o -p h e n y le n e d ia m in e
bridge." P r e se n c e o f th e c o n ju g a te d o -p h e n y le n e d ia m in e r e s u lte d in so m e
red sh ift over th e d ia m in e . S u b s titu tio n how ever, w ith th e n itro a ccep to r
g r o u p s g e n e r a te d a m ore sig n ific a n t red sh ift. A d d ition ally, th e D i B ella
w ork a lo n g w ith F igure 2 -3 a n d 2 -4 s u g g e s t th a t th e e lec tr o n a c ce p to rs
h a v e a str o n g e r in flu e n c e th a n do th e d o n a tin g g ro u p s.
D im eric M e ta llo -S c h iff-B a se . In a d d itio n to th e th ree se r ie s o f
c o m p o u n d s s y n th e s iz e d to a d d r e ss th e effect o f th e m e ta l, th e d on or
s u b s titu e n t, a n d th e p la c e m e n t o f th e a c ce p to r g ro u p s, a d im eric B is
sa lic y lim in e te tr a m in o m e ta llo -S c h iff-b a se s w a s m a d e. T h is co m p o u n d
u s e s 1 ,2 ,4 ,5 -te tr a m in o b e n z e n e a t th e c e n te r o f th e str u c tu r e to h elp
c h e la te tw o m e ta l a to m s (Figure 2 -5 ). T h is cen tra l b e n z e n e r ep la ce s th e
str o n g c y a n o a c ce p to r g r o u p s p r e se n t in th e r e st o f th e m o le c u le s stu d ie d
h ere. T he r e s t o f th e lig a n d r e s e m b le s a d im eric v e rsio n o f G R B l- 1 1-1
w ith fou r d ie th y la m in o g r o u p s in p e n d e n t p o sitio n s. T he r esu ltin g
s tr u c tu r e is s o m e w h a t a n a lo g o u s to a 4 -a r m e d , low g e n e r a tio n d en d rim er
w ith p e n d e n t e lec tr o n d o n a tin g g ro u p s. C o n ju g a ted lo w g en era tio n
o rg a n ic d en d rim ers w ith all d on or s u b s tit u e n ts (as o p p o se d to "pushp u ll” d o n o r-a cc e p to r su b stitu tio n ) h a v e e x h ib ite d h ig h tw o p h o to n c r o sss e c tio n s .7 In sp ite o f th e p o ten tia lly m u c h larger c o n ju g a tio n sy ste m in
th e dim er, th e a b so r p tio n is sig n ifica n tly b lu e -sh ifte d c o m p a red to th e
r e s t o f th e c o m p o u n d s. T h is is p ro b a b ly a t le a s t p a rtia lly d u e to a b s e n c e
o f a str o n g a c c e p tin g grou p in th e str u c tu r e . A d d itio n a lly th e sp e c tr u m
18
s h o w s a very b ro a d b a n d s tr u c tu r e d a b so r p tio n lik ely d u e to o verlap p in g
e le c tr o n ic tr a n sitio n s.
300
W avelength (nm)
400
500
600 700
C60XlO (O.lOmM/BN)
(0.05m M /B N
J \ ___^ P u m p ed at
/
\
532nm -
-9 I
34000
29000
24000
19000
1400
Frequency (cm"1)
(Figure 2-5) Ground state absorption of GRB I -19 and Ceo The Ceo absorption is
shown along with an indication of pumping frequency because of intermolecular
electron transfer experiments performed with this pair of molecules.
F lu o rim etry
F lu orim etry is a p ow erfu l g e n e r a l-p u r p o se tool for th e in v e stig a tio n
o f lin ea r o p tica l p ro p erties. F lu orim etry e x p e r im e n ts in co rp o ra tin g a n
in terfero m eter w ere c o n d u c te d b o th for th e p u r p o se o f m e th o d
19
d e v e lo p m e n t a n d for o p tica l c h a r a cter iz a tio n o f th e str o n g ly e m ittin g
S c h iff-b a se c o m p o u n d s.
T h e b a s ic co n fig u ra tio n o f a flu o rim eter c o n s is t s o f b ro a d b a n d lig h t
so u r c e , a n e x c ita tio n w a v e len g th sele c to r , a sa m p le c h a m b er , a n
e m is s io n w a v e le n g th selecto r, a n d a d etecto r. In a d d itio n to th e
straigh tforw ard a b so r p tio n a n d e m is s io n sp e ctra , th e s e c o m p o n e n ts
p erm it m e a s u r e m e n ts o f a th r e e -d im e n sio n a l to ta l e x c ita tio n -e m iss io n
sp e c tr u m . In c o n v e n tio n a l flu o rim eters, m o n o ch ro m a to rs are u s e d for
b o th th e e x c ita tio n w a v e len g th se le c tio n a n d th e e m is s io n w a v elen g th
s e le c tio n (w ith th e la tter so m e tim e s rep la ced w ith a sp e ctro g r a p h
u tiliz in g a n array detector). For th is w ork, u s e o f a M ich elso n
in terfero m eter for e m is s io n w a v e len g th d isc rim in a tio n in to ta l ex cita tio n e m is s io n s p e c tr o sc o p y (EES) w a s ex p lo red (or co n v ersely , ex cita tio n
w a v e le n g th s e le c tio n in e x cita tio n sp ectro sco p y ).
M ich elso n in terferom eter
A s d e p ic te d in F igure 2 -6 , a M ich elso n in terfero m eter u s e s a
b e a m sp litte r to s e n d th e lig h t d ow n tw o a rm s o f th e in str u m e n t; o n e w ith
a fixed m irror, th e o th er w ith a m o v a b le m irror. W hen th e lig h t
r e c o m b in e s a t th e b ea m sp litte r, h a lf o f th e lig h t is tu r n e d tow ard th e
d etecto r, a n d th e o th er h a lf is d irected b a c k a t th e s o u r c e . B e a m sp litte r s
t r a n s m i t a p p r o x im a te ly 3 0 % o f th e lig h t fro m th e u l t r a v io le t in to th e
n e a r in frared a n d c o n ta in a n ti-reflectio n c o a tin g s a lo n g w ith a
c o m p e n s a tin g w in d o w to h elp a s s u r e p a th c o n tin u ity , r ed u c in g p h a se
e rr o r s . 14
d
e
a
(Figure 2-6) Michelson interferometer chamber a) incoming light b) beamsplitter c)
stationary mirror d) movable mirror e) exiting light.
W h en th e m ovab le m irror is tr a n sla te d , it c r e a te s a p a th le n g th
d ifferen ce o f
2
x, w h ere x is th e d ifferen ce in m irror d is ta n c e to th e
b e a m sp litte r com p ared to th e sta tio n a ry m irror. A n arrow w a v elen g th
s o u r c e is u s e d to ca lib ra te th e m o v e m e n t o f th e m irror, in o u r c a se a
H eN e la ser . T he c h a n g e in p o sitio n o f th e m ovin g m irror c r e a te s a p h a se
change of
S = 4 TTXV
(I)
w h ere v is th e w a v e n u m b er o f ligh t in c m 1. W hen th e m irror is
tr a n sla te d th ro u g h a ran ge o f p o s itio n s, a c o n tin u o u s s ig n a l a t th e
d e te c to r is record ed a s
21
S(x) = K<j)y c o s 8
(2 )
w h ere K is d e te c to r r e s p o n se fa cto r a n d ^ i s th e a c tu a l sp e ctra l
in te n sity . A p lo t o f S(x) v s. x, w ill y ield in te n sity a s a fu n c tio n o f m irror
p o sitio n . T h is is k n o w n a s a n in terferogram . D is p la c e m e n t o f th e m irror
is d irectly rela ted to th e m a x im u m r e so lu tio n giving
(Ay) theoretical
I
(Ax) max imum-movement
(3)
C h a n g in g m irror p o sitio n w ill c a u s e a w a v e len g th p erio d ica lly to in terfere
w ith its e lf w h e n r ec o m b in in g in th e d ielectric m e d ia o f th e b ea m sp litter.
For th e c a s e o f a sin g le w a v e len g th th is p r o d u c e s a s in u s o id a l p a ttern
d u e to p h a s e sh ift d e p ic te d in E q u a tio n I . W hen m u ltip le w a v e le n g th s
are p a s s e d th r o u g h th e in terferom eter th e s in u s o id a l w a v e s r e su ltin g
from e a c h fre q u e n c y c o m b in e to crea te a c e n te r b u r st in th e
interferogram . T he b road er th e freq u en cy ran ge p a s s e d th r o u g h th e
s y s te m , th e narrow er th e c e n te r b u r st w ill b ecom e; th is is ca lle d th e
in v e r se relation .
U sin g F ou rier tra n sfo rm , a n in terferogram p r o d u ce d from a sig n a l
given b y E q u a tio n 2, c a n be co n v erted in to a sp ectru m ,
lf>v = J-SXx) COs(A)Gfv
(4)
In terferom eter b a s e d flu orim efer
A c o m p a r iso n o f in terfero m eter p ro p erties to th o s e o f a
m o n o ch ro m a to r in d ic a te s so m e a d v a n ta g e s th a t m a y b e a p p lica b le to
H n orim etery. In a m o n o ch ro m a to r h ig h r e so lu tio n r eq u ires a n arrow slit,
w h ic h d irectly lim its th r o u g h p u t a n d r e s u lts in a very n a rro w sp ectra l
b a n d p a s s (h en ce th e n a m e), w h ic h a ls o lim its in te n sity . T he
in terfero m eter r e so lu tio n is prim arily d e p e n d e n t o n m a x im u m m irror
d is p la c e m e n t in s te a d o f ap ertu re size provid in g a th r o u g h p u t a d v a n ta g e
over m o n o ch ro m a to rs. A s e c o n d b en efit, term ed th e m u ltip le x a d v a n ta g e,
r e s u lts from th e fa c t th a t a n in terfero m eter p a s s e s all w a v e le n g th s (over
th e b e a m s p litte r ’s o p era tio n a l range) s im u lta n e o u sly .
E x cita tio n S p ec tr o sco p y
In terferom eter u s e w a s te s te d in tw o d ifferent o p e r a tin g m o d e s o f
th e flu orim eter. T he first w a s e x cita tio n sp e c tr o sc o p y (Fig. 2 -7 ), w h ere a n
e m is s io n m o n o ch ro m a to r is s e t to a k n o w n lu m in e s c e n t w a v e len g th o f
th e sa m p le . In a c o n v e n tio n a l s y ste m , th e e m is sio n in te n s ity is
m o n ito r ed a t a fixed w a v e len g th a s a fu n c tio n o f th e e x c ita tio n
m o n o ch ro m a to r w a v e len g th , w h ic h is sc a n n e d . B e c a u s e e m is s io n m u s t
23
0 0020
0 0015
Wavelength (nm)
'I 0 0010
IC
00005
0 0000
22000
20000
18000
Frequency (cm-1)
Excitation
16000
Wavelength (nm)
500
500
C
.2
(Z)
(Z)
700
I
Ic
800
0005
IUUUU
IO V W
£U U U U
Ju C M W t
00000
Frequency (cm-1)
Excitation
(Figure 2-7) Excitation spectrum of Pt2 (pop)4 4"Probed at an emission wavelengths of
400 - 800 nm.
be p r e ce d e d b y e x cita tio n , th is p ro v id es a n in d irect m e a s u r e m e n t o f
a b so r p tio n . In th e c o n v e n tio n a l s y ste m , th e slit w id th a n d n arrow
b a n d w id th lim it th e a m o u n t o f lig h t a v a ila b le for sa m p le e x cita tio n . If a n
in terfero m eter is u s e d for ex cita tio n , m u ltip le w a v e le n g th s im p in g e o n
th e sa m p le s im u lta n e o u s ly b u t e a c h w ill b e m o d u la te d a t a u n iq u e
fr e q u e n c y b y th e m irror m o tio n . T he e m is s io n in te n sity is a ls o m o d u la te d ,
b u t in a w a y th a t c o r r e sp o n d s to th e a b so r p tio n w a v e le n g th ’s freq u en cy .
(This is illu str a te d b y c o n sid e r in g a c a s e w h ere th e a b so r p tio n sp e c tr u m
is a sin g le freq u en cy . T he b ro a d b a n d lig h t is m o d u la te d in a co m p lica ted
fa sh io n , givin g rise to a “c e n te r b u r st” ty p e o f in terferogram , b u t th e
sin g le w a v e le n g th th a t g e ts a b so r b e d is m o d u la te d sin u s o id a lly . H en ce,
th e e x c ita tio n is sin u s o id a lly m o d u la te d a n d th e e m is s io n is s in u so id a lly
m o d u la te d a t th e a b so r p tio n freq u en cy.) In a sa m p le th a t a b so r b s
m u ltip le w a v e le n g th s, e x cita tio n o c c u r s w ith all w a v e le n g th s
s im u lta n e o u s ly r e s u ltin g in stro n g er p u m p in g a n d str o n g e r e m issio n .
T h is str o n g e r e m is s io n sig n a l s h o u ld im p rove sig n a l-to -n o is e a n d c a n
p erm it u s e o f d e te c to r s w ith o u t in ter n a l g a in s. Figure 2 - 7 s h o w s a th ree
d im e n sio n a l e x cita tio n sp e c tr u m c o m p r ised o f Ptg (pop) 4 ^" tw o
d im e n sio n a l sp e c tr a p rob ed a t a n e m is s io n w a v e le n g th s ra n g in g from
4 0 0 -8 0 0 n m .
E x c ita tio n -E m is sio n S p ec tr o sco p y
T h e s e c o n d o p era tin g m o d e th a t w a s te ste d w a s to ta l ex cita tio n e m is s io n s p e c tr o sc o p y (EES). In a c o n v e n tio n a l in s tr u m e n t th e te c h n iq u e
is p erform ed by fixin g th e e x cita tio n m o n o ch ro m a to r, s c a n n in g th e
e m is s io n sp e c tr u m w ith th e s e c o n d m o n o ch ro m a to r, s te p p in g th e
e x c ita tio n to a n e w w a v e len g th , s c a n n in g th e e m is sio n m o n o ch ro m a to r,
a n d rep ea tin g . T he r e s u ltin g d a ta s e t is th r e e -d im e n sio n a l, p roviding
e m is s io n in te n s ity a s a fu n c tio n o f b o th ex cita tio n w a v e le n g th a n d
e m is s io n w a v elen g th .
For th e E E S o p era tin g m o d e, th e in terfero m eter is s u b s titu te d for
th e e m is s io n m o n o ch ro m a to r p rovid in g th r o u g h p u t a n d m u ltip le x
a d v a n ta g e s a s w ell a s rapid s c a n n in g a n d a n in h er e n tly m o d u la te d sig n a l
(w h ich r e d u c e s I / f n o ise ). A u to m a tio n o f th e ex cita tio n m o n o ch ro m a to r
s te p - e m is s io n in terferom eter s c a n s e q u e n c e w a s p erform ed b y u s e o f
TTL p u ls e h a n d s h a k in g b e tw e en a n A cto n NCL co n tro ller (con trollin g a n
A cto n 0 .2 5 m S p ectroP ro m on och ro m a to r) a n d a B ru k er IFS
66
in terferom eter. In terferom eter s c a n p a r a m e te rs, s u c h a s r e so lu tio n ,
n u m b e r o f s c a n s , etc, a s w ell a s h a n d s h a k in g w ere c o n tro lled u s in g a
m acro w r itte n in B ru k er's p roprietary softw are, OPUS. T he tw o em ittin g
S c h iff-b a se s, G R B I -1 9 (G19) a n d G R B l- 1 1 - 1 w ere b o th in v e stig a te d
26
h 0.0012
I- 0.0010
~
0.0008
Frequency (cm-1)
E m is sio n
0.0006
20000
18000
16000
0.0004
&
I
14000
h 0.0002 "
5- 0.0000
15000
20000
25000
30000
Frequency (cm 1)
Excitation
(Figure 2-8) 3D Fluorimeter data using PMT detector for GRBI-19.
u s in g E E S . T he th r e e -d im e n sio n a l sp e c tr u m for G 19 is sh o w n in F igure
2 -8 a n d its to p o g ra p h ic a l v iew in F ig u res 2 -9 a ,b .
T he s p e c tr u m s h o w s th e b road a b so r p tio n profile in d ic a te d in
F igure 2 -8 , a n d a b road , s o m e w h a t r ed -sh ifted , e m is s io n profile. The
27
20000
-
18000
16000
- 14000
-
12000
I
I
C
o
II
10000
8000
Frequency (cm-1)
Excitation
(Figure 2-9a) Frequency vs. frequency for Excitation vs. emission data of GRB1-19.
20000
18000
16000
14000
e
12000
I
10000
!I
§
8000
Wavelength (nm)
Excitation
(Figure 2-9b) Wavelength vs. frequency for Excitation vs. emission data of GRBI -19.
28
d ia g o n a l "streak", m ore v isib le in th e to p o g ra p h ica l view , is d u e to th e
s c a tte r e d e x c ita tio n lig h t a n d p ro v id es a referen ce lin e w h ere e x cita tio n
a n d e m is s io n fr e q u e n c ie s are eq u a l. B e c a u s e e m is sio n is lo w er freq u en cy
th a n th e e x cita tio n , th e p e a k w ill be o n th e Vem<vex sid e o f th e sca tter e d
lig h t d ia g o n a l. T w o -p h o to n a b so r p tio n , u n lik e ly a t th e lo w ex cita tio n
e n e r g ie s a v a ila b le w ith b ro a d b a n d s o u r c e s th ro u g h a m o n o ch ro m a to r,
w o u ld r e s u lt in a p e a k o n th e o th er sid e o f th e d ia g o n a l. A rtifacts, s u c h
a s s e c o n d order e x c ita tio n th ro u g h th e m o n o ch ro m a to r, or a lia sin g in th e
in terfero m eter co u ld a lso r e s u lt in p e a k s o n th e o th er sid e o f th e d ia g o n a l.
T h e E E S o f G R B l- 1 1 - 1 in sh o w n in F igure 2 -1 0 . T he ex cita tio n
profile m a tc h e s th e a b so r p tio n sp e c tr u m sh o w n in F igure 2 -2 (albeit a t
low er reso lu tio n ). T he e m is s io n profile is m u c h n arrow er in d ic a tin g
e fficien t rela x a tio n o f th e h ig h er e lec tr o n ic s ta te s in to th e lo w e st
e lec tr o n ic s ta te follow in g K a sh a ’s rule. O f in te r e st in th is s p e c tr u m is th e
w e a k p e a k a t Vex—4 7 0 n m , Vem- 1 9 6 9 9 .8 1 c m -1. B e c a u s e th is tra n sitio n
is c o m p le te ly o verlap p ed b y oth er, stro n g er a b so r p tio n s it is n o t
d e te c ta b le a s a sep a r a te tr a n sitio n in a sta n d a rd a b so r p tio n sp ectru m .
B e c a u s e it r eq u ires a d ifferen t e x cita tio n freq u en cy th a n th e d o m in a n t
p e a k , it w o u ld lik ely be overlook ed in sta n d a rd e m is sio n sp e c tr o sc o p y a s
w ell. S in c e th is p e a k d o e s n o t em it w h e n th e sa m p le is p u m p e d a t th e
G R B l- 1 1 - 1 a b so r p tio n w a v e le n g th s it is d u e to eith er a v e iy u n c o u p le d
29
00006
22000
20000
18000
.
16000
600
14000
Wavelength (nm)
Excitation
12000
Frequency (cm-1)
Emission
10000
(Figure 2-10) Total excitation-emission plot for GRBl-11-1 (-0.02 mM in BN)
se p a r a te ch r o m a p h o re in th e m o le c u le (unlikely) or it is d u e to a n
im p u rity.
In order to illu str a te a n a d d itio n a l a d v a n ta g e o f E E S , th e sp e c tr u m
o f a d ye m ix tu r e c o n ta in in g h ig h c o n c e n tr a tio n s o f a r h o d a m in e a n d a
c o u m a r in d ye w a s a c q u ir e d (Figure 2 -1 1 ). T he sp e c tr u m s h o w s th ree
p e a k s . T he tw o th a t are n e a r th e d ia g o n a l are e x cita tio n a n d e m is sio n o f
th e r h o d a m in e (at low er freq u en cy Vex= 5 5 0 n m , Vem= 1 6 9 9 2 .1 7 c m 1) a n d
e x c ita tio n a n d e m is s io n o f th e c o u m a r in (at h ig h er fr e q u e n c ie s Vex= 4 0 5
n m , Vem= 2 1 2 7 9 .2 6 c m 1). T he th ird , o ff-d ia g o n a l p e a k a t Vex=
30
(Figure 2-11) Total excitation-emission spectrum of coumarin-rhodamine dye mixture.
4 0 5 n m , Vem= 1 6 9 9 2 .1 7 c m 1, e x h ib its a c o u m a r in e x c ita tio n freq u en cy
b u t a r h o d a m in e e m is s io n freq u en cy in d ic a tin g in te r a c tio n (energy
transfer) b e tw e e n th e tw o m o le c u le s. It s h o u ld be n o te d th a t w ith th is
str o n g ly e m ittin g sa m p le , th e h ig h s ig n a l to n o is e in th e th re e d im e n sio n a l sp e c tr u m w a s o b ta in e d w ith a Si d iod e d etecto r.
CHAPTER 3
EXCITED STATE SPECTROSCOPY OF A SC H IFF-B A SE
E x tin ctio n C oefficient
G 19 e x h ib its a n ex cited sta te (d en oted b y *) a b so r p tio n fea tu re
a r o u n d 9 7 3 n m . C h a ra cteriza tio n o f th is p e a k for c o m p le te
u n d e r s ta n d in g o f th e c o m p o u n d is u se fu l; m oreover its e x tin c tio n
co effic ien t is req u ired to d eterm in e th e c o n c e n tr a tio n u s e d in electro n
tr a n sfe r c a lc u la tio n s.
E x p e rim en ta l. B le a c h in g M ethod
A b r o a d b a n d c o n tin u o u s x e n o n arc la m p w a s fo c u s e d th ro u g h th
sa m p le c u v e tte . T he r e fo c u se d arc la m p w a s a lig n ed o n th e s lit o f a n
O riel (m odel 7 7 2 0 0 ) m o n o ch ro m a to r (Figure 3 -1 ). T he m o n o ch ro m a to r
u s e s tw o g r a tin g s (Oriel 7 7 2 4 4 2 0 0 L /m m 6 0 0 -2 2 0 0 n m , O riel 7 7 2 3 0
2 4 0 0 L / m m 2 0 0 -6 0 0 n m ) in order to cover th e en tire sp e c tr a l ran ge
n e e d e d for b o th b le a c h in g a n d PIA m e a s u r e m e n ts. A C o h e r en t Infinity
NdiYAG la s e r p r o d u ce d a 2 m J ~ 7 n s p u ls e (50 Hz) a t 5 3 2 n m th a t w a s
32
q u a si-c o a x ia l w ith th e b ro a d b a n d lig h t p a th , illu m in a tin g th e sa m p le a t
o n e o f th e focal p o in ts. T he sig n a l o u t o f th e m o n o ch ro m a to r w a s
c o lle c te d b y a H a m a m a tsu R 8 1 0 5 s id e -o n PMT d e te c to r a n d reco rd ed by
a T ek tron ix (m odel T D S 7 8 4 c) o sc illo sc o p e . T he PMT is p o w ered by a
T h orn ( P M 2 8 8 /2 /4 ) EMI h ig h -v o lta g e su p p ly , a n d a S ta n fo rd R esea rch
S y s te m s am p lifier (m odel S R 4 4 5 DC-SOOMHz) e n h a n c e s its sig n a l. A
d e p ic tio n o f th e e x p e rim en t c a n be s e e n in Figure 3 -1 . D e p e n d in g u p o n
th e e x p e r im e n t perform ed , v a r io u s b a n d p a s s filters w ere u s e d to
e lim in a te th e sc a tte r e d la se r lig h t from e n te r in g th e m o n o ch ro m a to r, a n d
a n av era g e o f
1 0 ,0 0 0
p u ls e s w ere u s e d to g en era te th e d ata.
Ceo a t 99.9% p u rity, o b ta in e d from A ldrich a n d T ex a s F u lle re n e s,
w a s u s e d w ith o u t fu rth er p u rifica tio n in e x p e rim en ts req u irin g a n
e lec tr o n a ccep to r. S a m p le s w ere d e o x y g e n a te d by b u b b lin g a n in ert g a s
(n itrogen or argon) th ro u g h th e s o lu tio n for
10
m in u te s .
To fin d th e e x tin c tio n c o efficien t for G 19*, th e p o p u la tio n in th e
e x c ite d sta te a n d th e rela ted relative in te n s ity d u e to th a t p o p u la tio n
m u s t b e fo u n d . We c a n c a lc u la te th e p o p u la tio n in th e e x c ite d sta te by
d e te r m in in g d e p le tio n in th e g ro u n d s ta te p o p u la tio n th r o u g h o b serv in g
th e s ta n d a r d a b so r p tio n in te n sity drop (bleaching) a lo n g w ith u s in g th e
p r e v io u sly c a lc u la te d g ro u n d sta te e x tin c tio n co efficien t. A lon g w ith PIA
33
(Figure 3-1) Photo-bleaching experimental layout; a) Pulsed laser b) Beam dumps c)
Filters d) Sample e) W arc lamp f) Fiber optic cable g) Monochromator h) Detector.
34
tem p o ra l d e c a y c u r v es, th e b le a c h in g e x p erim en t w ill y ie ld th e
in fo rm a tio n n e e d e d to d eterm in e th e ex cited sta te e x tin c tio n coefficien t.
H-----h T t
ISC
Excited state
hv
H 1111I H+
»
Ground state
4 4 -H -S i
I
fast
I I
p
4— H Ti
B leach in g
I I
e
H— I—1-4 s O
(Figure 3-2) Photo-excitation from ground state to excited state and intersystem
crossing to G19 excited state.
W h en a sa m p le is ex cited from th e grou n d sta te , th e a b so r p tio n o f
th a t g ro u n d sta te d im in is h e s d u e to red u c tio n in p o p u la tio n o f th a t sta te
(Figure 3-2); th is is o ften referred to a s b lea ch in g . In G 19 th is effect is
n o t p erm a n en t; th e g ro u n d sta te p o p u la tio n is r ep le n ish e d a s th e ex cited
sta te d e c a y s. T h u s, a t tim e s after in te r s y ste m c r o ssin g is c o m p lete, th e
b le a c h in g a n d PIA s h o u ld e x h ib it th e s a m e rela x a tio n tim e d e p e n d e n c e .
It is im p o rta n t to n o te h ow ever, th a t e m is s io n c a n c a u s e sp e ctra l
in ter fe r en ce , m a k in g it d ifficu lt to m e a s u r e b le a c h in g reliab ly if it o c c u r s
a t th e s a m e w a v elen g th .
35
R e su lts & In terp retation
B le a c h in g e x p e r im e n ts w ere p erform ed th e G R B 1 -1 9 c o m p o u n d in
order to c a lc u la te th e ex cited sta te m o la r e x tin c tio n co efficien t. W h en Vw
e q u a ls th a t o f v o lta g e d u e to th e w h ite ligh t, a n d Vlw e q u a ls th a t o f w h ite
lig h t v o lta g e d irectly follow in g a la se r p u ls e , th e n
Vlw = Tw^
W
and
r . = r » r = /.e - " " r
w h ere
7
is th e sig n a l, F is th e d e te c to r r e s p o n se , m is th e g ro u n d sta te
c o n c e n tr a tio n , a n d n is th e ex cited s ta te co n c en tr a tio n . S o,
Vtw
=
,3,
I ^ e - s Im - n V r
giving,
I n— = —sn£
Vfu,
(4 )
W ith th e v o lta g e s c a lc u la te d a s a ratio in th is w ay n o ca lib r a tio n o f th e
d e te c to r is n e e d e d b e c a u s e all is s u e s in v o lv in g d etecto r r e s p o n s e are
36
0.15
PIA at 960nm
T ~ 150 ps
0.05
0 .0 0
-0.05
-
0. 10
-100 0
B le a c h in g a t 4 4 0 n m
T ~ 1 5 0 ns
100 200 300 400 500 600 700 800 900
T im e (ps)
(Figure 3-3) data using Equation 4 for GRB1-19 PIA and bleaching 31,800 L M 1 c m 1.
d ivid ed o u t. T h e se p lo ts form ed from E q u a tio n 4 c a n b e s e e n in F igure 3 3. T he tw o c u r v e s in th is figu re follow e a c h o th er after th e b le a c h in g
s ig n a l is p a s t a n y co rru p tin g c o n tr ib u tio n from la s e r in d u c e d
s c a tte r in g . 15 U sin g E q u a tio n 4 a n d B e e r ’s la w g iv es
O D bleacH _
ODpia
£ ground
Spia
(5)
w h ere OD is th e o p tica l d e n s ity o f b le a c h in g (su b sc rip t b lea ch ) an d
p h o to in d u c e d a b so r p tio n (su b sc r ip t PIA). T h is rea r r a n g e s to
= PDPIA
^ PIA
‘'ground
U U bleach
(6 )
37
w h ere Sgr0Und is th e g ro u n d sta te e x tin c tio n co efficien t a n d spia is th e
d e sir e d e x cited s ta te e x tin c tio n co efficien t. From th e s e b le a c h in g
e x p e r im e n ts th e e x cited sta te e x tin c tio n co efficien t o f G R B I -1 9 w a s
c a lc u la te d to b e 3 1 ,8 0 0 L M-1Cm-1.
CHAPTER 4
ELECTRON TRANSFER INVOLVING A SC H IFF-BA SE COMPOUND
S c h iff-b a se e lec tr o n tra n sfer
E lectro n tr a n sfe r is th e m o s t fu n d a m e n ta l o f c h e m ic a l r e a c tio n s
a n d is th e v ital m e c h a n is m in m a n y in te r e stin g p r o c e s s e s . P erh a p s th e
m o s t im p o rta n t a n d w id ely k n o w n p h o to in d u c e d e lectro n tr a n sfe r (PET)
p r o c e s s is p h o to s y n th e s is . 16 S y n th e tic PET s y s te m s are o f in te r e st for a
v a riety o f a p p lic a tio n s s u c h a s d a ta sto ra g e, en erg y sto r a g e, a n d o p tica l
lim itin g . 17 W ith a w e a lth o f a p p lic a tio n s, th e s tu d y a n d s y n th e s is of
c o m p o u n d s w ith th e ab ility to perform PET is a n a ttra ctiv e en d ea v o r
w ith in th e field o f p h y sic a l c h e m is tiy .
E x p erim en ta l, PIA M eth od ology
T h e M ich elso n in terferom eter n o rm a lly a cq u ires d a ta in r a p id -sc a n
m o d e. In th is m od e th e m ovab le m irror is tr a n sla te d in a c o n tin u o u s
fa s h io n , a n d d a ta a c q u isitio n is triggered a t th e zero c r o s s in g s o f th e s in e
w a v e g e n e r a te d b y th e in terferen ce o f a referen ce H eN e la s e r w ith itself.
39
S ig n a l a v era g in g c a n b e a c c o m p lish e d th ro u g h c y clin g th e m irror w ith
th is rap id a c q u isitio n c re a tin g a n in terferogram w ith h ig h sig n a l-to -n o is e .
R apid s c a n n in g is co n tro lled b y a n in ter n a l c lo ck a n d d ifficu lt to
co o rd in a te w ith a n e x te rn a l la se r p u lse .
In order to perform tim e-re so lv ed , p h o to in d u c e d a b so r p tio n
sp e c tr o sc o p y , it is n e c e s s a r y to sy n c h r o n iz e th e a c q u is itio n o f th e
in terferogram w ith th e p h o to - in itia tin g la se r p u lse . In order to
a c c o m p lis h th is, th e in terferom eter c a n b e op era ted in a s te p -s c a n m od e.
A s th e n a m e im p lie s, th is m od e p o s itio n s th e m o v in g m irror in a s te p ­
w is e fa s h io n , p la c in g it a t a H eN e zero c r o s s in g a n d h o ld in g it th ere w h ile
d a ta a c q u is itio n is triggered by a n e x te rn a l in str u m e n t. For c o m p letely
tim e -r e so lv e d sp e c tr o sc o p y , a n en tire tr a n s ie n t sig n a l is a cq u ired a t a
m irror p o s itio n by u s in g a tr a n s ie n t digitizer. T he m irror p o sitio n is th e n
ste p p e d to a n e w p o sitio n , fixed, a n d a n e w tr a n s ie n t is reco rd ed . T h is
p r o c e s s is rep ea ted for all m irror p o s itio n s y ield in g a d a ta s e t o f in te n sity
v s. m irror p o s itio n a n d tim e. In order to im prove sig n a l to n o is e ,
m u ltip le tr a n s ie n ts c a n b e sig n a l a v era g ed a t e a c h m irror p o sitio n . A t a
given tim e -slic e , th e d a ta a c r o s s all m irror p o sitio n s c a n b e Fourier
tr a n sfo r m e d to y ie ld a sp e c tr u m a t th a t tim e. T he r e s u lt is a se r ie s of
in terfero g ra m s w h ic h c a n b e m a n ip u la te d to form sp e c tr a ev o lv in g w ith
tim e.
40
(Figure 4-1) 3D plot of raw Fourier transformed signal from GRBI-19 [O.OSmM] and Ceo
[0.4mM] in BN.
In p h o to in d u c e d a b so r p tio n , lig h t from a c o n tin u o u s so u r c e is
p rojected th ro u g h th e sa m p le in order to d e term in e g r o u n d sta te
tr a n s m itta n c e . T he sa m p le is th e n s tr u c k b y a la ser , w h ic h p ro m o tes
p o p u la tio n from th e g ro u n d s ta te to a n e x c ite d o n e. A fter th e e x cita tio n ,
a n d e v o lu tio n o f a n y d y n a m ic a l p r o c e s s , th e s y ste m w ill d e c a y b a c k to it
origin al s ta te . F igure 4 -1 s h o w s a tim e d e p e n d e n t r e sp o n c e . The
tr a n s m itta n c e after p u m p in g c a n th e n b e d ivided by th e u n p u m p e d
g r o u n d s ta te a n d c o n v e rted to a b so r p tio n .
41
All PIA a n d p u m p -p r o b e e x p e r im e n ts u tiliz ed a n ex tern a l, c o n tin u o u s
b r o a d -b a n d lig h t so u r c e (75 W X e n o n arc or 5 0 W T u n g s te n h a lo g e n
bulb) fo c u s e d in to th e sa m p le c u v e tte a n d r efo cu se d in to a B ru k er IFS
or
88
66
in terferom eter, w ith proper f / # m a tch in g . A C o h e r en t Infinity
(m odel 4 0 -1 0 0 ) Nd:YAG p u ls e d la se r d o u b le d to 5 3 2 n m w a s u s e d to
e x cite th e sa m p le . T he la s e r p u m p b e a m w a s b r o u g h t in q u a si-c o a x ia lly
to th e b r o a d b a n d probe ligh t, o verla p p in g th e focal reg io n in th e sa m p le .
T h is fo ca l region w a s re-im a g ed o n to a n a p ertu re s e t to s e le c t th e c en ter
-3 0 % o f th e p rob e lig h t overlap p ed by th e la se r p u m p b efore th e lig h t
e n te r ed th e in terferom eter. W hile u s e o f o n ly th e c e n te r reg io n red u ced
th e in p u t lig h t in te n sity , it a lso r ed u c ed c o n tr ib u tio n s to th e sig n a l from
th er m a l g r a d ie n ts in th e p rob e reg io n a n d sig n ifica n tly e n h a n c e d S /N .
T he tr a n s ie n t record er w a s a S p ec tr u m PAD 1 2 3 2 th a t is a 12 bit, 40M H z
b a n d w id th digitizer provid in g u p to 2 5 n s tem p o ra l r e so lu tio n . B a n d p a ss
filters w ere p la c e d in th e 5 3 2 n m b e a m prior to sa m p le e x c ita tio n to
e lim in a te th e fu n d a m e n ta l 1 0 6 4 n m o f th e Infinity la ser. A p olarizer a n d
b e a m sp litte r w ere a lso p la c e d in th e 5 3 2 n m b ea m to c o n tr o l th e p ow er
level to 3 m J p er p u lse . 5 0 n s tem p o ra l r e so lu tio n w a s u s e d in th e s e PIA
e x p e r im e n ts a n d 8 0 tr a n s ie n ts w ere a v era g ed per fixed m irror p o sitio n in
order to in c r e a s e sig n a l to n o ise . T he sig n a l w a s c o lle c te d w ith a n INSB
d e te c to r s e a te d in th e B ru k er interferom eter. No s m o o th in g w a s
p erform ed o n th e d a ta p r e se n te d . T he PIA la y o u t s h o w n in F igure 4 -2 .
42
0
(Figure 4-2) PIA layout; a) Pulse laser b) Beam dumps c) Filters d) Polarizer e) Tungsten
lamp I) Sample position g) External focal point h) Interferometer i) Detector.
43
D a ta A n a ly sis
U sin g M a rcu s e q u a tio n s to form d ia b a tic free e n e rg y c u r v es, H u sh
first p r e se n te d p h o to in d u c e d e lectro n tra n sfer in th e m id 1 9 5 0 ’s
s p a w n in g a m u ltitu d e o f p a p er s o n th e su b je c t in c lu d in g refer en ce s 18
th r o u g h 2 9 . PET, a s sh o w n in F igure 4 -3 , is th e a b so r p tio n o f lig h t by
th e r e a c ta n ts , e x citin g th e m in to a n u p p e r en erg y cu rve. T he c u r v es in
F igure 4 -3 r e p r e se n t b o th th e r e a c ta n ts in volved in PET e v e n th o u g h o n ly
o n e o f th e m m a y b e ex cited .
F req u en tly , k in e tic s c h e m e s in v o lv in g a sin g le e x c ite d r e a c ta n t a n d
n o in te r m e d ia te s h a v e b e e n em p lo y ed to d escrib e th e d y n a m ic s of
PET .3 0 -31
hv
A +D
k et
A* + D -» A~ + D +
(7)
w h ere a n a s te r is k d e n o te s a n ex cited sta te a n d ket r e p r e s e n ts th e rate
c o n s ta n t for elec tr o n tran sfer. T he su p e r sc r ip t p lu s a n d m in u s s ig n s
sy m b o liz e th e c a tio n a n d a n io n for th e d o n o r a n d a c ce p to r, resp ectiv ely .
T h is sin g le e x cited sta te s c h e m e w a s later im p roved w h e n p o ssib le
in te r m e d ia te s a n d m u ltip le p a th w a y s w ere ta k e n in to a c c o u n t . 32"34
44
*
A
kd I
+ D —> |A
^ \ksep
••• D J —> A. + D
(8 )
A +D
In th is s c h e m e , th e g e m in a te r ec o m b in a tio n rate (Zcet) is in tro d u c ed a lo n g
w ith a n in ter m e d ia te for th e sy ste m . A d iffu sio n -lim ited rate o f form ation
(kd) for th e in ter m e d ia te is d eterm in ed by th e c o llisio n freq u en cy o f th e
r e a c ta n ts. T he in ter m e d ia te c a n th e n c a n go th ro u g h g e m in a te
Nuclear motion
(Figure 4-3) Photoinduced electron transfer free energy curves, R- reactant curve
(asterisk denotes one or both of the reactants in an excited state), P- product curve.
45
r e c o m b in a tio n or se p a ra te in to so lv a te d io n p a irs (ksep). T he a d d itio n o f
th e in te r m e d ia te s p ro v id es a m ore d e ta iled r e p r e se n ta tio n o f th e e lectro n
tr a n sfe r sy ste m .
M a x im u m io n c o n c e n t r a t io n
(c o r re cted )
M a x im u m io n c o n c e n t r a t io n
(u n c o r r e c te d )
(Figure 4-4) Raw data of ion concentration and ion concentration corrected for back
electron transfer.
A p ro b lem w ith E q u a tio n
8
is th a t r ec o m b in a tio n o f th e so lv a ted
io n s , a n ex p e rim en ta lly o b serv ed p h e n o m e n o n , is n o t a c c o u n te d for. T h is
is co rrected in th e follow in g m e c h a n is m in tro d u ced b y H a n a n d
S p an gler.
46
.
kd/ *
A + D -+[A
k si
-D
i kr
I k gr
A+D
A+D
r
<-
A~ + D +
(9)
k rec
w h ere k r is a r ela x a tio n rate c o n s ta n t o f th e r e a c ta n ts to th e
n e u tr a l s ta te s , k d r e m a in s th e d iffu sio n rate c o n s ta n t, k g r is g em in a te
r e c o m b in a tio n o f th e in ter m e d ia te (I), k Si is th e se p a r a tio n in to so lv a ted
io n s , a n d Zcrec is a r ec o m b in a tio n term for b a c k e lectro n tra n sfer. K inetic
tr e a tm e n t u s in g th is s c h e m e a c k n o w le d g e s th e b a c k e lec tr o n tra n sfer
(recom b in ation ) by in tro d u c in g it a s a reversib le p a th w a y w ith in th e
s y ste m .
H an a n d S p a n g ler sh o w ed th a t b y fittin g th e lo n g tim e s e c o n d
order r e c o m b in a tio n k in e tic s (after d e p le tio n o f th e p h o to in itia to r), a n d
s u b tr a c tin g th is from th e a c tu a l io n d y n a m ic s, a co rrected io n curve
c o u ld b e o b ta in e d th a t r ise s a sy m p to tic a lly to a c o n s ta n t v a lu e (Figure 4 4). T he u tility o f th is v a lu e is illu str a te d by c o n sid e rin g th a t m a n y
p u b lis h e d s tu d ie s rep ort a q u a n tu m y ie ld for electro n tr a n sfe r th a t is a
ratio o f th e e x p e rim en ta l m a x im u m io n c o n c en tr a tio n over th e m a x im u m
p h o to in itia to r c o n c e n tr a tio n , [D+]exp. max / [A*]max (Figure 4 -4 ). T here are
p r o b le m s w ith th is m e th o d . First, th e m a x im u m io n c o n c e n tr a tio n is
d e te r m in e d b y b o th forw ard a n d rev erse p r o c e s s e s , th eir e ffic ie n c ies, a n d
47
th eir relative r a te s. C o n se q u e n tly th e y ie ld rep orted is n o t rea lly for io n
fo rm a tio n b e c a u s e rec o m b in a tio n is fo ld ed in . S eco n d ly , th e u ltim a te io n
y ie ld is o b v io u sly zero b e c a u s e a ll io n s e v en tu a lly reco m b in e.
A
b e tter a p p ro a c h is to d efin e q u a n tu m e ffic ie n c ies for e a c h
p r o c e s s th a t c a n be in d iv id u a lly a d d r e sse d . B y su b tr a c tin g th e b a ck
e lec tr o n tr a n sfe r (BET) d y n a m ic s, a co rrected curve is o b ta in e d th a t
c o n ta in s o n ly forw ard (ion form ation) p r o c e s s e s . A ratio o f th e corrected
m a x im u m io n c o n c e n tr a tio n to m a x im u m p h o to in itia te d c o n c e n tr a tio n
([D+Jcorr. max
/ [A*]max) th e n y ie ld s a q u a n tu m efficien cy for th e forw ard
p r o c e s s (Figure 4 -4).
It w a s a lso p o in te d o u t th a t th e forw ard r ea ctio n is a tw o -ste p
p r o c e s s a n d th a t th e overall q u a n tu m efficien cy c o u ld b e e x p r e s s e d a s a
p r o d u c t o f th e q u a n tu m efficien cy for e a c h step .
®
(io)
w h ere
. W ]
* VD]+
(
11 )
1
and
®si =
k-si
^si + kgr
(
12 )
T h is tr e a tm e n t se p a r a te s th e q u e n c h in g efficien cy, th e p ro b a b ility th a t
a n A *- D c o llisio n w ill o ccu r, from th e efficien cy o f fo rm a tio n o f so lv a ted
io n s , Osi. T he la tter is a m e a su r e o f th e fra ctio n o f A*-D e n c o u n te r s th a t
48
a c tu a lly r e s u lts in ion form ation a n d is a b etter m e a su r e o f th e in trin sic
elec tr o n tra n sfer p ro p erties for th e m o le c u la r sy ste m .
B o th o f th e ab ove m e c h a n is m s d ea l w ith o n ly o n e p h o to in itia to r.
T h is th e s is p r e se n ts a k in etic tr e a tm e n t o f a sy ste m h a v in g tw o
p h o to in itia to r s a n d th e p o ssib ility o f b i-m e c h a n istic e lec tr o n transfer.
D onor
A c c e p to r
hv
(Figure 4-5) Energy level transfer scheme; a) hole transfer b) electron transfer.
49
K in etic Im p o rta n ce o f a B i-m e c h a n istic S y ste m
E x cita tio n o f th e d on or in s te a d o f th e a c cep to r r a is e s th e p o ssib ility
th a t th e in itia l in ter m e d ia te form ed c o u ld be different; i.e. (A -D i) vs.
(A*-D). T h ey m a y b o th p ro ceed to form a d elo ca lized e x c ip le x (A -JD)* or
m a y p r o c ee d d irectly to th e io n pair, (A-+D+). C on versely, a lo ca lized
e x c ip le x m a y b e form ed n ea rly in s ta n ta n e o u s ly u p o n e n c o u n te r o f th e
tw o s p e c ie s m a k in g (A*-D) v s. (A -D k) th e first r elev a n t in term ed ia te. In
order to a d d r e s s w h e th e r a differen t in itia l in term ed ia te e x is ts , it is
u s e fu l to c o n s id e r tw o m e c h a n is m s th a t a s s u m e it d o e s.
R a te s a n d in te r m e d ia te s r e s u ltin g from th e e x c ita tio n o f th e
a c ce p to r (donor) are la b e le d w ith th e s u b s c r ip t A (D). H ere, th e first
in ter m e d ia te in th e tw o differen t m e c h a n is m s are sh o w n a s lo ca lized
e x c ip le x e s th a t w o u ld h a v e d ifferen t e n e r g ie s an d , th erefo re, p o ten tia lly
d ifferen t k in e tic s. (If a d elo ca lized e x cip le x , (A-D)*, fo rm s u p o n c o llisio n ,
th e tw o m e c h a n is m s b e c o m e e s s e n tia lly id en tica l.) T he s e c o n d
in te r m e d ia te is sh o w n a s id e n tic a l in th e tw o m e c h a n is m s for r e a s o n s
b e s t u n d e r s to o d b y c o n sid e r in g th e r ec o m b in a tio n p r o c e s s . T he so lv a ted
io n s form ed b y e a c h m e c h a n is m s h o u ld be id en tica l. T herefore, th e
in ter m e d ia te g e n e ra ted b y c o llisio n o f th e so lv a ted io n s d u rin g
r ec o m b in a tio n , I2 = (A-- D +), s h o u ld b e id en tica l.
50
We n o w w ork o u r w a y th o u g h th e first m e c h a n is m (S ch em e 4 -la )
to illu str a te th e p r o c e s s . T he so lv e n t se p a ra ted r e a c ta n ts, A* a n d D
d iffu se a n d collid e w ith rate c o n s ta n t kdA . Ceo, a w ell d o c u m e n te d
p h o to in itia to r , w a s u s e d a s th e a c ce p to r in th e s e e x p e r im e n ts .3 5 ’36 A
6
c o m p e titiv e rate for lo s s o f p h o to in itia to r is krA w h ic h is th e rela x a tio n
rate o f th e e x cited a ccep to r. T he first in term ed ia te (7U ) is a n ex cip le x o f
th e r e a c ta n ts form ed by th e d iffu sio n p r o c e ss.
J la
c a n fu rth er evolve in to
th e s e c o n d in ter m e d ia te J2 w ith th e rate c o n s ta n t Zclj4 or rela x to n e u tr a l
s ta te s th r o u g h rate Zc2j4. T he s e c o n d in ter m e d ia te is n o t d e n o te d by a
s u b s c r ip t "A" b e c a u s e b o th th e d o n o r a n d a ccep to r io n p a ir s are
a s s u m e d to b e id e n tic a l for b o th m e c h a n is m s h ere, a s d is c u s s e d
*
A
td A /
\%1A I 12
+ D —> (A ••• DJ —> {a ~--- d +
A +D
A +D
kdA
A + D*
l k rD
A +D
- »
<Zcrec
A~+D+
(a)
A, +D
[ IlD A kW (
IA i--J) I > Ia
—
h
~
...£ )
i k 2D
A +D
^si
ksi
+h
' +-
A~ + D +
(b)
k rec
A +D
(Scheme 4-1) Electron transfer mechanism; (a) Acceptor excited case, (b) Donor excited
case.
51
p rev io u sly . R everse rate c o n s ta n ts are n o t in c lu d e d in th e first tw o s te p s
b e c a u s e th e y are n o t b eliev ed to o c cu r w ith a n y sig n ific a n t p rob ab ility. If
th e s e p a th w a y s w ere p r e se n t, th e lifetim e o f th e ex cited s ta te w o u ld
r eta in p o p u la tio n a s lo n g a s io n s e x iste d , w h ic h is n o t o b se rv e d in th e
d a ta (see F igure 4 -4 ). O n ce a gain , th e 1 2 io n pair c a n lo s e its energyth r o u g h g e m in a te r ec o m b in a tio n (kgr ) reform ing th e in itia l r e a c ta n t
s ta te s , or it c a n c o n tin u e to drift a p a rt form in g io n s th r o u g h p a th w a y
Zcsz- . T he free io n s c a n th e n reco m b in e th ro u g h th e Zcrec p a th w a y
reform in g th e io n pair.
We do n o t tr e a t th e c a s e for c o llisio n in volvin g b o th a n e x cited
d o n o r a n d a n e x cited a c cep to r (A*+D*) b e c a u s e th e low c o n c e n tr a tio n s o f
e a c h m a k e th is c o n tr ib u tio n sm a ll. U n d er th e e x p e rim en ta l c o n d itio n s,
a p p ro x im a te ly 13.5% o f a c cep to r is e x cited m a k in g th e D* c o llisio n rate
w ith A over se v e n tim e s m ore lik ely th a n w ith A*. S in c e th e D* is
q u e n c h e d m u c h fa ste r th a n A* (sh o w n later) m o s t A* c o llis io n s w ill be
w ith D , n o t D*, w h ic h o n ly h a s a p p ro x im a tely 2.9% ex cited .
A n a ly sis for B i-M ec h a n istic S y ste m
A lth o u g h PIA w a s perform ed o n all o f th e M iller c o m p o u n d s in
c o m b in a tio n w ith Ceo, G 19 w a s th e o n ly o n e w h ic h s h o w e d a p p recia b le
PET. T he raw a b so r p tio n d a ta o f th e G 19 s te p -s c a n PIA s p e c tr u m c a n be
52
s e e n in F igu re 4 -6 , w ith la s e r in d u c e d e m is s io n su b tr a c te d o u t. B e c a u s e
o f th e str o n g overlap o f th e 3 Ceo* a n d th e e m is s io n b a n d , s u b tr a c tio n o f
e m is s io n is n e c e s s a r y to g e n e ra te a c c u r a te tr a n s ie n t b eh a v io r for k in etic
a n a ly s is .A s th e 3 Ceo* a n d 3G R 19* p e a k s d eca y , a tr a n sitio n a t 1 0 8 0 n m
( - 9 ,3 0 0 c m 1) r is e s w h ic h c a n b e a ttrib u te d to th e w ell d o c u m e n te d C eo
a b so r p tio n , w h ic h p ro v id es p ro o f o f e le c tr o n tra n sfer. A very broad
tr a n sitio n p e a k in g a r o u n d 1 4 5 0 n m ( - 6 9 0 0 c m 1) e x h ib its th e sa m e
(Figure 4-6) 3D plot of raw PIA data for G19 [O.OSmM] and Ceo [0.4mM] in BN.
53
tem p o ra l b eh a v io r a s th e C eo- p ea k , a n d is in th e v ic in ity o f k n o w n
in te r v a le n c e b a n d s in o th er c o n ju g a te d m o le c u le s c o n ta in in g m u ltip le
s u b s titu te d a m in o g r o u p s a n d so a ttrib u ta b le to G 1 9 +. T h e p r e se n c e o f
fou r s p e c ie s ,
3 Ceo*,
Ceo , 3 GRlQ*, a n d G R lQ +, e a c h o f w h ic h h a v e broad
p e a k s in th e red to n e a r IR region o f th e sp e c tr u m le a d s to o verlap p in g
tr a n s itio n s w h ic h m u s t b e corrected in order to d e term in e a c cu ra te
c o n c e n tr a tio n s . A t lo n g tim e s, 3 Ceo* a n d 3 GRlQ* are c o n s u m e d so o n ly
ch a r g ed s p e c ie s co n tr ib u te to th e PIA. B y p e a k fittin g th e C eo- , th e
c o n tr ib u tio n o f G R lQ + to th e Ceo- c a n be d eterm in ed a n d a n a c cu ra te
C eo- in te n s ity ex tra cted .
From th is in te n s ity a n d th e liter a tu r e v a lu e for
th e m o la r e x tin c tio n co efficien t, th e Ceo- c o n c e n tr a tio n c a n be
d ete r m in e d . S in c e Ceo
a n d G R lQ + c o n c e n tr a tio n s are in te r d e p e n d e n t
a n d e q u a l, th e m olar e x tin c tio n c o efficien t for G R lQ + c a n b e d eterm in ed
from th e in ter v a le n c e b a n d p e a k in te n sity . P ea k fittin g o f th e slig h tly
o v erla p p in g 3 Ceo* a n d 3 GRlQ* y ie ld s relia b le in te n sity for 3 Ceo* a n d u s e o f
th e k n o w n m olar e x tin c tio n co efficien t a llo w s d e te r m in a tio n o f [3 Ceo*].
T he d e c o n v o lu tio n o f th e tr a n sitio n s is illu str a te d in F ig u r es 4 -7 a n d 4 -8 .
T he h ig h sig n a l-to -n o is e d a ta th a t is reso lv ed in b o th tim e a n d freq u en cy
th a t is a v a ila b le from th e ste p s c a n te c h n iq u e m a k e it p o s s ib le to do th is
level o f d e c o n v o lu tio n a n d still g e n era te a c cu ra te tr a n s ie n t r e sp o n se .
54
800
W avelength (nm)
1000
1200
1400 1600
G R B 1-19
G R B l-19
14000
12000
8000
10000
6000
F requency (cm" )
(Figure 4-7) Subtraction diagram of spectral data; solid line- early times, dash
line- late times, hatching shows separated peaks.
W avelength (nm)
1000
1200
1400
1600
0.300.25Nlntegrated
0 .2 0 -
=GRBl-19^
range
0.15-
Integratei
G RB1-19
range
0. 1012000
10000
8000
Frequency (c m 1)
(Figure 4-8) Integration ratio contribution diagram for ion intensity incorporated
into G19* peak. Hatch marks show respective integration ranges of G19* (higher
frequency) to that of G19+ (lower frequency) of which the contribution Ceo can be
determined for the G19 integration range at earlier times.
55
R e s u lts & In terp retation
D e c a y c u r v e s o f th e a c cep to r a n d d o n o r c a n be s e e n in Figure 4 -9 .
T he tw o lo n g er lifetim es are for s o lu tio n s c o n ta in in g o n ly o n e a n a ly te,
G 19 or C 6 0 . T he sh o rter d e c a y s (extracted from Figure 4 - 6 u s in g th e
p ro ced u re d e sc r ib e d in th e p rev io u s sectio n ) are from a s o lu tio n
c o n ta in in g b o th c o m p o u n d s sh o w in g th a t Ceo q u e n c h e s G 19* a n d G 19
q u e n c h e s Ceo*. T h is m u tu a l q u e n c h in g is a n in d ica tio n th a t b o th s p e c ie s
c a n a c t a s p h o to in itia to r s a n d th a t th e r ea ctio n m ig h t b e b i-m e c h a n istic .
F rom th e m e c h a n is m in S c h e m e 4 - la , w e c a n d e te r m in e th e rate
e x p r e s s io n for th e ex cited a c cep to r (A*),
^ r = - k d A l A * m - k rA{A*]
at
(is)
B e c a u s e o f th e g ro u n d sta te d on or c o n c e n tr a tio n b e in g large co m p a red to
th e c o n c e n tr a tio n o f A*, th e first term in E q u a tio n 13 is p s e u d o first
order:
(14)
T h is a llo w s sim p lific a tio n o f E q u a tio n I to,
d[A*]
dt
- k rA [A ] - kqA [A ] - -ftrA + ^qA ) lA * ]
In teg ra tio n o f th is e q u a tio n r e s u lts in,
(15)
y /G 1 9 /6 0
< w ith o u t accep tor
\ r = SOjrs
w ith o u t donor
x = 2 2 |lis
t=
0 .4 8 9 3 2 n s
Tim e (ns)
(Figure 4-9) Time decays for G19* & 3Ceo* without quenching counterpart (0.05 mM and
0.4 mM respectively) and when combined (0.05mM and 0.4mM respectively). (All
solutions made with BN.)
[A*l-[A*]0 e " ,'CrA+,C9A,<
(i6|
w h ic h a llo w s a n e x p r e s s io n for th e o b serv ed e x p e rim en ta l d e c a y rate o f
3C60*.
^obsA
^ r A + ^qA
^rA
+
^
(17)
We n o w e x a m in e th e rate o f fo rm a tio n for th e p r o d u c ts, in itially
c o n sid e r in g o n ly th o s e form ed by p u m p in g th e a ccep to r. T h e ion p ro d u ct
c o n c e n tr a tio n s are co m p le te ly in te r d e p e n d e n t w ith a o n e to o n e ratio for
[D+ ] a n d [A" ]. T h u s, b o th io n s c a n be follow ed by lo o k in g a t th e
form ation o f th e d on or c a tio n (c h o se n b e c a u s e its p e a k h a s le s s overlap
57
w ith o th er s p e c ie s ’ tr a n sitio n s). A gain, from th e m e c h a n is m in S c h e m e 4 la,
ar
= Jcs iIZ2 ] - f c r e c P 4-]2
(is)
w h ere [la] is th e s e c o n d in term ed ia te. R a te s in volvin g kiA, k si a n d kgr are
e x p e c te d to be m u c h fa ste r th a n th e d iffu sio n p r o c e ss d e n o te d by kda a n d
krec- T h is m e a n s th e in ter m e d ia te c o n c e n tr a tio n s w ill b e rela tiv ely
c o n s ta n t w ith r e s p e c t to tim e w h e n c o m p a red to o th er s p e c ie s a n d a
s te a d y s ta te a p p ro x im a tio n c a n be ap p lied .
^
= 0 = Zc1A [/1A ] - fcgr [Z2 ] - Jcsi [ / 2 ] + fcrec [D + ] 2
ar
(19)
W here [D+]2 =[A"][D+], sin c e [D+]=[A'] is u s e d in th e la s t term . E q u a tio n 19
c a n th e n b e rearran ged to Solve for th e in term ed ia te co n cen tra tio n ;
^J2 ^ _
^ i a I1Ia ] + KeclD+]2
tg r + tsi
(g o ,
We n o w a p p ly th e ste a d y sta te a p p ro x im a tio n a se c o n d tim e in order to
so lv e for th e first in ter m e d ia te
[ I i a ],
= 0 = Zcd l4 [A* ] [I)] - Zc2a [Z1A ] - Zc1a [Z1A ]
ai
(2 i)
a n d so lv in g for [Iia] gives,
kgAl-A ]
Ui a )
k-2A + ^cIA
(
22)
58
E q u a tio n 2 2 c a n be p lu g g ed in to E q u a tio n 2 0 , a n d n o w E q u a tio n 2 0 c a n
b e r ein tr o d u c e d in to E q u a tio n 19, giving,
KqAiA
klA
d[D + ]
*
\
+ i2
+ k rec
]
k 2 A + k IA
- K e c l D + ]2
si
k q r + k si
(23)
w h ic h r ea rra n g es in to ,
d[D + ]
k si
k IA
M
a * ] + k rec P + ]2
k g r + k s i k 2 A + k IA
ksi
- K e c l D +I2
K q r + k si
(24)
Q u a n tu m e ffic ie n c ies, for so lv a te d io n form ation , a n d o u t o f th e first
in te r m e d ia te are given by
k si
®si
k gr + k si
(25)
and
=
1A
k IA + k 2A
(26)
, c a n b e w r itte n w h ic h r e d u c e E q u a tio n 2 4 to
" I = 4>si » j 1AfcsA [ A * ] - ( l - I . si )krec P + ] 2
(27)
W e n o w c o n sid e r th e c a s e w h ere th e d o n o r is ex cited a n d fu n c tio n s a s
th e p h o to -in itia to r for th e e lectro n tra n sfer. T he m e c h a n is m for th is is
59
s h o w n in S c h e m e 4 - lb a n d th e k in etic tr e a tm e n t is e x a c tly a n a lo g o u s to
th e tr e a tm e n t from th e p r e v io u s m e c h a n is m r e su ltin g in
[D*] = [ D * ] e
(28)
and
k q D
[ D
]
- (I - 4»si)kreC[5+]2
at
(2 9 )
S in c e b o th th e d on or a n d a c cep to r a b so rb a t 5 3 2 n m , b o th m e c h a n is m s
c a n b e op erative a t th e s a m e tim e. C o m b in in g term s g iv es
S p - = OsiO 7lc kqD[D* j + OsiO7lil kqA[A ] - (I - OslOkrecIB+ f
ai
(so)
G rou p in g rate c o n s ta n ts a n d q u a n tu m y ie ld s c a n m a k e a n u m b e r of
sim p lific a tio n s p o ssib le . For ex a m p le, th e o b serv ed p r o c e s s for b a c k
e lec tr o n tr a n sfe r from th e se p a ra ted io n c a n be w ritten a s,
^bet =
(I
si)
^
T h is d e p le tio n p r o c e s s , w h ic h r e d u c e s th e tru e se p a ra ted io n
c o n c e n tr a tio n , r e s u lts in th e o b serv ed io n trace s e e n in F igure 4 -1 0 . T he
overall forw ard p r o c e s s , in volvin g d iffu sio n a l term s a n d b r a n c h in g ra tio s,
is given b y
etA
k d A ® si® \A
(32)
and
^ e tD ~ k d D ® s i ® W
(33)
60
for th e a c ce p to r a n d d on or, r esp ectiv ely . T he sim p lific a tio n s e x p r e s s e d in
E q u a tio n s 3 1 - 3 3 r e s u lt in a r ed u c tio n o f E q u a tio n 3 0 to a n in tu itiv e
form ,
=
Kr,
+
M
(3 4 )
w h ic h c o n ta in s tw o forw ard te r m s d u e to th e ex cited d o n o r a n d a ccep to r
(ketn a n d k etA, resp ectively), a n d o n e rev erse term (/cbet).
E q u a tio n 3 4 a lso e m p h a siz e s th e th ree c h e m ic a l s p e c ie s th a t c a n be
o b se rv e d on th is tim e s c a le (A*, D* a n d D +). F igure 4 - 1 0 s h o w s th e
[C60*]/
2
-5 d e c a y
U n c o r r e c te d [D+] r ise tim e
[G 19 ] d e c a y
(Figure 4-10) Raw data time decay traces of the G19 [O.OSmM] & Ceo [0.4mM] in BN
with 3mJ/pulse 532nm laser.
61
tem p o ra l b eh a v io r o f [Ceo*], [G19*] a n d [D+], w h ere c o n c e n tr a tio n s w ere
d e te r m in e d from in te n s itie s by u s in g e x tin c tio n c o effic ien ts o f 1 4 ,0 0 0 L
M
1
cm
1
for 3 Ceo*, 1 6 ,0 0 0 L M "1 c n r 1 for Ceo’, 3 7 ’40 a n d 3 1 ,8 0 0 for G19* a s
d e te r m in e d p re v io u sly in th is th e s is .
T he tem p o ra l tr a c e s a n d th e e q u a tio n ,
(derived p reviou sly) s u g g e s t a m eth o d to sep a ra te th e forw ard a n d
b ack w ard term s. At tim e s greater th a n 3 0 ps, [A*]=0 a n d [D*]s0. W ith
o n ly th e th ird term still p r e se n t,
(at tim e > 30p s) (36)
0.45 n
-I
0.35
50
52
54
56
58
60
Tim e (gs)
(Figure 4-11) One over donor ion concentration vs. time plot. The linear region at later
times gives a slope equal to the rate of back electron transfer.
62
w h ic h , w h e n in teg r a te d g ives,
I
,
m +i _
L
,
k B ett
I
+
H
(at
1
" 30^sj (37J
v m ax
A p lo t o f I /[.D+] v s. tim e (Figure 4 -1 1 ) y ie ld s a slo p e e q u a l to th e b a ck
e lec tr o n tr a n sfe r rate c o n s ta n t (kbet). W ith th is n o w k n o w n , it is p o ssib le
to m a th e m a tic a lly rem ove th e term from E q u a tio n 3 5 , r e s u ltin g in,
~
k qD[D
] + O
jj O
/i(k (]A[ 4
]
(corrected for b a c k elec tro n transfer) (38)
T h is e q u a tio n c o n ta in s o n ly forw ard te r m s th a t r e s u lt in io n p ro d u ctio n .
H e n c e, th e p lo t o f th is co rrected d a ta s h o u ld sh o w th e D + c o n c e n tr a tio n
r isin g to a fixed v a lu e w ith n o d eca y . F igure 4 -1 2 c o m p a r e s th e D +
tem p o ra l b eh avior, b o th u n co r r ec te d a n d corrected for b a c k electro n
tr a n sfe r a n d e x h ib its th e e x p e c te d b eh a v io r. If Ceo* w ere th e o n ly in itiator,
io n p r o d u c tio n c o u ld n o t o c cu r f a s t e r th a n Ceo* d eca y . T he io n rise tim e
clea rly in d ic a te s th e G 19* a lso fu n c tio n s a s a p h o to in itia to r.
T he p h o to in itia to r d e c a y c u r v es in F igure 4 -9 s h o w th a t th e D*
c o n c e n tr a tio n d e c a y s sig n ifica n tly fa ste r th a n th e A*. T h is is co n tro lled
b y th e relative c o n c e n tr a tio n s o f D a n d A. B e c a u s e A is p r e s e n t a t e ig h t
tim e s th e D c o n c e n tr a tio n , D* is q u e n c h e d a t a m u c h h ig h e r rate th a n A*.
A t tim e s w h e n [D*]=0 a n d [A*]^O, E q u a tio n 3 8 in d ic a te s th a t a p lo t of
d[D+] / d t v s. [A*] w ill y ie ld a str a ig h t lin e w ith a slo p e o f
. B u t if
63
Corrected [G19+] rise time
(Figure 4-12) Time decay traces of the G19 [0.05mM] & Ceo [0.4mM] in BN with
3mJ/pulse 532nm laser.
s o m e D* is p r e se n t, th is p lo t s h o u ld d ev ia te from lin earity. (It s h o u ld be
n o te d th a t low s c a tte r d a ta is n e e d e d to g en era te a w e ll-d e te r m in e d slo p e
in s u c h a
1 st
d erivative plot, a n d th a t th e s te p -s c a n te c h n iq u e d o e s
p rovid e th is q u a lity o f d ata.) F igure 4 - 1 3 sh o w s th e p lo t o f d[G19+]/ d t v s.
3 Ceo*.
A t th e right, th e p lo t is n o n -lin ea r . T h is region is for h ig h 3 Ceo*
c o n c e n tr a tio n s w h ic h o c cu r for early tim e s w h e n G 19* is still p re se n t,
a n d th e n o n lin e a r ity is d u e to th e G 19* c o n tr ib u tio n to io n p ro d u ctio n . At
la ter tim e s , w h e n
3 Ceo*
is still p r e se n t b u t G 19* h a s d e c a y e d aw ay, th e
p lo t s h o w s th e p red icted lin earity.
64
Slope 0 .0 3 3 6 7
Intercept 0 .0 6 8 4 5
(Figure 4-13) Plot of d[D*]/d t vs. [A*]. The slope at lower concentration gives
k q A ^ s i ® I i a for the Ceo case.
T h is lin ea r region a t lon ger tim e s c a n provide th e slo p e n e e d e d in
order to fin d
. R ein tro d u cin g E q u a tio n 17, a lo n g w ith th e slo p e
ta k e n from th e p lo t 3 -1 0 g ives,
_ slope _
Slope
slope
(39)
IA
k-qA
{k-obsA
^rA)
I
I
TobsA
TrA
w h ere r ^ i s th e lifetim e o f th e Ceo* w ith o u t th e p r e se n c e o f a don or. T he
fitted T0JysA for [Ceo*] c a n be s e e n in F igure 4 -9 . From E q u a tio n 3 9 th e
O sjO zh for th e Ceo portion o f th e s y ste m is c a lcu la te d . U sin g
2 2 /#
for th e
65
Ceo* on ly , trip let lifetim e O ij-O zi e q u a ls 0 .2 4 9 2 or 24.9% , m a k in g O gA
e q u a l to 74 .4 % a n d O a e q u a l to 18.5% .40"42
Intercept -0.17934
Slope 0.43254
(Figure 4-14) Plot of d[£>+]/dt vs. [A*]. The slope at higher concentration gives
/CqOsi1OjTjy for the G19 case. The inset shows the G19 effected region expanded with
[D‘] as x-axis.
T he n o n lin e a r region o f Figure 4 -1 3 is d u e to 3G 19* g e n e ra ted io n s,
b u t a ls o c o n ta in s a Ceo* c o n tr ib u tio n . B y ex tra p o la tin g th e stra ig h t lin e fit
in th e F igu re, th e Ceo* c o n tr ib u tio n c a n be d eterm in ed a n d su b tra c te d
from th e d a ta (Figure 4 -1 4 ). T h is is e q u iv a le n t to rem o v in g th e [A*]
d e p e n d e n c e in E q u a tio n 2 4 leavin g
66
R ep lo ttin g th e first d erivative o f th e co rrected d a ta a g a in s t th e 3G 19*
c o n c e n tr a tio n y ie ld s a str a ig h t lin e a s sh o w n in th e F igu re 4 - 1 4 in se t.
U sin g kqp (2 .0 0 8 jus) o b ta in e d from F igure 4 -9 , th e slo p e y ie ld s O 51O 10 =
21.7% . Og£) a n d O d are 98.4% a n d 20.7% , resp ectiv ely . K in etic a n d
q u a n tu m e fficien cy v a lu e s are p r e se n te d in T able 4 - 1.
Q u a n tity __________________ Cm Ix=Al___________________G 19 (x=D)
Trx
2 2 ps
3 0 (j.s
/Crx
0.0455 ns"1
0 .0 3 3 3 ns"1
'Cobsx
4.97198ns
0 .4 8 9 8 ns
/Cobsx
.2 0 1 1 (is"1
2 .0 4 1 6 ns"1
/Cqx
0.1557 ns"1
77.4%
2 .0 0 8 ns"1
O qx
fcbet
9 .S xlO 9 L M o f 1 i i s '1
9 .S x lO 9 L M o f 1 ns"1
O s iO lix
Ox
98.4%
%
21.5%
1 6 .7 %
21.1 %
2 1 .6
(Table 4-1) Kinetic values for bi-mechanistic sysytem.
67
CHAPTER 5
CONCLUSIONS
A b so rp tio n
S ta n d a r d g ro u n d sta te a b so r p tio n e x p e r im e n ts w ere perform ed o n
sev e r a l se r ie s o f B is sa lic y lim in e d im in o m e ta llo -S c h iff-b a se s in order to
in v e stig a te str u c tu r e-p r o p e rty r e la tio n sh ip s. T h is d a ta , c o m b in ed w ith
earlier o b se r v a tio n s b y D i B ella a n d co w o rk ers, r ev e a ls sev e r a l
tr e n d s .4 ’8 >10>n
>1512
1) In c o m p o u n d s c o n ta in in g lig a n d s w ith stro n g d o n o r s a n d
a c c e p to r s, th e o rgan ic lig a n d d o m in a te s th e sp e c tr u m . H ow ever,
th e m e ta l c a n h a v e a d ram a tic e ffect o n th e in te n s ity o f a b so rp tio n
w ith o n ly very s u b tle sh ifts in th e b a n d w a v e len g th a n d sh a p e . T he
m e ta l c h a n g e s are not m o n o to n ic w ith d orbital p o p u la tio n w h ic h
m a y b e d u e to th e o p e n sh e ll n a tu r e o f odd d elec tr o n
c o n fig u ra tio n s.
2) P r e se n c e o f eith e r stro n g d o n o rs or stro n g a c c e p to r s in th e
lig a n d c a u s e s d ra m a tic red sh iftin g o f th e lo w e st en e rg y a b so rp tio n .
68
3) M olar a b so rb tiv ity is d ra m a tica lly d e p e n d e n t o n th e str e n g th o f
th e d o n o rs a n d a c c e p to r s. P r e se n c e o f stro n g a c ce p to r g r o u p s n e a r
th e d ia m in e c h e la tin g “bridge” p la y s a p a rticu la rly sig n ific a n t role
in th e a b so r p tio n str e n g th a n d red sh iftin g o f th e sp e ctru m .
T he p r e se n c e o f str o n g (smax = 4 4 ,0 0 0 L m o b 1 cm -1) low fre q u e n c y (v s
1 7 ,0 0 0 c m -1) a b so r p tio n b a n d s in th e m e ta llo -S c h iff-b a se s, a n d th e
str o n g “tu n e a b ility ” o f th e a b so r p tio n w ith s u b s titu tio n o n th e ligan d
s u g g e s ts th a t th e s e c o m p o u n d s c a n b e ta ilo red for o p tica l p ro p erties in
m u c h th e s a m e m a n n e r a s c o n ju g a te d o rg a n ics. In fa ct, electric-field in d u c e d s e c o n d -h a r m o n ic g e n e ra tio n (EFISH) e x p e r im e n ts b y D i B ella
a n d co w o rk ers s h o w a sig n ific a n t /? v a lu e for G R B 1 -1 1 -1 , a n d b o th
G R B l- 1 1-1 a n d G R B I - 19 e x h ib it v isib le e m is sio n w h e n p u m p e d at
SOOnm w h ic h is in d ica tiv e Of tw o -p h o to n a b so rp tio n .
E lectro n T ran sfer
D iffu sio n -lim ite d e lectro n tra n sfer h a s p r e se n te d a h isto r ic a l
c h a lle n g e . W hile it is fairly straigh tforw ard to m e a su r e o verall rea ctio n
r a te s o n th e d iffu sio n -lim ited tim e sc a le , th is d o e s n o t p rovid e m u c h
in fo rm a tio n a b o u t th e a c tu a l electron transfer rate or efficien cy . The
r e a c ta n t a n d p r o d u ct s ta te s d e a lt w ith in M arcu s T h eory are a c tu a lly
69
in te r m e d ia te s
(Iia
and
Ia ,
resp ectively) in a d iffu sio n -lim ited m e c h a n is m
s u c h a s th o s e sh o w n in E q u a tio n 3 2 a n d 3 6 . If th e s e in te r m e d ia te s are
sh o r t-liv e d , th eir c o n c e n tr a tio n s w ill ty p ica lly be very sm a ll b e c a u s e o f
th e p r e ce d in g , slo w d iffu sio n ste p , m a k in g th e m d ifficu lt or im p o ssib le to
o b serv e. A s a r e su lt, th e o b serv a b le s p e c ie s in d iffu sio n lim ite d PET (the
p h o to in itia to r a n d freely so lv a te d io n s) are n o t th e s p e c ie s th a t c a n be
tr e a ted w ith a c c e p te d e lectro n tra n sfer th eory. T h is h a s led to n u m e r o u s
in v e s tig a tio n s w h ere q u a n tu m e ffic ie n c ies for PET are sim p ly rep orted a s
th e m a x im u m io n c o n c e n tr a tio n d ivid ed by th e m a x im u m p h o to in itia to r
c o n c en tr a tio n ; a v a lu e th a t h a s a s m u c h to do w ith th e d iffu sio n rate a n d
p h o to in itia to r lifetim e a s it d o e s th e efficien cy o f th e e lec tr o n tran sfer.
In th is th e s is , w e h a v e a ttem p te d to a d d itio n a lly p ro b e th e
in te r m e d ia te s a n d th e e lectro n tra n sfer efficien cy e v en th o u g h th e y
c a n n o t b e d irectly d e te c ted . B y in c lu d in g th e in te r m e d ia te s in th e
m e c h a n is m , a n d b y k in etic a n a ly s is , w e are ab le to g e n e ra te so m e
in fo rm a tio n a b o u t th e q u a n tu m efficien cy for th e fo rm a tio n o f so lv a ted
io n s. We are a lso ab le to d is tin g u is h th e c o n tr ib u tio n o f e a c h
p h o to in itia to r to th e overall rea ctio n e v e n w h e n th e y are s im u lta n e o u s ly
p r e se n t. T h a t th e s e tw o c o n tr ib u tio n s are d is tin g u is h a b le is read ily
a p p a r e n t in th e first d erivative p lo t o f d[D +] / dt v s. [3 Ceo*] in F igure 4 -1 3 ,
w h ic h d e se r v e s so m e a d d itio n a l co m m e n t. In sp e ctio n o f E q u a tio n 3 2
s h o w s th a t th e c h a n g e o f io n c o n c e n tr a tio n w ith tim e h a s th ree p o s sib le
70
c o n tr ib u tin g te r m s. Two are form a tio n te r m s d e p e n d e n t o n e a c h o f th e
p h o to in itia to r s G 19* a n d 3Ceo*, a n d th ere is a d e p letio n term d u e to
r e c o m b in a tio n o f th e so lv a te d io n s. A p lo t o f d [G 19+] / d t v s. [3Ceo*] for th e
co rrected d a ta th e n d is p la y s tw o r eg io n s ow in g to th e tw o form ation
te r m s. T h is m e th o d o f p lo ttin g th e p r o d u ct tim e d erivative a g a in s t th e
p h o to in itia to r c o n c e n tr a tio n is a g en era lly u s e fu l tool for g ettin g
c o n c e p tu a l in fo rm a tio n a b o u t th e m e c h a n is m s . S h a rp “k n e e s ” in th e
d a ta are v e iy lik ely in d ica tiv e o f m u ltip le p r o c e s s e s o ccu rrin g . In th is
c a s e , th e lin ea r low 3Ceo* c o n c e n tr a tio n reg io n is d u e to io n form ation
from 3Ceo* a lo n e . T he ste e p e r reg io n a t h ig h er c o n c e n tr a tio n is c a u s e d by
th e p r e se n c e o f G 19* a n d its g e n e ra tio n o f io n p ro d u ct.
W ith th e p r e se n c e o f th e tw o p h o to in itia to r s, th e p o s s ib ility e x is ts
th a t th e e n c o u n te r c o m p le x e s form ed by G 1 9 * -C 6 o a n d 3 C e o i - G 1 9
c o llis io n s are different. T h is is ta k e n in to a c c o u n t in th e m e c h a n is m s
c o n sid e r e d . R e d u c tio n o f th e d ata , h ow ever, r e s u lts in O iiaO si = OnoOsi =
2 1 .5 % , v a lu e s th a t are id e n tic a l to w ith in e x p e rim en ta l error. T here are
tw o r e a so n a b le in ter p r e ta tio n s o f th is r e su lt. O ne is th a t th e s p e c ie s
form ed after th e e n c o u n te r is id e n tic a l for th e tw o m e c h a n is m s m a k in g
th e m e c h a n is m s th e m se lv e s e s s e n tia lly id en tica l. T h is w o u ld b e th e c a s e
if th e e n c o u n te r c o m p le x w ere a h ig h ly d elo ca lized e x cip le x , s a y (A---D)*,
in s te a d o f th e lo ca lized e x c ip le x e s s h o w n in th e m e c h a n is m s ((A* ---D)
a n d (A---D*)).
71
A s e c o n d p o s sib ility is th a t th e m e c h a n is m s are d ifferen t for th e
d ifferen t p h o to in itia to r s, b u t in b o th c a s e s /cix» / c 2x. T h is w o u ld r e s u lt in
e s s e n tia lly all Iia a n d Im p r o c ee d in g to form b y ield in g th e sa m e
q u a n tu m e fficien cy e v en th o u g h th e first in term ed ia te is d ifferen t for th e
tw o m e c h a n is m s . T h is situ a tio n is c o m p le te ly r e a so n a b le g iv en th e
n a tu r e o f th e p h o to in itia to r s. B o th are lo n g -liv ed trip let s ta te s so th e
e n c o u n te r c o m p le x e s th e y form are lik ely a lso trip lets, m a k in g th e /c2a
a n d /c2 D r e la x a tio n s sp in forb id d en a n d slow . C o n seq u e n tly , th e e q u a lity
o f th e q u a n tu m e ffic ie n c ies d o e s n o t a llo w u s to d e term in e w h e th e r or
n o t th e first in ter m e d ia te is id e n tic a l in th e tw o m e c h a n is m s . In th is c a se ,
r e d u c tio n o f th e m e c h a n is m to a sin g le in term ed ia te (as p r e v io u sly
tr e a ted b y H an a n d Spangler) w o u ld still a llo w d e te r m in a tio n o f th e
q u a n tu m e fficien cy for th e io n fo rm a tio n after e n c o u n ter . A d d itionally,
th is m e th o d is c a p a b le o f y ie ld in g d is tin g u is h in g in fo rm a tio n in a bim e c h a n is tic s y s te m w h e n th e s y s te m p ro p erties are “c o o p era tiv e”. In
o th er w o rd s if a s y s te m h a s tw o p h o to in itia to r s, th e e n c o u n te r c o m p le x e s
form ed are d ifferen t for th e tw o in itia to r s, a n d for a t le a s t o n e o f th em ,
/C2 x is c o m p e titiv e w ith /cix.
F in ally, th e v a lu e s o f Ocma n d O ci9 in T able 4 -1 illu str a te th e
im p o rta n c e o f u n d e r s ta n d in g b o th th e c o n trib u tio n o f th e e lectro n
tr a n sfe r s te p s to th e overall p r o c e s s efficien cy a n d th e c o n tr ib u tio n o f
e a c h in d iv id u a l p h o to in itia to r. T he v a lu e s o f Ocm= 16.7% a n d
O gi9 =21.1% o b v io u sly differ, b u t in s p e c tio n o f th e r e s t o f th e ta b le
in d ic a te s th a t th is is sim p ly d u e to a differen ce in q u e n c h in g efficien cy
( O ffc6o = 77.4% , O 9cis= 98.4% ). S in c e th e s e tw o v a lu e s are largely d icta ted
b y th e relative c o n c e n tr a tio n s o f G l 9 a n d Ceo in so lu tio n , th e s p e c ie s
givin g th e larger overall q u a n tu m efficien cy , O x is n o t a g o o d m e a su r e o f
in tr in sic e lec tr o n tra n sfer efficien cy , a n d tr e a tm e n t o f th e k in e tic s u s in g
in te r m e d ia te s in th e m e c h a n is m is d esira b le.
73
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10 P. G. L acroix, S. D. B ella, I. L ed oux, “S y n th e s is a n d S eco n d -O rd er
N o n lin ea r O p tical P rop erties o f N ew Copper(II) a n d Zinc(II) S c h iff-B a se
C o m p lex e s. T ow ard a R ole o f In organ ic C h ro m o p h o res for S e c o n d
H arm on ic G e n e ra tio n ,” C hem . M ater. 8 (1 9 9 6 ) 541
74
11 S. D i B ella , I. F ragala, I. L edoux, M. A. D iaz-G arcia, T. J . M arks
“S y n th e s is , C h a ra cteriza tio n , O p tical S p ec tr o sco p ic, E lectro n ic S tru ctu r e,
a n d S eco n d -O rd er N o n lin ea r O ptical (NLO) P rop erties o f a N ovel C la ss o f
D o n o r-A ccep to r B is(salicylald im in ato)n ick el(II) S c h iff B a s e NLO
C h r o m o p h o re s,” J . Am . C hem . S oc. 1 19 (1 9 9 7 ) 9 5 5 0
12 B a s e “O n th e S eco n d -O rd er N o n ln ea r O p tical S tru ctu r e - Property
R e la tio n sh ip s o f M etal C h ro m o p h o res,” Inorg. C hem . 3 8 (1 9 9 9 ) 2 8 7
13 G. J . K avarnos , F u n d a m e n ta ls o f P h o to in d u c ed E lectro n T ran sfer, VCH
P u b lis h e r s (New York) 1 9 9 3 , ch a p . I Ss 6
14 J . G ron h oltz, W. H erres, U n d e r sta n d in g FT-IR D a ta P r o c e ssin g , Dr.
A lfred H u e th ig P u b lish in g , (Bruker) W est-G erm a n y .
15 P. G. L acroix, S. D. B ella , I. L edoux, “S y n th e s is a n d S eco n d -O rd er
N o n lin ea r O p tical P rop erties o f N ew Copper(II) a n d Zinc(II) S c h iff-B a se
C o m p lex e s. T ow ard a R ole o f In organ ic C h ro m o p h o res for S e c o n d
H arm on ic G e n e ra tio n ,” C hem . M ater. 8 (1 9 9 6 ) 5 4 1
16 G. J . K avarnos , F u n d a m e n ta ls o f P h o to in d u c ed E lectro n T ran sfer, VCH
P u b lish e r s (New York) 1 9 9 3 , ch a p . I Ss 6
17 N. S. S ariciftci a n d A. J . H eeger, “C h a p ter 8 :P h o to in d u c e d , C harge
S e p a r ta io n a n d D evice A p p lica tio n o f C o n ju g a ted P o ly m er/ F u lleren e
C o m p o s ite s ,” H a n d b o o k o f O rganic C o n d u ctiv e M o lecu les a n d P olym ers.
V o lu m e I C h arge-T ran sfer S a lts, F u lle r e n e s a n d P h o to c o n d u c to r s, ed. H.
S. N alw a (J o h n W iley Ss S o n s, 1997) 4 1 4 .
18B .R . A rnold, D. N o u k a k is , S. Farid, J . L. G ood m an , LR. G ould,
“D y n a m ic s in In terco n v ertio n o f C o n ta c t a n d S o lv e n t-S e p a r a te d R ad icalIon P a irs,” J . Am . C hem . S oc. 11 7 (1 9 9 5 ) 4 3 9 9
19 C. S erp a , L. G. A rn au t, “D o e s M o lecu la r Size M atter in P h o to in d u c ed
E lectro n T ran sfer R e a c tio n s? ,” U n iv ersity o f C olu m b ra (J. P h y s . C hem . A:
2 0 0 0 ) B.
20 H. T r ib u tsc h , L. P o h lm a n n , “E lectro n T ransfer: C la s sic a l A p p ro a ch es
a n d N ew F r o n tier s,” S c ie n c e 2 7 9 (1998): 1 8 9 1 .
21 J . R. B o lto n , M. D. A rcher, B a sic E lectro n -T ra n sfer T heory, U n iv ersity
o f W estern O ntario, N ew n h a m C ollege, 1 9 9 1 (Am. C h em . Soc.: 1991) 7.
22 M. J . W eaver, G. E. M cM anis III, “D y n a m ica l S o lv e n t E ffect o n
E lectro n -T ra n sfer P r o c esses: R e ce n t P rogress a n d P e r sp e c tiv e s,” A c c .
C h em . R es. 2 3 (1990): 2 9 4 .
23 N. S. H u s h , “D is ta n c e D e p e n d e n c e o f E lectro n T ran sfer R a te s,” Coord.
C h em . Rev. 6 4 (1985): 135.
24 N . S. H u s h , In e q u iv a len t X PS B in d in g E n erg ies in S y m m etrica l
D e lo ca lize d M ixed -V alen ce C o m p lex es, U n iv ersity o f S y d n e y , 1 9 7 5
(N orth-H olland: C h em ica l P h y sic s, 19 7 5 ) 3 6 1 .
25 N. S. N a sh , A d iab atic T heory o f O u ter S p h ere E lectro n -T ra n sfer
R e a c tio n s in S o lu tio n , U n iv ersity o f B risto l, B risto l 8 , 1 9 6 0 , 5 5 7 .
26 R. A. M a rcu s, “E x ch a n g e R e a ctio n s a n d E lectron T ra n sfer R ea ctio n s
In c lu d in g Iso to p ic E xch an ge: T heory o f O x id a tio n -R ed u ctio n R ea ctio n s
Involvin g E lectro n T ra n sfer,” P o ly tech n ic In stitu te o f B ro o k ly n I (New
York: 19 6 0 ) 2 1 .
27 R. A. M a rcu s, “O n th e T heory o f O x id a tio n -R ed u ctio n R e a ctio n s
In volvin g E lectro n T ran sfer. I*,” J . C h em . P h y s . 2 4 .5 (1956): 9 6 6 .
28 R. A. M a rcu s, E lectro n T ran sfer P a st a n d F u tu re, J o h n W iley & S o n s
(19 9 9 ) ed; J J o rtn er, M. B ix o n , S e r ies ed; I. P rigogin e, 8 . A. R ice
29 N S u tin , “E lectro n T ran sfer R e a ctio n s in S olu tion : A H isto rica l
P e r sp e c tiv e ,” A d v a n ce s in C h em ica l P h y sic s v o l.1 0 6 , J o h n W iley & S o n s
in c. (1999)
30 O. Ito , Y. S a sa k i, Y. Y osh ik aw a , A. W a ta n a b e , “S o lv e n t P olarity E ffect
o n P h o to in d u c e d E lectron T ran sfer b e tw e e n C 60 a n d
T etra m eth y lb e n z id in e S tu d ie d by L aser F la sh P h o to ly sis,” J . C hem . P h y s .
99
(
1995
) :
9838
.
31 A. W a n ta n a b e , 0 . Ito, “P h o to in d u c ed E lectro n T ra n sfer b e tw e e n C 60
a n d P o ly sila n e S tu d ie d b y L aser F la sh P h o to ly sis in th e N ear-IR R eg io n ,”
A m . C h em . S oc. 9 8 (1994) 7 7 3 6
321. R. C o u ld , R. H. Y ou n g, L. J . M ueller, S Farid, “M e c h a n ism o f
E x cip le x F orm ation . R oles o f S u p e r e x c h a n g e , S o lv e n t P olarity, a n d
D rivin g F orce for E lectro n T ran sfer,” J . A m . C hem . S o c. 1 16 (1994): 8 1 7 6 .
76
33 I. R. G ou ld , R. H. Y oun g, R. E. M oody, S. Farid, “C o n ta c t a n d S o lv en tS e p a r a te d G em in a te R ad ical Ion P airs in E lectro n -T ra n sfer
P h o to c h e m istr y ,” J . P h y s . C hem . 9 5 (1991): 2 0 6 8
341. R. G ou ld , S. Farid, “D y n a m ic s o f B im o le c u la r P h o to in d u c e d E lectro n T ran sfer R e a c tio n s ,” A c c . C hem . R es. 2 9 (1996): 5 2 2 .
35 Z. K iss, G. M andi, M. T. B eck , “A rtificial N eu tral N etw ork A p p roach to
P red ict th e S o lu b ility o f C 60 in V a rio u s S o lv e n ts,” J . P h y s . C hem . A 1 0 4
(2000): 8 0 8 1 .
36 S . H. G allagh er, R. S. A rm stron g, P. A. Lay, C. A. R eed , “S o lv e n t E ffects
o n th e E lectro n ic S p ec tr u m o f C 6 0 ,” J. P h y s . C hem . 9 9 (1995): 5 8 1 7 .
37 M. F u jitsu k a , C. Luo, 0 . Ito, “E lectro n -T ra n sfer R e a c tio n s b e tw e en
F u lle r e n e s (C 60 a n d C 70) a n d T etrak is (d im ethylam ino) e th y le n e in th e
G rou n d a n d E x cited S t a te s ,” J . P h y s . C hem . B 103 (1 9 9 9 ) 4 4 5
38Y. Kajii, T. N ak agaw a, 8 . S u zu k i, Y. A ch ib a, K. Obi, K. S h ib u y a ,
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39 L. B iczo k , H. L in sch itz, R. I. W alter, “E x tin ctio n C o efficien ts o f C 60
T riplet a n d A n ion R adical, a n d O n e-E lectro n R ed u ctio n o f th e T riplet by
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40 D. R. L aw son , D. L. F eid h eim , C. A. F o s s , P. K. D o rh o u t, C. M. E lliott,
C. R. M artin, B. P a rk in so n , “B u c k m in ste r fu lle r e n e A n io n s: A n
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L 68.
APPENDIX A
WARREN MILLER COM POUNDS
79
GRB 1-11-1
GRB 1-11-2
GRB 1-11-3
GRB 1-11-4
GRB 1-15
GRB 1-17
GRB 1-23
80
4 -d ie th y la m in o
sa lic y lim in e
in tern a l
lin e of
sy m m etry
d ia m in o m a leo n itrile
(from m a leic acid)
G R B l - 1 1-1
[N,N’-b is (4 -d ie th y la m in o s a lic y lim in e )-2 ,3 -d ia m in o m a le o n itrile ]Z n (II)
81
in tern al
lin e of
sym m etry
d ia m in o m a leo n itrile
(from m a leic acid)
sa lic y lim in e
G R B l - 1 1-2
[N ,N ,-b is (s a lic y lim in e )-2 ,3 -d ia m in o m a le o n itrile ]Z n (II)
82
in tern a l
lin e of
sym m etry
-2 -n a p th o x y
d ia m in o m a leo n itrile
(from m a leic acid)
I -im in o m e th y l
G R B l - 1 1-3
[N,N’- b is ( l -im in o m e th y l-2 -n a p h th y lo x y ) -2 , S d ia m in o m a le o n itrile jZ n (II)
83
4 -m e th o x y l
in tern a l
lin e of
sym m etry
■'( d ia m in o m a leo n itrile
(from m a leic acid)
sa lic y lim in e
G R B l - 1 1-4
[N,N’-b is (4 -m e th o x y ls a lic y lim in e )-2 ,3 -d ia m in o m a le o n itrile ]Z n (II)
84
4 -d ie th y la m in o
in tern a l
lin e of
sy m m etry
- 1 ,2 -d ia m in o p y ra zin e
sa lic y lim in e
-4 ,5 -d m itrile
GRB I - 1 5
[N ,N ’-b is(4 -d ie th y la m in o s a lic y lim in e )-1,2 -d ia m in o p y r a z in e -4 ,5 dinitrile]Zn(II)
85
in tern al
lin e o f
sy m m etry
-2 -n a p th o x y
- 1,2 -d ia m in o p y ra zin e
- 4 ,5 -dinitrile
I -im in o m e th y l
GRB I - 17
[N,N -b is( l-im in o m e th y l-2 -n a p h th y lo x y )- 1 ,2 -d ia m in o p y ra z in e4,5-dinitrile]Z n(II)
86
4 -d ie th y la m in o
sec o n d
in tern a l lin e
o f sym m etry
tetra a m in o
b en zen e
sa lic y lim in e
[N,N N ”,N
^ ^
G R B 1 -1 9
te tr a (4 -d ieth y la m in o sa licy lim in e )- 1,2 ,4 ,5 tetraam in ob en zen e]Z n (II )2
87
4 -d ie th y la m in o
sa lic y lim in e
in tern a l
lin e o f
sy m m etry
d ia m in o m a leo n itrile
(from m a leic acid)
GRBI -2 1
[N,N’-b is(4 -d ie th y la m in o sa lic y lim in e )-2 ,3 -d ia m in o m a le o n itr ile ]C u (II)
88
4 -d ie th y la m in o
sa lic y lim in e
in tern al
lin e of
sym m etry
d ia m in o m a leo n itrile
(from m a leic acid)
G R B I -2 3
[N, N ’-b is(4 -d ie th y la m in o sa lic y lim in e ) - 2 ,3 -d ia m in o m a leo n itrile] Ni(II)
■
I
I
39
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