SUPPLEMENTARY INFORMATION
Following Oxygen Consumption In Singlet Oxygen
Reactions Via Changes In Sensitizer Phosphorescence
Tingting Feng, Tod A. Grusenmeyer, Max Lupin and Russell H. Schmehl*
Department of Chemistry , Tulane University, New Orleans, LA, 70118, USA
1.
Kinetic Analysis
2.
Singlet oxygen quantum yield measurement of [Ru(bpy)2(pyrbpy)]Cl2
3. Determination of excited state lifetime of [Ru(bpy)2(pyr-bpy)]Cl2 in H2O and
D2 O
4.
Reproducibility of substrate oxidation reaction.
5.
Atmospheric oxygen diffusion into the photolysis solution and estimation of
its influence on the experimental system.
1. Kinetic Analysis
Given:
hv ∗1
S→
S
ISC ∗3
∗1
S→
S
For ruthenium complex, it is well accepted that inter system crossing has near unity
efficiency. In the following derivation, for simplicity, we will use *S to represent
∗3
S
in the system.
∗
S → S + hv′
kr
S → S
k nr
∗
∗
3
1
k en
∗
3
3
O2
kp
∗
3
S + O−
2
k et
∗
3
3
O2
kp
∗
3
S + O−
2
k et
S+
S+
S+
S+
S+
O2 → S +
O2 → S +
O2 →
+
O2 → S +
O2 →
O2
+
k q =k en +k p +k et and f = k en /k q
k q is the total oxygen quenching rate constant, and k en , k p and k et represent
energy transfer, physical quenching and electron transfer rate constant respectively.
Here we define f as the fraction of *S quechend by oxygen that gives rise to 1O2 .
1
O2 →
3
O2
ko
O2 + Sub → Sub − O2
k rxn
O2 + Sub → 3O2 + Sub
k op
1
1
k rxn and k 0p are chemical and physical reaction rate constant between singlet
oxygen and the substrate, respectively.
The net disappearance of groud state
oxygen equals that of substrate and we have
−d[ 3O2 ]
dt
=
−d[Sub]
(S1)
dt
For this solution, we assume that
d[ ∗S]
dt
=0
d[Sub]
= −k rxn [ 1O2 ][Sub]
dt
d[ 3O2 ]
= (k o + k op [Sub]) [ 1O2 ] − k en [ ∗S][ 3O2 ]
dt
−k rxn [ 1O2 ][Sub] = (k o + k op [Sub]) [ 1O2 ] − k en [ ∗S][ 3O2 ]
From the above expression, we can solve for [ 1O2 ]
k en [ ∗S][ 3O2 ]
[ O2 ] =
k rxn [Sub] + k o + k op [Sub]
1
This can be simplified to [ 1O2 ] = K1 [ ∗S][ 3O2 ]
where
K1 =
ken
o
(krxn +kp ) [Sub]+ ko
d[ 3O2 ]
= (k o + k op [Sub])K1 [ ∗S][ 3O2 ] − k en [ ∗S][ 3O2 ]
dt
d[ 3O2 ]
= ((k o + k op [Sub])K1 [ ∗S] − k en [ ∗S])[ 3O2 ]
dt
d[ 3O2 ]
[ 3 O2 ]
= ((k o + k op [Sub])K1 [ ∗S] − k en [ ∗S])dt
(S2)
We can simplify the right side of the equation
d[ 3O2 ]
[ 3 O2 ]
= −K 2 dt
krxn [Sub]ken [ ∗S]
Where K 2 = k
o
o +(kp +krxn )[Sub]
(S3)
Integrating yields
ln
[ 3O2 ]t
= −K 2 t
[ 3O2 ]0
[ 3O2 ]t = [ 3O2 ]0 e−K2t
This expression can be used for ground state oxygen concentration in a modified SternVolmer equation to express the change in luminescence intensity with time.
It = Imax [
It
=[
Imax
(I
1
]
1 + k q τem [ 3O2 ]t
1
1 + k en τem ([ 3O2 ]0 e−K2 t )
]
⁄I )−1
t
ln [k max
] = −K 2 t
τ [ 3O ]
q em
(S4)
2
(I
⁄I )−1
t
Plots of ln [k max
] vs t at each substrate concentration [Sub], should yield
τ [ 3O ]
q em
2
straight lines with an intercept of 0 and a slope of - K2.
This will only remain
true as long as the concentration of substrate does not change significantly. Thus,
data was collected only for early times in the photolysis. Since
k rxn [Sub]k en [ ∗S]
K2 =
k o + (k op + k rxn )[Sub]
we can rearrange it to get
(k op + k rxn )
1
k0
1
=
∗
+
K 2 fk q [ ∗S]k rxn [Sub] fk q [ ∗S]k rxn
Therefore, if we plot
(ko
p +krxn )
fkq [ ∗S]krxn
2.
1
K2
and a slope of
Determination
of
vs
1
, we would get a linear plot with an intercept of
[Sub]
k0
.
fkq [ ∗S]krxn
singlet
oxygen
formation
quantum
yield
for
[Ru(bpy)2(pyrbpy)]Cl2
In order to measure the efficiency of singlet oxygen production, we measured the
quantum yield of singlet oxygen generation by [Ru(bpy)2(pyrbpy)]Cl2 in D2O, using
tetrakis-(4-sulfonatophenyl) porphyrin (TSPP) as reference.
0.6
Ru-pyr
TSPP
Voltage/v
0.4
0.2
0.0
1230
1290
1260
Wavelength/nm
1320
Fig. S1: Singlet oxygen emission measurement for [Ru(bpy)2(pyrbpy)]Cl2 in D2O using
TSPP as reference with 532nm excitation
Calculation of quantum yield was based on the equation
F
ΦS=ΦR·F S ·(1-10−AR )/ (1-10−AS )
R
In which Φ is the singlet oxygen quantum yield, F is the integrated area of the emission
spectrum, A is the absorbance at the excitation wavelength. Subscription S and R stand
for sample and reference respectively.
Using the experimental measured values and ΦR of 0.57 for TSPP in D2O, and repeating
the measurement three times, a singlet oxygen quantum yield of 0.84, 0.65 and0.74
was obtained respectively, which yielded an average yield of 0.74±13%
3. Transient absorption and lifetime Measurements.
Lifetimes were obtained by pulsed laser excitation and direct detection of
luminescence, averaging 500 pulses per sample. Data was obtained in aerated and
deaerated H2O and D2O respectively. Decays were also obtained by transient
absorbance at 360 nm, shown in figures S2 below.
A.
Transient absorption at 360nm(Aerated H2O)
ExpDec1 Fitting of Lifetime
ΔOD
0.00
-0.05
τ=1.43μs + 2%
-0.10
-0.15
(a)
0
3
Time/μs
6
9
B.
Transient absorption at 360nm(Deaerated H2O)
ExpDec1 Fitting of Lifetime
ΔOD
0.00
-0.05
τ=24.8μs + 4%
-0.10
-0.15
(b)
-0.20
0
40
80
Time/μs
120
C.
0.02
Transient absorption at 360nm(Aerated D2O)
ExpDec1 Fiting of Lifetime
ΔOD
0.00
-0.02
τ=1.55μs + 4%
-0.04
-0.06
(c)
0
3
Time/μs
6
9
160
D.
Transient absorption at 360nm(Deaerated D2O)
ExpDec1 Fitting of Lifetime
ΔOD
0.00
-0.05
τ=30.7μs + 5%
-0.10
-0.15
(d)
0
80
160
Time/μs
240
Fig. S2 Lifetime measurement of Ru-pry using 360nm transient absorption after 460nm
excitation in (a) Aerated H2O solution (b) Deaerated H2O solution (c) Aerated D2O
solution (d) Deaerated D2O solution
4. Reproducibility of substrate oxidation reaction.
The photolysis were carried out in a 100 l cell as described in the experimental.
Repeat measurements were conducted using the same stock solution. Figure S3 shows
typical data for Ru-pyr intensity changes during photolysis in the presence of his (0.005
M).
First Trial
Second Trial
Third Trial
Relative Emission Intensity
1.0
0.5
0.0
0
5
10
15
20
25
30
35
40
45
50
55
60
65
t/s
Figure S3. Reproducibility of experiment using 0.005M His-[Ru(bpy)2(pyrbpy)]Cl2 H2O solution
under experimental condition
5. Oxygen diffusion rate and estimation of its influence on the experimental system
As has been previously stated, oxygen diffusion from the atmosphere will cause error
to the actual amount of oxygen that is being consumed by the substrate. For the
system we established right now, there is no easy way to completely isolate the system
from the atmosphere. Therefore, one simple experiment was carried out to evaluate
the rate of oxygen diffusion from air to solution. 100μl of deaerated Ru-pyr H2O
solution(without any substrate) was pipetted to the same micro cuvette, and its
emission intensity versus time was monitored. As time went by, oxygen would diffuse
from air into solution and oxygen quenching would cause ruthenium emission to
decrease. From the Stern-Volmer relation, we can calculate the oxygen concentration
in solution at any given time.
1.0
Emission Intensity Change
It/Imax
0.8
0.6
0.4
(a)
0
300
200
100
400
500
Time/s
0.03
[3O2]/mM
3
[ O2]
Change
0.02
0.01
0.00
(b)
0
100
200
300
Time/s
400
500
(A)
(B)
Fig. S4 (a)Decrease of emission intensity of a originally deaerated Ruthenium H2O
solution after exposure to air and (B) corresponding increase of molecular oxygen in
solution
From Fig. S4, we can see that after 500 seconds, the oxygen concentration has reached
0.025mM, about 10% of that of aerated aqueous solutions(0.27mM), even though
ruthenium emission intensity decreased to less than half of the maximum
intensity( due to high sensitivity of the emission of the sensitizer to oxygen). Therefore,
the 20 seconds reaction time used in this method avoids the concern of oxygen
diffusion from the atmosphere into solution.