Supporting Information
Copyright Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, 2012
Femtogram Detection of Explosive Nitroaromatics: Fluoranthene-Based
Fluorescent Chemosensors
N. Venkatramaiah, Shiv Kumar, and Satish Patil*[a]
chem_201201764_sm_miscellaneous_information.pdf
Table of Contents:
1. Synthesis of precursor materials
3
2. Single crystal X-ray analysis
11
3. Fluorescence quenching with different nitroaromatics in ethanol
14
4. NMR and electronic absorption titration experiment
15
5. Stern-Volmer plots
17
6. Selectivity
19
7. Fluorescence quenching of S 3 thin films on quartz plates
exposed to saturated vapors of various nitroaromatics
20
8. Fluorescence quenching of S 3 on thin layer silica chromatographic
21
plates with picric acid
9. Computational study
22
1. Synthesis of precursor materials
Scheme S1: Synthetic scheme of 1,2-bis(4-(hexyloxy)phenyl)ethyne.
Synthesis of 1-(Hexyloxy)-4-iodobenzene (P1).A mixture of 4-Iodophenol (5.0 g, 22.7 mmol)
and anhydrous potassium carbonate (6.28 g, 45.5 mmol) was taken in N,N-dimethylforamide (20
mL). To the above reaction mixture 1-bromohexane (5.63 g, 34.1 mmol) was added. Reaction
mixture was reflux for 16hours. Reaction mixture was poured into water (150 mL) and extracted
with dichloromethane. The organic layer was washed with distilled water. The organic layer was
dried over anhydrous sodium sulphate, filtered and subjected to rotary evaporation. Product was
further purified using column chromatography with 2% ethylacetate/hexane as eluent. Colourless
liquid was obtained (90% yield). 1H NMR (400 MHz, CDCl3, 25oC, TMS): d = 7.52 (d, 3J(H,H)
= 8.8 Hz, 2H), 6.66 (d,3J(H,H) = 9.2 Hz, 2H), 3.90 (t, 3J(H,H) = 6.4 Hz, 2 H), 1.79-1.75 (m, 2H),
1.47-1.43 (m, 2H), 1.35-1.31 (m, 4H), 0.90 ppm (t, 3J(H,H) = 4.32 Hz, 3 H);13C NMR (100
MHz, CDCl3, 25oC, TMS): d = 159.01, 138.12, 116.93, 82.36, 77.32, 77.00, 76.68, 68.11, 31.53,
29.09, 25.65, 22.56, 13.99 ppm
Synthesis of ((4-(hexyloxy)phenyl)ethynyl)trimethylsilane (P2). A reaction mixture of
compound
P1
(2.0
g,
6.5
mmol),
trimethylsilyacetylene
(0.7
g,
7.0
mmol),
bis(triphenylphosphine)palladium (II) dichloride (4% mol) and copper (I) iodide (10% mol) was
taken in triethylamine (20 mL). In above reaction mixture was stirred at room temperature for 15
min and then refluxed for 4hours under argon atmosphere. Reaction mixture was cooled to room
temperature and subjected to solvent evaporation under reduced pressure. Residue was directly
adsorbed over silica gel and purified using column chromatography with 2% ethylacetate/hexane
as eluent. Colourless liquid was obtained. 1H NMR (400 MHz, CDCl3, 25oC, TMS): d= 7.38 (d,
3
J(H,H)= 8.8 Hz, 2 H), 6.79 (d, 3J(H,H) = 8.8 Hz, 2 H), 3.93 (t, 3J(H,H) = 6.8 Hz, 2 H), 1.78-
1.72 (m, 2H), 1.46-1.42 (m, 2H), 1.34-1.31 (m, 4H), 0.90 (t, 3J(H,H) = 4.32 Hz, 3 H), 0.23 ppm
(s, 9H). 13C NMR (100 MHz, CDCl3, 25oC, TMS): d = 159.36, 133.42, 115.01, 114.34, 105.34,
92.24, 77.32, 77.00, 76.68, 68.04, 31.56, 29.14, 25.67, 22.57, 13.99, 0.06 ppm
Synthesis of 1-ethynyl-4-(hexyloxy)benzene (P3). Compound P2 (1.7 g, 6.2 mmol) was treated
with anhydrous potassium carbonate (85 mg, 0.6 mmol) in methanol (20 mL) at room
temperature for 3 hours under argon atmosphere. Solvent was evaporated and residue was
extracted with dichloromethane/water mixture. Organic layer dried over anhydrous sodium
sulphate, filtered and subjected to rotary evaporation. Product was further purified using column
chromatography with 2% ethylacetate/hexane as eluent. Colourless liquid was obtained (95%
yield). 1H NMR (400 MHz, CDCl3, 25oC, TMS): d= 7.4 (d, 3J(H,H) = 8.8 Hz, 2 H), 6.82 (d,
3
J(H,H) = 8.8 Hz, 2 H), 3.94 (t, 3J(H,H) = 6.8 Hz, 2 H), 2.98 (s, 1H), 1.80-1.73 (m, 2H), 1.53-
1.43 (m, 2H), 1.35-1.31 (m, 4H), 0.91 ppm (t, 3J(H,H) = 4.32 Hz, 3 H); 13C NMR (100 MHz,
CDCl3, 25oC, TMS): d = 159.56, 133.55, 114.47, 113.89, 83.78, 77.32, 77.00, 76.68, 75.61,
68.08, 31.55, 29.12, 25.67, 22.57, 13.99 ppm
Synthesis of 1,2-bis(4-(hexyloxy)phenyl)ethyne (P4). A mixture of compound P1 (1.9 g, 6.2
mmol), 3 (1.2 g, 5.9 mmol), bis(triphenylphosphinepalladium(II))dichloride (4% mol) and
copper iodide (10% mol) was taken in triethylamine (10 mL). In above reaction mixture was
stirred at room temperature for 15 min, and then refluxed for 4 hours under argon atmosphere.
Reaction mixture was cooled to room temperature and solvent was evaporated and residue
directly adsorbed over silica gel and purified using column chromatography with 2%
ethylacetate/hexane as eluent. Crystalline white flakes were obtained (87% yield). 1H NMR (400
MHz, CDCl3, 25oC, TMS): d = 7.42 (d, 3J(H,H) = 8.8 Hz, 4 H), 6.82 (d, 3J(H,H) = 8.8 Hz,4 H),
3.95 (t, 3J(H,H) = 6.8 Hz, 4 H), 1.80-1.73 (m, 4H), 1.53-1.43 (m, 4H), 1.35-1.31 (m, 8H), 0.91
ppm (t, 3J(H,H) = 4.32 Hz, 6 H);13C NMR (100 MHz, CDCl3, 25oC, TMS): d = 138.17, 132.85,
115.55, 114.54, 87.98, 68.10, 31.60, 29.71, 29.20, 25.72, 22.61 ppm; elemental analysis calcd for
C26H34O2: C 82.49, H 9.05, O 8.45. found: C 82.31, H 8.91.
Figure A1. 1H NMR spectra of compoudP1.
Figure A2. 13C NMR spectra of compoudP1.
1 0 5 5DZ ' DW
D
69
+ 1 0 5 0 + ] &' &O
i
-
+] + G
-
+] + W
-
+] + ± P + ± P + ± P + W
-
+ &
&+
2
6L
&+
&+
I SSP
1
Figure A3. H NMR spectra of compoudP2.
+ ] + V+
Figure A4. 13C NMR spectra of compoudP2.
Figure A5. 1H NMR spectra of compoudP3.
Figure A6. 13C NMR spectra of compoudP3.
Figure A7. 1H NMR spectra of compoudP4.
Figure A8. 13C NMR spectra of compoudP4.
' HVNW
RS
6
-
+ 1 0 5 0 + ] &' &O i
- +] + G
+ ] + GG
- + ] + ± P + V+ W
-
+] + W
-
+] + G
+] +
-
+] + G
+ &
&+
2
2
%U
%U
' HVNW
RS
6
I SSP
I SSP
-
+] + G
-
+] + G
-
+] + W
Figure A9. 1H NMR spectra of compoudS3.
Figure A10. 13C NMR spectra of compoudS3.
2. Single crystal X-ray analysis
Single crystal X-ray diffraction data was collected at 120 K on an Oxford Xcalibur (Mova)
diffractometer equipped with a EOS CCD detector using MoKa radiation (λ= 0.71073Å).1 The
crystal was maintained at the desired temperature during data collection using the Oxford
instruments Cryojet-HT controller. The structure was solved by direct methods using SHELXS97 and refined against F2 using SHELXL-97.2 H-atoms were fixed geometrically and refined
isotropically. The WinGX package was used for refinement and production of data tables, and
ORTEP-3 for structure visualization and making molecular representations showing the
ellipsoids at 30% probability level.3
Figure A11. The Unit cell packing diagram of S3.
Table S1. Crystal data and structure refinement parameters for S3.
Compound
S3
Formula
C 52H48Br2O2
Formula weight
864.70
Crystal system
Monoclinic
Space group
P21/c
a (Å)
12.9766(25)
b (Å)
22.9702(20)
c (Å)
14.7832(18)
a (°)
90
ß (°)
105.208(15)
? (°)
90
Volume (Å3)
4252.19(180)
Z
4
Density (gcm-3)
1.35
µ (mm-1)
1.947
F (000)
1783.8
h min, max
-15, 14
k min, max
-27, 23
l min, max
-17, 16
No. of measured
reflections
No. of unique
reflections
No. of reflections
used
R_ all, R_obs
15231
0.242, 0.083
wR2_ all, wR2_obs
0.134, 0.098
7422
2762
∆ρmin,max (e Å-3)
-0.507, 0.563
GOOF
0.869
3. Fluorescence quenching with different nitroaromatics in ethanol
Figure A12. The spectrofluorometric addition of different concentrations of various
nitroaromatics to S3 (5x10 -6, M) in ethanol at 25°C. The circles indicate the formation of new
emission peak upon addition of DDQ and PAQ to S3. NT: 4-nitro toluene, DNT:
2,4dinitrotoluene, TNT:2,4,6 trinitrotoluene, DNP: 2,4 dinitrophenol.
4. NMR and electronic absorption titration experiment
(a)
(b)
Figure A13. The 1H NMR spectra S3 treated with different mole ratio of picric acid (a) complete
region (b) aromatic region.
The formation of donor-acceptor complex was studied by 1H NMR spectroscopic
analysis. In a typical 1H NMR titration experiment, a pale yellow solution of picric acid
was mixed with fluorophore S3 in different mole ratios and is shown in the figure. Upon
addition of PA to S3, at 1:0.25 mole ratio, we have observed a significant up field shift of
the proton resonance at 7.75 ppm (doublet) corresponding to S3. The subsequent increase
in the mole ratio of S3 and PA, the progressive up field shift from 7.75 ppm to 7.72 ppm
was observed up to 1:1 mole ratio and reaches to equilibrium. Further increase in the
concentration of PA, we have not observed any significant change in the spectral pattern.
This indicates that the gradual up field shift is attributed to bound charge transfer
complex. The formation of charge transfer complex was further confirmed by electronic
absorption spectra.
Figure A14. The spectrophotometric titration of S3 (5x10-6) with different concentrations of
picric acid.
The spectrophometric titration of S3 (5x10-6 M) with different concentrations of picric acid (PA)
in ethanol is shown in the figure. Upon gradual addition of PA to S3, slight increase in the
absorption maxima at 303 nm with formation new broad absorption peak at 424 nm. The
intensity of the new absorption peak gradually increases with increase in the concentration of
PA. This indicates the formation of donor-acceptor complex between the p-electron rich S3
fluorophore and picric acid. Similar results were observed upon treated S3 with other electron
deficient nitroaromatics.
5. Stern-Volmer plots
The quenching behavior was studied by Stern-Volmer equation Io/I=1+Ksv[Q], where Io, I are
the fluorescence intensity before and after addition of the quencher, Ksv is the Stern-Volmer
quenching rate constant and [Q] is the concentration of the quencher. Linear SV response was
observed for common analytes indicating static quenching behaviour. However, the highly
electron deficient compounds like DDQ, PAQ chloronil and ANQ shows non-linear behaviour at
high concentration suggesting that the fluorescence quenching of S1 follows both static as well as
dynamic quenching pathways through the ground state complex formation.
1.12
Io/I
1.08
2.4
DCB
DBB
4-BBA
4-Apy
4-Hpy
2ClBN
2
I o /I
1.16
1.6
BQ
AQ
1-ClAQ
DDQ
ANQ
chloronil
1.04
1.2
1
0.96
0.E+00
2.E-04
4.E-04
6.E-04
Conc.of Quencher, M
0.8
0.E+00 2.E-04 4.E-04 6.E-04
Conc. of Quenchers, M
Figure A15. The Stern-Volmer plots for different concentrations of various analytes. The curves
for DDQ, 1-ClAQ, Chloronil and 1-ClAQ shows presence of both static and dyanmic quenching
when treated with S3.
6. Selectivity
Figure A16. The change in the fluorescent intensity of S3 upon addition of 10 µL of various
analytes before and after exposure to the UV light at 365 nm. DCB (1,4-dichloro benzene),
BBA(4-bromo
benzoic
acid),
APy
(4-amino
Pyridine),
HPy(4-hydroxy
Pyridine),
BP(benzophenone), AQ(anthraquinone), DDQ (1,2 dichloro 4,5-dicyano benzoquinone),
PA(picric
acid),TNT(2,4,6-trinitrotoulene),
DNP(2,4,6-trinitro
phenol),
dinitrotoulene), NT (4-nitro toluene), NP(4-nitro phenol) and NB (nitro benzene).
DNT
(2,4,-
7. Fluorescence quenching of S3 thin film on quartz plated exposed to saturated vapors of
various nitroaromatics
Saturated vapors of different nitroaromatics were generated by keeping the compounds in a
sealed tube for three days to ensure that the equilibrated vapor pressure is reached. The solid
state fluorescence quenching study was carried out by keeping the quartz plate in sealed tubes for
specific time. The fluorescence spectra of the exposed films were recorded immediately after
taking out from the sealed tube without any delay.
Figure A17. The time dependent emission spectra of S3 thin film upon exposure to saturated
vapors of various nitroaromatics at 60 sec interval of time.
8. Fluorescence quenching of S3 on thin layer silica chromatographic plates with picric acid
The high concentration of S3 (1x10 -3 M) solution was prepared in chloroform. Thin layer silica
chromatographic plates (200µm. Sigma Aldrich) were kept into the solution and allow to move
in solvent front on the chromatographic plate. The explosive solutions of various concentrations
were spotted on to the thinlayer silica chromatographic plate and allowed to dry completely in
vacuum. After evaporation the test pieces of the plates were exposed to UV light 0f 365 nm was
imaged to digital camera. Also a fluorescence spectrum wasrecorded to study the quantitative
quenching efficiency.
Figure A18. Fluorescence quenching of S3 on thin layer silica chromatographic plate with picric
acid
9. Computational study
Figure A19. Electron density profiles for different types of S 3-TNT complexes
-1
LUMO
-1.79
-2.97
-3
HOMO
-2.91
-3.48
Energy (eV)
-3.89
-5
-5.41
-7
-8.22
-8.11
-7.95
-8.43
-9
S3
PA
TNT
DNT
NT
Figure A20. The energy level diagram of S3with other nitroaromatics.