Intramolecular Proton Transfer in
2-(2'-Hydroxyphenyl)oxazolo[4,5-b]pyridine: Evidence For
Tautomer in the Ground State
Francis A. S. Chipem, Ashim Malakar, and Govindarajan Krishnamoorthy*
Department of Chemistry,
Indian Institute of Technology Guwahati,
Guwahati - 781 039
India
E-mail: [email protected]
Supporting Information
(a)
(b)
Figure S1. (a) 1H-NMR, and (b) 13C-NMR spectra of HPOP.
Figure S2. FT-IR spectrum of HPOP.
Figure S3. Purity results of HPOP from HPLC experiment.
Table S1. UV-Visible absorption band maxima (maxab, nm) and molar absorption
coefficient in Log εmax of HPOP in different solvents.
Dielectric
Solvent
max (Log εmax)
Constant
Cyclohexanea
2.02
288, 299, 329, 342
1,4-Dioxane
2.21
288 (3.80), 299 (3.93), 327 (3.90), 338 (3.88)
Toluene
2.48
287 (4.10), 299 (3.99), 329 (3.86), 341 (3.82)
Chloroform
4.81
289 (3.79), 299 (3.92), 329 (3.89), 341 (3.85)
Ethyl Acetate
6.02
287 (3.79), 298 (3.92), 326 (3.88), 338 (3.85)
Tetrahydrofuran
7.6
287 (3.80), 298 (3.92), 326 (3.88), 340 (3.85)
1-Butanol
17.8
289 (3.75), 298 (3.89), 329 (3.82), 342 (3.79)
1-Propanol
20.1
289 (3.75), 298 (3.89), 329 (3.82), 342 (3.79)
Ethanol
24.6
288 (3.79), 297 (3.90), 328 (3.83), 340 (3.81)
Methanol
32.63
289 (3.79), 299 (3.93), 328 (3.87), 338 (3.84)
N,N-Dimethylformamide
289 (3.76), 298 (3.89), 326 (3.88), 339 (3.84)
36.7
(DMF)
Acetonitrile
37.5
287 (3.76), 297 (3.89), 324 (3.85), 335 (3.83)
Glycerol
42.5
289 (3.26), 301 (3.28), 327 (3.15), 342 (3.15)
DMSO
289 (3.76), 300 (3.86), 327 (3.83), 341 (3.77),
47
400 (2.95)
Water (pH ~ 7.0)
78.54
288 (3.73), 299 (3.85), 324 (3.84), 334 (3.78)
a
saturated solution.
Table S2. Fluorescence lifetime (τ, ns) obtained by monitoring at the tautomer band
maxima of HPOP in different solvents using 375 nm laser as light source
Monitored at emT
Solvent
τ1
χ2
1-Butanol
4.8
1.4
1-Propanol
5.1
1.1
Ethanol
5.2
1.0
Methanol
5.1
1.0
DMSO
4.9
1.0
DMSO/ACN (70/30)
5.0
1.0
Normalized Intensity
1.0
0.8
1
0.6
2
0.4
0.2
3
0.0
325
375
4
425
475
525
Wavelength (nm)
575
Figure S4. Normalized fluorescence spectra of HPOP in acetonitrile (1) λexc = 290 nm, (2) λexc =
300 nm, (3) λexc = 375 nm, and (4) λexc = 395 nm.
-1
Stokes Shift (cm )
5000
4000
r = 0.91
3000
2000
1000
0
-0.02
0.08
0.18
Df
0.28
Figure S5. Lippert-Mataga plot for the normal emission.
-1
Tautomer Emission (cm )
24000
r = 0.92
21000
18000
15000
0.08
0.18
0.28
Df '
0.38
Figure S6. Plot of Δf' versus tautomer emission maxima. The emission maxima in glycerol and
water were not included in the fit.
0.8
0.6
2
1
Normalized Intensity
Normalized Absorbance
1.0
3
0.4
0.2
0.0
250
290
330
370
Wavelength (nm)
410
450
Figure S7. Normalized (1) absorption and fluorescence excitation spectra of HPOP in DMSO
monitored at (2) normal (387 nm), and (3) tautomer (480 nm) band.
(a)
0 % Gly,
100 % Water
Absorbance
0.12
0.09
100 % Gly,
0 % Water
0.06
0.03
0
260
280
300
320
340
Wavelength (nm)
360
(b)
100 % Gly
Intensity (a. u.)
1.5E+5
1.2E+5
0 % Gly
9.0E+4
6.0E+4
3.0E+4
0.0E+0
340
390
440
490
Wavelength (nm)
540
590
Figure S8. (a) UV-Visible absorption, and (b) fluorescence spectra (λexc = 300 nm) of HPOP in
water/glycerol binary solutions.
Intensity (a. u.)
3.5E+5
2.8E+5
70 % DMSO,
30 % Acetonitrile
100 % DMSO
0 % DMSO
2.1E+5
1.4E+5
7.0E+4
0.0E+0
340
390
440
490
Wavelength (nm)
540
590
Figure S9. Fluorescence spectra of HPOP in acetonitrile/DMSO binary solutions. λexc = 300 nm.
Normalized Intensity
1.0
2
1
0.8
0.6
0.4
0.2
0.0
250
300
350
Wavelength (nm)
400
450
Figure S10. Normalized fluorescence excitation spectra of (1) neutral (em = 464 nm), and (2)
monoanionic (em = 481 nm) forms of HPOP in methanol.
(a) 10000
Counts
1000
100
10
10
3.5
Residuals
(b)
7.5
11.5
15.5
Time (ns)
6
19.5
0
-6
10000
Counts
1000
100
10
0
1
Residuals
3
(c)
8
13
6
18
23
Time (ns)
28
33
38
0
-6
10000
Counts
1000
100
10
0
1
Residuals
3
6
8
13
18
23
28
Time (ns)
33
38
43
0
-6
Figure S11. Fluorescence decay profile of HPOP in DMSO for (a) normal emission band (λexc =
308 nm, λem = 385 nm), (b) tautomer emission band (λexc = 308 nm, λem = 470 nm), and (c)
tautomer emission band (λexc = 375 nm, λem = 485 nm). The black dotted ones are the lamp decay
profile.
0.08
pH = 10.51
Absorbance
0.06
0.05
pH = 7.0
0.03
0.02
0.00
250
300
350
400
Wavelength (nm)
450
Figure S12. UV-Visible absorption spectra of HPOP at different pH.
y = 0.99x + 9.36
pH
11
r 2 = 0.94
10
9
8
7
6
-2.3
-1.8
-1.3
-0.8
-0.3
0.2
0.7
1.2
Log[MA]/[N]
Figure S13. Henderson-Hasselbalch plot for the neutral-monoanion equilibrium of HPOP.
Intensity (a. u.)
1.2E+4
pH = 12.93
9.0E+3
6.0E+3
pH = 6.37
*
3.0E+3
0.0E+0
390
440
490
540
590
Wavelength (nm)
640
690
Figure S14. Fluorescence spectra of HPOP (exc = 370 nm) in pH range of 6.37 to 12.93. Water
Raman band is denoted by *.
(b) 0.08
(a)
0.08
283 K
283 K
348 K
0.04
Absorbance
Absorbance
0.06
0.06
(c)
280
300
320
340
Wavelength (nm)
0
280
360
300
320
340
Wavelength (nm)
360
(d)
0.06
283 K
0.08
0.05
Absorbance
293 K
Absorbance
0.04
0.03
373 K
0.02
0.06
373 K
0.04
0.02
0.01
0
285
373 K
0.02
0.02
0
260
0.04
315
345
375
405
Wavelength (nm)
435
0
280
300
320
340
Wavelength (nm)
360
Figure S15. UV Spectra of HPOP in (a) acetonitrile, (b) DMF, (c) DMSO, and (d) glycerol at
different temperatures.
(a)
283 K
Intensity (a. u.)
8.0E+4
6.0E+4
373 K
4.0E+4
2.0E+4
0.0E+0
335
385
435
485
Wavelength (nm)
535
585
(b)
293 K
Intensity (a. u.)
2.0E+5
1.5E+5
373 K
1.0E+5
5.0E+4
0.0E+0
335
385
435
485
Wavlength (nm)
535
585
535
585
(c)
283 K
Intensity (a. u.)
2.0E+5
1.5E+5
373 K
1.0E+5
5.0E+4
0.0E+0
335
385
435
485
Wavelength (nm)
Figure S16. Fluorescence spectra of HPOP in (a) DMF, (b) DMSO, and (c) glycerol at different
temperatures, λexc = 300 nm.
0.12
FN
0.09
0.06
0.03
0
280
300
320
340
Temperature (K)
360
Figure S17. Normalized fluorescence yield of normal emission of HPOP in acetonitrile (-▲-),
DMF (-♦-), DMSO (-■-), and glycerol (-●-) at different temperatures.
0.2
0.16
FT
0.12
0.08
0.04
0
280
300
320
340
Temperature (K)
360
Figure S18. Normalized fluorescence yield of tautomer emission of HPOP in acetonitrile (-▲-),
DMF (-♦-), DMSO (-■-), and glycerol (-●-) at different temperatures.
y = 4502 x - 13.1
r = 0.97
R ln (FT / FN)
2.5
0.5
y = 1608 x - 6.2
r = 0.95
-1.5
y = 4534 x - 15.0
r = 1.00
-3.5
0.00265
0.00285
0.00305 0.00325
1 / T (K-1)
0.00345
Figure S19. Van’t Hoff plot of HPOP in acetonitrile (-▲-), DMF (-♦-), and glycerol (-●-) at
different temperatures.
(a) 2.0E+4
343 K
(b)
1.0E+5
283 K
283 K
1.2E+4
8.0E+3
Intensity (a. u.)
Intensity (a. u.)
1.6E+4
4.0E+3
300
315
330
Wavelength (nm)
4.0E+4
280
300
320
Wavelength (nm)
340
360
(d)
293 K
1.6E+5
373 K
7.0E+4
0.0E+0
260
373 K
0.0E+0
260
345
Intensity (a. u.)
Intensity (a. u.)
285
2.1E+5
1.4E+5
6.0E+4
2.0E+4
0.0E+0
270
(c) 2.8E+5
8.0E+4
283 K
1.2E+5
8.0E+4
373 K
4.0E+4
280
300
320
340
Wavelength (nm)
360
0.0E+0
260
280
300
320
340
Wavelength (nm)
360
Figure S20. Excitation spectra of HPOP monitored at normal band in (a) acetonitrile (λem = 385
nm), (b) DMF (λem = 385 nm), (c) DMSO (λem = 385 nm), and (d) glycerol (λem = 385 nm).
(b)
(a) 5.0E+4
Intensity (a. u.)
4.0E+4
Intensity (a.u.)
4.0E+4
283 K
3.0E+4
343 K
2.0E+4
3.0E+4
373 K
2.0E+4
1.0E+4
1.0E+4
0.0E+0
270
283 K
300
330
360
390
Wavelength (nm)
0.0E+0
260
420
290
320
350
380
410
Wavelength (nm)
440
(d)
(c)
2.0E+5
2.0E+5
293 K
1.5E+5
373 K
1.0E+5
1.5E+5
1.0E+5
373 K
5.0E+4
5.0E+4
0.0E+0
260
Intensity (a.u.)
Intensity (a. u.)
283 K
300
340
380
420
Wavelength (nm)
460
0.0E+0
270
310
350
390
Wavelength (nm)
430
Figure S21. Excitation spectra of HPOP monitored at tautomer band in (a) acetonitrile (λem =
455 nm), (b) DMF (λem = 385 nm), (c) DMSO (λem = 480 nm), and (d) glycerol (λem = 385 nm).
1.0
IT / IE
0.8
0.6
0.4
0.2
280
300
320
340
Temperature (K)
360
380
Figure S22. Intensity ratio of the ground state cis-enol and tautomer structures obtained from the
excitation spectra recorded at the tautomer emission of HPOP in acetonitrile (-▲-), DMF (-♦-),
and DMSO (-■-) at different temperatures.