1. TWO-PROTON PHOTOTAUTOMERIZATION DYNAMICS OF 7-AZAINDOLE COMPLEXES -Tapas Chakraborty Indian Association for the Cultivation of Science Calcutta, India TK02, OSU ICMS 2013

2. Tautomeric forms of 7-azaindole S0S0 S1S1 4.2 eV 2.8 eV Normal Tautomer 0.65 eV (~ 15 kcal/mol )

3. Double proton transfer phenomenon UV light  300 nm Taylor, El-Bayoumi and Kasha, PNAS, 63 (1969) 253

4. Taylor, El-Bayoumi and Kasha, PNAS, 63 (1969) 253 UV light < 300 nm  DPT  1.1 ps Wavelength (nm) ~470 nm Tautomer emission Fluorescence spectra Wavelength (nm) 300 350 400 450 500550 ~320 nm >350 nm Normal emission Absorption spectra 10 -5 M 10 -3 M Double proton transfer phenomenon

5. UV light < 300 nm  DPT  1.1 ps Key Issues Double Proton Transfer sequence :Concerted vs Stepwise Role of exciton interactions Medium effect Double Proton Transfer Barrier (  1.5 kcal/mol) Double proton transfer phenomenon

6. UV light < 300 nm  DPT  1.1 ps Key Issues Double Proton Transfer sequence :Concerted vs Stepwise Role of exciton interactions Medium effect Double Proton Transfer Barrier (  1.5 kcal/mol) Double proton transfer phenomenon

7. Double proton transfer barrier (original expt.) Estimated barrier: 1.4 kcal/mol F2F2 F1F1

8. Tautomerization under jet-cooling condition (  10 K)

9. (7-azaindole) 2 is synthesized in Ar matrix

10. Inert gas (Ne, Ar, N 2, etc.) crystals pack in Face-Centered cubic lattice structures Pimentel (1922-1989) (7-azaindole) 2 is synthesized in Ar matrix

11. 3600 3400 3200 300028002600 Wavenumber (cm -1 ) a b c d Dimer in Ar Matrix Dimer in a supersonic jet expansion Dimer in CCl 4 solution (7-azaindole) 2 formation in Ar matrix is probed using infrared spectroscopy Mukherjee and Chakraborty, CPL 546 (2012) 74

12. Q e NORMAL S0S0 S1S1 Q e TAUTOMER Q V(Q) X DPT of (7-azaindole) 2 is inhibited in Ar matrix Mukherjee and Chakraborty, CPL 546 (2012) 74

13. 300 400500 Wavelength (nm) Intensity ex = 291.5 nm ex = 310 nm 330 315 338 X 300400 500 Annealed matrix Intensity Wavelength (nm) DPT of (7-azaindole) 2 is inhibited in Ar matrix 3600 3400 3200 300028002600 Wavenumber (cm -1 ) d Pre-annealed matrix

14. 7AICyclic amides O N N N H H C ThymineAdenine 7-azaindole∙∙∙amide complexes O N N N

15. 7-azaindole∙∙∙δ-valerolactum complex (7AI  VL) Normal (7AI  VL) Tautomer S0S0 S1S1 6.0 kcal/mol 18.5 kcal/mol ~67.0 kcal/mol 91.7 kcal/mol (7AI 2 ) Normal (7AI 2 ) Tautomer S0S0 S1S1 10.0 kcal/mol 14.5 kcal/mol 67.5 kcal/mol 92.2 kcal/mol 7AI  -valerolactam (  VL) Normal formTautomeric form CIS/6-311++G**

16. Wavelength (nm) ex = 312 nm 10 -5 M 7AI 10 -5 M 7AI + 10 -3 M  VL 1 2 1 2 7AI+  VL 350400 450500 550 Wavelength (nm) 1/[  VL] 1/A K a = 1.64  10 3 M -1 7AI+  VL 260280 300320 340  Efficient tautomeric conversion is observed in hydrocarbon solution at room temperature Tautomerization of 7-azaindole∙∙∙δ-valerolactum complex Mukherjee et al, JPCA, 2012

17. Wavelength (nm) 7AI+  VL 260 280300320 340 32200 32400 32100 32300 Wavenumber (cm -1 ) 22.5 69 76 114.5 149 137 153 171   prob = total fluorescence  45 92 99 145    Wavelength (nm) 311.5310.6 309.6 308.6 Energy Reaction Co-ordinate  v = 0 v =1 v = 2  v = n v  = 0 v  = 1 v  = 2 v  = n S0S0 S1S1 X X Tautomerization of the complex is inhibited under a jet-cooling condition

18.  Wavelength (nm) T(%) 22.5 45 114.5 149 69 76  prob = 300 – 400 nm (local emission)  32200 32400 32100 32300 Wavenumber (cm -1 ) 22.5 69 76 114.5 149 137 153 171   prob = total fluorescence  45 92 99 145       prob = 400 – 750 nm (tautomer emission) Wavelength (nm) T(%)  No tautomeric conversion in jet cooled condition 32054 cm -1 S0S0 S1S1 Mukherjee et al, JPCA, 2012 Tautomerization of the complex is inhibited under a jet-cooling condition

19. Photophysics of 7-azaindole  Pyrazole complex S0 S0 S1 S1 S1S1 S0S0 8.2 kcal/mol 13.4 kcal/mol 99.6 kcal/mol 78.0 kcal.mol 16 kcal/mol Karmakar and Chakraborty, CPL, 2013

20. Tautomerization of 7-azaindole  Pyrazole complex is inhibited in a supersonic jet Karmakar and Chakraborty, CPL, 2013

21. Complex vs homodimer 7-azaindole  Pyrazole complex 7-azaindole  cyclic amide complex

22. Concluding remarks Excited state tautomerization of 7-azaindole dimer is easily affected by external perturbations Compared to homodimer, the tautomerization barriers of mixed dimeric complexes appear much larger, and further studies are essential to understand the origin.

23. Acknowledgement: Co-workers: Dr. Moitrayee Mukherjee Ms. Shreetama Karmakar Funding: Department of Science and Technology, Govt. of India