61 st OSU ISMS 2006 Dispersed Fluorescence Spectroscopy

61 st OSU ISMS 2006 Dispersed Fluorescence Spectroscopy of Jet-Cooled p-Aminotoluene Partha Biswas, a) Montu Kumar Hazra a) and Tapas Chakraborty a, b) a) Department of Chemistry, Indian Institute of Technology Kanpur, UP 208016, india b) Department of Physical Chemistry, Indian association for the Cultivation of Science, Jadavpur, Calcutta 700032, india

p-Aminotoluene is an ideal system to investigate the ring-mediated coupling between the largeamplitude motions associated with methyl and amine p-Aminotoluene Methyl –internal rotation Amine –umbrella-type inversion and torsional motion How these two moieties interact with each other through the aromatic ring and what is the consequence of that? Yan, S. ; Spangler, L. H. J. Chem. Phys. 1992, 96, 4106 Tan, X. Q. ; Pratt, D. W. J. Chem. Phys. 1994, 100, 7061 Yan, . S. ; Spangler, L. H. J. Chem. Phys. 1992, 96, 4106.

d-substitution Ju, Q. . ; Parmenter, C. S. . ; Stone, T. A. ; Zhao, Z-Q. Israel J. Chem. 1997, 379. Fluorescence excitation spectra of a. p-Fluorotoluene b. p-Fluoroaniline and c. p-Aminotoluene

Ju, Q. . ; Parmenter, C. S. . ; Stone, T. A. ; Zhao, Z-Q. Israel J. Chem. 1997, 379. Dispersed Fluorescence spectra exciting the origin bands of a. p-Fluorotoluene b. p-Fluoroaniline and c. p-Aminotoluene

6 a Comparison of Dispersed Fluorescence spectra exciting the 6 a mode of p-Aminotoluene and p-Fluoroaniline

Comparison of Dispersed Fluorescence spectra exciting the 711 and 730 cm -1 band of p-aminotoluene and p-fluoroaniline respectively

6 a Comparison of Dispersed Fluorescence spectra exciting the Inversion mode of p-Aminotoluene and p-Fluoroaniline

Theoretical prediction is indicating the amino torsion (mode 44) mixed with outof-plane mode 39 and mode 41 and in-plane mode 42 upon electronic excitation but not with mode 45 (methyl torsion) of p-Aminotoluene S 1 modes Expansion in S 0 modes Q'39 Q'40 Q'41 Q'42 Q'43 =-0. 949 Q"38 + 0. 285 Q"39 + 0. 120 Q"40 =-0. 275 Q"38 -0. 942 Q"39 - 0. 177 Q"44 =-0. 109 Q"40 + 0. 634 Q"41 - 0. 760 Q"42 = 0. 996 Q"43 = 0. 165 Q"39 + 0. 161 Q"41 + 0. 128 Q"42 0. 960 Q"44 =-0. 747 Q"41 - 0. 630 Q"42 - 0. 179 Q"44 =-0. 996 Q"45 Q'44 Q'45 Mode-39 Frequency-527 cm-1 16 b Mode-41 Frequency-436 cm-1 16 a Mode-42 Frequency-430 cm-1 9 b Normal modes in the S 0 state those are mixed with amino torsion mode-44 (ab initio calculations are performed in CASSCF(8, 7)/6 -311 g** level) Limitation of the calculation in harmonic limit !!!

Dispersed Fluorescence spectral signatures of excited state IVR

Interact with each other via aromatic ring p-vinyltoluene Biswas, P. ; Panja, S. S. ; Manogaran, S. ; Chakraborty, T. J. Phys. Chem. A 2005, 109, 3225.

Hickman, C. G. ; Gascooke, J. R. ; Lawrence, W. D. J. Chem. Phys. 1996, 104, 4887. Fluorescence excitation spectra of a. p-vinylfluorobenzene b. toluene and c. pvinyltoluene,

Mode 49 – vinyl bending ; Mode 50 – vinyl torsion ; Mode 51 -methyl torsion Dispersed fluorescence spectra following excitations of the origin band , 214 & 235 cm-1 vibronic bands of the fluorescence excitation spectrum of p-vinyltoluene

* Appearance of these bands are indicative of partial mixing of in-plane and out of plane modes involving the methyl torsional mode upon electronic excitation Dispersed fluorescence spectra following excitations of the 335, 417, 450 and 507 cm-1 vibronic bands of the fluorescence excitation spectrum of p-vinyltoluene

Theoretical prediction is indicating the Duschinsky mixing of methyl torsion (mode 51) with vinyl torsion (mode 50) and out-of-plane vinyl bending (mode 49) modes upon electronic excitation of p-vinyltoluene S 1 modes Expansion in S 0 modes Q 47’ = 0. 139 Q 46’’ - 0. 960 Q 47’’ - 0. 161 Q 48’’ Q 48’ = -0. 129 Q 46’’ - 0. 215 Q 47’’ + 0. 944 Q 48’’ - 0. 139 Q 50’’ Q 49’ = -0. 111 Q 47’’ - 0. 204 Q 48’’ - 0. 760 Q 49’’ - 0. 562 Q 50’’ 0. 213 Q 51’’ Q 50’ = -0. 610 Q 49’’ + 0. 732 Q 50’’ + 0. 282 Q 51’’ Q 51’ = 0. 360 Q 50’’ - 0. 932 Q 51’’ Mode-51 Frequency- 15 cm-1 Mode-50 Frequency-12 cm-1 Mode-48 Frequency-305 cm-1 Mode-47 Frequency- 431 cm-1 Mode-49 Frequency-141 cm-1 Mode-46 Frequency- 486 cm-1 Normal modes in the ground electronic state (ab initio calculations are performed in CASSCF(8, 8)/6 -31 g** level)

Summary and Conclusion: In p-Aminotoluene……. The features of our measured dispersed fluorescence spectra presented here bear signatures of coupling of amine inversion and torsion with lowenergy modes involving the methyl group. Specifically, the dispersed fluorescence spectrum measured following excitation of a vibronic band of 711 cm-1 excess energy reveal coupling of amine torsion with the mode corresponds to methyl motion of out-of-plane bending type. Furthermore , dispersed fluorescence spectral features for excitation with 737 cm-1 excess energy shows that amine inversion motion is coupled with ring vibration of 16 a type with methyl torsion as well as out-of-plane methyl bending vibration. The details of the analysis will be published elsewhere.

Acknowledgement Ø Labmates: Chayan K. Nandi, Sujit S. Panja, V. Ramanathan, Amit Samanta, Prasenjit Pandey, Biman Bandopadhay Ø Prof. S. Manogaran , IIT Kanpur, India Ø Indian Institute of Technology Kanpur, INDIA Ø Department of Science and Technology, Govt. of India.