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

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

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, 37, 379. d-substitution

Dispersed Fluorescence spectra exciting the origin bands 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, 37, 379.

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

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

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

Theoretical prediction is indicating the amino torsion (mode 44) mixed with out-of-plane mode 39 and mode 41 and in-plane mode 42 upon electronic excitation but not with mode 45 (methyl torsion) of p-Aminotoluene Q' 39 =-0.949Q" Q" Q" 40 Q' 40 =-0.275Q" Q" Q" 44 Q' 41 =-0.109Q" Q" Q" 42 Q' 42 = 0.996Q" 43 Q' 43 = 0.165Q" Q" Q" Q" 44 Q' 44 =-0.747Q" Q" Q" 44 Q' 45 =-0.996Q" 45 Mode-39 Frequency-527 cm -1 16b Mode-41 Frequency-436 cm -1 16a Mode-42 Frequency-430 cm -1 9b Normal modes in the S 0 state those are mixed with amino torsion mode-44 S 1 modes Expansion in S 0 modes Limitation of the calculation in harmonic limit !!! (ab initio calculations are performed in CASSCF(8,7)/6-311g** level)

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.

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

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

* 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 Q 47 ’ = Q 46 ’’ Q 47 ’’ Q 48 ’’ Q 48 ’ = Q 46 ’’ Q 47 ’’ Q 48 ’’ Q 50 ’’ Q 49 ’ = Q 47 ’’ Q 48 ’’ Q 49 ’’ Q 50 ’’ Q 51 ’’ Q 50 ’ = Q 49 ’’ Q 50 ’’ Q 51 ’’ Q 51 ’ = Q 50 ’’ Q 51 ’’ S 1 modes Expansion in S 0 modes Mode-50 Frequency-12 cm -1 Mode-49 Frequency-141 cm -1 Mode-48 Frequency-305 cm -1 Mode-47 Frequency- 431 cm -1 Mode-46 Frequency- 486 cm -1 Mode-51 Frequency- 15 cm -1 Normal modes in the ground electronic state (ab initio calculations are performed in CASSCF(8,8)/6-31g** level)

In p-Aminotoluene……. The features of our measured dispersed fluorescence spectra presented here bear signatures of coupling of amine inversion and torsion with low- energy 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 16a type with methyl torsion as well as out-of-plane methyl bending vibration. The details of the analysis will be published elsewhere. Summary and Conclusion:

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