Intermolecular vibrational modes and orientational dynamics ofcooperative hydrogen-bonding dimer of 7-azaindole in solution

Abstract

We observed the low-frequency Raman-active intermolecular vibrational modes of 7-azaindole in CCl4 by femtosecond Raman-induced Kerr effect spectroscopy. To understand the dynamical aspects and vibrational modes of 7-azaindole in the solution, the ultrafast dynamics of 1-benzofuran in CCl 4 was also examined as a reference and ab initio quantum chemistry calculations were performed for 7-azaindole and 1-benzofuran. The cooperative hydrogen-bonding vibrational bands of 7-azaindole dimer in CCl4 appeared at 89 cm-1 and 105 cm-1 represent the overlap of stagger and wheeling modes and the intermolecular stretching mode, respectively. They are almost independent of the concentration in the solution. We further found from the low-frequency differential Kerr spectra of the solutions with neat CCl4 that the intermolecular motion in the low frequency region below 20 cm-1 was less active in the case of 7-azaindoleCCl 4 than in the case of 1-benzofuranCCl4. The slow orientational relaxation time in 7-azaindoleCCl4 is ∼3.5 times that in 1-benzofuranCCl4 because of the nature of the dimerization of 7-azaindole. © 2011 American Institute of Physics.