Time-resolved resonance Raman and molecular orbital studies of charge separation and intramolecular reorganisation

The application of resonance Raman, time-resolved resonance Raman spectroscopy and ab initio molecular orbital calculations to elucidate the structural manifestations occurring within TICT molecules following electronic excitation and to probe the fast timescale intramolecular component of the reorganisation accompanying electron transfer reactions is discussed. Studies of the molecules 4-dimethylaminobenzonitrile (DMABN), 4'-n-pentyl-4-cyanoterphenyl (cyanoterphenyl, CTP) and p-terphenyl (TP) are reported. The results and consequences of a detailed ab initio (CIS, MP2 methods, 6-31G* *, 6-311 + +(2d,p) basis sets) investigation of the excited states and corresponding equilibrium geometries of DMABN and CTP are reported. The results are corroborated with experimental data and suggest strongly that the charge transfer character of the excited state of each of these molecules is increased significantly by geometric changes which involve torsion with respect to the aromatic-CN plane. (C) 1998 Elsevier Science B.V. All rights reserved.