TRIPLET-STATE RESONANCE RAMAN AND ABSORPTION-SPECTROSCOPY OF A CONFIGURATIONALLY LOCKED (Z)-HEXATRIENE - 1,2-DIVINYLCYCLOPENTENE

1,2-Divinylcyclopentene (DVCP-d(0)) and its terminally tetradeuterated isotopomer (DVCP-d(4)) are studied as models for (Z)-1,3,5-hexatriene locked with respect to torsion around the central C-C bond. Preresona nce Raman (DVCP-d(0)) and resonance Raman (DVCP-d(4)) spectra of the g round state and time-resolved resonance Raman and absorption spectra a nd kinetics of the lowest excited triplet state of both isotopomers ar e reported. The observed spectra are compared with results from theore tical calculations. Optimized geometrics, vibrational frequencies, and resonance Raman intensities are calculated for S-0 and T-1 by both ab initio and semiempirical (QCFF/PI) methods. The triplet lifetime of D VCP-d(0) is found to be 3.4 mu s, a factor of 17 longer than for (Z)-1 ,3,5-hexatriene, demonstrating the importance of torsional motion arou nd the central C-C bond in the deactivation of 1,3,5-hexatriene. Termi nal deuteration prolongs the triplet lifetime even further, which seem s to indicate that deactivation in DVCP occurs through a vibration inv olving the terminal hydrogen atoms. Furthermore, a comparison of T-1 r esonance Raman spectra of different (Z)-1,3,5-hexatrienes leads to the suggestion of the existence of a marker band around 1273 cm(-1) chara cteristic for the presence of the planar Z conformation of hexatrienes in the T-1 state.