RESONANCE RAMAN CHARACTERIZATION OF THE TRIPLET-STATE OF ZINC TETRAPHENYLCHLORIN

The T-1 excited state of zinc(II) tetraphenylchlorin, ZnTPC, has been studied by nanosecond time-resolved transient absorption (TA) and tran sient resonance Raman (TR(3)) spectroscopy. The TA difference spectrum shows an induced absorption at 450 nm that is assigned as arising fro m a (3)(pi,pi) state. The most striking feature of the (3)(ZnTPC) TR( 3) spectrum is the significant frequency downshifts and strong intensi ty enhancements of the pyrrole half-ring stretch, nu(4), and of other pyrrole ring motions which together produce a broad band in the 1150-1 300-cm(-1) region. In addition, the enhancement of CalphaCm modes (nu 2 and nu(11)) changes with their phasing between the S-0 and T-1 state s. Weaker intensity enhancements, with no frequency shifts, are seen f or the phenyl substituent ring mode, Phi(4) and nu(1), and C-m-phenyl stretch. These findings suggest that there is less electronic particip ation from the phenyl rings in the resonant triplet state, T-n, for Zn TPC than for its parent metalloporphyrin, ZnTPP.