Resonance Raman characterization of the triplet state of zinc tetraphenylchlorin

The T{sub 1} excited state of zinc(II) tetraphenylchlorin, ZnTPC, has been studied by nanosecond time-resolved transient absorption (TA) and transient resonance Raman (TR{sup 3}) spectroscopy. The TA difference spectrum shows an induced absorption at 450 nm that is assigned as arising from a {sup 3}({pi},{pi}*) state. The most striking feature of the {sup 3}(ZnTPC) TR{sup 3} spectrum is the significant frequency downshifts and strong intensity enhancements of the pyrrole half-ring stretch, {nu}{sub 4}, and of other pyrrole ring motions which together produce a broad band in the 1150-1300-cm{sup -1} region. In addition, the enhancement of C{sub 12}C{sub m} modes ({nu}{sub 2} and {nu}{sub 11}) changes with their phasing between the S{sub 0} and T{sub 1} states. Weaker intensity enhancements, with no frequency shifts, are seen for the phenyl substituent ring mode, {Phi}{sub 4} and {nu}{sub 1}, and C{sub m}-phenyl stretch. These findings suggest that there is less electronic participation from the phenyl rings in the resonant triplet state, T{sub n}, for ZnTPC than for its parent metalloporphyrin, ZnTPP. 31 refs., 4 figs., 1 tab.