TRANSIENT RESONANCE RAMAN-SPECTROSCOPY OF COPPER(II) COMPLEXES OF MESO-TETRAPHENYLPORPHINE AND MESO-TETRAPHENYLCHLORIN

We report the transient resonance Raman spectra of five-coordinate Cu( II) complexes of meso-tetraphenylporphine (TPP) and meso-tetraphenylch lorin (TPC). With piperidine as a ligand, we observe a Raman spectrum that is consistent with either a (d,d) or a (d,pi) excited state. Wit h tetrahydrofuran (THF) as a ligand, two distinct excited states are o bserved. One of them is assigned to either a (d,pi) or a (d,d) state by analogy with the spectrum in piperidine. The other shows spectral f eatures that are similar to those observed for the cation radical of C uTPP. We assign the second state to a ring-to-metal (pi,d) charge-tran sfer excited state. The transient Raman spectrum of CuTPC in THF shows features that are consistent with a (pi,d) charge-transfer excited st ate only. Our results provide the first direct spectroscopic evidence for the existence of charge-transfer and, possibly, (d,d) excited stat es that Lie close in energy to the tripmultiplet excited states of CuT PP and CuTPC.