EVIDENCE FROM PICOSECOND TRANSIENT ABSORPTION AND KINETIC STUDIES OF CHARGE-TRANSFER STATES IN COPPER(II) PORPHYRINS.

Excited-state dynamics of copper(II) tetraphenylporphyrin left bracket Cu(TPP) right bracket and copper(II) etioporphyrin left bracket Cu(Etio) right bracket depends dramatically on the coordinating properties of the solvent system. Relaxation of transient absorption and recovery of ground-state bleaching following excitation with 35-ps flashes at 355 nm range from greater than 10 ns in the noncoordinating solvent, toluene, to approx. 100 ps in the coordinating solvent, piperidine. Lifetimes of intermediate duration are observed in toluene/piperidine mixtures; for Cu(TPP) the time constants are 650 ps and 2. 1 ns in 1 and 0. 3 M piperidine, respectively. Analogous results are found for Cu(Etio) and in pyridine. Despite such variation in kinetic behavior, transient difference spectra observed for both Cu porphyrins are essentially independent of solvent.