The lowest excited states of copper porphyrins

摘要

Relaxation processes of excited copper porphyrins were studied with relevance to the structure of the substates of the lowest excited states. Lifetimes of luminescence at room temperature were determined as 17, 29, 69, and 105 ns for T(EtO)PPCu lsqb;T(EtO) PP: 5, 10, 15, 20hyphen;tetra (phyphen;ethoxyphenyl)porphinrsqb;, TPPCu(TPP: 5, 10, 15, 20hyphen;tetraphenylporphin), TFPPCulsqb;TFPP: 5, 10, 15, 20hyphen;tetra(pentafluorophenyl)porphinrsqb;, and OEPCu(OEP: 2, 3, 7, 8, 12, 13, 17, 18hyphen;octaethylporphin) in toluene, respectively. Emission intensities and lifetimes of OEPCu and TFPPCu measured as a function of temperature show a variation ascribed to a Boltzmann distribution between the lowest tripndash;doublet and ndash;quartet with an energy gap of 300ndash;400 cmminus;1. The anomalous temperature dependence for TPPCu and T(EtO)PPCu is explained by a larger energy gap and larger vibronic distortions in the excited state. The difference in behavior is attributed to the orbital nature of the triplet: Verbar;2,4lsqb;b31(a1e)rsqb;rang; for OEPCu and TFPPCu but Verbar;2,4lsqb;b31(a2e)rsqb;rang; for TPPCu and T(EtO)PPCu. The assumption of a low energy charge transfer state is not necessary for our analysis.