EPR-SPECTRA, LUMINESCENCE DATA, AND RADIATIONLESS DECAY PROCESSES OF COPPER(II) PORPHYRINS

For a series of copper(II) porphyrins, we report EPR data from solid s olutions as well as Eo values for the first ring oxidation, emission s pectra, and luminescence lifetimes in methylene chloride. Although the EPR parameters are fairly constant, the potentials vary by almost 700 mV, and the room-temperature lifetimes range from 300 ns for Cu(TC12P P) to 15 ns for Cu(TMeOPP), where TC12PP denotes 5,10,15,20-tetra(2',6 '-dichlorophenyl)porphyrin and TMeOPP denotes 5,10,15,20-tetra(4'-meth oxyphenyl)porphyrin. The data show that the variation in the lifetime of the emitting pi-pi State is not due to the thermal population of a nother excited state of either d-d or charge-transfer parentage. Howev er, the results are consistent with a model originally introduced by A sano et al. who proposed that an important vibronic distortion occurs in the emitting trip-doublet and trip-quartet states when the excitati on involves the a(2u) orbital of the porphyrin (Asano, M.; Kaizu, Y.; Kobayashi, H. J. Chem. Phys. 1988, 89, 6567-6576). In view of the fact that the distortion is unique to the copper systems, we suggest that it involves movement toward a sitting-atop structure, consistent with the role the d(10) configuration is likely to have in the excited-stat e wave function.