PHOTOPHYSICS OF ENTWINED PORPHYRIN CONJUGATES - COMPETITIVE EXCITON ANNIHILATION, ENERGY-TRANSFER, ELECTRON-TRANSFER, AND SUPEREXCHANGE PROCESSES

Bisgold(III) bisporphyrins, in which a 1,10-phenanthroline spacer imposes a constrained geometry, have been synthesized. Flash photolysis studies indicate that, at high laser intensity, triplet exciton annihilation occurs with a diffusion coefficient of 4 x 10(-5) cm2 s-1. Two such molecules coordinate to a copper(I) ion, via the 1, 10-phenanthroline spacers, to form a tetrameric porphyrin ensemble in which triplet exciton annihilation competes with electron transfer from the copper(I) complex to a gold porphyrin triplet. A mixed multicomponent array, comprising gold(III) and zinc(II) bisporphyrins covalently-linked to a copper(I) bis(1,10-phenanthroline) complex, undergoes a variety of electron-transfer reactions according to which porphyrin absorbs the photon energy. The copper(I) complex participates in these electron-transfer processes via both direct (redox) and indirect (superexchange) mechanisms.