ELECTRONIC-ENERGY MIGRATION AND TRAPPING IN QUINONE-SUBSTITUTED, PHENYL-LINKED DIMERIC AND TRIMERIC PORPHYRINS

The synthesis and photophysical characterization of a series of quinon e-substituted, phenyl-linked dimeric and trimeric porphyrin arrays sui table for the study of electron transfer within closely-coupled subuni ts is presented. The excited singlet state of a porphyrin possessing a quinone substituent at a meso position is shortened to <350 fs due to electron donation to the appended quinone. Energy transfer between ad jacent porphyrins occurs with a rate constant of ca. 10(11) s-1, and t he photon is immediately trapped by the proximal porphyrin. For the li near porphyrin trimer, the photon can transfer between distal and cent ral porphyrins in an incoherent manner until it is trapped by the prox imal porphyrin. These arrays represent interesting models for natural photosynthetic organisms since they combine light harvesting, energy m igration and trapping, and photoinduced electron transfer in a single supramolecular entity.