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

The synthesis and photophysical characterization of a series of quinone-substituted, phenyl-linked dimeric and trimeric porphyrin arrays suitable for the study of electron transfer within closely-coupled subunits 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 adjacent porphyrins occurs with a rate constant of ca. 10(11) s-1, and the photon is immediately trapped by the proximal porphyrin. For the linear porphyrin trimer, the photon can transfer between distal and central porphyrins in an incoherent manner until it is trapped by the proximal porphyrin. These arrays represent interesting models for natural photosynthetic organisms since they combine light harvesting, energy migration and trapping, and photoinduced electron transfer in a single supramolecular entity.