PHOTOINDUCED ELECTRON-TRANSFER INVOLVING EOSIN TRYPTOPHAN CONJUGATES - LONG-LIVED RADICAL PAIR STATES FOR SYSTEMS INCORPORATING AROMATIC AMINO-ACID SIDE-CHAINS

The electron-transfer photochemistry of the covalent derivatives of th e dye eosin, in which the xanthene dye is covalently attached to the a mino acid L-tryptophan via the thiohydantoin derivative, the tryptopha n dipeptide, and an ethyl ester derivative, has been investigated. The singlet excited state of the dye is significantly quenched on attachm ent of the aromatic amino acid residue. Dye triplet states are also in tercepted through intramolecular interaction of excited dye and amino acid pendants. Flash photolysis experiments verify that this interacti on involves electron transfer from the indole side chains of tryptopha n. Rate constants for electron transfer are discussed in terms of the distance relationships for the eosin chromophore and aromatic redox si tes on peptide derivatives, the pathway for sigma-pi through-bond inte raction between redox sites, and the multiplicity and state of protona tion for electron-transfer intermediates. Selected electron-transfer p hotoreactions were studied under conditions of binding of the peptide derivatives in a high molecular weight, water-soluble, globular polyme r, poly(vinyl-2-pyrrolidinone).