Photochemically induced charge separation at the molecular level. A chromophore Quencher complex containing both an electron transfer donor and an acceptor

Examples are known of chromophore-quencher complexes where following optical excitation of a metal-to-ligand charge transfer (MLCT) or a porphyrin ..pi.. ..-->.. ..pi..* chromophore, oxidative or reductive intramolecular electron-transfer quenching occurs. In a recent example, photolysis of a porphyrin-based system containing both an electron-transfer donor and an acceptor led to a relatively long-lived (3 ..mu..s) photoinduced charge separation onto peripheral donor and acceptor redox sites where in terms of the redox potential stored, ..delta..G/sup 0/ > 1.0 eV. One value of such systems is that they begin to reveal how oxidative and reductive equivalents can be generated photochemically and stored within the same molecule. They report here that MLCT-based excitation of the complex (Ru(Me(bpy)-3DQ/sup 2 +/)(Me(bpy)-PTZ)/sub 2/)/sup 4 +/ is followed by a sequence of intramolecular events which lead with relatively high efficiency to a charge-separated state based on the PTZ and -DQ/sup 2 +/ redox sites for which the transiently stored free energy is ..delta..G/sup 0/' approx. 1.29 eV.