PHOTOINDUCED CHARGE SEPARATION IN A PORPHYRIN TETRAVIOLOGEN SUPRAMOLECULAR ARRAY

A porphyrin-tetraviologen supramolecule P–V4, in which a viologen molecule is appended to each of the porphyrin meso positions via a 1,3-propanoxy-4-phenyl chain, has been studied by picosecond and nanosecond laser flash photolysis techniques. In DMSO solution, rapid charge separation (CS) occurs from the first excited singlet state of the porphyrin, giving rise to long-lived redox products. These products recombine via first-order kinetics (τ = 6.4 ± 0.7 µs) to restore the ground-state reactants. Similar, but much slower, CS takes place from the porphyrin triplet excited state, which is formed in competition to CS from the singlet state. Quantum yields for formation of redox products and rates of both CS and charge recombination (CR) are solvent dependent, protic solvents favoring rapid CR. © 1990, American Chemical Society. All rights reserved.