PICOSECOND FLUORESCENCE STUDY OF A SEMIRIGID ZN-PORPHYRIN-VIOLOGEN DYAD - EVIDENCE FOR 2 DYAD CONFORMERS

Determined from picosecond time-resolved measurements the fluorescence decay of a semirigid Zn-porphyrin-viologen dyad in polar solvents is biexponential with a short-lived and a long-lived component. The long-lived component with lifetime close to that of the reference (Zn-meso-4-benzoxyphenyl-tris (4-tolyl) porphyrin) is responsible for the decay of the porphyrin singlet excited state in the opened conformer of the dyad with a long distance between the porphyrin and viologen moieties. The lifetime of the short-lived component is shortened by the intramolecular electron transfer quenching of the porphyrin singlet excited state by viologen in closed conformer of the dyad with a short distance between the porphyrin and viologen moieties.