PHOTOINDUCED ELECTRON-TRANSFER IN ISOLATED BICHROMOPHORIC AND SOLVATED TRICHROMOPHORIC SYSTEMS

After local photoexcitation of the acceptor chromophore, fast and virt ually barrierless charge separation over approximately 5 Angstrom is o bserved under supersonic jet isolated conditions in three rigid donor- bridge-acceptor (D-br-A) systems in which D and A are separated by thr ee sigma bonds. It is suggested that low frequency intramolecular vibr ational modes, discernible in the well-resolved excitation spectra, pl ay a role in enabling efficient internal conversion between the locall y excited and charge transfer states. Insertion of an extra piperidine unit in the bridge elongates its overall length to seven sigma bonds, while at the same time a tertiary nitrogen is added as an intermediat e donor site. In the resulting trichromophoric systems (D-2-br-D-1-br- A), stepwise charge separation occurs in solution with a strong solven t dependence.