PHOTOINDUCED ENERGY AND ELECTRON-TRANSFER OF COVALENTLY-LINKED ZINC(II)-PYROPHEOPHYTIN-ANTHRAQUINONE MOLECULES IN MONOLAYERS OF LANGMUIR-BLODGETT-FILMS

Electron donor-acceptor compounds of optically pure covalently linked Zn(II)-pyropheophytin-anthraquinone (ZnPQ) have been synthesized. Thes e compounds allow one to prepare highly ordered solid samples by means of the Langmuir-Blodgett technique. Monolayer films of the P4(S)-ZnPQ diastereoisomer were prepared in a dioleoyl phosphatidylcholine matri x with the concentration varied from 0.5 to 10 mol.%. The time-resolve d fluorescence properties of the films were interpreted in terms of th e presence of two types of P4(S)-ZnPQ conformers, the folded one and t he opened one. The folded conformer predominated and underwent fast in tramolecular electron transfer (rate constant > 10(11) s(-1)) from the Zn-pyropheophytin part to the anthraquinone moiety and was, therefore , not observed directly in the fluorescence study. The open conformer had a relatively long-lived singlet excited state and was quenched by an energy transfer process to the folded conformer at P4(S)-ZnPQ conce ntrations higher than 2 mol.% with an estimated quenching radius of 5 +/- 0.2 nm.