Characteristics of donor-acceptor complexes formed in porphyrin-polymer systems and their photoactivation in electron transfer photoreaction

Abstract

Donor-acceptor complexes formed between meso-tetra( p-aminophenyl)porphine moieties covalently bound to polymers (e.g. poly(methacrylic acid) (PMA) and the influence of substances with electron-accepting affinities (molecular bromine, hydrogen ions and benzylviologen) on the properties of these complexes were investigated using fluorescence and absorption spectroscopy. Electron transfer to the viologen in a system including a sacrificial electron donor (triethylamine) with accumulation of reduced benzylviologen under steady-state illumination was also studied. A correlation between IR emission assigned to charge transfer complex fluorescence and efficiency of electron transfer to the viologen has been revealed. The IR emission is the most intense in porphyrin covalently bound to PMA compared with other polymers. Differential absorption spectra of associated meso-tetra( p-aminophenyl)porphine bound to macromolecules indicate the involvement of macromolecule carboxyl groups in the structure of the donor-acceptor complex. Incorporation of molecular bromine or hydrogen ions in this structure due to non-valent interactions leads to a considerable change in the absorption spectrum of the complex. In the case of benzylviologen incorporation, its involvement in the complex structure occurs during the photoinduced electron transfer to benzylviologen in the system including the sacrificial electron donor. The appearance of unusual features in the latter system is interpreted as the photoactivation of the donor-acceptor complex.