Absorption Spectra of Pentamers of Tetrapyrrole Compounds in Aqueous Solutions

Pentamers of two types have been obtained in aqueous solutions containing mixtures of two tetrapyrrole compounds, in whose molecules there are positively or negatively charged peripheral groups. The pentamers of one type include one molecule of mesotetra(4Nmethylpyridyl) porphin (TMPP) and four molecules of the complex of mesomono(nsulfophenyl)etioporphyrin II with palladium (PdSPhEP), and the pentamers of the other type include one molecule of sulfonated phthalocyanine (PCS) and four molecules of TMPP. The absorption bands of the pentamers are broadened and shifted toward longer wavelengths in comparison with the bands obtained as a result of the addition of the spectra of the monomers. It seems that the changes in the absorption spectra are first of all due to the change in the interaction of the molecules of the pigments with the molecules of the surrounding in formation of associates and due to the influence of the resonance dipoledipole interaction between the molecules in the associates. The influence of the intermolecular photoinduced charge transfer is also possible (it is most probable for the associates with PCS). We have revealed an effective quenching of the fluorescence of PCS and TMPP solutions upon heteroassociation.