Systems Containing Two Oppositely Charged Polyelectrolytes. Behavior of Ionic Photosensitizers and Quenchers

Several photosensitizer-quencher systems containing both the negative polyelectrolyte poly-(styrenesulfonate) (PSS) and the positive polyion polybrene (PB) have been investigated. At relatively low concentrations, solutions containing both PSS and PB are stable with respect to precipitation even at equivalent concentrations. Interactions of the polyelectrolytes with the photosensitizer zinc tetrakis(sulfonatophenyl)porphyrin (ZnTPPS⁴) and meso-tetrakis(N-methylpyridinium-4-yl)porphyrin, ZnTMPyP⁴⁺, have been studied by spectrophotometric and spectrofluorimetric techniques. The concentration effect of the PSS induces the formation of charge-transfer complexes between a photosensitizer and the hydrophobic parts of the polymer, as well as photosensitizer dimers. The effects of the oppositely charged polyion on the absorption and emission spectra of the photosensitizers as well as the effect of several quenchers have been studied. The results lead to the conclusion that each of the two polyelectrolytes preserves part of its electrical field in its vicinity even when the oppositely charged polymer is in slight excess.