STRUCTURE AND SPECTRAL-FLUORESCENT PROPERTIES OF MEROCYANINE DYES IN POLYMER FILMS

Abstract

The absorption and fluorescence spectra of positively and negatively solvatochromic merocyanine dyes with the same structural type in polymer films of different polarities (polystyrene, polyvinyl butyral, and poly-N-epoxypropylcarbazole) are studied. It is found that negatively solvatochromic merocyanines are more prone to aggregation than positively solvatochromic dyes. Based on the quantum chemical DFT calculations, this is explained by the larger dipole moments of the former. It is shown that merocyanine aggregates have a sandwich-type structure, which results in the fluorescence quenching. It is found that in more polar polymers the aggregation occurs at higher dyes concentrations. It is established that, as in liquid solutions, the studied merocyanines have noticeable solvatochromism in polymer films. Although the fluorescence intensity of merocyanines increases in going from liquid solutions to polymer matrices, the most important factor determining their fluorescence ability in polymers is the polyene-polymethine transformations in their molecules.