High-pressure study of triphenylmethane dyes in polymeric and aqueous media

Optical absorption measurements have been made for the hydrogen, methyl, and ethyl derivatives of triphenylmethane dye molecules dissolved in aqueous solution (to 10 kbar) and in plastic films of poly(methylmethacrylate) and polycarbonate (to 150 kbar) at 295 K to study the effects of environment both on the A and B rotational isomers of the dye molecules and also on the isomerization process. Absorption peaks associated with the isomers generally shift red with pressure, as is characteristic of PI ..-->.. PI* electronic transitions. The partial molar volume of the system on isomerization from A to B increases slightly in all the media, depending on differences in the degree of solvation between the isomers. Anomalies associated with the ethyl derivative in aqueous solution are interpreted in terms of these differences. 18 references, 6 figures, 3 tables.