Aggregation and photofading behaviour of unsymmetrical squarylium dyes containing a quinolylidene moiety

Representatives of a new class of unsymmetrical squarylium dyes containing a quinolylidene moiety have been synthesised and characterised. These dyes absorbed at a longer wavelength (11-50 nm) than the corresponding symmetrical squarylium dyes. The influence of the quinolylidene moiety on the absorption of these dyes was studied and compared with that calculated by the PPP-MO method. The photostability properties of the dyes were investigated in chloroform with a high-pressure mercury lamp. The aggregation of the unsymmetrical squarylium dyes were also studied in different DMSO/water solutions, including solutions with gamma-cyclodextrin.