Complexation of crown-containing butadienyl dyes with alkali and alkaline earth metal cations in the ground and excited electron states

Spectrophotometry and steady-state fluorimetry were used for the study of complexation of crown-containing butadienyl dyes with alkali and alkaline earth metal cations in acetonitrile, as well as protonation of these dyes with trifluoroacetic acid. Complexation of the compounds studied with the metal cations leads to the 1: 1 product, whereas protonation with trifluoroacetic acid affords the 1: 2 product containing 2 moles of the acid per 1 mole of the dye. Stability constants of the complexes are varied from 10 to 106 L mol−1, basicity of the crown-containing dyes in the reaction with trifluoroacetic acid increases with the increase in the macrocycle size. On complexation, the fluorescence spectra are shifted considerably less than the absorption spectra. This indicates that photorecoordination of the cation in the complex excited molecules occurred. Based on the correlation of the spectral shifts with the metal cation charge density, three types of complexes differing in the extent of influence of the cation charge on the spectral shifts can be singled out: “tight”, “loose”, and “solvent-separated”.