Spectral characterization of selected stilbentriazine dyes – Structural trans–cis isomerisation

The paper deals with the spectral investigations of new stilbentriazine dyes containing amino groups or alkoxy group attached to the main molecular triazine ring. Absorption and fluorescence spectra of the dyes in aqueous solutions were recorded. The existence of two spectral structures absorbing at 275 and 350 nm was shown and they are assigned to cis- and trans- structures of dyes, respectively. It was indicated that absorption and fluorescence features of the dyes are not significantly affected by a kind of substituent; exception is ST2 which differs in molecular structure and in the absorption and emission properties from the remaining dyes. The quantum yields of dye fluorescence and the yields of cis–trans energy transfer were also evaluated. The influence of temperature, solution pH and radiation exposure on photoproperties of the dye spectral forms were also examined. The large impact of the radiative exposure time on molecular conformation changes was observed, whereas temperature and environmental pH do not affect the dye spectral parameters. The equilibrium ratios of the trans- to cis- structures were estimated.