Spectral–Kinetic Studies of Some Homodimer Styrylcyanine Dyes in Solutions

The spectral and kinetic characteristics of the dye Sbt ((E)-2-(4-(dimethylamino)styryl)-3-methylbenzo[d]thiazol-3-ium iodide) and its homodimers Dbt-5 and Dbt-10 in chloroform and its binary mixtures with solvents of different polarity have been studied. It has been found that nonfluorescent H-aggregates are formed with an increase in the proportion of hexane in chloroform solutions of these dyes. The spectral and photophysical parameters of the studied dyes are found to depend on the polarity and viscosity of the solvents. Quantum chemical calculations of the charge distribution and potential energy in the ground and excited states for the molecules of the studied compounds have been performed. The Sbt and Dbt-10 dyes are characterized by higher values of quantum yield and lifetime of the excited state in a viscous medium, which are associated with the formation of the TICT (twisted intramolecular charge transfer) state. The transition of molecules to this state leads to effective quenching of fluorescence.