Theoretical study of solvent effects on the intramolecular charge transfer of a hemicyanine dye

The formation of twisted intramolecular charge transfer (TICT) states by rotating part of the molecule around some of the chemical bonds in a hemicyanine dye, 4-(2-(4-dimethylaminophenyl)ethenyl)-1-methylpyridinium iodide (HR), was investigated using quantum chemical calculations in combination with a cylindrical solvation model. Experimental results showed that the structure of HR is a compromise between benzenoid and quinoid resonance forms. The TICT state can be formed by rotating the dimethylamino group to the perpendicular position in polar solvents.