Formation of mixed dimers in solutions of basic dyes

Abstract

The formation of mixed dimers of basic dyes has been studied in aqueous solution at room temperature. These mixed dimers have absorption bands in the visible region at wavelengths shorter and longer than those shown by the self dimers of the dyes having higher and lower excited states, respectively. Both transitions are allowed according to exciton theory. The angle between the dye molecules in the sandwich-like dimers was calculated from the molar absorption coefficients and is in the range 140°–160°. The non-alignment of the molecules may be due to steric hindrance caused by the bulky side groups.