Intramolecular charge transfer in merocyanine dye molecules enhanced by formation of J-aggregates

Abstract

Anisotropic visible and infrared (IR) absorption spectra of Langmuir–Blodgett (LB) films of mutually mixed merocyanine dyes deposited with Cd 2+ ions were recorded. In these films, a merocyanine dye ‘DO’ is included in J-aggregates, although in LB films of DO (not mixed with other merocyanine dyes), DO itself does not form J-aggregates. A difference spectrum method successfully separated the spectra observed into two components, one of which was due to J-aggregates. This component includes the contribution of the J-aggregated DO molecules and compared well with the absorption spectra observed for LB films of DO. This comparison detected, for the aggregated DO, red shifts of several IR bands due to softening of the bond alternation in the central conjugated system of the molecule, which thus suggested that intramolecular charge transfer is enhanced by the formation of J-aggregates.