Color tuning donor–acceptor-type azobenzene dyes by controlling the molecular geometry of the donor moiety

Abstract

Two series of donor–acceptor (D–A)-type azobenzene dyes with a tertiary amine as the donor were synthesized, and their photophysical and thermal properties were investigated. Although tertiary amines with the same Hammett constant were used, the properties of the molecules varied considerably depending on the molecular geometry of the tertiary amine. We found that the electron-donating properties could be controlled by the molecular geometry of the donor, as the geometry strongly affected the orientation of the n orbital of the donor relative to the p orbitals of the π-conjugated system of the phenyl ring. When the n orbital was fixed parallel to the p orbitals, the donor exhibited strong electron-donating properties. These results suggest that the molecular geometry should be considered in addition to the primary molecular structure for the design of highly functional materials.