骨格炭素のアザ置換による狭エネルギーギャップ化を基盤とした近赤外光学材料開発

The new strategy for modulating the energy levels of conjugated molecules without extending the π-conjugated system is described. In the distribution of frontier molecular orbitals (FMOs) which can be depicted with quantum calculation, when one of FMOs is distributed on the skeletal carbon, each of them is defined as the isolated highest occupied molecular orbital (HOMO) or the lowest unoccupied molecular orbital (LUMO). By substituting skeletal carbon to nitrogen (aza-substitution) at the isolated FMO, we found that efficient and selective lowering of the energy level of one of FMOs is realized. In this review, we explain recent progresses on the developments of near-infrared (NIR) light-absorbing and/or emitting materials based on the selective lowering of LUMO energy levels through the aza-substitution at the isolated LUMO. Initially, the representative examples on the regulation of energy levels of FMOs are illustrated with azaphenalene derivatives. Next, aggregation-induced emission (AIE) and/or crystallization-induced emission (CIE)-active complexes with longer wavelength emission are explained. Furthermore, the series of conjugated polymers having NIR-luminescent properties were obtained. The mechanism and applications for advanced optical materials are described. We show here that aza-substitution at the isolated LUMO is a powerful strategy for controlling the energy level of conjugated systems and creating superior functional materials.