Design for a Pure-Blue-Emissive Polymer Film through the Selective Perturbation of the Energy Level of the Highest Occupied Molecular Orbital in a Boron Complex

Abstract

The logical design for obtaining a blue-luminescent film based on a conjugated polymer is demonstrated. We recently found solid-state luminescent boron complexes with fused ketoiminate ligands (FBKIs). From quantum chemical calculations, it was proposed that there is a skeletal carbon having isolated highest occupied molecular orbital (HOMO) where the lobe in HOMO and the node in lowest unoccupied molecular orbital (LUMO) exist. From these results, we presumed that only the HOMO energy level could be selectively lowered by aza-substitution at this carbon atom. Based on this idea, we designed and synthesized the aza-substituted FBKI (azaFBKI). From the optical and electrochemical measurements, it was shown that azaFBKIs had solid-state luminescent properties and especially the wider energy gaps originating from the lower HOMO levels than the corresponding FBKIs. Next, the conjugated homopolymer including azaFKBI as a repeating unit was designed and obtained. Finally, it was observed that the synthesized polymer exhibited purely blue luminescence in film (λₑₘ = 440 nm, ΦPL, film = 0.48, CIE; 0.19, 0.18).