Through-bond/space conjugated nonaromatic dihydrobenzoquinolines: Luminogens with simple synthesis method, strong aggregation-induced emission and emissive excimers

Abstract

In recent years, AIE (aggregation-induced emission) fluorophores have attracted great interest owing to their advantages in wide areas and many AIE fluorophores have be designed by combing conventional fluorophores with AIEgens that exhibiting AIE attributes. However, only few efficient AIEgens were developed. Here, novel dihydrobenzoquinolines (h-DHBQs 4a−e and f-DHBQ 5a), a new kind of AIEgens with strong AIE, are reported. DHBQs were synthesized by a catalyst-free multi-component reaction (MCR) in good overall yield and their optical properties were investigated through steady-state and transient fluorescence spectra, single-crystal diffraction, calculated HOMOs and LUMOs. It was found that DHBQs have these characteristics: a) strong AIE, that is, their fluorescence quantum yields lower than 4.1% in solutions, but high to 90.5% in crystals; b) efficient through-bond and -space conjugated nonaromatic central heterocycle; c) radiative-process-favored but non-radiative-decay-prevented self-assemblies; d) emissive excimers; and e) easily tunable fluorescence color. This work affords a new kind of AIEgens with excellent optical properties in solids and a strategy to develop AIEgens by constructing nonaromatic heterocycle using simple MCRs.