Acceptor-density engineering of push-pull typed carbazole derivatives for improving luminescent efficiency and mechanoresponsive luminescence

Improving luminous efficiency and mechanoresponsive luminescent (MRL) performance are significant issues in developing functional fluorescent materials. Herein, three push-pull typed carbazole derivatives with similar building blocks but differing in 2-vinylphenylmalononitrile acceptor numbers form mono- (m-VPMCz) to bis- (b-VPMCz) and tetra- (t-VPMCz) were designed and synthesized. Their luminescent properties in solution and aggregate states, as well as MRL performance were investigated. It was demonstrated that t-VPMCz with the highest acceptor-density and a highly twisted configuration achieved the highest luminescent efficiency in both solution and aggregation. b-VPMCz adopting a moderately twisted structure with two acceptor units exhibited the most remarkable MRL performance accompanied with the most distinct phase transition upon grinding. Our results suggest that rational control over the acceptor-density on push-pull typed molecules would be a promising way for realizing advanced functional fluorescent materials.