An azabenz-annulated perylenediimide with tetraphenylethene units: Aggregation-induced emission, mechanochromic fluorescence, and cell imaging

Organic materials with strong solid-state fluorescence and sensitive stimuli responsiveness are highly desired for both fundamental research and practical applications. We report herein an azabenz-annulated perylenediimide (AzaBPDI)-based dye, AzaBP-TPE, which contains tetraphenylethene units in the planar aromatic structure. AzaBP-TPE undergoes typical intramolecular charge transfer, aggregation-induced emission, and mechanochromic fluorescence. In the solid state, AzaBP-TPE emits bright-yellow light with a photoluminescence quantum yield of 27%, and this emission becomes red fluorescence when MCF is induced, by using mechanical force to collapse the crystalline structure. Moreover, bright-yellow fluorescence can be recovered by exposing AzaBP-TPE powder to chloroform vapor. Notably, AzaBP-TPE nanoparticles can penetrate live cells and emit red light and, therefore, can be applied as a functional dye in bio-imaging.