Aggregation-mediated photo-responsive luminescence of cyanostilbene based cruciform AIEgens

Abstract

Photochromic materials have received tremendous attention owing to their unique photoresponsive behaviour and promising applications as smart materials. Herein, two cyanostilbene based AIEgens with a cruciform topology were synthesized and well characterized. Upon the addition of water, both fluorophores exhibited enhanced emission in the THF/water mixture owing to aggregate formation. In solution, the emission of these AIEgens can be gradually attenuated with blue-shifted absorption after irradiating with 365 nm UV light and recovered on exposure to 254 nm UV light. This phenomenon was attributed to the reversible E/Z isomerization of the cyanostilbene units and confirmed by NMR spectroscopy. By contrast, for the sample in the nano-aggregate or solid state, the emission can be efficiently quenched via [2+2] cycloaddition which had disrupted the conjugation backbone of the chromophore. Photochromic luminescence can also be realized by dispersing the fluorophores in a PMMA matrix and modulated by tuning their concentration in the polymer film. Meanwhile, the cruciform AIEgens also exhibited obvious mechanochromic luminescence in the solid state.