AIE-active smart cyanostyrene luminogens: polymorphism-dependent multicolor mechanochromism

Multicolor mechanochromic luminescent (MCL) materials are promising candidates in fundamental science and practical applications. In this paper, a series of novel smart luminescent compounds based on a cyanostyrene unit, NAIF, NA-15C5, NAPM, NAIP and NAPF, have been developed. NAIF, NAPM, NAPF and NAIP all exhibit aggregation-induced emission (AIE) characteristics and individually show red, orange, yellow and green emission in their aggregated state. Luminogens NA-15C5 and NAPM display reversible tricolor-changing MCL behaviors. NAIF and NAIP show bicolor switching mechanochromic phenomena. Additionally, different molecular packing modes of two crystalline polymorphs, NAPM-y and NAPM-o with bright yellow and orange luminescence color, rationally explain the tricolor-changing mechanochromic mechanism. Moreover, luminogen NAIP can be used as ink-free rewritable paper.