Polymorphism and light conversion properties of anthracene-based isomers

Abstract Polymorphism is playing a more important role in revealing the relationships between intermolecular arrangement, stacking and optical properties of luminogens, however, obtaining of polymorphism depends more on luck and accident. Here, two isomers named as 1APPA and 2APPA were designed and synthesized by furnishing twisted cyanostilbene backbone with planar anthracene unit. The two luminogens show similar solvatochromism and inconspicuous mechanochromism, but different in terms of AIEE activity and polymorphism. Only one crystal is obtained for 1APPA, while needle-like colorless 2APPA-c (kinetic control) and yellow massive 2APPA-y (thermodynamic control) can be obtained for 2APPA in the same solvents, significantly, their crystal growth has good repeatability. Theoretical calculation, solvatochromism combined with crystal analysis further confirm intramolecular charge transfer (ICT) effect from anthracene donor to cyanostilbene acceptor takes responsible for different polymorphism between 1APPA and 2APPA. Crystal analysis indicates that π-π stacking between adjacent anthracene unit leads to red-shifted fluorescence emission for 2APPA-y than 1APPA and 2APPA-c, while twisted molecular configuration, stable crystal phase and high fluorescence quantum yield are attributed to strong intermolecular hydrogen bonds and weak interactions. Besides, 2APPA can be used as potential light conversion agent due to matching fluorescence emission (485 nm), high fluorescence efficiency (0.52) and excellent photostability, and 93.9% of the initial intensity is reserved for 2APPA film after UV radiation of 20 h.