Supramolecular Interactions-Assisted Polymorphism and Unique Mechanofluorochromism in 9,10-Bis((E)-4-(trifluoromethyl)styryl)anthracene.

A fluorinated distyrylanthracene (DSA) derivative, 9, 10-bis((E)-4-(trifluoromethyl)styryl)anthracene abbreviated as 4FDSA with two crystalline polymorphs (4FDSA-G (green emission) and 4FDSA-O (orange emission)), showing remarkable aggregation-induced enhanced emission and mechanofluorochromic characteristics, was developed. One of the polymorphs in its crystalline arrangement exhibits the hardly seen F…F interactions. It questions the conventional belief of the non-polarisable nature of fluorine atoms in forming the halogen bond. The twisted molecular conformation facilitated by the various supramolecular interactions resulted in the formation of another intensely emissive bluer nanocrystal (4FDSA-NC) at aggregating conditions. Even though, the both polymorphs show distinct tricolor luminescence switching on the action of mechanical force, fumigation of ground crystals with solvent vapor resulted in the formation of a more thermodynamically favorable 4FDSA-NC form. The work demonstrates the effect of supramolecular interactions assisted conformational changes in tuning the unique mechanofluorochromic characteristics of the polymorphic crystals.