Tunable solid state emission of novel V-shaped fluorophores by subtle structure modification: Polymorphism, mechanofluoro-chromism and micro-fabrication

Abstract

A family of V-shaped fluorophores with different numbers and positions of vinyl are rationally designed, using which a largely wide and approximately successive range of solid-state emission wavelengths can be achieved before and after force stimuli. These compounds are intensely emissive and highly mechanofluorochromic (MFC), and many physical properties such as emission wavelengths, quantum yields, intramolecular charge transfer (ICT) extent, solvatochromism, aggregation-induced emission (AIE) activity and time consumed for restoration from amorphous phase are profoundly influenced by the number and site of vinyl groups. However, the emission wavelength shifts under force stimuli seem to be related to neither the number nor the position of vinyl. For a member with double polymorphs, the unqiue molecular pair packing in one of them revealed by X-ray crystallography is presumably responsible for its MFC inertia and the abnormally one-way phase transformation from the stable to the metastable one. Interestingly, a shape-dependent emission of self-assembled crystal with a fractal structure occurs when both of the two polymorphs are fumed in solvent vapor for long time. Moreover, the films made of these V-shaped compounds are successfully developed to be erasable mediums for information storage with robust fatigue resistance.