Protonation–Deprotonation Treatment Modulating the Aggregate Structure and Fluorescence Property of (9-Anthryl)vinyl(4-pyridyl)vinylbenzene Position Isomers

The solid-state fluorescence property of organic materials is sensitive to molecule arrangement. Herein, solid-state protonation–deprotonation reactions are used as a tool to tune the molecular packing and solid-state fluorescence of three (9-anthryl)­vinyl­(4-pyridyl)­vinylbenzene (APVB) isomers. Substitution pattern has drastic effects on the solid-state fluorescence and the fluorescence color change induced by the protonation–deprotonation treatment. From meta- to para-substitution, the solid-state emission of the as-prepared samples could change from blue green to orange, about an 110 nm spectral shift. Furthermore, 1,4-APVB displays a crystallization-induced emission enhancement behavior. After HCl–NH3 treatment, the solid-state fluorescence of 1,3-APVB could turn from blue green to white due to dual emission. In contrast, the solid-state fluorescence spectra of 1,2-APVB and 1,4-APVB display only a minor shift in comparison with their respective as-prepared sample. The X-ray diffraction analyses reveal that new polymorphs are produced for 1,2-APVB and 1,4-APVB isomers after the protonation–deprotonation reactions. These polymorphs are metastable and could turn back to the initial crystal phase after organic vapor or annealing treatment. As for 1,3-APVB, no phase transition was found after HCl–NH3 treatment. The new emission peak in the yellow range (about 565 nm) is possibly due to excimer-like emission, which has one dominant fluorescence lifetime component up to 85 ns. The dual emission of 1,3-APVB induced by HCl–NH3 treatment is proved to be closely related to the decreased crystallinity. By virtue of the weak alkalinity of pyridyl moiety, these isomers could be used in acid vapor sensing and anti-counterfeiting