Three multifunctional difluoroboron fluorescent dyes with five member N-heterocyclic ring for mechanofluorochromic behaviors, the ink-free writing and latent fingerprints imaging

To further advance the development of multifunctional fluorescent dyes, three difluoroboron compounds (F-1, F-2, and F-3) containing five-membered N-heterocyclic ring moieties that act as the electron-withdrawing units were synthesized. It was observed that compound F-1, which incorporated a 1,2,4-triazole segment, and compound F-3 with 1,2,3-triazole portion exhibited aggregation-induced emission activities suitable for latent fingerprints imaging. In contrast, compound F-2 featuring a pyrazole unit demonstrated an aggregation-caused quenching phenomenon. Additionally, all three compounds displayed mechanofluorochromic behaviors. Specifically, the emission spectra of compound F-1 in the solid state experienced only a slight shift of approximately 5 nm upon grinding, however, compound F-2 underwent a red shift from 475 to 501 nm while compound F-3 shifted from 482 to 507 nm. Furthermore, both compounds F-2 and F-3 could be utilized in ink-free writing applications. Notably, the safety paper prepared using compound F-2 was designed for single-use due to its irreversible mechanofluorochromic behavior, conversely, the safety paper derived from compound F-3 was rewritable owing to its reversible mechanofluorochromic behavior. It provided a foundation for exploration the application of multifunctional difluoroboron compounds with 1,2,3-triazole moiety.