Study on Two Carbazole‐Based Difluoroboron Dyes With Aggregation‐Induced Emission for Mechanofluorochromism, Ink‐Free Writing, and Latent Fingerprint Imaging

ABSTRACT

To develop multifunctional small organic molecules, two carbazole‐based difluoroboron compounds, AIE‐1 with a triphenylamine unit and AIE‐2 with two tert ‐butyl groups, were synthesized. The results of optical measurement indicated that the two compounds exhibited intramolecular charge transfer and solvatochromism phenomena in six organic solvents, and aggregation‐induced emission in EtOH/water mixtures. It could be explained through quantum chemical calculations. AIE‐2 had reversibly mechanofluorochromism property, originating from the phase transformation between the ordered crystalline and the disordered amorphous states, and possessed rewritable ink‐free writing behavior, but AIE‐1 did not due to its inherent amorphous characteristics. Furthermore, the two compounds could make latent fingerprint imaging on the surface of a blade, and all levels of feature details could be clearly identified. Further research indicated that these developers exhibited stability and the ability to extract aged fingerprints, which better satisfied the requirements of practical applications. The specific response of the two carbazole‐based difluoroboron compounds to oleic acid secreted by sweat was a key factor in the visualization of latent fingerprints. It implied a potential application in forensic chemistry and criminal investigation.