Visualization of latent fingerprints using two difluoroboron compounds containing pyrene and triphenylamine substituents.

Two difluoroboron compounds (2py-BF-TPA and 2TPA-BF-py), containing different amounts of pyrene and triphenylamine substituents, were synthesized to explore their potential application in latent fingerprint visualization. It was found that 2TPA-BF-py, featuring one pyrene and two triphenylamine groups, exhibited a more significant intramolecular charge transfer than 2py-BF-TPA, which contained one triphenylamine and two pyrene units). Both compounds displayed solvatochromism in seven organic solvents of varying polarity and aggregation-induced emission properties in DMSO/water mixtures. Their optical properties were well rationalized by quantum chemical calculation. The prepared staining agents successfully visualized latent fingerprints on the surfaces of three substrates. Sharp fingerprint patterns with well-resolved ridges were clearly detected, and all three levels of feature details could be also clearly identified. Further investigations demonstrated their stability over time and across temperature, ability to develop aged fingerprints, and inherent hydrophobicity. The specific response of two difluoroboron compounds to oleic acid-a component of sweat-was identified a key factor in latent fingerprints visualization. It was implied a potential application in forensic chemistry and criminal investigation.