Pyrene-pyridoxine azine as a functional fluorophore: developing LFPs and formulating security ink

A biocompatible fluorescent pigment, pyrene-pyridoxine azine (PyPy) derivative, has been designed that can display a vivid yellow hue under natural daylight and a cyano-green luminescence when exposed to UV light in solution. Interestingly, the same compound manifests a rich yellow color along with red fluorescence when integrated into solid-supported materials, like porous papers. Moreover, PyPy exhibits robust adherence to the paper surface, rapid drying, reasonable photostability, and considerable resistance to water, which can be considered advantageous for security-ink application. These observations strongly suggest that this probing molecule holds potential as a functional and environmentally friendly colorant for crafting water-based ink via flexography printing. Further, the notable high intensity of fluorescence, coupled with outstanding surface adhesion characteristics, facilitated the development of latent fingerprints (LFPs). These fingerprints, when illuminated, produce fluorescence images that offer distinct background contrast, thereby unveiling intricate level 1, level 2, and level 3 details on non-porous substrates that aid in individual identification. Moreover, the ink formulation of PyPy facilitated the identification of primary and secondary-level finger-mark details on both porous and non-porous surfaces. These results effectively showcase the successful utilization of the biocompatible PyPy fluorophore in fingerprint analysis, eliminating the necessity for additional adhesives and introducing a promising new tool for LFP detection. Graphical Abstract