Novel coumarin-oxadiazole azo dyes for enhanced latent fingerprint detection

Abstract

Organic azo dye molecules exhibit strong luminescent properties, which are useful for forensic experts to find and visualize invisible fingerprints in crime investigations. This study describes the newly developed heterocyclic azo dye, specifically (E)-4-hydroxy-3-((5-phenyl-1,3,4-oxadiazol-2-yl)diazenyl)-2H-chromen-2-one (coumarin-oxadiazole). The synthesis of coumarin-oxadiazole was achieved through a standard diazo-coupling reaction, employing 2-Amino-5-phenyl-1,3,4-Oxadiazole as a diazonium salt and 4-hydroxycoumarin as the coupling agent. The structural elucidation of the synthesized compound was carried out using spectroscopic techniques such as Infrared spectroscopy (IR), Proton nuclear magnetic resonance spectroscopy (¹H NMR), Carbon-13 nuclear magnetic resonance spectroscopy (¹³C NMR), Mass spectroscopy (MS) and Ultraviolet-visible (UV-Vis) spectroscopy were employed to confirm the structural characterization of the resultant molecule. Density functional theory analysis confirmed a donor–π–acceptor structure in the coumarin–oxadiazole dye, with a 3.65 eV HOMO-LUMO gap, supporting efficient charge transfer and strong fluorescence. The synthesized molecule was then successfully evaluated for its application in latent fingerprint (LFP) detection. Fingerprint pattern level I, level II and level III are clearly visible on both porous/non-porous surface with clear visibility under normal daylight and 365 nm UV light and ImageJ used to distinguish   ridges and furrows characteristics in fingerprint patterns, demonstrates its potential in forensic science.

Graphical abstract

Novel coumarin-oxadiazole azo dye via diazotization of 2-amino-5-phenyl-1,3,4-oxadiazole followed by a coupling reaction with 4-hydroxycoumarin. The resulting compound was characterized and evaluated for its applicability in latent fingerprint detection. The developed LFPs of all three levels were viewed under normal daylight and 365 nm UV light.