Highly emissive near-infrared solid organic fluorophores for visualization of latent fingerprints based on the powder dusting method

Abstract

The utilization of highly efficient fluorescent materials for latent fingerprints (LFPs) is attractively important for criminal investigations but remains challenging. Herein, we developed a low-cost near-infrared (NIR) emission composite powder made up of organic fluorophores doped into the montmorillonite (MMT) medium for the visualization of LFPs based on powder dusting. Our design of twisted donor–acceptor structures of CASN and TASN not only enables NIR emissions at 650 and 686 nm but also assures high solid state photoluminescence quantum yields (Φ_solid) of 0.17 and 0.32, respectively. Furthermore, TASN doped into the MMT medium has the merits of a high adsorptive capacity and a mass ratio as low as 10%. Compared with traditional magnetic and red fluorescent powders, the TASN/MMT powder could give reliable fluorescent images of LFPs with a higher contrast and resolution, under visible light (405 nm) rather than harmful UV (365 nm) excitation. Florescence fingerprint images of specific level 1–3 details on different substrates, including both smooth and rough surfaces, can be obtained within 10 s by mobile phone photography. These results prove that the TASN/MMT powder is a promising candidate for the forensic sciences.