Diphenylpyrimidinone–salicylideneamine – new ESIPT based AIEgens with applications in latent fingerprinting†
Diphenylpyrimidinone–salicylideneamine DPPS-1 undergoes concentration dependent self-assembly to form aggregates with rods – mimicking a ‘coral reef’ superstructure and a spherical morphology evident from dynamic light scattering (DLS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). DPPS-1 and DPPS-2 exhibit weak excited state intramolecular proton transfer (ESIPT) based emission in CH3CN and their binary mixtures with water, but in solutions containing >70% water fraction DPPS-1 and DPPS-2 molecules aggregate and ESIPT is facilitated to give a strong green ESIPT emission at 526 nm (ϕ = 0.273, 0.068). The ESIPT process remains active in the solid state and solid DPPS-1 and DPPS-2 appear as fluorescent green under 365 nm light illumination. The AIE-active nature of DPPS-1 and DPPS-2 finds applications in the visualization of latent fingerprints on aluminium, steel and glass surfaces. Even 24 h after the placement of the fingerprints, up to the second level of information viz. core, lake, ridge termination and dots, delta and bifurcation in the fingerprints could be identified.