An AIE-active orange-emitting cationic iridium(III) complex for latent fingerprints detection via a simple powder dusting method

An orange-emitting cationic iridium (III) complex [(PPPA)2Ir(Phen)]PF6 (PPPA: N,N-diphenyl-4'-(pyridin-2-yl)-[1,1′-biphenyl]-4-amine, Phen: 1,10-phenanthroline) was synthesized and characterized. [(PPPA)2Ir(Phen)]PF6 shows high aggregation-induced emission (AIE) activity mainly based on restrained intramolecular rotation (RIR) of the triphenylamine group in its main ligands. When it is dissolved in CH3CN–H2O mixtures (5.0 × 10−5 mol L−1) with water fractions (fw) from 0% to 90% (in vol %), only the solutions with fw ≥ 60% can emit bright orange light, the corresponding photoluminescence quantum yields (PLQY) increased from 2.3% (at fw = 60%) to 47.8% (at fw = 90%), the PLQY further increased to 52.2% in solid powders. This complex was successfully used for latent fingerprints (LFPs) visualization and detection on both non-porous and porous surfaces via a simple powder dusting method, due to its high AIE activity as well as good adhesion to secretion residues, under 365 nm UV light, the fingerprints developed from whether fresh or aged LFPs all show high brightness and high contrast, the first, second, and third level details of the fingerprints all can be clearly distinguished.