Abstract: A cationic iridium(III) complex [(ppy)2Ir(phen-CAA)]PF6 was synthesized by using 2-phenylpyridine (ppy) as the main ligand and 2-chloro-N-(1,10-phenanthrolin-5-yl)acetamide (phen-CAA) as the ancillary ligand. This complex exhibits an obvious aggregation-induced enhanced emission (AIEE) effect. In a CH3CN–H2O mixed solvent (1.0 × 10-5 mol·L-1), its luminescence intensity increased with the increasing volume fraction of water (fw), reaching a maximum photoluminescence quantum yield (PLQY) of 30.7% at fw = 60%, and then gradually decreased. [(ppy)2Ir(phen-CAA)]PF6 exhibited weak luminescence both in dilute solution (PLQY = 8.6%) and in the aggregated solid state (PLQY = 0.7%), making it difficult for practical applications. In water, using cetyltrimethylammonium chloride (CTAC) as the template agent and tetraethyl orthosilicate (TEOS) as the silica precursor, a silica-based composite containing the complex was prepared via hydrolysis. Under the optimal conditions, the composite exhibited a high PLQY of 25.9%, and the emission of [(ppy)2Ir(phen-CAA)]PF6 shifted from orange-red light (λem,max = 620 nm) to yellow light (λem,max = 562 nm). The composite was composed of spherical particles with a main size distribution of 70~90 nm. The obtained composite powder was used as a luminescent developer for latent fingerprints on both non-porous and porous substrates, and satisfactory detection performance was achieved. The first-, second-, and third-level fingerprint details could be identified after image magnification.

Key words:  Cationic iridium(III) complex, Latent fingerprint detection, Silica, Luminescent composite material, Aggregation-induced enhanced emission