An AIEE-Active Cationic Iridium(III) Complex Encapsulated in Hollow Silica-Based Nanospheres for Luminescent Detection of Latent Fingerprints

A novel yellow-green–emitting cationic iridium(III) complex [(ppy)₂Ir(DIP)]PF₆ (ppy: 2-phenylpyridine; DIP: 2-(1-dodecyl-1H-imidazol-2-yl)pyridine) was designed and synthesized. [(ppy)₂Ir(DIP)]PF₆ showed obvious aggregation-induced enhanced emission (AIEE) activity, and when it was dissolved in CH₃CN–H₂O mixtures at 1.0 × 10⁻⁵ mol·L⁻¹, its photoluminescence (PL) intensity increased 12.2 folds when the water fractions (f_w, vol %) increased from 0% to 90%. Using surfactant cetyltrimethylammonium bromide (CTAB) as a template agent and tetraethyl orthosilicate (TEOS) as a silica precursor, a silica-based composite containing [(ppy)₂Ir(DIP)]PF₆ was prepared by the sol–gel method combined with the template method. The composite was composed of uniformly sized hollow nanospheres, exhibiting better dispersibility, higher affinity, and adhesion to the fingerprint secretion residues than those of pure complex powders. Moreover, the PL quantum yield (41.7%) of the composite nanospheres was higher than that of the pure complex powders (38.4%), which suggested these composite nanospheres were more suitable for visualization and detection of latent fingerprints (LFPs). Using them as the luminescent developer, the fingerprint patterns developed from LFPs on both nonporous and porous surfaces all showed high brightness and contrast under 365nm UV light, and the first-, second-, and third-level details were all clearly distinguished, especially on nonporous surfaces.