Aggregation-induced phosphorescence emission-active heteroleptic Ir(III) complexes: Synthesis, photophysics, and latent fingerprint detection applications

Three heteroleptic Ir(III) complexes (Ir-TPA, Ir-CzPh and Ir-PhCz) with different electron-donating aryl groups on C^N ligands were synthesized. Their optical properties were systematically investigated by spectroscopic methods and theoretical calculations to elucidate the effects of introducing different electron-donating groups on their triplet excited state properties. All three complexes possess aggregation-induced phosphorescence emission (AIPE) behaviors. Critically, the relationship between the size of organic ligands and AIPE behaviors for these complexes has been characterized. Their significant AIPE properties predicted that they could be used as efficient latent fingerprint (LFP) developers. Rapid (within 10 s) incubation in Ir(III) complex solution produced high-resolution, naked-eye visible and mobile-photographable LFP images, which could provide fast, reproducible and identifiable analyses of level 3 details for LFPs accurately. In addition, complex Ir-PhCz shows the best imaging of the LFP due to its green light emission and high quantum yield (24.5 %) in solid state. This rapid and practical LFP visualization methodology based on AIPE developers could provide a reliable solution for LFPs detection and investigations in actual scenarios.