Aggregation-Controlled Dual-Emissive Room-Temperature Phosphorescence in Gold(I) <i>N</i>-Heterocyclic Carbene Complexes

Efficient phosphorescence at ambient temperatures and tunable luminescence behavior are highly desirable for various practical applications. Au(I) complexes with different ligands have been explored for their unique ability to form aurophilic interactions, strongly influencing luminescence behavior. This paper reports Au(I) complexes with N-heterocyclic carbene (NHC) ligands that exhibit distinct luminescence properties due to differences in their aggregated structures. The developed Au(I) complex 2, featuring a single flexible alkoxy tail on the benzimidazole backbone, exhibits unique dual emission behavior. The lifetimes of the emission bands are in the microsecond and millisecond range, implying a dual-phosphorescence nature of emission. By controlling the recrystallization conditions, two distinct emissive polymorphs of complex 2 are obtained. Additionally, a monotropic liquid-crystalline (LC) phase is observed during cooling scans over a short temperature range, which is absent in previously reported Au(I) NHC complexes. These findings highlight the unique luminescence behavior of complex 2 and its potential application in light-emitting devices.