Benzimidazole-based metal complexes: synthesis, coordination behaviour, and photophysical applications

Benzimidazole, a fused heterocyclic compound combining the Benzene and Imidazole rings, has attracted considerable interest in recent years in coordination chemistry due to its versatile donor sites and structural rigidity. Its strong N-donor characteristics and adaptable substitution at positions such as N1, C2, and C5-C6 make it ideal for creating structurally diverse and functionally tunable metal complexes. These benzimidazole-based complexes with transition, lanthanide, and post-transition metals exhibit unique coordination behaviors, often influenced by substituent effects, metal oxidation states, and ligand design. Notably, such complexes have demonstrated exceptional photophysical characteristics, including fluorescence, phosphorescence, and thermally activated delayed fluorescence (TADF), making them promising candidates in light-emitting devices, sensors, and bioimaging. This review comprehensively summarizes recent advances in the synthesis strategies for benzimidazole ligands and their corresponding metal complexes, delves into their coordination modes, and discusses the structure-property relationships that govern their photophysical behavior. While projecting future research directions, integrating computational design and green chemistry to develop next-generation multifunctional materials.