Cu+-Induced in-situ Methylene-Transformation and Aggregation-Induced emission activity

Benzimidazole and its derivatives have received great attention owing to its good biocompatibility and excellent optical properties. Furthermore, metal coordination polymers of benzimidazole have also attracted considerable interest. However, the synthesis of functional benzimidazole ligands involves quite complicated steps, which hinders their application. In this study, we designed and synthesized two benzimidazole coordination polymers, [(C15H10N4O)•CuBr] (CP-1) and [(C45H31N12)•(CuBr)4CH3OH] (CP-2), using CuBr and 1,3-bis(1H-benzo[d]imidazol-2-yl)-methane by solvothermal method. Notably, the methylene (–CH2-) in original organic ligand converses to carbonyl (-C = O-) and double bond (-C = C-) under different condition, the In-situ methylene-transformation is rare, as it involves two oxidation processes: oxygenation and dehydroxidation. With the change of the hybridization mode (sp3 to sp2) of the central carbon atom, the molecular conjugation greatly increases. Therefore, fluorescence properties of two CPs were investigated in detail that the CP-2 exhibits photoluminescence characteristics, and it emits yellow light under UV lamp. Meanwhile, the theoretical calculations were also carried out to study and verify the above conclusions, and the results showed high consistency. Consequently, this work might provide a new strategy to construct materials with C = C bond and photoluminescence effect.