Supramolecular complex assembly with build-in light-harvesting antenna enables efficient photocatalytic synthesis of benzimidazoles

Metal-polypyridine complexes are the fascinating transition-metal-ion-based photosensitizers (PSs) in photocatalytic reactions, while, they often suffer from moderate photo-catalytic activity due to their low sunlight utilization efficiency and high carrier recombination rates. Herein, we employed the iron-terpyridine complex as the building block to develop a novel supramolecular complex assembly through π-π stacking interaction. The iron-terpyridine complexes served as a visible light harvesting center that harvested sunlight to generate electron-hole pairs. Furthermore, the π-π stacking mode is conducive to formation the fast electron transport pathway in supramolecular complex assembly, which thus enhances the charge separation efficiency. As a result, the obtained supramolecular complex assembly was highly efficient and universal in the photocatalytic Phillips-Ladenburg reaction of o -phenylenediamine and aromatic aldehydes, giving a wide range of benzimidazoles with almost quantitative yields (90–98 %) in air under visible light irradiation at room temperature. These results provide a new method to enhance the light harvesting and charge separation of metal-polypyridine complexes through supramolecular assembly. It provides a high effective photocatalyst to achieve green synthesis of benzimidazoles under visible light irradiation.