Leaving the Dark Side: Transforming Imine-COFs into Highly Emissive Materials

Although imine-linked Covalent Organic Frameworks (COFs) are readily synthesized, their absence of intrinsic emission constrains their potential in optoelectronic applications. Moreover, the underlying mechanisms governing excited state energy dissipation remain poorly understood. To overcome these limitations, we present a straightforward strategy to transform non-emissive, anthracene-based imine-COFs (im-COF) into highly emissive amine-based COFs (am-COF) through NaBH3CN:benzoic acid reduction, achieving solid-state emission quantum yields reaching up to 30%. To clarify the excited state energy dissipation mechanisms in COFs, we synthesized molecular reference compounds featuring either imine or amine functionalities. Photophysical studies, supported by density functional theory (DFT) calculations, reveal that the excited states of both amines and imines exhibit weak charge transfer (CT) properties. Furthermore, a comparative analysis of the photophysical behavior of molecular references, im-COFs, and am-COFs demonstrate that COF emission arises from charge transfer processes modulated by interactions with the polymer matrix. These findings provide fundamental insights into the photophysical behavior of COFs, thus paving the way toward the development of emissive porous materials with promising advanced applications.