Continuous π-Conjugation in β-Ketoenamine Covalent Organic Frameworks Boosts Charge Transfer for Selective Photocatalysis

Alkynyl groups in the backbones of covalent organic frameworks (COFs) enable continuous π-conjugation, thereby unlocking enhanced visible light photocatalysis. Starting from TpBD-COF, the incorporation of acetylene and diacetylene into the linker yields two β-ketoenamine COFs, TpEDD-COF and TpBDD-COF, respectively. Accordingly, the greater planarity of TpEDD-COF and TpBDD-COF relative to TpBD-COF significantly amplifies π-electron delocalization across the COFs, as confirmed by density functional theory (DFT) calculations. Experimental measurements, corroborated by time-dependent DFT calculations, confirm the order of optoelectronic properties: TpBDD-COF > TpEDD-COF > TpBD-COF. Thus, the optoelectronic properties underpin the visible light photocatalysis: oxygen is activated, which in turn drives the selective oxidation of amines. Compared with TpBD-COF, the continuous π -conjugation in TpEDD-COF and TpBDD-COF boosts charge transfer. In the selective oxidation of benzylamines with oxygen, under 460 nm light irradiation, TpBDD-COF photocatalysis achieves twice the conversion of TpEDD-COF and four times that of TpBD-COF. Mechanistic studies reveal that in TpBDD-COF photocatalysis, superoxide radical anion serves as the predominant reactive oxygen species for imine formation. This work highlights that continuous π-conjugation of COFs offers a viable handle for enhanced selective photocatalysis.