Structural Conjugation Tuning in Covalent Organic Frameworks Boosts Charge Transfer and Photocatalysis Performances

Structural conjugation greatly affects the optical and electronic properties of COF photocatalyst. Herein, we show that 2D hydrazone COFs with either π-extended biphenyl (BPh-COF) or acetylene (AC-COF) framework demonstrated distinct charge transfer and photocatalytic performances. The two COFs show good crystallinity and decent porosity as their frameworks are enforced by intra-/interlayer hydrogen-bonding. However, computational and experimental data reveal that AC-COF managed broader visible-light absorption, narrower optical bandgaps and performs efficient photoinduced charge separation and transfer in comparison with BPh-COF, meaning that ethynyl skeleton with enhanced planarity better improves the π-conjugation of whole structure. As a result, AC-COF exhibited an ideal bandgap for rapid oxidative coupling of amines under visible-light irradiation. Furthermore, taking advantage on its better charge transfer properties, AC-COF demonstrated considerable enhanced product conversion and notable functional tolerance for metallaphotocatalytic C–O cross-coupling of wide range of both aryl bromides and chlorides with alcohols. More importantly, beside recoverable, AC-COF showcased the previously inaccessible etherification of dihaloarene. This report shows facile approach for manipulating structure–activity relationship and paves the development of COF photocatalyst for solar-to-chemical energy conversion.