Paired Photoproduction of HO and 3,4-Dihydroisoquinoline Over Covalent Pyrene-(Thio)urea Frameworks with Electron Push-Pull Effect.

Pairing photocatalytic 1,2,3,4-tetrahydroisoquinoline semi-dehydrogenation reaction (THIQ-SDR) with two-electron oxygen reduction reaction (2e ORR) is a green solar to chemical strategy by simultaneously utilizing the photo-excited electrons and holes. However, it is still short of high-efficiency photocatalyst to drive two reactions above. In the present work, crystalline pyrene-thiourea/urea covalent organic frameworks (COF-Py-S and -O) were synthesized and demonstrated as high-performance metal-free photocatalysts. In particular, COF-Py-S exhibited higher 2e ORR to HO yield rate of 19 mmol g h under visible light and finally solid HO products (NaCO ⋅ 1.5HO) was collected after long-time irradiation. Under natural sunlight conditions, the HO production rate over COF-Py-S further increased to ~51 mmol g h, among the best COF photocatalysts. COF-Py-S also showed high THIQ-SDR conversion (100 %) with 3,4-dihydroisoquinoline (DHIQ) selectivity of ~92 %. Theoretical calculations reveal stronger electron push-pull effect of COF-Py-S than COF-Py-O, enhancing its photoinduced charge carries, and a four-step 2e ORR mechanism with thiourea as the active sites has been confirmed as well as the mechanism of THIQ-SDR to DHIQ, featuring lower energy barriers for O adsorption and *HOOH desorption over thiourea units. This work provides a paired photosynthesis strategy of HO and DHIQ over high-efficiency pyrene-(thio)urea COF photocatalysts with electron push-pull effect.