Visible light-induced synthesis of biomass-derived quinoxaline by using Co phthalocyanine immobilized on pyridine-doped g-C3N4

Visible light-driven valorization of biomass has recently been a pioneering field for nitrogen-containing heterocyclics syntheses due to its sustainable features. Herein, various aromatic ring-doped g-C3N4 nanosheets (Ar-g-C3N4; Ar = Py, Pm, Ph) were precisely designed to modulate their intrinsic electronic and band structure, which involves pyridine (Py), pyrimidine (Pm), and benzene (Ph)-doped g-C3N4. Photocatalysts (CoPc/Ar-g-C3N4) of cobalt(II) phthalocyanine (CoPc)-fabricated Ar-g-C3N4 were then developed for oxidative cyclization of furoin with 1,2-phenylenediamines for syntheses of various biomass-derived quinoxalines under visible-light irradiation. The catalytic activity (in terms of TOFs) of serial CoPc/Ar-g-C3N4 samples increased with their transient photocurrents with CoPc/Py-g-C3N4 as the most active one. For CoPc/Py-g-C3N4, CoPc species functioned as both sensitizer and catalytic sites; while, doped Py led to a narrowed bandgap energy. Mechanism research further demonstrated that O2 was activated to superoxide radical (•O2−) by photoexcited high-level-energy electron (HLEE) transfer from Py-g-C3N4 to CoPc for the subsequent aerobic oxidation.