Donor-acceptor conjugated heptazine polymers: Boosting the Cr(VI) photoreductions via heteroatom engineering

Due to the high photoinduced charge seperations, donor-acceptor (D-A) conjugated heptazine polymers containing fluorene donors have attracted much attention for their high photocatalytic degradations towards organic pollutants. To have an insight into the impact of the electron-donating ability of the donor moieties, herein three D-A conjugated heptazine polymers containing fluorene-like donors with different heteroatoms (dibenzofuran, carbazole, dibenzothiophene, named as CHP-O, CHP-N and CHP-S, respectively) have been synthesized through reversible Friedel-Crafts reactions. Interestingly, the photocatalytic evaluations reveal that all three compounds exhibit an exceptional photocatalytic reduction activity towards hexavalent chromium (Cr(VI)) with the conversion rates of 97%, 95% and 90% for CHP-O, CHP-N and CHP-S, respectively, upon the visible-light irradiation, which is attributed to the narrow band gap and high charge transfer efficiency in the crystalline conjugated systems.