Photocatalysts have unique valence bands and conduction bands, which can dominate the redox reaction in the same photocatalyst. Herein, ultrathin polymers are prepared by combining cyclotriphosphazene with pyrimidine via ether bonds. The redox ability of polymers varies with the reaction time. In the photocatalytic reaction, the CH 4 activity of the optimal sample (MBAP) is 39.5 times that of the worst sample (EBAP), and their selectivity is 100 and 24%, respectively. In sp 3 C−H bond activation, the yield of MBAP remained much better than that of EBAP. High reduction ability in photocatalysts plays an important role in both reduction and oxidation reactions. The intrinsic reason is that the high reduction capacity enhances the chance of photogenerated electrons to participate in the reduction reaction, thus accelerating the separation of photoinduced carriers, while the holes in the valence band can participate in the oxidation reaction only after the electrons are bound in the conduction band. This work offers a fresh viewpoint on how to create polymer photocatalysts with multiple applications.