The competitive influence of the intramolecular electric field and hydrophilic active sites of D–A conjugated porous polymers on photocatalytic hydrogen evolution performance†

Conjugated porous polymers (CPPs) with a donor–acceptor (D–A) molecular structure usually exhibit good photocatalytic hydrogen evolution (PHE). The rational design of an electron donor and an electron acceptor is the key point to realize high photocatalytic performance. In this work, using dibenzothiophene sulfone (DBTO) as an electron acceptor and N-methyl-phenothiazine (MPTZ) as an electron donor, a donor–acceptor (D–A) structured conjugated porous polymer (PTBT) was prepared. To further enhance the conjugation of the polymer, N-phenyl-phenothiazine (PPTZ) was substituted for MPTZ, giving the photocatalyst PPTBT high mobility of light-generated carriers. Without Pt photosensitizers, PPTBT showed remarkable efficiency in hydrogen evolution, reaching 63.96 mmol g⁻¹ h⁻¹ under visible light illumination (λ ≥ 420 nm), with a quantum yield of 2.2% at 475 nm. To further investigate the influence of the intramolecular electric field and surface properties on the photocatalytic hydrogen production (PHP) properties, by oxidizing the phenothiazine units, PTOBT and PPTOBT were synthesized. The results indicate that although the electron donor combined with a sulfone structure increases the specific surface area of the polymer, it does not improve the photocatalytic hydrogen evolution performance, which could be attributed to the competitive influence of the intramolecular electric field and surface hydrophilicity. Finally, for a deeper understanding, the redox mechanism study of the photocatalysts, EPR analysis and DFT calculations were performed to study the free radicals and detailed electronic properties of both ground and excited states in the photocatalytic system, respectively.