Porphyrin-Based Conjugated Microporous Polymers with Oligomeric Acceptor Arms for Efficient Nonsacrificial Photocatalytic H2O2 Production

The invention of a photocatalyst that can efficiently and stably manufacture H₂O₂ using only water, oxygen, and solar light as starting materials is a dream for the sustainable H₂O₂ industry and our human society. Although donor–acceptor (D–A) conjugated polymers have been well documented in the design of such photocatalysts, less attention has been paid to the optimization of the lengths of D and A moieties in the structure. Herein, a series of D–A conjugated microporous polymers named P(TPP-DBTSO_x) by adopting tetraphenyl porphyrin (TPP) units as four-branched and donor moiety while oligomeric dibenzo[b,d]thiophene sulfone (DBTSO) segments with variable lengths (x = 1, 5, 50, and 200) as linear arms and acceptor moiety as well as the DBTSO homopolymer (PDBTSO) were synthesized and studied. It has been found that all these polymers can be used as photocatalysts for nonsacrificial light-driven H₂O₂ production from water and oxygen, but with the performance highly depending on their polymeric degrees of the (DBTSO)_x segments. Among the families, P(TPP-DBTSO₅₀) behaved the best and delivered the largest photocatalytic H₂O₂ production rate of 1064 μmol g^–1 h^–1 under visible-light irradiation. However, when reusability and stability were concerned, P(TPP-DBTSO₅₀) was found inferior to P(TPP-DBTSO₁), the conventional D–A alternative copolymer. In the work, the great impact of the polymeric degree of the (DBTSO)_x segments on the polymer photophysical properties, band alignments, charge carrier production and transport, and photocatalytic performance was studied and discussed in detail.