Excited-State Modulation by Sparse Acceptor Sites in Donor-Rich Linear Conjugated Polymer Nanoparticles for Photocatalytic Hydrogen Evolution

Abstract Donor-rich conjugated polymers are attractive photocatalysts owing to their strong light-harvesting capability, synthetic accessibility, and excellent processability. However, their photocatalytic performance is often limited by rapid excited-state relaxation and charge recombination. Here, we demonstrate a sparse acceptor strategy for regulating excited-state dynamics in donor-rich linear conjugated polymer nanoparticles. An alkoxy-poly(p-phenylene)-based polymer (PP) is modified with approximately 2 mol % benzothiadiazole (BT), thiophene-linked benzothiadiazole (DTBT), or thiophene-linked benzoselenadiazole (DTBSe) units and subsequently processed into aqueous nanoparticles through nanoprecipitation. Although all polymers retained donor-rich optical characteristics, sparse acceptor incorporation significantly influenced excited-state behavior. In particular, PP-DTBT exhibited spectroscopic signatures consistent with acceptor-mediated excited-state relaxation, prolonged photoluminescence lifetimes, and enhanced populations of long-lived photoexcited species. Transient spectroscopic analyses further revealed acceptor-mediated excited-state stabilization and Pt-mediated charge extraction under photocatalytic conditions. These characteristics were reflected in the photocatalytic performance, with PP-DTBT showing the highest hydrogen evolution activity of 1.2 mmol g–1 h–1, substantially outperforming the BT- and DTBSe-containing analogues. The results demonstrate that sparse acceptor incorporation can effectively regulate excited-state relaxation, generate long-lived excited states, and promote more favorable charge extraction and utilization pathways without disrupting the donor-rich nature of the polymer backbone. This work establishes sparse acceptor-site engineering as an effective strategy for controlling excited-state dynamics and enhancing photocatalytic hydrogen evolution in donor-rich polymer nanoparticles.