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

Donor–acceptor interactions within conjugated polymer backbones provide an effective strategy for regulating photoexcited-state dynamics in photocatalytic systems. Here, we report donor-rich linear conjugated polymer nanoparticles designed using a sparse acceptor strategy, in which a small fraction of acceptor units is incorporated into a predominantly donor-based polymer backbone. This molecular design aims to preserve the electronic and light-harvesting characteristics of the donor-rich polymer while introducing acceptor-related pathways for energy transfer, excited-state relaxation, and charge generation. A series of phenylene–bis(alkoxy)benzene-based polymers containing different sparse acceptor units was synthesized and processed into aqueous nanoparticles by nanoprecipitation. Optical and time-resolved spectroscopic analyses revealed that the acceptor-site structure strongly influenced donor-to-acceptor energy transfer, excited-state lifetime, and Pt-mediated charge extraction. In particular, the thiophene-linked benzothiadiazole-containing polymer exhibited distinct nanoparticle-state optical features, prolonged excited-state lifetime, and efficient charge extraction after Pt photodeposition. These favorable excited-state properties led to the highest photocatalytic hydrogen evolution performance among the polymer series. This work demonstrates that sparse intrachain acceptor incorporation can effectively modulate excited-state relaxation pathways and enhance photocatalytic hydrogen evolution in donor-rich conjugated polymer nanoparticles.