Intrinsic Charge Separation in Pt-Loaded Y-Series Nonfullerene Acceptor Nanoparticles: Implication for the Photocatalytic Hydrogen Evolution Reaction

Y-series nonfullerene acceptors (NFAs) have previously been investigated as Pt-loaded organic photocatalysts and homojunction solar cells due to their unique ability to generate charge in the absence of a donor material. Here, hydrogen evolution by Pt-loaded organic nanoparticles (NPs) composed of five different Y-series acceptors is compared, to reveal the structural differences in the NFA that lead to an improved photocatalytic hydrogen evolution rate. PY-IT is a polymerized Y-series acceptor that contains a thiophene linker to create a polymer with the core structure shared by the Y-series acceptors. The other acceptors studied, namely L8-BO, PC6, and Y7, have the same core structure as the well studied Y6 NFA but with alterations to side chains or terminal halogens. The results show that PY-IT and L8-BO NPs exhibit the highest hydrogen evolution rate, which is attributed to enhanced structural order and the resulting reduced energetic disorder. The rate of hydrogen evolution of the PY-IT NPs is (50.3 ± 2.5) mmol h –1 g –1, which is over 3.5 times that achieved by the Y6 NPs. Ultrafast spectroscopy measurements indicate enhanced intermolecular exciton dissociation in PY-IT compared with the small-molecule acceptors due to exciton delocalization over the PY-IT polymer chain. Overall, we report hydrogen evolution of Pt-loaded organic NPs PC6, L8-BO, and Y7 for the first time, and clarify the mechanism by which PY-IT exhibits a high hydrogen evolution rate.