This review provides the guidelines and knowledge gained so far on current strategies used to prepare, optimize and investigate polymer nanoparticles for fuel production, highlighting the future directions of polymer nano-photocatalyst development.

Utilization of solar energy in organic semiconductors relies on complicated photophysical processes due to the strong electron–hole interactions. To gain a better understanding of these processes and their effect on the photocatalytic performance of non-fullerene acceptors (NFAs) within nanoparticles (NPs), we compared the excited-state dynamics and photocatalytic hydrogen production activity of two NFA-based NPs, Y5 and Y6. Our results show that under LED light irradiation, Y5 NPs exhibit 14 times better hydrogen production activity than Y6 NPs. The hydrogen production activity was also evaluated under Xenon light irradiation (AM1.5G, 100 mW·cm–2) for Y5 NPs, yielding 410 mmol/g after 24 h. Time-resolved spectroscopy experiments revealed a longer triplet lifetime for Y5 compared to Y6 NPs, and the lifetime was reduced upon addition of the electron donor ascorbate. This suggests the involvement of the triplet state in reductive quenching and better hydrogen evolution reaction performance for Y5 NPs. The good agreement between fluorescence and triplet lifetimes observed for Y5 NPs was attributed to reverse intersystem crossing, which repopulates the excited singlet state through thermally activated delayed fluorescence (TADF). The absence of TADF in Y6 NPs could limit its efficiency for hydrogen evolution reaction, in addition to the intrinsically shorter triplet lifetime and reduction potential difference, making it an important factor to consider in Y series-based NPs.