Revising exciton diffusion lengths in polymer dot photocatalysts†

Abstract

Exciton migration in organic polymer dots (Pdots) is crucial for optimizing photocatalytic reactions at the particle surface, such as hydrogen evolution and carbon dioxide reduction. Despite the use of Pdots in photocatalysis, there is still a need for better understanding of exciton diffusion within these systems. This study investigates the exciton diffusion in PFBT Pdots stabilized with different weight percentages of the co-polymer surfactant PS–PEG–COOH and doped with perylene red as an internal quencher. Time-resolved fluorescence quenching data yields a quenching volume that the excitons explore during their lifetime (V_q), which is comparable to the volume of the hydrophobic core of PFBT Pdots. This indicates that excitons can migrate to the particle surface with high probability and suggests that the intrinsic exciton diffusion length (L_D ≈ 19 nm) for PFBT is significantly larger than previously reported in Pdot studies from the literature (5.3 and 8.6 nm). Additionally, a larger quenching rate constant (k_q) and smaller volume (V_q) is observed for the higher PS–PEG–COOH weight ratio, which are attributed to their smaller core. The study provides insights into the exciton migration within Pdots, with important implications for photocatalysis.