Regulating Exciton Dynamics through Molecular Packing in Conjugated Polymer Nanoparticles for Photocatalytic H2O2 Production

Abstract

Herein, two different types of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-{2,1’,3}-thiadiazole)] (PFBT) polymer nanoparticles have been fabricated by varying the molecular packing through solution-based miniemulsion techniques at various surfactant concentrations. The structural features and intermolecular interactions have been correlated with the underlying photophysical properties. The results suggest that at higher surfactant concentrations, polymer molecules follow highly defined molecular arrangements which enhance the effective π-conjugation within the nanoparticles. As a result, efficient charge separation is improved by minimizing the exciton binding energy and increasing the exciton diffusion length. Furthermore, charge separation through highly defined molecular packing facilitates the intrinsic transient dipole moment in the excited state of the nanoparticle, providing an additional driving force to the exciton diffusion process. On the contrary, the random packing of the conjugated polymer molecules within nanoparticles hinders charge separation and free carrier migration by creating unwanted defects or trap states throughout the nanoparticles, which essentially creates localized strong binding excitons. As a result, the photocatalytic activity decreases. Overall, the present work defines a simple solution-based strategy to regulate exciton dynamics in conjugated polymer nanoparticles and their utilization for photocatalytic H₂O₂ production.