Modulating molecular aggregates via nonconjugated bridges for enhanced photocatalytic hydrogen evolution

Abstract

Dye/polymer carbon nitride (PCN) composite systems demonstrate considerable promise for photocatalytic hydrogen evolution (PHE), owing to their extensive spectral absorption range and enhanced charge separation efficiency. However, severe charge recombination, often arising from the inherent molecular structure of organic dyes and their consequent aggregation tendencies, remains a critical issue, thereby presenting a major challenge in modulating electronic processes. Herein, this study employs integrated experimental and theoretical approaches to elucidate the impact of the bridge mode (conjugated versus nonconjugated) between electron donor (D) and acceptor (A) moieties on the aggregation behavior, recombination processes, and photocatalytic performance of dyes. Key findings reveal that the nonconjugated bridge of alkyl chains can efficiently hinder non-radiative transitions and charge recombination by twisted molecular conformations with suppressed intermolecular π–π interactions, thereby facilitating charge carrier transport. Consequently, organic dyes with nonconjugated bridges exhibit superior exciton dissociation and charge transport, which results in a significantly enhanced HER of 859.47 µmol h⁻¹, representing a more than two-fold increase over that of the conjugation-linked analogue dye (401.31 µmol h⁻¹). This work establishes bridge engineering as a powerful molecular-level strategy to control aggregation and charge recombination in organic photosensitizers, opening new avenues for designing highly efficient photocatalytic materials.