The light absorption properties of semiconductor-based photocatalysts to a large extent determine the relevant catalytic performance. Traditional strategies in broadening the light absorption range are usually accompanied with unfavorable changes in redox ability and dynamics of photoinduced species that would confuse the comprehensive optimization. In this work, we propose a nontrivial excitonic transition regulation strategy for gaining sub-bandgap light absorption in low-dimensional semiconductor-based photocatalysts. Using bismuth oxybromide (BiOBr) as a model system, we highlight that the light absorption cut-off edge could be effectively extended up to 500 nm by introducing Bi vacancies. On the basis of theoretical simulations and spectroscopic analyses, we attributed the broadening of light absorption to the promotion of excitonic transition that is generally forbidden in pristine BiOBr system, associated with Bi-vacancy-induced excited-state symmetry breaking. In addition, Bi vacancy was demonstrated to implement negligible effects on other photoexcitation properties like excited-state energy-level profiles and kinetics. Benefiting from these features, the defective sample exhibits a notable advantage in gaining visible-light-driven photocatalytic reactions.

Benefiting from their unique delocalized electronic structure, conjugated polymer-based semiconductors are widely applied in the fields of organic electronics, sensors, and biomedical applications. However, the photocatalytic properties of conjugated polymers have been seldom studied because of their unsuitable band structures. Herein, we creatively demonstrate that the band structures of conjugated polymers are strongly related to their degree of polymerization (DP), offering an effective strategy for the design of metal-free photocatalysts with tunable light absorption properties. Taking poly(3-hexylthiophene) (PHT) as an example, we show that PHT nanofibers with a suitable DP are a novel visible light-driven photocatalyst, which can readily convert molecular oxygen into superoxide ions. Benefiting from the high selectivity of the generated superoxides, the PHT nanofibers display outstanding activity for the aerobic oxidation of amines into imines with nearly 100% conversion and selectivity. This study offers a new strategy for the design of advanced conjugated polymer-based photocatalysts.