Orchestrating Excited-State Energy Flow in Benzobisthiazole Covalent Organic Frameworks for Solar Water Evaporation...

The competing pathways of photothermal conversion and photocatalytic H₂O₂ production present a long-standing challenge in solar energy utilization, as efficient nonradiative dissipation inherently suppresses the long-lived excited states required for catalysis. Herein, we demonstrate a precise molecular engineering strategy to orchestrate excited-state energy flow in isoreticular benzobisthiazole-linked covalent organic frameworks (BBT-COFs) via post-synthetic linker exchange. By rationally introducing steric hindrance (BBT-TAPB), intramolecular motions and nonradiative decay are boosted for exceptional photothermal heating. In contrast, a strong donor-acceptor (D-A) architecture (BBT-BTT) enhances intersystem crossing and triplet-state population for singlet oxygen-mediated H₂O₂ photosynthesis. When integrated into a self-rotating hydrogel evaporator, these COFs enable a dual-functional solar-driven platform for water evaporation and H₂O₂ generation. Under 1-sun irradiation, the BBT-TAPB-based hydrogel delivered an evaporation rate of 1.82 kg m^-2 h^-1, whereas the BBT-BTT-based hydrogel achieved an H₂O₂ production rate of 143 mM m^-2 h^-1. This work highlights a cooperative regulation between molecular motion and D-A interactions in modulating excited-state energy dissipation, providing a modular blueprint for tuning photothermal and photocatalytic solar energy conversion processes.