Triple-Regulation Strategy toward Multivariate Isomeric Covalent Organic Frameworks for Efficient Photocatalysis

As an important branch of structure chemistry, isomer structural chemistry has developed tremendously. However, the isomerization of periodic framework materials especially isomeric covalent organic frameworks (Iso-COFs) remains a great challenge due to their intrinsic structural complexity and lack of a systematic regulation strategy. In this work, we provided a triple synergic regulation strategy including geometric, positional, and linkage isomerism. Under the guidance of this multiple-regulation strategy, we successfully obtained recorded Iso-COFs with 15 kinds with the same structural framework and identical chemical formula (C₄₈H₃₆N₆O₃). With functional design, 6 model Iso-COFs synthesized through three isomerism strategies were chosen to reveal the influence of isomeric structural differences on their photochemical properties in H₂O₂ photosynthesis. Therefore, compared with other control samples, TDA-BTD COF, which possessed excellent optical properties and the lowest oxygen adsorption energy, exhibited satisfactory photochemical H₂O₂ production efficiency (2016.26 μmol g^-1h^-1) and an apparent quantum yield (AQY) of 3.67% at 420 nm. Density functional theory (DFT) calculations and in situ characterization results collectively demonstrated that positional, linkage, and geometric isomerisms regulate the substrate adsorption behavior, charge separation, and electronic structure of the catalyst. For the first time, this work put forward the multidimensional regulation strategy for designing periodic framework-based isomers, which realized the recorded number of Iso-COFs with identical chemical formula to date, also providing a pioneering structural illustration for in-depth exploration of the structure-performance relationship of Iso-COF from multiple dimensions.