Unlocking Long‐Range Exciton Diffusion via Hydrogen‐Bonded‐to‐Covalent Organic Framework Transformation for Photocatalytic H 2 O 2 Synthesis
Bai‐Tong Liu, Cheng Li, Yu‐Liang Dong, Timothy Y.‐Z. Li, Bohan Tang, Xueze Zhao, Enxu Liu, Yuehua Deng, Yi‐Kang Xing, Guangcheng Wu, Han Han, Sheng‐Nan Lei, Ruihua Zhang, Shuai Fang, Kaikai Ma, Bo Yu, Ziyue Huang, Hanlin Hou, Shu‐Qi Zhou, Dequan Zhang, Qiu‐Jin Wu, Yanli Zhao, J. Fraser StoddartABSTRACT
Controlling long‐range exciton diffusion remains a central challenge in organic photocatalysts because of the inherent trade‐off between extended π‐conjugation and long‐range structural order. Here, we report a topochemical polymerization strategy that converts a single‐crystalline hydrogen‐bonded organic framework (HOF) into a fully π‐conjugated covalent organic framework (COF) while largely preserving crystalline order. The preorganized hydrogen‐bonded precursor enables the formation of interlayer covalent linkages, resulting in a narrowed bandgap and enhanced electrical conductivity. Using power‐dependent femtosecond transient absorption spectroscopy, we quantitatively reveal exciton diffusion along the π‐conjugated channels with an average diffusion length of ∼12 nm. To illustrate the chemical consequences of exciton diffusion, the π‐conjugated COF is employed as a metal‐free photocatalyst for hydrogen peroxide (H 2 O 2 ) photosynthesis from O 2 and H 2 O without sacrificial agents. These results establish HOFs as versatile crystalline precursors for constructing previously inaccessible fully π‐conjugated COFs and highlight exciton diffusion as a key parameter linking framework structure to photocatalytic performance.