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NIR‐II‐emitting photosensitizers (PSs) have attracted great research interest due to their promising clinical applications in imaging‐guided photodynamic therapy (PDT). However, it is still challenging to realize highly efficient PDT on NIR‐II PSs. In this work, we develop a chlorination‐mediated π–π organizing strategy to improve the PDT of a PS with conjugation‐extended A‐D‐A architecture. The significant dipole moment of the carbon‐chlorine bond and the strong intermolecular interactions of chlorine atoms bring on compact π–π stacking in the chlorine‐substituted PS, which facilitates energy/charge transfer and promotes the photochemical reactions of PDT. Consequently, the resultant NIR‐II emitting PS exhibits a leading PDT performance with a yield of reactive oxygen species higher than that of previously reported long‐wavelength PSs. These findings will enlighten the future design of NIR‐II emitting PSs with enhanced PDT efficiency. [ABSTRACT FROM AUTHOR]

Two‐dimensional covalent organic frameworks (2D COFs), an emerging class of crystalline porous polymers, have been recognized as a new platform for efficient solar‐to‐hydrogen energy conversion owing to their pre‐designable structures and tailor‐made functions. Herein, we demonstrate that slight modulation of the chemical structure of a typical photoactive 2D COF (Py‐HTP‐BT‐COF) via chlorination (Py‐ClTP‐BT‐COF) and fluorination (Py‐FTP‐BT‐COF) can lead to dramatically enhanced photocatalytic H2 evolution rates (HER=177.50 μmol h−1 with a high apparent quantum efficiency (AQE) of 8.45 % for Py‐ClTP‐BT‐COF). Halogen modulation at the photoactive benzothiadiazole moiety can efficiently suppress charge recombination and significantly reduce the energy barrier associated with the formation of H intermediate species (H*) on polymer surface. Our findings provide new prospects toward design and synthesis of highly active organic photocatalysts toward solar‐to‐chemical energy conversion. [ABSTRACT FROM AUTHOR]