Planarity-engineered 1,2,3-triazole-based 1D covalent organic frameworks for enhanced visible-light photocatalytic C-3 thiocyanation of indoles

Abstract

Covalent organic frameworks (COFs) have emerged as efficient metal-free photocatalysts for green chemical synthesis. However, their performance is often limited by interlayer π–π stacking, which hampers charge transport and active site accessibility. To address this challenge, we report two one-dimensional (1D) donor–acceptor COFs (PYTZ-COF and ETTZ-COF) featuring 1,2,3-triazole linkages and tunable optoelectronic properties through precursor rigidity engineering. Compared to ETTZ-COF, PYTZ-COF exhibits a reduced torsional angle, broader visible-light absorption, smaller exciton binding energy, and a narrower band gap, along with a significantly larger BET surface area (414 m² g⁻¹). These features facilitate efficient charge separation and accelerate interfacial electron transfer, as confirmed by photoelectrochemical analysis and DFT calculations. Under blue light irradiation, PYTZ-COF efficiently generates superoxide radicals (O₂˙⁻), enabling selective C–H thiocyanation of indole derivatives. This study not only expands the structural diversity of 1D COFs but also introduces a general strategy for enhancing photocatalytic activity through molecular-level planar modulation, providing new insights into the design of redox-active COFs for visible-light-driven applications.