Regulation of the Photocatalytic Performance of Dithienothiophene-Modified Covalent Triazine Frameworks Based on Donor–Acceptor System Optimization

Covalent triazine frameworks (CTFs) have emerged as highly promising heterogeneous photocatalysts for various organic transformations owing to their exceptional structural stability, rich structural diversity, and facile synthesis, characterization, and modification. To enhance photocatalytic performance, this study designed dithienothiophene (DTT)-functionalized CTFs by strengthening donor–acceptor (D–A) interactions─a key strategy for boosting catalytic efficacy. Four CTFs (0S-CTF, 1S-CTF, 2S-CTF, 3S-CTF) were synthesized via aldehyde trimerization using monomers with 0 to 3 fused thiophene rings. Comprehensive characterizations confirmed successful synthesis, with 3S-CTF (incorporating DTT) exhibiting the broadest visible-light absorption (1.50 eV band gap), most efficient charge separation, and fastest charge transfer. In the photocatalytic C3–H selenocyanation of indoles, 3S-CTF achieved a 93% yield (vs 47% for 0S-CTF), demonstrated a broad substrate scope, and maintained stable activity over 5 cycles. Density functional theory (DFT) calculations verified that 3S-CTF featured enhanced electron transfer (0.413 e– from DTT to triazine), stronger O2/indole adsorption, a narrower HOMO–LUMO band gap, and a more intense internal electric field. This work demonstrates that DTT-enabled D–A strengthening is an effective strategy to optimize the photocatalytic performance of CTFs.