Fluorene and Triazine-Based Conjugated Polymer Networks\nwith Tuned Frontier Orbital Energy Levels for Improving Organic Photocatalysis

Here,\nwe describe a method for fine-tuning the frontier orbital\nenergy levels or redox potential of a conjugated polymer network (CPN)\nconsisting of triazine and fluorene by systematically introducing\nelectron-withdrawing groups at the fluorene moiety through simple\nstructural modification. The band gap of CPN decreases with an increase\nin the strength of the electron-withdrawing group, and the relative\nposition of the frontier orbital energy becomes more favorable for\nreactions like photocatalytic aerobic oxidation, which has been further\nconfirmed by theoretical and experimental studies. The CPN with a\nCN group at the 9 position of fluorene (CPN3) shows the maximum photocatalytic\nactivity (32% higher) compared to CPN1 (hydrogen at the 9 position)\nin white light. The best-performing catalyst CPN3 was further employed\nfor photocatalytic reactions under white light, like the oxidation\nof alcohols to carbonyl and boronic acid to the corresponding alcohol,\nwhich show noteworthy characteristics like low catalyst loading, high\nyield, and selectivity with broad substrate scope (aliphatic, aromatic,\nbiphenyl, and heterocyclic). CPN3 exhibited turnover frequencies of\n13.33 and 10.9 mmol g<sup>–1</sup> h<sup>–1</sup> in\n3 W blue and white LED lights, respectively, which are much higher\nthan those of state-of-art photocatalysts. The recyclability of the\ncatalyst was tested for up to 5 cycles without much change in the\ncatalytic activity. The practical usefulness of the suggested method\nwas further demonstrated by the CPN3-photocatalyzed gram-scale synthesis\nof high-value chemicals such as acetophenone from 1-phenylethanol\nand phenol from phenylboronic acid.