posted on 2024-02-07, 21:18authored byFulin Zhang, Yuexin Wang, Hongxiang Zhao, Xiaoyun Dong, Xiang-Kui Gu, Xianjun Lang
Olefin-linked covalent organic frameworks
(COFs) have exhibited
great potential in visible-light photocatalysis. In principle, expanding
fully conjugated COFs can facilitate light absorption and charge transfer,
leading to improved photocatalysis. Herein, three olefin-linked COFs
with the same topology are synthesized by combining 2,4,6-trimethyl-1,3,5-triazine
(TMT) with 1,3,5-triformylbenzene (TFB), 1,3,5-tris(4-formylphenyl)benzene
(TFPB), and 1,3,5-tris(4-formylphenylethynyl)benzene (TFPEB), namely,
TMT-TFB-COF, TMT-TFPB-COF, and TMT-TFPEB-COF, respectively. From TMT-TFB-COF
to TMT-TFPB-COF, expanding phenyl rings provides only limited expansion
for π-conjugation due to the steric effect of structural twisting.
However, from TMT-TFPB-COF to TMT-TFPEB-COF, the insertion of acetylenes
eliminates the steric effect and provides more delocalized π-electrons.
As such, TMT-TFPEB-COF exhibits the best optoelectronic properties
among these three olefin-linked COFs. Consequently, the photocatalytic
performance of TMT-TFPEB-COF is much better than those of TMT-TFB-COF
and TMT-TFPB-COF on the oxidation of organic sulfides into sulfoxides
with oxygen. The desirable reusability and substrate compatibility
of the TMT-TFPEB-COF photocatalyst are further confirmed. The selective
formation of organic sulfoxides over TMT-TFPEB-COF under blue light
irradiation proceeds via both electron- and energy-transfer pathways.
This work highlights a rational design of expanding the π-conjugation
of fully conjugated COFs toward selective visible-light photocatalysis.