The Interface-Functional Polymer Materials (iFPM) Group led by Prof. ZAHNG Tao at the Ningbo Institute of Materials Technology and Engineering (NIMTE) of Chinese Academy of Sciences (CAS), has synthesized two novel vinylene-linked two-dimensional covalent organic frameworks (v-2D-COFs) with isomeric structures via benzobisoxazole-mediated aldol polycondensation, which showed distinct photocatalytic properties. The study was published in Journal of the American Chemical Society.
Thanks to the excellent in-plane conjugation and high chemical stability, v-2D-COFs have attracted increasing interests and thus emerged as advanced semiconducting materials. However, exploring new synthesis approaches and delving into physical & chemical properties of v-2D-COFs remain challenging, owing to the limited chemical reactions and monomers applied in v-2D-COFs.
To address this issue, researchers at NIMTE proposed a solid-state benzobisoxazole-mediated aldol polycondensation reaction. Based on this innovative reaction, two novel isomeric benzobisoxazole-bridged v-2D-COFs (i.e. v-2D-COF-NO1 and v-2D-COF-NO2) with trans/cis configurations for benzobisoxazole linkages were constructed successfully.
The synthesized two isomeric v-2D-COFs showed similar crystalline structures in terms of molecular formulas, unit cells, and pore sizes.
Nevertheless, they exhibit evident differences in optoelectronic and electrochemical properties, such as light absorption & emission and charge-transfer properties, according to the results of the ultraviolet？visible (UV-vis) absorption spectra and ultraviolet photoelectron spectroscopy (UPS).
Specifically, under AM 1.5G irradiation at -0.3 V vs reversible hydrogen electrode (RHE), the v-2D-COF-NO1 with trans-benzobisoxazole showed better photoelectrochemical (PEC) performance (i.e., ～18 μA/cm2) than v-2D-COF-NO2 (i.e., ～9.1 μA/cm2).
Employing Pt as cocatalysts, the v-2D-COF-NO1 showed excellent photocatalytic hydrogen evolution rate of ～1.97 mmol h-1 g-1, twice the value of v-2D-COF-NO2 (i.e., ～0.86 mmol h-1 g-1).
The study has provided a novel approach of benzobisoxazole-mediated aldol polycondensation to enrich the family of v-2D-COFs, and shed light on the isomerization-mediated photocatalytic properties of v-2D-COFs.
This work was financially supported by the Excellent Youth Foundation of Zhejiang Province of China (Grant No. LR21E030001), the Leading Innovative and Entrepreneur Team Introduction Program of Zhejiang (No. 2021R01005), the National Natural Science Foundation of China (Grant No. 52003279), the National Key Research and Development Program of China (No. 2021YFA1500800) and CAS Project for Young Scientists in Basic Research YSBR-004.
Fig. The isomeric vinylene-linked covalent organic frameworks (Image by NIMTE)
Contact
LI Shengxu
Ningbo Institute of Materials Technology and Engineering
E-mail: lishengxu@nimte.ac.cn