Regulating Photocatalysis by Spin-State Manipulation of Cobalt in Covalent Organic Frameworks

Abstract

While catalysis is highly dependent on the electronic structure of the catalyst, the understanding of catalytic performance affected by electron spin regulation remains challenging and rare. Herein, we have developed a facile strategy to the manipulation of the cobalt spin state over covalent organic frameworks (COFs), COF-367-Co, by simply changing the oxidation state of Co centered in the porphyrin. Density functional theory (DFT) calculations together with experimental results confirm that CoII and CoIII are embedded in COF-367 with S = 1/2 and 0 spin ground states, respectively. Remarkably, photocatalytic CO2 reduction results indicate that COF-367-CoIII exhibits favorable activity and significantly enhanced selectivity to HCOOH, accordingly much reduced activity and selectivity to CO and CH4, in sharp contrast to COF-367-CoII. The results highlight that the spin-state transition of cobalt greatly regulates photocatalytic performance. Theoretical calculations further disclose that the presence of CoIII in COF-367-Co is preferable to the formation of HCOOH but detrimental to its further conversion, which clearly accounts for its distinctly different photocatalysis over COF-367-CoII. To the best of our knowledge, this is the first report on regulating photocatalysis by spin state manipulation in COFs.

Enlarging the π‐Conjugation of Cobalt Porphyrin for Highly Active and Selective CO2Electroreduction

“…[16] By enlarging the porphyrin π-conjugation, more electrons would be donated to the metal center, thus leading to the shift of absorption edge to lower energy as reflected by the XANES. [17] Furthermore, structural information on the Co center of the porphyrins was received from the extended X-ray absorption fine structure (EXAFS) analysis. Compared with the Co foil and CoPc, the Fourier-transformed k 3 -weighted EXAFS spectra of the CoTPP and CoTPyPP reveal one prominent peak in the first coordination sphere, which is attributed to the CoÀ N path as that of the CoPc (Figure S5).…”

Probe metal binding mode of imine covalent organic frameworks: cycloiridation for (photo)catalytic hydrogen evolution from formate

“…The imine bond reduction is likely mediated by an iridium hydride intermediate via an outer-sphere process. [64][65][66] The involvement of Ir in the imine reduction is supported by the fact that no imine reduction was observed in Py-1P COF during HER catalysis (Fig. S24 †) and the catalytic reduction of N-benzylideneaniline as an exogenous substrate in the presence of Py-1P-Ir COF was observed (Fig.…”

Chemical Fixation of Carbon Dioxide by Heterogeneous Porous Catalysts

“…Upon visible light irradiation, photoelectrons were generated and rapidly delocalized to other parts of the c‐COFdpy‐Co with the aid of full −C=C− bridging. Additionally, in a recent study, H−L Jiang et al [49] . established that spin‐state manipulation of metal in COF can regulate CO 2 photoreduction reaction.…”