Iridium(III) Complex Radical and Corresponding Ligand Radical Functionalized by a Tris(2,4,6-trichlorophenyl)methyl Unit: Synthesis, Structure, and Photophysical Properties

Organic radical luminescent materials with doublet excited state character based on tris(2,4,6-trichlorophenyl)methyl (TTM) have attracted extensive attention in recent years. However, how they affect the phosphorescent iridium(III) complex characterized by the triplet excited state has not been studied yet. Herein, a new iridium(III) complex radical (Ir-TTM) and corresponding ligand radical (ppy-TTM) with a TTM unit have been designed and synthesized, and their radical properties were confirmed by the single crystal structure and EPR spectra. Notably, the ligand radical ppy-TTM shows an efficient red light emission, whereas the iridium complex radical Ir-TTM emits no light, which resulted from the intramolecular quenching effect of the TTM radical unit on the iridium luminescence center. DFT calculations demonstrate that the lowest doublet (D1) excited state of ppy-TTM shows an intramolecular charge transfer character from the 2-phenylpyridine moieties to the TTM unit, whereas the D1 of Ir-TTM exhibits a significant charge transfer character from the iridium luminescence center moieties to the TTM unit, which further explains the luminescence quenching mechanism of the phosphorescent iridium complex radical

Oxygen-Vacancy-Induced Built-In Electric Field across MoCo Dual-Atomic Site Catalyst for Promoting Hydrogen Spillover in Hydrocracking and Hydrodesulfurization

The design and construction of highly efficient catalytic active sites for promoting hydrogen spillover are of great significance for improving hydrocracking (HCK) and hydrodesulfurization (HDS) performance in slurry-phase hydrogenation of vacuum residue (VR) but are still challenging. Herein, we report a carbon-supported MoCo dual-atomic site catalyst (MoCo DAC/C) and propose an oxygen-vacancy-induced built-in electric field (BIEF) regulation mechanism for promoting hydrogen spillover in HCK and HDS. It was found that the coordination structure of the MoCo dual-atomic was reconstructed and formed O vacancies in situ during hydrogenation process. The formation of O vacancies not only provided macromolecular adsorption sites but also broke the electronic balance and formed a weak BIEF between the Mo and Co atoms. Meanwhile, H2 was activated at the Mo sites to form active hydrogen species. The formation of BIEF promoted the active hydrogen spillover from Mo to Co sites by a Mo–C–Co bridging bond, thus improving the hydrogenation performance greatly. In HCK of VR, the MoCo DAC/C demonstrates remarkable catalytic hydrogenation activity with TOFT calculated for total metals up to 0.77 s–1 (two times enhancement than that of Mo single atoms (SAs)/C), the per pass conversion of VR of 76 wt %, liquid product yield of 92 wt %, and coke content of only 0.55 wt %. It also shows robust HDS performance with dibenzothiophene (DBT) conversion of 70 wt %. Density functional theory reveals that the formation of the O vacancies leads to the discrepancy of Bader charge between Mo and Co atoms, and the resulting local electric field can favor the diffusion of the positively charged (+0.10 e−) H atom. This work proposes an oxygen-vacancy-induced BIEF regulation mechanism from an atomic scale for enhancing the catalytic reaction process by promoting hydrogen spillover, which provided novel insights for the design and development of high-performance hydrogenation catalysts