Benzotrithiophene‐based Covalent Organic Framework Photocatalysts with Controlled Conjugation of Building Blocks for Charge Stabilization

Abstract

Covalent organic frameworks have recently shown high potential for photocatalytic hydrogen production. However, their structure-property-activity relationship has not been sufficiently explored to identify a research direction for structural design. Herein, we report the design and synthesis of four benzotrithiophene (BTT)-based covalent organic frameworks (COFs) with different conjugations of building units, and their photocatalytic activity for hydrogen production. All four BTT-COFs had slipped parallel stacking patterns with high crystallinity and specific surface areas. The change in the degree of conjugation was found to rationally tune the rate of photocatalytic hydrogen evolution. Based on the experimental and calculation results, the tunable photocatalytic performance could be mainly attributed to the electron affinity and charge trapping of the electron accepting units. This study provides important insights for designing covalent organic frameworks for efficient photocatalysts.

Recent advances on covalent organic frameworks (COFs) as photocatalysts: different strategies for enhancing hydrogen generation

“…Hence, adjusting the p-conjugation degree of building blocks is a valid method by which to influence the photocatalytic performance. [81][82][83][84][85][86][87] Jiang et al presented four COFs (USTB-7, USTB-8, USTB-9 and USTB-10) with varying bandgaps (Fig. 8).…”

“…Hence, adjusting the π-conjugation degree of building blocks is a valid method by which to influence the photocatalytic performance. 81–87…”

Novel Porous Organic Polymer Catalyst with Phosphate and Sulfonic Acid Sites for Facile Esterification of Levulinic Acid

“…Porous organic polymers (POPs) containing covalent linkages of organic precursors exhibit a high surface area, a tunable backbone, excellent physicochemical stability, and flexibility for rational design. Hence, they have been used in catalysis, adsorption, gas separation, sensor, proton conductor, and energy storage. − In particular, surface-functionalized POPs have shown potential as catalysts for biomass conversion. − Ravi et al converted fructose to 5-hydroxymethylfurfural (HMF) over novel phosphate-functionalized POPs with strong acidic sites, large surface areas, and high mesoporosity . Du et al introduced sulfonic acids into the aromatic sites of POP to catalyze fructose conversion to HMF .…”

Photoinduced Hydration Boosts O2 Evolution on Co-Chelating Covalent Organic Framework

“…33 Density functional theory (DFT) calculations of model compounds of building blocks of BtB-COF and Co@ BtB-COF show that the HOMO orbitals of the BtB-COF mainly distribute on benzotrithiophene units, and the LUMO orbitals mainly cover the benzothiadiazole units (Figures 4b and S18), implying the electron transfer tendency from benzotrithiophene unit to benzothiadiazole unit and a reinforcement of polarity of the imine group. 34 To detect the electron states of BtB-COF, electron paramagnetic resonance (EPR) spectra are recorded in darkness and under light irradiation (Figure S19). BtB-COF exhibits a strong EPR signal at g = 2.005.…”

“…Fluorescence spectra of BtB-COF show obvious PL quenching after Co doping (Figure S17), while the average emission lifetime decreased from 1.04 ns of BtB-COF to 0.93 ns of Co@BtB-COF, showing the efficient photogenerated charge separation and transfer . Density functional theory (DFT) calculations of model compounds of building blocks of BtB-COF and Co@BtB-COF show that the HOMO orbitals of the BtB-COF mainly distribute on benzotrithiophene units, and the LUMO orbitals mainly cover the benzothiadiazole units (Figures b and S18), implying the electron transfer tendency from benzotrithiophene unit to benzothiadiazole unit and a reinforcement of polarity of the imine group . To detect the electron states of BtB-COF, electron paramagnetic resonance (EPR) spectra are recorded in darkness and under light irradiation (Figure S19).…”