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

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.

Copper-Bridged Tetrakis(4-ethynylphenyl)ethene Aggregates with Photo-Regulated 1 O2 and O2 .- Generation for Selective Photocatalytic Aerobic Oxidation

Active species regulation is a key scientific issue that essentially determines the selectivity and activity of a photocatalyst. Herein, Cu^I -bridged tetrakis(4-ethynylphenyl)ethene aggregates (T₄ EPE-Cu) with photo-regulated ¹ O₂ and O₂ ^.- generation were demonstrated for selective photocatalytic aerobic oxidation. In this system, transient photovoltage combined with the density functional theory calculations confirmed that Cu-alkynyl was the main oxygen activation site. The adsorbed O₂ tends to produce O₂ ^.- because of the potential well effect of Cu-alkynyl under high-energy light excitation. But under low-energy light, O₂ tends to produce ¹ O₂ via resonance energy transfer with Cu-alkynyl. For α-terpinene oxidation, the ratios of ¹ O₂ products to O₂ ^.- products can be controlled from 1.3 (380 nm) to 10.7 (600 nm). Furthermore, T₄ EPE-Cu exhibited ultrahigh photocatalytic performance for Glaser coupling and benzylamine oxidation, with a conversion and selectivity of over 99 %.