Isomorphic BODIPY-based metal–organic frameworks for high-efficiency photoredox organic transformations

Abstract

Metal–organic frameworks (MOFs) are emerging as promising photocatalysts for effective organic transformation owing to their tunable energy band structures and excellent visible-light absorption ability. In this work, two novel isostructural BODIPY-based MOFs, [Zn₂(BODIPY)(TTFTB)] (1) and [Co₂(BODIPY)(TTFTB)] (2), with different center metals were successfully constructed from pyridine-functionalized boron dipyrromethene (BODIPY) and tetrathiafulvalene-3,4,5,6-tetrakis(4-benzoic acid) (H₄TTFTB) linkers. Compounds 1 and 2 exhibited excellent light adsorption and were applied as effective heterogeneous photocatalysts toward the dehalogenation of α-bromoacetophenone and oxidation of thiols. In particular, compound 1 exhibited superior performance compared to compound 2 in the photoreductive dehalogenation of α-bromoacetophenone, which could be attributed to the accelerated charge transfer and more negative LUMO potential with a stronger reduction ability. Of note, the TOF of compound 1 for photoreductive dehalogenation of α-bromoacetophenone, 133.33 mmol g⁻¹ h⁻¹, up to the highest among reported works. In contrast, owing to its higher HOMO potential, compound 2 achieved enhanced photocatalytic properties for the oxidation of thiols than compound 1. Further investigation of the underlying mechanism demonstrated that photogenerated electrons and α-carbonyl radicals play vital roles in the photoreductive dehalogenation of α-bromoacetophenone, while the superoxide radical (O₂˙⁻) serves as the main active species for the oxidation of thiols by charge transfer processes. Moreover, this research provides further insights into designing high-efficiency MOFs for photoredox organic transformations through band structure manipulation via a metal center modulation strategy.