Merging Charge Transfer into Metal-Organic Frameworks to Achieve High Reduction Potentials via Multiphoton Excitation

Utilization of multiphotons to achieve high reduction potentials is a highly demanding but still challenging task for reductive cleavage of inert bonds. Herein, we report a new charge transfer approach that simultaneously excites the electron-rich dye and the radical anionic of the electron-deficient one for photocatalytic activation of aryl chlorides with high reduction potentials (E_red ≈ -1.9 to -2.9 V). Interactions between the tetraphenylbenzene-1,4,-diamine dyes in the large pores of metal-organic frameworks and the adsorbed 9,10-dicyanoanthracene partly endows charge transfer in the ground state. The first photoexcitation led to the formation charge separation pairs containing both radical cation and anion for second photon excitation. The possibility of modifying each absorption band of the two dyes independently innovated the resultant aryl radicals applied in various useful transformations, expanding multiphoton manifolds on both the dye scopes and reaction versions. A comparison of the catalytic performance between different structural patterns of metal-organic frameworks with the same ligand demonstrated that the incorporating of the organic dyes within the pores of the frameworks was essential to form charge-transfer species and accelerate the interesting chemical conversion.