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 (Ered ≈ −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.