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

Abstract

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.

Encapsulating electron-deficient dyes into metal–organic capsules to achieve high reduction potentials

“…S19 †). 38,39 Firstly, the Zn-PAP is excited to form the triplet [Zn-PAP]* under illumination, which undergoes triplet-triplet energy transfer with AQ to form the radical anion AQ •− , which is subsequently photoactivated to form AQ •− *. This highly reducing species can then donate an electron to the π-system of the aryl chlorides to furnish the intermediate and regenerate AQ.…”

Enhancing energy transfer through visible-light-driven polymerization in a metal–organic framework

“…Via the Kubelka-Munk equation, 33,34 the energy bands (E g ) of Zr-MOF, Zr-MOF-hv, Zr-BBI and Zr-DPA were calculated to be 2.35 eV, 2.04 eV, 2.78 eV and 2.70 eV, respectively. Additionally, the results based on Mott-Schottky plots at different frequencies (1200 Hz, 1500 Hz) further illuminated the intrinsic electronic properties of Zr-MOF, Zr-MOF-hv, Zr-BBI and Zr-DPA with positive Mott-Schottky slopes, indicating the n-type semiconductor behavior of these MOFs.…”

Guest‐Induced Multilevel Charge Transport Strategy for Developing Metal‐Organic Frameworks to Boost Photocatalytic CO2 Reduction

“…[ 20–23 ] On the premise that the materials have unique metal nodes as the catalytic center, one potential design strategy involves expanding the number of electron transfer avenues in the catalyst to establish multi‐stage electron transport paths. [ 7,24–27 ]…”

“…[20][21][22][23] On the premise that the materials have unique metal nodes as the catalytic center, one potential design strategy involves expanding the number of electron transfer avenues in the catalyst to establish multistage electron transport paths. [7,[24][25][26][27] The transport of photogenerated charge in MOF photocatalyst systems can occur via three possible modes: hopping transport, through-bond conduction, and through-space charge transport. [28] Hopping conduction depends on the transmission of electron from donor to acceptor sites.…”