Polyoxometalate-dependent Photocatalytic Activity of Radical-doped Perylenediimide-based Hybrid Materials

Abstract

Inorganic-organic hybrid materials are a kind of multiduty materials with high crystallinity and definite structures, built from functional inorganic and organic components with highly tunable photochemical properties. Perylenediimides (PDIs) are a kind of strong visible light-absorbing organic dyes with π-electron-deficient planes and photochemical properties depending on their micro-environment, which provides a platform for designing tunable and efficient hybrid photocatalytic materials. Herein, four radical-doped PDI-based crystalline hybrid materials, Cl₄-PDI⋅SiW₁₂O₄₀ (1), Cl₄-PDI⋅SiMo₁₂O₄₀ (2), Cl₄-PDI⋅PW₁₂O₄₀ (3), and Cl₄-PDI⋅PMo₁₂O₄₀ (4), were attained by slow diffusion of polyoxometalates (POMs) into acidified Cl₄-PDI solutions. The obtained PDI-based crystalline hybrid materials not only exhibited prominent photochromism, but also possessed reactive organic radicals under ambient conditions. Furthermore, all hybrid materials could be easily photoreduced to their radical anions (Cl₄-PDI⋅^-), and then underwent a second photoexcitation to form energetic excited state radical anions (Cl₄-PDI⋅^-*). However, experiments and theoretical calculations demonstrated that the formed energetic Cl₄-PDI⋅^-* showed unusual POM-dependent photocatalytic efficiencies toward the oxidative coupling of amines and the iodoperfluoroalkylation of alkenes; higher photocatalytic efficiencies were found for hybrid materials 1 (anion: SiW₁₂O₄₀ ^4-) and 2 (anion: SiMo₁₂O₄₀ ^4-) compared to 3 (anion: PW₁₂O₄₀ ^3-) and 4 (anion: PMo₁₂O₄₀ ^3-). The photocatalytic efficiencies of these hybrid materials are mainly controlled by the energy differences between the SOMO-2 level of Cl₄-PDI⋅^-* and the LUMO level of the POMs. The structure-photocatalytic activity relationships established in present work provide new research directions to both the photocatalysis and hybrid material fields, and will promote the integration of these areas to explore new materials with interesting properties.

Keywords: hybrid material; perylenediimide; photocatalytic activity; photoinduced electron-transfer; structure-property relationship.