Confinement of Pyridine Derivatives into a Metal–Organic Framework Host as Electron Acceptors to Achieve Photoinduced Electron-Transfer

The photoinduced electron-transfer (ET) process plays an irreplaceable role in chemical and biological fields exemplified by enzymatic catalysis, artificial photosystems, solar energy conversion, and so forth. Searching for a new photoinduced ET system is of great importance for the development of functional materials. Herein, a series of host–guest compounds based on a magnesium metal–organic framework (Mg-MOF) as a host and pyridine derivatives as guests have been presented. Notably, strong O–H···N hydrogen bond between the oxygen atom of μ2-H2O and the nitrogen atom of pyridine enables proton delocalization between water molecule and pyridine guest. Despite the absence of photochromic modules in these host–guest compounds, long-lived charge-separated states with distinct color changes can be formed after UV-light irradiation. The substituents in pyridines and the proton delocalization ability between the host and guests have a great influence on their photoinduced ET process to endow the MOF materials with tunable photoinduced charge-separated states.