Manipulation of Metal‐to‐Metal Charge Transfer Toward Switchable Functions

Abstract

Since the first discovery of photomagnetic effects in Prussian blue [FeCo] analogs in 1996, metal-to-metal charge transfer (MMCT) complexes displaying the electron transfer between two metal ions have attracted enormous research interest. It has been established that MMCT provides two valence isomers with markedly different electronic configurations and magnetic properties, which can be manipulated by external stimuli, such as light, heat, pressure, and electric field. In addition, MMCT can induce a variation in oxidation and spin states, and it can cause significant changes in bond length, charge distributions, absorption, and fluorescence spectra. These changes result in unusual thermal expansion, electric and dielectric switches, and photochromic properties. Therefore, materials showing MMCT interactions, are promising candidates for information storage devices, smart switches, and sensors. In this chapter, the recent progress of MMCT complexes in cyanide-bridged systems will be reviewed and discussed, including the influencing factors on the MMCT property and its switchable functionalities. The flexibility and response to external stimuli render the MMCT molecular materials as versatile actuators for multifunctional devices whose magnetic, electric, mechanochemical, and optical properties can be fine-tuned.