Lone Pair Electron Manipulation: A Promising Avenue for Tuning Properties in Functional Materials

The expression of lone pair electrons (LPEs) in solid-state materials plays a significant role in a range of properties and functionalities. The ns² LPEs contribute to high lattice anharmonicity and strong distortion polarization, which are pivotal for the exceptional thermoelectric, optoelectronic, ferroelectric, and second-harmonic generation properties, among others. This review article examines the transformative impact of LPEs on the physical properties of functional materials, specifically focusing on metal halide perovskites, low-dimensional metal halides, metal chalcogenides, and inorganic molecular crystals. Experimental approaches for manipulating LPE expression are highlighted, including chemical tuning, temperature, and pressure, and the critical role of LPE expression evolution on physical properties is discussed. Additionally, perspectives on the future challenges and opportunities in the LPE regulation within fundamental research are provided. This theme offers a new insight into how the manipulation of LPE expression can be a powerful way to tune and optimize functional materials.