Mechanically Responsive Metal Halides-Based Smart Materials: Phenomena, Materials, and Mechanisms

Metal halides belong to a remarkable category of mechanically responsive smart materials with unique properties because of their both composition and dimensional engineering. These metal halides-based smart materials have earned significant attention because of their exceptional optical properties and advantages, making them versatile in a wide range of applications. In this regard, high pressure has recently been identified as a promising tool for regulating excitonic transitions in metal halides via continuous structural modulations. This technique offers a novel perspective for understanding their intriguing excitonic emissions. This chapter provides an in-depth and systematic analysis of these materials, with particular emphasis on organic-inorganic complex mechanofluorochromic materials. The band gaps and emission energy of metal halides, which are directly linked to the efficiency of excitonic formation, can be precisely modulated under compression through mechanisms such as contraction, distortion, and excitonic transitions. As a result, this chapter emphasizes a fundamental strategy for modulating and optimizing the optical properties of organic-inorganic hybrid metal halides through precise exciton regulation achieved via high-pressure methods.