Thermochromism Perovskite (COOH(CH 2 ) 3 NH 3 ) 2 PbI 4 Crystals: Single-Crystal to Single-Crystal Phase Transition and Excitation-Wavelength-Dependent Emission.

As a potential multifunctional phase transition material, the organic-inorganic hybrid perovskite has attracted extensive attention in recent years. Here, we report the single-crystal to single-crystal phase transition and excitation-wavelength-dependent emission (EDE) of layered perovskite (COOH(CH 2 ) 3 NH 3 ) 2 PbI 4 . Single-crystal X-ray diffraction indicated that the crystal structure changes from layered Ruddlesden-Popper (RP) at 302 K to "X" network composed of face-sharing and corner-sharing [PbX 6 ] 4- octahedra at 425 K. The material exhibits thermochromic change from orange to yellow at higher temperature. Considering the thermochromism of the material, we apply it for anticounterfeiting and information encryption. The material exhibits EDE properties with a fluorescence color changing from green to red upon 420 and 546 nm excitation, respectively. Time-dependent density functional theory indicated that this phenomenon is mainly related to the laser-induced crystal structural transfer. Our research shows that the (COOH(CH 2 ) 3 NH 3 ) 2 PbI 4 crystal has a potential application for multifunctional devices.