New Room-Temperature Ferroelectrics with Photoluminescent Properties

Organic–inorganic hybrid materials are highly versatile and can be easily modified, allowing for the deliberate construction of multifunctional ferroelectrics. In particular, the combination of photoluminescence and ferroelectricity in a single hybrid material holds great potential for various applications, such as lighting sensors, memory devices, and other multifunctional uses. In this study, we focused on 3-oxa-8-azabicyclo[3.2.1]octane hydrochloride (OAO) and designed two room-temperature ferroelectrics based on manganese (Mn): OAO-MnCl4 ((C6H12NO)2MnCl4·H2O) and OAO-MnBr4 ((C6H12NO)2MnBr4·H2O). Both of these compounds crystallize in the polar orthogonal space group Pna21, displaying robust photoluminescence and ferroelectricity at room temperature. The saturation polarizations of OAO-MnCl4 and OAO-MnBr4 are approximately 0.51 and 0.59 μC/cm2, respectively. Interestingly, the single crystal of OAO-MnCl4 demonstrates dual-emission bands at 550 and 670 nm, which are attributed to self-trapped excitons. Additionally, OAO-MnCl4 exhibits a reversible thermochromic phenomenon, displaying sensitive luminescent switching between green and red emissions within a narrow temperature range. This room-temperature molecular ferroelectric with photoluminescence opens up new avenues for designing novel multifunctional ferroelectrics and establishes a foundation for potential optoelectronic applications of these luminescent Mn-based materials.