A Z/E isomeric cation designed organic-inorganic cadmium chloride ferroelectric with broadband white-light emission

Abstract

Hybrid organic-inorganic metal halides (HOMHs) have attracted tremendous interest in the past decades due to their diverse functional properties, such as ferroelectricity and luminescence. However, although a large number of ferroelectric HOMHs and luminescent HOMHs have been reported, the HOMH ferroelectrics with white-light emission remain very sparse. Here, for the first time, by using the Z/E isomeric organic cation, we designed a cadmium-based HOMH ferroelectric [EE-PMU]CdCl₄ (EE-PMU = pyridin-2-ylmethanamide muconate) with broadband white-light emission. In contrast to the [ZZ-PMU]CdCl₄ with centrosymmetric crystal structure at room temperature, [EE-PMU]CdCl₄ adopts the polar crystal symmetry, which shows piezoelectricity with a piezoelectric coefficient of d₃₃ up to 19 pC/N and ferroelectricity with the saturated polarization of 1.52 µC/cm². Moreover, [EE-PMU]CdCl₄ exhibits a broadband white-light emission with an ultra-high color rendering index of 91 under UV excitation, which is related to the severely distorted [CdCl₄]²⁻ tetrahedron in the structure. To our knowledge, [EE-PMU]CdCl₄ is the first example of Z/E isomeric cation-designed HOMH ferroelectric and the first cadmium halide white-light emissive ferroelectric. This finding paves a new way for the design of organic-inorganic molecular ferroelectrics with white-light emission.