Organic–Inorganic Hybrid Hexagonal Perovskites (4-Methylpiperidinium)MnX₃ (X = Cl and Br) with High-Temperature Dielectric Phase Transitions and Photoluminescent Properties

Significant attention has been dovoted to the organic–inorganic hybrid perovskites in the realm of scientific research arising from their distinctive optical and dielectric properties along with structural tunability, rendering them highly versatile and adaptable materials. Herein, two novel one-dimensional organic–inorganic hybrid perovskites of (4-MPD)MnX3 (4-MPD = 4-methylpiperidinium, X = Cl (1), X = Br (2)) were synthesized and demonstrated to, respectively, undergo reversible phase transitions at 376 and 368 K, characterized by differential scanning calorimetry and dielectric measurements. It is instresting to note that the replacement of Br by the Cl halogen atom has maintained the crsytal structures but devoted a slight increase in phase transition temperature. Variable-temperature structural analyses signify that the order–disorder change of 4-MPD cations acts as the driving force for such phase transitions from the Pnma to P1̅ space group. In addition, compounds 1 and 2 both emit strong red photoluminescence under UV excitation. The two compounds with high-temperature dielectric switching and photoluminescent properties will offer fresh insights for the design and investigation of novel multifunctional organic–inorganic hybrid perovskites.