Chiral hybrid manganese(ii) chloride single crystals for achieving second harmonic generation and moderate circularly polarized luminescence

Abstract

Chiral hybrid metal halides have attracted much attention in optoelectronic fields such as encryption storage, security monitoring, and three-dimensional (3D) displays, due to their low cost, low toxicity, good stability, high luminescence efficiency, tunable emission, and chiroptical and nonlinear optical properties. Here, a pair of chiral manganese(II)-based hybrid chloride single crystals (R/S-2-mpip)MnCl₄·2H₂O and (rac-2-mpip)MnCl₄·2H₂O (mpip = methylpiperazinium) were synthesized by a slow evaporation method. The crystal structures, X-ray photoelectron spectroscopy (XPS), second harmonic generation, band gap calculation and photoluminescence (PL) were systematically studied. (R/S-2-mpip)MnCl₄·2H₂O and (rac-2-mpip)MnCl₄·2H₂O single crystals exhibited strong red emission characteristics caused by d–d transition of free Mn²⁺ when heated to 383 K. Moreover, heated (R/S-2-mpip)MnCl₄·2H₂O materials exhibit the obvious circular dichroism and red circularly polarized luminescence characteristics with a moderate luminescence dissymmetry factor g_lum value reaching ±1.2 × 10⁻³, which provides a new research direction for further applications from anticounterfeiting to 3D displays, as well as encryption storage.