Thermal/Water-Induced Phase Transformation and Photoluminescence of Hybrid Manganese(II)-Based Chloride Single...

Mn(II)-based hybrid halides have attracted great attention from the optoelectronic fields due to their nontoxicity, special luminescent properties, and structural diversity. Here, two novel organic-inorganic hybrid Mn(II)-based halide single crystals (1-mpip)MnCl₄·3H₂O and (1-mpip)₂MnCl₆ (1-mpip = 1-methylpiperazinium, C₅H₁₄N₂⁺) were grown by a slow evaporation method in ambient atmosphere. Interestingly, (1-mpip)₂MnCl₆ single crystals exhibit the green emission with a PL peak at 522 nm and photoluminescence quantum yields (PLQYs) of ≈5.4%, whereas (1-mpip)MnCl₄·3H₂O single crystals exhibit no emission characteristics. More importantly, there exists a thermal-induced phase transformation from (1-mpip)MnCl₄·3H₂O to emissive (1-mpip)₂MnCl₆ at 372 K. Moreover, a reversible luminescent conversion between (1-mpip)MnCl₄·3H₂O and (1-mpip)₂MnCl₆ was simply achieved when heated to 383 K and placed in a humid environment or sprayed with water. This work not only deepens the understanding of the thermal-induced phase transformation and humidity-sensitive luminescent conversion of hybrid Mn(II)-based halides, but also provides a guidance for thermal and humidity sensing and anticounterfeiting applications of these hybrid materials.