Green-Emissive Ferroelectric Optical Thermometer Based on Cyclometalated Dicyanidoplatinate(II) Ions

Multifunctional ferroelectric materials combine permanent polarization, which is switchable by the applied electric field, with an array of other functionalities. Among these, luminescent ferroelectrics are coming into the spotlight due to their potential in optical sensing, information storage, optoelectronics, and electrical modulation of light emission. Their functionality can be further improved if their emission is sensitive to different physical and chemical stimuli. Certainly, they would benefit from optical thermometry, which enables fast, contactless read-out of temperature. However, the construction of ferroelectric luminescent thermometers remains difficult, thus, we decided to explore the potential of photoluminescent cyanido metal complexes in this context. Here, we present the crystal structure and detailed physicochemical properties of methylquinuclidinium salt of dicyanido(2-phenylpyridinato)platinate(II), Meabco[Pt(CN)2(ppy)] (1). We report its room-temperature ferroelectricity, which was studied using the piezoelectric force microscopy (PFM) and is accompanied by the second harmonic generation (SHG) effect. The presence of green-emissive [Pt(CN)2(ppy)]− complexes introduces a temperature-variable photoluminescence (PL) signal, which we employed to present the potential of 1 in optical thermometry. Additionally, we demonstrate processability of this novel luminescent molecular ferroelectric into spin-coated thin films of excellent quality, which remains a highly desirable feature for their future applications.