Designing multifunctional organic thermochromic ferroelectric materials: remarkable melt-cool large thermal hysteresis of reversible single crystal to single crystal transformation

Abstract

Oxazolidinone-based organic ferroelectric compounds, namely (E)-4-(4-(benzylideneamino)benzyl)oxazolidin-2-one (BOA) and (E)-4-(4-(2-hydroxybenzylideneamino)benzyl)oxazolidin-2-one (HBOA), were synthesized. Both molecules have shown a reversible melting and solidification transformation from −50 °C to 250 °C as confirmed by differential scanning calorimetry (DSC) analysis. A large thermal hysteresis window of 100 °C and 87 °C was observed for BOA and HBOA, respectively, along with thermo chromic features. Variable temperature single crystal X-ray diffraction analysis reveals that an order–disorder transformation occurs for BOA while HBOA remains unchanged. Interestingly, both compounds exhibit significant reversible mechanofluorochromic (MFC) behavior upon grinding and fuming. The reversible MFC behavior was confirmed by cognate techniques like powder X-ray diffraction (PXRD), thermal analysis and fluorescence studies. Furthermore, the systems were investigated to demonstrate the structure–property relationship in realizing their ferroelectric behavior by SHG, PUND (positive up and negative down) and RT (room temperature) and HT (high temperature) thermal responses of PE and dielectric measurements. BOA and HBOA show ferroelectric hysteresis loops at high electric fields with a high voltage tolerance (up to 181 kV cm⁻¹). By measuring the PFM hysteresis loops at various V_dc frequencies, an explicit V_c could be found in the ferroelectric rather than in the non-ferroelectric material. These findings provide a potential perspective for designing new organic multifunctional materials for applications in light displaying and memory devices.