A series of organic nonlinear optical (NLO) materials based on the stilbazolium derivatives of 4-N,N-dimethylamino-4′-N′-methyl-stilbazolium tosylate (DAST) were synthesized, and the single crystals were grown from the solutions. Single-crystal structure determinations and Kurtz powder tests reveal that replacement of the p-toluenesulfonate anion in the DAST crystal, forming 4-N,N-dimethylamino-4′-N′-methyl-stilbazolium 4-aminotoluene-3-sulfonate (1) and 4-N,N-dimethylamino-4′-N′-methyl-stilbazolium p-chlorobenzenesulfonate (2), constructs new acentric crystals with quite a large powder second-harmonic generation (SHG) of more than 3 orders of magnitude larger than that of urea around 2.0 μm, whereas the other two complexes show their centrosymmetric structures without any SHG effects. A possible estimation of the molecular first hyperpolarizabilities β ijk performed on 2 further confirms its origin of its enhanced NLO merits. Furthermore, both 1 and 2 exhibit even higher environmental stabilities, including the antiwater performance and the formation of anhydrous phases in water-containing solutions. We believe that the findings of the further counterion modification will bring new stilbazolium derivatives with improved optical nonlinearities and the physicochemical performances.

A novel supramolecular phase change material (PCM) potassium hydrogen bis(dichloroacetate)-18-crown-6 (1), which undergoes a reversible second-order phase transition at 181.8 K (T c ), has been successfully synthesized and grown as bulk crystals. DSC measurements confirm its reversible phase transition with a thermal hysteresis of 1.6 K. Dielectric permittivities also display obvious anomalies approaching T c , being characteristic for the reversible phase transition. Variable-temperature X-ray singlecrystal diffractions demonstrate that 1 behaves as a molecular rotor above room temperature in which the chlorine atoms rotate around the C−C axis of the CHCl 2 COO − /CHCl 2 COOH exhibiting distinct pendulum-like motions, and the (18-crown-6)•K + part acts as a stator. Further studies reveal that the origin of its phase transition was ascribed to the moving close together of the whole set molecules from the original position, which is induced by the order− disorder transformation of the pendulum-like motions of the CHCl 2 COO − /CHCl 2 COOH units between the LT phase and RT phase. We believe that all the results would urge the exploration of new phase change functional materials.

A novel molecular electric ordered compound [(Hdabco)+ClF2CCOO–] (complex 1, dabco = 1,4-diazabicyclo[2.2.2]­octane) has been discovered as a switchable dielectric material, in which the N–H···O hydrogen bonds connect the anions and cations together to form a dimer structure. It undergoes a reversible second order solid state phase transition at 165 K (T c), which was confirmed by thermal analyses including differential scanning calorimetry (DSC) and specific heat (C p) and dielectric measurements. Variable temperature single crystal X-ray diffraction analyses revealed its order–disorder transformation of twisting motion characteristic behaviors for the phase transition. Owing to the ordering of twisting motions of the chlorodifluoroacetate anions, the structure of 1 demonstrates a phase transition from high crystallographic symmetry with space group of Pnma to the low state with space group of P21/c; that is, an Aizu notion of mmmF2/m occurs. Emphatically, the dielectric constant of 1 displays a distinctive step-like anomaly; namely, it possesses a high dielectric state in the room temperature phase (RTP) and a low state in the low temperature phase (LTP). Such distinctive dielectric performances disclose that 1 might be considered as a potential switchable dielectric material. We believe that all the findings would afford a useful strategy in exploring new electric ordering materials.