Remarkable Second Harmonic Generation Response in (C5H6NO)+(CH3SO3)-: Unraveling the Role of Hydrogen Bond in Thermal Driven Nonlinear Optical Switch

Heat-activated second harmonic generation (SHG) switching materials are gaining interest for their ability to switch between SHG on and off states, offering potential in optoelectronic applications. The novel nonlinear optical (NLO) switch, (C5H6NO)+(CH3SO3)- (4-hydroxypyridinium methylsulfonate, 4HPMS), is a near-room-temperature thermal driven material with a strong SHG response (3.3 × KDP), making it one of the most potent heat-stimulated NLO switches. It offers excellent contrast of 13 and a high laser-induced damage threshold (2.5 × KDP), with reversibility > 5 cycles. At 73 °C, 4HPMS transitions from the noncentrosymmetric Pna21 room temperature phase (RTP) to the centrosymmetric P21/c phase, caused by the rotation of the (C5H6NO)+ and (CH3SO3)- due to partially thermal breaking of intermolecular hydrogen bonds. The reverse phase change exhibits a large 50 °C thermal hysteresis. Density functional theory (DFT) calculations show that (C5H6NO)+ primarily dictates both the SHG coefficient (dij) and birefringence (▵n(Zeiss) = 0.216 vs ▵n(cal.) = 0.202 at 546 nm; Δn(Immersion) = 0.210 vs ▵n(cal.) = 0.198 at 589.3 nm), while the band gap (Eg) is influenced synergistically by (C5H6NO)+ and (CH3SO3)-. Additionally, 4HPMS-RTP also exhibits mechanochromism upon grinding as well as an aggregation-enhanced emission in a mixture of acetone and water.

Organic-Inorganic Hybrid Ferroelectric and Antiferroelectric with Afterglow Emission

Luminescent ferroelectrics are holding exciting prospect for integrated photoelectronic devices due to potential light-polarization interactions at electron scale. Integrating ferroelectricity and long-lived afterglow emission in a single material would offer new possibilities for fundamental research and applications, however, related reports have been a blank to date. For the first time, we here achieved the combination of notable ferroelectricity and afterglow emission in an organic-inorganic hybrid material. Remarkably, the presented (4-methylpiperidium)CdCl3 also shows noticeable antiferroelectric behavior. The implementation of cationic customization and halogen engineering not only enables a dramatic enhancement of Curie temperature of 114.4 K but also brings a record longest emission lifetime up to 117.11 ms under ambient conditions, realizing a leapfrog improvement of at least two orders of magnitude compared to reported hybrid ferroelectrics so far. This finding would herald the emergence of novel application potential, such as multi-level density data storage or multifunctional sensors, towards the future integrated optoelectronic devices with multitasking capabilities.

Two Manganese(II)-Based Hybrid Multifunctional Phase Transition Materials with Strong Photoluminescence, High Quantum Yield, and Switchable Dielectric Properties: (C6NH16)2MnBr4 and (C7NH18)2MnBr4

Multifunctional materials have always been an attractive research area, but how to combine multiple excellent properties in one compound remains a considerable challenge. Organic-inorganic hybrid compounds are widely used in the design of such materials due to their rich properties and flexible assembly. Herein, two new manganese(II)-based organic-inorganic hybrid compounds, (C₆NH₁₆)₂MnBr₄ (1) and (C₇NH₁₈)₂MnBr₄ (2), are prepared by the solution method. Compounds 1 and 2 both emit extremely strong green light under UV excitation, with high quantum yields of 45.93 and 50.98%, respectively. In addition, reversible solid-state phase transitions and obvious switchable dielectric properties are shown at 378/366 and 361/352 K, respectively. The coexistence of the dual stimulus-response characteristics of temperature and light in compounds 1 and 2 opens a new path for exploring more multifunctional phase transition materials.

Unusual symmetry breaking in high-temperature enantiomeric ferroelectrics with large spontaneous polarization

Chiral organic-inorganic hybrid perovskites have gained extensive research interest due to their combination of chirality and the excellent optical, electrical and spin properties of perovskite materials, especially in two-dimensional hybrid perovskites. Herein, we report two-dimensional organic-inorganic perovskite enantiomeric ferroelectric [(R)-β-MPA]₂CdCl₄ (1) and [(S)-β-MPA]₂CdCl₄ (2) (MPA⁺ =methylphenethylammonium). Their mirror relationships are verified by both circular dichroism (CD) and crystal structures. At the same time, the two exhibit very similar ferroelectricity and related properties, including high Curie temperature (343 K), large spontaneous polarization (4.65 μC cm^-2), and low coercive force field (13 kV cm^-1). Unusually, at room temperature the crystal phase is monoclinic with the space group C2 and above the phase transition temperature it is triclinic with the space group P1, which means that the symmetry decreases with the increase of temperature. In addition, it exhibits a flexible switchable SHG response, while [(R)-β-MPA]₂CdCl₄ and [(S)-β-MPA]₂CdCl₄ have wide band gaps of 4.21 and 4.26 eV, respectively, mainly contributed by inorganic CdCl₆ octahedra. This discovery opens a new way for the construction of two-dimensional enantiomeric molecular ferroelectrics.

A 1D chiral infinite chain organic metal halide hybrid with excellent SHG switching and moderate spontaneous polarization

A 1D chiral lead-free organic metal halide hybrid C8H20Cl5N2O2Sb (1) was successfully synthesized. Compound 1 reveals a phase transition and has a SHG “ON–OFF” switchable property, and also have ferroelectric.

Unusual high-temperature host–guest inclusion compound-based ferroelectrics with nonlinear optical switching and large spontaneous polarization behaviours

Host–guest inclusion compound-based ferroelectrics [Hcta-(18-crown-6)]+[BF4]− (1) and [Hcta-(18-crown-6)]+[ClO4]− (2) with a high Curie temperature (Tc = 403/394 K) and large spontaneous polarization (Ps = 5.7/4.7 μC cm−2) are reported.

Two quasi-spherical molecules [1,4-diazabicyclo(3.2.2)nonane]X (X = ClO4, ReO4) exhibit switchable phase transition, dielectric and second-harmonic-generation properties

Two quasi-spherical molecules [3.2.2-Hdabc]X (1,4-diazabicyclo[3.2.2]nonane = 3.2.2-dabcn, X = ClO4, ReO4) with a high phase transition temperature exhibited switchable phase transition as well as dielectric and SHG properties.

High-Temperature and Large-Polarization Ferroelectric with Second Harmonic Generation Response in a Novel Crown Ether Clathrate

Molecular ferroelectrics of high-temperature reversible phase transitions are very rare and have attracted increasing attention in recent years. In this paper is described the successful synthesis of a novel high-temperature host-guest inclusion ferroelectric: [(C₆ H₅ NF₃ )(18-crown-6)][BF₄ ] (1) that shows a pair of reversible peaks at 348 K (heating) and 331 K (cooling) with a heat hysteresis about 17 K by differential scanning calorimetry measurements, thus indicating that 1 undergoes a reversible structural phase transition. Variable-temperature PXRD and temperature-dependent dielectric measurements further prove the phase-transition behavior of 1. The second harmonic response demonstrates that 1 belongs to a non-centrosymmetric space group at room temperature and is a good nonlinear optical material. In its semiconducting properties, 1 shows a wide optical band gap of about 4.43 eV that comes chiefly from the C, H and O atoms of the crystals. In particular, the ferroelectric measurements of 1 exhibit a typical polarization-electric hysteresis loop with a large spontaneous polarization (P_s ) of about 4.06 μC/cm² . This finding offers an alternative pathway for designing new ferroelectric-dielectric and nonlinear optical materials and related physical properties in organic-inorganic and other hybrid crystals.

Crystal Structure and Ferroelectric Evidence of BaZnSi3 O8 , a Low-Permittivity Microwave Dielectric Ceramic

BaZnSi₃ O₈ ceramic was prepared by the conventional solid-state method and sintered at 1100 °C. XRD and synchrotron Rietveld refinement analyses revealed the BaZnSi₃ O₈ ceramic presented a monoclinic structure with a space group of P2₁ /a (No.14), which is reported for the first time. The BaZnSi₃ O₈ ceramic presented a weak ferroelectricity, which was confirmed by the P-E loop and the 90° nanoscale ferroelectric domain. Although ϵ_r -T displayed two ϵ_r abnormal peaks at 400 °C and 460 °C, the Curie temperature (T_c ) was located at 460 °C according to the dielectric loss and Curie-Weiss law. Moreover, the BaZnSi₃ O₈ ceramic exhibited optimized microwave dielectric properties with ϵ_r =6.55, Q×f=52400 GHz, and τ_f =-24.5 ppm/°C. Hence, the BaZnSi₃ O₈ ceramic in the ternary BaO-ZnO-SiO₂ system possessed both weak ferroelectricity and microwave dielectric properties. These results are expected to break the technical barrier of ferroelectric phase shifter applications in microwave and even millimeter-wave frequency bands.

Coupling Narrow Band Gap and Switchable SHG Responses in a New Molecule Ferroelectric: Imidazolyl Propylamine Pentabromo Stibium(III)

Due to the existence of some cross properties such as SHG (second-harmonic generation), ferroelectricity, piezoelectricity, and thermoelectricity, molecular ferroelectrics have been widely used as a composite multipurpose material. Particularly, organic-inorganic molecular ferroelectrics have received much interest recently because of their unique flexible structures, friendly environment, ease of synthesis, etc. Also, these hybrids show great flexibility in band-gap engineering. Here we report a new molecular halide, [C₆H₁₃N₃SbBr₅]_n (1; C₆H₁₃N₃ = 1-(3-aminopropyl)imidazole), which experiences a unique ferroelectric to paraelectric phase transition at around 230 K from space group P2₁ to P2₁/c. Significantly, compound 1 exhibits a narrow band gap with a value of 2.52 eV, large pronounced SHG-active, perfect rectangle hysteresis loops with a large spontaneous polarization of 6.86 μC/cm². DSC (differential scanning calorimetry) and dielectric dependence on temperature tests and the volume change before and after the phase transition show that compound 1 is characterized by a second-order phase transition. These findings will contribute to the multifunctional materials field of organic-inorganic hybrids.

Multifunctional rare earth molecular ferroelectrics with a piezoelectric response: ((nBu)4N)3[Ce(NO3)4(SCN)2]((CH3CH2CH2CH2)4N = tetrabutylammonium)

A new type of multipolar rare earth molecular ferroelectric: ((nBu)4N)3[Ce(NO3)4(SCN)2] (BuCH3CH2CH2CH2)4N), undergoes a high-temperature ferroelectric phase transition, possesses flexible switchable SHG effect, moderate spontaneous polarization and a narrow band gap.

Para–ferroelectric phase transition induces an excellent second harmonic generation response and a prominent switchable dielectric constant change based on a metal-free ionic crystal

A novel metal-free compound, [H₂(bpyp)][ClO₄]₂, undergoes a ferroelectric to paraelectric reversible phase transition at T_c, with excellent NLO response, prominent dielectric constant change, moderate ferroelectric polarization, and wide bandgap.

Successive Phase Transitions and Dual Dielectric Switching in an Organic-Inorganic Hybrid Perovskite

Molecular phase transition compounds have become a hot research area in recent years because of their potential as functional materials, such as ferroelectrics, ferroelastics, dielectric switches, etc. However, materials combining switchable dielectric properties and ferroelasticity are still rare. Here, we reported an organic-inorganic hybrid perovskite, [CPtmp][Cd(SCN)₃] (1) ([CPtmp]⁺ is a cyclopentyltrimethylphosphonium cation), with a potential ferroelastic property. This material undergoes three structural phase transitions at 247/226, 335/312, and 349/341 K (upon heating/cooling). The successive phase transitions are mainly caused by the stepwise ordering of [CPtmp]⁺ cations and the concomitant deformation of [Cd(SCN)₃]^- anionic chains revealed by structural analyses, which triggers the double-step dielectric switching in 1 as well. These results would inspire further exploration on molecular dielectric switches with ferroelastic properties.