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.

Unusual Thermal Quenching of Photoluminescence from an Organic-Inorganic Hybrid [MnBr4 ]2- -based Halide Mediated by Crystalline-Crystalline Phase Transition.

The ability to generate and manipulate photoluminescence (PL) behavior has been of primary importance for applications in information security. Excavating novel optical effects to create more possibilities for information encoding has become a continuous challenge. Herein, we present an unprecedented PL temporary quenching that highly couples with thermodynamic phase transition in a hybrid crystal (DMML)2 MnBr4 (DMML=N,N-dimethylmorpholinium). Such unusual PL behavior originates from the anomalous variation of [MnBr4 ]2- tetrahedrons that leads to non-radiation recombination near the phase transition temperature of 340 K. Remarkably, the suitable detectable temperature, narrow response window, high sensitivity, and good cyclability of this PL temporary quenching will endow encryption applications with high concealment, operational flexibility, durability, and commercial popularization. Profited from these attributes, a fire-new optical encryption model is devised to demonstrate high confidential information security. This unprecedented optical effect would provide new insights and paradigms for the development of luminescent materials to enlighten future information encryption.

Organic-Inorganic Rare-Earth Double Perovskite Ferroelectric with Large Piezoelectric Response and Ferroelasticity for Flexible Composite Energy Harvesters.

Hybrid organic-inorganic perovskite (HOIP) ferroelectric materials have great potential for developing self-powered electronic transducers owing to their impressive piezoelectric performance, structural tunability and low processing temperatures. Nevertheless, their inherent brittle and low elastic moduli limit their application in electromechanical conversion. Integration of HOIP ferroelectrics and soft polymers is a promising solution. In this work, a hybrid organic-inorganic rare-earth double perovskite ferroelectric, [RM3HQ]2RbPr(NO3)6 (RM3HQ = (R)-N-methyl-3-hydroxylquinuclidinium) is presented, which possesses multiaxial nature, ferroelasticity and satisfactory piezoelectric properties, including piezoelectric charge coefficient (d33) of 102.3 pC N-1 and piezoelectric voltage coefficient (g33) of 680 × 10-3 V m N-1. The piezoelectric generators (PEG) based on composite films of [RM3HQ]2RbPr(NO3)6@polyurethane (PU) can generate an open-circuit voltage (Voc) of 30 V and short-circuit current (Isc) of 18 µA, representing one of the state-of-the-art PEGs to date. This work has promoted the exploration of new HOIP ferroelectrics and their development of applications in electromechanical conversion devices.

The halogen substitution strategy of inorganic skeletons triggers dielectric and band gap regulation of hybrid perovskites.

Organic-inorganic hybrid perovskites (OIHPs) with dielectric switching functions have aroused comprehensive scientific interest, benefitting from their promising applications in sensors and information storage. However, to date, most of these materials discovered thus far possess a single function and are limited in their applicability, failing to meet the requirements of diverse applications. Moreover, the discovery of these materials has been largely serendipitous. Building multifunctional OIHPs with dielectric switching and semiconductors remains a daunting task. In this context, by introducing [C7H16N]+ as cations and in combination with lead halide with semiconducting properties, two OIHPs [C7H16N]PbI3 (1) and [C7H16N]PbBr3 (2) ([C7H16N]+ = (cyclopropylmethyl) trimethylammonium) have been successfully designed. They have dielectric switching properties close to 253 and 279 K and semiconducting behavior with band gaps of 2.67 and 3.22 eV. The phase transition temperature increased by 26 K through halogen substitution. In summary, our findings in this study provide insights into the application of the halogen substitution regulation strategy and open up new possibilities for designing perovskite semiconductors with dielectric switching functionality.

Targeted regulation and optimization of multifunctional phase transition materials by novel void occupancy engineering.

As an innovative form of stimulus-response materials, organic-inorganic hybrid phase transition materials have become a wonderful contender in the field of functional electronic equipment due to their versatile structure, intensive functions and straightforward preparation. However, the targeted regulation and optimization of the electrical/optical response, along with the establishment of regular structure-performance relationships, pose significant challenges in meeting the diverse demands of practical applications over an extended period. Herein, we conducted a systematic investigation into the role of lattice void occupancy in regulating phase transition temperature (Tp) and related optical/electrical bistability. By taking hybrid material [TMEA][Cd(SCN)3] featuring a flexible ammonium cation [TMEA]+ (TMEA = ethyltrimethylammonium) as the prototype, we successfully synthesized three phase transition materials, namely [DEDMA][Cd(SCN)3], [TEMA][Cd(SCN)3] and [TEA][Cd(SCN)3] (DEDMA = diethyldimethylammonium, TEMA = triethylmethylammonium, and TEA = tetraethylammonium), and the excellent regulation of the physical properties of these compounds was achieved through subtle engineering of void occupancy. More strikingly, [TEA][Cd(SCN)3] exhibits remarkable bistable properties in terms of dielectric and nonlinear optical responses (with second-harmonic generation intensity reaching 2.5 times that of KDP). This work provides a feasible avenue to reasonably customise organic-inorganic hybrid phase transition materials and finely adjust their intriguing functionalities.

Introducing Ferroelasticity into 1D Hybrid Lead Halide Semiconductor by Halogen Substitution Strategy.

Organic-inorganic hybrid lead halide perovskites (OLHPs), represented by (CH3 NH3 )PbI3 , are one of the research focus due to their exceptional performance in optoelectronic applications, and ferroelastic domain walls are benign to their charge carrier transport that is confirmed recently. Among them, the 1D OLHPs feature better stability against desorption and moisture, but related 1D ones possessing ferroelasticity are rarely investigated and reported so far. In this work, the 1D ferroelastic semiconductor (N-iodomethyl-N-methyl-morpholinium)PbI3 ((IDMML)PbI3 ) is prepared successfully by introducing successively halogenate atoms from Cl, Br to I into the organic cation of the prototype (N,N-dimethylmorpholinium)PbI3 ((DMML)PbI3 ). Notably, (IDMML)PbI3 shows the narrow bandgap energy (≈2.34 eV) according to the ultraviolet-visible absorption spectrum and the theoretical calculation, and possesses the evident photoconductive characteristic with the on/off ratio of current of ≈50 under the 405 nm light irradiation. This work provides a new case for the ferroelastic OLHPs and will inspire intriguing research in the field of optoelectronic.

Homochiral Chemistry Strategy to Trigger Second-Harmonic Generation and Dual Dielectric Switches.

Switchable materials have attracted enormous interest due to their promising applications in important fields such as sensing, electronic components, and information storage. Nevertheless, obtaining multifunctional switching materials is still a problem worth investigating. Herein, by incorporating (Rac-, L-, D-2-amino-1-propanol) as the templating cation, we have obtained (Rac-, L-, D-HTMPA)CdCl3 (HTMPA = 1-hydroxy-N, N, N-trimethyl-2-propanaminium). We have adopted a chiral chemistry strategy that causes (Rac-HTMPA)CdCl3 in the central symmetric space to crystallize in the chiral space group. Based on the modulation of the homochiral strategy, (L-, D-HTMPA)CdCl3 shows a dual phasic transition at 269 and 326 K and a switchable second-harmonic generation response. In addition, (L-, D-HTMPA)CdCl3 is chiral switchable material to exhibit stable dual dielectric and second-harmonic generation (SHG) switches. This work provides an approach to exploring multifunctional chiral switchable materials.

Methyl regulation triggers high-temperature ferroelastic phase transition.

The multifunctional tuning of solid-state dielectric switches constructed from organic-inorganic hybrid materials (OIHMs) has received great attention. In particular, molecular ferroelastics with dielectric phase transitions have considerable potential in the optical and electrical fields owing to their adjustable structures and physical features. However, it remains a challenge to effectively design ferroelastics with high phase transition temperature (Tc). We used [TTMA]2CdI4 (TTMA = tetramethylammonium, 1) as a template to continuously increase the molecular weight and change the structure of the hybrid material by modifying and extending the alkane chain in the cation. Therefore, a series of OIHMs were eventually developed: [TMEA]2CdI4 (TMEA = trimethylethylammonium, 2), [TMPA]2CdI4 (TMPA = trimethylpropylammonium, 3), and [TMIPA]2CdI4 (TMIPA = trimethyliso-propylammonium, 4). Among them, the Tc of ferroelastic 3 increased up to 387 K. DSC and temperature-related dielectric constant tests prove the occurrence of the phase transition for 1, 2, and 3. The structures further indicate that the phase transition is caused by the order-disorder cation motion. The extension of the alkyl chain greatly increases Tc and endows 3 with ferroelasticity at room temperature.

Fluorescence Emission Is Highly Structure-Dependent in Hybrid Lead Halides.

Hybrid lead halide perovskites have received extensive scientific attention owing to their great potential in the field of fluorescent displays and light-emitting diodes. Currently, most luminescent materials contain functional molecular and rare-earth metal ion parts. However, the mechanism of photoluminescence property in two-dimensional hybrid lead halide perovskites with different layered inorganic skeletons has been reported rarely. To better understand the effect of an inorganic skeleton on the fluorescence property, here, we report three organic-inorganic hybrid materials with different layered inorganic frameworks: (MACH)2·PbBr4 (Prv-1, MACH = cyclohexylmethylammonium), (2-MPQ)·PbBr4 (Prv-2, 2-MPQ = 2-methylpiperazinium), and (TMBA)4·Pb3Br10 (Prv-3, TMBA = N'N'N'-trimethylbenzylammonium). Among them, Prv-1 is a (100)-oriented perovskite, Prv-2 belongs to the (110)-oriented perovskite, and the inorganic framework of Prv-3 possesses [Pb3Br10] units. Interestingly, Prv-1 has a strong blue-violet fluorescence emission, while the luminescence effect of Prv-2 is very weak; notably, Prv-3 emits a charming bright-orange light. Meanwhile, results of theoretical computational studies also reveal that the electronic structure of all three compounds is highly dependent on structurally distorted [PbBr6] octahedra, and the frontier molecular orbital (FMO) analysis further suggests that HOMO and LUMO of Prv-3 are contributed by inorganic and organic components, respectively. In addition, all three materials belong to direct band gap semiconductors, and the band gaps are 2.79, 2.97, and 2.76 eV, respectively. Significantly, there are obvious differences in conduction bands. Based on the above analysis, the photoluminescence mechanism of three hybrid materials is explained from the electronic levels. Consequentially, this work might provide practical strategies and perspectives for exploring novel structure-related properties.

Superior ferroelectricity and nonlinear optical response in a hybrid germanium iodide hexagonal perovskite.

Abundant chemical diversity and structural tunability make organic-inorganic hybrid perovskites (OIHPs) a rich ore for ferroelectrics. However, compared with their inorganic counterparts such as BaTiO3, their ferroelectric key properties, including large spontaneous polarization (Ps), low coercive field (Ec), and strong second harmonic generation (SHG) response, have long been great challenges, which hinder their commercial applications. Here, a quasi-one-dimensional OIHP DMAGeI3 (DMA = Dimethylamine) is reported, with notable ferroelectric attributes at room temperature: a large Ps of 24.14 µC/cm2 (on a par with BaTiO3), a low Ec below 2.2 kV/cm, and the strongest SHG intensity in OIHP family (about 12 times of KH2PO4 (KDP)). Revealed by the first-principles calculations, its large Ps originates from the synergistic effects of the stereochemically active 4s2 lone pair of Ge2+ and the ordering of organic cations, and its low kinetic energy barrier of small DMA cations results in a low Ec. Our work brings the comprehensive ferroelectric performances of OIHPs to a comparable level with commercial inorganic ferroelectric perovskites.

Facile Control of Ferroelectricity Driven by Ingenious Interaction Engineering.

Construction of ferroelectric and optimization of macroscopic polarization has attracted tremendous attention for next generation light weight and flexible devices, which brings fundamental vitality for molecular ferroelectrics. However, effective molecular tailoring toward cations makes ferroelectric synthesis and modification relatively elaborate. Here, the study proposes a facile method to realize triggering and optimization of ferroelectricity. The experimental and theoretical investigation reveals that orientation and alignment of polar cations, dominated factors in molecular ferroelectrics, can be controlled by easily processed anionic modification. In one respect, ferroelectricity is induced by strengthened intermolecular interaction. Moreover, ≈50% of microscopic polarization enhancement (from 8.07 to 11.68 µC cm-2 ) and doubling of equivalent polarization direction (from 4 to 8) are realized in resultant ferroelectric FEtQ2ZnBrI3 (FEQZBI, FEtQ = N-fluoroethyl-quinuclidine). The work offers a totally novel platform for control of ferroelectricity in organic-inorganic hybrid ferroelectrics and a deep insight of structure-property correlations.

Nicotinic acid bromide: a simple organic salt optical-electrical ferroelastic with high Tc.

A new ferroelastic organic salt nicotinic acid bromide (N-Br) was connected by hydrogen bonding with nicotinic acid cations via a halogen substitution strategy. It exhibits a ferroelastic phase transition from P21/m to P1̄ with 2/mF1̄ Aizu notation with a high Curie temperature (Tc) of 402 K. Moreover, optical regulation from blue light to white light was achieved by halogen substitution.

Ferroelectric hybrid organic-inorganic perovskites and their structural and functional diversity.

Molecular ferroelectrics have gradually aroused great interest in both fundamental scientific research and technological applications because of their easy processing, light weight and mechanical flexibility. Hybrid organic-inorganic perovskite ferroelectrics (HOIPFs), as a class of molecule-based ferroelectrics, have diverse functionalities owing to their unique structure and have become a hot spot in molecular ferroelectrics research. Therefore, they are extremely attractive in the field of ferroelectrics. However, there seems to be a lack of systematic review of their design, performance and potential applications. Herein, we review the recent development of HOIPFs from lead-based, lead-free and metal-free perovskites, and outline the versatility of these ferroelectrics, including piezoelectricity for mechanical energy-harvesting and optoelectronic properties for photovoltaics and light detection. Furthermore, a perspective view of the challenges and future directions of HOIPFs is also highlighted.

A nickel(ii)-based one-dimensional organic-inorganic halide perovskite ferroelectric with the highest Curie temperature.

Organic-inorganic halide perovskites (OIHPs) are very eye-catching due to their chemical tunability and rich physical properties such as ferroelectricity, magnetism, photovoltaic properties and photoluminescence. However, no nickel-based OIHP ferroelectrics have been reported so far. Here, we designed an ABX3 OIHP ferroelectric (3-pyrrolinium)NiCl3, where the 3-pyrrolinium cations are located on the voids surrounded by one-dimensional chains composed of NiCl6-face-sharing octahedra via hydrogen bonding interactions. Such a unique structure enables the (3-pyrrolinium)NiCl3 with a high spontaneous polarization (P s) of 5.8 µC cm-2 and a high Curie temperature (T c) of 428 K, realizing dramatic enhancement of 112 and 52 K compared to its isostructural (3-pyrrolinium)MCl3 (M = Cd, Mn). To our knowledge, remarkably, (3-pyrrolinium)NiCl3 should be the first case of nickel(ii)-based OIHP ferroelectric to date, and its T c of 428 K (35 K above that of BaTiO3) is the highest among all reported one-dimensional OIHP ferroelectrics. This work offers a new structural building block for enriching the family of OIHP structures and will inspire the further exploration of new nickel(ii)-based OIHP ferroelectrics.

Halogen engineering of organic-inorganic hybrid perovskites displaying nonlinear optical, fluorescence properties and phase transition.

In order to meet the needs of social development, increasing research attention has been paid to multifunctional molecular-based phase-transition materials. The traditional phase-transition materials with a single functional property can be transformed into magnificent ones by adding additional functional properties-for instance photoluminescence and magnetic order- because having two or more functional properties simultaneously greatly broadens the fields of their applications. At present, there are very few multifunctional phase-transition materials showing excellent performance, and the crystal structure design and performance optimization of materials still need to be studied in depth. Herein, we report the development of two organic-inorganic hybrid materials: (MBA)2ZnI4 (1, MBA = 4-methoxybenzylammonium) with switchable dielectricity and a high phase-transition temperature (Tc = 359.55 K), and (MBA)2ZnBr4 (2) with green luminescence (λexc = 314 nm) and nonlinear optical properties (0.75× KDP). A two-dimensional (2D) fingerprint analysis of the Hirshfeld surface plots revealed a significant difference between the hydrogen-bonding interaction before the phase transition and that afterwards. The two compounds were further verified, from energy band structure calculations, to be direct-band-gap semiconductors. In conclusion, this work has provided a viable strategy, involving the application of chemical modifications, for designing various functional materials.

Halogen Engineering To Realize Regulable Multipolar Axes, Nonlinear Optical Response, and Piezoelectricity in Plastic Ferroelectrics.

Compared with uniaxial molecular ferroelectrics, multiaxial ferroelectrics have better application prospects because they are no longer subject to the single-crystal form and have been pursued in recent years. Halogen engineering refers to the adjustment of halogens in materials at the atomic level, which can not only explore multiaxial ferroelectrics but also help to improve piezoelectrics, recently. In this work, we successfully synthesized and characterized three multiaxial plastic ferroelectrics through the precise molecular design from I to Cl, confirming the increase of the number of polar axes of ferroelectrics from 3 to 6, the increase of second-harmonic generation density from 2.1 times to nearly 6 times of monopotassium phosphate, and the increase of piezoelectric coefficient by 140%. This systematic work has proved that halogen engineering can not only enrich the family of multiaxial plastic ferroelectrics but also promote the further development of nonlinear optical and piezoelectric materials.

Metal ion induced dual switchable dielectric and luminescent properties in hybrid halides.

A new multi-functional organic-inorganic hybrid compound was successfully obtained by regulating metal halides. Apart from excellent luminescence properties, in particular, the introduction of a Mn halide successfully achieved a dual-switchable dielectric property, which could lead to very interesting exploration in sensors.

Integrated Reversible Thermochromism, High Tc , Dielectric Switch and Narrow Band Gap in One Multifunctional Ferroic.

Organic-inorganic Hybrid (OIH) materials for multifunctional switchable applications have attracted enormous attention in recent years due to their excellent optoelectronic properties and good structural tunability. However, it still remains challenging to fabricate one simple OIH compound with multi-functionals properties, such as dielectric switching, thermochromic properties, semiconductor characteristics and ferroelasticity. Under this context, we successfully synthesized [2-(2-fluorophenyl)ethan-1- ammonium]2 SnBr6 (compound 1), which has a higher phase transition temperature of 427.7 K. Additionally, it exhibits a semiconducting property with an indirect band gap of 2.36 eV. Combining ferroelastic, narrow band gap, thermochromic, and dielectric properties, compound 1 can be considered as a rarely reported multi-functional ferroelastic material, which is expected to give inspiration for broadening the applications in the smart devices field.

Chlorine Substitution in Spirocyclic Derivatives Triggers SHG Response in Noncentrosymmetric Crystal.

Organic-inorganic hybrid phase transition materials with switchable properties have important potential applications in smart devices such as dielectric switches and storage. Nevertheless, it remains challenging to modify molecular structures efficiently to obtain materials simultaneously possessing multiple responsive properties. Herein, different from ordinary halogen substitutions in Metal Halide, we report a halogen regulation design of organic molecular strategy: (ASD)2 MnBr4 (ASD=5-azonia-spiro [4.5] decane) to (CASD)2 MnBr4 (CASD=8-chloro-5-azonia-spiro [4.5] decane). After organic molecular halogen regulation, the SHG response was excited and the dielectric phase transition temperature (Tc ) has also been greatly improved. Furthermore, under the irradiation of UV lamp, both showed green light with quantum yields above 50%. This work is of great significance for further exploration of multifunctional molecular switch materials through halogen modification strategies.

Competitive Dual-Emission-Induced Thermochromic Luminescence in Organic-Metal Halides.

Lead-free Halides, especially Mn-based ones, are preferred as hotspots in the exploration of photoluminescent materials. However, there are few reports on sensitive reversible thermochromism and switchable dual emission originating from self-trapped exciton emission in pure Mn-Based materials. Here, we report a new Mn-based hybrid material [TMPA]2MnI4 (TMPA = trimethylphenylammonium), which shows two emission peaks at 545 and 660 nm benefitting from the d-d orbital transition of Mn2+ and the generation of self-trapped excitons, respectively. Due to the different sensitivity to temperature, the stages of thermal activation and thermal quenching of the two emission types are also inconsistent, showing a certain competition relationship and dominating the emission colors in different temperature ranges, resulting in adjustable green-orange-green thermochromic luminescence from 100 to 403 K (both high and low temperatures correspond to green, and orange is displayed at near room temperature). Therefore, thermochromic luminescence can be easily achieved by controlling the temperature under the guidance of excited states. This work provides new insights into the synthesis and application of thermochromic materials. Therefore, it is certain that regulating temperature while being guided by excited states will achieve thermochromic luminescence. This research offers fresh perspectives on the development and potential of thermochromic materials.