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For environment friendly water splitting, development of highly efficient and stable oxygen evolution reaction (OER) catalyst composed of earth abundant elements is very challenging. Herein, highly efficient OER catalysts TMS@MOF-5 have been prepared by in-situ incorporation of pre-synthesized various transition metal sulfide (TMS = MnS, FeS, CoS, NiS, CuS and ZnS) nanoparticles into MOF-5. Structure, morphology and composition of prepared samples have been analyzed by powder X-ray diffraction, Fourier Transform Infrared Spectroscopy, Raman Spectroscopy, Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy, Elemental Mapping and Ultraviolet–Visible Spectroscopy. OER activity of all these samples was determined by coating them on Ni-foam to form TMS@MOF-5/NF as working electrode through cyclic voltammetry. Among all the samples, NiS@MOF-5/NF exhibited excellent stability and OER catalytic activity as it required just 174 mV overpotential to achieve the 10mAcm−2current density, which is better than many other 3d transition metal based and Ni-based OER catalysts. Present study provides new way to design more efficient Ni-based catalysts for electrochemical water splitting applications.

Solid–solid phase transition materials have attracted increasing attention because of their variety of applications in optoelectronic devices, data storage, and ferroelectric field-effect transistors. Hybrid organic–inorganic perovskite materials combine the characteristics of organic and inorganic components and thus might be promising candidates to obtain phase-transition materials. Here, we report a lead-free organic–inorganic hybrid (hexamethyleneimine)2BiBr5 (1), which displays successive phase transitions at 268 K, 304 K and 311 K upon heating; these phase transitions are induced by the distorted configurational change in organic cations and slight reorientational displacement of [BiBr5]n2− polyanionic zigzag chains. In addition, the UV/Vis optical spectrum indicates that 1 has an indirect bandgap of 2.70 eV. Furthermore, computational analyses disclose that the inorganic perovskite-like building blocks of 1 contribute significantly to its semiconducting properties. This study offers a pathway to explore new lead-free organic–inorganic hybrids with phase transition.

In the fields of chemical graph theory, topological index is a type of a molecular descriptor that is calculated based on the graph of a chemical compound. Topological indices help us collect information about algebraic graphs and give us mathematical approach to understand the properties of algebraic structures. With the help of topological indices, we can guess the properties of chemical compounds without performing experiments in wet lab. There are more than 148 topological indices in the literature, but none of them completely give all properties of under study compounds. Together, they do it to some extent; hence, there is always room to introduce new indices. In this paper, we present first and second reserve Zagreb indices and first reverse hyper-Zagreb indices, reverse GA index, and reverse atomic bond connectivity index for the crystallographic structure of molecules. We also present first and second reverse Zagreb polynomials and first and second reverse hyper-Zagreb polynomials for the crystallographic structure of molecules.

Carbon-carbon coupling play a vital role in the synthetic field of organic chemistry. Two novel pyridine derivatives: 3-bromo-5-(2,5-difluorophenyl)pyridine ( 1 ) and 3,5-bis(naphthalen-1-yl)pyridine ( 2 ) were synthesized via carbon-carbon coupling, characterized by XRD, spectroscopic techniques and also investigated by using density functional theory (DFT). XRD data and optimized DFT studies are found to be in good correspondence with each other. The UV–Vis analysis of compounds under study i.e. ( 1 ) and ( 2 ) was obtained by using “TD-DFT/B3LYP/6-311 + G(d,p)” level of theory to explain the vertical transitions. Calculated FT-IR and UV–Vis results are found to be in good agreement with experimental FT-IR and UV–Vis findings. Natural bond orbital (NBO) study was performed using B3LYP/6-311 + G(d,p) level to find the most stable molecular structure of the compounds. Frontier molecular orbital (FMO) analysis were performed at B3LYP/6-311 + G(d,p) level of theory, which indicates that the molecules might be bioactive. Moreover, the bioactivity of compounds ( 1 ) and ( 2 ) have been confirmed by the experimental activity in terms of zones of inhibition against bacteria and fungus. Chemical reactivity of compounds (1) and (2) was in dicated by mapping molecular electrostatic potential (MEP) over the entire stabilized geometries of the compounds under study. The nonlinear optical properties were computed with B3LYP/6-311 + G(d,p) level of theory which are found greater than the value of urea due to conjugation effect. Two state model has been further employed to explain the nonlinear optical properties of compounds under investigation.

To switch quadratic nonlinear optical (NLO) effects has become an exciting branch of the NLO material science. However, solid-state molecular crystals showing tunable and switchable NLO behaviors remain scarce. Here, we report an organic picrate-based binary molecular crystal, triethylammonium picrate (TEAP), which undergoes an above-room-temperature phase transition at Tc = 319 K, being solidly confirmed by the thermal and dielectric measurements. A large thermal hysteresis of ∼7 K discloses the first-order feature for its phase transition. More strikingly, the quadratic NLO effects of TEAP can be switched in the vicinity of Tc. That is, TEAP exhibits NLO-active response of ∼1.5 times as large as that of KDP below Tc (i.e., NLO-on state), while its NLO effects totally disappear above Tc (NLO-off state). Structure analyses disclose that the order-disorder transformations of triethylammonium cations and picrate anions collectively contribute to its phase transition, as well as switchable NLO behaviors. This work opens up a new pathway to the designing and assembling of stimuli-responsive materials.

An organic–inorganic semiconducting compound of 1-methylpiperidinium triiodoplumbate(II) (MPIP), adopting a one-dimensional ABX3 perovskite-like structure, has been synthesized. It is notable that MPIP undergoes a structural phase transition (SPT) at Tc ≅ 202 K, as confirmed by DSC and Cp analyses. Strikingly, MPIP exhibits remarkable switchable dielectric responses; that is, the distinct step-like anomalies in the vicinity of Tc. The switching between high-dielectric and low-dielectric states makes MPIP a potential switchable dielectric material. Single-crystal structural analysis reveals that the most distinct difference between its high-temperature phase (above Tc) and low-temperature phase (below Tc) is the order–disorder transformation of a 1-methylpiperidinium cation, which accounts for its SPT and striking dielectric response. Besides this, MPIP shows semiconducting behaviour with an optical bandgap of ∼2.48 eV, comparable to some other lead-iodide perovskites. The combination of semiconducting and dielectric attributes provides a new perspective for the design of hybrid perovskites as multifunctional materials.

A new molecule-based compound, N-ethyl-n-butylammonium 3, 5-dinitrobenzoate monohydrate, which undergoes a reversible solid-state phase transition at 197 K (Tc), has been successfully constructed based on long-chain alkylamine. Specific heat capacity and differential scanning calorimetry (DSC) measurements confirm that it is first-order phase transition with a 5 K thermal hysteresis between heating and cooling scans. Dielectric constants exhibit distinct anomalies around Tc accompanied with step-like responses between low and high dielectric states, which further confirm the phase transition. Variable-temperature single-crystal X-ray diffraction analyses illustrate that the phase transition was elucidated from ordering of the flexible N-ethyl-n-butylammonium cations coupled with reorientational motion of the alkylamine chain.

A novel molecular phase transition material (PTM), 1-methylpiperidinium perchlorate [18-crown-6] monohydrate (1), has been synthesized, which exhibits reversible switchable dielectric anomalies near room temperature. The phase transition in 1 is from noncentrosymmetric to noncentrosymmetric, displaying non-linear optical (NLO) properties with a second harmonic generation response of ∼0.8 times compared to that of potassium dihydrogen phosphate. Thermal analyses of 1, including differential scanning calorimetry and specific heat measurements, confirm the first-order solid-state phase transition at 260 K. The dielectric constants display temperature-dependent anomalies with the temperature approaching the transition point (Tc), where the evident step-like anomalies demonstrate two distinct states below and above the Tc value, respectively. Variable-temperature single crystal X-ray diffraction discloses that the origin of its phase transition is ascribed to the order–disorder transformation of perchlorate anion, the methyl group of cation and the torsional angular change in crown molecule; that is, all three components contribute to the emergence of this phase transition. This result suggests that 1 could be conceived as a potential switchable dielectric and NLO material, which provides an effective approach to design novel NLO switch materials.

A novel molecular switchable dielectric material N-methylpyrrolidinium hydrogen tartrate (NMPHT) has been synthesized, which undergoes above room temperature phase transition. Thermal measurements, e.g. differential scanning calorimetry and specific heat, confirm the presence of a phase transition around 317.5 K. The dielectric measurement displays a distinct step-like anomaly around Tc, showing two different dielectric states, which reveals that NMPHT is a switchable dielectric material. The single-crystal X-ray diffraction analyses at variable temperatures demonstrate that the phase transition emerges from the severe disordering of the N-methylpyrrolidinium (NMP) cation, and during the transition the symmetry of NMPHT is transformed from higher (C2/c) to lower (P21/n). These findings will provide a new horizon to design smart dielectric structural phase transition materials by incorporating a flexible NMP based scaffold.

A new organic–inorganic ABX3 perovskite-type semiconducting hybrid, N-methylpyrrolidinium trichlorocadmate (MPCC), has been synthesized. It is found that MPCC exhibits semiconducting behaviour with an optical bandgap of ∼4.65 eV, as well as remarkable dielectric switching properties. It displays a structural phase transition (SPT) at Tc = 254 K, being confirmed by DSC and specific heat measurements. Dielectric measurements display distinct step-like anomalies around Tc, suggesting MPCC as a switchable dielectric material. Variable temperature single-crystal X-ray diffraction reveals that symmetry-breaking occurs from Pnma (at 280 K, >Tc) to P21/c (at 230 K

A new high-temperature, hybrid, phase-transition material, 1-methylpiperidinium tetrabromozincate (1), that shows a reversible transition at 345 K was synthesized. Differential scanning calorimetry and specific heat capacity measurements confirmed this reversible transformation with a large heat hysteresis of 25 K, which describes a typical first-order phase transition in 1. The dielectric constant exhibited a steplike anomaly and showed high and low dielectric states in the high- and room-temperature phases, respectively, and therefore, this hybrid might be considered as a potential switchable dielectric material. The variable-temperature powder X-ray diffraction patterns displayed remarkable shifts between the experimental patterns at the two different phases. Single-crystal X-ray diffraction analyses at various temperatures revealed that the origin of this transformation could be attributed to disordering of the bromine atoms in the anion and the nitrogen atom of the cation. The cation also assumed a conformational change, which was likely induced by the disordered nitrogen atom. The conformational onset of the transformation of the cation from a planar conformer into a relaxed chair also occurred upon decreasing the temperature below transition point; thus, the combined order-disorder and conformational change induced the structural transformation and the change in symmetry.

A new molecular-ionic phase transition material, N-butyldiethanolammonium picrate monohydrate (BEAPM), which exhibits reversible switchable dielectric performances, has been successfully assembled. This compound undergoes a first-order solid-state phase transition at 160 K (Tc), which is confirmed by the thermal analyses including differential scanning calorimetry (DSC), specific heat (Cp) and dielectric measurements. Variable-temperature single crystal X-ray diffraction reveals that the origin of its phase transition is ascribed to the order–disorder transformation of oxygen atoms of the poly-nitro aromatic system, i.e. the picrate anions. Interestingly, the dielectric constants display clear temperature-dependant anomalies with the temperature approaching to Tc. The evident step-like anomalies of dielectric constants demonstrate two distinct states below and above the Tc, respectively. This result signifies that BEAPM could be conceived as a potential switchable dielectric material. These findings make us believe that BEAPM might be a potential solid–solid dielectric phase transition material.

A novel phase transition has been discovered where the phase transition is primarily accomplished by the order–disorder transformation of metal-coordinated halogen atoms in an organic–inorganic hybrid material [(C6H14)NH2]2·CuBr4 (1). Its phase transition behaviour was verified by specific heat capacity (Cp) and differential scanning calorimetry (DSC) measurements with a thermal hysteresis at 4.8 K. The dielectric measurements of 1 show a distinct step-like anomaly around Tc, demonstrating two states at two different phases, which enlightens that 1 can be conceived as a potential switchable dielectric material. Moreover, temperature-dependent single-crystal X-ray diffraction analyses of 1 disclose that disordering of metal-halides together with reorientations of the cations is the cause of this unique phase-transition material. All these results open a new way to design and assemble novel phase transition materials.

Bistable N-H···N hydrogen bonds between rotors and stators enable delicate modulation of dynamic molecular motion by slowing down the fast rotation in a N-H···N hydrogen-bonded organic co-crystal of 1,2-diazabicyclo(2.2.2)octane bis(thiourea), which has been elucidated by the combination of variable-temperature (VT) X-ray structure analyses and VT solid-state nuclear magnetic resonance techniques.

Perovskite-type ferroelectrics composed of organometallic halides are emerging as a promising alternative to conventional photovoltaic devices because of their unique photovoltaic effects (PVEs). A new layered perovskite-type photoferroelectric, bis(cyclohexylaminium) tetrabromo lead (1), is presented. The material exhibits an exceptional anisotropy of bulk PVEs. Upon photoexcitation, superior photovoltaic behaviors are created along its inorganic layers, which are composed of corner-sharing PbBr6 octahedra. Semiconducting activity with remarkable photoconductivity is achieved in the vertical direction, showing sizeable on/off current ratios (>10(4) ), which compete with the most active photovoltaic material CH3 NH3 PbI3 . In 1 the temperature-dependence of photovoltage coincides fairly well with that of polarization, confirming the dominant role of ferroelectricity in such highly anisotropic PVEs. This finding sheds light on bulk PVEs in ferroelectric materials, and promotes their application in optoelectronic devices.

A beryllium-free deep-ultraviolet (deep-UV) nonlinear optical (NLO) material K3Ba3Li2Al4B6O20F is developed mainly by the element substitution of Be for Al and Li from Sr2Be2B2O7 that was considered as one of the most promising deep-UV NLO materials. K3Ba3Li2Al4B6O20F preserves the structural merits of Sr2Be2B2O7 and thus exhibits no layering growth tendency and possesses the optical properties required for deep-UV NLO applications, including deep-UV transparency, phase-matchability, and sufficiently large second-harmonic generation (1.5 × KH2PO4). Furthermore, it overcomes the structural instability problem of Sr2Be2B2O7, which is confirmed by the obtainment of large single crystals and phonon dispersion calculations. These attributes make it very attractive for next-generation deep-UV NLO materials. The substitution of Be for Al and Li in beryllium borates provides a new opportunity to design beryllium-free deep-UV NLO materials with good performance.

Parasitic Cuscuta reflexa Roxb. possesses many medicinal properties and is a rich source of a variety of biologically relevant natural products. Natural products are the prime source of leads, drugs, and drug templates, and many of the anticancer and antiviral drugs are either based on natural product or derived from them. Cancer is a devastating disease and one of the leading causes of death worldwide despite improvements in patient survival during the past 50 years; new and improved treatments for cancer are therefore actively sought. Colorectal cancer is the fourth most prevalent cancer worldwide and is responsible for nearly 9% of all cancer deaths. Our search for anticancer natural products from C. reflexa has yielded four natural products: Scoparone (1), p-coumaric acid (2), stigmasta-3,5-diene (3) and 1-O-p-hydroxycinnamoylglucose (4) and among them 1-O-p-hydroxycinnamoyldlucose (4) showed promising antiproliferative activities in HCT116 colorectal cell lines, whereas compounds 1–3 showed moderate activities.