Control of the Hydroquinone/Benzoquinone Redox State in High-Mobility Semiconducting Conjugated Coordination Polymers.

Conjugated coordination polymers (c-CPs) are unique organic-inorganic hybrid semiconductors with intrinsically high electrical conductivity and excellent charge carrier mobility. However, it remains a challenge in tailoring electronic structures, due to the lack of clear guidelines. Here, we develop a strategy wherein controlling the redox state of hydroquinone/benzoquinone (HQ/BQ) ligands allows for the modulation of the electronic structure of c-CPs while maintaining the structural topology. The redox-state control is achieved by reacting the ligand TTHQ (TTHQ=1,2,4,5-tetrathiolhydroquinone) with silver acetate and silver nitrate, yielding Ag4TTHQ and Ag4TTBQ (TTBQ=1,2,4,5-tetrathiolbenzoquinone), respectively. In spite of sharing the same topology consisting of a two-dimensional Ag-S network and HQ/BQ layer, they exhibit different band gaps (1.5 eV for Ag4TTHQ and 0.5 eV for Ag4TTBQ) and conductivities (0.4 S/cm for Ag4TTHQ and 10 S/cm for Ag4TTBQ). DFT calculations reveal that these differences arise from the ligand oxidation state inhibiting energy band formation near the Fermi level in Ag4TTHQ. Consequently, Ag4TTHQ displays a high Seebeck coefficient of 330 µV/K and a power factor of 10 µW/m ⋅ K2, surpassing Ag4TTBQ and the other reported silver-based c-CPs. Furthermore, terahertz spectroscopy demonstrates high charge mobilities exceeding 130 cm2/V ⋅ s in both Ag4TTHQ and Ag4TTBQ.

Variation of the Orientations of Organic Structure-Directing Agents inside the Channels of SCM-14 and SCM-15 Germanosilicates Obtained by Ab Initio Molecular Dynamic Simulations.

We report ab initio molecular dynamic simulations of the organic structure-directing agent (OSDA) in the channels of SCM-14 and SCM-15 germanosilicates for models with different germanium distribution. Since OSDA was free to move inside the channels, independent of its initial orientation after the simulations in all structures the OSDA, protonated 4-pyrrolidinopyridine, is positioned almost perpendicular to the large channels of SCM-14. The structures obtained from the dynamic simulation are more stable by 157 to 331 kJ/mol than the structures obtained by initial geometry optimization. After simulations, the average distance between the N atom of the pyridine moiety of the OSDA and O from Ge-O-Ge is shorter by 0.2 Å than the same distance obtained from initial optimization. The stretching N-H frequencies in the IR spectra of the OSDA and other calculated vibrational frequencies are not characteristic of the orientation of the molecule and cannot be used to detect it.

Visualizing the Flexibility of RHO Nanozeolite: Experiment and Modeling.

Structural flexibility is an intrinsic feature of zeolites, and the characterization of such dynamic behavior is key to maximizing their performance and realizing their potential in both existing and emerging applications. Here, the flexibility of a high-aluminum nano-sized RHO zeolite is directly visualized with in situ TEM for the first time. Variable temperature experiments directly observe the physical expansion of the discrete nanocrystals in response to changes in both guest-molecule chemistry (Ar vs CO2) and temperature. The observations are complemented by operando FTIR spectroscopy verifying the nature of the adsorbed CO2 within the pore network, the desorption kinetics of carbonate species, and changes to the structural bands at high temperatures. Quantum chemical modeling of the RHO zeolite structure substantiates the effect of cation (Na+ and Cs+) mobility in the absence and presence of CO2 on the flexibility behavior of the structure. The results demonstrate the combined influences of temperature and CO2 on the structural flexibility consistent with the experimental microscopy observations.

Experimental and Theoretical Study on the Homodimerization Mechanism of 3-Acetylcoumarin.

In the present study, the reaction conditions for homodimerization process of 3-acetylcoumarin were achieved under sonication using combination of zinc and metallic salt (ZnCl2 or Zn(OAc)2). Appropriate frequency and sound amplitude have been identified as significant variables for the initiation of the reaction. On the base of first principal calculations and experimental results, the mechanism of the reaction was investigated. The relative stability of the possible intermediates has been compared, including evaluation on the ionic and radical reaction pathways for the dimerization process. Theoretical results suggested that the radical mechanism is more favorable. The C-C bond formation between the calculated radical intermediates occurs spontaneously (∆G = -214 kJ/mol for ZnCl2, -163 kJ/mol in the case of Zn(OAc)2), which proves the possibility for the homodimerization of 3-acetylcoumarin via formation of radical species. Both experimental and theoretical data clarified the activation role of the solvent on the reactivity of the Zn-salt. The formation of complexes of solvent molecules with Zn-atom from the ZnCl2 reduces the energy barrier for the dissociation of Zn-Cl bond and facilitate the formation of the dimeric product.

Defect Formation, T-Atom Substitution and Adsorption of Guest Molecules in MSE-Type Zeolite Framework-DFT Modeling.

We used computational modeling, based on Density Functional Theory, to help understand the preference for the formation of silanol nests and the substitution of Si by Ti or Al in different crystallographic positions of the MSE-type framework. All these processes were found to be energetically favorable by more than 100 kJ/mol. We suggested an approach for experimental identification of the T atom position in Ti-MCM-68 zeolite via simulation of infrared spectra of pyridine and acetonitrile adsorption at Ti. The modeling of adsorption of hydrogen peroxide at Ti center in the framework has shown that the molecular adsorption was preferred over the dissociative adsorption by 20 to 40 kJ/mol in the presence or absence of neighboring T-atom vacancy, respectively.

Interfacial Synthesis of Layer-Oriented 2D Conjugated Metal-Organic Framework Films toward Directional Charge Transport.

The development of layer-oriented two-dimensional conjugated metal-organic frameworks (2D c-MOFs) enables access to direct charge transport, dial-in lateral/vertical electronic devices, and the unveiling of transport mechanisms but remains a significant synthetic challenge. Here we report the novel synthesis of metal-phthalocyanine-based p-type semiconducting 2D c-MOF films (Cu2[PcM-O8], M = Cu or Fe) with an unprecedented edge-on layer orientation at the air/water interface. The edge-on structure formation is guided by the preorganization of metal-phthalocyanine ligands, whose basal plane is perpendicular to the water surface due to their π-π interaction and hydrophobicity. Benefiting from the unique layer orientation, we are able to investigate the lateral and vertical conductivities by DC methods and thus demonstrate an anisotropic charge transport in the resulting Cu2[PcCu-O8] film. The directional conductivity studies combined with theoretical calculation identify that the intrinsic conductivity is dominated by charge transfer along the interlayer pathway. Moreover, a macroscopic (cm2 size) Hall-effect measurement reveals a Hall mobility of ∼4.4 cm2 V-1 s-1 for the obtained Cu2[PcCu-O8] film. The orientation control in semiconducting 2D c-MOFs will enable the development of various optoelectronic applications and the exploration of unique transport properties.

Correction: Individual control of singlet lifetime and triplet yield in halogen-substituted coumarin derivatives.

[This corrects the article DOI: 10.1039/D0RA05737A.].

Engineering crystalline quasi-two-dimensional polyaniline thin film with enhanced electrical and chemiresistive sensing performances.

Engineering conducting polymer thin films with morphological homogeneity and long-range molecular ordering is intriguing to achieve high-performance organic electronics. Polyaniline (PANI) has attracted considerable interest due to its appealing electrical conductivity and diverse chemistry. However, the synthesis of large-area PANI thin film and the control of its crystallinity and thickness remain challenging because of the complex intermolecular interactions of aniline oligomers. Here we report a facile route combining air-water interface and surfactant monolayer as templates to synthesize crystalline quasi-two-dimensional (q2D) PANI with lateral size ~50 cm2 and tunable thickness (2.6-30 nm). The achieved q2D PANI exhibits anisotropic charge transport and a lateral conductivity up to 160 S cm-1 doped by hydrogen chloride (HCl). Moreover, the q2D PANI displays superior chemiresistive sensing toward ammonia (30 ppb), and volatile organic compounds (10 ppm). Our work highlights the q2D PANI as promising electroactive materials for thin-film organic electronics.

A semiconducting layered metal-organic framework magnet.

The realization of ferromagnetism in semiconductors is an attractive avenue for the development of spintronic applications. Here, we report a semiconducting layered metal-organic framework (MOF), namely K3Fe2[(2,3,9,10,16,17,23,24-octahydroxy phthalocyaninato)Fe] (K3Fe2[PcFe-O8]) with spontaneous magnetization. This layered MOF features in-plane full π-d conjugation and exhibits semiconducting behavior with a room temperature carrier mobility of 15 ± 2 cm2 V-1 s-1 as determined by time-resolved Terahertz spectroscopy. Magnetization experiments and 57Fe Mössbauer spectroscopy demonstrate the presence of long-range magnetic correlations in K3Fe2[PcFe-O8] arising from the magnetic coupling between iron centers via delocalized π electrons. The sample exhibits superparamagnetic features due to a distribution of crystal size and possesses magnetic hysteresis up to 350 K. Our work sets the stage for the development of spintronic materials exploiting magnetic MOF semiconductors.

Optimization and in-vitro/in-vivo evaluation of doxorubicin-loaded chitosan-alginate nanoparticles using a melanoma mouse model.

The present study evaluates the potential of encapsulated doxorubicin to reduce both the viability of melanoma cells and the tumor growth in a mouse melanoma model. The prepared doxorubicin loaded chitosan/alginate nanoparticles possessed mean diameter around 300 nm and negative zeta-potential. Classical molecular dynamic simulations revealed that the high encapsulation efficiency (above 90%) was mainly due to electrostatic interaction between doxorubicin and sodium alginate, although dipole-dipole and hydrophobic interactions might also contribute. The in vitro dissolution tests showed slower doxorubicin release in slightly alkaline medium (pH = 7.4) and faster release in acid one (pH = 5.5), indicating that higher concentration of doxorubicin might reach the acidic tumor tissue. The free and the encapsulated doxorubicin decreased the viability of melanoma cell lines (B16-F10 and B16-OVA) in a similar degree. However, the cytotoxic effect of the encapsulated doxorubicin still occurred in the more resistant B16-F10 cells even after removing the extracellular drug. The experiments on a syngeneic melanoma mouse model revealed that free and encapsulated doxorubicin elicited the control of the tumor growth (dose of 3 mg/kg). Thus, the encapsulation of doxorubicin into chitosan/alginate nanoparticles could be considered advantageous because of the better intracellular accumulation and longer cytotoxic effect on the investigated melanoma cells.

Conformational isomerism controls collective flexibility in metal-organic framework DUT-8(Ni).

Metal-organic frameworks (MOFs) are coordination networks with organic ligands containing potential voids. Some MOFs show pronounced structural flexibility that may result in closing and re-opening these pores. Here, we show that collective flexibility in a MOF-DUT-8(Ni) - is controlled by conformational isomerism. DUT-8(Ni), a pillared-layer MOF with Ni2 paddle-wheels, dabco pillars and naphthalene dicarboxylate (ndc) linkers, can crystallize in many conformational isomers that depend on the orientation of the non-linear ndc linkers with respect to each other. While the open form is compatible with several of these conformations, only one of them, with alternating linker orientations, is stable as the closed form. We show, by means of first principles calculations, that in the stable closed form, the appreciable lattice strain is compensated by London-dispersion forces between the ndc linkers that arrange with maximum overlap in a stacking order similar to the stacking in graphite. We substantiate these results by well-tempered metadynamics calculations on the DFT-based Born-Oppenheimer potential energy surface, by refined X-ray diffraction data and by nitrogen adsorption data obtained by experiment and grand-canonical Monte-Carlo simulations based on the DFT-optimized and PXRD-derived geometries. While the reported origin of flexibility cannot be generalized to all flexible MOFs, it offers a rational design concept of folding mechanisms in switchable MOFs by exploitation of the stabilization effect of linker stacking in the closed form.

High-mobility band-like charge transport in a semiconducting two-dimensional metal-organic framework.

Metal-organic frameworks (MOFs) are hybrid materials based on crystalline coordination polymers that consist of metal ions connected by organic ligands. In addition to the traditional applications in gas storage and separation or catalysis, the long-range crystalline order in MOFs, as well as the tunable coupling between the organic and inorganic constituents, has led to the recent development of electrically conductive MOFs as a new generation of electronic materials. However, to date, the nature of charge transport in the MOFs has remained elusive. Here we demonstrate, using high-frequency terahertz photoconductivity and Hall effect measurements, Drude-type band-like transport in a semiconducting, π-d conjugated porous Fe3(THT)2(NH4)3 (THT, 2,3,6,7,10,11-triphenylenehexathiol) two-dimensional MOF, with a room-temperature mobility up to ~ 220 cm2 V-1 s-1. The temperature-dependent conductivity reveals that this mobility represents a lower limit for the material, as mobility is limited by impurity scattering. These results illustrate the potential for high-mobility semiconducting MOFs as active materials in thin-film optoelectronic devices.

Interaction of Na+, K+, Mg2+ and Ca2+ counter cations with RNA.

Alkaline and alkaline earth ions, namely Na+, K+, Mg2+ and Ca2+, are critical for the stability, proper folding and functioning of RNA. Moreover, those metal ions help to facilitate macromolecular interactions as well as the formation of supramolecular structures (e.g. the ribosome and the ribozymes). Therefore, identifying the interactions between ions and nucleic acids is a key to the better comprehension of the physical nature and biological functions of those biomolecules. The scope of this review is to highlight the preferential location and binding sites of alkaline and alkaline earth metal ions compensating the negatively charged backbone of nucleic acids and interacting with other electronegative centers, focusing on RNA. We summarize experimental studies from X-ray crystallography and spectroscopic analysis (infrared, Raman and NMR spectroscopies). Computational results obtained with classical and ab initio methods are presented afterwards.

Dynamics of the OH stretching mode in crystalline Ba(ClO4)2·3H2O.

The vibrational dynamics of the OH stretching mode in Ba(ClO4)2 trihydrate are investigated by means of femtosecond infrared spectroscopy. The sample offers plane cyclic water trimers in the solid phase that feature virtually no hydrogen bond interaction between the water molecules. Selective excitation of the symmetric and asymmetric stretching leads to fast population redistribution, while simultaneous excitation yields quantum beats, which are monitored via a combination tone that dominates the overtone spectrum. The combination of steady-state and time-resolved spectroscopy with quantum chemical simulations and general theoretical considerations gives indication of various aspects of symmetry breakage. The system shows a joint population lifetime of 8 ps and a long-lived coherence between symmetric and asymmetric stretching, which decays with a time constant of 0.6 ps.

Solid state organic amine detection in a photochromic porous metal organic framework.

A new Mg(ii) based photochromic porous metal-organic framework (MOF) has been synthesized bearing naphthalenediimide (NDI) chromophoric unit. This MOF (Mg-NDI) shows instant and reversible solvatochromic behavior in presence of solvents with different polarity. Mg-NDI also exhibits fast and reversible photochromism via radical formation. Due to the presence of electron deficient NDI moiety, this MOF exhibits selective organic amine (electron rich) sensing in solid state. The organic amine detection has been confirmed by photoluminescence quenching experiment and visual color change.

Ab initio molecular dynamics of Na⁺ and Mg²âº countercations at the backbone of RNA in water solution.

The interactions between sodium or magnesium ions and phosphate groups of the RNA backbone represented as dinucleotide fragments in water solution have been studied using ab initio Born-Oppenheimer molecular dynamics. All systems have been simulated at 300 and 320 K. Sodium ions have mobility higher than that of the magnesium ions and readily change their position with respect to the phosphate groups, from directly bonded to completely solvated state, with a rough estimate of the lifetime of bonded Na(+) of about 20-30 ps. The coordination number of the sodium ions frequently changes in irregular intervals ranging from several femtoseconds to about 10 ps with the most frequently encountered coordination number five, followed by six. The magnesium ion is stable both as directly bonded to an oxygen atom from the phosphate group and completely solvated by water. In both states the Mg(2+) ion has exactly six oxygen atoms in the first coordination shell; moreover, during the whole simulation of more than 100 ps no exchange of ligand in the first coordination shells has been observed. Solvation of the terminal phosphate oxygen atoms by water molecules forming hydrogen bonds in different locations of the ions is also discussed. The stability of the system containing sodium ions essentially does not depend on the position of the ions with respect to the phosphate groups.