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1.
Solid State Nucl Magn Reson ; 97: 31-39, 2019 02.
Artigo em Inglês | MEDLINE | ID: mdl-30597399

RESUMO

Cellulose nanocrystal films with either disordered or chiral nematic structures of varying helical pitch were investigated using 23Na solid-state nuclear magnetic resonance (NMR) spectroscopy. Spin lattice relaxation of 1H correlated with 23Na analyzed by indirect observation using polarization transfer from 1H nuclei to 23Na nuclei showed that the Na+ cations are well hydrated in the cellulose nanocrystal films. Linewidth analysis in solid-state 23Na NMR showed that the Na+ cations move in confined spaces, and that the Na+ cations in the film having disordered structure are more dynamic than in the films having ordered structure. From lineshape analysis of the 23Na 2D nutation NMR spectra, we can distinguish the Na+ environments within the ordered and disordered films, and find trends in anisotropic interaction parameters between ordered samples with different pitches. These are the first detailed 23Na NMR spectroscopic studies of CNC-Na+ films, and they show that this technique may be a powerful probe for characterizing the extent of order in nanocellulose samples.

2.
Nat Commun ; 10(1): 479, 2019 01 29.
Artigo em Inglês | MEDLINE | ID: mdl-30696824

RESUMO

Confinement of polymers in nano-spaces can induce unique molecular dynamics and properties. Here we show molecular weight fractionation by the confinement of single polymer chains of poly(ethylene oxide) (PEO) in the one-dimensional (1D) channels of crystalline pillar[5]arene. Pillar[5]arene crystals are activated by heating under reduced pressure. The activated crystals are immersed in melted PEO, causing the crystals to selectively take up PEO with high mass fraction. The high mass fractionation is caused by the greater number of attractive CH/π interactions between PEO C-H groups and the π-electron-rich 1D channel of the pillar[5]arene with increasing PEO chain length. The molecular motion of the confined PEO (PEO chain thickness of ~3.7 Å) in the 1D channel of pillar[5]arenes (diameter of ~4.7 Å) is highly restricted compared with that of neat PEO.

3.
J Am Chem Soc ; 141(2): 785-789, 2019 Jan 16.
Artigo em Inglês | MEDLINE | ID: mdl-30612427

RESUMO

State change is a key phenomenon in materials science. We report the first observation of vapor-responsive reversible structural liquid-to-solid and solid-to-structural liquid state changes. We observed that a macrocyclic compound, a pillar[6]arene derivative bearing 12 n-hexyl substituents, is a room temperature structural liquid with unique properties. Formation of a host-guest complex between the pillar[6]arene cavity and the n-hexyl substituent results in a structural liquid with nanoscale structural heterogeneities. The structural liquid solidifies when exposed to competitive cyclohexane guest vapor, whereupon cyclohexane replaces the n-hexyl substituents in the pillar[6]arene cavity and the n-hexyl substituents located outside of the cavity crystallize into distinct nanolayer assemblies. The solid reverts back to the structural liquid when the cyclohexane guest is removed through heating under reduced pressure because of rethreading of the n-hexyl substituents into the cavity. The structural liquid-to-solid and solid-to-structural liquid changes are reversible through the uptake and release of cyclohexane guest vapor.

4.
Chemistry ; 25(10): 2497-2502, 2019 Feb 18.
Artigo em Inglês | MEDLINE | ID: mdl-30565324

RESUMO

Host-guest complexation has been mainly investigated in solution, and it is unclear how guest molecules access the assembled structures of host and dynamics of guest molecules in the crystal state. In this study, we studied the uptake, release, and molecular dynamics of n-hexane vapor in the crystal state of pillar[5]arenes bearing different substituents. Pillar[5]arene bearing 10 ethyl groups yielded a crystal structure of herringbone-type 1:1 complexes with n-hexane, whereas pillar[5]arene with 10 allyl groups formed 1:1 complexes featuring a one-dimensional (1D) channel structure. For pillar[5]arene bearing 10 benzyl groups, one molecule of n-hexane was located in the cavity of pillar[5]arene, and another n-hexane molecule was located outside of the cavity between two pillar[5]arenes. The substituent-dependent differences in molecular arrangement influenced the uptake, release, and molecular dynamics of the n-hexane guest. The substituent effects were not observed in host-guest chemistry in solution, and these features are unique for the crystal state host-guest chemistry of pillar[5]arenes.

5.
Solid State Nucl Magn Reson ; 95: 12-16, 2018 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-30243098

RESUMO

Indium-doped zinc oxide, a potential alternative material to indium tin oxide, was analyzed in powder form via 67Zn magic angle spinning nuclear magnetic resonance (MAS NMR). The 67Zn MAS NMR results show that the line shapes of zinc oxide were broadened by sintering, which was also observed for indium-doped zinc oxide, in which the broadening also depended on the sintering time. Furthermore, the line shapes of indium-doped zinc oxide were significantly broader than those of the corresponding zinc oxide, and were independent of the degree of indium doping. This indicates that indium atoms are associated into cluster-like structures in this compound.

6.
Phys Chem Chem Phys ; 20(15): 10311-10318, 2018 Apr 18.
Artigo em Inglês | MEDLINE | ID: mdl-29610782

RESUMO

Composite materials of acidic polymers and basic molecules have high proton-conductivity. Understanding the proton conduction mechanism of the composite materials, which depends on hydrogen bond characteristics, is an important task for developing materials with high proton-conductivity. This work is focused on poly(vinylphosphonic acid)-imidazole and alginic acid-imidazole as examples of composite materials of acidic polymers and basic molecules and examines the local structure and hydrogen bond characteristics of imidazole (Im) molecules in composite materials using density functional theory. The results show that Im molecules interact strongly with polymeric acids in these composite materials and that the interaction energy increases with the increase in the number of Im molecules. The rotational motion of Im molecules occurs in the segment where only Im molecules without excess protons are hydrogen-bonded to each other. The calculation results for the various segments, which depend on the hydrogen bonding environment, show that the proton conduction process in composite materials consists of the following steps: proton transfer in the segment where Im molecules interact with polymeric acids, proton transfer in the segment where Im molecules are affected by excess protons, and Grotthuss diffusion with reorientation of Im molecules in the segment where only Im molecules without excess protons are bonded to each other.

7.
Org Biomol Chem ; 15(39): 8440-8447, 2017 Oct 11.
Artigo em Inglês | MEDLINE | ID: mdl-28952635

RESUMO

A pair of optically pure triptycene derivatives ((R,R)- and (S,S)-3) containing fluorescent pyrene-based π-conjugated pendant groups attached through amide spacers were prepared via a resolution step using chiral high-performance liquid chromatography. Their absorption, circular dichroism, photoluminescence and circularly polarized luminescence (CPL) properties were investigated under various solution conditions. (R,R)- and (S,S)-3 exhibited clear solvent- and concentration-dependences of the optical and chiroptical properties as a result of the interconversion between molecularly dispersed and aggregate states. We also observed that (R,R)- and (S,S)-3 emitted left- and right-handed circularly polarized light, respectively, upon UV irradiation under aggregation conditions, and their dissymmetry factors were found to be greater than 1.0 × 10-3. Based on the contrasting result that almost no CPL signal appeared in the monomeric solution state, the resulting CPL was considered to arise from the supramolecular chirality induced in the hydrogen-bonded aggregate, wherein the pyrenyl pendants of 3 were most likely arranged in a preferred-handed twisting structure.

8.
Phys Chem Chem Phys ; 19(25): 16857-16866, 2017 Jun 28.
Artigo em Inglês | MEDLINE | ID: mdl-28627543

RESUMO

We propose a simple method for potential construction in the diabatic picture and the estimation of thermal rate constants for intermolecular proton transfer reactions using quantum dynamics simulations carried out on the constructed potentials. For symmetrical and asymmetrical proton transfer pairs, the obtained potentials and rate constants were in good agreement with the reference values. Furthermore, our method is used for the analysis of proton transfer in crystalline imidazolium succinate and discusses the proton conductivity in terms of intermolecular proton transfer. This approach can be used to estimate proton transfer rate constants for large molecular systems, even when the calculation of the transition state is impossible.

9.
Phys Chem Chem Phys ; 18(27): 18555-62, 2016 Jul 21.
Artigo em Inglês | MEDLINE | ID: mdl-27346613

RESUMO

Thermodynamic and dynamic properties of water confined in mesoporous silica glass SBA-16 were investigated by DSC, and (1,2)H NMR spectroscopy and (2)H NMR spin-lattice relaxation time (T1) as a function of pore size. SBA-16 possesses the main spherical pores, interconnecting channels and micropores (corona). Water in the characteristic spherical pores of SBA-16 freezes at the homogeneous nucleation temperature of water. Between room and freezing temperatures, the correlation time of the isotropic rotation of water in the pores of SBA-16 followed the Vogel-Fulcher-Tammann (VFT) relation, which reflects the formation and growth of clusters of fragile water for changing to the strong water. The vitrification of water in micropores around 200 K was observed by (2)H NMR. Above 200 K, the correlation time of the rotation of water in micropores exhibited non-Arrhenius behavior, which is correlated with the gradual decrease in the mobility of water due to the growth of hydrogen bonding, forming low density water before vitrification. After vitrification, the activation energy of the rotation of water in micropores was 25-33 kJ mol(-1), which was similar to that in ice Ih for all samples. The freedom of cluster formation and water rotation increased with the increasing the pore size.

10.
J Phys Condens Matter ; 28(30): 304001, 2016 08 03.
Artigo em Inglês | MEDLINE | ID: mdl-27294380

RESUMO

Recent developments in the arena of charge-transfer complexes composed of the D 6h-symmetric polycyclic aromatic hydrocarbon, coronene, are highlighted with emphasis on the structural and physical properties of these complexes. Because of the dual electron-donating and -accepting abilities of coronene, this group involves structurally-defined four cation salts and three anion salts. The Jahn-Teller distortions and in-plane motion of coronene molecules in the solids, both of which are closely associated with the high symmetry of coronene molecules, and syntheses of clathrate-type complexes are also presented.

11.
Chemistry ; 22(17): 6023-30, 2016 Apr 18.
Artigo em Inglês | MEDLINE | ID: mdl-26989854

RESUMO

Coronene, which is the smallest D6h -symmetric polycyclic aromatic hydrocarbon, attracts particular attention as a basic component of electronic materials because it is the smallest fragment of graphene. However, carrier generation by physical methods, such as photo- or electric field-effect, has barely been studied, primarily because of the poor π-conduction pathway in pristine coronene solid. In this work we have developed unprecedented π-stacking columns of cationic coronene molecules by electrochemical hole-doping with polyoxometallate dianions. The face-to-face π-π interactions as well as the partially charged state lead to electrical conductivity at room temperature of up to 3 S cm(-1) , which is more than 10 orders of magnitude higher than that of pristine coronene solid. Additionally, the robust π-π interactions strongly suppress the in-plane rotation of the coronene molecules, which has allowed the first direct observation of the static Jahn-Teller distortion of cationic coronene molecules.

12.
Angew Chem Int Ed Engl ; 55(22): 6443-7, 2016 05 23.
Artigo em Inglês | MEDLINE | ID: mdl-27027409

RESUMO

The radical polymerization of vinyl monomers was performed in a tetrahedral imine-linked organic cage with extrinsic porosity (CC3). Because of its dynamic and responsive packing structure, CC3 endowed the polymerization with specific behaviors. The adsorption of styrene triggered a change in the CC3 assembly, resulting in a monomer arrangement that was suitable for polymerization within the host matrix. The polymerization reaction was strongly dependent on the crystallinity of CC3 and was promoted by amorphization of the host in a cooperative manner, which is not possible with conventional rigid porous materials. Furthermore, CC3 can recognize the polarity of substrates, and thus polar monomers, such as methyl methacrylate and acrylonitrile, could not induce the structural changes in CC3 that are required for polymerization. This monomer specificity governed by the flexibility of CC3 is useful to the prevent incorporation of unfavorable monomers into the polymeric products.

13.
Angew Chem Int Ed Engl ; 55(2): 708-13, 2016 Jan 11.
Artigo em Inglês | MEDLINE | ID: mdl-26609906

RESUMO

Strong interchain interactions render unsubstituted polythiophene un-fusible, non-melting, and insoluble. Therefore, control of the packing structure, which has a profound effect on the optical and electronic properties of the polymer, has never been achieved. Unsubstituted polythiophene was prepared in the one-dimensional channels of [La(1,3,5-benzenetrisbenzoate)]n, where polymer chains form unprecedented assembly structures mediated by the host framework. It is noteworthy that the emission and carrier transport properties were drastically changed by varying the number of chains within a particular assembly. The response of the composite to additional guests is also examined as a method to use the composites as low-concentration sensors. Our findings show that the encapsulation of polymer chains in host materials is a facile method for understanding the intrinsic properties of conjugated polymers, along with controlling and enhancing their functions.

14.
Chemistry ; 21(27): 9682-96, 2015 Jun 26.
Artigo em Inglês | MEDLINE | ID: mdl-26032896

RESUMO

A newly synthesized one-dimensional (1D) hydrogen-bonded (H-bonded) rhodium(II)-η(5)-semiquinone complex, [Cp*Rh(η(5)-p-HSQ-Me4)]PF6 ([1]PF6; Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl; HSQ = semiquinone) exhibits a paraelectric-antiferroelectric second-order phase transition at 237.1 K. Neutron and X-ray crystal structure analyses reveal that the H-bonded proton is disordered over two sites in the room-temperature (RT) phase. The phase transition would arise from this proton disorder together with rotation or libration of the Cp* ring and PF6(-) ion. The relative permittivity εb' along the H-bonded chains reaches relatively high values (ca., 130) in the RT phase. The temperature dependence of (13)C CP/MAS NMR spectra demonstrates that the proton is dynamically disordered in the RT phase and that the proton exchange has already occurred in the low-temperature (LT) phase. Rate constants for the proton exchange are estimated to be 10(-4)-10(-6) s in the temperature range of 240-270 K. DFT calculations predict that the protonation/deprotonation of [1](+) leads to interesting hapticity changes of the semiquinone ligand accompanied by reduction/oxidation by the π-bonded rhodium fragment, producing the stable η(6)-hydroquinone complex, [Cp*Rh(3+)(η(6)-p-H2Q-Me4)](2+) ([2](2+)), and η(4)-benzoquinone complex, [Cp*Rh(+)(η(4)-p-BQ-Me4)] ([3]), respectively. Possible mechanisms leading to the dielectric response are discussed on the basis of the migration of the protonic solitons comprising of [2](2+) and [3], which would be generated in the H-bonded chain.

15.
J Am Chem Soc ; 134(11): 5083-9, 2012 Mar 21.
Artigo em Inglês | MEDLINE | ID: mdl-22364147

RESUMO

A quasielastic neutron scattering and solid-state (2)H NMR spectroscopy study of the polymeric spin-crossover compound {Fe(pyrazine)[Pt(CN)(4)]} shows that the switching of the rotation of a molecular fragment--the pyrazine ligand--occurs in association with the change of spin state. The rotation switching was examined on a wide time scale (10(-13)-10(-3) s) by both techniques, which clearly demonstrated the combination between molecular rotation and spin-crossover transition under external stimuli (temperature and chemical). The pyrazine rings are seen to perform a 4-fold jump motion about the coordinating nitrogen axis in the high-spin state. In the low-spin state, however, the motion is suppressed, while when the system incorporates benzene guest molecules, the movements of the system are even more restricted.

16.
Nat Mater ; 10(10): 787-93, 2011 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-21892178

RESUMO

The development of a new methodology for visualizing and detecting gases is imperative for various applications. Here, we report a novel strategy in which gas molecules are detected by signals from a reporter guest that can read out a host structural transformation. A composite between a flexible porous coordination polymer and fluorescent reporter distyrylbenzene (DSB) selectively adsorbed CO2 over other atmospheric gases. This adsorption induced a host transformation, which was accompanied by conformational variations of the included DSB. This read-out process resulted in a critical change in DSB fluorescence at a specific threshold pressure. The composite shows different fluorescence responses to CO2 and acetylene, compounds that have similar physicochemical properties. Our system showed, for the first time, that fluorescent molecules can detect gases without any chemical interaction or energy transfer. The host-guest coupled transformations play a pivotal role in converting the gas adsorption events into detectable output signals.

17.
Chem Commun (Camb) ; 47(27): 7632-4, 2011 Jul 21.
Artigo em Inglês | MEDLINE | ID: mdl-21660332

RESUMO

We have demonstrated downsizing effects of the soft porous crystal, [Zn(isophthalate)(4,4'-bipyridyl)](n) (CID-1), on the adsorption behavior between CID-1 and CID-1 nanocrystal (NCID-1). The difference results from the packing crystal structures and the dynamics of the frameworks.


Assuntos
Nanopartículas/ultraestrutura , Ácidos Ftálicos/química , Polímeros/química , Piridinas/química , Compostos de Zinco/química , Adsorção , Espectroscopia de Ressonância Magnética , Modelos Moleculares , Nanopartículas/química , Porosidade
18.
Dalton Trans ; 40(10): 2177-9, 2011 Mar 14.
Artigo em Inglês | MEDLINE | ID: mdl-21293828

RESUMO

A photoreactive rhodium dithionite complex [(RhCp(Et))(2)(µ-CH(2))(2)(µ-O(2)SSO(2))] (1(Et)) with Cp(Et) (η(5)-C(5)Me(4)Et) ligands was newly synthesized. Upon short-time irradiation with low intensity light, two kinds of stepwise surface morphology changes of the crystal 1(Et) were observed. Prolonged irradiation with high intensity light caused cracking and breaking down of the crystal.

19.
Chem Commun (Camb) ; 46(8): 1227-8, 2010 Feb 28.
Artigo em Inglês | MEDLINE | ID: mdl-20449258

RESUMO

The title compound adopts a structure reminiscent of metallocene analogues, in which two disk-like units [Pd(II)(3)(THBQ)(tben)(3)](2+) bind to one naked Pd(0) metal in a sandwich form through each C(6)O(6)(4-) (THBQ(4-)) ring with an eta(6)-binding fashion.


Assuntos
Benzoquinonas/química , Compostos Organometálicos/química , Paládio/química , Cristalografia por Raios X , Modelos Moleculares
20.
Nat Mater ; 8(10): 831-6, 2009 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-19734885

RESUMO

The development of anhydrous proton-conductive materials operating at temperatures above 80 degrees C is a challenge that needs to be met for practical applications. Herein, we propose the new idea of encapsulation of a proton-carrier molecule--imidazole in this work--in aluminium porous coordination polymers for the creation of a hybridized proton conductor under anhydrous conditions. Tuning of the host-guest interaction can generate a good proton-conducting path at temperatures above 100 degrees C. The dynamics of the adsorbed imidazole strongly affect the conductivity determined by (2)H solid-state NMR. Isotope measurements of conductivity using imidazole-d4 showed that the proton-hopping mechanism was dominant for the conducting path. This work suggests that the combination of guest molecules and a variety of microporous frameworks would afford highly mobile proton carriers in solids and gives an idea for designing a new type of proton conductor, particularly for high-temperature and anhydrous conditions.

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