Terminal fluorinated nitroxide radical liquid crystalline compounds

We have synthesized a new series of all-organic paramagnetic liquid crystalline (LC) compounds, which include a five-membered ring nitroxide radical (NR) moiety in the mesogen core and fluorine atoms as terminal substituents. These new compounds are the structural analogs of the previously reported NR-LC compounds, and showed remarkable fluorine substituent effects. The introducing fluorine atom into terminal unit stabilizes nematic phase. However, an excess of fluorination leads to the destabilization of nematic phase.This is an Accepted Manuscript of an article published by Taylor & Francis in Molecular Crystals and Liquid Crystals on 24 May 2015, available at https://doi.org/10.1080/15421406.2015.1032732

Mechanochemical Synthesis of Dispersible Platinum Nanosheets for Enhanced Catalysis in a Microreactor

Nanosheet fabrication usually requires some self-assembly process of the ingredients themselves or self-assembled templates to lead to the local anisotropy. Macroscopic forces and dynamics cannot usually generate the local anisotropy to synthesize nanosheets in a solution because the anisotropies of the macroscopic mechanical forces and dynamics are promptly relaxed in the molecular scale in a liquid phase. Here, we report the mechanochemical synthesis of dispersible platinum nanosheets (PtNSs) using a microreactor. This work is the first example of bottom-up nanosheet synthesis of a nonexfoliable compound in a microflow reactor. The nanosheets grow through the lateral fusion of nanoplatelets in the hydrophilic space of the stable hyperswollen lyotropic lamellar (HL) phase of a surfactant solution. The lateral fusion is accelerated as the flow rate increases because the area of the bilayer in the HL phase increases with shear stress. The mechanical energy to promote the growth of the PtNSs can also be extracted in different ways. Most simply, syringe pumps electrically generate it. We also illustrate mechanochemical synthesis using gravity, the most universal and eco-friendly energy source on the earth. It is also the first example of the fabrication of anisotropic nanoparticles using gravity. Larger PtNSs show higher catalytic activity for the reduction reaction from 4-nitrophenol to 4-aminophenol due to their dispersibility; surprisingly, the exponential increase of the fusion patterns of nanoplatelets dramatically reduces the agglomeration of PtNSs. These PtNSs perform better in catalysis and should be promising for hydrogen production, fuel cells, and sensors because of their large surface area and dispersibility. This method could open up a pathway to valuable nanosheets.Koki Sasaki, Koji Miyake, Yoshiaki Uchida et al. Mechanochemical Synthesis of Dispersible Platinum Nanosheets for Enhanced Catalysis in a Microreactor. ACS Applied Nano Materials, 5 (4), 4998-5005, April 22, © 2022 American Chemical Society. https://doi.org/10.1021/acsanm.1c0458

Nanosheet Synthesis of Metal Organic Frameworks in a Sandwich-like Reaction Field for Enhanced Gate-Opening Pressures

Elastic layer-structured metal-organic frameworks (ELMs) are a family of flexible nanoporous metal organic frameworks (MOFs) showing gate-opening gas adsorption. The gate-opening pressure shifts to a higher value by crystal downsizing. However, the MOF nanoparticles and nanorods showing the gate-opening gas adsorption grow more than 50 nm even for their shortest sides. Here, we describe the synthesis and unique gas adsorption behavior of the first example of nanosheets of ELMs (ELM-NSs). The thickness and horizontal width of the ELM-NSs obtained from a new synthetic method using the inside the bilayers in hyperswollen lyotropic lamellar (HL) phases as sandwich-like reaction fields (SRFs) are a few nanometers and several hundreds of nanometers, respectively. The previously reported rationalization of the temperature dependence of the gate-opening pressures for ELMs enables us to discuss the size effects in terms of the adsorption-induced structural transitions and the Helmholtz free energy change of the host.Takeru Omiya, Koki Sasaki, Yoshiaki Uchida et al. Nanosheet Synthesis of Metal Organic Frameworks in a Sandwich-like Reaction Field for Enhanced Gate-Opening Pressures. ACS Applied Nano Materials, 1 (8), 3779-3784, August 18, © 2018 American Chemical Society. https://doi.org/10.1021/acsanm.8b0115

Thermal Molecular Motion Can Amplify Intermolecular Magnetic Interactions

Against a sensible expectation that molecular mobility in fluids generally disrupts magnetic orderings that depend on intermolecular interactions, some molecular compounds with isolated electrons, which are called radicals, exhibit the increase of magnetic susceptibility in melting. Here we first propose a simple model to explain the thermomagnetic anomaly unique to fluids; the effect of the magnetic interactions in each of the contacts could be accumulated on each of the molecular spins as if the molecular motion amplified the first coordination number of each molecule hundredfold. The huge coordination number theoretically guarantees the retention of memory of interactions at equilibrium; molecules might be able to conserve the memory of molecular conformations, configurations, electric charges, energies as well as magnetic memory with each other.Yoshiaki Uchida, Go Watanabe, Takuya Akita et al. Thermal Molecular Motion Can Amplify Intermolecular Magnetic Interactions, The Journal of Physical Chemistry B 124 (28), 6175-6180, July 16, ©2020 American Chemical Society. https://doi.org/10.1021/acs.jpcb.0c0540

Temperature-dependent Color Change of Cholesteric Liquid Crystalline Core-shell Microspheres

We have fabricated water-in-oil-in-water (W/O/W) double emulsion droplets with a cholesteric liquid crystalline (CLC) material, which is a mixture of a nematic liquid crystalline compound, 4-cyano-4′-pentylbiphenyl (5CB), and a chiral dopant, cholesteryl oleyl carbonate (COC), as the middle phase and an aqueous poly(vinylalcohol) (PVA) solution as the inner and outer phases (CLC core-shell microspheres). Here we report the strongly temperature-dependent color change of CLC core-shell microsphere.This is an Accepted Manuscript of an article published by Taylor & Francis in Molecular Crystals and Liquid Crystals on 3 July 2015, available at https://doi.org/10.1080/15421406.2015.1066548

Magnetic properties of terminal iodinated nitroxide radical liquid crystals

We designed and synthesized terminal iodinated nitroxide radical liquid crystalline compounds (NR-LCs) with octyloxy side chain (±)-8-I and dodecyloxy side chain (±)-12-I to understand the substitution effects of an iodine atom on the phase transition behavior and on the magnetic properties in crystalline (Cr), liquid crystalline (LC) and isotropic (Iso) phases. These NR-LCs show monotropic nematic phases because the iodine atom is too short and apolar as a terminal group to stabilize LC phases. Furthermore, the SQUID magnetometry and electron paramagnetic resonance (EPR) spectroscopy indicate that the magnetic properties in the Cr phase depend on the length of the alkoxy side chain; antiferromagnetic interactions occur in (±)-8-I, whereas ferromagnetic interactions occur in (±)-12-I, and the paramagnetic susceptibility of (±)-8-I slightly decreases (J¯0) at each of the Cr-to-Iso phase transitions. These results suggest that the most frequent type of the magnetic interactions in LC and Iso phases is similar to those in the Cr phases among the various types of intermolecular magnetic interactions induced by the inhomogeneous intermolecular contacts.Akita T., Yamazaki T., Uchida Y., et al. Magnetic properties of terminal iodinated nitroxide radical liquid crystals. Polyhedron 136, 79 (2017); https://doi.org/10.1016/j.poly.2017.02.030

Effects of photonic band gap of cholesteric liquid crystal on chemiluminescence

We have fabricated glass cells filled with cholesteric liquid crystalline materials (CLC reflectors), which are mixtures of a nematic liquid crystalline mixture, ZLI-2293 (Merck), and a chiral dopant, MLC-6248 (Merck). We reported the enhancement of the maximum emission intensity of luminol reaction by the photonic band gap (PBG) of the CLC reflectors. Here, we report the effect of the relative position of PBG of the CLC reflectors to the emission spectra of luminol reaction on the enhancement of the maximum emission intensity. © 2015This is an Accepted Manuscript of an article published by Taylor & Francis in Molecular Crystals and Liquid Crystals on 24 May 2015, available at https://doi.org/10.1080/15421406.2015.1032725

Large negative magneto-LC effects induced by racemic dimerization of liquid crystalline nitroxide radicals with a terminal cyano group

This article reports the synthesis and mesomorphism of new nitroxide radical compounds with a terminal cyano group and discusses the magneto-LC effects in the new compounds; one of the new compounds shows the largest decrease of paramagnetic susceptibility at the crystalline-to-liquid crystalline (LC) phase transition (negative magneto-LC effects) in the all-organic LC radicals reported thus far. The origins of the phenomenon are rationalized on the basis of the racemic magnetic dipolar interaction model using electron paramagnetic resonance (EPR) spectroscopy; the temperature dependences of the Lorentzian and Gaussian components of the line widths obtained by fitting EPR spectra with Voigt function provide important insights.Akita T., Kiyohara D., Yamazaki T., et al. Large negative magneto-LC effects induced by racemic dimerization of liquid crystalline nitroxide radicals with a terminal cyano group. Journal of Materials Chemistry C 5, 12457 (2017); https://doi.org/10.1039/c7tc04699e

Molecular clustering behaviour in the cybotactic nematic phase of a spin-labelled liquid crystal

A newly synthesised liquid crystalline nitroxide radical (LC-NR) with a terminal trifluoromethyl group as spin-labelled LC compounds exhibits an anomalous phase transition behaviour. It is likely attributed to non-covalent interactions between the trifluoromethyl groups of the adjacent molecules. X-ray diffractometry of the LC-NR suggests the existence of a cybotactic nematic (Ncyb) phase with a transient and local layer order between the normal nematic (N) and smectic A (SmA) phases. The EPR spectroscopy of the spin-labelled LC implies no discontinuity in magnetic susceptibility around the N-to-Ncyb phase transition. Intermolecular contacts between nitroxide radicals seem to change continuously. These results imply that the interactions between trifluoromethyl groups induce the cybotactic clusters, where molecules move in and out.Uchida Y., Akita T., Hanada K., et al. Molecular clustering behaviour in the cybotactic nematic phase of a spin-labelled liquid crystal. Journal of Materials Chemistry C 10 , 6621 (2022); https://doi.org/10.1039/d2tc00626j