Molecular Mobility Effect on Magnetic Interactions in All-Organic

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Cite This: J. Phys. Chem. B XXXX, XXX, XXX−XXX

Molecular Mobility Effect on Magnetic Interactions in All-Organic Paramagnetic Liquid Crystal with Nitroxide Radical as a HydrogenBonding Acceptor Sho Nakagami,† Takuya Akita,† Daichi Kiyohara,† Yoshiaki Uchida,*,† Rui Tamura,‡ and Norikazu Nishiyama† †

Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama-cho, Toyonaka, Osaka 560-8531, Japan Graduate School of Human and Environmental Studies, Kyoto University, Yoshida-Nihonmatsu-cho, Sakyo-ku, Kyoto 606-8501, Japan

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‡

S Supporting Information *

ABSTRACT: We synthesized new chiral all-organic liquid crystalline (LC) compounds with nitroxide (NO) and hydroxy (OH) groups, which form intermolecular hydrogen bonds between the NO and OH groups. The LC compounds show hexagonal columnar phases at room temperature, which solidify as LC glasses at low temperature. The experimental magnetic susceptibility of each of the compounds in the LC and isotropic phases is larger than that theoretically estimated on the simple assumption about the amount of the spins, whereas it accords with the theoretical one in the LC glass state. It is called magneto-LC effects. The difference between experimental and theoretical magnetic susceptibilities gradually increases as temperature increases through the LC glass state-to-LC phase transition. It suggests that molecular mobility is one of the origins of the magneto-LC effects.

1. INTRODUCTION

In this context, it is quite natural that the self-assembled nanostructures affect magnetic properties in LC materials. As magnetic LC compounds, there are metallomesogens with paramagnetic metal ions 19,20 and organic radical LC compounds with stable radicals.21−26 In particular, the magnetic susceptibilities of paramagnetic LC compounds with a nitroxide (NO) radical moiety (LC-NRs) abruptly increase at the crystalline (Cr)-to-LC phase transition (positive magneto-LC effect).27−29 The positive magneto-LC effect has been reported to be induced by intermolecular magnetic interactions unique to LC phases; after the Cr-to-LC phase transition, the molecular mobility should increase and the intermolecular contacts should become generally random there. The inhomogeneity of the magnetic interactions has already been proved to be one of the origins of the positive magneto-LC effect.28 To distinguish the contributions of the two factors, molecular mobility and the inhomogeneity of intermolecular contacts, to the magneto-LC effects, we focused on the introduction of H-bonds to the LC-NRs. The difference in the magnetic susceptibility between two states, LC glass state and LC phase, with an identical structure, which have the inhomogeneity of intermolecular contacts at the same level, should provide required information to separate the effect of molecular mobility from that of the intermolecular

Noncovalent interactions are useful to control one-, two-, and three-dimensional (1-D, 2-D, and 3-D) nanostructures of organic functional materials by means of self-assembly.1−3 Hydrogen (H) bonding is one of the noncovalent interactions observed very often in biological self-assembled nanostructures like DNA and proteins. The self-assembly of nanostructures can also induce unique properties that isolated constituents never show. In fact, most of biological functions arise from the self-assembly of molecules.4 We can learn the methodology to design the functions of artificial molecular materials from the biological systems.5 In fact, H-bonding has already been reported to be extremely helpful to design and construct functional materials, especially liquid crystals.1,6,7 Since the first H-bonded liquid crystalline (LC) material, 4butoxybenzoic acid, was reported,8 a lot of H-bonded LC compounds have been documented;1,9 in particular, supramolecular LC compounds forming an H-bond between a pyridine ring and a carboxyl group6,10 attracted a great attention of materials scientists, chemists, physicists, and so on, because the control of H-bonded nanostructures is highly effective to create new functions. For example, highly preprogrammed H-bonded LC compounds show 1-D,11 2D,12 or 3-D13 ion conduction selectively, H-bonded columnar LC compounds exhibit unique dielectric properties,14,15 Hbonding broadens the temperature range of LC phases,16 and H-bonding improves electro-optic responsivity.17,18 © XXXX American Chemical Society

Received: April 24, 2018 Revised: June 22, 2018

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DOI: 10.1021/acs.jpcb.8b03839 J. Phys. Chem. B XXXX, XXX, XXX−XXX

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solution was added, and the aqueous mixture was extracted with diethyl ether (50 mL × 2). The combined extract was dried over MgSO4, and the solvent was evaporated. The residue was purified by flash column chromatography on silica gel to afford the individual NR compound (±)-1−3 in the yield of 27.0, 92.3, and 73.8%, respectively. Compound (±)-1 was separated into the enantiomers by using HPLC with a chiral column (DAICEL CHIRALCEL OD-H, 20 mm × 250 mm, particle size 5 μm) and hexane/2propanol (9:1) as a mobile phase. The separated eluent was evaporated to obtain enantiomerically enriched (2R,5R)-1 and (2S,5S)-1 with 98.9% ee and 99.9% ee, respectively. Mass spectra and magnetic susceptibilities are measured by means of a high-resolution mass spectrometer (HRMS) and superconducting quantum interference device (SQUID). (±)-1: EPR (THF): g = 2.0058, aN = 1.35 mT; IR (KBr): 3327, 2924, 2854, 1735, 1587, 1508, 1465, 1431, 1338, 1199, 1116, 1016, 833, 756, 578 cm−1; HRMS (m/z): [M]+ calcd for C61H96NO7, 954.7187; found, 954.7178; analysis (calcd, found for C61H96NO7): C(76.68, 76.34), H(10.13, 10.34), N(1.47,1.55); SQUID: C = 0.386 emu K mol−1, θ = −0.056 K. (2R,5R)-1: [a]D19 + 85° (c = 0.075, hexane); SQUID: C = 0.370 emu K mol−1, θ = −0.425 K. (±)-2: EPR (THF): g = 2.0059, aN = 1.33 mT; IR (KBr): 2927, 2854, 1735, 1589, 1506, 1463, 1431, 1381, 1334, 1197, 1118, 1018, 862, 757, 700 cm−1; HRMS (m/z): [M]+ calcd for C61H96NO6, 938.7238; found, 938.7237; analysis (calcd, found for C61H96NO6): C(77.99, 77.92), H(10.30, 10.38), N(1.49, 1.54); SQUID: C = 0.369 emu K mol−1, θ = −0.024 K. (±)-3: EPR (THF): g = 2.0060, aN = 1.33 mT; IR (KBr): 2924, 2850, 2731, 1728, 1701, 1585, 1502, 1467, 1429, 1388, 1332, 1205, 1110, 1051, 1018, 958, 860, 831, 794, 751, 657, 590 cm−1; HRMS (m/z): [M]+ calcd for C62H96NO7, 966.7187; found, 966.7189; analysis (calcd, found for C62H96NO7): C(76.97, 77.15), H(10.00, 10.38), N(1.45, 1.52); SQUID: C = 0.368 emu K mol−1, θ = −2.59 K.

contacts. To obtain easily vitrified LC materials, polymerization is one of the promising approaches;16,30 in particular, supramolecular polymerization with noncovalent bonding is more favorable for self-assembled functional structures.2,3,16,31,32 For the supramolecular polymerization of LCNRs, the crystal structures of some NRs consisting of Hbondings between an NO moiety and a hydroxy group (N− O···H−O bonding) could provide a useful clue.33,34 Here, we report the synthesis of a new LC-NR, 1 (Figure 1), with a

Figure 1. Molecular structures of NR compounds 1−3.

phenolic OH group showing both the LC phase and LC glass state with identical structures, confirm the existence of the intermolecular N−O···H−O bonds, and discuss the effects of the molecular mobility on the magneto-LC effects by comparison between the LC and LC glass states.

2. EXPERIMENTAL SECTION Unless otherwise noted, solvents and reagents were reagent grade and used without further purification. Tetrahydrofuran (THF) used for synthesis was distilled from sodium/ benzophenone ketyl under nitrogen. Transition behaviors were determined by differential scanning calorimetry (DSC) analysis at a scanning rate of 5 °C/min (SHIMADZU DSC60), polarized optical microscopy (Olympus BX51), and X-ray diffraction (XRD) analysis. A hot stage (Japan High Tech, 10083) was used as the temperature control unit for the microscopy. Enantiomeric excess was determined by highperformance liquid chromatography (HPLC) using a chiral stationary phase column (DAICEL CHIRALCEL OD-H, 4.6 mm × 250 mm, particle size 5 μm), a mixture of hexane and 2propanol (9:1) as the mobile phase at a flow rate of 1.0 mL/ min, and a UV detector (254 nm). Infrared (IR) spectra were recorded with SHIMADZU IRAffinity-1 using the KBr-pellet technique. Magnetization was recorded with QUANTUN DESIGN MPMS-3. Electron paramagnetic resonance (EPR) spectra were recorded with a JEOL JES-FE1XG at room temperature and with a JEOL JES-FA-200 for variabletemperature measurements. XRD patterns at room temperature were recorded by using the Bruker D8 ADVANCE diffractometer in continuous scan with Cu Kα radiation, and those at −50 °C were recorded by using the Philips X’PertMPD diffractometer with Cu Kα radiation. The esterification of NR compounds (±)-4−633−35 with 3,4,5-tris(dodecyloxy)benzoic acid gave the products (±)-1−3, respectively. Enantiomerically enriched (2R,5R)-1 was isolated by HPLC separation. The precursor NR compounds (±)-4−6 were prepared according to the previously reported procedures.22,35 Dichloromethane (50 mL) was charged with the phenolic NR compound (±)-4, (±)-5, or (±)-6 (0.3 mmol), 3,4,5tris(dodecyloxy)benzoic acid (0.33 mmol), 1-(3(dimethylamino)propyl)-3-ethylcarbodiimide hydrochloride (EDC·HCl, 0.33 mmol), and 4-(dimethylamino)pyridine (DMAP, 0.09 mmol). After each mixture was stirred for 12 h at room temperature, a saturated aqueous NaHCO3 (50 mL)

3. RESULTS AND DISCUSSION We synthesized both racemic and enantiomerically enriched NRs (±)-1 and (2R,5R)-1 with an OH group as an H-bond donor, and as reference compounds, we also synthesized racemic NRs (±)-2 and (±)-3 with an H atom and a formyl group instead of the OH group, respectively (Figure 1 and Scheme 1). The phase transition behaviors were characterized by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and X-ray diffraction (XRD) analysis. Compounds (±)-1 and (2R,5R)-1 with an OH group showed enantiotropic LC phases at room temperature; their clearing points were 38.6 and 46.9 °C in the heating process, as shown in Figures 2 and S1, respectively. No other peaks were observed below the clearing points in the DSC analyses for (±)-1 and (2R,5R)-1. In contrast, DSC analyses (Figure S1) and POM for (±)-2 and (±)-3 without a phenolic OH group failed to show an LC phase. These results indicate that the LC phases are stabilized by the OH group in (±)-1 and (2R,5R)-1. To confirm the existence of N−O···H−O bonding, we measured their IR spectra in the LC phases at room temperature using the KBr-pellet technique. The absorption bands corresponding to the intermolecular H-bonded O−H stretching vibration were observed at 3327 and 3400 cm−1 for (±)-1 and (2R,5R)-1, as shown in parts a and b of Figure 3, respectively, whereas the IR spectra of (±)-2 and (±)-3 do not have such absorption bands, as shown in Figure S2. These B

DOI: 10.1021/acs.jpcb.8b03839 J. Phys. Chem. B XXXX, XXX, XXX−XXX

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The Journal of Physical Chemistry B Scheme 1. Synthesis and Molecular Structures of NR Compounds 1−3

Figure 4. XRD patterns for (a) (2R,5R)-1 and (b) (±)-1 at room temperature.

1.58 nm in the ratio of 1:1/ 3 :1/2:1/ 7 that could correspond to (100), (110), (200), and (210) reflections, respectively, as shown in Figure 4a. The LC phase of (2R,5R)1 at room temperature is likely to be a hexagonal columnar (Colh) phase, as illustrated in Figure 5a. Similarly, the XRD pattern for (±)-1 presents one sharp peak corresponding to the layer spacing of 4.22 nm, which could correspond to the (100) reflection, and two small and broad peaks corresponding to 2.34 and 1.58 nm, as shown in Figure 4b. The broad peak corresponding to 2.34 nm is likely to be overlapped, and peak separation would give two peaks corresponding to (110) and (200) reflections. The XRD patterns for both (±)-1 and (2R,5R)-1 show broad peaks between 15 and 25°, indicating the disorder inside the columns. These results indicate that the LC phase of (±)-1 at room temperature is also a Colh phase. The phase transition behaviors of 1−3 are summarized in Figure S3. Furthermore, the XRD patterns for (±)-1 and (2R,5R)-1 at −50 °C show peaks corresponding to (100) in a small angle region, as shown in Figure S4; the peak positions are very close to those at 25 °C. We can expect that, when the fluidity disappears at such a low temperature, the multiple long alkyl chains could inhibit the intercolumn interactions to stabilize crystalline states and the polymerization with H-bonding involving the OH groups would keep the LC structures of (±)-1 and (2R,5R)-1; therefore, (±)-1 and (2R,5R)-1 are not in Cr phases but in LC glass states in the low temperature range, which enables us to discuss the effects of the molecular mobility on the magneto-LC effects. We have to examine if some intermolecular H-bondings involving the OH groups stabilize the LC structures. In addition, XRD patterns gave information on the degree of ordering of the structures. The correlation length (ξ) can be estimated from the peaks for (100) reflections in XRD patterns as follows.36 First, the XRD profile as a function of the diffraction angle 2θ is converted to a scattering function of the scattering vector length q according to 4π q= sin θ (1) λ

Figure 2. Polarized optical microphotographs of (a) (±)-1 at 34.5 °C and (b) (2R,5R)-1 at 35.4 °C.

Figure 3. IR spectra of (a) (±)-1 and (b) (2R,5R)-1.

results indicate that compounds (±)-1 and (2R,5R)-1 form N−O···H−O bonding between adjacent molecules and the intermolecular H-bonds stabilize the LC structures. POM for (±)-1 and (2R,5R)-1 in the cooling process at a rate of 0.01 °C/min from the isotropic phase exhibits focal conic textures, as shown in Figure 2, which are characteristic of LC phases with layer structures. XRD analysis could give a lot of information on such layer structures in the LC phases. The highly sensitive XRD analysis for (±)-1 and (2R,5R)-1 at room temperature gives the patterns with some peaks, as shown in Figure 4. The XRD pattern for (2R,5R)-1 presents one sharp peak and three small peaks corresponding to layer spacings of 4.38, 2.55, 2.20, and C

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Figure 5. Structure in the disordered Colh phases estimated by XRD analysis. (a) The Colh phase of (2R,5R)-1 consists of columns with a diameter of 5.06 nm. (b) The H-bonding was previously reported to constitute 1-D homochiral chains in a crystal of the analogue of 1. (c) H-bonded chain constitutes around the center of the columns.

where λ is the wavelength of the X-ray. Second, by fitting the XRD profiles using the following Pearson VII equations, the half widths at half-maximum wR (q > q0) and wL (q < q0) were determined. When q > q0, I(q) = ÄÅ ÅÅ ÅÅ1 + ÅÅ ÅÇ

ÉÑmR ÑÑ (21/ mR − 1)ÑÑÑ ÑÑÖ

(2-a)

ÉÑmL ÑÑ − 1)ÑÑÑ ÑÑÖ

(2-b)

I0 q − q0

2

( ) wR

When q < q0,

I(q) = ÄÅ ÅÅ ÅÅ1 + ÅÅ ÅÇ

I0 q − q0

2

( ) (2 wL

1/ mL

Herein, I0 and q0 denote the peak height and the peak position and mR and mL are parameters, respectively. Finally, the correlation length ξ was determined using the following equation.

ξ=

1 wR + wL

(3)

The correlation lengths for (±)-1 and (2R,5R)-1 could be estimated to be 4.35 and 20.47 nm, respectively. These results indicate that the positional order in the Colh phase of (2R,5R)1 has a much longer range than that of (±)-1. It is consistent with the fact that (2R,5R)-1 shows a higher clearing point than (±)-1; it means the Colh phase of (2R,5R)-1 is more stable than that of (±)-1. In general, heterochiral ingredients prefer centrosymmetric dimerizarion in most crystals, whereas most homochiral ingredients like to form crystal structures with screw axes better.37 In fact, the chain structures with H-bonds between NO and OH groups for the crystal of the analogue of compound 1 have been reported, as shown in Figure 5b.33,34 Thus, in the homochiral columns for (2R,5R)-1, the H-bonds could be connected in succession around the center of the columns, as illustrated in Figure 5c, whereas the columns for (±)-1 are heterochiral so that the H-bonds should be unconnected here and there, and there could be heterochiral dimers. Since the chaining of the H-bonds could unidirectionally align the columns, the difference in the chain length of the H-bonds between the LC phases of (±)-1 and (2R,5R)-1 could decide the difference in the correlation length of the hexagonal structures. We measured the temperature dependence of magnetic susceptibilities of (±)-1 and (2R,5R)-1 at magnetic fields of 0.5 and 0.05 T in the temperature range from 210 to 350 K by using a SQUID magnetometer, as shown in Figures 6 and S5, respectively. Here we define the sum of paramagnetic and

Figure 6. Temperature dependences of χparaT for (a) (±)-1 and (b) (2R,5R)-1 at a magnetic field of 0.5 T. The circles denote the experimental data in the heating run, and the horizontal solid lines denote the Curie−Weiss fitting curves for the LC glass state. The vertical broken lines denote the estimated glass state-to-LC phase transition temperatures, and the solid lines on the circles to the right of the broken lines denote the fitting curves for LC and Iso phases.

diamagnetic susceptibilities (χpara and χdia) as molar magnetic susceptibility (χM = χpara + χdia = C/(T − θg) + χdia). Although we cannot exactly determine the χpara in LC phases due to the unknown temperature dependence of the χdia in LC phases,38 here we assumed that χdia is constant in the whole temperature range. The χparaT−T plots obeyed the Curie−Weiss law in the temperature range between 200 and 250 K, where the Weiss constant is θg = −0.056 and −0.425 K and the Curie constant is C = 0.386 and 0.370 emu K mol−1 for (±)-1 and (2R,5R)-1 at 0.5 T, respectively. The magnetic properties are similar to ordinary paramagnetic radical crystals in the low temperature range. In contrast, χparaT begins to increase from around 260 K for both (±)-1 and (2R,5R)-1. The increases in χparaT from the fitting curves for (±)-1 and (2R,5R)-1 at 350 K at 0.5 T are 11.4 and 11.8%, respectively, as shown in Figure 6, whereas those at 0.05 T are 20.3 and 20.2%, respectively, as shown in Figure S5. These results indicate that the weaker the applied magnetic field becomes, the stronger the positive magneto-LC effect becomes. This tendency of magnetization is consistent with the spin-glass-like behavior arising from the inhomogeD

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Figure 7. Temperature dependences of (a) χrel, (b) χrelT, (c) g-value, and (d) ΔHpp for (2R,5R)-1 in the heating run by EPR spectroscopy at a magnetic field of 0.33 T. The circles denote the experimental data, and the solid lines in parts a and b denote the Curie−Weiss fitting curves.

by using a quartz tube (5 mm φ). Therefore, by using the parameters directly from the differential curves, such as maximum peak height (I′m and −I′m), g-value (g), and peakto-peak line width (ΔHpp), paramagnetic susceptibility (χpara) could be derived as follows from the Bloch equation, as shown in Figure 728

neous intermolecular magnetic interactions for the previously reported LC-NR materials showing a positive magneto-LC effect.28 Furthermore, in contrast to previously reported abrupt increases of magnetic susceptibilities at Cr-to-LC phase transitions, χparaT looks to gradually increase even around the LC glass state-to-LC phase transitions for both (±)-1 and (2R,5R)-1. Even after LC-to-Iso phase transitions, χparaT continues to increase for both (±)-1 and (2R,5R)-1. Since the magnetic interactions are much smaller than temperature, χpara could obey the Curie−Weiss law. χparaT =

θy i C T ∼ C jjj1 + f zzz T − θf T{ k

χpara =

3 hνH1

(6)

where μB is Bohr magneton, h is Planck’s constant, ν is the frequency of the absorbed electromagnetic wave, and H1 is the amplitude of the oscillating magnetic field. For plotting the temperature dependence of χpara, the relative paramagnetic susceptibility (χrel), which is defined as

(4)

The data for the LC and Iso phases were well fitted with quadratic equations, as shown in Figure 6, and therefore, the Weiss constants for the fluid phases could be represented like θf = aT 3 + bT 2 + cT

2μBgIm′ ΔHpp2

χrel = χpara /χ0

(7)

where χ0 is the standard paramagnetic susceptibility at 223 K in the heating run, was used in place of χpara to simplify the treatment. The magnetic data are the mean values of four measurements at each temperature to estimate χrel with the maximum accuracy. The temperature dependence of χrel for (2R,5R)-1 is shown in Figure 7a, and we fitted the data with the Curie−Weiss law in the temperature range of the LC glass state. Moreover, we also plotted χrelT as a function of T to compare the results with those of SQUID magnetometry (Figure 7b). The value of χrelT changed little between 223 and 278 K and obeyed the Curie− Weiss law; however, above 278 K, χrelT gradually increased. We can conclude that the LC glass state-to-Colh phase transitions for (2R,5R)-1 would be determined to be around 278 K, respectively. And even when the compound turned into the isotropic phase, the slope angle of χrelT also increased. The temperature dependence of χrelT obtained by EPR spectroscopy is consistent with that of χparaT obtained by SQUID magnetometry. The g-value does not show enough change to account for the temperature dependence of the χrelT observed for all of the previously reported compounds (Figure 7c), indicating a negligible molecular reorientation effect caused by the molecular anisotropy (Δχ).

(5)

We can expect that T such that θf = θg ∼ 0 for the LC phases is the LC glass state-to-LC phase transition temperature. For the fluid phases of (±)-1, the parameters a, b, and c were estimated as 8.14 × 10−6 K−2, −3.76 × 10−3 K−1, and 1.66 × 10−1, respectively. For the Colh phase of (2R,5R)-1, the parameters a, b, and c were estimated as 9.50 × 10−6 K−2, −4.38 × 10−3 K−1, and 4.93 × 10−1, respectively, whereas they were estimated as 9.75 × 10−6 K−2, −4.50 × 10−3 K−1, and 4.93 × 10−1 for the Iso phase, respectively. Thus, the LC glass stateto-LC phase transition temperatures for (±)-1 and (2R,5R)-1 were estimated as 247 and 267 K, as shown in Figure 6, respectively. Although we cannot understand the origin of the formulation and parameters at this stage, the positive correlation between T and θf indicates that molecular mobility is one of the most important origins of the positive magnetoLC effect. This assumption ought to be discussed microscopically. The temperature dependence of EPR spectra for (2R,5R)-1 in the LC glass state and LC phase were measured from 223 K in the heating process at a magnetic field of 0.33 T (X-band) E

DOI: 10.1021/acs.jpcb.8b03839 J. Phys. Chem. B XXXX, XXX, XXX−XXX

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The Journal of Physical Chemistry B Author Contributions

To discuss the relationship between intermolecular magnetic interactions and molecular mobility, the temperature dependence of the peak-to-peak line width ΔHpp could give significant information. In the LC glass state, ΔHpp gradually decreased, ΔHpp began to increase at the LC glass state-to-Colh phase transition, and ΔHpp increased in the isotropic phase, as shown in Figure 7d. Generally, ΔHpp depends on the following three factors: (i) narrowing due to spin−spin exchange interactions, (ii) broadening due to spin−spin dipolar interactions, and (iii) motional narrowing.28 The delicate balance of the three factors is likely to give rise to the complicated behavior of the temperature dependence of ΔHpp. The most likely scenario is that molecular mobility increases as temperature increases in the whole temperature range, and the spin−spin dipolar interactions in the LC and isotropic phases become stronger than those in the LC glass state. Considering that the local molecular motion without displacement of the molecules in the LC glass state could not induce the distinct magnetic interactions, macroscopic molecular flow should be needed for the magnetic interactions in the fluid phases. Generally speaking, the temperature dependence of viscosity above glass transition points is proportional to exp(E/kB(T − T0)), where E is an activation energy for viscous flow, T0 denotes a temperature associated with the glass transition, and kB is the Boltzmann constant39 and fluidity is defined as the reciprocal of viscosity. Therefore, the fluidity seems to give rise to the positive correlation between T and θf.

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. S.N.: data analysis, lead; investigation, lead; visualization, supporting; writingoriginal draft, lead; writingreview and editing, supporting. T.A.: conceptualization, supporting; funding acquisition, supporting; data analysis, supporting; investigation, supporting; methodology, lead; visualization, supporting; writingreview and editing, supporting. D.K.: investigation, supporting; methodology, supporting; writingreview and editing, supporting. Y.U.: conceptualization, lead; funding acquisition, lead; project administration, lead; visualization, lead; supervision, equal; writingoriginal draft, supporting; writingreview and editing, lead. R.T.: funding acquisition, supporting; supervision, equal; writing review and editing, supporting. N.N.: supervision, equal; writingreview and editing, supporting. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank Professor Tsuyoshi Kimura, Osaka University, for experimental support, including measurement of magnetic susceptibility. Also, the authors extend appreciation to Professor Yasuhiro Sakamoto, Osaka University, for experimental support, including measurement of X-ray diffraction. This work was supported in part by the Japan Science and Technology Agency (JST) “Precursory Research for Embryonic Science and Technology (PRESTO)” for a project of “Molecular technology and creation of new function” and by Japan Society for the Promotion of Science (JSPS) KAKENHI (Grant numbers 17H04896 and 26248024). T.A. is very grateful to the JSPS Research Fellowships for Young Scientists JP16J05585.

4. CONCLUSIONS We have succeeded in the synthesis of the first chiral allorganic NR compounds with an OH group showing disordered Colh phases, which have a new type of mesogen core including intermolecular N−O···H−O H-bonds. The Colh phases are stable at room temperature for both (±)-1 and (2R,5R)-1. Moreover, both (±)-1 and (2R,5R)-1 show LC glass states in the lower temperature range. The results of SQUID magnetometry and EPR spectroscopy strongly imply that the molecular mobility is one of the origins of the positive magneto-LC effect. That might mean that not local molecular motion but global molecular flow makes the spin−spin dipolar interactions stronger. We expect that the molecular origin of the effect of molecular mobility on magneto-LC effects could be clarified by incorporating the effect of molecular diffusion into the mean field theory of spin glasses. And the theory could be testable by means of molecular dynamics simulation. In addition, these Hbonded LC-NRs have a potential as chemical sensing materials for H-bonding donor and acceptor compounds.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpcb.8b03839.

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REFERENCES

(1) Kato, T.; Mizoshita, N.; Kishimoto, K. Functional LiquidCrystalline Assemblies: Self-Organized Soft Materials. Angew. Chem., Int. Ed. 2006, 45, 38−68. (2) Fouquey, C.; Lehn, J.-M.; Levelut, A.-M. Molecular Recognition Directed Self-assembly of Supramolecular Liquid Crystalline Polymers from Complementary Chiral Components. Adv. Mater. 1990, 2, 254− 257. (3) Kang, J.; Miyajima, D.; Mori, T.; Inoue, Y.; Itoh, Y.; Aida, T. A Rational Strategy for the Realization of Chain-growth Supramolecular Polymerization. Science 2015, 347, 646−651. (4) Israelachvili, J. N.; Mitchell, D. J.; Ninham, B. W. Theory of Selfassembly of Lipid Bilayers and Vesicles. Biochim. Biophys. Acta, Biomembr. 1977, 470, 185−201. (5) Ogi, S.; Sugiyasu, K.; Manna, S.; Samitsu, S.; Takeuchi, M. Living Supramolecular Polymerization Realized Through a Biomimetic Approach. Nat. Chem. 2014, 6, 188−195. (6) Kato, T.; Frechet, J. M. J. Hydrogen Bonding and the Selfassembly of Supramolecular Liquid-crystalline Materials. Macromol. Symp. 1995, 98, 311−326. (7) Kato, T. Self-assembly of Phase-segregated Liquid Crystal Structures. Science 2002, 295, 2414−2418. (8) Bradfield, A. E.; Jones, B. Two Apparent Cases of Liquid Crystal Formation. J. Chem. Soc. 1929, 0, 2660−2661. (9) Paleos, C. M.; Tsiourvas, D. Thermotropic Liquid Crystals Formed by Intermolecular Hydrogen Bonding Interactions. Angew. Chem., Int. Ed. Engl. 1995, 34, 1696−1711. (10) Kato, T.; Frechet, J. M. J. New Approach to Mesophase Stabilization Through Hydrogen-bonding Molecular Interactions in Binary Mixtures. J. Am. Chem. Soc. 1989, 111, 8533−8534.

Figures S1−S5 (PDF)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone: +81-6-68506256. Fax: +81-6-6850-6256. ORCID

Yoshiaki Uchida: 0000-0001-5043-9239 Rui Tamura: 0000-0002-4123-6795 F

DOI: 10.1021/acs.jpcb.8b03839 J. Phys. Chem. B XXXX, XXX, XXX−XXX

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The Journal of Physical Chemistry B

(30) Angell, C. A. Formation of Glasses from Liquids and Biopolymers. Science 1995, 267, 1924−1935. (31) Kato, T.; Frechet, J. M. J. Stabilization of a Liquid-crystalline Phase Through Noncovalent Interaction with a Polymer Side Chain. Macromolecules 1989, 22, 3818−3819. (32) Sijbesma, R. P.; Beijer, F. H.; Brunsveld, L.; Folmer, B. J. B.; Hirschberg, J. H. K. K. Reversible Polymers Formed from Selfcomplementary Monomers Using Quadruple Hydrogen Bonding. Science 1997, 278, 1601−1604. (33) Ikuma, N.; Tamura, R.; Shimono, S.; Kawame, N.; Tamada, O.; Sakai, N.; Yamauchi, J.; Yamamoto, Y. Crystal Structure and Magnetic Properties of Novel Chiral Nitroxides Existing as Racemic Conglomerates. Mendeleev Commun. 2003, 13, 109−111. (34) Ikuma, N.; Tsue, H.; Tsue, N.; Shimono, S.; Uchida, Y.; Masaki, K.; Matsuoka, N.; Tamura, R. Spontaneous Racemization and Epimerization Behavior in Solution of Chiral Nitroxides. Org. Lett. 2005, 7, 1797−1800. (35) Suzuki, K.; Uchida, Y.; Tamura, R.; Shimono, S.; Yamauchi, J. Observation of positive and negative magneto-LC effects in allorganic nitroxide radical liquid crystals by EPR spectroscopy. J. Mater. Chem. 2012, 22, 6799−6806. (36) Nishiya, W.; Takanishi, Y.; Yamamoto, J.; Yoshizawa, A. Molecular design for a cybotactic nematic phase. J. Mater. Chem. C 2014, 2, 3677−3685. (37) Jacques, J.; Collet, A.; Wielen, S. H. Enantiomer, Racemates and Resolutions; Krieger: Malabar, FL, 1994. (38) Uchida, Y.; Tamura, R.; Ikuma, N.; Shimono, S.; Yamauchi, J.; Shimbo, Y.; Takezoe, H.; Aoki, Y.; Nohira, H. Magnetic-field-induced Molecular Alignment in an Achiral Liquid Crystal Spin-labeled by a Nitroxyl Group in the Mesogen Core. J. Mater. Chem. 2009, 19, 415− 418. (39) Brillo, J.; Pommrich, A. I.; Meyer, A. Relation between SelfDiffusion and Viscosity in Dense Liquids: New Experimental Results from Electrostatic Levitation. Phys. Rev. Lett. 2011, 107, 165902.

(11) Yoshio, M.; Mukai, T.; Ohno, H.; Kato, T. One-dimensional Ion Transport in Self-organized Columnar Ionic Liquids. J. Am. Chem. Soc. 2004, 126, 994−995. (12) Yoshio, M.; Mukai, T.; Kanie, K.; Yoshizawa, M.; Ohno, H.; Kato, T. Layered Ionic Liquids: Anisotropic Ion Conduction in New Self-organized Liquid-crystalline Materials. Adv. Mater. 2002, 14, 351−354. (13) Ichikawa, T.; Yoshio, M.; Hamasaki, A.; Kagimoto, J.; Ohno, H.; Kato, T. 3d Interconnected Ionic Nano-channels Formed in Polymer Films: Self-organization and Polymerization of Thermotropic Bicontinuous Cubic Liquid Crystals. J. Am. Chem. Soc. 2011, 133, 2163−2169. (14) Kishikawa, K.; Nakahara, S.; Nishikawa, Y.; Kohmoto, S.; Yamamoto, M. A Ferroelectrically Switchable Columnar Liquid Crystal Phase with Achiral Molecules: Superstructures and Properties of Liquid Crystalline Ureas. J. Am. Chem. Soc. 2005, 127, 2565−2571. (15) Miyajima, D.; Araoka, F.; Takezoe, H.; Kim, J.; Kato, K.; Takata, M.; Aida, T. Ferroelectric Columnar Liquid Crystal Featuring Confined Polar Groups Within Core−shell Architecture. Science 2012, 336, 209−213. (16) Kato, T.; Kihara, H.; Uryu, T.; Fujishima, A.; Frechet, J. M. J. Molecular Self-assembly of Liquid Crystalline Side-chain Polymers Through Intermolecular Hydrogen Bonding. Polymeric Complexes Built from a Polyacrylate and Stilbazoles. Macromolecules 1992, 25, 6836−6841. (17) Kato, T.; Mizoshita, N.; Kutsuna, T.; Kondo, G.; Hanabusa, K. Electro-optic Effects and Phase Behavior of Liquid-crystalline Physical Gels: Self-assembly of Hydrogen-bonded Molecules for the Formation of Dynamically Functional Composites. Macromol. Symp. 2000, 154, 15−24. (18) Kiani, S.; Zakerhamidi, M. S.; Tajalli, H. Hydrogen Bonding Intermolecular Effect on Electro-optical Response of Doped 6PCH Nematic Liquid Crystal with Some Azo Dyes. Opt. Mater. 2016, 55, 121−129. (19) Griesar, K.; Haase, W. In Magnetic Properties of Organic Molecules; Laht, P. M., Ed.; Marcel Dekker: New York, 1999. (20) Serrano, J.-L. Metallomesogens: Synthesis, Properties, and Applications; VCH: Weinheim, Germany, 1996. (21) Tamura, R.; Uchida, Y.; Ikuma, N. Paramagnetic All-organic Chiral Liquid Crystals. J. Mater. Chem. 2008, 18, 2872−2876. (22) Ravat, P.; Marszalek, T.; Pisula, W.; Müllen, K.; Baumgarten, M. Positive Magneto-LC Effect in Conjugated Spin-bearing Hexabenzocoronene. J. Am. Chem. Soc. 2014, 136, 12860−12863. (23) Castellanos, S.; López-Calahorra, F.; Brillas, E.; Julia, L.; Velasco, D. All-organic Discotic Radical with a Spin-carrying Rigidcore Showing Intracolumnar Interactions and Multifunctional Properties. Angew. Chem., Int. Ed. 2009, 48, 6516−6519. (24) Bajzíková, K.; Kohout, M.; Tarábek, J.; Svoboda, J.; Novotná, V.; Vejpravová, J.; Pociecha, D.; Gorecka, E. All-organic Liquid Crystalline Radicals with a Spin Unit in the Outer Position of a Bentcore System. J. Mater. Chem. C 2016, 4, 11540−11547. (25) Jasinski, M.; Szczytko, J.; Pociecha, D.; Monobe, H.; Kaszynski, P. Substituent-dependent Magnetic Behavior of Discotic Benzo[E][1,2,4]Triazinyls. J. Am. Chem. Soc. 2016, 138, 9421−9424. (26) Jasiński, M.; Pociecha, D.; Monobe, H.; Szczytko, J. Tetragonal Phase of 6-Oxoverdazyl Bent-core Derivatives with Photoinduced Ambipolar Charge Transport and Electrooptical Effects. J. Am. Chem. Soc. 2014, 136, 14658−14661. (27) Uchida, Y.; Ikuma, N.; Tamura, R.; Shimono, S.; Noda, Y.; Yamauchi, J.; Aoki, Y.; Nohira, H. Unusual Intermolecular Magnetic Interaction Observed in an All-organic Radical Liquid Crystal. J. Mater. Chem. 2008, 18, 2950−2952. (28) Uchida, Y.; Suzuki, K.; Tamura, R.; Ikuma, N.; Shimono, S.; Noda, Y.; Yamauchi, J. Anisotropic and Inhomogeneous Magnetic Interactions Observed in All-organic Nitroxide Radical Liquid Crystals. J. Am. Chem. Soc. 2010, 132, 9746−9752. (29) Uchida, Y.; Suzuki, K.; Tamura, R. Magneto-LC Effects in Hydrogen-bonded All-organic Radical Liquid Crystal. J. Phys. Chem. B 2012, 116, 9791−9795. G

DOI: 10.1021/acs.jpcb.8b03839 J. Phys. Chem. B XXXX, XXX, XXX−XXX