The reported layer spacings (dsmectic) of six homologues of mesogens exhibiting orthogonal smectic phases (SmE, SmB, and SmA phases) are reexamined. The slopes of the linear dependences on chain length (n, the number of carbon atoms in the hydrocarbon chain) are clearly categorized into two groups: 1.9 Å (CH2)−1 and 1.4 Å (CH2)−1. It is clarified that in the former the molecules take a rod-like form (rod-form; category-I), whereas in the latter the molecules are bent around the connection between the core and chain moieties (bent-form; category-II). The average relative positions of adjacent molecules within the smectic structures are deduced from the intercept of the linear functions of dsmectic against n. The relation between and the features of molecules belonging to the two categories are discussed for molecular design of functional smectic liquid crystals.

Phase behaviors of two homologous binary systems of 4-alkyl-4′-cyanobiphenyl (nCB, n being the number of carbon atoms in the alkyl chain) and 4-alkoxy-4′-cyanobiphenyl (nOCB) were investigated. Their phase diagrams were drawn against an averaged chain length, n*. The phase boundary curves between neamtic (N) and smectic Ad (SmAd) phases in nCB/mCB (n = 3–6; m = 8, 9) binary systems were classified into four depending on four combinations of even- and odd-numbered n and m; even/even, odd/even, even/odd, and odd/odd. The similar odd–even effect was confirmed for nOCB/mOCB (n = 5, 6; m = 8, 9) binary systems. To elucidate the odd–even effect on the phase diagrams, the SmAd structures were investigated through an analysis of n (n*) dependence of the layer spacing of the SmAd structure, dSmAd, of neat nCB (n = 8–10), neat nOCB (n = 8–10), and nCB/8CB (n = 0–7) binary mixtures. The odd–even effect, the behavior of 0CB/8CB system, and the difference between nCB and nOCB were clarified based on their SmAd structures.

Effects of monovalent and monatomic salts on lamellar repeat distances d of nonionic surfactants (monomyristolein and \({\mathrm {C_{12}E_{2}}}\)) are investigated using small-angle X-ray diffraction. The lamellar repeat distances (sum of thicknesses of a bilayer and a sandwiched water layer) increase with increasing salt concentration with a strong anion dependence (Br\(^->\) Cl\(^- \)). The increase of the thickness of the water layer is found to dominate the increase in d. Since the anion dependence is inconsistent with the ion dependence of the strength of the primary hydration, we reported previously (Hishida et al. J Chem Phys 142:171101, 2015), the hydration force classically considered is not the origin of the increase in d. This means the increase in d cannot be explained by the existing model of the forces between neutrally charged bilayers. The temperature dependence of d also supports the necessity for a new mechanism of the effect of ions. The new mechanism seems to be related to the water structure beyond the primary hydration water, i.e., the secondary hydration water, which depends on the ion species.

The photocontrol of a bilayer-to-nonbilayer phase transition (the liquid-crystalline Lα phase to the inverted hexagonal HII phase) of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) by the photoisomerization of incorporated stilbene molecules was examined by utilizing differential scanning calorimetry, small-angle X-ray diffraction, ultraviolet (UV)/visible absorption, and attenuated total reflectance Fourier transform infrared spectroscopies. cis-Stilbene lowered the transition temperature, Th, to a greater extent than did trans-stilbene, and the difference was at most ca. 10 °C. At temperatures higher than the Th of POPE/cis-stilbene but lower than that of POPE/trans-stilbene, the photoisomerization from the trans to the cis form of the stilbene molecules by irradiation with UV light caused a Lα–HII phase transition. The UV irradiation partially induced the HII phase at a constant temperature because of the incomplete photoisomerization of stilbene (ca. 60%). The reduction in Th by the incorporation of stilbenes was caused mainly by the reduction in the spontaneous radius of curvature of the lipid monolayer, R0. The greater bulkiness of cis-stilbene as compared to the trans form resulted in a more effective reduction in R0 and stabilization of the HII phase.

Molecules incorporated into biomembranes often bear both a core and an alkyl chain in a single molecule (e.g., sterols). To clarify the effects of these two parts of a molecule, the phase behavior of a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) bilayer containing 4-n-alkyl-4′-cyanobiphenyl (nCB) (n = 0–8) was investigated. The trends of the main transition temperature (Tm) with respect to n and of the pretransition temperature (Tp) with respect to nCB content changed at n = 3. It was therefore suggested that the two parts of the molecule had opposing effects on the phase behavior of DPPC bilayers. The core appears to perturb molecular ordering in the gel phase and lowers Tm (like cholesterol), while alkyl chains appear to order the lipids in the gel phase and raise Tm (like n-alkanes). In addition, Tm exhibits the so-called odd–even effect based on the alkyl chain length of the minor component, nCB. Depending on the value of n, the variation in Tp was dependent on the additive content, although the pretransition was rarely observed at high contents.

Landau expansion of free energy assuming dual instabilities for the nano-segregated SmA phase is analyzed. In addition to known phase sequences (on cooling, disordered isotropic liquid → nematic phase → smectic phase, and disordered isotropic liquid → smectic phase), a new sequence (disordered isotropic liquid → density wave with subsidiary nematic order → smectic phase) and the existence of a critical point are demonstrated in the case where the instability for density wave formation occurs at a higher temperature.

Change in lamellar repeat distances of neutrally charged lipids upon addition of monovalent salts was measured with small-angle X-ray scattering for combinations of two lipids (PC and PE lipids) and six salts. Large dependence on lipid head group is observed in addition to those on added cation and anion. The ion and lipid dependences have little correlation with measured surface potentials of lipid membranes. These results indicate that the lamellar swelling by salt is not explained through balance among interactions considered previously (van der Waals interaction, electrostatic repulsion emerged by ion binding, etc.). It is suggested that effect of water structure, which is affected by not only ions but also lipid itself, should be taken into account for understanding membrane–membrane interactions, as in the Hofmeister effect.

To test metal complexes as potential compounds for heat-storage materials, two Schiff-base Ni(II) complexes derived from two differently N-substituted toluidine isomers were examined. Comparing the behavior with that of a similar complex previously reported, it was found that the cold crystallization was realized in polymorphic complexes. The activation energy for crystallization estimated by using differential scanning calorimetry was well correlated to the ease of supercooling necessary for the cold crystallization. DFT calculations of molecular energy suggested that the cold crystallization phenomenon is closely related to a molecular flexibility that prevents normal crystallization during cooling. The molecular flexibility controls the ease in the supercooling of liquid and the nucleation–growth process of crystallization by altering the activation energy for crystallization.

Thermodynamic and diffraction analyses were performed to establish the phase diagram for a binary system between 4-n-nonyl-4′-isothiocyanatobiphenyl (9TCB) and n-nonane. The swollen SmE structure is identified in the binary system. Upon swelling, a characteristic two-dimensional herringbone array is maintained whereas the layer spacing of SmE structure increases with the content of n-nonane. Considering the difficulties in explaining the experimental findings based on the traditional model of SmE structure, a new model, lamellar with two types of sublayers consisting of aromatic core and alkyl chain moieties, is proposed.

To confirm the molten state of the alkyl chain in soft crystalline phase, smectic E (SmE) phase, thermodynamic and spectroscopic analyses were performed on 4-n-alkyl-4′-isothiocyanatobiphenyl (nTCB, n: the number of carbon atoms in the alkyl group). DSC results of 11TCB and 12TCB, having extra smectic A phase besides smectic E phase, show that their chain-length dependence of entropies of transition (ΔtrsS) from the ordered crystalline (OC) phase to the SmE phase matches the trend found for nTCB (n = 4–10), while no chain-length dependence is observed in ΔtrsS at the SmE-to-SmA and SmA-to-isotropic liquid (IL) phase transitions in 11TCB and 12TCB. Temperature dependences of FT-IR spectra of six compounds (n = 2, 3, 5, 8, 10, and 12) were recorded. The CH stretching modes of the chain exhibited more pronounced change at the transition from the OC to the SmE phase than at the transition from the SmE phase to the IL or SmA phase. These results indicate that the alkyl chain is molten in the SmE phase as in IL. The disordering process of nTCB molecules from the OC to IL via anisotropic mesophases is discussed in terms of entropy.

Mechanism of successive ferroelectric–paraelectric phase transitions exhibited by an organic ferroelectric, trichloroacetamide, is clarified through structural and calorimetric experiments. The transition mechanism, intramolecular disordering, reasonably explains the polarization reversal. This mechanism is only possible in molecular solids and is applicable to other compounds as a possible strategy to design new molecular ferroelectrics. Also revealed is the incommensurate nature of the intermediate phase, the origin of which is briefly discussed at phenomenological and molecular levels.

We have investigated the photo-chemical reaction from tetra-tert-butylcyclobutadiene (TB-CBD) to tetra-tert-butyltetrahedrane (TB-THD) and its reverse thermo-chemical reaction processes in the ground state by using CASSCF and MRMP2 computational methods. According to our results, the initial step of the photochemical reaction is the HOMO–LUMO single-electron excitation (11B1 state) and the arrangement from TB-CBD to TB-THD occurs via the HOMO–LUMO double electron excited state (21A1 state). After the transition from the 11B1 to the 21A1 state, most TB-CBD molecules show only photo-physical property without any reactions because the final point of the minimum-energy-path (MEP) calculation at the MRMP2//CASSCF level is the S1/S0 conical intersection (ionic like structure), which results in turning back to TB-CBD in the S0 state. However, on the way to the final point of the MEP, it is possible for some TB-CBD to transit at another S1/S0 conical intersection (tetra radical like structure), which is related to the photoreaction from TB-CBD to TB-THD. On the other hand, two routes from TB-THD to TB-CBD were found in the S0 state. One is the route via bicyclodiradical transition state. The other is the ionic transition state. In both reaction paths, only one TS is there in contrast to the plural step reaction suggested previously.Highlights► Cyclobutadiene isomerizes to tetrahedrane via the HOMO–LUMO double electron excited state. ► Electronic effect of t-Bu group enables the photoreaction from cyclobutadiene to tetrahedrane. ► Steric effect between t-Bu groups plays a role to stabilize tetrahedral shape.

To clarify the influence of cis and trans double bonds on conformational disordering of unsaturated hydrocarbon-chain of lipids in bilayer formed in the binary system with water, calorimetric study was conducted for systems of unsaturated monoacylglycerols; monoolein (MO), monovaccenin (MV), and monoelaidin (ME). Heat capacities of the binary systems were measured by adiabatic calorimetry. The observed entropies of transition (ΔtrsS) from lamellar phase (Lα) to fluid isotropic (FI) phase are very small and depend on lipids: ΔtrsS of MO/water, MV/water, and ME/water were ca. 0.8 J K–1 (mol of lipid) –1, ca. 0.9 J K–1 (mol of lipid) –1, and ca. 0.4 J K–1 (mol of lipid) –1, respectively. These show that the conformational disordering of the hydrocarbon chain over gauche and trans conformations is suppresed in Lα phase. Through the comparison of ΔtrsS among the binary systems, the suppresed conformational disordering of hydrocarbon chain in the bilayer is discussed.

To understand the role of intramolecular degrees of freedom in forming mesophases, thermodynamic analysis was performed for 4-n-alkyl-4′-isothiocyanatobiphenyl (nTCB, n is the number of carbon atoms in the alkyl group), which exhibits the crystal E (CrE) phase as a mesophase. The heat capacities of 2TCB and 5TCB were measured by adiabatic calorimetry. Their entropies of transition (ΔtrsS) were compared with those of other nTCBs (n ≤ 10). ΔtrsS of the phase transition from the ordered crystal to CrE phase increased with their alkyl chain length, whereas that of fusion of the CrE phase remained essentially constant. These behaviors clearly show that the alkyl chain of nTCB is fully disordered even in the CrE phase. Through the comparison of ΔtrsS among 5TCB, 4-pentyl-4′-cyanobiphenyl (5CB), and pentylbiphenyl, the role of the alkyl chain for the formation of mesophases is discussed.

We report the result of comparison between two reaction coordinates [on the potential energy surface of the first excited state (S1)] produced by CASSCF and these energies recalculated by MRMP2 in the Z to Ephotoisomerization of penta-2,4-dieniminium (PDI) as the minimal model of the retinal protonated Schiff base (RPSB). One coordinate is the S1 state minimum-energy-path (MEP) in mass-weighted coordinates from the S1 vertically excited point, where a strong hydrogen-out-of plane (HOOP) motion is not exhibited. The energy profile of the S1MEP at the MRMP2//CASSCF level shows a barrier for the rotation around the reactive C–C and hits the S1/S0 degeneracy space where the central C–C–C–C dihedral angle is distorted by 65°. The other coordinate is an S1 coordinate obtained by the relaxed scan strategy. The relaxed coordinate along the central C–C–C–C dihedral angle, which we call the HOOP coordinate, shows strong HOOP motion. According to the MRMP2//CASSCF calculation, there is no barrier on the HOOP coordinate. Furthermore, the S1 to S0 transition may be possible without the large skeletal deformation by HOOP motion because the HOOP coordinate encounters the S1/S0 degeneracy space where the central C–C–C–C dihedral angle is distorted by only 40°. Consequently, if PDI is a suitable model molecule for the RPSB as often assumed, the 11-cis to all-transphotoisomerization is predicted to be accelerated by the HOOP motion.

The heat capacities of two members of a representative cubic mesogen, 4′-alkoxy-3′-nitrobiphenyl-4-carboxylic acid, were measured precisely. In accordance with the tendency reported previously for other members, the heat capacity in the cubic phase is smaller than that in the neighboring smectic C phase. The chain-length dependence of the reduction in the heat capacity upon the phase transition showed opposing trend depending on symmetry of the cubic phase (Ia3d or Im3m). This finding is rationalized by assuming the existence of two aggregation modes (rod and shell) in the Im3m phase in contrast to only the former mode in the Ia3d phase.The alkyl chain-length dependence of heat capacity supports the complex structural model of the liquid crystal with Im3m symmetry.

Nonmonotonous temperature dependence was detected in the heat capacity and dielectric constant of the title compound in the liquid state. A coherent analysis of FT-IR spectra, heat capacity, and dielectric constants shows that the neat liquid at low temperatures consists of closed (square) tetramers via H-bonds.

The heat capacity of [Hdamel]2[CuII(tdpd)2]·2THF was measured from 6 to 250 K by adiabatic calorimetry. There are four heat anomalies around 150 K associated with disordering in the orientation of the uncoordinated THF molecules and in the conformation of the out-of-plane allyl groups of [Hdamel]+ units. The total entropy of transition was determined to be 19.8 J K−1 mol−1, less than the 4R ln 2 (R = gas constant) expected from the crystal structure at room temperature. The smallness of the total entropy change on phase transitions proves the presence of the strong motional correlation between the adjacent allyl groups. The calorimetric conclusion agreed with the crystal structure at 200 K re-examined in this study.

A possible deduction is proposed of channel length distribution in one-dimensional porous materials from the kinetic data obtained in isothermal thermogravimetry (TG). The method utilizes the absorption/desorption of small molecules into one-dimensional nano-channel. In the surface-controlled absorption/desorption, the second derivative with respect to time is directly proportional to the channel-length distribution function. Even in the diffusion-controlled case, the second derivative with respect to the square root of time gives rough information on the distribution function.

Structure of a complex superstructure self-organized by thermotropic mesogen, 1,2-bis(4′-n-alkoxybenzoyl)hydrazine [BABH(n), where n is the number of carbon atoms in an alkoxy chain] was studied while paying special attention to the structure at the molecular level. Maximum entropy (MEM) analysis revealed that the molecular cores form two kinds of aggregates: Jungle gym with 3-fold junctions roughly on P minimal surface and spherical shells.

Configurational entropy due to structural disorder in complex crystals is considered in some details. It is reminded that motional correlation and equivalence of plural entities (such as molecule or group) have potentially serious effects on the entropy. Possible appearance of entropy plateaus in its temperature dependence is suggested.

•X-ray study of molecular liquids consisting of large molecules.•Coarse-grained analysis from data in limited q-range.•Clear effect of hydrogen bonding through comparison of two alcohols with bulky substituents.The formation of globular associate on cooling, which was previously claimed on the basis of small dielectric constant, is supported through measuring X-ray scattering from dicyclohexylmethanol (DCHM). Radial distribution function of the DCHM molecules exhibits strong temperature dependence between 65 °C and 130 °C in contrast to a little change in that of tricyclohexylmethanol (TCHM), which is similar to DCHM but essentially non-associating in experimental conditions (95–160 °C).

We report the result of comparison between two reaction coordinates [on the potential energy surface of the first excited state (S1)] produced by CASSCF and these energies recalculated by MRMP2 in the Z to Ephotoisomerization of penta-2,4-dieniminium (PDI) as the minimal model of the retinal protonated Schiff base (RPSB). One coordinate is the S1 state minimum-energy-path (MEP) in mass-weighted coordinates from the S1 vertically excited point, where a strong hydrogen-out-of plane (HOOP) motion is not exhibited. The energy profile of the S1MEP at the MRMP2//CASSCF level shows a barrier for the rotation around the reactive C–C and hits the S1/S0 degeneracy space where the central C–C–C–C dihedral angle is distorted by 65°. The other coordinate is an S1 coordinate obtained by the relaxed scan strategy. The relaxed coordinate along the central C–C–C–C dihedral angle, which we call the HOOP coordinate, shows strong HOOP motion. According to the MRMP2//CASSCF calculation, there is no barrier on the HOOP coordinate. Furthermore, the S1 to S0 transition may be possible without the large skeletal deformation by HOOP motion because the HOOP coordinate encounters the S1/S0 degeneracy space where the central C–C–C–C dihedral angle is distorted by only 40°. Consequently, if PDI is a suitable model molecule for the RPSB as often assumed, the 11-cis to all-transphotoisomerization is predicted to be accelerated by the HOOP motion.