Ab initio calculations on the barrier to pseudorotation of model 2′-deoxyfuranose and 2′-deoxy-2′-fluorofuranose rings

Model ring systems 2′-deoxy-2′-fluororibofuranose and deoxyribofuranose have been investigated using ab initio calculations with the 3–21G basis set. The energy barrier to pseudorotation between the N and S states has been evaluated for the three preferred orientations of the (3′)-OH group. Positions of the energy minima and the transition state have been optimized with respect to the (3′)-OH orientation. The barrier to pseudorotation of 2′-deoxy-2′-fluorofuranose is high and asymmetrical (ΔE_N→S ≈ 20, ΔE_N←S ≈ 8 kJ/mol), whereas the barrier of 2′-deoxyfuranose is lower and almost symmetrical (ΔE ≈ 11–12 kJ/mol). The results obtained show that the preferred configuration of the 2′-deoxy-2′-fluororibo-furanose (N state) is stabilized by an internal O(3′)-H…?F interaction in accord with the crystallo-graphic data.     

Fully aromatic thermotropic liquid crystalline polyesters of 3-phenyl-4,4′-biphenol with 4,4′-benzophenone dicarboxylic acid

A series of fully aromatic, thermotropic polyesters, derived from 3-phenyl-4,4′-biphenol (MPBP), nonlinear 4,4′-benzophenone dicarboxylic acid (4,4′-BDA), and various other comonomers was prepared by the melt polycondensation method and characterized for their thermotropic liquid crystalline behavior by a variety of experimental techniques. The homopolymer of MPBP with 4,4′-BDA had a fusion temperature (T_f) at 240°C, exhibited a nematic liquid crystalline phase, and had a narrow liquid crystalline range of 60°C. All of the copolyesters of MPBP with 4,4′-BDA and either 30 mol % 4-hydroxybenzoic acid (HBA), 6-hydroxy-2-naphthoic acid (HNA) or 50 mol % terephthalic acid (TA), 2,6-naphthale-nedicarboxylic acid (2,6-NDA) and low T_f values in the range of 210–230°C, exhibited a nematic phase, and had accessible isotropization transitions (T_i) in the range of 320–420°C, respectively. As expected, each of them had a broader range of liquid crystalline phase than the homopolymer. They had a “frozen” nematic, glassy order as determined with the wide-angle X-ray diffraction (WAXD) studies. The morphology of each of the “as-made” polyesters had a fibrous structure as determined with the scanning electron microscopy (SEM), which arises because of the liquid crystalline domains. Moreover, they had higher glass transition temperatures (T_g) in the range of 167–190°C than those of other liquid crystalline polyesters, and excellent thermal stabilities (T_d) in the range of 500–533°C, respectively. © 1995 John Wiley & Sons, Inc.     

Synthesis and characterization of mesogen‐jacketed liquid‐crystal polymers based on 2,5‐bis(4′‐alkoxyphenyl)styrene

A series of novel mesogen‐jacketed liquid‐crystal polymers, poly[2,5‐bis(4′‐alkoxyphenyl)‐styrene] (P‐n, n = 1–11), were prepared via free‐radical polymerization of newly synthesized monomers, 2,5‐bis(4′‐alkoxyphenyl)styrene (M‐n, n = 1–11). The influence of the alkoxy tail length on the liquid‐crystalline behaviors of the monomers and the polymers was investigated with differential scanning calorimetry (DSC), thermogravimetry, polarized optical microscopy (POM), and wide‐angle X‐ray diffraction (WAXD). The monomers with n = 1–4, 9, and 11 were monotropic nematic liquid crystals. All other monomers exhibited enantiotropic nematic properties. Their melting points (T_m's) decreased first as n increased to 6, after which T_m increased slightly at longer spacer lengths. The isotropic–nematic transition temperatures decreased regularly with increasing n values in an odd–even way. The glass‐transition temperatures (T_g's) of the polymers first decreased as the tail lengths increased and then leveled off when n ≥ 7. All polymers were thermally stable and entered the mesophase at a temperature above T_g. Upon further heating, no mesophase‐to‐isotropic melt transition was observed before the polymers decomposed. WAXD studies indicated that an irreversible order–order transition for the polymers with short tails (n ≤ 5) and a reversible order–order transition for those with elongated tails (n ≥ 6) occurred at a temperature much higher than T_g. However, such a transition could not be identified by POM and could be detected by DSC only on heating scans for the polymers with long tails (n ≥ 7). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1454–1464, 2003     

Mesomorphic phase transitions of a series of D-phase compounds

Abstract

Mesomorphic phase transitions of 4′-n-alkoxy-3′-nitrobiphenyl-4-carboxylic acids (ANBC) with numbers of carbons (n) in the alkoxy group ranging from 11 to 22 have been studied by differential scanning calorimetry (DSC) and polarizing optical microscopy. The D phase, a mesophase of particular interest through its being optically isotropic, was observed for the n = 17, 19, 20, 21, and 22 members of the ANBCs, as well as for the n = 16 and 18 members, as reported previously. The S_c-D phase transition temperature decreased with increasing n, so that the temperature range of the D phase extended over 64° at n = 22. In the n = 15 member, the D phase was certainly observed on first heating, but was not seen on subsequent cooling and second heating processes.     

Segmented polyurethanes with 4,4′-bis-(6-hydroxyhexoxy)biphenyl as chain extender. Part 2. Synthesis and properties of MDI-polyurethanes in comparison with 2,4-TDI-polyurethanes

Linear segmented polyurethanes based on poly(butylene adipate)s (PBA) of different molecular weight (M_n 2000, 1000, and 600), 4,4′-diphenylmethane diisocyanate (MDI) and the mesogenic diol 4,4′-bis-(6-hydroxyhexoxy)biphenyl (BHHBP) as well as the unsegmented polyurethane consisting of MDI/BHHBP units have been synthesized and characterized by elemental analysis, ¹³C-NMR and SEC. The thermal behavior and the morphology were studied by DSC, polarizing microscopy, and DMA. The properties of the MDI-polyurethanes were discussed in relation to the BHHBP chain extended 2,4-TDI-polyurethanes and common 1,4-butanediol chain-extended MDI products. MDI polyurethanes based on PBA (M_n 2000) exhibit a glass transition temperature T_g of about −40°C independent of the hard segment content up to ∼50% hard segments. At higher hard segment contents increasing T_gs were observed. Polyurethanes, based on the shorter polyester soft segments PBA (M_n 1000 or 600), reveal an increase in the glass transition temperatures with growing hard segment content. The thermal transitions caused by melting of the MDI/BHHBP hard segment domains are found at 50 K higher temperatures in comparison with the analogous TDI products with mesogenic BHHBP/TDI hard segments. Shortening of the PBA chain length causes a shift of the thermal transitions to lower temperatures. Polarizing microscopy experiments indicate that liquid crystalline behavior is influenced by both the content of mesogenic hard segments and the chain length of the polyester. © 1996 John Wiley & Sons, Inc.     

Wholly aromatic thermotropic liquid crystalline polyesters of 3,3′-bis(phenyl)-4,4′-biphenol with 4,4′-benzophenone dicarboxylic acid

A series of wholly aromatic, thermotropic polyesters, derived from 3,3′-bis(phenyl)-4,4′-biphenol (DPBP), nonlinear 4,4′-benzophenone dicarboxylic acid (4,4′-BDA), and various linear comonomers, were prepared by the melt polycondensation reaction and characterized for their thermotropic properties by a variety of experimental techniques. The homopolymer of DPBP with 4,4′-BDA had a fusion temperature (T_f) at 265°C, exhibited a nematic phase, and had a liquid crystalline range of 105°C. All of the copolyesters of DPBP with 4,4′-BDA and either 30 mol % 4-hydroxybenzoic acid (HBA), 6-hydroxy-2-naphthoic acid (HNA), or 50 mol % terephthalic acid (TA), 2,6-naphthalenedicarboxylic acid (2,6-NDA) had low T_f values in the range of 220–285°C, exhibited a nematic phase, and had accessible isotropization transitions (T_i) in the range of 270–420°C, respectively. Their accessible T_i values would enable one to observe a biphase structure. Each of the copolymers with HBA or HNA had a much broader range of liquid crystalline phase. In contrast, each of the copolymers with TA or 2,6-NDA had a relatively narrow range of liquid crystalline phase. Each of these polyesters had a glassy, nematic morphology that was confirmed with the DSC, PLM, WAXD, and SEM studies. As expected, they had higher glass transition temperatures (T_g) in the range of 161–217°C than those of other liquid crystalline polyesters, and excellent thermal stabilities (T_d) in the range of 494–517°C, respectively. Despite their noncrystallinity, they were not soluble in common organic solvents with the exception that the homopolymer and its copolymer with TA had limited solubility in CHCl₃. However, they were soluble in the usual mixture of p-chlorophenol/1,1,2,2-tetrachloroethane (60/40 by weight) with the exception of the copolymer with 2,6-NDA. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 769–785, 1997     

Heteroleptic FeII Complexes of 2,2′‐Biimidazole and Its Alkylated Derivatives: Spin‐Crossover and Photomagnetic Behavior

Three iron(II) complexes, [Fe(TPMA)(BIM)](ClO₄)₂?0.5H₂O ( 1 ), [Fe(TPMA)(XBIM)](ClO₄)₂ ( 2 ), and [Fe(TPMA)(XBBIM)](ClO₄)₂ ?0.75CH₃OH ( 3 ), were prepared by reactions of Fe^II perchlorate and the corresponding ligands (TPMA=tris(2‐pyridylmethyl)amine, BIM=2,2′‐biimidazole, XBIM=1,1′‐(α,α′‐o‐xylyl)‐2,2′‐biimidazole, XBBIM=1,1′‐(α,α′‐o‐xylyl)‐2,2′‐bibenzimidazole). The compounds were investigated by a combination of X‐ray crystallography, magnetic and photomagnetic measurements, and Mössbauer and optical absorption spectroscopy. Complex 1 exhibits a gradual spin crossover (SCO) with T_1/2=190 K, whereas 2 exhibits an abrupt SCO with approximately 7 K thermal hysteresis (T_1/2=196 K on cooling and 203 K on heating). Complex 3 is in the high‐spin state in the 2–300 K range. The difference in the magnetic behavior was traced to differences between the inter‐ and intramolecular interactions in 1 and 2 . The crystal packing of 2 features a hierarchy of intermolecular interactions that result in increased cooperativity and abruptness of the spin transition. In 3 , steric repulsion between H atoms of one of the pyridyl substituents of TPMA and one of the benzene rings of XBBIM results in a strong distortion of the Fe^II coordination environment, which stabilizes the high‐spin state of the complex. Both 1 and 2 exhibit a photoinduced low‐spin to high‐spin transition (LIESST effect) at 5 K. The difference in the character of intermolecular interactions of 1 and 2 also manifests in the kinetics of the decay of the photoinduced high‐spin state. For 1 , the decay rate constant follows the single‐exponential law, whereas for 2 it is a stretched exponential, reflecting the hierarchical nature of intermolecular contacts. The structural parameters of the photoinduced high‐spin state at 50 K are similar to those determined for the high‐spin state at 295 K. This study shows that N‐alkylation of BIM has a negligible effect on the ligand field strength. Therefore, the combination of TPMA and BIM offers a promising ligand platform for the design of functionalized SCO complexes.     

2′, 3′-Dideoxy-3′-fluorotubercidin and Related Dideoxyribonucleosides:. Synthesis via a 2′-deoxy-3′-oxoribofuranoside intermediate and conformation studies

An efficient synthesis of the unknown 2′-deoxy-D-threo-tubercidin ( 1b ) and 2′, 3′-dideoxy-3′-fluorotubercidin ( 2 ) as well as of the related nucleosides 9a, b and 10b is described. Reaction of 4-chloro-7-(2-deoxy-β-D-erythro-pentofuranosyl)-7H-pyrrolo[2,3-d]pyrimidine ( 5 ) with (tert-butyl)diphenylsilyl chloride yielded 6 which gave the 3′-keto nucleoside 7 upon oxidation at C(3′). Stereoselective NaBH₄ reduction (→ 8 ) followed by deprotection with Bu₄NF(→ 9a )and nucleophilic displacement at C(6) afforded 1b as well as 7-deaza-2′-deoxy-D-threo-inosine ( 9b ). Mesylation of 4-chloro-7-{2-deoxy-5-O-[(tert-butyl)diphenylsilyl]-β-D-threo-pentofuranosyl}-7H-pyrrolo[2,3-d]-pyrimidine ( 8 ), treatment with Bu₄NF (→ 12a ) and 4-halogene displacement gave 2′, 3′-didehydro-2′, 3′-dideoxy-tubercidin ( 3 ) as well as 2′, 3′-didehydro-2′, 3′-dideoxy-7-deazainosne ( 12c ). On the other hand, 2′, 3′-dideoxy-3′-fluorotubercidin ( 2 ) resulted from 8 by treatment with diethylamino sulfurtrifluoride (→ 10a ), subsequent 5′-de-protection with Bu₄NF (→ 10b ), and Cl/NH₂ displacement. ¹H-NOE difference spectroscopy in combination with force-field calculations on the sugar-modified tubercidin derivatives 1b , 2 , and 3 revealed a transition of the sugar puckering from the ^3′T_2′ conformation for 1b via a planar furanose ring for 3 to the usual ^2′T_3′ conformation for 2.     

Two reversible enantiotropic phase transitions in a pentacoordinate silicon complex with an O,N,O′‐tridentate valinate ligand

Dimethyl[N‐(4‐oxidopent‐3‐en‐2‐ylidene)valinato‐κ³O,N,O′]silicon(IV), C₁₂H₂₁NO₃Si, (II), crystallizes in the orthorhombic space group P2₁2₁2₁. The chiral compound undergoes two sharp enantiotropic phase transitions upon cooling. The first transformation occurs at 163 K to yield a unit cell with one axis having double length. This intermediate‐temperature form has the monoclinic space group P2₁. The second transition takes place at 142 K and converts the single crystal into the low‐temperature form in the orthorhombic space group P2₁2₁2₁. This transition proceeds under tripling of the a axis of the high‐temperature form. Both phase transitions are fully reversible and correspond to order–disorder transitions of the isopropyl group of the valine unit in the ligand backbone. The phase transitions presented here raise questions, since they do not fit into the rules of group–subgroup relationships.     

Reactions of the iso-butyl radical during 1,1′-azoisobutane pyrolysis

Quantitative analysis of the products formed in 1,1′-azoisobutane pyrolyses in the temperature range of 553°–602°K has shown that the major reactions of the iso-butyl radical are Analysis of initial rate data gave log₁₀k₄/(k_c)^1/2(cm^?3/2.mol ^1/2.sec^?1/2) = 7.54±0.44 ? (136.5 + 4.8) kJ/mol/2.303RT, the Arrhenius parameters obtained being in good agreement with thermodynamic data for reaction (4). Measured values of k_a/(k_c)^1/2 where k_a is the rate constant of the reaction iC₄H₉ + AIB → iC₄H₁₀ +. AIB were consistent with published parameters determined by photolysis of 1,1′-azoisobutane. Combination of photolysis and pyrolysis data gave log₁₀ k_a/(k_c)^1/2(cm^3/2.mol^?1/22.sec^?1/2) = 3.68 ± 0.15 ? (27.2 ± 1.2) kJ/mol/2.303RT. The crosscombination ratio for methyl and iso-butyl radicals has been found to be 0.25, indicating that the geometric mean rule does not hold for methyl and iso-butyl radicals.     

Desymmetrization of 3,3′‐Bis(acylamino)‐2,2′‐bipyridine‐Based Discotics: The High Fidelity of Their Self‐Assembly Behavior in the Liquid‐Crystalline State and in Solution

Two novel nonsymmetrical disc‐shaped molecules 1 and 2 based on 3,3′‐bis(acylamino)‐2,2′‐bipyridine units were synthesized by means of a statistical approach. Discotic 1 possesses six chiral dihydrocitronellyl tails and one peripheral phenyl group, whereas discotic 2 possesses six linear dodecyloxy tails and one peripheral pyridyl group. Preorganization by strong intramolecular hydrogen bonding and subsequent aromatic interactions induce self‐assembly of the discotics. Liquid crystallinity of 1 and 2 was determined with the aid of polarized optical microscopy, differential scanning calorimetry, and X‐ray diffraction. Two columnar rectangular mesophases (Col_r) have been identified, whereas for C₃‐symmetrical derivatives only one Col_r mesophase has been found. 1 In solution, the molecularly dissolved state in chloroform was studied with ¹H NMR spectroscopy, whereas the self‐assembled state in apolar solution was examined with optical spectroscopy. Remarkably, these desymmetrized discotics, which lack one aliphatic wedge, behave similar to the symmetric parent compound. To prove that the stacking behavior of discotics 1 and 2 is similar to that of reported C₃‐symmetrical derivatives, a mixing experiment of chiral 1 with C₃‐symmetrical 13 has been undertaken; it has shown that they indeed belong to one type of self‐assembly. This helical J‐type self‐assembly was further confirmed with UV/Vis and photoluminescence (PL) spectroscopy. Eventually, disc 2 , functionalized with a hydrogen‐bonding acceptor moiety, might perform secondary interactions with molecules such as acids.     

Novel hydrazone derivatives of 7‐hydroxy‐3′,3′‐dimethyl‐3′H‐spiro[chromene‐2,1′‐isobenzofuran]‐8‐carbaldehyde

The structures of new oxaindane spiropyrans derived from 7‐hydroxy‐3′,3′‐dimethyl‐3′H‐spiro[chromene‐2,1′‐isobenzofuran]‐8‐carbaldehyde (SP1), namely N‐benzyl‐2‐[(7‐hydroxy‐3′,3′‐dimethyl‐3′H‐spiro[chromene‐2,1′‐isobenzofuran]‐8‐yl)methylidene]hydrazinecarbothioamide, C₂₇H₂₅N₃O₃S, (I), at 120 (2) K, and N′‐[(7‐hydroxy‐3′,3′‐dimethyl‐3′H‐spiro[chromene‐2,1′‐isobenzofuran]‐8‐yl)methylidene]‐4‐methylbenzohydrazide acetone monosolvate, C₂₇H₂₄N₂O₄·C₃H₆O, (II), at 100 (2) K, are reported. The photochromically active C_spiro—O bond length in (I) is close to that in the parent compound (SP1), and in (II) it is shorter. In (I), centrosymmetric pairs of molecules are bound by two equivalent N—H...S hydrogen bonds, forming an eight‐membered ring with two donors and two acceptors.     

四氯合金属(II)酸正烷铵在280-500K间的热力学性质和相变 II: 四氯合锌(II)酸正十二烷铵

研究了四氯合锌(II)酸正十二烷铵(C12H25NH3)2ZnCl4(1)]在280-500K间的热力学性质和相变热参数. 据报导(RNH3)MX4型化合物在300-380K间有相变焓很大的固-固相变, 是很有开发前景的固-固相变低温储能材料, 本文为(1)的应用提供了精确的热数据.     

Synthesis and characterization of liquid crystalline copolymethacrylates,copolyacrylates, and copolysiloxanes containing 4-methoxy-4′-hydroxy-α-methylstilbene and 4-hydroxy-4′-methoxy-α-methylstilbene constitutional isomers as side-groups

The synthesis of methacrylates and acrylates containing 4-methoxy-4′-hydroxy-α-methylstilbene and 4-hydroxy-4′-methoxy-α-methylstilbene constitutional isomers attached to the polymerizable group through flexible spacers containing 11, 8, 6, 3, and respectively 2 methylenic units is described. The radical copolymerization of a 1/2 or 2/1 mole ratio of the two constitutional isomeric monomers led to thermotropic side-chain liquid crystalline polymers in all cases. The synthesis of copolysiloxanes based on the same constitutional isomeric mesogens as side groups, and flexible spacers containing 11, 8, 6, 5, and respectively 3 methylenic units is also described. All polymers were characterized by differential scanning calorimetry and optical polarization microscopy. The polymers containing 11 methylenic units in the spacer exhibit S_c mesomorphism, while the other polymers are nematic. Copolymethacrylates do not undergo side-chain crystallization. Only the copolyacrylate containing 11 methylenic units in the spacer exhibits side-chain crystallization. All the copolysiloxanes display side-chain crystallization. The number of melting transitions seen for these polymers decreases with increasing spacer length. Copolysiloxanes containing dissimilar spacer length were also prepared. Only the copolymer synthesized with highly dissimilar spacer lengths, i.e., containing 3 and 11 methylenic units, does not undergo side-chain crystallization. These results have demonstrated that while the type of mesophase is dictated only by the spacer length, the degree of decoupling of the motion of the side-groups from the motion of the main chain is strongly dependent on the nature of the polymer backbone. For the same mesogenic unit and spacer length, the thermal stability of the mesophase is also dictated by the nature of the polymer backbone. The use of constitutional isomers of mesogenic units as side groups in liquid crystalline polymers provides at least qualitative information on the degree of decoupling of the side groups from the polymer main chain.     

Enhanced third‐order nonlinear optical properties determined in thin films using the Z‐scan technique: bis(μ‐4,4′‐oxydibenzoato)bis[(4′‐phenyl‐2,2′:6′,2′′‐terpyridine)cobalt(II)]

π‐Conjugated organic materials exhibit high and tunable nonlinear optical (NLO) properties, and fast response times. 4′‐Phenyl‐2,2′:6′,2′′‐terpyridine (PTP) is an important N‐heterocyclic ligand involving π‐conjugated systems, however, studies concerning the third‐order NLO properties of terpyridine transition metal complexes are limited. The title binuclear terpyridine Co^II complex, bis(μ‐4,4′‐oxydibenzoato)‐κ³O,O′:O′′;κ³O′′:O,O′‐bis[(4′‐phenyl‐2,2′:6′,2′′‐terpyridine‐κ³N,N′,N′′)cobalt(II)], [Co₂(C₁₄H₈O₅)₂(C₂₁H₁₅N₃)₂], (1), has been synthesized under hydrothermal conditions. In the crystal structure, each Co^II cation is surrounded by three N atoms of a PTP ligand and three O atoms, two from a bidentate and one from a symmetry‐related monodentate 4,4′‐oxydibenzoate (ODA²⁻) ligand, completing a distorted octahedral coordination geometry. Neighbouring [Co(PTP)]²⁺ units are bridged by ODA²⁻ ligands to form a ring‐like structure. The third‐order nonlinear optical (NLO) properties of (1) and PTP were determined in thin films using the Z‐scan technique. The title compound shows a strong third‐order NLO saturable absorption (SA), while PTP exhibits a third‐order NLO reverse saturable absorption (RSA). The absorptive coefficient β of (1) is −37.3 × 10⁻⁷ m W⁻¹, which is larger than that (8.96 × 10⁻⁷ m W⁻¹) of PTP. The third‐order NLO susceptibility χ⁽³⁾ values are calculated as 6.01 × 10⁻⁸ e.s.u. for (1) and 1.44 × 10⁻⁸ e.s.u. for PTP.     

Wholly aromatic thermotropic liquid crystalline polyesters of 4,4′-biphenol,substituted biphenols,and 1,1′-binaphthyl-4,4′-diol with 3,4′-benzophenone dicarboxylic acid

Wholly aromatic, thermotropic homopolyesters, derived from 4,4′-biphenol, substituted biphenols, or 1,1′-binaphthyl-4,4′-diol and 3,4′-benzophenone dicarboxylic acid, and two copolyesters, each of which contained 30 mol % of 6-hydroxy-2-naphthoic acid, were prepared by acidolysis polycondensation reactions and characterized for their liquid crystalline properties. The solubility behavior of these polymers has also been investigated. The two homopolymers of phenyl-substituted biphenols with 3,4′-benzophenone dicarboxylic acid were soluble in many common organic solvents. All of the homopolymers had lower T_m/T_f values than those with terephthalic acid, which was attributed to the incorporation of the asymmetric 3,4′-benzophenone dicarboxylate units in a head-to-head and head-to-tail fashion along the polyester chain. Two copolymers had lower T_m values than those of the respective homopolymers, as expected. They formed nematic phases which persisted up to 400°C, except those of phenyl-substituted biphenols with 3,4′-benzophenone dicarboxylic acid. Each of these two polymers also exhibited an accessible T_i transition, and had a broad range of LC phase. They had glass transition temperatures, T_g, in the range of 139-209°C and high thermal stabilities in the temperature range of 465-511°C. © 1995 John Wiley & Sons, Inc.     

A solid‐state 13C‐NMR study of the mesophases of PEIM‐9 (poly(4,4′‐phthaloimidobenzoylnonamethylene‐oxycarbonyl))

On cooling from the melt, poly(4,4′‐phthaloimidobenzoylnonamethyleneoxycarbonyl) (PEIM‐9) forms a monotropic, smectic liquid crystal phase (T_i = 369.2 K). The main driving force for this mesophase formation is the attainment of nanophase separation of the mobile nonamethylene spacer from the geometrically rigid, but irregular, phthaloimidobenzoyl group, coupled with partial conformational ordering of the CH₂ groups (about 20% of the CH₂ groups attain trans‐conformations). It is shown by nuclear magnetic resonance that PEIM‐9 consists at room temperature of two motionally distinguishable components. One is the liquid crystal that remains mobile to its glass transition temperature (T_g ≈ 323 K), the other a more rigid crystal with a large degree of conformational disorder. In this crystal phase (T_m ≈ 415 K) the conformationally disordered nonamethylene spacer has a similar amount of disorder than in the liquid crystal phase and the phthaloimidobenzoyl group is also not fully ordered. Even after long‐term annealing, all molecules remain conformationally disordered, but T_m increases to about ≈ 437 K.     

Mesomorphism and Photophysics of Some Metallomesogens Based on Hexasubstituted 2,2′:6′, 2′′‐Terpyridines

The luminescent and mesomorphic properties of a series of metal complexes based on hexacatenar 2,2′:6′,2′′‐terpyridines are investigated using experimental methods and density functional theory (DFT). Two types of ligand are examined, namely 5,5′′‐di(3,4,5‐trialkoxyphenyl)terpyridine with or without a fused cyclopentene ring on each pyridine and their complexes were prepared with the following transition metals: Zn^II, Co^III, Rh^III, Ir^III, Eu^III and Dy^III. The exact geometry of some of these complexes was determined by single X‐ray diffraction. All complexes with long alkyl chains were found to be liquid crystalline, which property was induced on complexation. The liquid‐crystalline behaviour of the complexes was studied by polarising optical microscopy and small‐angle X‐ray diffraction. Some of the transition metal complexes (for example, those with Zn^II and Ir^III) are luminescent in solution, the solid state and the mesophase; their photophysical properties were studied both experimentally and using DFT methods (M06‐2X and B3LYP).     

Segmented polyurethanes with 4,4′-bis-(6-hydroxyhexoxy) biphenyl as chain extender. I. Synthesis and characterization of 2,4-tdi-polyurethanes

Polyurethanes composed of 2,4-toluene diisocyanate (TDI), poly (butylene adipate) diols (PBA) of different molecular weights, and 4,4′-bis-(6-hydroxyhexoxy) biphenyl (BHHBP) were prepared by a two-step solution polymerization process. The polyurethanes were char-acterized by elemental analysis, NMR, and SEC. The thermal properties were investigated by DSC, DMA, and optical polarizing microscopy. Dependent on the molecular weight of the PBA, a shift in the glass transition temperature T_g of the polyurethanes has been observed by DSC and DMA. Polyurethanes based on poly (butylene adipate)s of M_n ～ 2000 exhibited a T_g nearly independent on the hard-segment content up to 50% LC hard segments, indicating the existence of mainly phase separated soft and hard segments. By shortening the PBA chain length up to 1,000 and further to 600, the T_g of the polyester soft-segment phase increases with growing hard-segment content, a consequence of enhanced interaction between the hard and soft segments. This tendency is observed to the greatest extent at polyurethanes with the shortest, polyester diol and can be interpreted as a partial miscibility or compatibility of hard and soft segments. Although in polyurethanes with PBA 2000 the mesophase can be proven at a hard-segment content of ～ 40%, its appearance in polyure-thances prepared with PBA 1000 or PBA 600 requires a hard-segment content > 60%. © 1995 John Wiley & Sons, Inc.     

Synthesis and characterization of thermotropic liquid crystalline polyurethanes from 4,4′‐bis(6‐hydroxyhexoxy) biphenyl and aliphatic diols

A series of thermotropic liquid crystalline polyurethanes (LCPUs) were synthesized by the polyaddition reactions of 2,4‐toluene diisocyanate (2,4‐TDI) with 4,4′‐bis(6‐hydroxyhexoxy)biphenyl (BHHBP) and aliphatic diol. The intrinsic viscosities of the polymers were measured by Ubbelohde viscometer, and the chemical structure was confirmed by Fourier transform infrared spectroscopy (FT‐IR). The LCPUs were examined by differential scanning calorimetry (DSC), polarized optical microscopy (POM), wide angle X‐ray diffraction (WAXD), and thermogravimetric analysis (TGA). The intrinsic viscosities were 0.56–0.83 dl/g. According to the melting point (T_m) and the isotropic temperature (T_i) of the LCPUs, the temperature range of the liquid crystalline phase became wider with increased number of methylene spacers in the polyurethane. The LCPUs exhibited a nematic phase with a threaded texture and had a wide mesophase temperature range. The decomposition temperature of the LCPUs was >300°C. On WAXD, the LCPUs give a dispersing peak at 2θ ≈ 20°, and a strong diffraction peak at 2θ ≈ 25°. Copyright © 2008 John Wiley & Sons, Ltd.