Hiroshi Hasebe

Discotic Liquid Crystals of Transition Metal Complexes 9: Synthesis and Properties of Discotic Liquid Crystals of Tetrapyrazinoporphyrazine Derivatives

Abstract Octa(dodecyl)etrapyrazinoporphyrazine (C12)8PzH2 the corresponding metal (II) complexes (C12)8PzM3M: Cu, Ni, Co, octa(2-ethylhexyl)tetrapyrazinoporphyrazine (2-EtC6)8PzH2 and the corresponding copper (II) complex (2-EtC6)8PzCu have been synthesized and their liquid crystalline states characterized. These properties have been compared to those of the corresponding phthalocyanines. The metal free (C12)8P2H2 derivative forms a hexagonal disordered columnar mesophase (Dhd) like (C12)8PcH2, whereas (C12)8PzM2 (M: Cu, Ni, Co) lead to centered rectangular disordered columnar mesophases (Drd). The branched chain substituted metal free derivative (2-EtC6)8PzH2 leads to a tetragonal mesophase as (2-EtC6O)8PcH2. (2-EtC6O)8PcCu forms an oblique mesophase, whereas (2-EtC6)8PzCu leads to an unidentified liquid crystal. The tetrapyrazinoporphyrazine compounds are the first π-acceptor columnar mesogens; the half-wave reduction potentials are −0.41 V.or (C12)8PzH2 and −0.55 V.or (C12)8PzM.M: Cu, Ni). In compariso...

Discotic Liquid Crystals of Transition Metal Complexes 111: The First π-Acceptor in Discotic Columnar Liquid Crystals Obtained from Octasubstituted Bis(diphenylethane-1,2-dithiolene)nickel Complexes

Abstract Disk-like complexes, bis[l,2-di(3′,4′-di-n-alkylphenyl)ethane-l,2-dithiolene]nickel (n-alkyl = n-hexyl, n-octyl) and bis[1,2-di(3′,4′-di-n-decyloxyphenyl)ethane-1,2-dithiolene]nickel have been synthesized and characterized. It was found that n-decyloxy derivative exhibits a hexagonal disordered columnar (Dhd) mesophase while n-alkyl derivatives are not discotic liquid crystals but isotropic liquids at room temperature. The half-wave potentials for reduction of these complexes is -0.04 ∼ -0.06V. n-Decyloxy derivative is the first π-acceptor in discotic columnar liquid crystals.

π-Acceptors in discotic columnar liquid crystals; an octasubstituted bis(diphenylethane-1,2-dithiol)nickel complex

Bis[1,2-bis(3′,4′-di-n-decyloxyphenyl)ethane-1,2-dithiol]nickel, the reduction potential of which is –0.06 V (vs. saturated calomel electrode in CH2Cl2), has a hexagonal disordered columnar mesophase (Dhd) at 84–112°C.

Discotic liquid crystals of transition metal complexes 25: influence of the central metal on columnar mesomorphism and π-acceptor properties of the octa-alkoxy-substituted bis(diphenyldithiolene)metal complexes

Abstract In order to investigate the influence of the central metal on mesomorphism and π-acceptor properties of the octa-alkoxy-substituted metal complexes, novel homologs, bis[di(n-alkoxy)phenyldithiolene]palladium and bis[di(n-alkoxy)phenyldithiolene]platinum (n-alkoxy=CnH2n+1O, n=1 to 12), have been synthesized. The mesophases were established by microscopic observations, DSC, and temperature-dependent X-ray diffraction techniques. As reported previously, the nickel complexes show a Colh mesophase for n=5 to 12. On the other hand, the present palladium and platinum complexes show a Colh mesophase for n=4 to 12 and n=6 to 12, respectively. Thus, they give the Colh mesophase for a shorter length of alkoxy chain in the order Pd, Ni, Pt. For 6≤n≤12, the clearing points become higher in the order Pt Ni>Pd. Hence, the order of stacking distances is apparently related to the order of clearing points. Moreover, the Pt, Ni and Pd complexes show reduction potentials at −0.09±0.01, −0.055±0.005, and 0.00≤0.01 V (versus SCE in CH2Cl2), respectively. They become better π-acceptors in the order Pt

Disk-like liquid crystals of transition metal complexes. Part 20.‡—Pursuit of chemistry to directly visualize van der Waals interactions

This work reports on mesomorphic thermochromism caused by metal centres leading to visualization of van der Waals interactions. We succeeded in obtaining columnar liquid crystals exhibiting very interesting thermochromism by introduction of long chains into disk-like bis(glyoximato) d8 metal(ii) complexes. These long-chain-substituted NiII, PdII and PtII complexes, (CnO)8-M, containing one-dimensional metal chain change color according to the metal–metal stacking distance. With increasing temperature, the metal–metal distance increases leading to an enlargement of the band gap between the filled ndz2 valence band and the empty (n+1)pzconduction band of the central metal. Generally speaking, when mesomorphic materials are heated, the peripheral alkyl chains melt, whereas the central aromatic part remains rigid. Adjacent peripheral long chains tend to lie within the van der Waals radius at lower temperatures, which results in a shortening of the distance between the central d8 metals in the present (CnO)8-M systems. This ‘fastener effect’ of the van der Waals interaction of peripheral long chains is weakened with increasing temperature, leading to visible color changes due to the ndz2–(n+1)pz interaction in the central metal chain. The 4;mmol) and 85% potassium hydroxide (12.9 g, 185 mmol) were added and the mixture was stirred vigorously forca. 1 h and filtered to remove precipitates. 3,3′,4,4′-Tetradecyloxybenzil 5 (3.00 g, 2.83 mmol) was added to the filtrate and under a nitrogen atmosphere the mixture was refluxed with stirring for 12.5 h. To the hot reaction mixture was added potassium tetrachloroplatinate(ii) (0.64 g, 1.54 mmol) dissolved in a small amount of ethane-1,2-diol. Immediately the solution was neutralized with glacial acetic acid as confirmed by pH test paper. After neutralization, reflux was continued for more than 6 h during which dark green precipitates gradually appeared. After reflux, the hot reaction mixture was filtered and the dark green precipitate collected on filter paper. The product was dissolved in chloroform and the solvent evaporated to give dark green liquid crystals. Purification was carried out by column chromatography [silica gel, chloroform–benzene (1:1 v/v), Rf=0.70] and reprecipitation carried out by adding acetone to a hot solution of the product in chloroform to give dark green liquid crystals (0.37 g, yield: 10%).

Thermochromism and solvatochromism of bis[1,2-bis(3,4-di-n-alkoxyphenyl)ethanedione dioximato]nickel(II) complexes

The long-alkoxy-chain substituted bis(glyoximato)nickel(II) complexes, bis[1,2-bis(3,4-di-n-alkoxyphenyl)ethanedione dioximato]nickel(II)(n-alkoxy =n-C8H17O1n-C12H25O), exhibit ‘mesomorphic thermochromism’ and solvatochromism. The effect of temperature and polarity of the solvent on electronic spectra of these complexes has been investigated. It was found that the thermochromism and the solvatochromism are due to the 3dz2–4pz interband transition, which is sensitive to the one-dimensional Ni–Ni stacking distance. This transition shifts to higher energy with increasing temperature. It is closely correlated to aggregation of these complexes both in the mesophase and in solution.

Discotic Liquid Crystals of Transition Metal Complexes 131: Synthesis and Discotic Columnar Mesomorphism of π-Donor Bis[1,2-di(3′,4′-di-n-alkoxyphenyl)ethane-1,2-dioximato]nickel(II) Complexes

Abstract Disk-like complexes, bis[1,2-di(3′,4′-di-n-alkoxyphenyl)ethane-1,2-dioximato]nickel(II) (abbreviated as [(CnO)4DPG]2Ni, n = 4, 8, 12) have been synthesized and characterized. The [(CnO)4DPG]2Ni (n = 4, 8, 12) complexes exhibit discotic hexagonal disordered columnar (Dhd) mesophases. Interestingly, it was found that the [(C8O)4DPG]2Ni complex has two kinds of Dhd mesophases. These complexes are the first discotic columnar liquid crystals in the bis(glyoximato)metal(II) system.

Discotic Liquid Crystals of Transition Metal Complexes 121: The Effect of the Alkoxy Chain Length on the Mesomorphism of Bis[1,2-di(3′,4′-di-n-alkoxyphenyl)ethane-1,2-dithiolene]nickel Complexes

Abstract A series of disk-like complexes, bis[1,2-di(3′,4′-di-n-alkoxyphenyl)ethane-1,2-dithiolene]nickel (abbreviated as [(CnO)4DPD]2Ni, n = 1 ∼ 12) have been synthesized in focusing our interest on the effect of the alkoxy chain length on the discotic mesomorphism. It was found that the [(CnO)4DPD]2Ni (n = 2 ∼ 4) complexes have a monotropic discophase, and that the [(CnO)4DPD]2Ni (n = 5 ∼ 12) complexes have an enantiotropic discophase (Dhd). The half-wave potentials for reduction of the [(CnO)4DPD]2Ni (n = 1 ∼ 12) complexes are -0.05 ∼ -0.06V (vs. SCE in dichloromethane solution). It is noteworthy that the π-acceptor discotic columnar liquid crystals can be obtained without impairment of the π-acceptor ability by introduction of the long alkoxy chains to the bis(dithiolene)nickel complex.

Discotic Liquid Crystals of Transition Metal Complexes 71 : Dimer Discotic Rectangular Ordered Mesophase in Bis(p-n- alkoxybiphenylbutane-1,3-dionato)copper (II) Complexes

Abstract A novel series of bis(p-n-alkoxybiphenylbutane-1,3-dionato)copper(II) complexes (n-alkoxy = CnH2n+1, O, n = 8 ∼ 12, 16, 18) have been synthesized and characterized. The CnO-Cu complexes for n = 9 ∼ 12, 16, and 18 have a unique dimer discotic rectangular ordered columnar (D10 mesophase. The X-ray diffraction powder pattern of the D10 mesophase of the C16O-Cu complex at 185[ddot]C gave the intradimer distance 5.12 A, the interdimer distance in the column 9.40 A, and the two-dimensional rectangular lattice constants a = 46.8 A, b = 16.7 A. The type of the present D10, mesophase could be assigned as D10 (C2/m).

Mesomorphism and Unusual Multiple Melting Behavior via Smectic E Phase in p-n-Alkoxybiphenylbutane-1,3-dione

Abstract 4-n-Alkoxy-4′-acetylbiphenyl(C n O-A: 8 ∼ 12, 16, 18) and p-n-alkoxybiphenylbutane-1,3-dione(CnO- Lig: 8 ∼ 12,16, 18) have been synthesized and characterized. The CnO-A (n = 8 ∼ 12, 16) derivatives have a smectic E mesophase. The CnO-Lig(n = 8 ∼ 12, 16, 18) have two mesophases, smectic E and smectic A mesophases. Interestingly, each of the CnO-Lig(n = 8 ∼ 12) compounds has three crystalline polymorphs. The CnO-Lig derivatives for n = 8, 10, and 12 show two types of double melting behavior via the smectic E mesophase. The CnO-Lig derivatives for n = 9 and 11 exhibit triple melting behavior via the smectic E mesophase.