Keiichi Moriya

Dielectric Studies of Ferroelectric Phase Transitions in Pb2xSn2(1-x)P2S6 Single Crystals

The dielectric constant of Pb 2 x Sn 2(1- x ) P 2 S 6 single crystals was measured at several frequencies from 0.1 to 100 kHz between 3.7 and 420 K. No phase transition is observed at x =1.0. The ferroelectric-paraelectric phase transition temperature decreases linearly as x increases, but curves slightly around x =0.3 and bends at x =0.61. The lowering of the phase transition with an increase in x is considered to be a result of the motion of the Sn 2+ ion. At x =0.61 and 0.66, the relatively large dispersions were interpreted as diffuse phase transitions caused by the fluctuation of the concentration of Pb 2+ ions.

Stable supramolecular helical structure of C6-symmetric hydrogen-bonded hexakis(phenylethynyl)benzene derivatives with amino acid pendant groups and their unique fluorescence properties

A highly stable supramolecular helical structure was formed by the self-assembly of novel C6-symmetric hydrogen-bonded discotic molecules, hexakis(phenylethynyl)benzene derivatives with chiral alanine parts, and exhibited orange excimer emission with a large Stokes shift.

POLYMESOMORPHISM IN A HOMOLOGOUS SERIES OF 2-(4-ALKOXYPHENYL)-5-(4-METHYLPHENYL)PYRIDINES

A new series of 2-(4- n -alkoxyphenyl)-5-(4-methylphenyl)pyridines (CH C H C H NC HOC H, n 1-10) (APMPP), which are teraryl compounds containing a pyridine ring in n 2 m 1 the centre position of the rigid core, was synthesized and the phase transitions of the homologues were studied using DSC measurements, polarizing optical microscopy and miscibility tests with terephthalylidene-bis-4- n -pentylaniline (TBPA). Only a nematic phase was found for the shorter alkoxy homologues with n 4. The longer alkoxy homologues with n 4 showed the sequence of enantiotropic phase transitions CrG-SmF-SmC-SmA-N-I, while a monotropic CrH phase was observed for the n 5-10 homologues. Interestingly, the polymesomorphisms appear when n is larger than 4. 3 6 4 5 3 6 4

Liquid Crystalline Phase Transition in Hexakis(4-(N-(41-alkoxyphenyl)iminomethyl)phenoxy)cyclotriphosphazene

Abstract A new series of cyclotriphosphazenes bearing Schiff bases with different carbon number alkoxy end groups(HAICP) in the side chains were synthesized and their phase transitions and liquid crystallinity were studied using DSC measurements and polarizing microscope observations. We found a monotropic Sml phase for n = 3 and an enantiotropic Sml phase for n = 4 −5, enantiotropic Sml, SmC and SmA phases for n = 6 – 7, enantiotropic SmC and SmA phases for n = 8 – 10, and enantiotropic Sm2, SmC and SmA phases for n=11 and 12 in the HAICP series. The Sml phase is a low-order uniaxial smectic phase and Sm2 phase is a low-order biaxial smectic phase. The melting point decreased with an increase in the end alkoxy carbon number, n, of the cyclotriphosphazenes, but the clearing point decreased with an increase in n. As a result, the mesomophic region expands with an increase in n. The melting and clearing points do not show clear odd-even effects, which is caused by the peculiar shape of the cyclotriphosphazenes.

Liquid-crystalline phase transition in organophosphazenes

Organophosphazenes with a similar mesogenic moiety were prepared and their mesogenicity was studied by differential scanning calorinetry (DSC) measurements and polarizing microsope observations. In cyclotriphosphazenes with alk- oxybiphenyl and Schiff base moieties, meso- morphic phase transitions were observed, but no mesomorphic phase was observed for the corre- sponding cyclotetraphosphazenes. In polyphos- phazenes with an alkoxybiphenyl moiety, no mesomorphic phase was observed. The molecu- lar structure of cyclotriphosphazenes facilitated the formation of a mesomorphic layer structure; in contrast, the formation of a mesomorphic layer structure did not occur in cyclotetrapho- sphazenes and polyphosphazenes, even though they bore a similar mesogenic moiety. Moreover, in cyclotriphosphazenes with an optically active alkoxybiphenyl group, a smectic C * phase was observed. The spontaneous polarization of the compound wasˇ190 m Cm ˇ 2 at 436 K in 25 m in

The synthesis and liquid crystalline behaviour of 2-(4-n-alkoxyphenyl)-5-methylpyridines

We have synthesized a new series of polyphenylene compounds with a pyridine ring, 2-(4-n-alkoxyphenyl)-5-methylpyridines (CH3C5H3NC6H4OC i H2i1) (1a-i ; the carbon number, i, of the alkoxy group is 1-9), and studied their phase transitions and mesogenicity using DSC and polarizing microscopy. In the homologous series of 1a-i , no mesomorphic phase appeared for i=1-5 and only a monotropic nematic phase was observed for i=6-9. The mesomorphic potential is relatively weaker for the 1a-i than for the 2a-i and 3a-i homologues, which are pyridine-containing three- and four-ring similar systems. This lowering of the mesogenicity may be due to the lack of a phenyl ring between the pyridine ring and the methyl group in the 1a-i homologues.

Solvent-induced chirality inversion involving supramolecular helix transformation and color-tunable fluorescence of a C6-symmetric hexakis(phenylethynyl)benzene derivative

A C(6)-symmetric disk-like molecule, a hexakis(phenylethynyl)benzene derivative bearing chiral alanine parts, L-1, exhibited a solvent-induced supramolecular helix-sense inversion involving conformational changes followed by destruction of the supramolecular helical column. This phenomenon has been found by investigating the supramolecular assembly state of L-1 in mixed solvents of various chloroform (CHCl(3))/n-hexane (Hx) ratios. L-1 forms a stable helical columnar assembly via multiple noncovalent bonding interactions in nonpolar Hx, while the molecules in relatively polar CHCl(3) are in a molecularly dispersed state. Although one would expect disruption of the helical column with the addition of nonhelicogenic CHCl(3), an opposite-handed helical columnar structure was formed at 8-15 vol% of CHCl(3), and subsequently the inverted helical column was disassembled by a further increase of CHCl(3). In addition, this morphological transformation was accompanied by a significant change in fluorescent color, which varies over a wide visible range from orange in an original helical columnar state to light blue in a molecularly dispersed state through yellow in an inverted helical columnar state. These unprecedented behaviors are shown by the spectroscopic results, and the molecular conformations of L-1 and the driving force for the helical sense inversion are discussed.

Liquid crystalline phase transitions in hexakis(4-(4′-heptyloxy)biphenoxy)cyclotriphosphazene

Abstract Hexakis(4-(4′-heptyloxy)biphenoxy)cyclotriphosphazene (HHCP) was synthesized from hexachlorocyclotriphosphazene and 4-heptyloxy-4′-hydroxybiphenyl. The mesogenicity of HHCP was studied by DSC, FTIR spectroscopy and polarizing microscopy. Enantiotropic smectic C and nematic phases were observed between 450 and 455 K and 455 and 456 K, respectively, on heating, and between 456 and 455 K (nematic) and 455 and 440 K (smectic C) on cooling from the isotropic liquid phase. The introduction of the heptyloxybiphenoxy groups as side chains into cyclotriphosphazene has generated the liquid crystalline phase. FTIR spectroscopy showed that the P=N and P-O-(C) stretching vibrations converted to lower frequencies from 1224 to 1210 cm−1 and from 920 to 910cm−1, respectively, at the crystalline (C)-Sc phase transition. This result suggests that the state of the cyclotriphosphazene ring dramatically changes near the C-Sc phase transition.

The liquid crystalline state in organophosphazenes with biphenyl mesogenic groups

Hexakis[4-(4′-decyloxy)biphenoxy]cyclotriphosphazene (HDBCTP), hexakis [4-(4′-cyano)biphenoxy]cyclotriphosphazene (HCBCTP), poly{bis[4-(4′-decyloxy) biphenoxy]phosphazene} (PDBP), and poly{bis[4-(4′-cyano)biphenoxy] phosphazene} (PCBP) were synthesized from hexachlorocyclotriphosphazene or polydichlorophosphazene and the corresponding sodium alkoxide. Their phase transition and liquid crystalline state were then studied by differential scanning calorimetry (DSC) measurements and polarizing microscope observation. We found enantiotropic smectic C in HDBCTP between 431 and 457 K and monotropic nematic between 529 and 488 K in HCBCTP only in the cooling process. No mesomorphic state was found in PDBP and PCBP.

Liquid crystalline phase transitions of the 2-(4-alkoxybiphenyl-4-yl)-5-(4-methylphenyl)pyridines

The mesomorphic phase transitions have been studied for a series of 2-(4-alkoxybiphenyl-4-yl)5-(4-methylphenyl)pyridines (4R-Pn; the carbon number, n, of the alkoxy group is 1-10) by use of DSC and polarizing optical microscopy. The 4R-Pn compounds showed only a nematic phase for n=1 and 2, but underwent characteristic polymesomorphic sequences when n>3; Cr CrH SmF SmC SmA N I with n=3 and 4, and Cr CrH SmF SmA N I with n=5-10. This mesomorphic phase transition behaviour was similar to that of the 2-(4-alkoxyphenyl)-5-(4-methylphenyl)pyridine (3R-Pn) series reported previously and it is proposed that the 4R-Pn and 3R-Pn compounds have a minimum terminal alkoxy length (critical alkoxy length) for the generation of LC polymorphism.