Twenty preparatively useful azomethines have been quantitatively (100% yield at 100% conversion) obtained as hydrates by grinding together solid anilines with solid benzaldehydes without passing through liquid phases. Unlike (acid catalyzed) azomethine syntheses in solution, the solid–solid condensations proceed ‘waste-free’. The solid-state mechanisms have been elucidated by atomic force microscopy (AFM) and in part by scanning near-field optical microscopy (SNOM) in three cases. The results indicate long distance migration of the aldehydes into the lattice of the aniline derivatives. Stumpy protrusions are formed at the direct points of contact but also close distance sublimation (100 nm range) is successful in the case of p-chlorobenzaldehyde and p-nitroaniline. Long-range flow of 4-hydroxybenzaldehyde molecules on its (010)-face into contacting crystals of p-toluidine or p-anisidine occurs along two different cleavage planes. Steep hills and valleys are left behind. The molecular migrations through the sites of contact are interpreted in terms of crystal packing. The ease of these solid–solid condensation reactions relies on the crystal packing.

Quantitative solid–solid synthesis of azomethines

A homologous series of 8-(4′-n-alkoxybenzoyloxy) quinolines were synthesized by established methods [5,6]. On evaluation by optical microscopy, none of the homologues were found to exhibit mesogenic behavior even in the monotropic condition. Then, each homologue (B) was mixed with a liquid crystal component (A) and binary systems were studied by optical microscopy. Solid–mesomorphic or isotropic–nematic transition temperatures of binary mixtures were determined and plotted to obtain the phase diagram for transition temperatures versus percentage composition of component (A). The nematic–isotropic transition curve was extrapolated to zero mole percentage of component (A) (100%B) to determine the latent transition temperature (LTT) of each nonmesomorphic homologue. The number of carbon atoms in the n-alkyl chain of each homologue versus LTT is plotted and a phase diagram is obtained. The isotropic–nematic transition curve behaves in a normal manner like a curve behaving for a typical nematogenic homologous ...

Determination of Latent Mesogenic Behavior in Nonmesogenic Compounds by Extrapolation Method

A new homologous series viz. Isobutyl-p-(p′-n-alkoxy cinnamoyloxy) cinnamates consisting of 11 homologs has been synthesized with an isobutyl cinnamate end group and a further cinnamate moiety as a linking group. The methyl to butyl homologs are nonmesomorphic, and the pentyl to hexadecyl derivatives are enantiotropic nematogens without exhibition of any smectic phases. The average thermal stability for the nematic phase is 138.1°C with a middle ordered melting point. The structures of the novel materials were confirmed by spectroscopic techniques. The liquid crystal phase type was determined by optical polarizing microscopy and all textures are of the threaded type. The mesomorphic behavior of the series is compared with a structurally similar homologous series.

Synthesis and Mesomorphism of Novel Liquid-Crystalline Isobutyl-p-(p′-n-Alkoxy Cinnamoyloxy) Cinnamates

In order to investigate the influence of the central linkage and terminal substitutions on mesophase behaviour of liquid crystalline compounds we have synthesised six homologues series viz. 4′-(naphthalen-1-yldiazenyl)biphenyl-4-yl-4-alkoxybenzoate (Series-A), 4′-[(4-cyanophenyl)diazenyl]biphenyl-4-yl-4-alkoxybenzoate (Series-B), 4′-[(4-fluorophenyl)diazenyl]biphenyl-4-yl-4-alkoxybenzoate (Series-C), 4′-(naphthalen-1-yldiazenyl)biphenyl-4-yl(2E)-3-[4-alkoxyphenyl]prop-2-enoate (Series-D), 4′-[(4-cyanophenyl)diazenyl]biphenyl-4-yl(2E)-3-[4-alkoxyphenyl]prop-2-enoate (Series-E) and 4′-[(4-fluorophenyl)diazenyl]biphenyl-4-yl(2E)-3-[4-alkoxyphenyl]prop-2-enoate (Series-F). Series-A, -B and -C have azo-ester central linkages whereas Series-D, -E and -F have azo-cinnamate central linkages and naphthalene, 4-cyanophenyl and 4-fluorophenyl as terminal groups, respectively. All these compounds were characterised by elemental analyses and spectroscopic techniques (ultraviolet-visible, Fourier transform infrared, pr...

Mesomorphic properties of liquid crystalline compounds with biphenyl moiety containing azo-ester, azo-cinnamate central linkages and different terminal group†

Effect of azo and ester linkages on rod shaped Schiff base liquid crystals and their photophysical investigations

In binary systems, consisting of two structually similar components of which one is a liquid crystal, extrapolation of the transition curves should yield values for latent transition temperatures of the non-liquid crystalline substances. The reliability of this method of arriving at the latent transition temperatures has been questioned by some research workers. An attempt has been made under this investigation to arrive at some conclusive evidence in regard to the reliability of the method. Several binary systems with suitable Schiff's bases as one component and the well-known p-azoxyanisole or p-azoxyphenetole as the other liquidcrystal component have been studied from which a fair conclusion in favour of the dependability of the extrapolation method may be drawn. Yet, there cannot be a final word since some of the binary systems under study pose a difficulty in understanding their behaviour although discrcpancies observed have been accounted for in terms of polarity and non-ideality of the mix...

Studies in Mixed Mesomorphism: Determination of Latent Transition Temperatures by Extrapolation

Binary mixtures both components of which are liquid crystals are known to form continuous mixed liquid crystals.1 Most of them do not undergo any change in their mesomorphic textures, though a few have been found to give rise to different textures.2 We report here a binary system consisting of (A) p-nitrophenyl-p'-n-amyloxycinnamate (90.5–120.5°) and (B) p-methoxyphenyl-p'-n-heptyloxycinnamate (91.0–120.5°) which transforms the original nematic texture into a mixed smectic A texture over a range of temperature and concentration. Both components individually are nematic liquid crystals. In their binary mixtures, a two dimensional more ordered mixed Smectic A mesophase emerges between 5.0–92.5 mol% of p-methoxyphenyl-p'-n-heptyloxycinnamate over a temperature range of about 50–105° at its maximum. The mixed smectic-nematic transition curve shows a marked rounded concavity, extrapolation of which on either side yields values of latent transition temperatures 77.0° and 66.5° for the components A and ...

Emergence of Smectic Mesophase in Binary Mixtures of Pure Nematogens

The homologous series p-nitrophenyl-p'-n-alkoxycinnamates is a medium melting homologous series; the first two members are non-mesogens and do not exhibit even monotropy. The nematic phase begins from the third derivative in monotropic condition; from the fourth member enantiotropic mesomorphism commences. Polymesomorphism begins from the sixth member with the appearance of smectic mesophase and ends at the seventh member. The rest of the homologues up to the octadecyl are purely smectogens. Thus the homologous series is predominantly smectogenic even though -NO2 group is reported to be enhancing nematic character.' Within the polymesomorphic region the nematic mesophase is homeotropic; however, it shows a clear threaded texture where it is the only mesophase shown. The N-I transitions do not exhibit the usual alternation in transitions which is a rare phenomenon. The N-I transition curve is unusually neither rising nor falling though a slight curve is seen; it merges with the S-I curve which sho...

Effect of Nitro Terminal Substituent on the Liquid Crystalline Characteristics of Ester Mesogens: p-Nitrophenyl-p'-n-Alkoxycinnamates

Two new homologous series of liquid crystals viz. p-(p'-n-alkoxycinnamoyloxy) benzylidene p”-anisidines (1) and p-(p'-n-alkoxycinnamoyloxy) benzylidene anilines (2) comprising twenty four mesogens have been synthesized. Both are high melting series of mesomorphs. In the homologous series (1) the nematic mesophase is exhibited from the very first member; however, the first five compounds decompose at high temperatures before passing into isotropic liquid condition. Polymesomorphism is exhibited with the appearance of the smectic mesophase at the octyl derivative and remains up to the last viz. octadecyl homologue. Within polymesomorphic region the nematic mesophase is homeotropic; however, it shows a clear threaded texture where it is the only mesophase shown i. e. in the first seven members of the homologous series (1). The smectic mesophase shows focal conic fan shape texture belonging to smectic-A variety. The nematic-isotropic curve shows descending tendency as the series is ascended-a charact...

Synthesis and Study of New Mesogens II: p-(p′-n-Alkoxycinnamoyloxy)-benzylidene p″ -anisidines (1) and p-(p′-n-Alkoxycinnamoyloxy)- benzylidene anilines (2)

Two new homologous series comprising vinyl carboxy,—CH = CH—COO—, and azomethine,—CH = =N—, as central groups have been synthesized by treating p-(p'-n-alkoxycinnamoyloxy) benzaldehydes with p-amino N, N-dimethyl (I) and diethyl (II) anilines. All the twenty-four compounds are mesogenic in nature. Both series of liquid crystals are primarily nematogenic in character and high melting. Very wide range of mesomorphism is observed in all the homologues. In series (1) the first seven members decompose before passing into isotropic liquid form at higher temperatures because of which observation of the usual odd-even effect is missed. However, the series (II) homologues exhibit the usual odd-even effect since they do not decompose at higher temperatures. While the mesomorphic range is quite wide in series (I), that in series (II) is relatively less wide. The thermal stabilities are comparable. The special feature is that the smectic mesophase makes its appearance at very late stage; in series (I) at the...

Schiffs Base Homologous Series of New Mesogens: p-(p′-n-Alkoxycinnamoyloxy) benzylidene-p″-N, N-Dimethylaminoanilines and p-(p′-n-Alkoxycinnamoyloxy) benzylidene-p″-N, N-Diethylaminoanilines

J. M. Lohar

Papers

Studies in Mixed Mesomorphism: Determination of Latent Transition Temperatures by Extrapolation

Emergence of Smectic Mesophase in Binary Mixtures of Pure Nematogens

Effect of Nitro Terminal Substituent on the Liquid Crystalline Characteristics of Ester Mesogens: p-Nitrophenyl-p'-n-Alkoxycinnamates

Synthesis and Study of New Mesogens II: p-(p′-n-Alkoxycinnamoyloxy)-benzylidene p″ -anisidines (1) and p-(p′-n-Alkoxycinnamoyloxy)- benzylidene anilines (2)

Schiffs Base Homologous Series of New Mesogens: p-(p′-n-Alkoxycinnamoyloxy) benzylidene-p″-N, N-Dimethylaminoanilines and p-(p′-n-Alkoxycinnamoyloxy) benzylidene-p″-N, N-Diethylaminoanilines