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_iH_2i1) (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.     

Ultraviolet absorption spectra of 2-alkylamino-, 2-phenylamino-,2-morpholino-3-(or 5)-nitro-4-methylpyridines and some 2-alkylamino-3,5-dinitro-4-methylpyridines

Electronic spectra of thirteen title compounds were measured and the substituent effect on _max and _max were discussed. It was found that there is a disturbance of mutual electronic interaction of substituent by a steric ortho-effect. The obtained results provide evidence that the investigated 2-akylamino compounds exist in amino form.Department of Organic Chemistry, Academy of Economics, Wroclaw PL-53-432. Published in Khimiya Geterot siklicheskikh Soedinenii, No. 9, pp. l228–l231, September, 1996. Original article submitted August 20, 1995.     

The synthesis and mesomorphic properties of 4-n-alkoxyphenyl 4-[(4-n-alkoxy-2,3,5,6-tetrafluorophenyl)ethyl]benzoates

4-n-Alkoxyphenyl4-[(4-n-alkoxy-2,3,5,6-tetrafluorophenyl)ethynyl]benzoates (compound A) are synthesised by a convenient method. These compounds exhibit only enantiotropic nematic phases and have very high clearing points. These compounds (As) can be transformed into corresponding ethane derivatives, via hydrogenation using a palladium catalyst (Pd/C), which exhibit monotropic nematic phases. The effect of the ethylene bridge (–CH₂CH₂–) on the mesomorphic behaviour is discussed.     

The synthesis and liquid crystalline behaviour of alkoxy-substituted derivatives of 1,4-bis(phenylethynyl)benzene

Despite the prevalence of organised 1,4-bis(phenylethynyl)benzene derivatives in molecular electronics, the interest in the photophysics of these systems and the common occurrence of phenylethynyl moeties in molecules that exhibit liquid crystalline phases, the phase behaviour of simple alkoxy-substituted 1,4-bis(phenylethynyl)benzene derivatives has not yet been described. Two series of 1,4-bis(phenylethynyl)benzene derivatives, i.e. 1-[(4'-alkoxy)phenylethynyl]-4-(phenylethynyl)benzenes (5a-5f) and methyl 4-[(4'-alkoxy)phenylethynyl-4'-(phenylethynyl)] benzoates (18a-18f) [alkoxy = n-C₄H₉ (a), n-C₆H₁₃ (b), n-C₉H₁₉ (c), n-C₁₂H₂₅ (d), n-C₁₄H₂₉ (e), n-C₁₆H₃₃ (f)] have been prepared and characterised. Both series have good chemical stability at temperatures up to 210°C, the derivatives featuring the methyl ester head-group (18a-18f) offering rather higher melting points and generally stabilising a more diverse range of mesophases at higher temperatures than those found for the simpler compounds (5a-5f). Smectic phases are stabilised by the longer alkoxy substituents, whereas for short and intermediate chain lengths of the simpler system (5a-5c) nematic phases dominate. Diffraction analysis was used to identify the SmB_hex phase in (5d-5f) that is stable within a temperature range of approximately 120-140°C. The relationships between the organisation of molecules within these moderate temperature liquid crystalline phases and other self-organised states (e.g. Langmuir-Blodgett films) remain to be explored.     

Thermodynamic properties of chiral liquid crystalline material (S)-4-(2-methylbutyl)-4′-cyanobiphenyl (5*CB)

As a part of a project of clarifying the physical properties and dynamics of cyanobiphenyls with chiral molecules, thermodynamic properties of (S)-4-(2-methylbutyl)-4′-cyanobiphenyl (5*CB) were investigated by adiabatic calorimetry between T = (5 and 350) K. The complicated phase behaviour was solved and the thermodynamic functions were determined. A new glass transition was identified in the phase II (metastable crystal) at T = 105 K. No inversion of the stability between two crystalline phases was found, being contrary to the expectations from the previous neutron scattering studies.     

study of liquid crystalline N -[4-(4- n -alkoxybenzoyloxy)-2-hydroxybenzylidene]methylanilines

New homologous series of N-[4-(4-n-alkoxybenzoyloxy)-2-hydroxybenzylidene]methylanilines [nAHmM(n=1-8/10; m=2: ortho, m=3: meta, m=4: para)] were synthesized. They exhibited a nematic phase except for 1AH3M. The temperature dependence of their Raman spectra was observed in the spectral range of 900–1700 cm^-1. In one group of nAHmM compounds, the Raman band at about 1360 cm^-1 abruptly decreased in intensity and wavenumber when the crystalline solid-liquid crystal phase transition was approached. In another group, the corresponding band increased through the phase transition. The bands have been assigned to the coupling mode between the in-plane CCH deformational vibration and the ring-N stretching vibration. Such a behaviour can be explained by the molecular conformation with different twist angles of the aniline ring in relation to the Schiff's base plane of the molecule. Some nAHmMs exhibited photochromism.     

study of liquid crystalline N -[4-(4- n -alkoxybenzoyloxy)-2-hydroxybenzylidene]methylanilines

New homologous series of N -[4-(4- n -alkoxybenzoyloxy)-2-hydroxybenzylidene]methylanilines [ n AH m M( n =1-8/10; m =2: ortho , m =3: meta , m =4: para )] were synthesized. They exhibited a nematic phase except for 1AH3M. The temperature dependence of their Raman spectra was observed in the spectral range of 900-1700 cm -1 . In one group of n AH m M compounds, the Raman band at about 1360 cm -1 abruptly decreased in intensity and wavenumber when the crystalline solid-liquid crystal phase transition was approached. In another group, the corresponding band increased through the phase transition. The bands have been assigned to the coupling mode between the in-plane CCH deformational vibration and the ring-N stretching vibration. Such a behaviour can be explained by the molecular conformation with different twist angles of the aniline ring in relation to the Schiff 's base plane of the molecule. Some n AH m Ms exhibited photochromism.     

The synthesis of liquid crystalline lanthanide complexes of Schiff's base ligands: N -(4- n -alkoxysalicylidene)-4'- n -alkylanilines

The reaction of N -(4- n -alkoxysalicylidene)-4'- n -alkylanilines with freshly prepared lanthanide salts leads to mesomorphic terbium and dysprosium complexes exhibiting the smectic A phase.     

Raman spectroscopy of liquid crystalline N-[4-(4-n-alkoxybenzoyloxy)-2-hydroxybenzylidene]-3-aminopyridines

New homologous series of N-[4-(4-n-alkoxybenzoyloxy)-2-hydroxybenzylidene]-3-aminopyridines were synthesized, they exhibited a nematic phase. The temperature dependence of their Raman spectra has been observed in the spectral range 900–1800?cm^?1. Some Raman bands show a marked change in their intensity and frequency through the phase transition from crystalline solid to nematic. These bands are ascribed to the vibrational modes related to the core part of the molecule. Such behaviour can be explained by the change of molecular conformation related to the core. Some members of these series exhibited photochromism in the solid state.     

Raman spectroscopy of liquid crystalline N-[4-(4-n-alkoxybenzoyloxy)-2-hydroxybenzylidene]-3-aminopyridines

New homologous series of N-[4-(4-n-alkoxybenzoyloxy)-2-hydroxybenzylidene]-3-aminopyridines were synthesized, they exhibited a nematic phase. The temperature dependence of their Raman spectra has been observed in the spectral range 900-1800 cm^-1. Some Raman bands show a marked change in their intensity and frequency through the phase transition from crystalline solid to nematic. These bands are ascribed to the vibrational modes related to the core part of the molecule. Such behaviour can be explained by the change of molecular conformation related to the core. Some members of these series exhibited photochromism in the solid state.     

New liquid crystalline compounds based on 2-arylthiophenes and 2-(biphenyl-4-yl)thiophenes

A general and versatile route to the 2-alkyl-5-(4'-cyanophenyl)thiophenes was established, involving the condensation of an aryl vinyl ketone with an aldehyde in the presence of a thiazolium catalyst (Stetter procedure) to give a 1,4-diketone which with Lawesson's reagent undergoes ring-closure to give the corresponding arylthiophene. In the final step the exchange of a bromo substituent on the phenyl ring for a cyano group is accomplished by copper(I) cyanide in N,N-dimethylforamamide at reflux. The same sequence afforded 2-alkyl-5-(4'-cyanobiphenylyl)thiophenes. Several of the 1,4-diketones were obtained by conjugate addition of nitroalkanes to aryl vinyl ketones, and treatment of the γ-nitroketones with silica gel-supported potassium permanganate. Three alkyl 5-(4-cyanophenyl)thiophene-2-carboxylates were prepared by condensing β-chlorovinylaldehydes with thioglycolates. The cyanophenylthiophenes exhibited only monotropic phases, but incorporation of an additional phenyl ring provided cyanobiphenylylthiophenes of wide nematic ranges. Transition temperatures of binary mixtures of the cyanophenylthiophenes with 4-n-pentyl-4'-cyanobiphenyl were measured, and extrapolated virtual nematic-isotropic transition temperatures were determined.     

Influence of spacer variation on phase behaviour of liquid crystalline copolymethacrylates containing cholesteryl and S-(-)-4-chloropropionyloxybiphenyl-4-yl groups

Liquid crystalline side group copolymers containing cholesteryl and S-(-)-chloropropionyloxybiphenyl groups were synthesized and investigated by size exclusion chromatography, 1H NMR spectroscopy, polarization microscopy, X-ray diffraction and differential scanning calorimetry. The spacer of the cholesteryl-containing side groups was changed by the substitution of two methylene groups by ether groups. The existence of a cholesteric phase on copolymerization of two monomers containing chiral tail groups, from which the homopolymers exhibit only smectic phases, could be observed. This cholesteric phase only exists over a narrow range of copolymer composition. The temperature dependence of the reflection wavelength for the cholesteric phase was determined. For the cholesteryl-containing homopolymer, an SA bilayer phase was observed, whereas the S-(-)-chloropropionyloxybi2 phenyl homopolymer showed a higher ordered SB phase below an SA monolayer phase. The layer periodicities of the SA phases of the copolymers depend on the composition. The substitution of two methylene groups of the spacer by ether groups led to disappearance of the cholesteric phase. Simultaneously, over a small range of copolymer composition a biphasic region was obtained.     

Spectroscopic study of liquid crystalline N-[4-(4-n-alkoxybenzoyloxy)2-hydroxybenzylidene]hydroxyanilines

New homologous series of N-[4-(4-n-alkoxybenzoyloxy)-2-hydroxybenzylidene]hydroxyanilines were synthesized. All 4-hydroxyaniline derivatives exhibited a nematic phase, while 3-hydroxyaniline and 2-hydroxyaniline derivatives exhibited only a nematic phase as the terminal alkoxy group was lengthened. Infrared spectra suggest that the 4-hydroxyaniline derivatives form intermolecular hydrogen bonding of the single bridge type, while the 3-hydroxy and 2-hydroxy derivatives form the polymer type. The Raman band at around 1360 cm^-1 exhibited large differences in intensity among these derivatives. This can be explained by the effect of intermolecular or hydrogen bonding molecular conformation.     

Spectroscopic study of liquid crystalline N-[4-(4-n-alkoxybenzoyloxy)2-hydroxybenzylidene]hydroxyanilines

New homologous series of N-[4-(4-n-alkoxybenzoyloxy)-2-hydroxybenzylidene]hydroxyanilines were synthesized. All 4-hydroxyaniline derivatives exhibited a nematic phase, while 3-hydroxyaniline and 2-hydroxyaniline derivatives exhibited only a nematic phase as the terminal alkoxy group was lengthened. Infrared spectra suggest that the 4-hydroxyaniline derivatives form intermolecular hydrogen bonding of the single bridge type, while the 3-hydroxy and 2-hydroxy derivatives form the polymer type. The Raman band at around 1360 cm^-1 exhibited large differences in intensity among these derivatives. This can be explained by the effect of intermolecular or hydrogen bonding molecular conformation.     

A novel synthesis of 2-(disubstituted amino)-5(4)phenylimidazoles

The reaction of 1-phenyl-1,2-propanedione with 1,1-disubstituted guanidines in methanol yielded 2-(disubstituted amino)-4-hydroxy-4-methyl-4H-imidazoles (III). Compound III produced 5(4)methylimidazoles by catalytic hydrogenation and 5(4)chloromethylimidazoles (IV) by concentrated hydrochloric acid treatment. Solvolysis of IV in water and alcohols gave 5(4)hydroxymethyl- and 5(4)alkoxymethylimidazoles, respectively.     

Synthesis and liquid crystalline behaviour of substituted (E)-phenyl-4-(phenyldiazenyl) benzoate derivatives and their photo switching ability

Azobenzene derivatives containing phenyl/4-halogen-phenyl 4-{(E)-[4-(pent-4-en-1-yloxy)phenyl]diazenyl}benzoate group with different electronegative substituent (H, F, Cl, Br and I) at other end was synthesised. These azo-based benzoate derivatives have been characterised by FTIR, ¹H-NMR, ¹³C-NMR, elemental analyser, POM and UV-Vis spectroscopy. Photosaturation at 358 nm obtained after 82 s of UV irradiation and the longest thermal back relaxation time of 45 h recorded by UV-Vis. The azo derivative could be possible photolock under UV light, as observed by the improved thermal back relaxation time. The resulting photolockable chain of azobenzene might prove valuable in the development of optical device application. These azobenzene moieties also exhibit liquid crystalline behaviour with respect to the halogen substitution as an electron withdrawing group shows that strong structure property relationship exists among them.     

The synthesis and comparison of the liquid crystalline properties of certain 1-(4'-n-alkoxypolyfluorobiphenyl-4-yl)-2-(trans-4-n- pentylcyclohexyl)-ethenes and -ethanes carrying four, six or eight fluoro-substituents

The synthesis and mesomorphic properties of a variety of polyfluorinated alkylaryl-ethanes and-ethenes are reported. The number and position of the symmetrically disposed fluorosubstituents has been varied from six to four and the mesomorphic properties of the compounds are compared with those of the analogous octafluoro-substituted compounds previously reported. All the compounds are moderately low melting, mesomorphic and the type of mesophase formed is dependent upon the number and position of the fluoro- substituents. Increasing the number of fluoro-substituents from four, to six and to eight in a series of polyfluoro-alkylarylethanes decreases the mesophase thermal stability in a stepwise manner and eliminates smectic properties whilst retaining the nematic phase.     

2-(4-N-硝基，N-甲基氨基苯基)-(4-硝基苯基)-5-(2,4,6- 三硝基苯基)噻唑的 合成及其性能研究

为解决非线性光学活性有机分子透明性差及熔点低的问题,设计合成了2-(4-N-硝基,N-甲基氨基苯基)-(4-硝基苯基)-5-(2,4,6-三硝基苯基)噻唑化合物,并研究了其热性能及光学性质。根据实验结果得出由于杂环的引入,提高了化合物的裂解温度,并较好地改善了有机分子的透明性。     

4-(5-Arylvinyl-2-oxazolyl)- and 4-(5-arylbutadienyl-2-oxazolyl)-naphthalic anhydrides

4-(5-Arylvinyl-2-oxazolyl)- and 4-(5-arylbutadienyl-2-oxazolyl)naphthalic anhydrides were synthesized by a phosphonate modification of the Wittig reaction from 4-(5-bromomethyl-2-oxazolyl)naphthalic anhydride. The structures of the aryl radicals and the steric hindrance created by some of them have a substantial effect on the absorption and luminescence of these compounds in solution. The introduction of each of the vinylene groups between the aryl and heterocyclic radicals causes approximately identical shifts in the spectra, but the Stokesian shift increases. These effects are reinforced considerably under the influence of electron-donor substituents in the aryl radical. The luminescence maxima of the investigated substances range from 515 to 710 nm, and the absolute quantum yields range from 0.12 to 0.51.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 611–613, May, 1977.     

New liquid crystal compounds ( )-4-[5-(2-Methylbutyl)-1,3-dioxan-2-yl]phenyl 4-alkoxybenzoate

New liquid crystal compounds, (+)-4-[5-(2-methylbutyl)-1,3-dioxan-2-yl] phenyl 4-alkoxybenzoates (5), were synthesized. The mesomorphic behaviour of these compounds is compared with that of (+)-4-(5-alkyl-1,3-dioxan-2-yl)-phenyl 4-(2-methylbutoxy)benzoates (6). While compounds 6 exhibited a chiral smectic C phase, the corresponding compounds 5 did not. This might mean that for the appearance of a chiral smectic C phase in these types of compounds, it is necessary that the carbonyl and the chiral groups exist at nearby positions. Transition temperatures to those isotropic state for compounds 5 were lower than those for compounds 6. This result is common in both cases of (+)-4-alkoxycarbonylphenyl-4-[5-(2-methylbutyl)-1,3-dioxan-2-yl]benzoates (7), and (+)-4-(2-methylbutoxy-carbonyl)phenyl 4-(5-alkyl-1,3-dioxan-2-yl)-benzoates (8).