Synthesis And Characterization Of Isoflavone Derivatives Exhibiting Liquid Crystalline Properties
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Date
2008-07
Authors
Yam, Wan Sinn
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Abstract
Six series of classical rod-like, calamitic liquid crystals had been synthesized and
characterized. These liquid crystals contained 3-phenyl-4H-4-0ne-benzopyran or generally
known as isoflavone within the central moiety. The syntheses of these liquid crystalline
compounds involved alkylation, Friedel-Crafts acylation, cyclization and esterification reactions.
CHN microanalysis, FTIR, ID and 2D-NMR spectroscopic methods were used to elucidate the
structures of these compounds. The transition temperatures of the synthesized compounds and
respective enthalpy values were determined by differential scanning calorimetry whilst a
polarized optical microscope was used for texture observation. The first four series, each
consisted of eight homoiogues, incorporated isoflavone within their central cores with either
one or two flexible acyloxy or alkyloxy terminal chains in odd or even parity. The cOJqpounds
thus obtained exhibited nematic (N), smectic A (SmA) and smectic C (Sme) phases.
Compounds from the fifth and sixth series, on the other hand, were isoflavone derivatives
bearing decyloxy chain on one end and different substutuents. R, on the other. of which R = F.
CI. Br. CH), OCH3 and H. Compounds with substituents, R = F, C1 and Br are smectogenic
displaying only SmA phase whilst compound with R = OCH3 was nematogenic. Compound
with R = CH3 exhibited both N and SmA phases. Compound with R = H was non-mesogenic in
the fifth series but the elongated derivative bearing the same substituent was mesogenic
showing SmA phase in the sixth series. In order to investigate the molecular packing associated
with the intermolecular attraction as well as the correlation between the thermal behaviour of
these molecules with their anisotropy properties in Nand smectic phases, the X-ray diffraction
studies had been carried out on representative compounds 7-n-hexyloxy-3-(4-nhexyloxyphenyl)-
4H-l-benzopyran-4-one. ALAB-OC, and 7-n-hexadecyloxy-3-( 4-nhexadecyloxyphenyI)-
4H-l-benzopyran-4-one, ALAB-oC1, from the second series, 7-nxxxi
decanoyloxy-3-[ 4' -(3-methylbutyloxyphenyl)]-4H-l-benzopyran-4-one, MBPB-COOC, from
the third, 7-n-decanoyloxy-3-(4'-methylphenyl)-4H-l-benzopyran-4-one, lOPB-CH3 and 7-
(4" -n-decyloxybenzoyloxy )-3-( 4' -fluorophenyl)-4H-l-benzopyran-4-one, IOBB-F from fifth
and sixth series, respectively. From the X-ray data, molecules of compounds ALAB-OC, were
arranged in layers in SmA phase whilst the molecular tilt angles, 9 from the normal to layer
within the SmC phase was approximately 150 as obtained at 11°C below the transition
temperature. However, the molecular tilt angles, 9 for compounds ALAB-OC1, and MBPBCOOC,
could not be determined due to a first order transition from crystal to SmC phases in
these compounds. The X-ray diffiaction analyses also revealed that the molecules in compound
lOPS.CH3 were intercalated in SmA phase. Molecules in compound IOBB-F were arranged in
bilayers in crystal phase but monolayers were favoured in SmA phase. Single crystal X-ray
diffraction analyses had also been carried out on compounds ALAB-OC" MBPB-COOC" 7-nhexyloxy-
3-[4' -(3-methylbutyloxyphenyl)]-4H-l-benzopyran-4-one, MBPB-OC, and tOPBCH;
b wherein all crystals were found to be triclinic. The molecular structures of the earlier
mentioned compounds were confinned for the first time by X-ray crystallography and found to
conform to those as inferred from FTIR and NMR techniques. The long flexible terminal chains
of these crystals were found to be fully stretched. except for compound ALAB-OC, which had a
highly disordered structure. Compound IOPS-CH3 had the lowest torsion angle in any hitherto
reported isoflavone derivatives. The packing of molecules of these compounds showed that they
lay anti-parallel to one another and the crystal cohesion resulted from dipolar interactions
between anti-parallel ether or ester groups as well as van der Waals interaction of neighbouring
molecules stabilized the packing of the molecules.
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Keywords
Chemical Sciences , Synthesis And Characterization