Synthesis and Mesomorphic Properties of New Fluorinated Schiff Base Liquid Crystalsdownloads.hindawi.com/journals/isrn.materials.science/... · 2014. 5. 8. · Liquid crystals (LCs)

Research ArticleSynthesis and Mesomorphic Properties of New FluorinatedSchiff Base Liquid Crystals

Sie-Tiong Ha and Teck-Leong Lee

Department of Chemical Science Universiti Tunku Abdul Rahman Jln Universiti Bandar Barat 31900 Kampar Perak Malaysia

Correspondence should be addressed to Sie-Tiong Ha hast utaryahoocom

Received 10 September 2013 Accepted 21 October 2013 Published 16 January 2014

Academic Editors S X Dou H Higashimura V Ji and B Li

Copyright copy 2014 S-T Ha and T-L Lee This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

Two new compounds 4-alkanoyloxybenzylidene-41015840-fluoroaniline and 4-fluorobenzylidene-41015840-n-alkanoyloxyaniline comprisinga terminal fluorosubstituent were studied The fluoro substituent contributes to the molecular polarizability thus affectingintermolecular interactions and hence resulting in smectic mesomorphism The mesomorphic properties were studied usingdifferential scanning calorimetry and polarizing optical microscopy techniques The mesomorphic properties of compoundsstudied are strongly dependent on the orientation of the imine (CH=N) linkage The former Schiff base exhibited smectic A phasewhereas the latter compound did not display any mesophase Reversed imine linkage has caused depression of mesomorphicproperty in the compound studied (4-fluorobenzylidene-41015840-n-alkanoyloxyaniline) The mesomorphic properties of the presentcompounds were compared with other structurally related series to establish the chemical structure-mesomorphic propertyrelationship

1 Introduction

Liquid crystals (LCs) have many practical applications inscientific and technological areas in particular as displaydevices OLEDs anisotropic networks photoconductors andsemiconductor materials [1ndash3] Strong demand of new LCsfor applications has led to the synthesis of wide range ofmesogens in particular thermotropic liquid crystals [4 5]Most thermotropic liquid crystals belonged to the calamiticmolecules which have a rigid core that consisted of two ormore phenyl rings and one or more flexible terminal alkylchains Schiff base is one of the most well-known linkinggroups used in connecting the rigid core groups Althoughit provides a stepped core structure it maintains molecularlinearity therefore providing better stability and inducingformation of mesophase [6 7] Numerous works have beenreported in this area ever since the discovery of MBBAwhichexhibited room temperature nematic phase [8] Recentlyester type of Schiff bases has received considerable attentionsowing to their interesting properties and substantial temper-ature range [9ndash18]

Structure-property relationship is essential knowledge formolecular modifications of the synthesis of new mesogens

with targeted properties and future practical applications [6]Typical terminal substituents exhibiting LC properties arethose with electronegative atoms such as halogens Halogensare polar substituents possessing strong dipolemoments thushaving the ability to promote mesomorphic properties [19ndash21] The increased dipole moment enhances the stability ofthe lattice and melting temperatures [7] As the ionic radiusof the terminal substituent increases the molecules tendto orientate in a parallel arrangement [22] Thus smecticpolymorphism is not unusual for mesogens with a terminalhalogen substituent and this has been frequently observedas the length of the alkyl or alkoxy chains increases [20 23]However the present compound with fluoro substituentexhibited single mesophase

In this continuation study we aim to change the orienta-tion of imine linkage on the existing system and to study theinfluence of reversed imine linkage on mesomorphism ofSchiff bases The involved compounds are 4-alkanoyloxy-benzylidene-41015840-fluoroaniline and 4-fluorobenzylidene-41015840-n-alkanoyloxyaniline (Figure 1) FT-IR 1H and 13C NMR EI-MS and elemental analysis were employed to elucidate themolecular structure of the title compound whereas the liquid

Hindawi Publishing CorporationISRN Materials ScienceVolume 2014 Article ID 904657 7 pageshttpdxdoiorg1011552014904657

2 ISRNMaterials Science

F

N

8FBAA heating Cr 758(24) I cooling I 255(20) Cr12FBAA heating Cr 897(52) I cooling I 626(51) Cr

N F

8ABFA heating Cr 656(26) I cooling I 424(39) SmA 272(21) Cr12ABFA heating Cr 805(53) I cooling 741(74) SmA 496(43) Cr

Cnminus1H2nminus1COO


Where n = 8 12

Where n = 8 12

Figure 1 Molecular structure and phase transition temperature(∘C) of fluorinated liquid crystals Note associated enthalpy changes(ΔH kJmolminus1) are expressed in parentheses

crystal properties were determined by DSC and POM anal-ysis In spite of the structural similarity the smectic natureof the series is quite different In addition the relationshipbetween themolecular structure and liquid crystal properties(see Table 1) is also discussed in this paper

2 Experimental

Octanoic acid dodecanoic acid 4-fluorobenzaldehyde4-aminophenol 4-fluoroaniline 4-hydroxybenzaldehyde4-dimethylaminopyridine and NN1015840-dicyclohexylcarbodi-imide were of analytical grade and used without furtherpurification The intermediate and title compounds wereprepared according to previously reported methods [10 11]

Electron ionizationmass spectrum (EI-MS)was recordedusing a Finnigan MAT95XL-T mass spectrometer operatingat 70 eV ionizing energy Samples were introduced usinga direct inlet system with a source temperature of 200∘CFT-IR data were acquired with a Perkin Elmer 2000-FTIRspectrophotometer in the frequency range of 4000ndash400 cmminus1with samples embedded in KBr pellets 1H and 13C NMRspectra were recorded in CDCl

3using a Bruker Avance

300MHz NMR Spectrometer with TMS as the internalstandard Thin layer chromatography analyses were carriedout using aluminum backed silica gel plates (Merck 60 F

254)

and were examined under shortwave UV lightThe phase transition temperatures were measured using

a Mettler Toledo DSC823 differential scanning calorimeter(DSC) at a scanning rate of 10∘Cminminus1 Liquid crystallineproperties were investigated by Carl Zeiss polarizing opticalmicroscope attached to a Linkam Hotstage The texture ofthe compounds was observed using polarized light withcrossed polarizers the sample being prepared as a thin filmsandwiched between a glass slide and a cover A video camera(Video Master coomo20P) was installed on the polarizing

CH3OH

(2) DCC DMAP(3) THF

HO NH2

(1)

F

H

O

F

HO N

F

NCnminus1H2nminus1COO

Cnminus1H2nminus1COOH

+

Scheme 1 Synthetic route towards the formation title compound

microscope and coupled to a video capture card (VideoMaster coomo600) allowing real-time video capture andimage saving

21 Synthesis of 4-Fluorobenzylidene-41015840-hydroxyaniline (OHF-BAA) Equal amounts (5mmol) of 4-fluorobenzaldehydeand 4-aminophenol along with 30mL of methanol wererefluxed for three hours The mixture was cooled to roomtemperature and filtered The yellow product was washedwith methanol

22 Synthesis of 4-Fluorobenzylidene-41015840-n-dodecanoyloxyan-iline (12FBAA) OHFBAA (4mmol) 3mmol of dodecanoicacid DMAP (06mmol) and DCC (3mmol) were mixedand stirred at room temperature for six hours in appropriateamount of THF (see Scheme 1) Solvent of reaction mixturewas removed by evaporation till dryness Precipitate obtainedwas recrystallized several times with hexane and ethanolwhereupon pure compound was isolated

EI-MS IR and 1H and 13C NMR data of the representa-tive compound 12FBAA are given as follows

IR (KBr) Vmax cmminus1 2954 2915 2849 (CndashH aliphatic) 1753

(C=O ester) 1628 (C=N) 1203 1094 (CndashO ester) 1H NMR(300MHz CDCl

3) 120575ppm 09 (t 3H CH

3ndash) 13ndash15 (m 16H

CH3ndash(CH

2)8ndash) 18 (m 2H ndashCH

2ndashCH2ndashCOOndash) 26 (t 2H

ndashCH2ndashCOOndash) 71ndash73 (m 6H ArndashH) 79 (m 2H ArndashH) 84

(s 1H ndashCH=Nndash) 13CNMR(100MHzCDCl3) 120575ppm 17239

(C=O ester) 15882 (ndashC=Nndash) 14934 14896 13252 1308512222 12169 11608 11579 for aromatic carbons 3442(ndashCOOndashCH

2ndash) 3190 (ndashCOOndashCH

2ndashCH2ndash) 2959 2945

2932 2925 2912 for methylene carbons [ndash(CH2)6CH2

CH2CH3] 2496 (ndashCH

2CH2CH3) 2267 (ndashCH

2CH3) 1409

(ndashCH3) EI-MSmz (rel int ) 397(3) (M)+ 215(100)

ISRNMaterials Science 3

Table 1 Mesomorphic data of structurally related compounds

Compound Structure Phase transition (∘C)

F-AB [26]N F

C8H17OCr (551)lowast SmB 622 SmA 652 I

Cl-AB [19]N Cl

C8H17OCr 610 SmB 877 SmA 985 I

Br-AB [19]N Br

C8H17OCr 890 SmB 1040 SmA 1130 I

F-ABOH [27]

OH

N FC8H17O Cr 64 SmA 76 I

Cl-ABOH [27]

OH

N ClC8H17O Cr 67 SmA 123 I

Br-ABOH [27]

OH

N BrC8H17O Cr 73 SmA 132 I

I-ABOH [27]

OH

N IC8H17O Cr 109 SmA 133 I

8FBAAF

NC7H15COOCr 76 I

8ABFAN F

C7H15COOCr (424)lowast SmA 66 I

8BACl [28]N Cl

C7H15COOCr (802)lowast SmB 840 SmA 1048 I

8BABr [29]N Br

C7H15COOCr 896 SmB 944 SmA 1106 I


Table 1 Continued


8BAI [30]N I


()lowastindicates monotropic phase

9 8 7 6 5 4 3 2 1(ppm)

Figure 2 1H NMR spectrum of 12FBAA

3 Results and Discussion

Structural identification of 12FBAA was carried out by usingspectroscopic techniques (IR 1H and 13CNMR and EI-MS)Molecular ion peak at mz 397 suggested molecular formulaof C25H32FNO2 which supported the proposed structure of

12FBAA

31 FTIR 1H NMR and 13C NMR Spectral Studies Based onFT-IR spectrum of 12FBAA absorption peak at 2954 2915and 2849 cmminus1 can be assigned to aliphatic (CH

3and CH

2)

groups Three absorption peaks due to the ester group wereobserved at 1753 1203 and 1094 cmminus1 Absorption peak ofimine (C=N) group was observed at 1622 cmminus1 In the 1HNMR spectrum (Figure 2) two triplets at 120575= 09 ppm and 120575 =26 ppmwere respectively ascribed to themethyl andmethy-lene protons (ndashCH

2COOndashAr) while the multiplet between

120575 = 13ndash15 ppm was assigned to the methylene protons of thelong alkyl chain ndash(CH

2)8ndash The multiplet signals between

120575 = 71ndash79 ppm were indicative of the aromatic protons Thesinglet observed at the most downfield region 120575 = 84 ppmsupported the presence of the imine linking group [18] Themolecular structure of 12FBAA was further verified by using13CNMR spectroscopy (Figure 3)The peak at 120575 = 1409 ppmwas attributed to the methyl carbon while the peaks between120575 = 2267ndash3442 ppm represented the methylene carbons ofthe long alkyl chain Twelve aromatic carbons are resonatedbetween 120575 = 11579ndash14934 ppm The peaks at 120575 = 15882 ppmand 120575= 17239 ppmconfirmed the presence of the azomethinecarbon and the carbonyl group in the molecule

32 Mesomorphic Properties 12ABFA exhibited interestingthermotropic properties and its melting behavior was care-fully monitored by POM during both heating and coolingscans The results from the POM observation were verifiedby the DSC measurements Optical photomicrograph andDSC thermogram of 12ABFA are shown in Figures 4 and 5as representative illustration The transition temperaturesenthalpy changes and phase sequences are summarizedin Figure 1 Phase identification was based on the opticaltextures and the magnitude of isotropization on enthalpies isconsistent with the assignment of eachmesophase type usingthe classification systems reported by Sackmann and Demus[24] andGray andGoodby [25] Under POM focal conic fan-shaped and homeotropic textures of a smectic A (SmA) phasewas observed during the cooling cycle (Figure 4)

33 Influence of Alkyl Chain Length on Mesomorphic Proper-ties Members from the nABFA series are monotropic smec-togen whereby mesophase (SmA) was only observed duringthe cooling scan Inmonotropicmesogens themelting pointswere always equal to or higher than the clearing points henceexhibiting supercooling properties As fornFBAAseries bothmembers did not possess mesomorphic properties

As the alkyl chain length increases the melting pointshows ascending trend It has been reported that melt-ing point within a homologous series vary depending onmolecular mass wherein molecule with lower mass possesseslower melting point in comparison to member with highermass [6] Melting point increases when polarizability of thecompounds within the same series increases

34 Structure-Mesomorphic Property Relationships Molecu-lar structure of organic compounds and their liquid crys-talline properties are closely related Table 1 summarizes thetransition temperatures mesomorphic behavior and molec-ular structures of 8FBAA 8ABFA and structurally relatedcompounds reported in the literature [19 26ndash30]

Halogen groups at the terminal position showed stronginfluence on the mesomorphic properties of a molecule asindicated by the current work (Table 1) It can be seen thatthe transitions temperatures of 8ABFA are lower than those of8BACl 8BABr and 8BAI Size of fluorosubstituent is smallerthan the chloro- bromo- and iodosubstituents and thereforeless easily polarized due to the electrons on this atom whichare tightly held and located closer to the nucleus [31] Lowermolecular polarizability attributed to the smaller size offluoro substituent decreased the phase stability in 8ABFA [15]This phenomenon is supported by the similar characteristic


180 160 140 120 100 80 60 40 20(ppm)

(a)

297 296 295 294 293 292 291(ppm)

(b)

150 145 140 135 130 125 120(ppm)

115

(c)

Figure 3 13C NMR spectrum of 12FBAA (a) full spectrum (b) expanded spectrum for aliphatic region and (c) expanded spectrum foraromatic region

Figure 4 Optical photomicrograph of 12ABFA showing the coexis-tence of fan-shaped and homeotropic textures It showed character-istics of SmA phase

observed for X-AB and X-ABOH series (where X = F Cl BrI) wherein the melting and transition temperatures ascendedas the size of halogen group increased

Secondly polarisability of halogen terminal groups canalso control the phase stability of liquid crystal moleculesCompound having lower polarisability halogen group(8ABFA and 8BACl) possessed less stable monotropicsmectic phase than 8BABr and 8BAI which exhibited enan-tiotropic smectic phase Similar pattern was also reported forX-AB series whereby F-AB (monotropic phase) possessed

Heating

Cooling Cr

Cr I

ISmA

20 m

W

20 30 40 50 60 70 80 90 100 110(∘C)

Figure 5 DSC thermogram of 12ABFA

lower phase stability than Cl-AB and Br-AB (enantiotropicphase)

Difference in the linking groups (ester group in 8ABFAand ether group in F-AB) between the phenyl ring andthe alkyl chain can also cause change in the mesomorphicproperties The ether linking group provides greater linearityto molecules rather than the ester group thus resulting in thewider phase range being observed in F-AB when comparedto 8ABFA In addition 8ABFA possessed higher meltingpoint than F-AB owing to the 120587-electrons associated with


the carbonyl group which provides greater intermolecularinteractions among molecules [32]

Influence of lateral hydroxyl groupwas relatively apparenton the mesomorphic properties of Schiff base Intramolec-ular hydrogen bonding between ortho-hydroxyl group andnitrogen atom has increased the molecular polarisabilityand therefore compounds with hydroxyl group (X-ABOHseries) possessed higher melting and clearing temperaturesthan their analogous compounds without hydroxyl groupHowever the increased polarisability at the lateral of amolecule caused depression of SmB arrangement and thusimpeding SmB formation in the X-ABOH series

The position of the imine linking group defines thedirection of the carbonyl group The different directions ofthe carboxyl groups between the phenyl and alkyl unitscause remarkable changes on the dipole moment as thatreported for somebanana-shapedmesogens [33]The smecticproperties of the molecules are strongly affected by notonly the electrostatic interactions but also the geometricalcircumstances [34] Furthermore nFBAA series possessedhigher melting point compared to nABFA having the samenumber of carbons (n) at the alkyl chain and subsequentlyimpeded the mesophase formation This suggests that thereversed imine linkage can also depress the thermal stabilityof a compound (nFBAA)

Conflict of Interests

The authors do not have a direct financial relation withthe commercial identities mentioned in the paper includingFinnigan Perkin Elmer Bruker Merck Mettler Toledo CarlZeiss and Linkam that might lead to a conflict of interest forany of the authors

Acknowledgments

The authors would like to thank Universiti Tunku AbdulRahman and the Ministry of Higher Education of Malaysiafor the financial supports and research facilities

References

[1] L Petti M Rippa A Fiore L Manna and P Mormile ldquoOpti-cally induced light modulation in an hybrid nanocompositesystem of inorganic CdSeCdS nanorods and nematic liquidcrystalsrdquo Optical Materials vol 32 pp 1011ndash1016 2010

[2] N A Shurpo M S Vakshtein and N V Kamanina ldquoEffectof CdSeZnS semiconductor quantum dots on the dynamicproperties of nematic liquid-crystalline mediumrdquo TechnicalPhysics Letters vol 36 no 4 pp 319ndash321 2010

[3] M H Hoang M J Cho K H Kim T W Lee J-I Jinand D H Choi ldquoSemiconducting 23671011-Hexakis [4-(5-dodecylthiophen-2-yl)phenyl] ethynyl triphenylene and itsdiscotic liquid crystalline propertiesrdquo Chemistry Letters vol 39no 4 pp 396ndash397 2010

[4] F Yuksel D Atilla and V Ahsen ldquoSynthesis and charac-terization of liquid crystalline unsymmetrically substitutedphthalocyaninesrdquo Polyhedron vol 26 no 15 pp 4551ndash45562007

[5] B Y Zhang F B Meng M Tian and W Q Xiao ldquoSide-chainliquid-crystalline polysiloxanes containing ionic mesogens andcholesterol ester groupsrdquo Reactive and Functional Polymers vol66 pp 551ndash558 2005

[6] P J Collings and M Hird Introduction to Liquid CrystalsChemistry and Physics Taylor amp Francis London UK 1998

[7] S Singh and D A Dunmur Liquid Crystals FundamentalsWorld Scientific London UK 2002

[8] H Kelker and B Scheurle ldquoA liquid crystalline (nematic) phasewith a particularly low solidification pointrdquoAngewandteChemieInternational Edition vol 8 pp 884ndash885 1969

[9] B B Eran A Nesrullajev and N Y Canli ldquoCharacterizationand investigation of the mesogenic thermo-morphologic andthermotropic properties of new chiral (S)-5-octyloxy-2-[4-(2-methylbuthoxy)-phenylimino(methyl]phenol liquid crystallinecompoundrdquo Materials Chemistry and Physics vol 111 no 2-3pp 555ndash558 2008

[10] S T Ha L K Ong S T Ong et al ldquoSynthesis andmesomorphicproperties of new Schiff base esters with different alkyl chainsrdquoChinese Chemical Letters vol 20 no 7 pp 767ndash770 2009

[11] S T Ha G Y Yeap and P L Boey ldquoSynthesis and liq-uid crystalline properties of new schiff bases N-[4-(4-n-alkanoyloxybenzoyloxy)benzylidene]-4-cyano- 4-hydroxy- 4-thio-and 4-nitroanilinesrdquo Australian Journal of Basic amp AppliedSciences vol 3 no 4 pp 3417ndash3422 2009

[12] M Parra J Vergara C Zuniga E Soto T Sierra and J L Ser-rano ldquoNew chiral Schiff rsquos bases with a 134-thiadiazole ring inthe mesogenic core synthesis mesomorphic and ferroelectricpropertiesrdquo Liquid Crystals vol 32 no 4457 462 pages 2004

[13] A K Prajapati and M C Varia ldquoAzomesogens with polarchloro nitro and phenolic -OH substituentsrdquo Liquid Crystalsvol 35 no 11 pp 1271ndash1277 2008

[14] R Vora A K Prajapati and J Kevat ldquoEffect of terminalbranching on mesomorphismrdquo Molecular Crystals and LiquidCrystals vol 357 no 1 pp 229ndash237 2001

[15] G-Y Yeap S-T Ha P-L Lim et al ldquoSynthesis and meso-morphic properties of schiff base esters ortwo-hydroxy-para-alkyloxybenzylidene-para-substituted anilinesrdquo Molecu-lar Crystals and Liquid Crystals vol 423 pp 73ndash84 2004

[16] G Y Yeap S T Ha P L Boey W A K Mahmood M MIto and Y Youhei ldquoSynthesis and characterization of somenew mesogenic schief base esters N-[4-(4-n-hexadecanoyl-oxybenzoyloxy)-benzylidene]-4-substituted anilinesrdquo Molecu-lar Crystals and Liquid Crystals vol 452 no 1 pp 73ndash90 2006

[17] G-Y Yeap S-T Ha P-L Lim et al ldquoNematic and smectica phases in ortho-hydroxy-para-hexadecanoyloxbenzylidene-para-substituted anilinesrdquo Molecular Crystals and Liquid Crys-tals vol 452 no 1 pp 63ndash72 2006

[18] G-Y Yeap S-T Ha P-L Lim et al ldquoSynthesis physicaland mesomorphic properties of Schiff rsquos base esters contain-ing ortho- meta- and para-substituents in benzylidene-41015840-alkanoyloxyanilinesrdquo Liquid Crystals vol 33 no 2 pp 205ndash2112006

[19] Z Galewski ldquoMolecular crystals and liquid crystals science andtechnology Section A molecular crystals and liquid crystalsrdquoMolecular Crystals and Liquid Crystals vol 249 pp 43ndash49 1994

[20] Z Galewski and H J Coles ldquoLiquid crystalline propertiesand phase situations in 4-chlorobenzylidene-41015840-alkylanilinesrdquoJournal of Molecular Liquids vol 79 no 1 pp 77ndash87 1999

[21] S Sakagami andM Nakamizo ldquoLiquid crystalline properties ofN-(4-alkoxybenzylidene)-4-halogenoanilinesrdquo Bulletin of theChemical Society of Japan vol 53 no 1265 266 pages 1980


[22] J S Dave and M Menon ldquoAzomesogens with a heterocyclicmoietyrdquo Bulletin of Material Science vol 23 pp 237ndash238 2000

[23] V F Petrov M Duan H Okamoto J Mu Y Shimizu and STakenaka ldquoHalogenation in achiral liquid crystals terminal andlinking substitutionsrdquo LiquidCrystals vol 28 no 3 pp 387ndash4102001

[24] H Sackmann and D Demus ldquoThe polymorphism of liquidcrystalsrdquo Molecular Crystals and Liquid Crystals vol 2 pp 81ndash102 1966

[25] G W Gray and J W Goodby Smectic Liquid Crystals Texturesand Structures Leonard Hill London UK 1984

[26] C Gandolfo D Grasso G Buemi and G Torquati ldquoPhasetransitions and structural studies of p-n-alkoxybenzyliden-1199011015840-fluoro-anilinesrdquo Il Nuovo Cimento D vol 10 no 11 pp 1363ndash1371 1988

[27] S Sakagami T Koga and A Takase ldquoLiquid crystalline prop-erties and photochromism of 4-halogeno-N-(4-alkoxysalicyl-idene) anilinesrdquoMolecular Crystals and Liquid Crystals vol 373no 1 pp 71ndash81 2002

[28] S-T Ha L-K Ong Y Sivasothy et al ldquoMesogenic schiffbase esters with terminal chloro group synthesis thermotropicproperties and X-ray diffraction studiesrdquo International Journalof Physical Sciences vol 5 no 5 pp 564ndash575 2010

[29] S T Ha T L Lee H C Lin et al ldquoMesogenic Schiff basewith bromo end group synthesis and thermotropic propertiesrdquoAsian Journal of Chemistry vol 24 no 8 pp 3679ndash3684 2012

[30] S-T Ha T-L Lee S-L Lee S Sreehari Sastry and Y-F WinldquoSchiff base liquid crystals with terminal iodo group synthesisand thermotropic propertiesrdquo Scientific Research and Essaysvol 6 no 23 pp 5025ndash5035 2011

[31] T W G Solomons Fundamentals of Organic Chemistry JohnWiley amp Sons New York NY USA 1994

[32] S Kumar Liquid Crystals Experimental Study of PhysicalProperties and Phase Transitions Cambridge University PressCambridge UK 2001

[33] S A R Krishnan W Weissflog G Pelzl et al ldquoDFT andMD studies on the influence of the orientation of ester linkagegroups in banana-shapedmesogensrdquo Physical Chemistry Chem-ical Physics vol 8 no 10 pp 1170ndash1177 2006

[34] Y Sakurai S Takenaka H Miyake H Morita and T IkemotoldquoMolecular structure and smectic properties Part 1 The effectof linkages on smectic A thermal stability in three aromaticring compounds linked by ester groupsrdquo Journal of the ChemicalSociety Perkin Transactions 2 no 9 pp 1199ndash1204 1989

Submit your manuscripts athttpwwwhindawicom

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


F

N

8FBAA heating Cr 758(24) I cooling I 255(20) Cr12FBAA heating Cr 897(52) I cooling I 626(51) Cr

N F

8ABFA heating Cr 656(26) I cooling I 424(39) SmA 272(21) Cr12ABFA heating Cr 805(53) I cooling 741(74) SmA 496(43) Cr



Where n = 8 12

Where n = 8 12

Figure 1 Molecular structure and phase transition temperature(∘C) of fluorinated liquid crystals Note associated enthalpy changes(ΔH kJmolminus1) are expressed in parentheses

crystal properties were determined by DSC and POM anal-ysis In spite of the structural similarity the smectic natureof the series is quite different In addition the relationshipbetween themolecular structure and liquid crystal properties(see Table 1) is also discussed in this paper

2 Experimental

Octanoic acid dodecanoic acid 4-fluorobenzaldehyde4-aminophenol 4-fluoroaniline 4-hydroxybenzaldehyde4-dimethylaminopyridine and NN1015840-dicyclohexylcarbodi-imide were of analytical grade and used without furtherpurification The intermediate and title compounds wereprepared according to previously reported methods [10 11]

Electron ionizationmass spectrum (EI-MS)was recordedusing a Finnigan MAT95XL-T mass spectrometer operatingat 70 eV ionizing energy Samples were introduced usinga direct inlet system with a source temperature of 200∘CFT-IR data were acquired with a Perkin Elmer 2000-FTIRspectrophotometer in the frequency range of 4000ndash400 cmminus1with samples embedded in KBr pellets 1H and 13C NMRspectra were recorded in CDCl

3using a Bruker Avance

300MHz NMR Spectrometer with TMS as the internalstandard Thin layer chromatography analyses were carriedout using aluminum backed silica gel plates (Merck 60 F

254)

and were examined under shortwave UV lightThe phase transition temperatures were measured using

a Mettler Toledo DSC823 differential scanning calorimeter(DSC) at a scanning rate of 10∘Cminminus1 Liquid crystallineproperties were investigated by Carl Zeiss polarizing opticalmicroscope attached to a Linkam Hotstage The texture ofthe compounds was observed using polarized light withcrossed polarizers the sample being prepared as a thin filmsandwiched between a glass slide and a cover A video camera(Video Master coomo20P) was installed on the polarizing

CH3OH

(2) DCC DMAP(3) THF

HO NH2

(1)

F

H

O

F

HO N

F

NCnminus1H2nminus1COO

Cnminus1H2nminus1COOH

+

Scheme 1 Synthetic route towards the formation title compound

microscope and coupled to a video capture card (VideoMaster coomo600) allowing real-time video capture andimage saving

21 Synthesis of 4-Fluorobenzylidene-41015840-hydroxyaniline (OHF-BAA) Equal amounts (5mmol) of 4-fluorobenzaldehydeand 4-aminophenol along with 30mL of methanol wererefluxed for three hours The mixture was cooled to roomtemperature and filtered The yellow product was washedwith methanol

22 Synthesis of 4-Fluorobenzylidene-41015840-n-dodecanoyloxyan-iline (12FBAA) OHFBAA (4mmol) 3mmol of dodecanoicacid DMAP (06mmol) and DCC (3mmol) were mixedand stirred at room temperature for six hours in appropriateamount of THF (see Scheme 1) Solvent of reaction mixturewas removed by evaporation till dryness Precipitate obtainedwas recrystallized several times with hexane and ethanolwhereupon pure compound was isolated

EI-MS IR and 1H and 13C NMR data of the representa-tive compound 12FBAA are given as follows

IR (KBr) Vmax cmminus1 2954 2915 2849 (CndashH aliphatic) 1753

(C=O ester) 1628 (C=N) 1203 1094 (CndashO ester) 1H NMR(300MHz CDCl

3) 120575ppm 09 (t 3H CH

3ndash) 13ndash15 (m 16H

CH3ndash(CH

2)8ndash) 18 (m 2H ndashCH

2ndashCH2ndashCOOndash) 26 (t 2H

ndashCH2ndashCOOndash) 71ndash73 (m 6H ArndashH) 79 (m 2H ArndashH) 84

(s 1H ndashCH=Nndash) 13CNMR(100MHzCDCl3) 120575ppm 17239

(C=O ester) 15882 (ndashC=Nndash) 14934 14896 13252 1308512222 12169 11608 11579 for aromatic carbons 3442(ndashCOOndashCH

2ndash) 3190 (ndashCOOndashCH

2ndashCH2ndash) 2959 2945

2932 2925 2912 for methylene carbons [ndash(CH2)6CH2

CH2CH3] 2496 (ndashCH

2CH2CH3) 2267 (ndashCH

2CH3) 1409

(ndashCH3) EI-MSmz (rel int ) 397(3) (M)+ 215(100)




F-AB [26]N F


Cl-AB [19]N Cl


Br-AB [19]N Br

C8H17OCr 890 SmB 1040 SmA 1130 I

F-ABOH [27]

OH


Cl-ABOH [27]

OH


Br-ABOH [27]

OH


I-ABOH [27]

OH


8FBAAF

NC7H15COOCr 76 I

8ABFAN F


8BACl [28]N Cl


8BABr [29]N Br



Table 1 Continued


8BAI [30]N I



9 8 7 6 5 4 3 2 1(ppm)




12FBAA


3and CH

2)












180 160 140 120 100 80 60 40 20(ppm)

(a)

297 296 295 294 293 292 291(ppm)

(b)

150 145 140 135 130 125 120(ppm)

115

(c)





Heating

Cooling Cr

Cr I

ISmA

20 m

W

20 30 40 50 60 70 80 90 100 110(∘C)










Acknowledgments


References











































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






F-AB [26]N F


Cl-AB [19]N Cl


Br-AB [19]N Br

C8H17OCr 890 SmB 1040 SmA 1130 I

F-ABOH [27]

OH


Cl-ABOH [27]

OH


Br-ABOH [27]

OH


I-ABOH [27]

OH


8FBAAF

NC7H15COOCr 76 I

8ABFAN F


8BACl [28]N Cl


8BABr [29]N Br



Table 1 Continued


8BAI [30]N I



9 8 7 6 5 4 3 2 1(ppm)




12FBAA


3and CH

2)












180 160 140 120 100 80 60 40 20(ppm)

(a)

297 296 295 294 293 292 291(ppm)

(b)

150 145 140 135 130 125 120(ppm)

115

(c)





Heating

Cooling Cr

Cr I

ISmA

20 m

W

20 30 40 50 60 70 80 90 100 110(∘C)










Acknowledgments


References











































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




Table 1 Continued


8BAI [30]N I



9 8 7 6 5 4 3 2 1(ppm)




12FBAA


3and CH

2)












180 160 140 120 100 80 60 40 20(ppm)

(a)

297 296 295 294 293 292 291(ppm)

(b)

150 145 140 135 130 125 120(ppm)

115

(c)





Heating

Cooling Cr

Cr I

ISmA

20 m

W

20 30 40 50 60 70 80 90 100 110(∘C)










Acknowledgments


References











































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




180 160 140 120 100 80 60 40 20(ppm)

(a)

297 296 295 294 293 292 291(ppm)

(b)

150 145 140 135 130 125 120(ppm)

115

(c)





Heating

Cooling Cr

Cr I

ISmA

20 m

W

20 30 40 50 60 70 80 90 100 110(∘C)










Acknowledgments


References











































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials









Acknowledgments


References











































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials
























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



Documents

Synthesis and Mesomorphic Properties of New Fluorinated Schiff Base Liquid Crystalsdownloads.hindawi.com/journals/isrn.materials.science/... · 2014. 5. 8. · Liquid crystals (LCs)