Synthesis, characterization and study of liquid crystal properties of new homologous chalcone series

Article abstract of DOI:10.1080/15421406.2016.1217707

Onenewmesogenic homologous series of chalconyl derivativewith two ring (3/-(4/- (decyloxy) phenyl-1-(4-(alkoxy) phenyl) prop-2-en-1-one) has been synthesized and characterized by a combination of elemental analysis and standard spectroscopic methods. In the series, the lower members (C₄ and C₅) exhibit only enantiotropic nematic mesophase but middle and higher members exhibit enantiotropic nematic as well as smecticmesophase. The nematicmesophase commence from C₄ homologue and smectic mesophase (smectic-A type texture) commence from C₆ homologue as enantiotropic and persists up to the lastmember synthesized. The mesomorphic properties of present serieswere compared with other two structurally similar series to study the effects of change of meta and para position on the mesomorphism.

Full text of DOI:10.1080/15421406.2016.1217707

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Synthesis, characterization and study of liquid
crystal properties of new homologous chalcone
series
B. B. Jain & R. B. Patel
To cite this article: B. B. Jain & R. B. Patel (2016) Synthesis, characterization and study of liquid
crystal properties of new homologous chalcone series, Molecular Crystals and Liquid Crystals,
638:1, 27-34, DOI: 10.1080/15421406.2016.1217707
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Date: 19 November 2016, At: 02:31

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –
http://dx.doi.org/./..
Synthesis, characterization and study of liquid crystal properties
of new homologous chalcone series
B. B. Jain and R. B. Patel
Chemistry Department, K.K. Shah Jarodwala Maninagar Science College, Gujarat University, Ahmedabad,
Gujarat, India
ABSTRACT
KEYWORDS
Enantiotropic; liquid crystal;
mesomorphism; nematic;
smectic
Onenewmesogenichomologousseriesofchalconylderivativewithtwo
ring (3/-(4/- (decyloxy) phenyl-1-(4-(alkoxy) phenyl) prop-2-en-1-one) has
been synthesized and characterized by a combination of elemental
analysis and standard spectroscopic methods. In the series, the lower
members (C4 and C5) exhibit only enantiotropic nematic mesophase but
middle and higher members exhibit enantiotropic nematic as well as
smecticmesophase. ThenematicmesophasecommencefromC4 homo-
logue and smectic mesophase (smectic-A type texture) commence from
C6 homologue as enantiotropic and persists up to the last member syn-
thesized. The mesomorphic properties of present series were compared
with other two structurally similar series to study the effects of change
of meta and para position on the mesomorphism.
GRAPHICAL ABSTRACT
Introduction
Liquid crystals [1] flow like liquid on a surface and possesses optical properties like crys-
tals. These substances are neither fully crystal nor liquid. The chalconyl derivatives with
two ring and −CH═CH-COO- as central linkage exhibit thermotropic liquid crystal proper-
ties (LC) with biological activity, which is very useful for society in the manufacture of LC
devices and the pharmaceutical preparations [2–9]. This work includes synthesis, charac-
terization by analytical, thermal and spectral data and results and discussion on the basis
of thermometric data and thermal behaviors of novel series. The object of this work to
understand the effect of molecular structure on liquid crystal properties with reference to
changing molecular flexibility through lateral groups of the present and analogous series
[10–15].
CONTACT B. B. Jain
bijendrajain@gmail.com
College, Gujarat University, Ahmedabad, Gujarat, India.
Chemistry Department, K.K. Shah Jarodwala Maninagar Science
©  Taylor & Francis Group, LLC

28
B. B. JAIN AND R. B. PATEL
Scheme . Synthetic route to the series.
Experimental
Synthesis
Alkylation of 4-hydroxy benzaldehyde to give 4-n-alkoxy benzaldehyde is carried out by
reported method [16] and 4-n-alkoxy acetophenone is obtained by alkylation of 4-hydroxy
acetophenone by reported method [17] Thus, the chalconyl homologue derivatives (C) were
prepared by usual establish method [18]. Homologues were filtered, washed with ethanol solu-
tion dried and purified until constant transition temperatures obtained using an optical polar-
izing microscope equipped with a heating stage. Alkyl halides, EtOH, KOH, 4-hydroxy ace-
tophenone, 4-hydroxy benzaldehyde, etc., required for synthesis were used as received except
solvents which were dried and distilled prior to use. The synthetic route to the series is men-
tioned below as Scheme 1.
Characterization
Representative homologues of a series were characterized by elemental analysis, Infrared spec-
1
1
troscopy, H NMR spectra, IR spectra were recorded on Perkin-Elmer spectrum GX, H
NMR spectra were recorded on Bruker using CDCl3 as solvent. Microanalysis was performed

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
29
Table . Elemental analysis for () hexyloxy () decyloxy () tetradecyloxy and () octadecyloxy derivatives.
%Elements found
%Elements theoretical
Sr. No
Molecular formula
C
H
C
H

CHO
CHO
HO
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.



C
CHO
Table . Texture of nematic phase of C, C, C, C by miscibility method.
Sr. No.
Homologue
Texture

C
C
C
C
Threaded
Threaded
Schlieren
Schlieren



on Perkin-Elmer PE 2400 CHN analyzer (Table 1). Transition temperature (Table 3) and
LC properties (Textures) were determined using an optical polarizing microscopy equipped
with heating stage and digital camera (POM). Texture images of nematic phase were deter-
mined by miscibility method (Table 2), thermodynamic quantities enthalpy (ꢀH) and entropy
(ꢀS = ꢀH/T) are qualitatively discussed.
Analytical data
IR spectra in cm−1 for hexyloxy and decyloxy derivatives
–
–
Hexyloxy: 2912 (C H str. of alkane), 2848 (C H str. of –(CH2-)n group of −OC6H13 alkyl
chain, 1602–1656 (C=O str. of carbonyl carbon of chalconyl group), 1610 (C=C str. of
–
alkene), 1512, 1563 (C=C str. of aromatic ring), 997 (C H bending of alkene), 1180 (C-O
str. of ether linkage), 1286, 1245 (C-O str. of carbonyl group), 778 Polymethylene (-CH2-) of
–
−OC10H21, 680 Polymethylene (-CH2-)n of −OC6H13, 828 (−C H- def. m di-substituted-
Para),IR data confirms the molecular structure.
Table . Transition temperature in °C.
Transition temperatures in °C
Sr. no
R = n-alkyl group
Smectic
Nematic
Isotropic













C
C
C
C
C
C
C
C
C
C
C
C
C
—
—
—
—
—
.
.
.
.
.
.
.
.
—
—
—
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.

30
B. B. JAIN AND R. B. PATEL
–
–
Decyloxy: 2914 (C H str. of alkane), 2850 (C H str. of –(CH2-)n group of −OC10H21
group, 1601–1660 (C=O str. of carbonyl group of chalconyl group), 1608(C=C str. of alkene),
–
1514, 1568 (C=C str. of aromatic ring), 1002, (C H bending of alkene), 1186 (C-O str. of ether
linkage), 1238, 1252 (C-O str. of carbonyl group), 774 Polymethylene (-CH2-) of −OC10H21,
–
826 (−C H- def. m di-substituted-Para), IR data confirms the molecular structure.
1HNMR spectra in CDCl3 in δ ppm for heptyloxy and dodecyloxy derivative
Heptyloxy: 0.87 (t, -CH3 of polymethylene −C7H15 and −C10H21), 1.77 (p, CH3-CH2-
CH2-CH2-CH2- of −OC7H15 and −OC10H21), 1.26 (m, −CH2-CH2-CH2- of −OC7H15 and
−OC10H21), 1.35 (q, -CH2-CH3), 4.04(t,-OCH2-CH2-), 7.62 (d,-CH = CH-), 7.42, 7.27 &
7.82 (para substituted phenyl ring), 7.54 & 7.95 (phenyl ring with alkoxy chain). NMR data
confirms the molecular structure.
Dodecyloxy: 0.88 (t, -CH3 of −C12H25 and −C10H21), 1.82(CH3-CH2-CH2-CH2-CH2-
CH2 of -OC12H25 and −OC10H21), 1.28 (polymethylene −CH2-CH2-CH2- of −OC12H25 and
−OC10H21), 1.34 (q, -CH2-CH3), 4.06 (t, -OCH2-CH2-), 7.59 (d, -CH = CH-),7.44, 7.26, and
7.83 (para substituted phenyl ring), 7.56 and 7.97 (phenyl ring with alloy chain), NMR data
confirms the molecular structure.
Result and discussion
The novel homologous series have been synthesized by reaction between 4-n-alloy benzalde-
hyde and 4-decyloxy acetophenone which include thirteen homologues. In present series
C1−C3 are nonmesomorphic and C4−C18 homologues are enantiotropically nematic which
includes C6 to C18 homologues as the enantiotropically smectic in addition to nematic charac-
ter. The transition temperature Table 3 determined with the help of polarizing optical micro-
scope (POM) equipped with the hot stage and plotted against the number of carbon atoms
present in n-alkyl chain ‘R’ of –OR group and then transition curves Cr-N/I, N-I and Sm-N
are obtain on linking like or related transition points as shown in a phase diagram (Fig. 1).
Transition Curve for Cr-N/I adopted zigzag path of rising and falling manner with overall
descending manner and behaved in normal manner. N-I transition curve initially descended
up to C10 homologue and then ascended to C12 homologue and descended to C14 homologue
and then ascended to C16−C18 homologue with exhibition of very narrow and short odd-even
effect up to C9 homologue. Sm-N transition curve rises from C8 to C12 and descended after
passing through maxima at C12, till the last homologue C18 with absence of odd-even effect.
Thus, all the transition curves behaved in normal manner. Thermal stabilities are 54.8 °C and
68.5 °C for smectic and nematic, respectively whose maxima to minimum phase lengths are
06 °C to 13.0 °C and 10 °C to 14.0 °C, respectively. Thus, novel homologous series is low
melting type series. Analytical, spectral and thermal data supported molecular structures of
homologues.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
31
Figure . Phase behavior of series.
The changing style of LC properties from homologue to homologue in the present novel
series is observed. The exhibition of mesomorphism by C4−C18 homologues of a present
novel series is attributed to the suitable magnitudes of anisotropic forces of intermolecular
cohesions and closeness as a consequence of fittest molecular rigidity, polarizability and favor-
able flexibility. The flexibility from homologue to homologue in the same series undergo vari-
ations keeping molecular rigidity and the part of flexibility due to para substituted −OC10H21
right end tailed unaltered. The nonmesomorphic behaviors of C1−C3 homologues is due to
the low magnitudes of dispersion forces and low magnitudes of dipole–dipole interactions
leading to high crystallizing tendency and inducing unsuitable magnitudes of anisotropic
forces of end to end attractions. Diminising of odd-even effect for higher homologues beyond
C9 homologue of longer n-alkyl chain ‘R’ of –OR and −OC10H21 right end flexible groups is
attributed to coiling, bending, flexing and coupling with the major axes of core structure of a
molecule.
The condensation of nonmesomorphs 4-n-alkoxy benzaldehydes with 4-n-decyloxy ace-
tophenone extends molecular lengths, polarity and polarizability, rigidity and flexibility, per-
manent dipole moment across the long molecular axis, intermolecular end to end and lateral
attractions, suitable magnitude of dispersion forces and dipole-dipole interaction etc. Which
induces resistivity and disalignment of molecules at an angle ninety degree or/and less than

32
B. B. JAIN AND R. B. PATEL
Figure . Structurally analogous series.
ninety degree with the plane of floating surface under the influence of exposed thermal vibra-
tions to maintain the floating with statistically parallel orientational order and/or with sliding
layered molecular arrangement for different range or ranges of temperatures to facilitate only
nematic or smectic plus nematic mesophase formation for C4−C18 homologues. The varia-
tions in LC properties and the degree of mesomorphism from homologue to homologue in the
same series or from series to series for the same homologue is attributed to the changing mag-
nitudes of molecular rigidity and flexibility due to varied molecular polarity and polarizabil-
ity and other related parameters concerning suitable magnitudes of intermolecular cohesions
and closeness. The LC properties of presently investigated homologous Series-1 are compared
with structurally similar series A [19] and B [20] as under in Fig. 2.
Homologous seires-1, A and B are identical with respect to two phenyl rings and one central
bridge −CH=CH-CO- contributing to total molecular rigidity and the left n-alkoxy termi-
nals –OR for the same homologue from series to series. However, they differ with tailed end
group viz. para −OC10H21, meta −OC12H25, meta −OC7H15 for the same homologue from
series to series and homologue to homologue in the same series which partly contributes to
the total molecular flexibility. Therefore, variations in liquid crystal (LC) properties are due
to differing features of their molecular structures which differs with respect to flexibility of
tailed end groups differing by −CH2-CH2- and their position of substitutions para or meta
as shown in Figure 2. Following Table 4 represents some evaluated thermometric data indi-
cating mesogenic behaviors and the degree of mesomorphism for the series-1, A and B under
comparative study.
From Table 4, it is clear that,
• Smectogenic mesomorphism commences from C6 homologue in series-1 whereas it
commences C4 and C10 homologue in series-A and B, respectively
• Nematogenic mesomorphism commences from C4 homologue in series-1 whereas it
commences from C2 and C7 homologue in series –A and B, respectively.
• Thermal stability for smectic is less for the series −1 as compared to series A.
• Thermal stability for nematic is more for series-A as compared to series 1 and series-X.
Table . Thermal stability in °C.
Series →
Para −OCH
. (C−C) C
. (C−C/) C
. to . C C
Meta −OCH
. (C−C) C
. (C−C) C
Meta −OCH
Fraction of °C or °C (C - C) C
. (C - C) C
Sm-I or Sm-N Commencement
of smectic phase
N-I Commencement of nematic
phase
Total mesophase lengths in °C
minimum to maximum
. to . C/ C
. to . C// C

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
33
• Homologous series under comparison are predominantly nematogenic and partly smec-
togenic in enantiotropic and/or monotropic condition.
The present novel series-1 has para substituted −OC10H21 group whereas Series -A and B
have meta substituted lateral −OC12H25 and −OC7H15 groups so there are difference in the
geometry of series-1 as compared to series-A and B. Thus, the two opposing effects of inter-
molecular attractions due to para and meta substituted tail ended n- alkoxy groups play role
in facilitating smectic and/or nematic mesophase formation through predominancy of either
molecular polarity or polarizability factor. The dipole moment, magnitudes of dipole-dipole
interactions, molecular rigidity and flexibility, length of breath ratio, intermolecular closeness
all are play important role in mesomorphism and the degree of mesomorphism. The increas-
ing order of nematic thermal stability is attributed to the increasing order of intermolecu-
lar cohesions corresponding to increasing number of carbon atoms present from Series-A
(-OC12H25 (m)) to series-1 (-OC10H21(p)) to Series-B (-OC7H15(m)) due to increasing order
of polarities and polarizability caused by their lateral groups or para substitutents for the same
homologue in series A, 1 and B, respectively. The alternation of nematic thermal stability or
mesophase lengths are related with the combined effects of molecular rigidity in combition
with flexibility and the unexpected status of both ended n-alkoxy end groups, which may fluc-
tuate with the status of flexible groups and their polarity or polarizability. Therefore, it may
acquire increasing or decreasing or alternating order of facilitating or stabilizing mesophase
or mesophases in enantiotropic manner. Thus, present chalconyl homologous series is pre-
dominantly nematogenic and partly smectogenic of low melting type and shorter mesophase
lengths.
Conclusions
• Novel homologous series of single central bridge linking two phenyl rings and n-alkoxy
terminal groups is enantiotropically nematogenic and smectogenic.
• The group efficiency order derived on the basis of (a) thermal stability (b) early com-
mencement of mesophase (c) mesophaselengths for smectic and nematic are as under
(1) Smectic
−OC12H25 > −OC10H21 > −OC7H15
Nematic
−OC12H25 > −OC10H21 > −OC7H15
(2) Smectic
−OC12H25 > −OC10H21 > −OC7H15
Nematic
−OC12H25 > −OC10H21 > −OC7H15
(3) Sm
N
Upper: −OC12H25 > −OC10H21 > −OC7H15
Lower: −OC7H15 > −OC10H21 > −OC12H25
• Mesomorphism is depended on suitable magnitudes of molecular rigidity and flexibility.
• Present investigation may be useful for LC devices, Their pharmaceutical or biological
activity may be exploited for pharmaceutical preparation and agricultural production
to reduce the consumption of insecticides and pesticide as they are antibacterial and
antifungal.
• Present study supports and raises credibility to the conclusions drawn earlier.

34
B. B. JAIN AND R. B. PATEL
Acknowledgments
The authors thank Dr. R. R. Shah, Principal of K. K. Shah Jarodwala Maninagar Science College,
Ahmedabad. The authors also thank the NFDD Centre for the analytical and spectral services.
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