Synthesis and mesomorphic properties of achiral and chiral esters with high tilted synclinic and anticlinic phases

Article abstract of DOI:10.1080/15421400490435224

Two series of three ring esters with chiral chain (derivative of (S)-octanol-2) and achiral chain (the swallow type) with high tilted synclinic and anticlinic phases were chosen to studies. The aim of presented studies was to find how the changes of diffe

Full text of DOI:10.1080/15421400490435224

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Synthesis and Mesomorphic
Properties of Achiral and
Chiral Esters with High Tilted
Synclinic and Anticlinic Phases
J. Gasowska a , R. Dabrowski a , W. Drzewinski a , K.
Kenig a , M. Tykarska a & J. Przedmojski b
a Military University of Technology , Warsaw, Poland
b Warsaw University of Technology , Warsaw, Poland
Published online: 18 Oct 2010.
To cite this article: J. Gasowska , R. Dabrowski , W. Drzewinski , K. Kenig , M.
Tykarska & J. Przedmojski (2004) Synthesis and Mesomorphic Properties of Achiral and
Chiral Esters with High Tilted Synclinic and Anticlinic Phases, Molecular Crystals and
Liquid Crystals, 411:1, 231-241, DOI: 10.1080/15421400490435224
To link to this article: http://dx.doi.org/10.1080/15421400490435224
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Mol. Cryst. Liq. Cryst., Vol. 411, pp. 231=[1273]–241=[1283], 2004
Copyright # Taylor & Francis Inc.
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080=15421400490435224
SYNTHESIS AND MESOMORPHIC PROPERTIES OF
ACHIRAL AND CHIRAL ESTERS WITH HIGH TILTED
SYNCLINIC AND ANTICLINIC PHASES
J. Gasowska, R. Dabrowski, W. Drzewinski, K. Kenig,
and M. Tykarska
Military University of Technology, Warsaw 00-908, Poland
J. Przedmojski
Warsaw University of Technology, Warsaw 00–662, Poland
Two series of three ring esters with chiral chain (derivative of (S)-octanol-2)
and achiral chain (the swallow type) with high tilted synclinic and anticlinic
phases were chosen to studies. The aim of presented studies was to find how the
changes of different molecule units influence the mesomorphic properties of the
compounds (temperatures, enthalpies and the sequence of phase transitions)
and to find members with the best properties for mixture formulation. The com-
pounds were studied by polarising microscope, differential scanning calor-
imetry, miscibility and X-ray diffraction methods.
Keywords: anticlinic and synclinic phase; antiferroelectrics; ferroelectrics; phase transition;
synthesis
INTRODUCTION
During few recent years we have synthesized and investigated meso-
morphic properties of three ring chiral esters having an perfluorinated unit
in one terminal chain [1,2]. We have found that compounds with
CsF2s þ 1COO(CH2)3O tail have the smectic layer with anticlinic order and
a very large tilt [3]. AFLC mixtures with the tilt 45ꢀ in a broad temperature
range were formulated [4]. They are called now the orthoconic antiferro-
electrics, because the neighborhood smectic layers give a cone of 90ꢀ.
Financial support from the Polish Government (K.B.N) – PBS 634 and European Program
‘HEMID’ – TST-2001-33836.
Address correspondence to J. Gasowska, Military University of Technology, Warsaw
00-908, Poland.
231=[1273]

232=[1274]
J. Gasowska et al.
These new materials have been investigated parallel in Lagerwall’s lab-
oratory [4–7]. It was found that the orthoconic AFLC mixture is uniaxial
negative liquid crystalline mixture. It behaves in normal surface stabilized
cell as an isotropic medium and surface defects are not seen, what generates
the excellent dark state. When this AFLC material is switched from the anti-
ferroelectric state (AF) into one of two synclinic ferroelectric states (ꢁ F,
being biaxial positive states) extremally high contrast is obtained. It seems,
that these materials are the most perspective for applications among the
antiferroelectric mixtures prepared until now [7] and therefore their further
development is desirable. All orthoconic antiferroelectrics (AFLC) already
prepared show high spontaneous polarization (200 nC=cm2 or higher) and
very short pitch (below p ¼ 1 mm) [4,8]. The material with smaller spon-
taneous polarization S and longer p are necessary to obtain.
Weissflog [9] as the first synthesized achiral molecules with one swallow
type alkyl tail in the terminal position. We have sinthesized a similar com-
pound [10] and found that it exhibit the smectic layer with an anticlinic or-
der. Nishiyama, Goodby [11–13] et al. investigated achiral molecules with
one swallow type alkyl tail in the terminal position and found many com-
pounds with the anticlinic phase.
We decided to prepare similar structures with a fluorinated fragment in
another terminal chain.
Two series of esters of the general formula were chosen to studies:
The first one (I, n ¼ m ¼ 3) is the achiral structure and the second one
(II, n ¼ 6, m ¼ 1) is the chiral derivative of (S)-octanol-2, R was chosen
as C6F13C2H4, CF3CH2O(CH2)5, CsF2s þ 1COO(CH2)5, CsH2s þ 1COO(CH2)5
group. The compounds with the spacing group (CH2)5 were prepared in-
stead of (CH2)3 used before [8] in the aim to decrease the tendency to form
a higher ordered smectic IA phase.
The aim of presented studies was to find how the changes of different
molecule units influence the mesomorphic properties of the compounds
(temperatures, enthalpies and the sequence of phase transitions) and to
find members with the best properties for mixture formulation.
SYNTHESIS
The used methods of syntheses of esters I and II are given in Scheme 1 in
the case of R ¼ 1H,1H,2H,2H-perfluorooctyl or 5-(1,1,1,-trifluoroethoxy)-

Synthesis of Achiral and Chiral Esters
233=[1275]
SCHEME 1 Synthetic route of eteroesters I (n ¼ m ¼ 3) and II (n ¼ 6, m ¼ 1);
R ¼ C6F13CH2CH2- or CF3CH2O(CH2)5-.
pentyl and in Scheme 2 in the case of R ¼ 5-(alkanoyloxy)pentyl or 5-
(perfluoroalkanoyloxy)pentyl.
The detailed description of preparative procedures and purification
methods are given in earlier papers [2,14] for similar esters.
MESOMORPHIC PROPERTIES
The phase transition temperatures and enthalpies of esters I and II were
measured by DSC (SETARAM 141) and were confirmed by polarizing

234=[1276]
J. Gasowska et al.
SCHEME 2 Synthetic route of triple esters I and II; R0 ¼ CsF2s þ 1- or CsH2s þ 1-.
microscopy observations (BIOLAR PZO connected with LINKAM TMS-91
heating stage), by the miscibility with the compounds of known phase
situation and by X-ray diffraction patterns. The results of studies are
summarized in Table I and II.
The swallow type chain esters I (derivatives of 4-heptanol) exhibit the
poor number of smectic phases. The smectic A phase at higher tempera-
ture range and only a single tilted phase at lower temperature range are
observed, except for the compound I.5, which has only SmA phase. The
tilted phases are either the synclinic smectic C phase (SmC) or the anticli-
nic smectic C phase (SmCAnti). The substituted esters with fluorine in the
nearest benzene ring to the swallow type tail have higher melting points,

235=[1277]

236=[1278]

Synthesis of Achiral and Chiral Esters
237=[1279]
higher melting enthalpies and lower clearing points than unsubstituted
analogues. Their smectic phases are only monotropic.
The chiral esters II being derivatives of octanol-2 (having less branched
but longer chain than in series I) show a richer smectic polymorphism. The
anticlinic (SmCantiꢃ), synclinic (SmCꢃ) and orthogonal SmA phases are sim-
ultaneously observed. Here the compounds with (CH2)5O- between the
fluorinated alkanoyloxy unit and the biphenyl ring have the phase sequence
and the phase stability very similar as was observed in their analogues with
(CH2)3O- spacing group [2]. A positive change with comparison to the latter
ꢃ
structure is that a higher ordered SmIA phase is not observed and the
melting points here are decreased although slightly. In case of the series
II fluoro substitution in lateral position decreases slightly the melting point
and stronger the clearing point.
X-RAY MEASUREMENTS
The change of smectic layer spacing (d) for some compounds I (I.2, I.6)
were measured. Their temperature dependence of the ratio d=dA is
presented in Figure 1, where the data for compounds II (II.3, II.7, II.9)
are also presented for comparison.
FIGURE 1 Temperature dependence of d/dA smectic layer spacing for I.2, I.6,
II.3, II.7 and II.9. TC-A – transition temperature to a tilted phase.

238=[1280]
J. Gasowska et al.
A very strong drop of the layer spacing d during transition from the or-
thogonal smectic A phase to the tilted phase is observed. It correlated with
the strong first order character of this transition as it results from the
observed values of the transition enthalpy, see Table 1. This drop expressed
by decreasing d=l or d=dA ratio changes in the following order for the
chains:
CF3CH2-OðCH2Þ5O- < C3H7COOðCH2Þ5O < C3F7COOðCH2Þ5O-
d=dAequals
0:94
0:92
0:9
at temperatures 10 deg below the transition SmCAnti-SmA. The same was
recently reported for the compounds with the (CH2)3 spacer [8].
The compound I.6 has the smectic layer tilted the same high as it was
found for the chiral compound with the chain C4F9COO(CH2)3O or
C3F7COO(CH2)3O [8].
PHASE DIAGRAM AND THE INDUCTION OF AN ANTICLINIC
PHASE STUDIES
Similarity in the tilt values of achiral and chiral analogues is confirmed by
miscibility phase diagrams studies, Figure 2.
It is known, that the smectic C phase is destabilized and the phase bor-
der SmC-SmA decreases strongly when the compounds with different layer
tilts are mixed [16]. The Figures 1a and 1b show that the achiral compound
FIGURE 2 Phase diagrams of mixtures I.1–II.1 – a and I.6–II.7 – b, x – melting
points.

Synthesis of Achiral and Chiral Esters
239=[1281]
FIGURE 3 Phase diagrams of mixtures I.2-III – a and I.2-IIIa – b, x – melting
points.
I.1 and chiral compounds II.1 mix themselves additively and form the
simple eutectic in the solid phase, also the same behavior is observed for
the pair of compounds I.6–II.7.
The achiral fluorinated compound I.2 exhibiting only the synclinic SmC
ꢃ
and orthogonal SmA phase is able to induce anticlinic smectic CA phase,
when is mixed with chiral protonated compounds, for example compound
III, as well as its racemic (R, S) form compound IIIa, see Figures 3a, b.
Phase transition
Cr1 60.8 Cr 79.6 (SmIA 65.8ꢃ) SmCb 118.6 Sma 119.6 SmA 144.1 I (S) [17]
ꢃ
ꢃ
ꢃ
Cr 79 (SmIA 65.8) SmCb 118.6 Sma 119.6 SmA 144.1 I (S,R) [17]
CONCLUSION
Achiral esters I with a swallow type terminal chain such as arised from
4-heptanol and having a fluorinated part in another chain may form a high
tilted smectic phase with the synclinic or anticlinic layering. Therefore they
can be used as the components of orthoconic mixtures decreasing their
spontaneous polarization and elongating the helical pitch.
The lateral substitution by a fluorine atom of the rigid core of ester
molecule is not convenient in the case of strongly branched esters, because

240=[1282]
J. Gasowska et al.
it produces mesogenes with high melting points and high melting enthal-
pies, but may be recommended for molecules with less branched and
longer tails. It is possible to induce smectic anticlinic phase (SmCAnti),
when the synclinic achiral esters (SmC) are mixed with other sinclinic
ester which molecules are chiral or racemic.
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