Structural analysis of chiral dopants in nematic systems by example of ether-ester-substituted 1,4:3,6-dianhydrohexitols

Article abstract of DOI:10.1080/15421406.2013.833476

Series of ether-ester-substituted 1,4:3,6-dianhydrohexitols were synthesized and studied as chiral dopants to nematics as compositions with 4′-pentyl-4-cyanobiphenyl. The most helical twisting power was found for bis-esters. Lesser values were found for mixed ether-esters with certain configuration. Other ethers and ether-esters revealed noticeably smaller values. Supramolecular peculiarities of such systems and their role in helical twisting are discussed. 2014 Copyright

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Structural Analysis of Chiral Dopants
in Nematic Systems by Example of
Ether-Ester-Substituted 1,4:3,6-
Dianhydrohexitols
Ivan M. Gellaa, Tatyana G. Drushlyaka, Nikolay L. Babaka, Nataly B.
Novikovaa & Victoria V. Lipsona
a SSI Institute for Single Crystals, National Academy of Sciences of
Ukraine, Kharkov, Ukraine
Published online: 08 Apr 2014.
To cite this article: Ivan M. Gella, Tatyana G. Drushlyak, Nikolay L. Babak, Nataly B. Novikova &
Victoria V. Lipson (2014) Structural Analysis of Chiral Dopants in Nematic Systems by Example of
Ether-Ester-Substituted 1,4:3,6-Dianhydrohexitols, Molecular Crystals and Liquid Crystals, 591:1,
34-44, DOI: 10.1080/15421406.2013.833476
To link to this article: http://dx.doi.org/10.1080/15421406.2013.833476
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Mol. Cryst. Liq. Cryst., Vol. 591: pp. 34–44, 2014
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2013.833476
Structural Analysis of Chiral Dopants in Nematic
Systems by Example of Ether-Ester-Substituted
1,4:3,6-Dianhydrohexitols
IVAN M. GELLA, TATYANA G. DRUSHLYAK,∗ NIKOLAY L.
BABAK, NATALY B. NOVIKOVA, AND VICTORIA V. LIPSON
SSI Institute for Single Crystals, National Academy of Sciences of Ukraine,
Kharkov, Ukraine
Series of ether-ester-substituted 1,4:3,6-dianhydrohexitols were synthesized and studied
as chiral dopants to nematics as compositions with 4ꢀ-pentyl-4-cyanobiphenyl. The
most helical twisting power was found for bis-esters. Lesser values were found for
mixed ether-esters with certain configuration. Other ethers and ether-esters revealed
noticeably smaller values. Supramolecular peculiarities of such systems and their role
in helical twisting are discussed.
Keywords Chiral dopant; helical twist; induced cholesterics; substituted 1,4:3,6-
dianhydrohexitols
Introduction
Chiral nematic liquid crystals (N∗-LC) possess properties of selective light reflection, high
optical rotation, and circular dichroism, that is the base of their applications for different
devices, first of all liquid crystalline displays [1, 2], holography [3, 4], LC lasers [5] and
electro-active lenses [6]. Recently, new applications of N∗-LC were proposed, such as a
nematicon generation (nematicons are spatial solitons in a chiral nematic that lead to the
formation of an optical waveguide by self-focusing of an optical beam) [7, 8], and UV-filters
for medical applications and cosmetics [9]. Also, a new application area for liquid crystals
arises – it is biomedical engineering for medical displays, sensors, actuators, and so on
[10].
Chiral nematic mesophase (N∗-LC) may be obtained by adding a chiral dopant (CD)
to a nematic liquid crystal, which is achiral previously. CD induces helical supramolecular
structure in a mesophase [11] that leads to the molecular chirality amplification [12].
The question of how molecular chirality is transferred into bulk chirality of the liquid
crystalline phase is a fundamental problem. This phenomenon gives a unique potential to
investigate the relationship between molecular structure, intermolecular interactions, and
mesoscale organization [13].
The helical twisting power (HTP) defines the ability of a dopant to induce a helical
submolecular structure in the LC host [14]. The HTP is the easiest of access characteristic
∗Address correspondence to T. G. Drushlyak, SSI Institute for Single Crystals, National Academy
of Sciences of Ukraine, 60 Lenin Ave, Kharkov 61001, Ukraine. Tel.: (38) (057)-341-04-21, (38)
(057)-341-03-13, Fax:. (38) (057)-341-02-73. E-mail: drushlyak@isc.kharkov.com
34

1,4:3,6-Dianhydrohexitols in Chiral Nematics
35
of chirality transfer from single molecule to a macroscopic scale, both for measurements
and modeling.
A collection of CDs that induce a great HTP (100 μm−1 and more) in nematics has
been made [15–22]. Isosorbide (1,4:3,6-dianhydro-D-glucitol) esters refer to the most well-
known chiral compounds with great HTP. Recently, a series of isosorbide esters with better
solubility in LC hosts was synthesized [23, 24].
We have synthesized the new collection of 1,4:3,6-dianhydrohexitol ethers and mixed
ether-esters, measured their HTP in 4,4ꢀ-pentylcyanobiphenyl (5CB), and revealed that only
esters in this collection show a great twisting power (up to 176 μm−1), not ethers. The HTP
of mixed ether-esters varies from 0 μm−1 to 70 μm−1 depending on their structure.
In this paper, we undertook an attempt to interpret how molecular structure of CD had
an effect on its HTP in nematics, and to reveal distinction in ester and ether groups in this
aspect.
Theoretical Basis
The explicit connection between geometrical parameters of constituent molecules and
HTP generated by them is absent in theoretical grounds. Theoretical physics [25, 26 and
references therein] and molecular modeling of N∗-LC [27–31] do not give a possibility to
segregate fragments of molecules having influence on HTP. Whole shape of molecule and
its surroundings define chirality transfer from chiral molecule to a mesophase.
Method of Wilson et al. [27, 28] uses the structure of CD molecule in molecular
dynamics simulation. Surface chirality model (shape model earlier) [29–31] interprets a
pitch of an induced cholesteric phase on the base of intermolecular interactions between a
CD molecule and nematic solvent as an interplay between surface chirality and orientational
order. In that model, HTP is proportional to the contraction of the two second-rank tensors
Q(2) and S, where Q(2) is the chirality tensor, and S is the ordering matrix for the solute
molecule. With fundamental nature of this work, authors do not give a possibility to see
what elements of molecular structure are the most responsible for the great HTP.
As shown in [30], macroscopic chirality is controlled by the difference in size of the
substituents at the asymmetric carbon atom. However, the example of HTP difference in
ester and ether derivatives of dianhydrohexitols shows that it is not enough.
We have made an attempt to understand the nature of difference in HTP for dianhy-
drohexitols in a nematic mesophase.
Experimental
Synthetic Procedure of Chiral Dopants
Procedures for synthesis of new CDs are given in Figure 1. Chemical shifts of protons (δ,
ppm) in 1H NMR spectra (DMSO-d6) for newly synthesized compounds 3a-c, 4a-e, 5a-c,
6a-l, 7 are given in Table 1. Other analytical data are given in Table 2.
2-O-(aroyl)-5-O-(aryl)-1,4:3,6-dianhydro-D-sorbitol (3a, 3b)
I. 5-O-(4-cyanophenyl)-1,4:3,6-dianhydro-D-sorbitol
Sodium hydride (50%, 2 g; 41.6 mmol) was added to the solution of isosorbide (4.8 g;
33 mmol) in dry DMF (50 ml). The mixture was magnetically stirred at room temper-
ature for 30 min, and 4-fluorobenzonitrile (4 g, 33 mmol) was added in small portions.

36
I. M. Gella et al.
R1COOH
DCC, DCM
p-CNC6H4F, NaH,
DMF
NC
O
O
HO
H
H
NC
O
H
H
H
O
O
O
O
O
O
H
OH
O
OH
3
R1
3'
1
R1
O
R2OH
R1COOH
H
H
HO
HO
HO
H
H
O
O
H
H
O
O
K2CO3, DMF
DCC, DCM
O
TsCl
O
O
O
O
O
R2
H
4
H
OH
R
2
O
OTs
2
4'
2'
HO
R
1O
H
R2OH
H
H
p-CNC6H4F,
NaH, DMF
HO
H
H
O
O
O
K2CO3, DMF
O
O
5c
O
H
R
O
OTs
2
R
O
2'
2
5'c
NCAr
O
H
H
HO
p-CNArHal,
NaH, DMF
H
O
O
O
O
OArCN
H
OH
5a,b
1
O
O
R2COOH
O
O
H
H
H
H
R1
R1
DCC, DCM
HO
O
O
O
H
(R1CO)2O, PbO
O
O
O
O
O
OH
6
6'
H
OH
1
R2
HO
H
O
H
HO
R
OH
HO
O
H
H
O
O
O
O
O
O
R
O
O
O
O
H
O
H
O
H
O
O
H
H
7
OTs
O
O
2'
C5H11-n
R =
7'
H
OH
Figure 1. Synthetical methods for preparation of chiral dopants investigated.
Then the mixture was stirred at 55◦C for 3 hr. After cooling, the reaction mixture was
treated with a solution of ammonium chloride, and the product was extracted with
ethylacetate. Then solvent was evaporated, and the residue was separated at silica gel
(eluent DCM (dichloromethane) – ethylacetate). First fractions after crystallization from
a cyclohexane–acetone mixture give 0.35 g of 2,5-O,O-Bis(4,4ꢀ-cyanophenyl)-1,4:3,6-
dianhydro-D-sorbitol, that was identical to known product [32]. Fraction crystallization
from more polar fractions gives 1.24 g of product with mp 138.5◦C, Rf = 0.18 (toluene-
ethanol), that differs from isomeric 2-О-(4-cyanophenyl)-1,4:3,6-dianhydro-D-sorbitol

37

38
I. M. Gella et al.
Table 2. Analytical data for newly synthesized compounds
Elemental analysis
Calculated, %
Found, %
Yield, Molecular
formula
MW
EIMS
%
calculated (m/z, M+)
C
H
Other
C
H
Other
3a 43 C21H19F3O5
3b 37 C33H35NO5
408.38
525.65
306.32
522.60
634.82
662.87
573.70
517.59
499.57
574.68
458.52
474.52
516.60
512.49
424.45
408
525
306
522
634
662
573
517
499
574
458
474
516
512
424
668
616
608
943
61.76 4.69 F 13.96 61.63 4.51 F 13.60
75.41 6.71 N 2.66 75.25 6.64 N 2.48
3c
41 C16H18O6
62.74 5.92
75.84 5.79
77.57 7.30
77.92 7.60
—
—
—
—
62.56 6.01
75.90 5.59
77.61 7.51
77.73 7.79
—
—
—
—
4a 46 C33H30O6
4b 52 C41H46O6
4c
41 C43H50O6
4d 33 C37H35NO5
77.46 6.15 N 2.44 77.28 6.39 N 2.27
76.58 5.26 N 2.71 76.49 5.31 N 2.90
72.13 5.85 N 2.80 72.25 5.91 N 2.59
4e
5c
6c
43 C33H27NO5
56 C30H29NO6
34 C28H34O8
71.06 6.67
73.35 5.72
70.87 5.52
72.08 6.24
—
—
—
—
71.23 6.81
73.24 5.57
70.65 5.70
72.20 6.07
—
—
—
—
6d 67 C28H26O6
6e
6f
68 C28H26O7
56 C31H32O7
6g 55 C28H23F3O6
65.62 4.52 F 11.12 65.46 4.66 F 10.89
67.91 5.70 67.89 5.55
6i
6j
56 C24H24O7
—
—
63 C42H40N2O6 668.80
6k 61 C36H28N2O8 616.63
70.12 4.58 N 4.54 70.23 4.44 N 4.30
74.99 4.64 N 4.60 75.05 4.56 N 4.37
6l
7
45 C38H28N2O6 608.66
47 C60H62O10 943.16
76.41 6.63
—
76.58 6.79
—
[32], and which was identified by its spectroscopic data as 5-O-(4-cyanophenyl)-1,4:3,6-
dianhydro-D-sorbitol. Its characteristics are: 1H NMR (500 MHz, DMSO) δ 7.73 (d, J
= 8.8 Hz, 2H), 7.15 (d, J = 8.8 Hz, 2H), 5.16 (d, J 3.4 Hz, 1H, OH), 4.99 (m, 1H, H-5),
4.90 (m, 1H, H-4), 4.30 (d, J = 4.0 Hz, 1H, H-3), 4.09 (m, 1H, H-2), 3.90 (dd, J =
9.6, 5.7 Hz, 1H, H-6), 3.77 (dd, J = 9.5, 4.6 Hz, 1H, H-6), 3.67 (m, 1H, H-1), 3.61 (m,
1H, H-1).13C NMR (126 MHz, DMSO) δ 162.00 (s), 134.48 (s), 119.60 (s), 116.46 (s),
103.34 (s), 89.14 (s), 80.48 (s), 77.98 (s), 75.69 (s), 75.32 (s), 70.74 (s). MW calculated
246.9, C13H13NO4, EIMS (m/z, M+) 247.
II. The next stage (esterification with DCC and DMAP, Fig. 1) was carried out in known
way with proper carboxylic acid [for example, 33]. The purification of the product was
carried out by column chromatography on silica gel (eluent DCM). Yields 37%–43%.
Product 3c was obtained by esterification of isosorbide with 4-methoxycinnamic acid
as above. Yield 41%.
2-O-(4-aryloxy)-5-O-(4-aryloyl)-1,4:3,6-dianhydro-D-sorbitol (4)
I. Isomannide monotosylate 2ꢀ was obtained like in [34].
II. Isosorbide monoether 4ꢀ.
4-Alkoxy-4ꢀ-hydroxybiphenyl (AHB, 0.74 mmol) and 132 mg of potassium carbonate
were added to 0.67 mmol of isomannide monotosylate 2ꢀ in 10 ml of DMF. The mixture
was stirred and boiled with reflux for 6–14 hr until AHB convert (control by TLC (silica
gel, eluent dichloroethane)). Then the mixture was poured into an aqueous solution
of hydrochloric acid with pH near 2, and the precipitate was filtered and washed with

1,4:3,6-Dianhydrohexitols in Chiral Nematics
39
an aqueous solution of Na2CO3. Product 4ꢀ, which was identified by its spectroscopic
data, was dried in air. Yields 70%–80%.
III. Isosorbide ether-esters were obtained by means of isosorbide monoether 4ꢀ acylation
with proper carboxylic acid, DCC and DMAP like the protocol used in [33]. The
crude products were washed with propanol-2 and dried, and then they were purified
by column chromatography on silica gel, eluent DCM.
1,4:3,6-Dianhydro-D-sorbityl-2,5-diether (5)
Bis-ethers of 1,4:3,6- dianhydro-D-sorbitol 5a and 5b were obtained like in [32]. The
synthesis of product 5c differs from above.
Intermediate 2-O-(4ꢀ-butoxydiphenyl)-1,4:3,6-dianhydro-D-sorbitol 5ꢀc
4-Hydroxy-4ꢀ-butoxydiphenyl (250 mg, 1.1 mmol), isomannide monotosylate (330 mg,
1.1 mmol) were dissolved in DMF (10 ml) in 50 ml round-bottomed flask, and potash
(260 mg, 2 mmol) was added. The resulting mixture was boiled at reflux for about 6 hr
(control by TLC). Then the reaction mixture was diluted with water (100 ml), and obtained
precipitate was filtered and washed three times with water. Yield 92%. mp 160◦C. 1H NMR
(200 MHz, DMSO) δ 7.52 (dd, J = 8.6, 4.8 Hz, 4H), 6.98 (dd, J = 8.6, 6.4 Hz, 4H), 4.95 (d,
J = 6.2 Hz, 1H, OH), 4.84 (s, 4H), 4.48 (d, J = 2.5 Hz, 2H), 4.23–3.84 (m, 4H), 3.85–3.66
(m, 1H), 3.40 (dd, J = 15.4, 7.8 Hz, 1H), 1.82–1.56 (m, 1H), 1.43 (dd, J = 14.8, 7.0 Hz,
1H), 0.92 (t, J = 7.3 Hz, 3H).
2-O-(4ꢀ-butoxydiphenyl-4-yl)-5-O-(4-cyanophenyl)-1,4:3,6-dianhydro-D-sorbitol (5c)
Compound 5ꢀc (0.32 mmol) was dissolved in dry DMF in round-bottomed flask at room
temperature. Sodium hydride (50%, 1.3 mmol) was added to the stirred solution. When
evolution of hydrogen finished, p-fluorobenzonitrile (0.35 mmol) was added slowly. The
resulting mixture was heated at 75◦C till reaction was finished (control by TLC). Then the
reaction mixture was diluted with water, and obtained precipitate was filtered, washed with
water and recrystallized from ethyl acetate. Yield 72%.
2-O-aroyl-5-O-aroylꢀ-1,4:3,6-dianhydro-D-sorbitol (6a-h)
I. D-isosorbide monoester.
DCM (25 ml) and PbO (0.01 g) were added to the mixture of D-isosorbide (0.29 g;
2 mmol) and substituted benzoic acid anhydride (3 mmol) (like in [35]). Then the
mixture was stirred at room temperature up to full utilization of isosorbide (TLC
control). Then resulting suspension was filtered, and the solvent was removed from
the filtrate under reduced pressure. The residue was recrystallized from ethanol or
ethylacetate. Products were identified by their spectroscopic data. Yields 27%–70%.
II. Isosorbide bis-esters were obtained by means of D-isosorbide monoesters acylation
with proper carboxylic acid, DCC and DMAP like in [33]. Yields of 6 were 41%–78%.

40
I. M. Gella et al.
bis-(5-(4ꢀ-n-pentylbiphenyl-4-oyl)-1,4:3,6-dianhydro-D-sorbit-2-yl)-(biphenyl-4,4ꢀ-
diylbis(oxy)) (7)
I. Bis-(1,4:3,6-dianhydro-D-sorbit-2-yl)-biphenyl-4,4ꢀ-diylbis(oxy) (7ꢀ)
4,4ꢀ-Dihydroxydiphenyl (150 mg, 0.806 mmol) and isomannide monotosylate (510 mg,
1.7 mmol) were dissolved in DMF (25 ml). Then potash (270 mg, 1.96 mmol) was added,
and the resulting mixture was heated at reflux for about 10 hr to 4,4ꢀ-dihydroxydiphenyl
conversion (control by TLC). The reaction mixture was diluted with water (100 ml),
and the precipitate obtained was filtered. Yield 84%.
II. Bis-ester 7 was obtained from 7ꢀ by means of acylation with 4ꢀ-n-pentyldiphenyl-4-
carboxylic acid, DCC and DMAP like the protocol used in [33].
Physical Measurements
Structures of newly synthesized compounds have been proved by nuclear magnetic reso-
nance (1H NMR) and mass spectrometry (MS). 1H NMR spectra were measured in CDCl3
and DMSO-d6 using a Varian Mercury VX-200 NMR and Bruker AVANCE DRX 500
spectrometer with tetramethylsilane as an internal standard. 13C NMR spectra were mea-
sured using a Bruker AVANCE DRX 500 spectrometer at 125 MHz with CDCl3 both as a
solvent and the internal standard. Mass spectra were recorded on Varian 1200 L GS-MS.
Elemental analyses were carried out using Element Analyzer EA-3000 (Eurovector, Italy).
Measurements of melting points were carried in an open capillary with PTP(M) device (PO
Khimlaborpribor, Klin, Russia).
Fabrication of CLC Cells and Measurements of HTP
Glass substrates were cleaned with a detergent solution and then rinsed with isopropyl
alcohol and acetone. One percent water solution of polyvinyl alcohol was used for LC
alignment layer formation (for a planar orientation of LC molecules) by spin-coating with
postheating at 120◦C–130◦C for 30 min. After cooling to room temperature, its surface was
rubbed with a velvet cloth perpendicular to wedge gradient and coated with LC composition
between two glasses.
Values of the induced helical pitch, p, were measured by the conventional
Grandjean–Cano wedge method as described in [36] using a PZO polarizing microscope
(Warszawa, Poland) equipped with a heating stage with an accuracy of temperature mea-
surement of 0.5◦C. For all CD, the enantiomeric purity r was about 1 (0.98 0.01). The CD
concentration in N∗ systems on the base of 5CB was taken at about 0.25 mol%–5 mol%.
The Adams–Haas equation [37] was used for the identification of the helix handedness in
N∗ systems under study.
Computations
Quantum-chemical computations of equilibrium geometry of CD have been made with
AM1 and PM6 [38] MOPAC2009 Package by James J. P. Stewart [39].

1,4:3,6-Dianhydrohexitols in Chiral Nematics
Results and Discussion
41
Helical Twisting Power of New Chiral Dopants and Its Connection with Peculiarities of
Their Molecular Structure
The HTP of N∗-LCs, HTP, and a temperature gradient of a helical pitch, dP/dT values,
obtained for systems on the base of 5CB and CDs 3–7 are listed in Table 3.
As can be seen from Table 3, the highest HTP values of 70 μm−1–176 μm−1 were
obtained for CD 6 with two ester groups except 6j and 6k (HTP of 22 μm−1–24 μm−1
)
with four-methylene spacers that separate two rigid fragments. Thereby, non-rigid fragment
(spacer) introduction in a CD structure considerably decreases HTP value. Chirality is con-
nected with a rigid core unit in the structures of CDs that induce a great HTP in nematics
(binaphthyl derivatives [16], (α,α,αꢀ,αꢀ-tetraaryl-1,3-dioxolan-4,5-dimethanol derivatives
(Taddols) [17], 2,6,9-trioxabicyclo[3.3.1]nonanes [18], esters of 1,4:3,6-dianhydrohexitols
[19–21]). Mesogenic functionalization provides a considerable increase in HTP [40], prob-
ably, due to the extension of CD’s rigid part and essential increase in interaction of a CD
molecule with host.
Interestingly, though ester groups COO separate rigid fragments in isosorbide esters
6a-i, it does not inhibit obtaining a great HTP. Ester group seems to be non-rigid because
of probable rotation about an ordinary C–O bond.
A connection of rigid fragments by means of ester group produces quite tough immobi-
lization of the propeller-shaped dianhydrohexitol core, as can be seen from potential energy
Table 3. Comparison of helical twisting power (HTP, μm−1) between several types of CD
3–7 in nematic 4-pentyl-4ꢀ-cyanobiphenyl (5CB)
HTP, μm−1
dP/dT,
CC
R1
R2
(C in mol%)
μm/degree
3a
3b
3c
4a
4b
4c
4d
4e
5a
5b
5c
6a
6b
6c
6d
6e
6f
4-CF3C6H4
4-NC-C6H4
4-NC-C6H4
H
4-(4-CH3OC6H4)C6H4
4-(4-n-C5H11OC6H4)C6H4
4-(4-n-C4H9OC6H4)C6H4
4-(4-NCC6H4)C6H4
4-(4-NCC6H4)C6H4
4-NC-C6H4
2-(5-NC-Pyridinyl)
4-(4-n-C4H9C6H4)C6H4
4-CH3C6H4
4-CH3OC6H4
4-n-C7H15OC6H4
4-(4-CH3C6H4)C6H4
4-(4-CH3C6H4)C6H4
4-(4-n-C4H9C6H4)C6H4
4-(4-CH3C6H4)C6H4
4-(4-CH3C6H4)C6H4
4-CH3C6H4
4-(4-NC-C6H4)C6H4-(CH2)4-n
4-(4-NC-C6H4)C6H4-OCH2
4-(2-Ph-Quinolinyl)
—
+35.21 1.33
+70.11 0.84
0.6 0.30
+8.38 0.27
−6.96 0.25
−9.22 0.27
0.6 1.33
0.016 0.004
−0.006 0.006
7.62 6.12
4-(4-n-C7H15C6H4)C6H4
4-CH3OC6H4CH CH
4-(4-CH3C6H4)C6H4
4-(4-n-C5H11C6H4)C6H4
4-(4-n-C8H17C6H4)C6H4
4-(4-n-C5H11C6H4)C6H4
4-(4-n-CH3C6H4)C6H4
4-NC-C6H4
2-(5-NC-Pyridinyl)
4-NC-C6H4
4-CH3C6H4
4-CH3OC6H4
4-CH3OC6H4
4-CH3C6H4
4-CH3OC6H4
4-CH3OC6H4
4-CF3C6H4
4-(4-CH3C6H4)C6H4
4-CH3OC6H4CH CH
4-(4-NC-C6H4)C6H4-(CH2)4-n
4-(4-NC-C6H4)C6H4-OCH2
4-(2-Ph-Quinolinyl)
—
precipitate
−0.10 0.03
−0.16 0.05
—
−4.24 0.45
+12.49 0.33
+9.99 0.46
+10.16 0.40
+70.03 1.05
+72.94 3.77
+95.68 2.03
+119.22 0.24
+112.05 3.09
+110.23 1.22
+107.25 0.61
+176.56 4.54
+71.66 1.04
+24.22 0.39
+21.67 0.20
−3.92 0.58
−27.49 0.79
−0.12 0.01
−0.017 0.003
0.122 0.001
−0.17 0.01
0.004 0.002
−0.010 0.004
−0.003 0.001
−0.01 0.001
−0.014 0.002
−0.012 0.001
−0.008 0.001
−0.01 0.001
−0.01 0.003
0.101 0.007
0.084 0.005
1.48 0.14
6g
6h
6i
6j
6k
6l
7
−0.18 0.03

42
I. M. Gella et al.
Figure 2. Molecular shape for ether-esters of 1,4:3,6-dianhydrohexitol 3b and 4b, ether 5a and ester
6a obtained by quantum-chemical energy minimization.
curve for rotation about CO group in those groups and adjacent to them. These curves have
the narrowest minima as compared with rotation about CO bond in ethers, whether bind-
ing with dianhydrohexitol core or aryl substituent. Also, rotation about CO bond in esters
changes little the shape of molecules while in ethers by rotation the shape of molecules
changes considerably. Rigid fragment in a chiral molecule is a guide for nematic solvent
molecules that transfer bend of the shape of chiral molecule to its molecular environment.
Similar conception was proposed in modeling the interactions between a dichiral molecule
and host one. A twist interaction between the binaphthyl group and a host molecule there
was assumed to be organized by the core–core interaction [41].
As could be seen from Table 3, HTP of ethers of 1,4:3,6-dianhydrohexitols 5 is
considerably less than esters 6 (absolute HTP 10 μm−1–12 μm−1 for compounds 5a-c
and 70 μm−1–176 μm−1 for compounds 6a-h). In both cases, substituents in ethers and
esters are rigid or have a lengthy rigid part adjacent with dianhydrohexitol core (4-NC-
C6H4, 2-(5-NC-Pyridinyl), 4-RC6H4, 4-ROC6H4, 4-(4ꢀ-RC6H4)C6H4, where R is alkyl or
CF3 group). But according to quantum-chemical modeling (AM1, PM6), obtained shape is
almost rod-like in the case of ethers 5 as opposed to esters 6 where shape is propeller-like
(Figure 2).
It should be noted that quantum-chemical modeling describes the conformations of
dianhydrohexitol core like the result of X-ray analysis [42].
The lowest HTP values were observed when CDs were mixed ether-esters (com-
pounds 4a-e), where substituent in 2 position is bound by the use of exocyclic ether
group and substituent in 5 position by the use of endocyclic ester one (absolute HTP of
0.6 μm−1–9.2 μm−1). In this case, substituents in both cyclopentane rings are arranged
in this way, so that chiral fragment (dianhydrohexitol core) appears almost completely
shaded, and its influence on nematic solvent molecules is hindered. However, HTP values
of compounds 3b-c were rather great (35.2 μm−1–70.1 μm−1). In this case, substituent in
5 position is bound by the use of endocyclic ether group, and substituent in 2 position by
the use of exocyclic ester one, and the shape of molecule is propeller-like as for compound
6 with the greatest HTP in examined case.
Low values of HTP for bis-esters of iditol [19] also may be accounted for their drawn
rod-like shape.

1,4:3,6-Dianhydrohexitols in Chiral Nematics
43
The results observed speak in favor of surface chirality model [29–31] correctness with
conformational mobility accounting [43].
Conclusion
We have synthesized series of 1,4:3,6-dianhydrohexitol ethers, esters, mixed ether-esters,
and have investigated their HTP and thermal dependence of the helical pitch in a nematic
solvent (4,4ꢀ-pentylcyanobiphenyl). The most HTP has been found for bis-esters 6. Some
less HTP values have been found for mixed ether-esters with certain configuration 3 with
ester substituent in 2 positions and ether substituent in 5 positions. The lowest HTP values
were observed when CDs were mixed ether-esters (compounds 4a-e) with ether substituent
in 2 positions and ester substituent in 5 positions. Bis-ethers 5 have some more values
of HTP. The reason for preference of ester bridge group against ether one in molecular
structures for HTP generation is lesser conformational mobility of structures with ester
group.
Acknowledgments
We thank the National Academy of Science of Ukraine for the financial support, grant no.
0110U000623.
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