Proceedings of International Forum for Green Asia 2017
Special issue of Evergreen - Joint Journal of Novel Carbon Resource Sciences & Green Asia Strategy

P-01

Synthesis and Helical Twisting Power of (R)-6,6’-Harogenated and -Methylated
Binaphthyl Type Chiral Dopants
1Yu Narazaki, Hiroya Nishikawa,2 Hiroki Higuchi2, Yasushi Okumura2 andHirotsugu Kikuchi2
1

Interdisciplinary Graduate School of Engineering Sciences, Kyushu University
2
Institute for Materials Chemistry and Engineering, Kyushu University
6-1, Kasuga-koen, Kasuga, Fukuoka 816-8580, Japan,Abstract
We synthesised (R)-6,6’-halogenated and -methylated binaphthyl derivatives to create chiralnematic liquid crystals (N*LCs) by doping them into two types of host nematic liquid crystals(NLCs) such as fluorinated and azomethyne type NLCs. The influence of substituent
properties of the synthesised chiral dopants, steric, polarity and polarizability, on the helicaltwisting power (HTP) and their temperature dependence of HTP (HTPt.d.) were investigated in
the two above-mentioned NLCs. Our understating suggested that the chiral dopant bearing
less steric and larger polarizability properties, i.e. the 6,6’-chlorinated chiral dopant,possessed the considerable large HTP value. Besides, the HTPt.d. values of the chiral dopants
were affected by their substituents.
We synthesised the 6,6’-fluorinatedbinaphthyl-typechiraldopant(1b)
possessing a large HTP value, meaning goodchirality transfer from a chiral dopant to hostNLC, in the fluorinated host NLC as
reported previously. [3] However, a chiralitytransfer mechanism between the chiraldopant and host NLC has not been wellunderstood.
Much
progressandadvancement would has been made in theliquid crystal science and technology, if themechanism was to be understood.
In this study, we synthesised 6,6’-nonsubstituted (1a), -halogenated (1b-1e) and-methylated (1f) binaphthy-type chiraldopants and examined dominant molecularfactors like size, polarity and polarizabilityof their substituents affecting the induced
absolute HTP (|HTP|) and their temperaturedependence.

1. Introduction
The lack of mirror symmetry, referred
to as chirality, has a remarkable influence on
the microscopic physical properties ofmaterials. Especially the chiral liquid
crystals (CLCs), chiral nematic liquid
crystals (N*LCs) and blue phase liquid
crystals (BPLCs), exhibit unusual physicalproperties such as selective reflections in avisible wave length region. [1] The CLCs
have potential applications in low energy
consumption reflective liquid crystal
displays because of their optical properties.
[2] The development of CLCs or chiraldopants which enable to form N*LCs fromachiral nematic liquid crystals (NLCs) has,
therefore, attracted considerable attention.
Chiral dopants are asymmetriccompounds possessing chirality such as
central, axial, planer and helical chirality.
The ability of chiral dopants to form N*LCs
from host NLCs is evaluated by helicaltwisting power (HTP) expressed as below,
HTP = (P×cw)-1
where HTP is helical twisting power (m-1),
P is helical pitch of the chiral nematic phaseand cw is weight percent concentration of thechiral dopant [wt%].

Figure 1. The chemical structures ofsynthesised chiral dopants.

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Proceedings of International Forum for Green Asia 2017
Special issue of Evergreen - Joint Journal of Novel Carbon Resource Sciences & Green Asia StrategyP-01
̅̅̅̅̅̅)⁄∆T ×100HTPt.d. = (∆HTP⁄HTP
where HTP is the difference between themaximum and minimum |HTP| values, and̅̅̅̅̅̅
HTP is the arithmetic mean of the |HTP|
values in the temperature range from T – Tc
= −5 to 25°C. [3] The HTPt.d. values of 1a-1f
were 0.46 (-H), 0.43 (-F), 0.59 (-Cl), 0.60(-Br), 0.69 (-I) and 0.64 (-Me) %∙T−1 inJC-1041XX, respectively. By contrast, thoseof 1a-1f were 0.49 (-H), 0.73 (-F), 0.85 (-Cl),
0.87 (-Br), 0.87 (-I) and 0.82 (-Me) %∙T−1 in
MBBA. These values in two host nematics
exhibited to correlate with steric andpolarizability
substituent
parameters(JC-1041XX: the HTPt.d. values vs. stericparameter; R2 = 0.91 and vs. polarizability
parameters; R2 = 0.83. MBBA: the HTPt.d.
values vs. steric parameter; R2 = 0.73 and vs.
polarizability parameters; R2 = 0.54.).
Arene-arene
interactions
involvingpolarizability can impact the HTPt.d. valuesof the smaller substituents (-H < Vvdw < -Cl)of synthesised chiral dopants because theseHTPt.d. values gradually increase as theirpolarizability increased. Moreover, thechiral dopants possessing a larger
substituent (-Br and -I) should promote a
disaggregation
ofthe
arene-arene
interactions between these chiral dopants
and the host NLC molecules.

2. Results and Discussion
2.1. Effect of substituents on the induced|HTP| value

The |HTP| values of 1a–f influorinated (JC-1041XX) and azomethyne
type (MBBA) NLCs are plotted for stericparameter (Vvdw) in Fig. 2 to exhibit arelationship between the steric effect of theirsubstituents and their |HTP| values.

3. Conclusion
Our systematic studies of the6,6’-substituted bridged, binaphthyl chiraldopants suggested that the |HTP| and HTPt.d.
values were significantly affected by
6,6’-substituents of binaphthyl chiral dopant.

Figure 2. Plots of the |HTP| values of 1a-f in(a) JC-1041XX and (b) MBBA vs. the Vvdwof their substituents.

The chiral dopant possessing less stericandlarger
polarizability,i.e.
the6,6’-chlorinated and -methylated bridgedbinaphthyl chiral dopant, tended to increasethe |HTP| value in two different host NLCs,
since the induce N*LC phase is composedof arene-arene interactions, affecting sterichindrance and polarizability between chiraldopants and NLC molecules.
2.2. Effect of substituents on
temperature dependence of HTP value

Acknowledgment
This work was partially supported
by Advanced Graduate Program in Global
Strategy for Green Asia.
Reference[1] a) H. K. Bisoyi, Q. Li, Acc. Chem. Res., 2014,47, 3184.
[2] J. Chen, C. T. Liu, IEEE Access, 2013, 1, 150.
[3] K. Kakisaka, H. Higuchi, Y. Okumura, H.
Kikuchi, Chem. Lett., 2014, 43, 624.

theThe temperature dependence of HTP(HTPt.d.) value was defined as below,5