Mesogenic Properties of Noncollinear (Bent)
Liquid Crystals
Applications to Environmental Sensing
David Davis, Kent State UniversityAdvisor: Dr. Robert Twieg
Bent Core Liquid Crystals
• Historically, liquid crystal synthesis has been most concerned with structures incorporating a rigid core bearing one or more flexible tails in what’s known as a calamitic (rod-like) liquid crystal.
• Since the early 1990’s much effort has been spent on the synthesis of bent core (noncollinear) liquid crystals, and the study of their properties1. Here the bend exists between ring components in the core.
Calamitic LC
Bent-Core LC
Core
Core
Tail Tail
Tail Tail
Properties of Bent-Core Liquid Crystals• Bent-core LCs exhibit new and
unique but by now very well documented phases.
• Bent core LCs may also possess more controversial phases, e.g. the biaxial nematic phase.
• Posesses increased flexoelectricity- capable of spontaneous electrical polarization in response to strain (2 orders of magnitude higher than calamitic LCs)2.
• Create strain on a liquid crystal layer to achieve a measurable electrical polarization (induce electron flow and measure current), create foundation for a sensor3.
First instance of a Biaxial Nematic phase reported in bent-core liquid crystals (2004)4.
Are There Other Types of Noncollinear Liquid Crystals?
• While studies have focused on the synthesis of materials with the bend in the core, can the bend be placed elsewhere to observe similar properties?
• Current area of study: Synthesis of materials with the bend at the tail-core juncture (e.g., meta-substituted alkoxy tails).
• Target: 28 unique terphenyl-core compounds with differing permutations of meta-, para-, and null substitution of methoxy (C1), hexyloxy (C6), and dodecyloxy (C12) tail lengths.
C6H13O
OC6H13
Bent-core liquid crystal Bend at tail-core juncture
Examples of Materials Synthesized(Identical Length Tails)
C6H13O OC6H13
C6H13O
OC6H13
C6H13O
OC6H13
Cr 67.9 Cr 74.8 Cr 191.6 Sm 225.1 Sm 246.3 Iso LiqIso Liq 244.9 Sm 223.6 Sm 188.5 Cr 72.5 Cr 63.4 Cr
Cr 48.7 Cr 76.8 Iso LiqIso Liq 59.3 Sm 45.1 Cr
Cr 112.7 Iso LiqIso Liq 102.9 Cr
Examples of Materials Synthesized(Non-Identical Length Tails)
C6H13O
OC12H25
C12H25O
OC6H13
C6H13O
OC12H25
C6H13O OC12H25
Phase data TBD Cr 69.2 Iso LiqIso Liq 99.9 Cr
Cr 93.8 Cr 105.2 Iso LiqIso Liq 100.5 Cr 88.2 Cr
Cr 105.9 Iso LiqIso Liq 99.9 Cr
Sample Synthetic Pathways
OC6H13C6H13O
II
B(OH)2H3CO
Pd(PPh3)4, Na2CO3Toluene, EtOH
OCH3H3CO
N
H ClHO OH
C6H13I, K2CO3DMF
HO BrC12H25I, K2CO3
C12H25O Br
HO
BrC6H13I, K2CO3
C6H13O
Br
1) n-BuLi, THF2) B(OMe)3
3) HCl (aq)B(OH)2
C6H13O
Pd(PPh3)4, Na2CO3
Toluene, EtOH
C6H13O
OC12H25
87%
quant.
35%
98%
93% 10%
62%
DMF
DMF
Future Direction of Project• Explore other series of cores for bent molecules to discover possible
mesogenic activity and flexoelectric properties.– Quaterphenyls (work underway Summer ’10)– 1,4-bis(phenylethynyl)benzenes– 1,4-dibenzoyloxybenzenes
RO OR'
RO OR'
RO
O
O
O
O
OR'
References
• 1. Link, D.L. et. al. Spontaneous Formation of Macroscopic Chiral Domains in a Fluid Smectic Phase of Achiral Molecules. Science. 1997, 278, 1924-1927.
• 2. Tschierske, C. Liquid Crystals Beyond Display Applications. J. Mater. Chem. 2008, 18, 2869-2871.
• 3. Jakli, A.I. et. al. Methods and Systems for Determining Flexoelectric Effect in a Liquid Crystal. US Patent Appl. 20100182026, July 22, 2010.
• 4. Madsen, L.A. et. al. Thermotropic Biaxial Nematic Liquid Crystals. Phys. Rev. Lett. 2004, 92, 14505/1-14505/4
Additional References
• Dierking, I. Angew. Chem. Int. Ed. 2010, 49, 29-30.• Lehmann, M. et. al. Chem. Eur. J. 2010, 16, 8275-8279.• Bisoyi, H.K. et. al. Beil. J. Org. Chem. 2009, 5, No. 52.• Reddy, R. A.; Tschierske, C. J. Mat. Chem. 2006, 16,
907-961.• Takezoe, H.; Takanishi, Y. Jpn. J. Appl. Phys. 2006, 45,
597-625.• Etxebarria, J.; Ros, M.B. J. Mat. Chem. 2008, 18, 2919-
2926.
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