Molecular structure of calamitic LCs
rigid ring systemsterminal groups
bridging groups
(+linking groups)terminal groups
N
N
S
(+linking groups)
phenyl
biphenyl
cubane
thiophene
cyclohexyl
pyrimidinylcarbonates
esters
ketones
O
O
O
OO
O
N
NN
vinyl (stilbenes)
acetylene (tolanes)
azo
azomethine, imine(Schiff’s Base)
C8H17H17C8
NN
H17C8O
C6H13
O
NH11C5O
C7H15
Structure and Properties
p-hexaphenyl; Cr 435 S 465 N 565 I
4,4’-bis-(n-octyl)-p-terphenylCr 176 S 191 I
4-n-propyl-4’-n-heptanoyloxy-azobenzeneCr 42 N 71 I
4-n-heptyl-N-(4-n-pentyloxy-benzylidene)-anilineCr 29.5 CrG 33.9 SmB 51.0 SmC 53.1 SmA 62.8 N 78 I
CNH(n+1)Cn
Longer chains lower the meltingpoint and promote smectic
mesomorphism
n = 1: Cr 109 N (45) In = 5: Cr 24 N 35 In = 8: Cr 21 SmA 33 N 40n = 10: Cr 44 SmA 50 I
The Odd-Even EffectTerminal side-chains with odd carbon atoms generate higher clearing points thaneven numbered chains of comparable length. The carbon that makes the chaineven generates a deviation from the linear structure of the more favourableall-trans conformation of the chain. Both, melting and clearing temperatures arelowered due to this “disturbance”.
CNH(n+1)Cn
n = 3: Cr 66 (N 25) In = 4: Cr 48 (N 16) I
Branched Side-Chains
CN Cr 4 (SmA -50 N -30) I
Phasmids and Polycatenar Mesogens
R5
R4
R6
OOCOOCCOO
R1
R2
R3R2 = R5 = C12H25: Cr 110 SmC 277 N >300 I;R1 = R2 = R5 = C12H25: Cr 126 SmC 211 I;R1 = R3 = R5 = C12H25: Cr 120 Col 125 N I;
R4
R1
R2
R3
R4
R3
R1
R2
R3
R4 R1
R2
R1
R2
R3
R5
R4
R6
Tetracatenars HexacatenarsN for short R (<C4)
Col for long R (>C12)SmC in-between
Col
Cub
Chain-Number Mediated Mesomorphism of Polycatenars
Dicatenar
SmA
Tetracatenar
SmC
Hexacatenar
Col
Each molecular layer of the columnar stackscontains an assembly of 3-4 hexacatenars
Synthesis of Intermediates
S
Br Br
BrBr
O
O
S
N
N
RP
RP
O
S
Br Br
O
S II
CNNC
NMeMeN
O
1 2Bn THP
1) iPrMgCl, THF, 40 ºC
2) NC-Tos, THF, 0 ºC-rt
CuCN, DMI, 120 ºC
DMI =
50%
CuCN, DMI, 120 ºC
65%Sonogashira
95%
?
1) 2 eq. LDA, THF, -78 ºC
2) I2, -78 ºC-rt
80%
Sonogashira
2.5 eq.+
+ 2.5 eq.
1
2
3
Synthesis of Polycatenars
O
O
O
O
S
N
N
RO
OR
R
R
O
O
S
H
H
N
N
R
O COOH
R
O
O
S
N
N
RP
RP
3
deprotectionBrB-catechol, DCM, 0 ºC-rt or TsOH, MeOH, rt
95%
(iPr)N=C=N(iPr), DMAP,
DCM, rt
70-90%
R = OCnH2n+1, HH2n+1Cn
H2n+1Cn
H2n+1Cn
Phase Diagram of Dicyanotetracatenars
4 5 6 7 8 9 10 11 1280
90
100
110
120
130
140
150
160
170
Tem
pera
ture
(o C
)
n (CnH
2n+1)
N Col SmC Cryst.
OO
OO
O
S
N N
OO OH2n+1Cn
H2n+1Cn CnH2n+1
CnH2n+1
New Columnar Mesophase Structure withPolar Bent-Rod Polycatenars
0.7-0.75 nm
Colh
0.7-0.8 nm
154ºbent angle
6.3 Dlocal dipole
(AM1)
OO
H23C11O
H23C11O
OO
OC11H23
OC11H23
S
N N
OO
OO O
O
OO
S
N N
OO
OO
OO O
O
OO
S
N N
OO
New type of anti-parallel columnar packing of polar bent-rod hexacatenar
Antiparallel Dipole-Dipole Nearest Neighbor Correlation
Single Crystal Structure:Space Group P21
Nematic liquid crystallinemodel compound
O O
S
N N
Nearest Neighbor Interactions Dictated byShape and Dipolar Anisotropy
O
O
S
R
R
NC
NC
O
O
S
R
R
NC
NC
O
O
S
R
R
NC
NC
polar arrangement non-polar arrangement• ferro- and anti-ferroelectric
materials• flexoelectric materials• NLO active materials
• biaxial N and SmA mesophases
O
O
RO
RO
O
O
OR
OR
S
N N
6.3D (AM1)
bent angle 154o
Smectic C
Columnar
Nematic
Mesomorphism of Bent-Rod Catenars with Strong Lateral DipoleS. Holger Eichhorn, Alexander Paraskos, Keiki Kishikawa, Timothy M. Swager
Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue,Cambridge, Massachusetts 02139, USA