Molecular structure of calamitic LCs

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