Hydrogen bonded networks with variable functionalized netpoints: A probe of mesophase stability
Wiegel
Research:
Careening
from
catastrophe to
catastrophe
since 2000
Phillip J. Schieffer, Matthew D. Hammers, David K. Witte and Kurt N. Wiegel
Department of Chemistry, University of Wisconsin, Eau Claire, Eau Claire WI 54702
Thermal Analysis
•
•Materials that exhibit long-range and some short-range
directional ordering in a fluid state.
•Composed of mesogens (shaped molecules) and flexible
spacers
•Different types of mesogens based on molecular shape
(calamitic: rod-shaped)
Molecular Self-assembly Through Halogen Bonding
•Non-covalent interaction between an electron deficient
halogen (iodine or bromine) and a strong electron donor
(pyridine and nitrile)
I
N
OR
51.5
0
-5
-10
F
F
63.6
-15
-20
0
20
40
60
80
100
120
140
160
o
Temperature ( C)
•Specific and directional associations
•Thermodynamically weaker than hydrogen bonds
• Preliminary work from several groups show the capability
of forming liquid crystalline assemblies from nonmesogenic precursors through halogen bonding.
Materials Used/Synthetic Methodologies
C10FI C8OAzo
8
6
Heating Curve
4
2
46.3
0
40
6
30
4
2
0
20
10
0
-2
-10
-4
0
20
40
60
80
100
120
0
140
20
40
60
80
100
120
140
o
o
Temperature ( C)
Temperature ( C)
DITFB 5Eo Sb
DITFB 4-cyano pyridine
Results
•Nitriles failed to produce any liquid crystalline phases
when used as a donor
•Electron density on the nitrile may be insufficient to
form a stable halogen bond
• Changing the electron density in the ring could drive
halogen bond formation
• 1,4-diiodotetrafluorobenzene failed to produce any liquid
crystalline phases when used as an acceptor
•Initial calculations showed no significant electron
density difference between the iodine atoms on C10FI
and DITFB
•The crystallization enthalpy on DITFB may have been
too strong to form a mesogen
•Stilbazole species provided more ordered smectic species
•The azo donors produced more nematic phases
• Azo donors also provided liquid crystalline phases that
existed at sub ambient temperatures.
-2
I
F
F
+ HO
F
5
Y
X= N, C
Y=C, N
F
44.7
Heat Flow mW
Exo up
RO
F
10
Heat Flow (mW)
Exo Up
F
Results/Observations
8
Heat Flow mW
Exo Up
Complexes synthesized through solution-complex
methodology
• Components stoichiometrically weighed and mixed in a
common solvent (methylene chloride or THF)
• The solvent was allowed to evaporate in a covered flask
• DSC data determined on a Mettler-Toledo STAR e1 DSC at
10°C/Min heating rate unless otherwise noted
• Optical micrographs were measured using a Mettler-Toledo
FP82 Hotstage Mounted on an Olympus BHT polarizing
light microscope at a 10°C/Min heating.
Liquid Crystals
X
Results/Observations
Heat Flow mW
Exp up
Background
OH
10
F
Cs2CO3
F
F
F
F
19.3
F
Observations/Conclusions
-4
I
O
I
I
O
I
0
10
20
40
60
80
100
o
F
F
F
F
F
F
C10FI
Temperature ( C)
F
DITFB
C10FI 4EO Azo
10
O
+
H
8
RO
46.1
N
CnOSb
nEOSb
H2N
N
N
(1) HCl/NaNO2
RO
(2) Cs2CO3/RBr
O
CN
4-Cyanopyridine
N
77.3
6
Heat Flow mW
Exo up
HO
(1)Acetic Anhydride
N
(2) Cs2CO3/R-Br
4
2
•Halogen bonds form liquid crystalline assemblies from
non-mesogenic components
• Azo-based halogen bond donors provide liquid crystalline
phases at markedly lower temperatures than analogous
stilbazole species
Acknowledgements
0
N
CnOAzo
nEOAzo
N
-2
-4
-20
0
20
40
60
80
100
120
140
160
o
Temperature ( C)
C10FI 7OSb
This work was funded by the Petroleum Research
Foundation (54134-B7), the National Science Foundation
(award number 0804428) and UW-EC Office of Research
and Sponsored Programs.