JOURNAL OF DISPLAY TECHNOLOGY, VOL. 2, NO. 3, SEPTEMBER 2006
247
High Performance Room Temperature Nematic
Liquid Crystals Based on Laterally Fluorinated
Isothiocyanato-Tolanes
Sebastian Gauza, Shin-Tson Wu, Fellow, IEEE, Anna Spadło, and Roman Dabrowski
Abstract—High birefringence and low viscosity isothiocyanates
liquid crystal single compounds and eutectic mixtures, based
solely on laterally fluorinated aromatic rigid core structures, are
reported. Extraordinarily high values of figure-of-merit were
observed at room temperature and also elevated temperatures
for the nematic mixtures we formulated. Potential applications
of such mixtures for laser beam steering at = 1 55 m using
optical phased arrays are emphasized.
Index Terms—Fast response time, high birefringence, high
figure-of-merit, low viscosity, nematic liquid crystals.
I. INTRODUCTION
and low viscosity nematic
IGH birefringence
liquid crystal (LC) mixtures are critically needed for infrared applications, such as laser beam steering at
m
phase change
, the
[1]. In order to retain a
should increase proportionrequired optical path length
ally as the wavelength increases; here, denotes the cell gap
of the homogeneous LC cell. Meanwhile, the response time of
and visco-elastic coefficient
a LC device is proportional to
. To achieve fast response time, low rotational visLC mixture and thin cell gap are two preferred apcosity
proaches [2]–[4]. However, high birefringence and low viscosity
do not go hand-in-hand. A highly conjugated LC compound
usually exhibits a high viscosity because of its increased moment of inertia. Moreover, high birefringence LC compounds
usually possess high melting temperatures. To lower the melting
temperature, many LC structures need to be developed and eutectic mixtures formulated.
The most effective way to increase birefringence is to elongate the -electron conjugation lengths of the LC compounds
[11]–[13]. Conjugation length can be extended by multiple
bonds or unsaturated rings in the rigid core. Four problems
associated with highly conjugated LC compounds are high
melting temperature, increased viscosity, reduced UV stability,
and relatively low resistivity because of ion trapping near the
polyimide alignment interfaces. The high melting temperature
can be overcome through the use of eutectic mixtures. The
H
Manuscript received February 15, 2006; revised April 24, 2006. This work
was supported by DARPA Bio-Optics Synthetic Systems program under Contract W911NF04C0048 and by the NATO Programme Security Through Science, Collaborative Linkage Grant CBP.EAP.CLG 981323.
S. Gauza and S.-T. Wu are with the College of Optics and Photonics, CREOL,
Orlando, FL 32816 USA (e-mail: sgauza@creol.ucf.edu).
A. Spadło and R. Dabrowski are with Institute of Chemistry, Military University of Technology, 00-908 Warsaw, Poland.
Digital Object Identifier 10.1109/JDT.2006.878770
increased viscosity is inherent to all the highly conjugated
compounds. Cyano (CN) and isothiocyanato (NCS) are two
commonly employed polar groups used for elongating the
molecular conjugation. The NCS compounds are less viscous
than the CN ones; but on the other hand, they tend to exhibit
smectic phases [14]. The CN group has a larger dipole moment
than NCS
because of its linear
structure. However, due to the very strong polarization of the
carbon-nitrogen triple bond, the Huckel charges of carbon
and nitrogen are high and well localized [15]. Accordingly,
dimmers are formed by strong intermolecular interactions
between the nitrile groups. This is the main reason responsible
for the observed relatively high viscosity of the cyano-based
LC mixtures [16]. In contrast, the dipole moment of the NCS
group is 30% lower than that of a CN. The NCS compounds
do not form dimmers so that their viscosity is lower than the
corresponding CN compounds.
Based on the rationales mentioned above, we synthesize some
isothiocyanate compounds with totally unsaturated rigid cores.
Molecular structures, mesomorphic, and electro-optic properties of the single compounds and eutectic mixtures are reported.
Potential applications of these mixtures for laser beam steering
using an optical phased array are discussed.
II. EXPERIMENT
Several measurement techniques are typically involved in
characterizing the physical properties of the LC compounds
and mixtures in our laboratory. Measuring a birefringence
nm) requires a different setup than
greater than 0.3 (at
the classic refractometric method using Abbe refractometer
of
because the extraordinary refractive index
the LC is beyond the instrument’s upper limit. Thus, the
electro-optic measurements are needed in order to overcome
Abbe’s limitation. We prepared homogeneously aligned cells
m while a linearly
with cell gaps ranging from
polarized He–Ne laser
nm was used as the light
source. A linear polarizer was placed at 45 with respect to the
LC cell rubbing direction and an analyzer was crossed. The
light transmittance was measured by a photodiode detector
(New Focus Model 2031) and recorded digitally by a LabVIEW
data acquisition system (DAQ, PCI 6110). An ac voltage with
1-kHz square waves was used to drive the LC cell whose inner
surfaces were coated with indium–tin–oxide (ITO) electrodes.
On top of the ITO, the substrates were covered with a thin
polyimide alignment film. The buffing induced pretilt angle
was about 2 –3 . The cell was held in a Linkam LTS 350 Large
1551-319X/$20.00 © 2006 IEEE
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JOURNAL OF DISPLAY TECHNOLOGY, VOL. 2, NO. 3, SEPTEMBER 2006
Area Heating/Freezing Stage equipped with Linkam TMS94
of the
Temperature Programmer. The phase retardation
homogeneous cells was measured by the LabVIEW system.
at wavelength and temperature
The LC birefringence
can be obtained by measuring the phase retardation
of
the homogeneous cell from the following equation [11]:
(1)
Birefringence results obtained from the electro-optic method are
in good agreement to that measured by the Abbe refractometer.
value measured
Typically, we observed about 1%–2% lower
by our electro-optic setup than the one we measured from Abbe
refractometer.
The measured data in the visible spectral region allow us to
at
m by using a single band bireextrapolate the
,
fringence dispersion model [17]:
is the proportionality constant and
is the mean
where
electronic transition wavelength. By measuring the LC birefringence at two visible laser wavelengths, we can obtain and .
Once these two parameters are determined, the birefringence at
m, can be extrapoany wavelength of interest, e.g.,
lated.
To characterize the performance of liquid crystal mixtures,
a figure-of-merit (FoM) which takes optical phase change and
response time into account has been defined as [18]:
(2)
is the splay elastic constant,
is the birefrinwhere
gence, and is the rotational viscosity. All of these parameters
,
are temperature dependent. The dielectric anisotropy
, and elastic constants
were
threshold voltage
measured by the LCAS II system purchased from LC Vision.
All the measurements were conducted at a room temperature of
23 C and the applied ac voltage frequency was 1 kHz unless
otherwise mentioned. All the thermal analyses were performed
using a high sensitivity differential scanning calorimeter (DSC,
TA Instrument Model Q-100). Phase transition temperatures
were measured using small samples ( 1.5 mg) at a 2 C/min
scanning rate. The observed LC phase transitions were confirmed by the polarizing optical microscopy (POM) method.
The UV absorption spectra of the single LC compounds were
measured by using a dual channel Cary 500 UV/VIS/IR spectrophotometer. To avoid detector saturation, the LC samples
were dissolved in cyclohexane solutions with 2 10 molar
concentrations. Standard quartz semimicrocells with 10-mm
thickness were used in the sample and reference channels of
the spectrophotometer.
III. SINGLE COMPOUNDS
Our study focuses on the thermotropic, rod-like molecular
systems with a polar isothiocyanate terminal group. The rigid
cores of the molecules and lateral substitutions vary, aiming to
get a
value as high as possible while keeping a relatively
low viscosity. Therefore, the residues typically used for the rigid
core of our nematic LC compounds are the aromatic ones like
phenyl (benzene) and naphthalene rings. Phenyl ring and naphthalene ring system are unsaturated residues, both are rich in the
-electrons. Thus, these rings are particularly desirable to elongate the -electrons conjugation through the rod-like molecule
and to increase the polarizability along the principal molecular
axis. Another source of -electrons, which may contribute to
the -electron conjugation thru the molecule, is the unsaturated
double and triple carbon-carbon bonds, which bridge unsaturated rings of the rigid core. Double carbon–carbon bonds [19]
were reported as extremely weak under UV and even daylight
conditions [20] so we concentrated on the tolane-based rigid
cores because their photochemical stability appears to be better.
Four different groups of high birefringence LC compounds were
chosen for discussion.
Table I lists the compound structures and their phase transition temperatures with respect to the different formations of
the rigid core. Previous reports by different authors [14], [21],
[22] found that the birefringence of NCS-tolane is below 0.4 at
nm and room temperature. We looked closely on this
group of compounds as an attractive base for forming high birefringence eutectic mixtures. Table I lists the compound structures we investigated. The simple, non-fluorinated NCS-tolanes
with short alkyl chains (Comp. 1 and 2) do not show any enantiotropic liquid crystal phase. Instead, highly ordered smectic K
and E phases appear during monotropic transition. Elongating
the flexible chain lowers the melting temperature so that the
enantiotropic smectic phases occur [23]. Single lateral fluorination of the phenyl ring in the direct neighborhood of the NCS
group lowers the melting point but these compounds still do not
show mesomorphic properties (Compounds 3, 4, 5 and 6). The
double fluorinations further decrease the melting point but
the enantiotropic nematic phase still does not exist if short alkyl
or alkoxy chain is in use (Compounds 7, 8 and 9). The double
laterally fluorinated tolane with pentyloxy flexible chain (Compound 11) shows a short range of nematic phase without the
presence of any highly ordered smectic phase. It suggests that
double fluorinated tolane compound may be the right dopant
to suppress the highly ordered smectic phases existing in the
LC compounds. We validated this idea by making our
high
two base mixtures (UCF-Base-1 and UCF-Base-2) which differ
only by the addition of double fluorinated alkoxy-tolanes. The
second group of compounds with an NCS terminal group that
we chose for our experiment is based on the terphenyl rigid core,
shown in Table II. The terphenyl rigid core has been widely used
in commercial high birefringence mixtures. A popular example
is 4-cyano-4 -pentyl-terphenyl, also known as 5CT [24]. The
phase transition temperatures of 5CT are relatively high, with
a melting point at 130 C and clearing point at 239 C.
Based on our experience with highly conjugated linear molecular structures, we decided to start from single laterally fluorinated cores and then extend to the double fluorinated ones. The
melting point of the single fluorinated compound PPP(3F)3NCS
is 130 C and clearing point 265 C, which is rather similar
to that of 5CT. By introducing another fluoro group to the neighborhood of the NCS group, the melting point of PPP(3,5F)3NCS
and PPP(3,5F)5NCS is reduced to 106 C and 95 C, respectively. However, the second compound exhibits a smectic phase
GAUZA et al.: HIGH PERFORMANCE ROOM TEMPERATURE NEMATIC LCS
TABLE I
TOLANE-BASED COMPOUNDS
249
TABLE II
TERPHENYL-BASED COMPOUNDS
TABLE III
BIPHENYL-TOLANE BASED LC COMPOUNDS
up to 108 C. The
of the mixture based on the above-mentioned terphenyl LCs is 0.35–0.38 depending on the detailed
compositions and final clearing temperature.
In order to achieve a higher birefringence, it is necessary to
use compounds with longer -electron conjugation.
Extension of the rigid core could be realized either by introducing unsaturated bond(s) or/and unsaturated cyclic structures [25]. However, adding an unsaturated bond right next to
the tolane core will result in severe photochemical instability
[26], [27]. Replacing a phenyl ring on the flexible chain side
by a naphthalene ring will increase conjugation and boost birefringence to 0.46 [22]. However, naphthalene exhibits a lower
UV stability and is more viscous than the linear tolane structure. The most preferable choice in this case is to use biphenyl-
tolane unit in place of tolane as a rigid core. However, such
a highly linearly conjugated structure possesses a strong tendency to form smectic phases and high melting point temperatures, well above 100 C (see Table III). Phenyl-tolane with an
NCS terminal group without lateral substitution shows two different crystalline forms with transitions at 169 C and 207 C,
which is also the transition to smectic phase, then at 221 C
where the transition to nematic phase takes place. Finally, the
isotropic state occurs at 270 C. The high melting temperature
and smectic phase limit the usefulness of this compound, especially from the mixture formulation viewpoint. To lower the
melting point temperature and avoid smectic phases, we synthesized laterally fluorinated homologues. The melting point drops
to 140 C and 65 C, respectively, for the single and double fluorinated compounds with four carbons in the alkyl chain. The
smectic phase was suppressed below 181 C and 50.1 C, respectively; see detailed structures in Table III.
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Fig. 2. Measured absorption spectra of four isotiocyanate compounds in comparison to the penthyl-cyano-biphenyl (5CB) compound. Each LC compound
molar concentrations.
was dissolved in cyclohexane solution with 2 10
Cell gap is 1 cm.
2
Fig. 1. The temperature dependent FoM of (a) PPTP(3F)-2NCS and (b)
PPP(3,5F)-3NCS. Dots are experimental results and lines are fittings using (3).
Although the mesomorphic properties of the discussed single
compounds appear to be far away from ideal, they exhibit superior electro-optic properties when filled into a LC cell. The
birefringence of the isothiocyanato-terphenyls is approximately
0.36–0.38. A similar birefringence is observed for the isothiocyanato-tolanes, but for their phenyl derivatives the birefrinvalue degence is increased to 0.48–0.52. The extrapolated
pends on the host mixture if the guest–host method is used. The
will influence the measured
value
clearing temperature
according to (3)
(3)
where
is the birefringence at
K and is a material constant. If a guest–host mixture has a higher clearing
point, then the extrapolated birefringence value for the guest
compound would be higher at room temperature. Thus, the
guest–host method provides a quick reference, but its accuracy
is limited. For example, in [28] where Comp. 16 has an extrapat
nm and
C based
olated
on the 10/90 wt% guest–host system with E44. In our studies,
the host mixture we selected (NCS-tolanes and NCS-cyclohexyl-tolane) has similar structure as the guest compounds. The
values we report here are extrapolated from the mixtures
with a clearing temperature in the range of 140 C–160 C.
Specifically, we obtained a consistent birefringence value of
nm and
C from both
0.52 for Comp. 16 at
80/20 wt% and 40/60 wt% guest–host systems.
Fig. 1(a) and 1(b) plots the temperature dependent FoM for
the single fluorinated PPTP(3F)2NCS and double fluorinated
PPP(3,5F)3NCS compounds, respectively. Their maximum
C) reach 250 m s and 120 m s,
FoM values (at
respectively. The FoM of PPTP(3F)2NCS is by far the highest
we have ever found, although its operating temperature is as
high as 150 C. High temperature operation is quite undesirable
because it involves a heat stage. Thus, we extrapolate the FoM
C. We fit the data measured
of these two compounds to
at elevated temperatures using (2) and find that the FoM stays
20 m s and 10 m s for the phenyl-tolane and terphenyl
compounds, respectively, as shown in Fig. 1(a) and 1(b).
Typically, high birefringence compounds are solid at room
temperature. Thus, we measured the UV absorption spectra
from a cyclohexane solution. Fig. 2 shows the measured UV
absorption spectra of some of the single compounds listed
in Tables II and III. All of the presented NCS compounds
nm ,
have a longer absorption tail than that of 5CB
shown as a benchmark for comparison. This is chiefly because they all have a longer -electron conjugation than the
pentyl-cyano-biphenyl. Due to the extended -electron conjugation, NCS-phenyl-tolane (Comp. 7) has an absorption
nm. From the terphenyl group, the
tail as far as
nm.
PP(3,5F)5NCS (Comp. 14) has absorption tail at
Overall, this means that all of these compounds absorb the
long-wavelength UV light. Extra caution of protecting these
nm expohigh birefringence LC devices from UV
sure should be taken. In general, these highly conjugated LC
structures are not suitable for the applications that require a UV
curing process [29].
We favor the tolane rigid cores because of their high birefringence and low viscosity. A disadvantage of the tolane (biphenyl
tolane) structure is its inadequate UV stability [27]. However,
for infrared application the photostability is not a big concern.
IV. EUTECTIC MIXTURES
Based on the single component results, we formulated some
test mixtures. First, two different high birefringence mixtures
were formulated. As mentioned before, double lateral fluorination of the tolane rigid core effectively lowers the melting point
of the NCS tolanes. Thus, these two base mixtures only differ
by the amount of the double fluorinated tolanes. UCF-Base-1
contains only non-fluorinated or single fluorinated tolanes and
GAUZA et al.: HIGH PERFORMANCE ROOM TEMPERATURE NEMATIC LCS
251
TABLE IV
PHYSICAL PROPERTIES OF UCF-BASE MIXTURES
Fig. 3. Temperature dependent birefringence of UCF-Base-2, UCF-A, UCF-B,
and UCF-C mixtures. = 633 nm.
UCF-Base-2 has 30% of the double fluorinated tolanes, Compounds 9, 10, and 11. Although, both mixtures have almost the
same physical properties, their melting temperatures are significantly different. UCF-BASE-1 melts at 21.8 C but stays as
smectic up to 2.0 C, and then nematic clears at 109.8 C. On
the other hand, UCF-Base-2 melts at 54 C, stays nematic and
clears at 100 C; no smectic phase occurs. Thus, UCF-Base-2 is
our natural choice, even its electro-optic performance is slightly
worse than that of UCF-Base-1. A commercial high birefringence mixture E44 from Merck is included in Table IV for comparison.
Both UCF-Base mixtures were doped by high birefringence
compounds 16, 17, and 18. As expected, when UCF-Base-1
was doped by a small amount of difluoro-biphenyl-tolane (10%
of Comp. 17), smectic phase appears at 15 C above room
temperature. Thus, UCF-Base-1 cannot serve as a base mixture
for biphenyl NCS-tolanes if the guest compound concentration
is higher than 10%. Under such a circumstance, the extrapolated birefringence at room temperature would not exceed
0.4. Second base mixture, UCF-Base-2, shows a much higher
tolerance for eutectic composition of compounds 16, 17 and 18
up to 45% where the melting point stays at 5 C and smectic
phase below 10 C. Based on the composition comparison, the
laterally difluorinated tolanes are a better choice than the single
fluorinated ones. A large amount of biphenyl-tolane dopant and
the increased clearing temperature leads to a high birefringence
measured at 25 C and
nm). The nematic
(
range was relatively wide with melting point at 9.8 C and
clearing point at 135.8 C [UCF-A]. The smectic phase was
observed with the phase transition into nematic at 14.0 C.
Further increase of biphenyl-tolane-NCS concentration results
in increased melting and smectic-nematic phase transition
temperatures. The highest concentration of compounds 16
and 15 we were able to mix into UCF-Base-2 was 50%. The
mixture’s melting point was 25 C and monotropic smectic to
nematic transition was 18 C. This mixture (UCF-B) exhibits
10 C wide supercooling effect. Unfortunately, we found
a
that the UCF-B system was not thermodynamically stable and
the dopant compound was precipitated from the mixture after
several hours of storage at room temperature. In this case additional compounds which may effectively destabilize smectic
order are necessary to obtain room temperature mixture. To
Fig. 4. Temperature dependent FoM of UCF-Base-2, UCF-A, UCF-B, and
UCF-C mixtures. = 633 nm.
enforce usability of the biphenyl-tolane isothiocyanates for
high birefringence LC mixtures, we prepared a test mixture
(UCF-C) which contains 30% of cyclohexyl-tolane-NCS
4-(trans-2-butylcyclohexyl)-3-fluoro-4-isothiocyanatotolane)
instead of 30% biphenyl-tolane-NCS, Comp. 17, to match the
clearing point of UCF-A. Doping 30% of cyclohexane compound results in increased melting and clearing temperatures
from [ 54.0 C, 100.0 C] to [15.1 C, 127.6 C], respectively,
for UCF-Base-2 and UCF-C. As expected, birefringence is
significantly higher for biphenyl-tolane doped UCF-A mixture
at
C
than for UCF-C. We measured
nm. This mixture is thermodynamically stable;
and
there is no sign of mixture recrystalization due to excessive
amount of highly conjugated biphenyl-tolanes. For comparison,
UCF-B shows
at the same experimental conditions.
Temperature dependent birefringence for the discussed mixtures is shown in Fig. 3. At this stage, UCF-A is the highest
birefringence LC mixture with room operation capability.
An interesting phenomenon was observed by comparing the
temperature dependent FoM (see Fig. 4) and visco-elastic coefficient (see Fig. 5) of the UCF-A and UCF-B. FoM was higher
for UCF-A with a lower concentration of biphenyl tolane compounds (16, 17 and 18) than for UCF-B with larger content of
highly conjugated compounds 16 and 17.
This effect comes from the lower visco-elastic coefficient value in the case using three homologues of biphenyl
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m s.
under the same experimental conditions are
The high birefringence of our UCF mixtures enable the use of
a thinner cell gap which efficiently reduces the response time
while the required optical phase change is still maintained. The
on-off-on switching time obtained for UCF-Base-1 mixture
using a 2- m cell gap was 640 s at 35 C, which is the fastest
optical modulator driven by simple square waves. The response
time could be further reduced if UCF-A or UCF-B mixture will
be applied to electro-optical cell with thickness below 2- m.
The applications for various OPA and optical shutter devices are
foreseeable. The potential applications for telecommunication
industry are also foreseeable.
Fig. 5. Temperature dependent viscoelastic coefficient of UCF-Base-2,
UCF-A, UCF-B, and UCF-C mixtures.
tolanes than just using Comp. 16 and 17. Higher melting
point of UCF-B could also contribute to the observed higher
visco-elastic coefficient value.
V. DISCUSSION
There is a common concern about the reliability of highly
polar (CN and NCS) LCs in terms of resistivity, ionic concentration, and voltage holding ratio. Recently it was reported that
by introducing one or two fluoro groups at the 3- or (3,5)-positions of the phenyl ring where CN or NCS resides, the voltage
holding ratio is improved to better than 95% [15], [30]. Thus,
the fluorinated NCS or CN compounds are useful for active matrix displays.
We also purified NCS-based high birefringence mixtures
, with acceptable yield, up to resistivity level
of 10
[31]. In addition, mixtures with birefringence of
nm) allow us to use a relatively thin
0.43–0.45 (at
nm to obtain the required
phase
cell gap at
change. According to the single band birefringence dispersion
model [17], the birefringence of UCF-B is estimated to be
–
at
m. Thus, we consider our UCF
mixture an excellent candidate for laser beam steering using
optical phased arrays and light shutters where a high voltage
holding ratio is not crucially needed.
VI. CONCLUSION
We have designed several new, high birefringence, and
relatively low viscosity mixtures for applications that require
operating conditions at room temperature. By using high birefringence compounds based solely on the unsaturated rigid core
structures with highly polar NCS terminal group, we obtained
a record-high FoM value in such conditions. For the first time,
nm and
we formulated a high birefringence of 0.43
simultaneously high performance nematic mixture with FoM
C. It is particularly difficult
greater than 15.0 m s at
due to severe rotational viscosity increase with -electron conjugation increase and multiple lateral substitutions. Previously,
to get such performance we would have to operate at an elevated
temperature in order to shorten the response time. The best
results for commercial high birefringence nematic mixtures
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Sebastian Gauza received the Ph.D. degree in
chemistry from the Military University of Technology, Warsaw, Poland, in 2001.
He is currently a research scientist at College of
Optics and Photonics/CREOL/FPCE, University of
Central Florida, Orlando, FL. His current research is
to develop novel high birefringence nematic liquid
crystals single compounds and mixtures for photonic
applications.
253
Shin-Tson Wu (M’98–SM’99–F’04) received
the B.S. degree in physics from National Taiwan
University, Taipei, and the Ph.D. degree from the
University of Southern California, Los Angeles.
He is currently a PREP professor at College of
Optics and Photonics, University of Central Florida,
Orlando. His studies at UCF concentrate in foveated
imaging, bio-photonics, optical communications,
liquid crystal displays, and liquid crystal materials.
He has coauthored three books, Fundamentals of
Liquid Crystal Devices (Wiley, 2006), Reflective
Liquid Crystal Displays (Wiley, 2001), and Optics and Nonlinear Optics of
Liquid Crystals (World Scientific, 1993), 4 book chapters, over 300 papers, and
55 issued and pending patents.
Dr. Wu is a Fellow of the Society for Information Display (SID) and Optical
Society of America (OSA).
Ania Spadło graduated from the Department of
Chemistry, Radom Technical University, Radom,
Poland, in polymer technology in 1999, and received
the Ph.D degree in organic chemistry from the Institute of Chemistry, Military University of Technology
(MUT), Warsaw, Poland, in 2004. She is a doctorate
of organic chemistry.
She is involved in European Research Training
Network SAMPA (Synclinic and Aticlinic
Mesophases for Photonic Applications”) at the
Polytechnic of Madrid, Madrid, Spain.
Roman Dabrowski received the Ph.D. degree in
polymer technology from Warsaw Technical University, Warsaw, Poland, in 1966, and the Sc.D. degree
from the Military University of Technology (MUT),
Warsaw, Poland, in organic semiconductors studies
in 1970.
He is currently full Professor of organic chemistry
and Director of the Institute of Chemistry in the Military University of Technology (MUT). Since 1975,
he changed his interest to liquid crystals, searching
for new LC materials for displays and photonic applications and investigating relations between the chemical structure of molecules
and their mesogenic and physical properties. He has authored over 300 publications and conference presentation.
Dr. Dabrowski was a member of Scientific and Organizing Committees of International Liquid Crystal Conferences and a recipient of the Frederick’s Medal
in 2005.