Transition Temperatures and Related Properties of Three-Ring Systems without Bridging Groups

208 Pages·1993·7.751 MB·English

by  V. Vill (auth.), J. Thiem (eds.)

Introduction 1
Introduction
1 General remarks
1.1 Selection of data
In these tables all thermotropic one-component liquid crystals are included.
The scope of compounds listed in these tables is much larger than that of older data collections of liquid crystals
[60K1,74D1,82Dl]. An important class of liquid crystalline compounds the liquid crystalline polyols [llF1,19Gl]
although well known was previously not included.
In addition some compounds not yet proven to be liquid crystalline are incorporated, because the proof of mesogenmic
properties often depends on the method applied. Frequently monotropic phases are not noticed, but in the case of
dopants extrapolated data may be as important as directly measured temperatures. Sometimes it is helpful oto obtain
information on compounds studied in vain, because this prevens unnecessary repetitions of experiments or may
c
indicate approaches towards further experiments. A large number of mesogenic compounds was never studied with
respect to their thermotropic liquid crystalline properties until today. These include surfac.tants, glycolipids, lipids, e
steroids and others. Such derivatives are included if mesogenic properties were expectfed and melting points or specwial a r
d o ft
melting anomalies (sintering, softening) are known. s
F
p D
P
Data are given for: S
s R T
A
-- liquid crystals t n o f
r o
(compounds with proven thermotropic liquid crystalline propertiseis)
-- non liquid crystals with mesoagenicstructures which are v e r
o
- chiral dopants . m
e
w d
- dyes a
g
- mesogenic compounds studied with non liquid crystal properties
w si
- compounds not yet studied (=>d cleuaring parameter 0)
e
w - basic structures for liquidd ifcirystals (e.g. pure mesogenic groups).
o
m
Compiled for each compound aree: n
e
b
s
-- the sohlida-solid transitions temperatures
F
-- Dthe liquid crystalline transitions temperatures
P
his-- the heats of transition.
T
Data for lyotropic liquid crystals, liquid crystal mixtures and statistic copolymers, are not included.
1.2 Sources of data
All references with respect to liquid crystals were included de novo beginning with 1850. The literature surveys
originated from CAS and Beilstein searches, specialized journals, from conference reports and older review articles.
Incorporated are the sources refereed by CAS until the end of 1991 and patents until the end of 1990. Japanese
patents were only included if corresponding European or American patents existed. The most important sources for
these tables were taken from journals, patents, conference proceedings, monographs and German doctoral theses.
Land&-Bixnstein
New Series IVnc
2 Introduction
1.3 Arrangement of data
Liquid crystal research is an interdisdplenary area. Thus, an arrangement of compounds based solely on physical
aspects could hardly satisfy the chemist. He would then find smectic phenyl benzoates next to smectic alkyl
glycosides but could not deduce from this where to incorporate a novel liquid crystalline compound. On the other
hand, an arrangement following purely chemical aspects could hardly satisfy the physicist. He would find columnar-
discotic and smectic inositols in one table, and in case of a search for certain properties the whole material would
have to be scanned from the beginning to the end.
Therefore, the arrangement was selected according to a stepwise dominance of chemical and physical principles. First
there is a chemical classification into monomeric and polymeric compounds. The most important class of monomeric
compounds is classified following physical principles into calamitic and discotic liquid crystals. These classes in turn
are subdivided according to chemical-physical aspects into amphiphilic and monophilic liquid crystals. The largest
class of monophilic calamites is again subdivided according to chemical aspects into simple calamites, acids and
steroids.
m
The assignment of these classes of compounds to the individual systems proceeds according to formal chemical
aspects such as the number and succession of fragments: o
c
Order principles for mcsogenic groups (systems):
1. number of rings . e
2. number of bridging groups d f o ft w a r
3. priority of rings F s
4. priority of bridging groups p P D
5. priority of side groups s R T S
A
Priority of rings: t n o f
r o
3.1. benzene si
a e r
3.2. substituted benzenes v
o
isomers < deu.terated benzenes < halogen-substmituted benzenes < alkyl-substituted benzenes
e
w d
3.3. six-membered aromatic rings a
g
3.4. other monocyclic aromatic rings n
w si
3.5. cyclohexane d u
e
w 3.6. alicyclic rings difi
o
3.7. complex ring msystems
3.8. metal come pnle xes
e
b
s
a
Priohrity of side groups:
F
D 5.1. compounds without terminal alkyl chains
P
his 5.2. compounds with one terminal alkyl chain
T
5.3. compounds with two terminal alkyl chains
The easiest approach for a compound search is given in the system overview. Here only structural depictions of
mesogenic groups and the corresponding pages are included.
Ianddt-Bixnstein
New Series lvf7c
Introduction 3
1.4 Continuation
A future update of this series by supplement volumes is intended. New supplement volumes will incorporate the
material of previous supplement volumes, and this allows the user of the series to find updated material always in two
volumes.
2 Chemical structures
Within recent years the number of liquid crystals reported has increased exponentially. Thus, registration and m
assessment of all compounds is only feasable employing computer-aided approaches. In contrast, the previously
classification of the compounds according to purely synthetic aspects [60K1,74D1,82Dl] is impossible tooday. On the
other hand a classification of compounds following just the connectivity of atoms [CAS-Online, Beilstein-Online] is
c
difficult to display in tables. Therefore, the documentation of liquid crystals required a novel fragment-oriented data
bank system, which is predominantly based on the scientific language used among resear.chers in the liquid crystal e
field. d f o ft w a r
An unequivocal presentation and classification of all compounds on a more sophisticated level than the coFn nesctivities
of atoms is required, as shown below. p P D
S
s R T
link bridge ring terminal gAroup
t o f
n
r o
si
a e r
v
o
. m
e
w d
a
side group mesogenic n g group side group
w si
u
L d R
e
w difi
o
m
A liquid crystalline compound is nsu bdivided into the mesogenic group and the side groups. The mesogenic group is
e
subdivided into the fragments e rings and bridges. The side groups are subdivided in links and terminal groups.
b
s
a
h
In addition, there Fa re some specific fragments such as discs in case of monophilic discotics, polymer backbones in
D
the case osf siPde group polymers, steroids etc.
hi
T
Each liquid crystalline compound is divided into a linear sequence of fragments. Fragments are connected by single
bonds. Some fragments can bind on one side a number of identical fragments These types are used for discotics,
twins and forked compounds.
LanddtBlxnstdn
New Series IVf7c
4 Introduction
3 Thermotropic liquid crystalline phases
3.1 The liquid crystalline state
Liquid crystals represent a state of order between crystals and liquids. Crystals have a three dimensional long range
order of both position and orientation (Fig. 1). Liquids, in contrast, do not show any long range order (Fig. 2). In
mesophases imperfect long range orders are observed, and thus they are between crystals and liquids. In mesophases
two cases can be distinguished, these are the liquid crystals and the plastic crystals. In liquid crystals (ordered
liquids, anisotropic liquids), orientational order is maintained, but positional order is lost. In plastic crystals
(oricntationly disordered crystals, Fig. 3), the reverse occurs, positional order is maintained, but orientational order is
lost.
Reasons for the formation of mesophases can be the molecular shape [19V1,56Fl] which may induce an advantaged
packing. Alternatively or additionally, the amphiphilic character [88Sl] may be responsible which induces a micro
m
separation of different molecular parts. In addition, an anisotropy of van-der-Waals interaction was refcred to as an
interpretation of liquid crystalline behavior [58Ml].
Generally mesogenic molecules have the following shapes: o
c
rod-like molecules, which form calamitic liquid aystals (-> nematic and smectic phases).
gdlioscb-ulilkaer mmoolleeccuulleess,, wwhhiicchh ffoorrmm pdliassctoicti c aylisqtaulisd. crystals (-> discdoid fncma.tic and discotic phaseosf).t w a r e
s
F
p D
P
S
s R T
A
t o f
n
r o
si
a e r
v
o
. m
e
w d
a
g
n
w si
u
d
e
w difi
o
m
Fig. 1: Crystal e n Fig. 2: Isotropic liquid Fig. 3: Plastic crystal
e
b
s
a
h
F
D
P
s
hi
T 3.2 Nematic phases
The simplest and most abundant liquid crystalline phase is nematic. Here the molecular centers are statistically
located within the medium, but the long axes are orientated in one direction (director n, Fig. 4).
A special class of nematic phases is the cholesteric phase (Fig. 5). Here the orientation of the director n does not
apply for the whole medium but rather for a virtual layer. Perpendicular to this layer the director follows a helix with
a certain pitchp.
In case of the blue phases such a helical structure is formed not only in one but all three dimensions. Thus, highly
complex arrangements with mostly chiral cubic symmetry are generated.
Not only rod-like but also disc-like molecules can form nematic phases: the discoid-nematic phase (Fig. 6).
Landdt-Bhstein
New Series IVnc
Introduction 5
Fig. 4: Nematic phase Fig. 5: Cholesteric phase Fig. 6: Discoid-nematic phase
m
o
3.3 Smectic phases
c
Rod-like molecules arranged in layers form smectic phases. They are subdivided into fa co.nsiderable number of w a r e
different species [66Sl]. These classifications result from various arrangements dof their molecules within the laoyfetrs
and different restrictions of movement. F s
p D
P
S
The smectic A phase, the simplest smectic phase, can be regardsed as a two-dimensional liquidR. TT he molecules are
arranged normal to the layers (Fig. 7). A
t o f
n
r o
The smectic A phase and the smectic C phase are similar except that in the lattesri the molecules are tilted within the
a e r
layers by a tilt angle 0 (Fig. 9). o v
A particular case of smectic C is the .chiral smectic C’ phase, wheree mthe tilt angle varies from layer to layer forming a
w d
helical structure. a
g
n
w si
u
The smectic B phase can be interpretated as the dc losest packing of rod-like molecules, so that within the layers each
e
moleculew has a hexagonal environment (Fdigi.f i8).
o
m
n
e
e
b
s
a
h
F
D
P
s
hi
T
Fig. 7: Smectic A phase Fig. 8: Smectic B phase Fig. 9: Smectic C phase
For discussion of other smectic phases ( D to Q) as well as their further subclassifications the reader may consult the
current literature and the references given in chapter 3.7 .
Landdt-B6rnstein
New Series Nfi’c
6 Introduction
3.4 Discotic phases
In discotic phases the disc-like compounds are arranged in columns. Again in this group various phases are possible
depending of the orientation of the molecules within the columns and the order between the columns. The most
simple phase is the Dhd phase. It can be regarded as a one-dimensional liquid. The columns have a hexagonal order
(Fig. 10).
m
o
c
. e
Fig. 10: Hexagonal disordered discotic phfase w a r
d o ft
s
F
p D
P
S
s R T
A
3.5 Classificatitons and other technical o f terms
n
r o
si
Lyotropic liquid crystals are formed a by aggregation of micelles. Thue sr, they are multi-component systems and not
v
molecular dispers. Normally they are made of an amphiphilic sou bstance and one or more solvents. In contrast,
. m
thennotroplc liquid wcrystals are formed by pure compoudndes. Sometimes, thermotropic liquid crystals which also
form lyotropic liquid crystals with suitable solventsg aar e called amphotropic.
n
w si
u
In amphiphilic liquid crystals the amphipd h ilic character of the molecule is the reason for the formation of the liquid
e
wcrystalline behavior such as in soadpisf iand alkyl glycosides. In contrast, in monophilic liquid crystals the molecular
o
m
form causes the liquid crysnt allin properties.
e
e
b
Rod-like molecua less will form calamitic liquid crystals, disc-like molecules will form discotic liquid crystals. Bowlic
h
and pyramFid al liquid crystals are closely related to discotic liquid crystals and not separated in these tables.
D
P
s
T hiA molecular shape between rods and discs is present for phasmidlc liquid crystals.
Enantiotropic liquid crystalline phases exist above the melting point. Thus, these phases are observed during the
heating and the cooling period. Monotropic liquid crystalline phases exist only in the supercooled area below the
melting point. Thus, these phases are only observed during the cooling period.
Landdt-Bbnstdn
NW Saks Ivflc
Introduction 7
3.6 References
llF1 Fischer, E., Helferich, B.
LiebigsAnn. Chem. 383 (1911) 68.
19Gl Gaubert, M.P.
C. R. Hepb. SeancesAd. Sci. 168 (1919) 277.
19Vl Vorllnder, D.
Z. Phys. Chem. 105 (1919) 211.
56Fl Flory, P.J.
Proc. Roy. Sot. A234 (1956) 73; Adv. Polymer Science 59 (1984) 1.
Flory, P.J. and Ronca, G.
Mol. Ctyst. Liq. Cry& 54 (1979) 289. m
58Ml Maier, W., Saupe, A.
o
Z. Ndurforsch. 13a (1958) 564; 14a (1959) 882; 15a (1960) 287.
c
60Kl Kast, w. . e
Landolt-Blirnstein, 6th Edition, Vol. II, part 2, p. 266-333 (1960). f w a r
d o ft
s
F
66Sl Sackmann, H., Demus, D. p D
P
Mol. Cryst. 2 (1966) 81; Fortschr. them. Forschg. 12 (1969) 349; Mol. Cry&. Liq. Cry&. S 2 1 (1973) 239.
s R T
A
74Dl Demus, D., Demus, H., Zaschke, H. t o f
n
“Flfissige Kristalle in Tabellen” r o
si
Deutscher Verlag fiir Grundstoffindusatrie, Leipzig, 1974. e r
v
o
. m
e
82Dl Demus, D., Demus, wH., Zaschke, H. d
a
“Fliissige Kristalle in Tabellen II” g
n
Deutscher wVerlag fir Grundstoffindustrie, uLesiipzig, 1982.
d
e
88sl wSkoulios, A., Guillon, D. o difi
m
Mol. Cryst. Liq. Cry&. 16n 5 (1988) 317.
e
e
b
s
a
h
F
D
P
s
hi
T
Laaddt-B6rnst.h
New Series IVh
8 Introduction
3.7 Review articles and monographs
Friedel, M.G.
“Les Stats Mesomorphes de la Matibre”
Ann Physique [9] 18 (1922) 273-474.
Gray, G.W., Winsor, P.A.
“Liquid Crsytals and Plastic Crystals”, Vol I and II
Ellis Hot-wood Publishers, Chichester, 1974.
De Gennes, P.G.
“The Physics of Liquid Crystals”
Clarendon Press, Oxford, 1974.
Chandrasekhar, S. m
“Liquid Crystals”
Cambridge Univerity Press, Cambridge, 1977.
o
Demus, D., Richter, R. c
“Textures of Liquid Crystals” . e
Verlag Chemie, Weinhcim, 1978. f w a r
d o ft
s
F
Kelker, H., Hab, R. p D
P
“Handbook of Liquid Crystals” S
Verlag Chemie, Weinheim, 1980. s R T
A
t o f
n
Destrade, C., Nguyen H.T., Gasparoux, Hr., Malthcte, J. Levclut, A.M. o
si
“Disc-Like Mesogens: A Classificatioan” e r
v
o
Mol. Crysr. Liq. Crysr. 71 (1.981) 111. m
e
w d
a
Gray, G.W., Goodby, J.W.G. g
n
“Smectic wLiquid Crystals - Textures and Sturuscitures”
d
Leonard Hill, Glasgow, 1984. e
w difi
o
m
Finkelmann, H. n
e
e
“Liquid Crystal Polybmers”
s
Angew Chemh. aInf. Ed. Engl. 26 (1987) 816.
F
D
P
Rsin gsdorf, H., Schlarb, B., Venzmer, J.,
hi
T “Molecular Architecture and Function in Polymeric Oriented Systems - Models for the Study of Organisation,
Surface Recognition, and Dynamics in Biomembranes”
Angew. Chem. Int. Ed. Engl. 27 (1988) 113.
Pershan, P.S.
“Structure of Liquid Crystal Phases”
World Scientific, Singapore, 1988.
Jeffrey, J., Wing+ L.M.
“Carbohydrate Liquid Crystals”
Liq. Crysr. 12 (1992) 179-202.
Ianddt-BErnskin
New Series IVf7c
Introduction 9
4 Symbols and abbreviations
4.1 Notation of thermotropic liquid crystalline properties
The complete transition sequence is formed by (1) the description of the solid state (2) the liquid crystalline
transitions and (3) the clearing parameter.
Every phase symbol is followed by the upper temperature limit. Every temperature is given as measured during the
heating and not during the cooling period.
Liquid crystalline phases are arranged according to increasing temperature with the exception of an extrapolated
nematic phase at the end of a sequence.
If a transition temperature of a liquid crystalline phase is lower than the melting point this phase only occures
monotropically. Parantheses are not used to underline monotropic behavior.
Examples:
m
Cr34N561 The compound melts at 34’C into the nematic phase, at 56°C it changes into
the isotropic phase, normal behavior. o
Cr 56.5 A 45 I The compound melts at 56.5’C into the isotropic phase. A monotropic
c
smectic A phase exists below 45X.
Cr12OB 134N56E The compounds melts at 12O’C into the smectic B. phase. At 134-C the e
isotropic phase is formed. A nematic clearing fpoint of 56’C is extrapolated w a r
d o ft
from mixtures. s
F
Cr, 78 CrI 212 N ? Z The compound shows a crystal-cprystal-transition at 78°C and a Dmelting point
P
of 212’C into a nematic phase. The clearing point is unknoSw n because
s R T
decomposition takes place. A
t o f
n
r o
si
a e r
v
o
. 4.2 Solid state m
e
w d
a
Cr crystalline, melting point n g
w si
Cr2 crystal-crystal transition d u
g wglassy state difie
melting point of another crystaol modification
mp2 m
Tg glass transition tempereatunr e
e
b
s
a
h
F
D
P
s
hi
T
Imddt-Bbnsttin
New Series lV/7c
10 Introduction
43 Liquid crystalline phases
N nematic
reentrente nematic
NT,
ch cholesteric, chiral nematic
BP blue phase
S smectic
A smectic A
B smectic B, smectic Bhex
C smectic c
SmD smectic D (only in comments, normally Q is used)
E smectic E
F smectic F
G smectic G m
H smectic H
SmI smectic I(1 is reserved for the isotropic phase) o
J smectic J
c
K smectic K
L smectic L, smectic B,,, . e
M smectic M f w a r
d o ft
s
F
smectic C, antiferroelectric p D
CA P
S
s R T
P plastic (high ordered smectic or cubic rotatory phase) A
t o f
n
r o
D discotic, H, si
a e r
v
o
Q cubic . m
e
w d
a
g
Y reentrente isotropic n
w si
u
d
e
wX liquid crystalline, unknowdinfi typ
o
m
tr unknown transeitino n
e
b
s
a
h
F
D
P
s
hi
T
IaddtB&skin
New Series rVnc