Table Of ContentSurvey of Volume IV/7
A monomeric calamitic liquid crystals Subvol.
1. one-ring systems a
2. two-ring systems without bridging groups
3. two-ring systems with bridging groups L
4. three-ring systems without bridging groups
5. three-ring systems with one bridging group d”
6. three-ring systems with two bridging groups e
7. four-ring systems f
8. five-ring systems f
9. more than five rings f
10. metallomesogens g
11. acyclic compounds g
12. acids g
13. steroids g
B other monomeric liquid crystals
14. discotic liquid crystals h
15. polyols / sugars h
16. salts h
C polymers
17. monophilic side group polymers
18. amphiphilic side group polymers
19. main chain polymers
20. natural polymers
J
21. elastomers, other polymers J
Landolt-Biirnstein
Numerical Data and Functional Relationships in Science and Technology
New Series / Editor in ChieE W. Martienssen
Group IV: Macroscopic Properties of Matter
Volume 7
Liquid Crystals
Subvolume F
Transition Temperatures and Related Properties
of Four-Ring Systems, Five-Ring Systems,
and More than Five Rings
I? Vi11
Edited by J. Thiem
‘Springer
ISSN 0942-8011 (Macroscopic Properties of Matter)
ISBN 3-540-58853-1 Springer-Verlag Berlin Heidelberg New York
Library of Congress Cataloging in Publication Data
Zahlenwerte und Funktionen aus Naturwissenschaften und Tcchnik, Neue Serie
Editor in Chief: W. Martienssen
Vol. IV/7F: Edited by J.Thiem
At head of title: Landolt-B6rnstcin. Added t.p. : Numerical data and functional relationships in science and technology.
Tables chietly in English.
Intended to supersede the Physikalisch-chemische Tabellen by H. Landolt and ft. Bernstein of which the 6th ed. began
publication in 1950 under title: Zahlenwcrte und Funktionen aus Physik, Chemie,Astronomie, Geophysik und Technik.
Vols. published after v. 1 of group I have imprint: Berlin, New York, Springer-Verlag
Includes bibliographies.
1. Physics--Tables. x Chemistry--Tables. 3. Engineering--Tables.
I. B6rnstein. R. (Richard), 1852-1913. II. Landolt, H. (Hans), 1831-1910.
Physikalisch-chemische Tabcllcn. IV.Titlc: Numerical data and functional relationships in science and technology.
QC61.23 501’.12 62-53136
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Editor
J. Thiem
Institut fiir Organische Chemie der UniversitIt
Martin-Luther-King-Platz 6, D - 20146 Hamburg
Author
v.vill
Institut fir Organische Chemie der Universitzt
Martin-Luther-King-Platz 6, D - 20146 Hamburg
Preface
Volume IV/7 “Liquid Crystals” of the New Series is concerned with critically selected and
assessed data in the field of liquid crystalline compounds.
Liquid crystalline research extends physics via chemistry to the biosciences. Over the years this
borderline status generated fascinating interactions and developments both in basic and applied
research.
This currently expanding area in research and application became evident to the public recently
when the 1991-Nobel Prize in Physics was awarded to P.G. de Gennes for his contribution to
the understanding of the liquid crystalline state. Further, displays in all sorts of equipment and
machines in daily use are dependent on liquid crystalline phases and their technical
employment. An area of rapidly growing interest and studies in biochemistry, bioorganic and
organic chemistry is concerned with membrane formation, stability and molecular-molecular
interactions and recognition. Liquid crystalline phenomena are connected with detergents,
lipids, and steroids. Recently polymeric materials with liquid crystalline properties proved
valuable in “high tech” areas such as space research and household equipment.
Some data on liquid crystals appeared previously in LB 6th Edition, Vol II, part 2 in 1960 (by
W. Kast). More recent collections of data were published in tables by Deutscher Verlag ftir
Grundstoffindustrie, Leipzig, in 1974 and 1982 (by D. Demus, H. Demus and H. Zaschke). By
the end of 1982 some 14000 liquid crystalline compounds were reported, 10 years later the
number has increased to approximate 50000.
The nucleus of the present volume resides in the data bank project LIQCRYST, which is almost
completed. Here all available data of liquid crystals have been collected, critically selected,
assessed and compiled including those of the above mentioned monographs and also back into
very old literature. In addition to this printed data collection the data bank LIQCRYST contains
all available physical data of liquid crystals. This allows a facile access to any substructure and
property search.
The present Vol. IV/7 is not published to compete with this data bank. On the contrary, the
width of individual information available there is intended to be complemented by the
advantages of printed tables. Here an overall picture of the liquid crystalline field will become
evident. This should allow ready comparison of corresponding data, and the elucidation of
structure-function relationships. Furthermore, a book generally is more easily accessible than a
file and it does not require any electronic equipment. Finally, the complete review of all the
relevant data about liquid crystals between 1850 and 1991 will be appreciated as a document in
itself.
First of all it is a particular pleasure to acknowledge the single author’s careful, deligent, and
most competent work and engagement, which did not require much of an external driving force.
It should be emphasized that the Springer-Verlag, Heidelberg (Dr. R. Stumpe) and the Federal
Ministry of Science and Technology, Bonn, jointly supported the data bank project LIQCRYST
the data of which could be critically selected and assessed. Further, our own research in the
liquid crystalline area enjoyed continuous support by the Deutsche Forschungsgemeinschaft.
Finally we want to thank the Chamber of Commerce, Hamburg and E. Merck, Darmstadt, for
providing the patent literature. Special support was obtained and is acknowledged by Dipl.-
Chem. Mrs. Angela Hartwig and Mrs. Renate Poehls (Hamburg), DipI.-Phys. Alois Jandausch
and Prof. Dr. Fred Fischer (Miinster).
Last but not least, we are grateful to the Landolt-Bornstein editorial staff in particular to Dr. H.
Seemtiller for their competent support as well as the production department for their usual high
quality completion of this volume.
Hamburg, June 1995 The Editor
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 mesogenic
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 to obtain
information on compounds studied in vain, because this prevens unnecessary repetitions of experiments or may
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 surfactants, glycolipids, lipids,
steroids and others. Such derivatives are included if mesogenic properties were expected and melting points or special
melting anomalies (sintering, softening) are known.
Data are given for:
liquid crystals
(compounds with proven thermotropic liquid crystalline properties)
non liquid crystals with mesogenic structures which are
- chiral dopants
- dyes
- mesogenic compounds studied with no liquid crystal properties
- compounds not yet studied (=> clearing parameter 0)
- basic structures for liquid crystals (e.g. pure mesogenic groups).
Compiled for each compound are:
__ the solid-solid transitions temperatures
__ the liquid crystalline transitions temperatures
__ the heats of transition.
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&-Bbnstein
New Series Nflf
2 Introduction
13 Arrangement of data
Liquid crystal research is an interdisciplenary area. Thus, an arrangement of compounds based solely on physical
asp&s could hardly satisfy the chemist. He would then find smedic phenyl benzoates next to smectic alkyl
glycosides but could not deduce from this where to incorporate a novel liquid crystalline compound. On the other
band, 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 dassified following physical principles into calamitic and discotic liquid crystals. These dasses 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.
The assignment of these classes of compounds to the individual systems proceeds aaording to formal chemical
aspects such as the number and succession of fragments:
Order principles for mesogenic groups (systems):
1. number of rings
2. number of bridging groups
3. priority of rings
4. priority of bridging groups
5. priority of side groups
Priority of rings:
3.1. benzene
3.2. substituted benzenes
isomers < deuterated benzenes < halogen-substituted benzenes c alkyl-substituted benzenes
3.3. six-membered aromatic rings
3.4. other monocyclic aromatic rings
3.5. cyclohexane
3.6. alicydic rings
3.7. complex ring systems
3.8. metal complexes
Priority of side groups:
5.1. compounds without terminal alkyl chains
5.2. compounds with one terminal alkyl chain
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.
Lmddt-Bimstdn
New Series lVl7f
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
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 today. On the
other hand a classification of compounds following just the connectivity of atoms [CAS-Online, Beilstein-Online] is
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 researchers in the liquid crystal
field.
An unequivocal presentation and classification of all compounds on a more sophisticated level than the connectivities
of atoms is required, as shown below.
link bridge ring terminal group
side group mesogenic group side group
L R
A liquid crystalline compound is subdivided into the mesogenic group and the side groups. The mesogenic group is
subdivided into the fragments rings and bridges. The side groups are subdivided in links and terminal groups.
In addition, there are some specific fragments such as discs in case of monophilic discotics, polymer backbones in
the case of side group polymers, steroids etc.
Each liquid crystalline compound is divided into a linear sequence of fragments. Fragments arc 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.
LanddtBi*nste.in
New Series NTlf
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.a re 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
(orientationly disordered crystals, Fig. 3), the reverse occurs, positional order is maintained, but orientational or&r 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
separation of different molecular parts. In addition, an anisotropy of vander-Waals interaction was refered to as an
interpretation of liquid crystalline behavior [58Ml].
Generally mesogenic molecules have the following shapes:
rod-like molecules, which form calamitic liquid crystals (-> nematic and smectic phases).
disc-like molecules, which form discotic liquid crystals (-> discoid nematic and discotic phases).
globular molecules, which form plastic crystals.
Fig. 1: Crystal Fig. 2: Isotropic liquid Fig. 3: Plastic crystal
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 dass of nematic phases is the cbolesteric 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 pitch p.
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).
Imddt-BCrmteh
New Series lVnf
