LiqCryst 2.1 - Database and Scientific Tool

Volkmar Vill, Henry Sajus, Thies Thiemann

LCI Publisher GmbH, Eichenstrasse 3, D-20259 Hamburg, Germany
Fax: + 49 (40) 404 564
E-mail: henry@liqcryst.chemie.uni-hamburg.de


ABSTRACT

The database LiqCryst 2.1 contains chemical structure and physical properties of about 70000 thermotropic liquid crystals, extracted from 14000 references. Program and data represent a scientific tool which allows statitical analysis of structure-property-relationships and the prediction of phase transition temperatures by an similarity approach.

1. Introduction

The proliferation of data in many areas of science and technology has become immense. For the individual researcher it is increasingly difficult to search for vital information relevant to his subject. Moreover, it is often nearly impossible to see and evaluate new results within the context of existing data. A purely bibliographical documentation of knowledge is no longer suitable for these purposes. Very often only recent publications can be noted and information on neighboring areas of research can no longer be handled adequately.

One such area that has enjoyed an explosive development of information over the last three decades is liquid crystal science (LCS).1 Currently, LCS is represented by about 1% of the total entries in Chemical Abstracts (CAS). In addition, much information on LCS comes from patents, conference abstracts, and MSc- and PhD-theses, a great many of which have not even been incorporated within CAS. Clearly LCS would benefit from a subject-specific database.

2. Discussion

The original idea for the development of the database LiqCryst 1.0 was to provide a comprehensive documentation of all known liquid crystalline substances. Today LiqCryst 2.12 has matured from a pure data collection to a scientific tool which allows the user to test hypotheses on the relationship chemical structure - thermotropic behavior of mesomorphic compounds.

Currently the database includes:

Thus it has become possible to generate new data (analysis and prediction) from the compiled data. Examplary, this is shown below.

Currently the database encompasses the characteristics of 70.000 liquid crystalline compounds.4 These include simple aromatic systems such as stilbenes as well as such varied substances as steroids, lipids, tensides, organometallic compounds, and synthetic and natural polymers. Apart from the thermal behaviour of the compounds, references have been included on spectroscopic, dielectric, viscoelastic and other physical properties, loosely associated with the physical order of molecules. For the year 2000 more than 100.000 known liquid crystalline compounds can be expected. Updates of the database will be provided every 6 months (twice a year).

The program is based on Windows 3.1/95. Search entries for molecular structures can be performed either graphically or by text.The program operates with a newly developed substructure search engine. Physical characteristics such as phase transition temperatures or melting points, authors’ names, patent numbers or chemical similarity are only a few of the possible search modi. Apart from the actual output of the stored data, the program also offers a comparison of compounds or substructures in their liquid crystalline behaviour. Here, it is often possible to assess the change in liquid crystalline properties caused by a small change in molecular structure.

As an example an analysis of the difference in transition temperature ^T(N->I) of LCs with the substructure C5H11-Cy-COO-(R1) and C5H11-Ph-COO-(R1) is given in the following figures. Figure 1 shows just one pair of compounds with ^T(N-I) = 252°C - 270°C = -18°C. Figure 2 gives the complete statistical analysis of all pairs.


figure 1

Here, only the compounds are analysed, for which entries exist for both the phenyl- and the cyclohexyl compound.5 The graph of the difference in DTNI (cyclohexyl/phenyl) as a function of the transition temperature of the molecules themselves (in this case of the phenyl compounds) clearly shows that for compounds with a high transition temperature the cyclohexyl compounds show less thermal stability of the nematic phase than their aromatic counterparts.


figure 2

As a further function the database LiqCryst 2.1 provides the means for the prediction of the thermal behavior of a compound. The properties of the sought compound are calculated by using similarity relationships to known compounds of the total database. An example of an aromatic ester C8H17-O-Ph-OOC-Ph-COO-Ph-O-C8H17 is shown in Figure 3.


figure 3

Of the 19590 compounds within the database exhibiting a nematic phase, the TNI of 82% could be predicted to within +/- 10°C and of 93% to within ± 15°C.

3. Conclusion

Further developments of the program are scheduled for the near future. The application of neural networks for the prediction of liquid crystalline behavior has already been tested.6 The phase characteristics of mixtures of compounds are to be included soon. Within this context special emphasis is to be put on technically important mixtures. Furthermore, the relationship between intermolecular forces and molecular shape on the one hand and macroscopic data on the other is to be put into stronger perspective.


4. References

  1. V. Vill, Adv. Mater. 6, 527 (1994)
  2. V. Vill, LiqCryst 2.1 - Database of Liquid Crystalline Compounds for Personal Computers, Fujitsu Kyushu Systems (FQS) Ltd., Fukuoka, Japan, 1996; LCI Publisher GmbH, Hamburg, 1996. http://liqcryst.chemie.uni-hamburg.de
  3. T. Thiemann, V. Vill, Liq. Cryst., in press.
  4. for comparison: approximate number of LCs studied (by year): 35 (1900); 100 (1907); 1000 (early 1940s); 2000 (early 1950s); see also: F. Voegtle, Supramolekulare Chemie, Teubner Verlag, Stuttgart 1989, Chpt. 8.
  5. The effect of exchanging a phenyl-group as the central building block for a reduced cyclic structure was already studied in the 1970s: M. J. S. Dewar, R. S. Goldberg, J. Am. Chem. Soc. 92, 1582 (1970). With LiqCryst, however, such analysis can be performed using >>90% of the published literature data
  6. R. Schroeder, H. Kraenz, V. Vill, B. Meyer, J. Chem. Soc., Perkin Trans. 1685 (1996).

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