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Classification
Liquid crystalline (mesogenic) compounds can be differentiated into thermotropic, and lyotropic3. Thermotropic liquid crystals change phase with temperature. The transition from the crystalline solid to the mesophase is often termed as the melting point, while that from the highest mesophase to the isotropic liquid is called the clearing point. The mesophases often appear turbid while the isotropic liquid is clear. Thermotropic liquid crystals change phase upon heating or cooling.
When the mesophase is obtained by heating the crystalline solid as well as by cooling the isotropic liquid, the mesophase is said to be enantiotropic. Sometimes however, it is only possible to obtain a mesophase by cooling the isotropic liquid.
Such a mesophase is said to be monotropic. Lyotropic phases are formed by molecules in a solvent (generally water), and the concentration as well as the temperature control the appearance of the mesophase. Soap is an everyday example of a lyotropic liquid crystal.
Thermotropics can be further subdivided into two main groups, depending on their structural features. Liquid-crystal mesophases may be classified on the basis of the shape of the molecules, which give rise to the properties of the phase. The rod-like molecules are calamitic and the disc-like molecules are discotic4. Calamitic compounds have a structure in which the axial part is larger than the radial part (Figure 1.2).
Chapter General Introduction
1.1 Liquid Crystals
1.2 Classification
1.3 Mesophase characterization
1.4 Applications of Liquid Crystals
1.5 Metallomesogens
1.6 Thiophene as building block
1.7 Dithiocarboxylate ligands
1.8 Aim of Study
References
Chapter 2 Nickel(II) complexes with thiophene-containing ligands
2.1 Introduction
2.2 Results and discussion
2.3 Experimental section
2.4 Conclusion
References
Chapter 3 Zinc(II) complexes with thiophene-containing ligands
3.1 Introduction
3.2 Results and discussion
3.3 Experimental section
3.4 Conclusion
References
Chapter 4 Rhenium(I) complexes with thiophene-containing ligands
4.1 Introduction
4.2 Results and discussion
4.3 Experimental section
4.4 Conclusion
References
Chapter 5 Carbene complexes of Manganese(I) with thiophene-containing ligands
5.1 Introduction
5.2 Results and discussion
5.3 Experimental Section
5.4 Conclusion
References
Appendix 1
Appendix 2
