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New Heterocyclic Liquid Crystals

Final Activity Report Summary - HETEROLICS (New Heterocyclic Liquid Crystals)

When Dr Kozhevnikov arrived to undertake this project, he already had status as a lecturer in Russia. He made this experience count and rapidly assembled a wide range of new and exciting materials.

Firstly, he showed that the basic 1,2,4-triazine methodology could be applied to the preparation of some new liquid-crystalline materials with wide liquid crystal phase ranges, as reported by V. N. Kozhevnikov, S. J. Cowling, P. B. Karadakov and D. W. Bruce, in the Journal of Materials Chemistry, 2008, 18, 1703-10. This approach was extended to the preparation of new platinum(II) complexes of ligands containing both pyridine and thiophene as part of a project led by Dr Kozhevnikov and co-funded by the University of York, the Ural State Technical University in Ekaterinberg in Russia, i.e. his home institution, and The Royal Society of London. This work moved towards the preparation of efficient, light-emitting liquid crystals and was prepared for publication by the time of the project completion (V. N. Kozhevnikov, M. M. Ustinova, D. W. Bruce and D. N. Kozhevnikov, in preparation). Moreover, it led to a related project on the preparation of platinum(II) complexes of liquid-crystalline 2-phenylpyridine derivatives with emissive properties. The project was funded by the University of York as a PhD studentship which was co-supervised by Dr Kozhevnikov and Prof. Bruce. A full paper based on work carried out in during 2006 and 2007 was anticipated to be soon submitted for publication (A. Santoro, V. N. Kozhevnikov and D. W. Bruce, in preparation).

However, more significant was the extension of this methodology into the area of bent-core liquid crystals. This exciting area, developed during the last ten years, showed how chiral liquid crystal phases might be found in non-chiral molecules and led to a fresh look being taken at the interplay between molecular and mesophase symmetry. The first result in this area was the demonstration, for the first time, of inherently liquid-crystalline terpyridines, as described by V. N. Kozhevnikov, A. C. Whitwood and D. W. Bruce in Chemical Communications, 2007, 3826-8. This was significant as the terpyridine ligand was ubiquitous in coordination chemistry. These bent-core mesogens also showed spontaneous chiral phase formation; it was though found that grafting a fused cyclopentene ring onto the edge of the molecule changed the overall shape sufficiently, so that it behaved as a rod and not as a bent molecule. Furthermore, some metal complexes were prepared and found to be luminescent.

This general approach was then extended to the preparation of 1,3-di(2-pyridyl)benzene systems, whose chloroplatinum(II) complexes were known to be highly emissive. The approach was successful and emissive materials that formed columnar phases were prepared and protected by patent (V. N. Kozhevnikov and D. W. Bruce, UK Patent Application No. GB0718909.5; V. N. Kozhevnikov, B. Donnio and D. W. Bruce, submitted). More than that, it was found that the nature of the emission was subject to reversible tribological control. The way in which this could be exploited was pursued, by the time of the project completion, with the Physics Department at Imperial College.