Mesogenic properties of single ring compounds: dipentyl derivatives of p-carboranes and bicyclo[2.2.2]octane

Abstract

The dipentyl derivatives of 10- and 12-vertex p-carboranes and bicyclo[2.2.2]octane have been prepared and studied in the pure state and in binary mixtures with a nematic host. Only 1,4-dipentylbicyclo[2.2.2]octane was found to exhibit a monotropic nematic transition. The extrapolated virtual nematic-isotropic transition temperatures provide the expected order of ring effectiveness in supporting the nematic mesophase: bicyclo[2.2.2]octane>12-vertex p-carborane >10-vertex p-carborane. The results for the single ring derivatives [1]b were compared with clearing temperatures for the two-ring mesogens [2]c.

References

1. The only exceptions observed thus far are for those capable of forming intermolecular hydrogen bonding (e.g., carboxylic acids, diols) or with partially stiffened tails using e.g. fluorocarbons (S. Takenaka, Chem. Commun., 1992, 1748) and sigmatropic interactions (A. Mori, H. Takeshita, K. Kida and M. Uchida, J. Am. Chem. Soc., 1990, 112, 8635). For other examples see V. Vill, LiqCryst 3.1 database, LCI Publisher GmbH, Hamburg, Germany (http://liqcryst.chemie.uni-hamburg.de).
2. H. M. Abdullah, G. W. Gray and K. J. Toyne, Mol. Cryst. Liq. Cryst., 1985, 124, 105.
3. P. Kaszynski, J. Huang, G. S. Jenkins, K. A. Bairamov and D. Lipiak, Mol. Cryst. Liq. Cryst., 1995, 260, 315.
4. P. Kaszynski and D. Lipiak, in Materials for Optical Limiting, eds. R. Crane, K. Lewis, E. V. Stryland and M. Khoshnevisan, MRS, Pittsburgh, 1995, vol. 374, p. 341.
5. A. G. Douglass, M. Mierzwa and P. Kaszynski, SPIE, 1997, 3319, 59.
6. K. Czuprynski, A. G. Douglass, P. Kaszynski and W. Drzewinski, Liq. Cryst., 1999, 26, 261.
7. A. G. Douglass, K. Czuprynski, M. Mierzwa and P. Kaszynski, Chem. Mater., 1998, 10, 2399.
8. A. G. Douglass, K. Czuprynski, M. Mierzwa and P. Kaszynski, J. Mater. Chem., 1998, 8, 2391.
9. P. Kaszynski and K. Czuprynski, Liq. Cryst., submitted.
10. A. G. Douglass and P. Kaszynski, J. Org. Chem., submitted.
11. H. M. Abdullah, M.Sc. Thesis, Hull University, 1983.
12. G. M. Rubottom and C.-W. Kim, J. Org. Chem., 1983, 48, 1550.
13. Huang-Minlon, J. Am. Chem. Soc., 1949, 71, 3301.
14. A. D. Petrov, G. I. Nikishin and V. D. Vorob'ev, Bull. Acad. Sci. USSR, Div. Chem. Sci., 1960, 675.
15. The virtual transitions were extrapolated from a single data point and that for the pure host (ref. 2). The danger of such a procedure is apparent from the case of 2 for which some deviation from linearity is observed.
16. V. ReiVenrath and F. Schneider, Z. Naturforsch., 1981, 36a, 1006.
17. Correlation in Fig. 4 should be treated semiquantitatively at best at this point of investigations. Additional assumptions include a) virtual [T_NI] for 1,4-dipentylbenzene (4[1]b) in the host, b) equal treatment of N–I and S–I transitions for [2]c, c) equal effect of extending pentyl chain to the heptyl chain on mesogenic properties in the series.