EPR studies of the dynamics and phase behaviour of dithiadiazolyl radicals derived from mesogenic precursors
✍ Scribed by Jeremy M. Rawson; Caroline S. Clarke; Duncan W. Bruce
- Publisher
- John Wiley and Sons
- Year
- 2009
- Tongue
- English
- Weight
- 160 KB
- Volume
- 47
- Category
- Article
- ISSN
- 0749-1581
- DOI
- 10.1002/mrc.2326
No coin nor oath required. For personal study only.
✦ Synopsis
Abstract
A series of liquid‐crystalline materials based on 4‐substituted cyanobiphenyls, RC~6~H~4~C~6~H~4~CN (R = C~5~H~11~, C~6~H~13~, C~7~H~15~, C~8~H~17~ and C~12~H~25~, commonly referred to as 5CB, 6CB, 7CB, 8CB and 12CB, respectively) were functionalised to give the corresponding dithiadiazolyl organic radicals RC~6~H~4~C~6~H~4~CNSSN^•^ (compounds 1^•^, 2^•^, 3^•^, 4^•^ and 5^•^, respectively). EPR spectra of n‐C~12~H~25~C~6~H~4~C~6~H~4~CNSSN^•^ (5^•^) reveal that it adopts a dimeric diamagnetic structure in the solid state with a small number of paramagnetic defect sites. Variable temperature electron paramagnetic resonance (EPR) studies reveal a thermally activated rotation about the molecular long axis at temperatures above 314 K. The energy barrier to rotation about the phenylene–dithiadiazolyl bond was estimated as 25 kJ mol^−1^ using density functional theory (DFT). At elevated temperatures thermal annealing was also observed, quenching the sample's paramagnetism. Copyright © 2008 John Wiley & Sons, Ltd.