Electron spin resonance study of nitroxide spin probes dissolved in the discotic mesophase of hexakis(n-hexyloxy)triphenylene

ESR spectra of five nitroxide spin probes dissolved in the discotic mesophase of hexakis(hexyloxy)triphenylene (THE6) were measured as function of temperature in the mesophase region. The different spin probes exhibit a variety of line shapes and temperature dependencies. The results could be explained in terms of the existence of two solvation sites for the probe molecules. These sites are assumed to correspond to (I) probe molecules intercalated within the columnar structures of the discotic mesophase and (II) probe molecules dissolved in the aliphatic region between the columns. In one case (CSL) the experimental results actually exhibited distinct spectra due to two solvation sites. The other spin probes gave simpler spectra but their temperature dependence was unusual and could in general be interpreted in terms of fast dynamic equilibrium between the two solvation sites.