The ESR Study of Gelator - Liquid Crystal Interactions

Thermotropic liquid crystal trans-4-heptylcyclohexanecarboxylic acid (HCCA) doped with 4-oxo-2, 2, 6, 6, -tetramethyl-1-piperidinyloxy spin probe (Tempone) is investigated by electron spin resonance (ESR) spectroscopy in the presence of chiral bisoxalamide gelator (1) during both cooling and heating cycles. In the temperature range where HCCA displays isotropic, nematic, smectic B and crystalline phases, the impact of (1) self-organization was investigated by partitioning of the spin probe in the environments varying in the polarity and the gelator oncentration. The evidence of the onset of the gelator network self-assembly in the nematic phase was detected by ESR at higher temperatures than the ones reported by other experimental techniques. The spectral analysis points to the switching of polarity in the vicinity of the spin probe when the transfer of chirality from (1) to HCCA occurs upon cooling the sample from isotropic to chiral nematic phase. When the gelation proceeds in the smectic phase, the melting of the gelator network appears in the nematic phase and could be studied during the heating cycle. The experimental evidence is provided that gelator network confines the HCCA into the domains within the bulk crystalline matrix where the local molecular dynamics are still not frozen.