Orientational order of guest molecules in aligned liquid crystal 4-cyano-4′-pentylbiphenyl (5CB) is studied via optical dichroism and electron paramagnetic resonance (EPR) spectra measurements. The guest molecules used are bifunctional molecules bearing paramagnetic nitroxide group and photochromic azobenzene moiety. The bifunctional probe with rigidly bonded nitroxide and azobenzene moieties was found to align as a whole, while flexible long spacer between the moieties provides independent alignment for the nitroxide and azobenzene parts. Intermolecular interactions responsible for the alignment of azobenzene and nitroxide moieties of the probe molecules are discussed. The molecules with cis-configuration of azobenzene moiety are able to align in the liquid-crystalline medium, but to a lesser extent than the molecules with trans-configuration. Directions of orientational axes and characteristics of rotational mobility of spin probes are determined. Second, fourth and, in some cases, sixth rank order parameter values are found.

The orientational alignment of graphene oxide membranes was determined quantitatively using the spin probe technique; the values of the orientational order parameters up to the 6th rank were obtained.

Stable nitroxide radicals with rigid core were used as spin probes for investigation of orientational order of nematic liquid crystals MBBA and 5CB, uniaxially stretched polyethylene and porous polyethylene. The orientation distribution functions of probe molecules were determined. The order parameters of the true orientation axes were estimated. It was demonstrated that the novel nitroxide radicals show orientational alignment of both liquid crystals and polymers more effectively than ordinary spin probes.