ИСТИНА

It is known that EPR spectra contain information on the orientation distribution of anisotropic paramagnetic molecules in a sample. The information is reflected in the dependence of the spectrum shape on a sample position relatively to the magnetic field direction. Commonly the averaged parameters characterizing orientation of radicals are determined from EPR spectra. Recently, a special method was developed, which allows to determine the most exact characteristics of the orientational order – the orientation distribution function ρ(α,β,γ) by analysis of the EPR spectra angular dependence [Vorobiev A. Kh., Chumakova N. A., J. Magn. Reson. 175 (1) (2005) 146-157.]. The method is based on simultaneous numerical modelling of the EPR spectra, recorded at various positions of the sample in magnetic field. At present time the method is successfully applied for determination of structure and dynamic properties of aligned liquid crystals and stretched polymers. Various nitroxide radicals were used as spin probes. The considerable increasing of sensitivity of the method has been achieved by the use of a new type of nitroxide radicals which possess liquid crystal properties: 2,5-dimethyl-2-alkoxyphenyl-5-[4-(4-alkoxybenzenecarbonyloxy)phenyl]pyrrolidine-1-oxy derivatives.