ИСТИНА

The most detailed characteristic of molecular orientation is the orientation distribution function (ODF) that gives quantity of molecules oriented in given angular interval. A method which allows determining ODF of the magnetic axes of paramagnetic molecules by numerical simulation of EPR spectra angular dependence was developed. Recently a special procedure was worked up for determination ODF of a principal orientational axis of spin probe molecule. In the present work this method as well as the well-known method [D.E.Budil, S.Lee,S.Saxena, J.H.Freed, J. Magn. Reson. Ser.A, 120 (1996) 155-189.] were applied for investigation of structure and dynamic properties of nematic and smectic liquid crystals aligned by magnetic field or by surface of pores in porous polyethylene. Radicals R1, which are rigid molecules with anisometric shape, and radicals R2, bearing photoactive azobenzene and paramagnetic nitroxide moieties, were used as a paramagnetic probes. ODFs of the spin probes were determined in various liquid crystals. It was found that difference between liquid crystal orientation in different mesophases and at different temperatures can be quantitatively studied using radicals R1. It was shown that orientational alignment of R2 changes dramatically as a result of cis-trans isomerization of azobenzene fragment.