Novel nitroxide biradical probe with spiro-fused rigid core for EPR determination of rotational mobility and orientational order of soft materials

Abstract High sensitivity of electron paramagnetic resonance spectra of spiro-fused dinitroxide probe to dynamical and structural characteristics of the matrix was experimentally demonstrated. Geometrical parameters describing the relative position and orientation of nitroxide fragments of the biradical, as well as characteristics of dipolar and exchange interaction between the nitroxide moieties were determined from experimental spectra. Orientation order parameters of biradical dissolved in aligned smectic and supercooled smectic media determined by numerical simulation of the angular dependence of electron paramagnetic resonance spectrum show very high degree of orientation of the probe in the liquid-crystalline matrix.