Electron spin resonance spectra and orientation of 3,4-bis(dicyanomethylene)cyclobutane-1,2-dione and tetracyanoquinodimethane radical anions in liquid crystals

Abstract

The e.s.r. spectra of 3,4-bis(dicyanomethylene)cyclobutane-1,2-dione (BDCB) and tetracyanoquinodimethane (TCNQ) radical anions have been recorded in the isotropic and nematic phases of p-azoxyanisole. The variations of the 14N and 13C hyperfine splitting constants are used to evaluate the preferred orientation of the molecules in the liquid crystals. The experimental data are best accounted for by assuming for BDCB a non-axial orientation matrix, and for TCNQ a nearly axial orientation matrix with the singular direction coincident with the long axis of the molecule.