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.