ESR of the Perinaphthenyl Radical in a Liquid Crystal

Abstract

The electron spin resonance spectrum of the perinaphthenyl radical has been studied in the isotropic and nematic phases of p‐azoxyanisole. The g tensor and hyperfine splitting tensors for the two proton couplings and three of the four carbon−13 couplings have been determined, and were found to agree in most cases with theoretical estimates. Ordering of the radical was also deduced as a function of temperature in the liquid‐crystal range, and corresponded to the ordering of the solvent molecules. A general expression for the effective spin Hamiltonian of a radical in a liquid crystal is derived. Zeeman anisotropy and dipolar electron—nuclear couplings are shown to result in g shifts and changes in the hyperfine splitting coefficients.