An extensive study of interactions between nitroxide spin probe solutes and the liquid crystalline solvent 4-cyano-4’-n-pentylbiphenyl (5CB) has been carried out. The visual results show that, at the spin probe concentrations used in the ESR experiment, the spin probe does not affect the sharpness of the nematic-to-isotropic transition temperature. As expected the ESR results show that both the hyperfine splitting a and the g-value depend on the ordering matrix parameter. Moreover, hyperfine splitting values were used to arrive at values for the order parameter of PD-Tempone and solvent potential parameters at different temperatures. The line-width analysis of the ESR spectra of PD-Tempone in the nematic and isotropic phases of 5CB was carried out to examine the different factors affecting the relaxation mechanism of PD-Tempone. Our analysis shows that anisotropy in both the nematic and isotropic phases, orientational fluctuation on either side of the nematic;to-isotropic transition, and the ordering potential in the nematic and crystal phases are the main factors influencing the relaxation mechanism of PD-Tempone.