ELECTRON-SPIN-RESONANCE LINEWIDTH STUDIES OF VANADYL TETRAPHENYLPORPHYRIN

The linewidths of the hyperfine components of the ESR spectra of vanadyl tetraphenylporphyrin in liquid toluene have been measured as a function of temperature and analyzed in detail. This has allowed the separate contributions to the observed ESR linewidths from spin rotational, g tensor anisotropy, hyperfine anisotropy and unresolved nitrogen hyperfine coupling to be evaluated. These results have been used to estimate the size of the nitrogen isotropic hyperfine coupling constant and thus the extent of delocalization of the unpaired electron onto the nitrogen atoms.