Hyperfine structure observed in EPR spectra of polyphenylacetylene solutions

Abstract
The high‐temperature (>120C) electron paramagnetic resonance (EPR) spectrum of solutions of polyphenylacetylene have been deconvoluted into the spectra of two separate radicals, a delocalized π radical, whose EPR spectrum consists of a single 15‐G wide Gaussian line comprising about 90% of the total signal and a second, more localized π radical exhibiting complex hyperfine structure in its EPR spectrum. Some possible structures for the minor component radical are suggested and their hyperfine splitting constants calculated using molecular orbital theory.