Pi Complexes between Organic Free Radicals

Abstract

The spectroscopic and magnetic properties of N‐ethylphenazyl and Wurster's blue perchlorate show characteristic changes at low temperatures. Using Mulliken's charge‐transfer theory, we have shown that the formation of π complexes can account for these changes. The intense long wavelength absorption band which appears at low temperatures in both cases, is attributed to a transition to a state which is an antisymmetrical combination of two charge‐transfer configurations, in which all the electrons are paired. We have compared the properties of these π complexes with the properties of the biradicals related to 4,4′‐bis‐diphenylmethylenediphenyl (chichibabin hydrocarbon.)