Trapped Anions in Organic Crystals

Abstract

This chapter describes the structure and reaction of the radical anions of organic molecules studied mainly by single crystal ESR and ENDOR spectroscopy. The study makes it possible to precisely determine ESR parameters such as g, hyperfine, and quadrupole tensors. The geometrical and electronic structures of the radicals can be deduced from these parameters by comparing the tensor axes with the molecular orientation in the crystals. Analysis of the matrix ENDOR spectra yields information on the crystalline environment of the radicals which provides for a better understanding of the radical reactions in crystals. The radical anions can be formed along with the counter cations by irradiating the crystal with ionizing radiation. The anions are usually unstable but can be trapped in low temperature solids. Firstly, a characterization of the anions is given in terms of simple molecular orbital theory. Secondly, the details of the structures and reactions of the anions reflecting the electronic state, conformation, and crystalline environment of the radical are discussed.