Organic Radical Cations and Neutral Radicals Produced by Radiation in Low-Temperature Matrices

Abstract

Paramagnetic species produced by ionizing radiation in organic materials were studied extensively by EPR for 60 years. Using low temperature matrices made it possible to characterize a wide class of highly reactive radicals. More recently, the focus was shifted to the investigations of ionized molecules (radical cations). Several approaches based on frozen solution technique, trapping in porous media and rigorous matrix isolation method has been developed up to 1990s. The knowledge on structure and properties of radical ions is crucial for understanding fundamental processes in radiation chemistry and important for a number of various areas, including, radiobiology, physical organic chemistry and molecular electronics. This chapter presents a review of progress in the field during the past two decades with particular attention to the EPR studies of radical cations and radicals generated by high-energy irradiation of moderate-size organic molecules in solid noble gas matrices. The mechanisms and selectivity of the primary radiation-induced processes in organic solids are discussed with special impact on the role of “fine tuning” and matrix effects.