Triplet state electron spin resonance studies of aryl cations. Part 5.—The aryl cation/aryl radical product ratio in photolysis of arenediazonium salts at 77 K1

Abstract

An e.s.r. study has been made of the factors (solute concentration, matrix, irradiation wavelength and time, post-photolysis storage) affecting the relative yields of ³Ar⁺ and Ar˙ in the photolysis of an arenediazonium salt at 77 K. The principal findings are: (i)(in contrast with the situation prevailing in solution) photoheterolysis is the sole primary process; (ii) production of Ar˙ during irradiation comes from photoreduction of ³Ar⁺; (iii) there is a very powerful solute-concentration dependence of the photo-conversion of ³Ar⁺ into Ar˙(which does not proceed at very low solute concentrations); (iv) conversion of ³Ar⁺ into Ar˙ proceeds slowly in the dark. Mechanistic aspects of these observations are discussed.