The 30 year anniversary of a seminal paper on radical ions in solution (Radical ions in photochemistry. I. The 1,1-diphenylethylene cation radical)

This article was written to serve as an introduction to this issue of the Canadian Journal of Chemistry that honors the contributions to chemistry of Professor D.R. Arnold. It summarizes the observations reported in a communication that appeared in the Journal of the American Chemical Society 30 years ago in June 1973. This historically important communication laid the foundation for his program on the photochemical generation and reactivity of radical ions in solution and also served as a guide for a developing area of interest of many other research groups. Key words: photochemical electron transfer, radical cations, photo NOCAS, benzylic radicals.