Assignment of the Excited Electronic States of Two Methylazabenzyl Radicals

Abstract

The radicals 3,5‐dimethyl‐4‐azabenzyl and 3‐methyl‐2‐azabenzyl have been prepared from s‐collidine (2,4,6‐trimethylpyridine) and 2,6‐lutidine (2,6‐dimethylpyridine) by photolysis in a rigid organic solution and studied by means of three‐step photoselection. Two excited states of the radicals are found, one at about 2.6 eV and the other at about 4.1 eV. These are assigned the symmetries ${}^2{A}_2$ and ${}^2{B}_2$ (in $C_{\text{2υ}}$ ), respectively. The phosphorescence of s‐collidine in an organic matrix is described. The novel technique of “changing‐axis” photoselection is described and is used in the assignment of the 3‐methyl‐2‐azabenzyl radical. This technique also substantiates the in‐plane character of the transition moment of 2,6‐lutidine in its 270‐nm absorption band.