Polarized absorption spectra of diphenylnitroxide

A polarization study of the low-lying electronic states of the diphenylnitroxide radical imbedded in a benzophenone single crystal is presented. Assignments are made for the first two electronic excited states: ${}^2\text{B}{}_2\text{(n → π}{}^1\text{)}$ at 569 nm and ${}^2\text{B}{}_1\text{(π → π}{}^1\text{)}$ at 431 nm. Vibronic coupling is invoked in inducing the $\text{n → π}{}^1$ transition. The electronic structure of the nitroxide bears some resemblance to the corresponding carbonyl. The delocalization of the π electrons is also discussed.