Paramagnetic resonance in phosphorescent aromatic hydrocarbons

Abstract

Electron resonance spectra are presented of the phosphorescent state of the mesitylene species C₆H₃(CD₃)₃ in a B-trimethylborazole host crystal. The fine structure does not correspond to trigonal symmetry of the spin distribution and it varies with temperature:

The z axis is perpendicular to the molecular plane and the y axis along a H-C-C-CD₃ diagonal to within a few degrees.

Hyperfine structure is only resolved for H‖x, where one obtains a doublet with a splitting of 12–13 g. The data are consistent with a dominant interaction with a single proton bonded to a carbon atom carrying a spin density of about 0·34.

The results are discussed in terms of the pseudo Jahn-Teller instability of the ³ B _1u state of the benzene π-electron system.