Paramagnetic resonance in phosphorescent aromatic compounds

Magnetic resonance spectra were recorded of glassy solutions of a number of positive aromatic ions in their triplet state, which theory predicts to be orbitally degenerate. The phenalenylium (I) and triphenylcyclopropenylium (II) cations, rather than exhibiting trigonal symmetry in their resonance spectra, are distorted. The distortion seems to result from a Jahn-Teller instability of the trigonally symmetric conformations, together with interaction with the solvent. In the triphenylmethyl cation (III) steric hindrance has a dominant influence. A symmetrical propeller type of structure has been proposed in the literature, but this model does not agree with our resonance spectra.