Dual phosphorescence from 5-methylbicyclo[4.3.01,5]non-1-en3-one

Phosphorescence has been simultaneously observed from both a ³π, π* and a ³n,π* level of 5-methylbicyclo-4.3.0^1,5non-1-en-3-one. The emission from the higher energy ³n,π* state, which is in thermal equilibrium with the ³π,π* state, is quenched by lowering the temperature and also quenched by increasing the solvent polarity so as to raise the energy of the ³n,π* state relative to the ³π,π* state.