Electron paramagnetic resonance study of the photo-excited triplet state of pyrene-d-10

Electron paramagnetic resonance absorption has been observed at room temperature in pyrene-d-10 orientated in fluorene when irradiated with light from an AH6 mercury lamp. Measurements were made at a frequency of 9·4Gc.p.s. The long principal magnetic axis in the plane of the pyrene-d-10 was taken as the x-axis, the short axis in the plane to be the y-axis, and the normal to the plane to be the z-axis. The results have been described by the spin Hamiltonian. with The pyrene-d-10 does not fit perfectly into a fluorene substitutional site. The pyrene plane is inclined to the fluorene crystal b axis at 30°0′ ± 15′, as compared to 34°50′ for the fluorene host molecules.