DEUTERATION EFFECT ON THE SPIN DYNAMICS OF THE PHOTO-EXCITED TRIPLET-STATE OF PENTACENE IN P-TERPHENYL CRYSTALS

The kinetic parameters of the photo-excited triplet state of pentacene in p-terphenyl crystals have been calculated from the electron spin e cho (ESE) decay curves in the temperature range of 5-300 K. The result s suggest the calculated decay parameters depend strongly on guest deu teration, especially from the long-axis T-x spin substate which can be explained in terms of the isotope effect on the non-radiative transit ions arising mainly from the Franck-Condon factor. The relative popula tions of the triplet sublevels and spin-lattice relaxation show little or no dependence on the deuteration of the pentacene molecule.