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 echo (ESE) decay curves in the temperature range of 5–300 K. The results suggest the calculated decay parameters depend strongly on guest deuteration, especially from the long-axis Tx spin substate which can be explained in terms of the isotope effect on the non-radiative transitions arising mainly from the Franck-Condon factor. The relative populations of the triplet sublevels and spin-lattice relaxation show little or no dependence on the deuteration of the pentacene molecule.