VIBRATIONAL POPULATION RELAXATION OF PERYLENE IN ITS GROUND AND EXCITED ELECTRONIC STATES

We report a novel scheme for the measurement of molecular vibrational population relaxation in both ground and excited electronic states using ultrafast stimulated spectroscopy. We demonstrate this technique using 10(-5) M perylene in n-pentane, n-hexane, and n-heptane. The vibrational population relaxation times (T-1) of the perylene v(7) mode are 304 +/- 44 ps in the ground state and 140 +/- 11 ps in the first excited singlet state, and both T-1 times are solvent independent to within the experimental uncertainty. In contrast, we find that the T-1 relaxation time of the perylene ground state v(5) mode exhibits a measurable solvent dependence, ranging from 160 +/- 37 ps in n-pentane to 308 +/- 41 ps in n-heptane.