Tunneling dynamics of doped organic low-temperature glasses as probed by a photophysical hole-burning system

We studied the photophysical hole-burning system tetracene in alcohol glass. The relaxation dynamics of the hole obeys logarithmic time laws. The analysis of the logarithmic laws yields information on the dispersion of the relaxation processes involved. Experiments with deuterated alcohol glass show that the spectral diffusion is governed by proton-tunneling processes. From the observation of two isoabsorptive points and the fact that the integrated absorption of the product is less than that of the hole, it is concluded that the photoreaction is most probably due to a light-induced rotation of the probe molecule in the glass. The barrier heights of the product state are sampled between 3 and 25 K and are shown to follow closely the tunneling model. We finally report on thermally induced spectral diffusion processes which are shown to follow a nonlinear power law in temperature.