Logarithmic decay of photochemically induced two-level systems in an organic glass

The recovery dynamics of photochemically labeled, metastable sites are investigated via photochemical hole burning in the visible spectral range. It is shown that, in a glass matrix, the recovery follows a logarithmic law. The experimental data are interpreted with the concept of two-level systems (TLSs). This interpretation is supported by the observed large isotope effect. The tunneling rates for protons and deuterons and the heights of the pertinent tunneling barriers are discussed.