Persistent photoexcited conducting states in functionalized pentacene

The photoexcited states in single crystals of functionalized forms of penatcene were analyzed. It was observed that relaxation rate of such forms is thermally activated, which was determined from time-and temperature-dependent measurements of photoconductivity after illumination. The thermally stimulated current (TSC) was observed in dark current with an increasing temperature, after low-temperature illumination. The TSC behavior indicates that carrier associated with photoexcited states are thermally activated at low temperatures, with an energy less than both intrinsic band-gap and trap energy. The results show that TSC signal allows estimation of energies associated with excited states.