Anisotropy of transient photoconductivity in functionalized pentacene single crystals

We report on the anisotropy of transient photoconductivity in functionalized pentacene single crystals using ultrafast optical pump-terahertz probe techniques. Functionalized pentacene crystals with tri-isopropylsilylethynyl (TIPS) and tri-ethylsilylethynyl (TES) side groups were studied, characterized by crystal structures favoring two-dimensional and one-dimensional charge transports, respectively. Charge carrier mobility anisotropies in the a - b plane of 3.5 ± 0.6 and 12 ± 6 were obtained in the TIPS and TES crystals, respectively, consistent with the degree of π overlap along different directions in the crystals. A photogeneration efficiency anisotropy was also observed in both types of crystals.