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 pi overlap along different directions in the crystals. A photogeneration efficiency anisotropy was also observed in both types of crystals.
Ostroverkhova, O., Cooke, D., Hegmann, F. A., Tykwinski, R. R., Parkin, S. R., & Anthony, J. E. (2006). Anisotropy of transient photoconductivity in functionalized pentacene single crystals. Applied Physics Letters, 89(19), 192113. https://doi.org/10.1063/1.2387135