Electronic and optical properties of functionalized pentacene compounds in the solid state

We describe physical measurements on a unique class of pentacene-based compounds [e.g., 6,13-bis(triisopropylsilylethynyl)pentacene] where additional symmetric side groups have been added to enhance their solubility in common organic solvents. Single crystals of these materials formed from precipitation consist of various it stacking configurations (columnar) of the pentacene molecules which are different from the herringbone motif of unsubstituted pentacene. Here we report the anisotoropic resistivity of single crystals of these materials, including the determination of activation gaps (of order 1 eV) obtained from Arrhenius analysis of the temperature dependent resistivity. We find that the resistivity at room temperature lies in the range 10(+5)-10(+10) Omega cm, depending on crystallographic direction and side-group placement and composition. We further describe the response of the conductivity to optical excitation, and present preliminary studies of the dependence of the conductivity on Iodine doping and hydrostatic pressure. (C) 2001 Elsevier Science B.V. All rights reserved.