| Abstrakt: |
Electron mobilities have been measured in vapor-deposited layers of N-(1,2-dimethylpropyl)benzo[k,l]thioxanthene-3,4-dicarboximide-7,7-dioxide (BTDD) and N,N'-bis(1,2-dimethylpropyl)-1,4,5,8-naphthalenetetracarboxylic diimide (NTDI). BTDD is a highly polar acceptor molecule that incorporates both an imide and a sulfone electronegative functionality. NTDI is a weakly polar acceptor molecule that contains two imide functionalities. The results are described by a formalism based on disorder, due to Bässler and coworkers. The formalism is based on the assumption that transport occurs by hopping through a manifold of localized states that are distributed in energy. The key parameter of the formalism is ?, the energy width of the hopping site manifold. The width is described by a model based on dipolar disorder. The model is premised on the argument that the width is comprised of a dipolar component ?dand a van der Waals component ?vdW. Describing the dipolar component by an expression due to Young yields ?d=0.133 eV for BTDD and 0.009 eV for NTDI. The van der Waals component for both molecules is 0.092 eV. The difference in the dipolar component is the principal reason for the large difference in mobility of these molecules. |
