ELECTRON-TRANSPORT IN VAPOR-DEPOSITED NAPHTHALENE DICARBOXIMIDE GLASSES

Electron mobilities have been measured in vapor-deposited layers of nz o[k,1]thioxanthene-3,4-dicarboximide-7,7-dioxide (BTDD) and dimethylpr opyl)-1,4,5,8-naphthalenetetracarboxylic diimide (NTDI). BTDD is a hig hly polar acceptor molecule that incorporates both an imide and a sulf one electronegative functionality. NTDI is a weakly polar acceptor mol ecule that contains two imide functionalities. The results are describ ed by a formalism based on disorder, due to Bassler 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 sigma, the energy width of the hopping site manifold. The width is described by a model based on dip olar disorder. The model is premised on the argument that the width is comprised of a dipolar component sigma(d) and a van der Waals compone nt a,dw. Describing the dipolar component by an expression due to Youn g yields sigma(d) = 0.133eV for BTDD and 0.009eV 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.