Ortho- vs Bay-Functionalization: A Comparative Study on Tetracyano-Terrylenediimides

In this paper n-type semiconductors synthesized via selective fourfold cyanation of the ortho- and bay-positions (2,5,10,13- and 1,6,9,14-positions respectively) of teyrrylenediimides are reported. A detailed study about the impact of the diverse functionalization topologies on the optoelectronic properties, self-organization from solution, solid-state packing, and charge carrier transport in field-effect transistors is presented. The ortho-substitution preserves the planarity of the core and favors high order in solution processed films. However, the strong intermolecular interactions lead to a microstructure with large aggregates and pronounced grain boundaries which lower the charge carrier transport in transistors. In contrast, the well-soluble bay-functionalized terrylenediimide forms only disordered films which surprisingly result in n-type average mobilities of 0.17 cm2/Vs after drop-casting with similar values in air. Processing by solvent vapor diffusion enhances the transport to 0.65 cm2/Vs by slight improvement of the order and surface arrangement of the molecules. This mobility is comparable to highest n-type conductivities measured for solution processed PDI derivatives demonstrating the high potential of TDI-based semiconductors.