To date, the development of high-performance n-type organic semiconductors has remained challenging due to the scarcity of highly electron-deficient π-conjugated structural units and the difficulty of controlling intermolecular packing in the thin-film state. In addition, there have been few reports on the use of dimer design to tune the optoelectronic properties of materials. Herein, we report new cyano-substituted fluoranthene imide-based dimers (F16 and F17) for small-molecule n-type organic semiconductors. It is noteworthy that substituents at different positions lead to different film morphologies and very distinct thermal aggregation behaviors due to different dihedral angles. The self-assembly behavior of F17 improves thermal stability. Therefore, F17, which has a closer cyano groups structure, exhibits better field-effect transistor performance, with a maximum mobility of 6.6 × 10-4 cm2 V-1 s-1, while F16 does not exhibit any transistor performance.