Four families of core-expanded naphthalene diimide (NDI) derivatives were designed and synthesized, namely, NDI-DTYM2 (1−7, of which 1 and 2 were previously reported), NDI-DTDCN2 (8 and 9), NDI-DTYCA2 (10 and 11), and NDI-DCT2 (12), where the NDI core fuses two 2-(1,3-dithiol-2-ylidene)malonitrile (DTYM) groups, two 1,4-dithiine-2,3-dicarbonitrile (DTDCN) groups, two alkyl 2-(1,3-dithiol-2-ylidene)cyanoacetate (DTYCA) groups, and two 2,3-dicyanothiophenes (DCT), respectively. The NDI cores of the present compounds bear the branched N-alkyl substituents with the carbon atom numbers from 12 to 24, which guarantees good material solubility. The solution-processed, bottom-gate organic thin film transistors based on new compounds 3−12 operate well in air with the electron mobility ranging from ∼10−6 to 0.26 cm2 V−1 s−1, depending on the nature of the branched N-alkyl substituent and the π-backbone structure.