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The incorporation of heavy atoms into molecular backbone is an extremely straightforward strategy for fine-tuning the optoelectronic properties of organic semiconductors.However,it is rarely studied in n-type small molecules.Herein,by selenium substitution of NDI3HU-DTYM2,two Se-decorated core-expanded naphthalene diimides (NDI) derivatives DTYM-NDI3HU-DSYM (1) and NDI3HU-DSYM2 (2) were synthesized.In comparison with the reference S-containing compound NDI3HU-DTYM2,the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of 1 and 2 were fine-tuned with ΔHOMO of about 0.2 eV,ΔLUMO of 0.1 eV and the narrowed HOMO-LUMO gaps.More surprisingly,the as-spun organic thin film transistors (OTFTs) based on 1 and 2 both showed μe,sat values as high as 1.0 cm2 V-1 s-1,which are 2-fold higher than that of NDI3HU-DTYM2 with the same device structure and measurement conditions.In addition,the single crystal OFET devices based on Se-containing compound NDI2BO-DSYM2 showed a high μe,sat value of 1.30 cm2 V-1 s-1.The molecular packing of NDI2BO-DSYM2 in single crystals (two-dimensional supramolecular structure formed by intermolecular Se…Se interactions) is quite different from that of a S-containing compound NDI-DTYM2 (one dimensional supramolecular structure formed by intermolecular π-π stacking).Therefore,the Se substitution can cause dramatic change about molecular stacking model,giving rise to high n-type OTFT performance.Our results demonstrated an effective strategy of the heavy atom effect for designing novel organic semiconductors.