Impact of Alkyl Side Chain Length on Morphological Properties and Magnetic Field Response Characteristics of Naphthalenediimide-Based Conjugated Polymer

The molecular structure and magnetic properties of two conjugated polymer molecules, which have the same core of naphthalene diimide (NDI) but varying alkyl side chain lengths of 2-hexyldecyl (P(NDI2HD-T2)) and 2-octyldodecyl (P(NDI2OD-T2)), are compared. Microstructural characterizations revealed that the P(NDI2HD-T2) film exhibits a shorter π-π stacking distance and more pronounced crystalline behaviors when compared to the P(NDI2OD-T2) film. In addition, the magnetically aligned P(NDI2HD-T2) film exhibited a higher degree of chain alignment compared to the P(NDI2OD-T2) film grown using the same film preparation method. The organic field-effect transistor (OFET) based on the resulting P(NDI2HD-T2) film exhibited an average electron mobility of 1.49 cm2 V−1 s−1, which is about a 13.5-fold enhancement compared to the spin-coat film. The findings of our study offer valuable insights into the process of magnetic manipulation, thereby offering guidelines for the rational selection of polymers to fabricate highly ordered films via the magnetic alignment method.