Isoindigo-based aza-BODIPY small molecule for N-type organic field-effect transistors

To date, most of the reported conjugated materials are p-type semiconductors, while the advances in n-type or ambipolar conjugated materials greatly fall behind those in p-type counterparts. Well-defined n-type semiconductors should possess suitable electron-deficient groups and relatively low lowest unoccupied molecular orbitals (LUMO) levels that facilitate the electron injection and stabilize the electron transport. Thus, developing novel n-type semiconductor materials with strong electron-deficient property, high electron mobility, and competitive stability is still highly desirable, though challenging. Herein, a new isoindigo-based dimeric aza-boron dipyrromethene (aza-BODIPY) chromophore (IIDG-AB) is designed and synthesized. IIDG-AB contains multiple fluorine and unsaturated nitrogen atoms, which endow it with strong electron-deficient property as well as an ultra-low LUMO level of only −4.24 eV. In addition, IIDG-AB features a large conjugation system and a high degree of coplanarity, which are beneficial for effective intermolecular charge transfer. The UV/visible absorption spectra, X-ray diffraction analysis, and morphological studies via atomic force microscopy imaging indicate that the IIDG-AB thin film presents strong aggregation, good π-π stacking, and long-range order packing, all of which are favorable for the electron transfer between neighboring molecules. Furthermore, IIDG-AB-based organic field-effect transistors exhibit a moderate stable n-type behavior with the highest electron mobility of 1.1 × 10−1 cm2 V−1 s−1. This work provides a simple and effective strategy to synthesize highly functional n-type chromophores via a Schiff base reaction between bislactams and heteroaromatic amines, and also paves the way for future design to fabricate high-performance n-type semiconductor materials for a wide range of applications.