Rational Design of Ambipolar Organic Semiconductors: Is Core Planarity Central to Ambipolarity in Thiophene–Naphthalene Semiconductors?

Herein, we report a new family of naphthaleneamidinemonoimide‐fused oligothiophene semiconductors designed for facile charge transport in organic field‐effect transistors (OFETs). These molecules have planar skeletons that induce high degrees of crystallinity and hence good charge‐transport properties. By modulating the length of the oligothiophene fragment, the majority carrier charge transport can be switched from n‐type to ambipolar behavior. The highest FET performance is achieved for solution‐processed films of 10‐[(2,2′‐bithiophen)‐5‐yl]‐2‐octylbenzo[lmn]thieno[3′,4′:4,5]imidazo[2,1‐b][3,8]phenanthroline‐1,3,6(2 H)‐trione (NDI‐3 Tp), with optimized film mobilities of 2×10−2and 0.7×10−2cm2V−1s−1for electrons and holes, respectively. Finally, these planar semiconductors are compared with their twisted‐skeleton counterparts, which exhibit only n‐type mobility, in order to understand the origin of the ambipolarity in this new series of molecular semiconductors.