Alkyl-Substituted N,S-Embedded Heterocycloarenes with a Planar Aromatic Configuration for Hosting Fullerenes and Organic Field-Effect Transistors

Cycloarenes and heterocycloarenes display unique physical structures and hold great potential as organic semiconductors. However, the synthesis of (hetero)cycloarenes remains a big challenge, and there are limited reports on their applications. Herein, a series of nitrogen- and sulfur-codoped cycloarenes NS-Octulene-n (n = 2, 3, 4) with branched alkyl substituents containing linear spacer groups from C2 to C4 have been conveniently synthesized. Compared with their isoelectronic analogues Octulene and S-Octulene, both having a saddle-shaped configuration, the coincorporation of two nitrogen atoms and two sulfur atoms leads to a fully coplanar aromatic backbone structure. Each of these three planar heterocycloarenes acts as a supramolecular host for encapsulation of both fullerenes C60 and C70 with a stronger donor–acceptor interaction for the complexation between the heterocycloarene and C70 due to the unique molecular geometry and defined cavity. Meanwhile, the electron-rich nitrogen atoms also slightly increase the energies of both highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) in this series of planar heterocycloarenes, indicating that they can be used as p-type semiconductors. Most importantly, benefitting from the planar π-conjugated backbone structure accompanied by excellent crystallinity and ordered molecular packing, as well as upon the engineering of the alkyl chain branching position, thin-film field-effect transistors of NS-Octulene-3 with moderate alkyl branching point exhibit the maximum hole mobility of 0.86 cm2 V–1 s–1, which is the highest for (hetero)cycloarene-based organic semiconductors. This study will shed new light on designing novel high-performance macrocyclic polycyclic aromatic hydrocarbon (PAH) semiconductors.