Extended π‑Conjugated Molecules Derived from Naphthalene Diimides toward Organic Emissive and Semiconducting Materials

In this paper, a new synthetic way to modify naphthalene diimide (NDI) at “shoulder” positions is reported. The key step of the transformation is the intramolecular cyclization involving ethynyl and imidecarbonyl groups. The structure of the intermediate pyrylium cation was confirmed by X-ray crystal structural analysis. New conjugated molecules 1a–g were successfully synthesized in acceptable yields. Their absorption and fluorescence spectra were measured. Among them 1c–f are strongly emissive in solutions. Furthermore, 1b–f are also fluorescent in their solid states; in particular, 1b exhibits a typical aggregation-induced enhanced emission feature. Yellow-emissive microfibrils of 1d show potential optical waveguide behavior. HOMO/LUMO energies of 1a–f were determined based on their cyclic voltammograms. The results also reveal that HOMO/LUMO energies of these new conjugated molecules are influenced by the two flanking moieties. Notably, the thin film of 1c that is emissive shows p-type semiconducting behavior with hole mobility up to 0.0063 cm2 V–1 s–1 based on the transfer and output characteristics of the OFET (organic field effect transistor).