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).