Structure and properties of naphthalene-diimide N-functionalized with stilbene

Derivatives of naphthalene-diimide (NDI) are among the most studied and popular organic semiconductors showing n-type conductivity. However, the structure and optoelectronic properties of crystalline NDIs N-functionalized with conjugated donors have not been investigated yet. In this study, a novel donor-acceptor compound NDI-Stb bearing one NDI core, as an acceptor, and two stilbene moieties covalently linked via imide positions of NDI, as a donor, was synthesized. A combined experimental and theoretical approach was applied to study the structure and properties of NDI-Stb molecules and its crystals. We found and explained why optical absorption and high-frequency Raman spectra are inherited from those of donor and acceptor moieties, but photoluminescence is determined by the properties of the whole molecule. We resolved the structure of NDI-Stb single crystals and found that strong intermolecular interactions operate along two directions, for which NDI cores stack either on similar cores or on stilbene moieties. These interactions cause suppression of dynamic disorder indicated by a weak low-frequency Raman signal and solid-state luminescence enhancement. Ambipolar charge transport was predicted, and electron transport was experimentally observed in NDI-Stb polycrystalline thin films. The results obtained highlight the potential of using NDIs N-functionalized with conjugated donor moieties in optoelectronic applications, and improve the understanding of structure-property relationships necessary for the rational design of novel donor-acceptor organic semiconductors.