Naphthalene diimides, which have for a long time been in the shadow of their higher homologues the perylene diimides, currently belong to the most investigated classes of organic compounds. This is primarily due to the initial synthetic studies on core functionalization that were carried out at the beginning of the last decade, which facilitated diverse structural modifications of the naphthalene scaffold. Compounds with greatly modified optical and electronic properties that can be easily and effectively modulated by appropriate functionalization were made accessible through relatively little synthetic effort. This resulted in diverse interesting applications. The electron-deficient character of these compounds makes them highly valuable, particularly in the field of organic electronics as air-stable n-type semiconductors, while absorption bands over the whole visible spectral range through the introduction of core substituents enabled interesting photosystems and photovoltaic applications. This Review provides an overview on different approaches towards core functionalization as well as on synthetic strategies for the core expansion of naphthalene diimides that have been developed mainly in the last five years.

Core‐chlorinated naphthalene tetracarboxylic diimides (NDIs) with fluoroalkyl chains are synthesized and employed for n‐channel organic thin‐film transistors (OTFTs). Structural analyses of the single crystals and thin films are performed and their charge‐transport behavior is investigated in terms of structure–property relationships. NDIs with two chlorine substituents are shown to exhibit a herringbone structure with a very close π‐plane distance (3.3–3.4 Å), a large π‐stack overlap (slipping angle ca. 62°), and high crystal densities (2.046–2.091 g cm−3). These features result in excellent field‐effect mobilities of up to 1.43 cm2 V−1 s−1 with minimal hysteresis and high on–off ratios (ca. 107) in air. This is similar to the highest n‐channel mobilities in air reported so far. Despite the repulsive interactions of bulky Cl substituents, tetrachlorinated NDIs adopt a slip‐stacked face‐to‐face packing with an interplanar distance of around 3.4 Å, resulting in a high mobility (up to 0.44 cm2 V−1 s−1). The air‐stability of dichlorinated NDIs is superior to that of tetrachlorinated NDIs, despite of their higher LUMO levels. This is closely related to the denser packing of the fluorocarbon chains of dichlorinated NDIs, which serves as a kinetic barrier to the diffusion of ambient oxidants. Interestingly, these NDIs show an optimal performance either on bare SiO2 or on octadecyltrimethoxysilane (OTS)‐treated SiO2, depending on the carbon number of the fluoroalkyl chains. Their synthetic simplicity and processing versatility combined with their high performance make these semiconductors highly promising for practical applications in flexible electronics.

A novel naphthalene diimide with a fully conjugated, extended π-core was synthesized in a one-pot, two-step reaction. This organic semiconductor exhibits ambipolar transport properties with a large hole mobility of 0.56 cm(2) V(-1) s(-1) and a current on/off ratio of 10(6) in bottom-gate, top-contact thin-film transistors prepared by vacuum deposition.

High charge carrier mobility solution‐processed n‐channel organic thin‐film transistors (OTFTs) based on core‐chlorinated naphthalene tetracarboxylic diimides (NDIs) with fluoroalkyl chains are demonstrated. These OTFTs were prepared through a solution shearing method. Core‐chlorination of NDIs not only increases the electron mobilities of OTFTs, but also enhances their air stability, since the chlorination in the NDI core lowers the lowest unoccupied molecular orbital (LUMO) levels. The air‐stability of dichlorinated NDI was better than that of the tetrachlorinated NDIs, presumably due to the fact that dichlorinated NDIs have a denser packing of the fluoroalkyl chains and less grain boundaries on the surface, reducing the invasion pathway of ambient oxygen and moisture. The devices of dichlorinated NDIs exhibit good OTFT performance, even after storage in air for one and a half months. Charge transport anisotropy is observed from the dichlorinated NDI. A dichlorinated NDI with −CH2C3F7 side chains reveals high mobilities of up to 0.22 and 0.57 cm2 V−1 s−1 in parallel and perpendicular direction, respectively, with regard to the shearing direction. This mobility anisotropy is related to the grain morphology. In addition, we find that the solution‐shearing deposition affects the molecular orientation in the crystalline thin films and lowers the d(001)‐spacing (the out‐of‐plane interlayer spacing), compared to the vapor‐deposited thin films. Core‐chlorinated NDI derivatives are found to be highly suitable for n‐channel active materials in low‐cost solution‐processed organic electronics.

A new diketopyrrolopyrrole derivative 1 exhibits excellent hole mobilities of 0.7 cm(2) V(-1) s(-1) and a current on/off ratio of 10(6) under ambient conditions in bottom-gate, top-contact organic thin film transistors (OTFTs) fabricated by vacuum deposition.