Diketopyrrolopyrrole (DPP) and its derivatives have been widely studied in the past few years due to its intrinsic physical and chemical properties, such as strong electron-withdrawing, deep color, high charge carrier mobility, strong aggregation, good thermal-/photo-stability. In the 1970s, DPP was developed and used only in inks, paints, and plastics. Later, DPP containing materials were found to have potential other applications, typically in electronic devices, which attracted the attention of scientists. In this feature article, the synthesis pathway of DPP-based materials and their applications in organic field-effect transistors, photovoltaic devices, sensors, two photo-absorption materials, and others are reviewed, and possible future applications are discussed. The review outlines a theoretical scaffold for the development of conjugated DPP-based materials, which have multiple potential applications.

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Recent research on organic semiconductors has revealed that the composition of the constituent organic material, as well as the subtle changes in its structure (the stacking order of molecules), can noticeably affect its bulk properties. One of the reasons for this is that the charge transport in conjugated materials is strongly affected by their structure. Further, the charge mobility increases significantly when the conjugated materials exhibit self-assembly, resulting in the formation of ordered structures. However, well-organized nanostructures are difficult to obtain using classical solution processing methods, owing to their disordered state. A simple strategy for obtaining well-ordered material films involves synthesizing new conjugated materials that can self-organize. Introducing hydrogen bonding in the materials to yield hydrogen-bonded material superstructures can be a suitable method to fulfill these critical requirements. The formed hydrogen bonds will facilitate the assembly of the molecules into a highly ordered structure and bridge the distance between the adjacent molecules, thus enhancing the intermolecular charge transfer. In this minireview, hydrogen-bonded small molecules and polymers as well as the relationship between their chemical structures and performances in organic field-effect transistors are discussed.

Device-to-device (D2D) content sharing, as a promising solution to rapidly growing mobile data traffic, is facing serious security issues. Hence, how to ensure its security is challenging and meaningful work. Covert communication is regarded as an emerging and cutting-edge security technique for its higher level of security and less need for channel state information (CSI), and accordingly, has attracted wide attention. However, it is not easy to directly apply covert communication to D2D content sharing to ensure both security and efficiency. In this paper, a novel covert communication model is constructed in D2D content sharing scenario, where the co-channel interference (CCI) introduced by spectrum reusing is exploited as the cover of contents so that the contents are hidden from the warden. Then, we propose a secure and efficient resource allocation scheme to ensure both security and efficiency of D2D content sharing by addressing the following two issues: 1) In order to guarantee the robustness of our scheme, covert constraints are learned by analyzing the detection performance at the warden, i.e., the security of D2D content sharing is guaranteed even considering some extremely adverse environments. 2) The joint spectrum allocation and power control is modeled as a two-sided matching problem and then reformulated as the one-to-one matching game based on the principle of mutual benefit, in order to ensure the quality of service (QoS) requirements of both D2D pairs and cellular users. Then, covert constraints guaranteed resource allocation algorithm based on Gale-Shapley algorithm is proposed. Its properties such as stability, optimality, convergence, and complexity are analyzed. The extensive simulation results are provided to verify the theoretical analyses and demonstrate the efficiency of our proposed algorithm, which has at least 7.63% performance gain compared with some existing approaches and no more than 4.83% performance loss compared with the exhaustive search. INDEX TERMS D2D content sharing, covert communication, co-channel interference, resource allocation, matching game.