Acene‐Modified Small‐Molecule Donors for Organic Photovoltaics

The Journey for the Synthesis of Large Acenes

Acenes, the group of polycyclic aromatic hydrocarbons (PAHs) with linearly fused benzene rings, possess distinctive electronic properties with potential applicability in material science. Hexacene was the largest acene obtained and characterized in the last century, followed by heptacene in 2006. Since then, a race for obtaining the largest acene resulted in the development of several members of this family as well as diverse innovative synthetic strategies, from solid-state chemistry to the promising on-surface chemistry. This last technique allows the obtention of large acenes, up to tridecacene, the largest acene so far. This review presents the different methodologies employed for the synthesis of acenes, highlighting the newest studies, to provide a much more thorough understanding of the essence of the electronic structure of this captivating group of organic compounds.

On surface synthesis of an eleven-ring sulfur-doped nonacene

Dithienoacenes with a heptacene core, heptaceno[2,3-b:11,12-b']bis[1]benzothiophene, have been synthesized through the combination of solution and surface assisted chemistry. The atomic composition, structural arrangement and electronic properties of the molecules on the Au(111) surface have been deeply explored by non-contact atomic force microscopy (nc-AFM), bond-resolved scanning tunnelling microscopy (BR-STM) and scanning tunneling spectroscopy (STS) corroborated by density functional theory (DFT) calculations. Our combined experiments reveal modifications induced by sulfur substitution.

Octopus-inspired deception and signaling systems from an exceptionally-stable acene variant

Multifunctional platforms that can dynamically modulate their color and appearance have attracted attention for applications as varied as displays, signaling, camouflage, anti-counterfeiting, sensing, biomedical imaging, energy conservation, and robotics. Within this context, the development of camouflage systems with tunable spectroscopic and fluorescent properties that span the ultraviolet, visible, and near-infrared spectral regions has remained exceedingly challenging because of frequently competing materials and device design requirements. Herein, we draw inspiration from the unique blue rings of the Hapalochlaena lunulata octopus for the development of deception and signaling systems that resolve these critical challenges. As the active material, our actuator-type systems incorporate a readily-prepared and easily-processable nonacene-like molecule with an ambient-atmosphere stability that exceeds the state-of-the-art for comparable acenes by orders of magnitude. Devices from this active material feature a powerful and unique combination of advantages, including straightforward benchtop fabrication, competitive baseline performance metrics, robustness during cycling with the capacity for autonomous self-repair, and multiple dynamic multispectral operating modes. When considered together, the described exciting discoveries point to new scientific and technological opportunities in the areas of functional organic materials, reconfigurable soft actuators, and adaptive photonic systems.

Anthrathiadiazole Derivatives: Synthesis, Physical Properties and Two-photon Absorption

Anthrathiadiazole is a key synthon for the construction of large azaacenes, however, the attachment of different substituents onto the skeleton of anthrathiadiazole is difficult but highly desirable because it could be easy to enrich the structures of azaacenes. Here, it is demonstrated that anthrathiadiazole derivatives with -Br, -CN, and -OCH₃ groups could be easily constructed through a simple [4+2] cycloaddition reaction between a,a,a',a'-tetrabromo-o-xylenes derivatives and benzo[c][1,2,5]thiadiazole-4,7-dione. The structures of the as-prepared compounds with different substituents were carefully characterized. Moreover, the basic physical properties of the as-prepared anthrathiadiazole derivatives were fully investigated, where the cyano-substituted derivative (BTH-CN) has the highest stability and the methoxy-substituted derivative (BTH-OCH₃ ) is easy to be oxidized. Moreover, the two-photon absorption (TPA) characteristics of different anthrathiadiazoles are also studied by using the femtosecond Z-scan technique. The results show that the fused anthrathiadiazole skeletons possess large TPA cross-section values δ₂ in the range of 3000-5000 GM, where the nature, position and strength of the substituted groups have strong effect on these values.