A soluble directly 2,2′‐linked tetracene dimer was synthesized. Dimerization of 8‐bromo‐2,3‐dihexyl‐5,12‐tetracenequinone afforded the corresponding bitetracenequinone, which was converted into a tetracene dimer by sequential addition of 1‐hexynyllithium and SnCl2/HCl. The synthesized tetracene dimer with four hexyl and four 1‐hexynyl groups was highly soluble in CH2Cl2 and THF, and the solutions were unstable under air and room light. The compound was studied by X‐ray single crystal analysis, UV/Vis, and fluorescence spectroscopy, cyclic voltammetry, and density functional theory (DFT) calculations. In the crystal, two tetracene rings take a coplanar conformation although DFT calculations demonstrated that such a molecular structure is energetically unfavorable. The tetracene dimer had red‐shifted absorption maxima and large molar extinction coefficients compared with the corresponding tetracene monomer. The tetracene dimer also showed amphoteric redox properties and p‐type semiconducting behavior.
The Front Cover shows a piece of ice in one glass and water in another glass; the former represents the solid phase of an unsubstituted directly‐2,2'‐linked tetracene dimer (2,2'‐TD), and the latter is the solution of the multi‐substituted 2,2'‐TD. The unsubstituted 2,2'‐TD reported by Rehan's group in 2017 could not be characterized, which may have been be due to its low solubility. On the other hand, the multi‐substituted 2,2'‐TD was highly soluble in organic solvents and could be characterized by several techniques such as NMR, UV/Vis spectroscopy, and X‐ray crystallography. More information can be found in the Full Paper by T. Honda, C. Kitamura et al.
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