As-Indaceno[3,2,1,8,7,6-Ghijklm]terrylene: A Near-Infrared Absorbing C70-Fragment

Carbon and hydrogen are fundamental components of organic molecules and a fascinating plethora of functions can be generated using these two elements. Yet, realizing attractive electronic structures only by using carbon and hydrogen remains challenging. Herein, we report the synthesis and properties of the C70 fragment as- indaceno[3,2,1,8,7,6-ghijklm]terrylene, which exhibits near-infrared (NIR) absorption (up to ca. 1300 nm), even though this molecule consists of only 34 carbon and 14 hydrogen atoms. A remarkably small HOMO–LUMO gap was confirmed by electrochemical measurement and theoretical calculations. Nevertheless, as-indacenoterrylene is surprisingly stable despite the absence of peripheral substituents, which contrasts with the cases of other NIR-absorbing hydrocarbons such as biradicaloids and antiaromatic molecules. The low-energy absorption was attributed to the intramolecular charge- transfer from the electron-rich terrylene segment to the electron-deficient as- indacenopyrene segment. The results of this study thus offer fundamental insights into the design of hydrocarbons with a small band gap.

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