How we obtained the abnormal NIR-absorbing hydrocarbon.
The focused paper describes the synthesis and properties of a new C70-fragment exhibiting NIR-absorption up to 1300 nm. In this article, I would like to describe the personal background to obtain this abnormal polycyclic aromatic hydrocarbon.
The focused paper "as-Indaceno[3,2,1,8,7,6-ghijklm]terrylene as a near-infrared absorbing C70-fragment" describes the synthesis and properties of a new C70-fragment exhibiting NIR-absorption up to 1300 nm. Importantly, as-indacenoterrylene is stable despite the absence of peripheral substituents, which contrasts with the cases of other NIR-absorbing hydrocarbons such as diradicaloids and antiaromatic molecules. 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. The results of this study thus offer fundamental insights into the design of hydrocarbons with a small band gap.
The paper describes the general background, results, discussion, and importance of this study. However, it doesn't include the personal background to obtain this abnormal polycyclic aromatic hydrocarbon. In this article, I would like to describe it.
Our motivation for the research is to create interesting molecules by means of the power of synthetic organic chemistry with our original guideline for the molecular design, rather than to produce some "apparently" useful molecules. Accordingly, several internally oxidized aromatic hydrocarbons were synthesized, including methoxy-substituted as-indacenoterrylene (compound 7 in the paper). The initial motivation was to find novel phenomena driven by the unique structure. However, during this study, we noticed that this molecule could be converted to a new C70-fragment by several-step transformations. As driven by our curiosity, we put the initial motivation aside and transformed the "desired molecule" to as-indacenoterrylene. Finally, we obtained a surprising result that the as-indacenoterrylene exhibits NIR-absorption reaching 1300 nm.
The current finding is a serendipity at least for me. as-Indacenoterrylene is distinctly different from other NIR-absorbing hydrocarbons such as diradicaloids and antiaromatic molecules because this molecule doesn't require kinetic stabilization by peripheral substituents. Although the exact reason for the NIR-absorption remains unclear, the current study demonstrates that NIR-absorption is compatible with high stability even in aromatic hydrocarbons. We are planning to synthesize other NIR-absorbing aromatic hydrocarbons with our new guidelines. These molecules will be useful in the future for the development of next-generation solid-state materials such as organic conductors and organic batteries.
Yuki Tanaka, Norihito Fukui & Hiroshi Shinokubo
as-Indaceno[3,2,1,8,7,6-ghijklm]terrylene as a near-infrared absorbing C70-fragment
Nat. Commun.11, 3873. (2020)
Group website: http://www.chembio.nagoya-u.ac.jp/labhp/organic1/index.html