Looking from different perspectives! Proper electronic structure of near-infrared absorbing functional dyes discovered

An Osaka Metropolitan University joint research group has discovered that near-infrared absorbing dyes, which had previously been considered to have closed-shell electronic structures, have an intermediate electronic structure, between closed- and open-shell structures. They also found that as the wavelength of near-infrared light that can be absorbed becomes longer the contribution of open-shell forms increases within the dye. These newly discovered characteristics are expected to be utilized to develop new near-infrared absorbing dyes that can absorb longer wavelength near-infrared light.

Illustration of properties and electronic structure of a near-infrared absorbing dye in an intermediate state between closed- and open-shell states

Near-infrared light, whose wavelength is longer than visible light, is invisible and can pass through many substances. Organic materials that efficiently absorb near-infrared light are essential for technological innovations that utilize near-infrared light, such as the dyes in the infrared blocking filters of smartphone cameras and security inks. These and many more technical applications make developing new dyes that can absorb longer wavelengths of near-infrared light desirable.

Previously, near-infrared absorbing organic materials were treated as closed-shell molecules without unpaired electrons. However, a joint research group led by Associate Professor Takeshi Maeda, Assistant Professor Daisuke Sakamaki, and Professor Hideki Fujiwara from Osaka Metropolitan University discovered that near-infrared absorbing oxocarbon-based dyes have an intermediate state between closed-shell and open-shell electronic configurations. They also found that as the wavelengths of near-infrared light absorbed increase, so does the contribution of open-shell forms in the dye.

"We have clarified the proper electronic structure of near-infrared absorbing oxocarbon-based dyes that are regarded as pure closed-shell molecules. We hope that this will lead to advances in the molecular design, properties, functions, and applications of near-infrared absorbing dyes and to the development of new near-infrared absorbing organic materials that be used in society,” Professor Maeda concluded.

The results were published in Chemical Science on January 16, 2023, and was selected as 2023 Chemical Science HOT Article Collection.

Other authors on the paper include: graduate student Taishi Oka, Assistant Professor Naoya Suzuki, Professor Shigeyuki Yagi from Osaka Metropolitan University, Dr. Kenji Kamada from National Institute of Advanced Industrial Science and Technology, and Mr. Tatsuki Konishi.


About OMU 
Osaka Metropolitan University is a new public university established in April 2022, formed by merger between Osaka City University and Osaka Prefecture University. For more research news visit https://www.omu.ac.jp/en/ or follow @OsakaMetUniv_en and #OMUScience.

Published: 27 Mar 2023

Contact details:

Rina Matsuki

3-3-138 Sugimoto, Sumiyoshi-ku,
Osaka 558-8585 JAPAN

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Title: Unveiling a new aspect of oxocarbons: open-shell character of 4- and 5-membered oxocarbon derivatives showing near-infrared absorption
DOI: 10.1039/D2SC06612B
Author: Takeshi Maeda, Taishi Oka, Daisuke Sakamaki, Hideki Fujiwara, Naoya Suzuki, Shigeyuki Yagi, Tatsuki Konishi, Kenji Kamada
Publish: 16 January 2023
URL: https://doi.org/10.1039/D2SC06612B

Funding information:

Japan Society for the Promotion of Science JP16H06048, JP21K05215, JP21H01887
ENEOS Tonen General Research/Development Encouragement & Scholarship Foundation
The Futaba Foundation