In a recent groundbreaking discovery, a research group led by Associate Professor Masahito Murai and Professor Shigehiro Yamaguchi has developed antiaromatic molecules that exhibit absorption and fluorescence bands in the near-infrared (NIR) region. This research, published in Angewandte Chemie International Edition, has significant implications for the fields of health care, optoelectronics, and materials science. By exploring the interaction between light and matter, the researchers have successfully developed organic molecules that emit light in the NIR region, specifically wavelengths between 800 and 1100 nm.
The NIR region, also known as the “optical window of living tissue,” is of great importance in medical applications. It offers unique advantages such as deep biological imaging, photodynamic therapy, and photothermal therapy. Compared to other regions of the electromagnetic spectrum, NIR light can penetrate tissues more deeply with reduced scattering and minimal photodamage. This makes it a valuable tool in health care and life science research.
Developing organic molecules with absorption and emission properties in the NIR region has been a challenge in the past. Conventional dyes often suffer from reduced solubility and increased lipophilicity, making it difficult to mold and process the molecules for use as electronic materials and to apply them to biological imaging. However, the team led by Professors Murai and Yamaguchi overcame these obstacles through the fusion of thiophene, a less aromatic heterocyclic ring, with azepine.
By fusing thiophene with azepine, the researchers were able to effectively balance antiaromatic and polymethine characters in the molecules. This balance increased the likelihood of electronic transitions of antiaromatic compounds, enabling the acquisition of absorption and fluorescence wavelengths in the NIR region. This breakthrough has the potential to lead to the creation of diverse NIR luminescent materials.
The team designed and synthesized a series of azepine derivatives with electron-accepting groups and used single-crystal X-ray structure analysis to reveal significant structural differences between them. While the curved dibenzoazepine exhibited absorption and fluorescence at shorter wavelengths, the highly planar dithienoazepine analog exhibited absorption and fluorescence at wavelengths longer than 700 nm. The utility of the molecular framework was further demonstrated by synthesizing a dithienoazepine with cationic indolium groups, which displayed a strong absorption band at 846 nm and a narrow fluorescence band at 878 nm.
The research conducted by Professors Murai and Yamaguchi opens up promising avenues for the development of materials with strong absorption and fluorescence properties in the NIR range. The dithienoazepine core used in their study proved to be useful in achieving long-wavelength absorption and emission despite its small tricyclic skeleton. The application potential of these molecules spans a wide array of fields, including fluorescence imaging, sensing, and materials science. There is a particular focus on deep-tissue imaging and non-invasive diagnostics, highlighting Nagoya University’s commitment to pushing the boundaries of science and innovation to improve health care using cutting-edge technology.
The development of antiaromatic molecules that exhibit absorption and fluorescence bands in the NIR region is a significant breakthrough in the fields of health care, optoelectronics, and materials science. By overcoming the challenges associated with conventional dyes, Professors Murai and Yamaguchi have paved the way for the creation of diverse NIR luminescent materials. These materials have immense potential in applications such as deep biological imaging, photodynamic therapy, and photothermal therapy. As technology continues to advance, the boundaries of science and innovation will be pushed further, ultimately improving health care outcomes and enhancing our understanding of the world around us.