Kitagawa Yuichi, Tomikawa Toranosuke, Aikawa Kota, Miyazaki Shiori, Akama Tomoko, Kobayashi Masato, Wang Mengfei, Shoji Sunao, Fushimi Koji, Miyata Kiyoshi, Hirai Yuichi, Nakanishi Takayuki, Onda Ken, Taketsugu Tetsuya, Hasegawa Yasuchika
Faculty of Engineering, Hokkaido University, Kita 13, Nishi 8, Kita-ku, Sapporo, Hokkaido, 060-8628, Japan.
Institute for Chemical Reaction Design and Discovery (WPI-ICReDD), Hokkaido University, Kita 21, Nishi 10, Kita-ku, Sapporo, Hokkaido, 001-0021, Japan.
Commun Chem. 2025 Jan 28;8(1):24. doi: 10.1038/s42004-025-01420-6.
Photoinduced metal-to-ligand (or ligand-to-metal) charge-transfer (CT) states in metal complexes have been extensively studied toward the development of luminescent materials. However, previous studies have mainly focused on CT transitions between d- and π-orbitals. Herein, we report the demonstration of CT emission from 4f- to π-orbitals using a trivalent europium (Eu(III)) complex, supported by both experimental and theoretical analyses. The Eu(III) complex exhibits an eight-coordination structure, comprising three anionic nitrates and two neutral electron-donating ligands containing a carbazole unit. The diffuse reflectance spectrum of the complex displays an absorption band at 440 nm and time-resolved emission analyses reveal a characteristic emission band at 550 nm. Comparative studies employing a trivalent gadolinium (Gd(III)) complex, alongside quantum chemical analyses, confirm that the observed absorption and emission bands are associated with CT transitions between π- and 4f-orbitals. The observation of CT emission based on the 4f-orbital offers novel insights into the field of molecular luminescence science and technology.
金属配合物中的光致金属到配体（或配体到金属）电荷转移（CT）态已针对发光材料的开发进行了广泛研究。然而，先前的研究主要集中在d轨道和π轨道之间的CT跃迁。在此，我们报告了使用三价铕（Eu(III)）配合物从4f轨道到π轨道的CT发射的证明，并得到了实验和理论分析的支持。Eu(III)配合物呈现八配位结构，由三个阴离子硝酸盐和两个含有咔唑单元的中性给电子配体组成。该配合物的漫反射光谱在440 nm处显示一个吸收带，时间分辨发射分析揭示在550 nm处有一个特征发射带。使用三价钆（Gd(III)）配合物的对比研究以及量子化学分析证实，观察到的吸收和发射带与π轨道和4f轨道之间的CT跃迁有关。基于4f轨道的CT发射的观察为分子发光科学与技术领域提供了新的见解。
