Multinuclear Complexes

Circularly polarised luminescence (CPL) involves two types of emission: right- and left-handed circularly polarised light. It has great potential for use in 3D displays, security technologies and sensing. CPL-active luminophores can be broadly classified into four categories: (i) chiral organic small molecules (e.g. helicenes and binaphthyls with cyclic or tubular structures); (ii) chiral metal complexes; (iii) lanthanide complexes; and (iv) supramolecular assemblies or helical polymers. However, conventional CPL materials face several significant challenges: (1) reliance on expensive chiral sources or rare metals; (2) the requirement for complex and environmentally burdensome organic synthesis; (3) low thermal and chemical stability, which often leads to racemisation upon heating or solvent changes. In this study, we are developing a new class of CPL-active materials based on neutral, triple-stranded, dinuclear helicates composed of three tetradentate ligands and two trivalent main-group metal ions (Al, Ga or In). These complexes offer several key advantages: (1) they are optically active due to their helical chirality (P- and M-enantiomers), eliminating the need for expensive chiral auxiliaries; (2) they can be synthesised straightforwardly via coordination-driven self-assembly; and (3) they possess high thermal and chemical stability, even under strongly acidic or basic conditions. Furthermore, these helicates act as highly emissive dyes with tunable emission colours, making them promising candidates for next-generation CPL materials.

Dinuclear Triple-Stranded Helicates Composed of Tetradentate Ligands with Al(III) Chromophores: Optical Resolution and Multi-Color Circularly Polarized Luminescence Properties
Toshikazu Ono,* Kohei Ishihama, Ai Taema, Takunori Harada, Kiyohao Fukusho, Yuki Nojima, Masashi Hasegawa, Masaaki Abe, Yoshio Hisaeda*
Angew. Chem. Int. Ed. 2021, 60, 2614-2618.
https://doi.org/10.1002/anie.202011450

Dinuclear Triple-stranded Helicates Comprising Al(III), Ga(III), or In(III) and a Hydrazine-linked Bisiminopyrrolyl Ligand: Synthesis, Structure, Optical Resolution, and Chiroptical Properties

Kohei Ishihama, Toshikazu Ono,* Toru Okawara, Takunori Harada, K. Furusho, Yuki Nojima, Masashi Hasegawa, Taro Koide, Masaaki Abe, Yoshio Hisaeda*

Bull. Chem. Soc. Jpn. 2021, 94, 573-578.
https://www.journal.csj.jp/doi/abs/10.1246/bcsj.20200327

多色発光かつ高い発光量子収率を示す新たな蛍光色素の開発が望まれています。特に円偏光発光(CPL: Circular Polarized Luminescence)を示すキラルな発光体の創製は、構造多様性や発光色について、まだ発展途上にあり、新たな分子デザインが望まれています。

本研究では、強発光性のビルディングブロックとしてピロール系ホウ素錯体に着目し、2,2'-ビピロールを前駆体とする配位子を用いることで、ホウ素（BF2)を含む四核錯体のワンポット合成を行いました。これらの錯体は、強発光性を有するとともに、溶液および固体状態でCPLを示すことや、量子収率が最大で100%に達する多色発光を達成しました。単結晶X線結晶構造解析、フェムト秒過渡吸収分光法などの光学測定、計算化学によって、これらの錯体を包括的に評価しました。結果として、ビピロールの2,2'軸周りの回転障壁エネルギーを適度に調整することにより、剛直性と柔軟性のバランスがとれた旗蝶番型色素となることが明らかとなりました。さらに固体状態でエナンチオマーを会合させることにより、緑、緑黄、黄色などの多色CPLの発光を観測することができました。

Highly Fluorescent Bipyrrole-based Tetra-BF2 Flag-hinge Chromophores: Achieving Multicolor and Circularly Polarized Luminescence　
Luxia Cui, Hyuga Shinjo, Takafumi Ichiki, Koichi Deyama, Takunori Harada, Kohei Ishibashi, Takumi Ehara, Kiyoshi Miyata, Ken Onda, Yoshio Hisaeda* and Toshikazu Ono*
Angew. Chem. Int. Ed. 2022, 61, e202204358  (Front Cover)
https://onlinelibrary.wiley.com/doi/10.1002/anie.202204358