Electronic strain effect on Eu(iii) complexes for enhanced circularly polarized luminescence

Makoto Tsurui; Yuichi Kitagawa; Koji Fushimi; Masayuki Gon; Kazuo Tanaka; Yasuchika Hasegawa

doi:10.1039/d0dt00699h

Electronic strain effect on Eu(iii) complexes for enhanced circularly polarized luminescence

Dalton Trans. 2020 Apr 28;49(16):5352-5361. doi: 10.1039/d0dt00699h.

Authors

Makoto Tsurui¹, Yuichi Kitagawa², Koji Fushimi³, Masayuki Gon⁴, Kazuo Tanaka⁴, Yasuchika Hasegawa²

Affiliations

¹ Graduate School of Chemical Sciences and Engineering, Hokkaido University, Kita 13, Nishi 8, Kita-ku, Sapporo 060-8628, Japan.
² Faculty of Engineering, Kita 13, Nishi 8, Kita-ku, Sapporo, 060-8628, Japan and Institute for Chemical Reaction Design and Discovery (WPI-ICReDD), Hokkaido University, Kita 21, Nishi 10, Kita-ku, Sapporo 001-0021, Japan. hasegaway@eng.hokudai.ac.jp.
³ Faculty of Engineering, Kita 13, Nishi 8, Kita-ku, Sapporo, 060-8628, Japan.
⁴ Graduate School of Engineering, Kyoto University, Kyoto daigaku-katsura, Nishikyo-ku, Kyoto 615-8510, Japan.

PMID: 32255114
DOI: 10.1039/d0dt00699h

Abstract

Luminescent Eu(iii) complexes with point-chiral phosphine oxide ligands, [Eu(hfa)3((R,R)-B2QPO)] (hfa: hexafluoroacetylacetonato, B2QPO: 2,3-bis(tert-butylmethylphosphine oxide)quinoxaline) and [Eu(hfa)3((R)-B3QPO)] (B3QPO: 2-tert-butylmethylphosphine oxide-3-(di-tert-butylphosphineoxide)quinoxaline), are reported for the investigation of the electronic strain effect on the coordination sphere. Single crystal X-ray crystallography reveals the strong structural strain of the hfa ligands in [Eu(hfa)3((R,R)-B2QPO)]. The emission quantum yields of [Eu(hfa)3((R,R)-B2QPO)] in solution (55%) and solid (63%) are comparable to those of previously reported bright luminescent Eu(iii) complexes. The chiroptical properties of [Eu(hfa)3((R,R)-B2QPO)] and [Eu(hfa)3((R)-B3QPO)] were characterized using circular dichroism (CD) and circularly polarized luminescence (CPL) spectra. The dissymmetry factor of [Eu(hfa)3((R,R)-B2QPO)] was estimated to be 0.08. The chiroptical phenomena of the Eu(iii) complexes are closely related to their structural (geometry) and electronic (LMCT: ligand-to-metal charge transfer) strains.