The Enhanced Intramolecular Energy Transfer and Strengthened ff Luminescence of a Stable Helical Eu Complex in Ionic Liquids

Yuki Hasegawa; Ayumi Ishii; Yudai Inazuka; Naho Yajima; Shogo Kawaguchi; Kunihisa Sugimoto; Miki Hasegawa

doi:10.3390/molecules23020055

The Enhanced Intramolecular Energy Transfer and Strengthened ff Luminescence of a Stable Helical Eu Complex in Ionic Liquids

Molecules. 2018 Jan 24;23(2):55. doi: 10.3390/molecules23020055.

Authors

Yuki Hasegawa¹, Ayumi Ishii^{2

3}, Yudai Inazuka⁴, Naho Yajima⁵, Shogo Kawaguchi⁶, Kunihisa Sugimoto⁷, Miki Hasegawa⁸

Affiliations

¹ Department of Chemistry and Biological Science, College of Science and Engineering, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara 252-5258, Kanagawa, Japan. y.hasegawa106@gmail.com.
² Department of Chemistry and Biological Science, College of Science and Engineering, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara 252-5258, Kanagawa, Japan. ayumi@chem.aoyama.ac.jp.
³ JST, PRESTO, 4-1-8 Honcho, Kawaguchi 332-0012, Saitama, Japan. ayumi@chem.aoyama.ac.jp.
⁴ Department of Chemistry and Biological Science, College of Science and Engineering, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara 252-5258, Kanagawa, Japan. zoo-injpn@outlook.com.
⁵ Department of Chemistry and Biological Science, College of Science and Engineering, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara 252-5258, Kanagawa, Japan. nahoyn@gmail.com.
⁶ Research & Utilization Division, Japan Synchrotron Radiation Research Institute (JASRI/SPring-8), 1-1-1 Kouto, Sayo 679-5198, Hyogo, Japan. kawaguchi@spring8.or.jp.
⁷ Research & Utilization Division, Japan Synchrotron Radiation Research Institute (JASRI/SPring-8), 1-1-1 Kouto, Sayo 679-5198, Hyogo, Japan. ksugimoto@spring8.or.jp.
⁸ Department of Chemistry and Biological Science, College of Science and Engineering, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara 252-5258, Kanagawa, Japan. hasemiki@chem.aoyama.ac.jp.

Abstract

The luminescence of a Eu complex (EuL) is enhanced by stabilization of the coordination structure in highly viscous ionic liquids. The EuL was found to maintain a stable single helical structure both in organic solvents and in the ionic liquids [BMIM][PF₆] and [EMIM][PF₆]. A colorless solution of EuL dissolved in [BMIM][PF₆] exhibits bright red luminescence with a quantum yield of 32.3%, a value that is much higher than that in acetonitrile (12%). Estimated rate constants for the energy relaxation pathway indicate that the energy transfer efficiency is enhanced in [BMIM][PF₆] as a result of the suppression of molecular fluctuations in the ligands. Additionally, a highly luminescent helical structure is preserved in [EMIM][PF₆] up to 120 °C.

Keywords: Eu complex; energy transfer; ionic liquid; luminescence; molecular fluctuation.

MeSH terms

Algorithms
Energy Transfer*
Europium / chemistry*
Ionic Liquids*
Luminescence*
Luminescent Agents / chemistry
Models, Chemical
Molecular Structure
Spectrum Analysis
Temperature
Viscosity

Substances

Ionic Liquids
Luminescent Agents
Europium