Issue 8, 2010
From the journal:

Dalton Transactions

Excited state intramolecular proton transfer (ESIPT) in six-coordinated zinc(ii)-quinoxaline complexes with ligand hydrogen bonds: their fluorescent properties sensitive to axial positions†

Ken-ichi Sakai,*a   Sami Takahashi,a   Ataru Kobayashi,a   Tomoyuki Akutagawa,b   Takayoshi Nakamura,b   Masaaki Dosen,c   Masako Katoc  and  Umpei Nagashimad  

* Corresponding authors

a Department of Bio- & Material Photonics, Chitose Institute of Science and Technology, Chitose, Japan
E-mail: k-sakai@photon.chitose.ac.jp
Fax: +81 123 27 6054
Tel: +81 123 27 6054

b Research Institute for Electronic Science, Hokkaido University, Sapporo, Japan

c Department of Chemistry, Hokkaido University, Sapporo, Japan

d Research Institute for Computational Science, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan

Abstract

Zinc(II)-quinoxaline complexes, [Zn(hqxc)2(py)2] and [Zn(hqxc)2(DMSO)2] (hqxc = 3-hydroxy-2-quinoxalinecarboxylate, py = pyridine, DMSO = dimethyl sulfoxide), were prepared and characterized by X-ray crystallography and fluorescence spectroscopy. In both complexes, the zinc ion is six-coordinated by two equatorial bidentate hqxc ligands with an intramolecular hydrogen bond and two axial monodentate ligands such as pyridine or DMSO. In spite of similar coordination geometries, there is a remarkable difference between their solid-state fluorescent properties. The pyridine complex is strongly fluorescent (fluorescence quantum yield Φ = 0.22), giving rise to a significantly Stokes-shifted spectrum. From its thin film photopumped by a nitrogen gas laser, amplified spontaneous emission was observed. These results suggest that the fluorescence occurs by way of excited-state intramolecular proton-transfer (ESIPT) in the hydrogen bond of hqxc. On the other hand, the DMSO complex shows fluorescent intensity (Φ = 0.08) lower than that of the pyridine complex, and shows normal emission in addition to ESIPT emission. From IR measurements for these complexes, it is concluded that axial ligands influence the hydrogen bond strength of the equatorial hqxc ligand via zinc and thus the ESIPT efficiency.

Graphical abstract: Excited state intramolecular proton transfer (ESIPT) in six-coordinated zinc(ii)-quinoxaline complexes with ligand hydrogen bonds: their fluorescent properties sensitive to axial positions

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Article information

DOI
https://doi.org/10.1039/B919613G
Article type
Paper
Submitted
21 Sep 2009
Accepted
20 Nov 2009
First published
05 Jan 2010

Dalton Trans., 2010,39, 1989-1995

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Excited state intramolecular proton transfer (ESIPT) in six-coordinated zinc(II)-quinoxaline complexes with ligand hydrogen bonds: their fluorescent properties sensitive to axial positions

K. Sakai, S. Takahashi, A. Kobayashi, T. Akutagawa, T. Nakamura, M. Dosen, M. Kato and U. Nagashima, Dalton Trans., 2010, 39, 1989 DOI: 10.1039/B919613G

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