Structure Study and Luminescence Thermochromism in Hexanuclear 6-Methyl-2-Pyridinethiolato Copper(I) Crystals

• Published in: The journal of physical chemistry. B Vol. 109; no. 19; pp. 9339 - 9345
• Main Authors: Xie, Haiyan, Kinoshita, Isamu, Karasawa, Tsutomu, Kimura, Kentarou, Nishioka, Takanori, Akai, Ichiro, Kanemoto, Katsuichi
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 19-05-2005
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp0446985

The structure of hexanuclear 6-methyl-2-pyridinethiolato copper(I) [Cu6(6-mpyt)6] crystals has been studied by the X-ray diffraction analysis. These crystals show highly efficient luminescence whose color changes drastically from red to green-blue with lowering temperature from room temperature (RT) to liquid nitrogen temperature (LNT). This is a new example of luminescence thermochromism for hexanuclear copper(I) cluster compounds. Two relaxed luminescence bands appear predominantly:  one (CC-band), red luminescence appearing in the lower-energy region around 1.8 eV at higher temperature, is assigned to the transition between intramolecular orbitals (MO) of a Cu cluster center (CC), and the other (CT-band), green-blue luminescence appearing at the higher energy side of 2.6 eV than the CC-band at lower temperature, is assigned to a charge transfer (CT) transition from the CC-MO to a ligand MO. Additionally, the CT band can be deconvoluted to two subbands CTL and CTH. The intensities of the CC- and the CT-bands change complementarily with temperature via a thermal activation process, giving the thermochromism. All of these band shapes can be fitted by a Gaussian function, and their widths are fairly large obeying the hyperbolic cotangent law. These features reflect our system to be a strong electron−lattice coupling one. The relaxation process of the photoexcited states is discussed in terms of a configuration coordinate model.