SOLID-STATE ABSORPTION-SPECTROSCOPY AND SPECTROSCOPIC OBSERVATION OF A LASER-INDUCED METASTABLE STATE IN DIBROMOBIS-(4-METHYLTHIAZOLE)NICKEL(II)

Solid-state absorption spectroscopy in the visible and near-infrared s pectral regions is applied to dibromobis(4-methylthiazole)nickel(II), a compound reported to be irreversibly thermochromic. Three intense sp in-allowed transitions are observed at 4,000-6,000 cm(-1), 8,900 cm(-1 ) and 15,200 cm(-1). Their energies and intensities are indicative of a tetrahedral coordination geometry of nickel(II) in the blue single-c rystal-line form of the compound. The sharp, polarized spin-forbidden transitions observed between 20,000 cm(-1) and 26,000 cm(-1) confirm a distorted tetrahedral coordination geometry. Laser excitation into an excited electronic state beads to a partial inversion of the thermall y irreversible thermochromism, trapping the title compound in a metast able state. Optical switching between the two forms of this thermochro mic system is much faster than the traditional thermal switching. The laser-induced metastable state of dibromobis(4-methylthiazole)nickel(I I) has a lifetime of more than 1 h at 30 K, 20 min at 80 K and less th an 5 min at 150 K, indicative of thermal relaxation.