Red-to-yellow pressure-induced phase transition in Pt(bpy)Cl2:: Spectroscopic study supported by DFT calculations

The combination of spectroscopic and computational methods has been employed to explore the origin of the luminescence in the red and yellow forms of Pt(bpy)Cl-2. The luminescence of the red (linear-chain) form of Pt(bpy)Cl-2 (bpy 2,2'-bipyridine) has been measured as a function of hydrostatic pressure up to 65 kbar. The luminescence band maximum is redshifted (-147 cm(-1) kbar(-1)), and the intrachain Pt-Pt distance decreases from 3.46 to 3.25 angstrom between ambient pressure and 17.7 kbar. Strong discontinuities in the optical properties at 17.7 kbar were interpreted in terms of a crystallographic phase transition from the red to a denser yellow form of Pt(bpy)Cl-2. First-principles calculations based on density functional theory were used to study the red to yellow phase transformation. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007).