Ligand-centered 3ππ* emission and Raman activity of [Pt(bpy-h₈)n(bpy-d₈)2-n]²⁺ (n = 0, 1, 2)

Abstract

Highly resolved emission and excitation spectra as well as emission decay data of [Pt(bpy-h₈)n(bpy-d₈)2 -n]²⁺ (n=0, 1, 2; bpy = 2,2'-bipyridine) are presented. These compounds are investigated as traps in neat [Pt(bpy)₂(CIO₄)₂ matrices. The traps, having their emitting states several cm⁻¹ below those of the majority of complexes, lead to spectral resolutions, which are by a factor of several hundreds better than hitherto published. The highest resolution of ca. 4 cm⁻¹ is found for [Pt(bpy-h₈)₂]²⁺ doped into [Pt(bpy-d₈)₂](CIO₄ )₂. The low-lying electronic origins ( 0-0 lines), e.g. at 21237 cm⁻¹ for [Pt(bpy-h₈)₂]²⁺ in [Pt(bpy-h₈)₂](CIO₄ )₂, and the well-resolved vibrational satellite structures carry the information needed for a classification of the lowest electronic states. They are assigned as ligand centered of ³ππ* character with small metal admixtures. The partially deuterated [Pt(bpy-h₈)(bpy-d₈)]²⁺ emits only from the energetically lower lying (bpy-h₈)-Iigand due to an effective intra-molecular energy transfer, which quenches the emission from the (bpy-d₈)-ligand and prevents a dual emission. The spectra reveal further that a significant vibrational ligand-ligand coupling of (high-energy) internal ligand modes does not take place. Raman spectra of the neat perchlorate materials are also presented. In particular, the Raman spectrum of [Pt(bpy-h₈)(bpy-d₈)]²⁺ consists of a superposition of (bpy-h₈)- and (bpy-d₈)-ligand modes. Interestingly, the (bpy-d₈)-Iigand exhibits much higher Raman scattering intensities than the (bpy-h₈)-Iigand. An important message is found from the comparison of the emission with the Raman spectrum of [Pt(bpy-h₈)(bpy-d₈)]²⁺. This comparison demonstrates the different kinds of information carried by the two types of spectra. Raman lines are observed for both Iigands, while the emission spectrum is highly selective and displays just the information about the spatial region of the complex, which is responsible for the electronic transition.