Abstract
Polarized emission spectra of single-crystal [Ru(bpy)₃](PF₆)₂ are reported for the temperature range from 1.6 to
300 K. A detailed energy-level diagram for the emitting states including hitherto unresolved states is presented. The assignment of the excited states is accomplished within the D₃' symmetry group. The very lowest excited states being only 5-10 cm⁻¹ apart are both of E' character, ...
Abstract
Polarized emission spectra of single-crystal [Ru(bpy)₃](PF₆)₂ are reported for the temperature range from 1.6 to
300 K. A detailed energy-level diagram for the emitting states including hitherto unresolved states is presented. The assignment of the excited states is accomplished within the D₃' symmetry group. The very lowest excited states being only 5-10 cm⁻¹ apart are both of E' character, however, exhibiting different amounts of singlet admixture. They are responsible for the drastic change of the emission properties between 1.6 and 4.2 K. According to their E' character, the E perpendicular c-polarized emission component is far more intense than the E parallel c-polarized one. With increasing temperature a E parallel c-polarized transition appears which emerges from a higher lying A₂' state. This transition carries at about 70 K more than half of the total emission intensity. For higher temperatures (T >~ 100 K) an emission from a third E' state becomes important and dominates at room temperature. Thus, at 300 K, the E perpendicular c-polarized component delivers the major part of the emission intensity (about 95%). Another emission band appears in the E parallel c-polarized spectrum for T >~ 250 K. This band results, as has been assigned previously, from a further A₂' state. The presented polarized emission spectra of single-crystal [Ru(bpy)₃](PF₆)₂ deliver no compelling reason to assume a reduced symmetry of the emitting states compared to the ground-state symmetry. It is proposed that the symmetry reduction in the excited states of [Ru(bpy)₃]²⁺ as observed by other authors is not an intrinsic property of the complex but occurs through an interaction with the solvent sphere.
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