On the zero-phonon structure of single-crystal [Ru(bpy)₃](PF₆)₂

Abstract

Further evidence is presented that in single-crystal [Ru(bpy)₃](PF₆)₂ at low temperatures one observes two zero-phonon lines corresponding to the lowest excited states at 17809 cm⁻¹ (line I, A’₁ ‹—› 1E’ in D’₃) and at 17816 cm⁻¹ (line II, A’₁ ‹—› 2E’). It is shown that the observed electronic states can be adequately described in a model of isolated [Ru(bpy)₃]²⁺ chromophores. The zero-phonon line II has been recorded in absorption, emission and excitation at exactly the same energy. Its molar extinction coefficient has a value of ε ca. 5 1·mol⁻¹·cm⁻¹, while ε for line I is estimated to be about 0.03 1·mol⁻¹·cm⁻¹, and therefore line I could not be detected in absorption. An assignment of the zero-phonon structure to impurity centers - as has been speculated elsewhere - is definitely excluded.