Abstract

During the past decade [Ru(bpy)₃]²⁺ complexes have been investigated intensively.[1-4] From measurements with dissolved complexes it has been concluded that the second coordination sphere (solvent sphere) strongly influences the spectroscopic behavior. Thus, it is near at hand to analyze crystalline compounds with different counter-ions, leading to a more defined variation of the second coordination spheres. Such investigations are presented here for the first time. Fig. 1 reproduces the emission spectra of two compounds and Table I summarizes spectroscopic data for different counter-ions and crystal water contents. These results show that counter-ions and/or crystal water strongly influence the emission spectra and their temperature behavior, the decay properties, and the emission intensities and their temperature dependence. For instance, the intensity of the PF₆-salt is at 300 K appreciably larger than that for other salts. However, with temperature reduction all compounds seem to come to a comparable value. This can be understood on the basis of an electronic state strongly coupled to lattice vibrations, only accessible over an activation barrier. An equivalent behavior has also been found for dissolved complexes.[4] The corresponding quenching state has been assigned in [4] to a charge-transfer-to-solvent state and in [2] to a Ru 4d state. Our results indicate the significance of the counter-ion redox potential. This suggests - in analogy to [4] - that a charge-transfer state coupled to the second coordination sphere (counter-ion) is responsible for the quenching properties.

© 1984 Optical Society of America