Revisited Photophysics and Photochemistry of a Ru-TAP Complex Using Chloride Ions and a Calix[6]crypturea

Abstract

The effects of the nonprotonated and protonated calix[6]­crypturea <b>1/1^•</b><b>H⁺</b> on the PF₆^– and Cl^– salts of a luminescent Ru-TAP complex (TAP = 1,4,5,8-tetraazaphenanthrene) were investigated. Thus, the phototriggered basic properties of this complex were examined with <b>1^•H⁺</b> in acetonitrile (MeCN) and butyronitrile (BuCN). The Ru excited complex was shown to be able to extract a proton from the protonated calixarene, accompanied by a luminescence quenching in both solvents. However, in BuCN, the Cl^– salt of the complex exhibited a surprising behavior in the presence of <b>1/1^•</b><b>H⁺</b>. Although an emission decrease was observed with the protonated calixarene, an emission increase was evidenced in the presence of nonprotonated <b>1</b>. As the Cl^– ions were shown to inhibit the luminescence of the complex in BuCN, this luminescence increase by nonprotonated <b>1</b> was attributed to the protection effect of <b>1</b> by encapsulation of the Cl^– anions into the <i>tris</i>-urea binding site. The study of the luminescence lifetimes of the Ru-TAP complex in BuCN as a function of temperature for the PF₆^– and Cl^– salts in the absence and presence of <b>1</b> led to the following conclusions. In BuCN, in contrast to MeCN, in addition to ion pairing, because of the poor solvation of the ions, the luminescent metal-to-ligand charge transfer (³MLCT) state could reach two metal-centered (³MC) states, one of which is in equilibrium with the ³MLCT state during the emission lifetime. The reaction of Cl^– with this latter ³MC state would be responsible for the luminescence quenching, in agreement with the formation of photosubstitution products