Inorganic Chemistry, Vol.53, No.5, 2635-2644, 2014
Revisited Photophysics and Photochemistry of a Ru-TAP Complex Using Chloride Ions and a Calix[6]crypturea
The effects of the nonprotonated and protonated calix[6]crypturea 1/1(center dot)H(+) 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 1/1(center dot)H(+) 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 1/1(center dot)H(+). Although an emission decrease was observed with the protonated calixarene, an emission increase was evidenced in the presence of nonprotonated 1. As the Cl- ions were shown to inhibit the luminescence of the complex in BuCN, this luminescence increase by nonprotonated 1 was attributed to the protection effect of 1 by encapsulation of the Cl- anions into the tris-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 1 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 ((MLCT)-M-3) state could reach two metal-centered ((MC)-M-3) states, one of which is in equilibrium with the (MLCT)-M-3 state during the emission lifetime. The reaction of Cl- with this latter (MC)-M-3 state would be responsible for the luminescence quenching, in agreement with the formation of photosubstitution products.