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 •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•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 •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 (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. © 2014 American Chemical Society.SCOPUS: ar.j