Thermodynamic Study of Ion-Pairing Effects between Reduced Double-Decker Lutetium(III) Phthalocyanines and a Cationic Matrix

Abstract

The thermodynamics of ion paring between electrochemically reduced [(C6H13S)8Pc]2Lu or [(C12H25S)4Pc]2Lu and a cationic tetra-n-octylphosphonium bromide (4C8P+Br-) matrix that was deposited in a gel-like cast film on a basal plane pyrolytic graphite electrode was investigated in an aqueous KCl solution that varied in concentration from 0.005 to 1.0 M. The purpose of this study was to elucidate ion-pairing effects between reduced double-decker lutetium(III) phthalocyanines with charges of −1 to −5 and cationic sites of the 4C8P+Br- matrix. Both phthalocyanines undergo five one-electron reductions in the film, and a linear relationship was observed between the measured half-wave potentials (E1/2) for these processes and the Cl- concentration of the electrolyte in the film. The apparent number of electrons transferred in each reduction step was obtained from plots of E1/2 versus ln[Cl-], which gave Nernstian slopes of −23.5 ± 2.3 mV (or −54.1 ± 5.3 mV from plots of E1/2 vs log[Cl-]) over a chloride concentra...