Multicolored electrogenerated chemiluminescence from ortho-metalated iridium(III) systems

The electrogenerated chemilumescence (ECL) of F(Ir)pic (bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl))iridium 111) and (btp)(2)Ir(acac) (bis[2,(2'-benzothienyl)pyridinato-N,C3'](acetlyacetonate)Ir(III) has been investigated in acetonitrile (MeCN), mixed MeCN/H2O (50:50, v/v), and aqueous solutions using the oxidative reductive coreactant tri-n-propylamine. ECL was also studied in the presence of the nonionic surfactant Triton X-100 (poly(ethylene glycol) tert-octylphenyl ether). F(Ir)pic is a blue emitter (lambda(ECL) similar to 470 nm), and (btp)(2)Ir(acac) emits in the red (lambda(ECL) similar to 600 nm). The ECL spectrum of each compound is identical to its photoluminescence spectrum, indicating the same metal-to-ligand (MLCT) excited states. The ECL emission spectrum of F(Ir)pic can be distinguished from Ru(bpy)(3)(2+) when both are present in the same solution, raising the possibility of using these compounds for detection of multiple analytes in the same solution. ECL intensity increased in the presence of surfactant up to 6-fold for F(Ir)pic and up to 20-fold for (btp)(2)Ir(acac). Oxidative current also increased for both compounds. These data support the theory of surfactant adsorption at the electrode surface, leading to greater concentrations of TPrA and Ir species near the electrode surface and higher ECL intensities.