Electrogenerated Chemiluminescence. 59. Rhenium Complexes

Re(L)(CO)3Cl complexes (where L is 1,10-phenanthroline, 2,2′-bipyridine, or a phenanthroline or bipyridine derivative containing methyl groups) are photoluminescent in fluid solution at room temperature. In acetonitrile solutions, these complexes display one chemically reversible one-electron reduction process and one chemically irreversible oxidation process. λmax for the luminescence is dependent on the nature of L, and a linear relationship between λmax and the difference in electrode potentials for oxidation and reduction is evident. Electrogenerated chemiluminescence (ECL) was observed in acetonitrile solutions of these complexes (Bu4NPF6 as electrolyte) by stepping the potential of a Pt disk working electrode between potentials sufficient to form the radical anionic and cationic species. The relative amount of light produced during the anodic and cathodic pulses was dependent on the potential limits and pulse duration. ECL was also generated in the presence of coreactants, i.e., with tri-n-propylamine upon stepping the potential sufficiently positive to form the deprotonated tri-n-propylamine radical and the cationic rhenium(II) species Re(L)(CO)3Cl. When S2O8 was present in solution, ECL was also observed for all of the complexes upon stepping to potentials sufficient to form (Re(L)(CO)3Cl) and the strong oxidant SO4. In most cases, the ECL spectrum was identical to the photoluminescence spectrum, indicating that the chemical reactions following electrochemical oxidation or reduction form the same metal-to-ligand charge-transfer (MLCT) excited states that are generated in the photoluminescence experiments.