Photonic and electrochemical properties of adsorbed [Ru(dpp)2(Qbpy)]2+ luminophores.

Dense monolayers of [Ru(dpp)2Qbpy]2+, where dpp is 4,4'-diphenylphenanthroline and Qbpy is 2,2':4,4' ':4'4' '-quarterpyridyl, have been formed by spontaneous adsorption onto clean platinum microelectrodes. The cyclic voltammetry of these monolayers is nearly ideal, and three redox states are accessible over the potential range of +/-1.3 V. Chronoamperometry conducted on the microsecond time scale has been used to probe the dynamics of heterogeneous electron transfer and indicates that the standard heterogeneous electron-transfer rate constant, k degrees , is approximately 106 s-1. The metal complex emits at approximately 600 nm in fluid and solid solution as well as when bound to a platinum electrode surface within a dense monolayer. In the case of the monolayers, it appears that the excited states are not completely deactivated by radiationless energy transfer to the metal because electronic coupling between the adsorbates and the electrode is weak. The dynamics of lateral electron transfer between the electronically excited Ru2+* and ground-state Ru3+ species has been explored by measuring the luminescence intensity after defined quantities of Ru3+ have been produced electrochemically within the monolayer. The rate of lateral electron transfer is between 8 x 106 and 3 x 108 M-1 s-1, indicating efficient electron transfer between adsorbates in close-packed assemblies. Voltammetry conducted at megavolt per second scan rates has been used to directly probe the redox properties of the electronically excited species.