The behavior of light-emitting electrochemical cells (LEC) based on solid films ( approximately 100 nm) of tris(2,2'-bipyridine)ruthenium(II) between an ITO anode and a Ga-In cathode was investigated. The response times were strongly influenced by the nature of the counterion: small anions (BF(4)(-) and ClO(4)(-)) led to relatively fast transients, while large anions (PF(6)(-), AsF(6)(-)) produced a slow time-response. From comparative experiments of cells prepared and tested in a glovebox to those in ambient, mobility of the anions in these films appears to be related to the presence of traces of water from atmospheric moisture. An electrochemical model is proposed to describe the behavior of these LECs. The simulation results agreed well with experimental transients of current and light emission as a function of time and show that the charge injection is asymmetric at the two electrodes. At a small bias, electrons are the major carriers, while for a larger bias the conduction becomes bipolar.

The factors affecting the operating life of the light-emitting electrochemical cells (LECs) based on films of tris(2,2'-bipyridine)ruthenium(II) both in sandwich (using an ITO anode and a Ga:Sn cathode) and planar (using interdigitated electrode arrays (IDAs)) configurations were investigated. Stability of these devices is greatly improved when they are produced and operated under drybox conditions. The proposed mechanism of the LEC degradation involves formation of a quencher in a small fraction of tris(2,2'-bipyridine)ruthenium(II) film adjacent to the cathode, where light generation occurs, as follows from the observed electroluminescence profile in the LECs constructed on IDAs, showing that the charge injection in such devices is highly asymmetric, favoring hole injection. Bis(2,2'-bipyridine)diaquoruthenium(II) is presumed to be the quencher responsible for the device degradation. A microscopic study of photo- and electroluminescence profiles of planar light-emitting electrochemical cells was shown as a useful approach for studies of charge carrier injection into organic films.

We report the use of scanning electrochemical microscopy (SECM) to control the generation of Tl(I) at a mercury substrate and detect this species at a mercury-coated tip to study the transport of these ions through ion channels. The transport of Tl(I) across gramicidin D half-channels imbedded in a dioleoylphosphatidylcholine (DOPC) monolayer supported on a Tl amalgam hanging mercury drop electrode (HMDE) was studied using the substrate generation-tip collection mode of SECM. A Hg/Pt "submarine" electrode, used as the SECM tip, was made through simple contact of the Pt ultramicroelectrode with the HMDE. The tip transient response for the collection of generated Tl(I) at the amalgam HMDE was recorded for several tip to substrate distances. This collection-generation experiment was repeated with a DOPCmodified Tl/HMDE and a gramicidin-DOPC-modified Tl/HMDE. An apparent heterogeneous rate constant (khet ) 2.8 ((0.1) × 10 -4 cm/s) for the transport of Tl(I) through the gramicidin to the tip was extracted.

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