Solid-State Diode-like Chemiluminescence Based on Serial, Immobilized Concentration Gradients in Mixed-Valent Poly[Ru(vbpy)₃](PF₆)₂ Films

Abstract

The electronic conductivity and electrogenerated chemiluminescence (ECL) of thin, electropolymerized films of the fixed-site redox polymer poly[Ru(vbpy)3](PF6)2 (vbpy = 4-vinyl-4‘-methyl-2,2‘-bipyridine) on Pt interdigitated array electrodes were examined for both solvent-swollen and dry films. In both cases emission arose from *Ru2+ produced via the electron-transfer reaction between Ru3+ and Ru1+ states within the film (Ru = Ru(vbpy)3). Dry films contained fixed concentration gradients of Ru3+, Ru2+, and Ru1+ states which were first introduced in an acetonitrile-swollen film via the constant potential oxidation and reduction of Ru2+ at opposing IDA fingers. The gradients were then immbolized by drying and cooling the film while retaining the inter-electrode bias (2.6 V). The resulting dried and cooled films responded rapidly to changes in voltage bias and exhibited diode-like characteristics, conducting and emitting light at biases ≥2.6 V and undergoing a reverse bias breakdown current, unassociated with light emission, at ca. −5.5 V. At 0 °C the optimum quantum efficiency of solid-state ECL emission (φECL) was similar to that in solvent-swollen films: 0.0003 photon/electron. In contrast to the dry films, solvent-swollen films were slow to respond to changes in voltage bias and did not exhibit diode-like behavior.