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.

Luminescent Ionic Transition‐Metal Complexes for Light‐Emitting Electrochemical Cells

“…[27] In this approach, the Ru II complex and its counterion [PF 6 À ] play several key roles: promotion of charge injection from the electrodes, electron and hole transport through the device and, thanks to the intrinsic orange emission, luminescence. Nowadays, iTMC-LECs are mostly based on luminescent ionic biscyclometalated Ir III complexes [36] (the archetypal complex of this large family of complexes is 2, Figure 3), [37] which, like the original Ru II complex, may sustain charge injection and transport while affording, at the same time, light emission.…”

“…LEC materials can be either conjugated light-emitting polymers or ionic transition-metal complexes, the related devices are termed polymer-LECs (PLECs) [26,30] or iTMCLECs, [27][28][29][31][32][33][34] respectively. Both types of LECs have been studied for over 15 years, [26,27] throughout which many materials, device concepts, and driving schemes have been tested.…”

“…[26,30] The second type is even simpler as it uses an ionic emitter that enables single-component devices; this type of LECs is referred to as iTMCLECs. [24,[27][28][29][31][32][33][34] This Review illustrates the fundamentals of LEC technology, focuses on the most promising luminescent materials for iTMC-LECs, particularly ionic Ir III complexes, and highlights the latest achievements and remaining challenges of iTMC-LECs in the frame of the rapidly developing area of lighting technologies.…”

Self-absorption in a light-emitting electrochemical cell based on an ionic transition metal complex

“…5 Two main classes of LEC-devices can be identified: (i) the conjugated polymer LEC (CP-LEC) 2,6 and (ii) the ionic transition metal complex LEC (iTMC-LEC). [7][8][9] The active material in CP-LECs is composed of an EL conjugated polymer intermixed with an electrolyte, where the former performs the tasks of electron transport and light emission and the latter allows for ion transport. The iTMC can in contrast perform all of these LEC-fundamental tasks within one single material (although a second electrolyte is commonly added to shorten the turnon time).…”

ANOMALOUS BEHAVIOR OF Ir(III) CYCLOMETALATED COMPLEXES: APPLICATION IN LIGHT-EMITTING ELECTROCHEMICAL CELLS

“…3 The luminescent materials used in LEC devices can be conjugated lightemitting polymers together with an inorganic salt (PLECs) 1 or ionic transition metal complexes (iTMC). [4][5][6][7] In the case of iTMC, the fabrication consist in the deposition of a single layer of the iTMC material by spin coating onto ITO (Indium Tin Oxide) followed by a metallic cathode deposited by evaporation under vacuum. 8 In the case of the OLED devices, the fabrication consists in a multilayer architecture, including the emitter layer (neutral molecule or polymer), sandwiched between two electrodes.…”