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Interesting ionic materials can be transformed into room temperature molten salts by combining them with polyether-tailed counterions such as polyether-tailed 2-sulfobenzoate (MePEG-BzSO3 -) and polyether-tailed triethylammonium (MePEG-Et3N+). Melts containing ruthenium hexamine, metal trisbipyridines, metal trisphenanthrolines, and ionic forms of aluminum quinolate, anthraquinone, phthalocyanine, and porphyrins are described. These melts exhibit ionic conductivities in the 7 × 10-5 to 7 × 10-10 Ω-1 cm-1 range, which permit microelectrode voltammetry in the undiluted materials, examples of which are presented.

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The attachment of two polyethylene glycol tails (n = 7, MW = 350) to ruthenium tris(bipyridine) via ester links on the 4,4‘-positions of one of the bipyridine ligands yields a highly viscous (η ≈ 107 cP) molten salt (abbreviated [Ru(bpy)2(bpy(CO2MePEG350)2)](ClO4)2) that glasses at ca. −5 °C. At room temperature, the ionic conductivity of the melt is sufficiently high that application of 2.4 V across the fingers of a Pt interdigitated electrode array (IDA) coated with the melt leads to the electrolytic development of serial concentration gradient microstructures of RuIII/II and RuII/I states. At the intersection of the two concentration gradients, in the interior of the coating, reaction between the RuIII and RuI states leads to ECL emission with an efficiency of 0.2% photons/electron. Cooling a concentration gradient-containing film to −20 °C under voltage bias, so as to preserve the gradient microstructure, yields a film that has an emission efficiency of 0.1%, a current and light emission response that rapidly changes with the applied voltage bias, and a diode-like current−voltage profile with a ca. 100 rectification ratio.

The coupling of electron self exchange reactions with physical diffusion has been used to measure electron transfer rate constants in a series of undiluted metal complex molten salts [M(bpy(CO2MePEG)2)3](ClO4)2 where M = Co(II/I) and Fe(III/II) and MePEG is an oligomeric polyether of MW 150, 350, and 550. Physical self-diffusion rates in the melts vary with attached polyether chain length by over 103-fold while the electron transfer rate constants show no strong systematic dependence. The electron transfer rates and activation parameters indicate that the metal complex cores move rapidly within their attached polyether “solvent” shells relative to the rates of electron transfers, which are near adiabatic with large activation barriers reflecting the apparent inability of the attached polyether chains to act as a freely mobile “solvent”. Ionic conductivities of the melts were measured in order to inspect for ionic and electronic migration effects which are present to minor degrees. Diffusion and heterogeneous transfer rates are also reported for dilute solutions of the cobalt complexes in a polyether solvent.