A new type of spectroelectrochemical sensor that demonstrates three modes of selectivity (electrochemistry, spectroscopy, and selective partitioning) is demonstrated. The sensor consists of an optically transparent electrode (OTE) coated with a selective film. Sensing is based on the change in the attenuation of light passing through the OTE that accompanies an electrochemical reaction of the analyte at the electrode surface. Thus, for an analyte to be detected, it must partition into the selective coating and be electrolyzed at the potential applied to the electrode, and either the analyte or its electrolysis product must absorb light at the wavelength chosen. Selectivity for the analyte relative to other solution components is obtained by choice of coating material, electrolysis potential, and wavelength for optical monitoring. The sensor concept is demonstrated with an OTE consisting of an indium−tin oxide coating on glass that has been over-coated with a sol−gel-derived charge-selective thin film. Attenuated total reflection (ATR) is used as the optical detection mode. The selective coating was an anionically charge-selective sol−gel-derived PDMDAAC−SiO2 composite film, where PDMDAAC = poly(dimethyldiallylammonium chloride). Fe(CN)6 4- was used as a model analyte to demonstrate that the change in the transmittance of the ATR beam resulting from oxidation of Fe(CN)6 4- to Fe(CN)6 3- can be used to quantify an analyte. The unoptimized sensor exhibited the following characteristics:  linear range, 8.0 × 10-6−5.0 × 10-5 M; sensitivity, 8.0 × 103ΔA/M; and detection limit, 8.0 × 10-6 M.

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Solution electrogenerated chemiluminescence (ECL) was evaluated for molecules of interest for organic light-emitting diodes (OLEDs), using high-frequency voltage pulses at a microelectrode. Radical cations of different energies were electrogenerated from a series of triarylamine hole-transport materials (x-TPD), in the presence of radical anions of a high electron affinity sulfonamide derivative of tris(8-hydroxyquinoline)aluminum (Al(qs) 3 ), or a bis(isoamyl) derivative of quinacridone (DIQA). The resultant emission was from the excited singlet states 1 Al(qs) 3 * or 1 DIQA*, the same excited state produced in OLEDs based on these molecules. In solution, the majority of the reaction pairs had insufficient energy to populate 1 Al(qs) 3 * or 1 DIQA* directly, but could form the triplet states 3 Al(qs) 3 * or 3 DIQA*. The reaction order and the temporal response of the emission were consistent with subsequent formation of the excited singlet states via triplet-triplet annihilation (TTA). For reactions with a low excess Gibbs free energy to form the triplet state (∆ T G), the efficiency increased exponentially with an increase in driving force (increase in oxidation potential of x-TPD), then reached a plateau. At the maximum, the efficiencies for formation of 1 Al(qs) 3 * or 1 DIQA* via the TTA route reach as high as a few percent. The computed energetics of these reactions suggest that similar lightproducing electroluminescent reactions, proceeding via triplet formation, could also occur in condensed phase organic thin films.

The influence of the initial molar ratio of water relative to tetraethyl orthosilicate (TEOS) precursor and the content of Nafion ionomer in sol−gel-derived silica composites on the voltammetric response of electrodes modified with these composites for [ReI(DMPE)3]+ was investigated. The slow diffusion of [ReI(DMPE)3]+ in Nafion can be significantly improved by dispersing Nafion in sol−gel-derived silica, and the diffusion of [ReI(DMPE)3]+ in such a composite increases with the increase in water/TEOS molar ratio and the decrease in Nafion content. With the mass ratio of Nafion relative to sol−gel-derived silica being 40:100 and the initial molar ratio of water relative to TEOS being 20:1, the electrodes modified with the derived Nafion−silica nanocomposite exhibited an apparent peak current increase rate, during preconcentration of [ReI(DMPE)3]+, that was approximately three times faster than the corresponding Nafion-modified electrode. Compared with bare indium−tin oxide (ITO) glass, the composite-coated ITO glass showed a 25-fold enhancement in voltammetric response to [ReI(DMPE)3]+. The suitability of the developed optically transparent Nafion−silica composite for spectroelectrochemical sensing of [ReI(DMPE)3]+ was demonstrated. The [ReI(DMPE)3]+ extracted into the coating (∼0.4 μm in thickness) was electrolyzed to [ReII(DMPE)3]2+. Under attenuated total reflection mode, the in-situ electrogenerated chromophore [ReII(DMPE)3]2+ was monitored by probing its interaction with the evanescent field of light of a selected wavelength. Thus, the elements required for a spectroelectrochemical sensor with three modes of selectivity were demonstrated:  partitioning into the film on an electrode surface and an electrochemically modulated optical signal.