The first enzyme-based catalyst that is superior to platinum in the four-electron electroreduction of oxygen to water is reported. The smooth Pt cathode reached half and 90% of the mass transport-limited current density at respective overpotentials of -0.4 and -0.58 V in 0.5 M sulfuric acid, and only at even higher overpotentials in pH 7.2 phosphate buffer. In contrast, the smooth "wired" bilirubin oxidase cathode reached half and 90% of the mass transport-limited current density at respective overpotentials as low as -0.2 and -0.25 V. The mass transport-limited current density for the smooth "wired" enzyme cathode in PBS was twice that with smooth Pt in 0.5 M sulfuric acid. Under 1 atm O2 pressure, O2 was electroreduced to water on a polished carbon cathode, coated with the "wired" BOD film, in pH 7.2 saline buffer (PBS) at an overpotential of -0.31 V at a current density of 9.5 mA cm-2. At the same overpotential, the current density of the polished platinum cathode in 0.5 M H2SO4 was 16-fold lower, only 0.6 mA cm-2.

We introduce single-molecule spectroelectrochemistry (SMS-EC), a powerful new technique for studying electrochemical kinetics in highly heterogeneous systems. This technique uses fluorescence single-molecule spectroscopy to indirectly measure electrochemical kinetics one molecule at a time, offering for the first time the distribution of key electrochemical variables, such as the half-wave potential, E1/2, not just the ensemble averages. In SMS-EC, the potential of the working electrode of an electrochemical cell is linearly scanned while simultaneously measuring the florescence intensity, Ifl(t), of individual single molecules as a function of time in a wide-field microscope. SMS-EC is used herein to study the oxidation at an indium tin oxide (ITO) electrode of single molecules of the organic conjugated polymer F8BT. The results reveal both excited singlet state and ground state oxidation of F8BT. The latter process occurs over a narrow distribution of single-molecule half-wave potential values, indicating a relatively uniform electrochemical potential at the electrode.

The concentrated electric field (E-field) in the vicinity of a voltage-biased near-field optical probe is used to modulate the photoluminescence of organic thin films on the ∼100 nm scale. The samples are bilayers comprising a self-organized-thin-film (50−500 nm) layer of zinc-octakis (β-decoxyethyl) porphyrin (ZnODEP) on top of an indium tin oxide (ITO) coated glass electrode. The Al coated-optical-fiber-near-field probe functions simultaneously as a noncontacting moveable electrode and a local source of optical excitation (30−70 nm aperture). When the ITO electrode is charged positive relative to the probe (yielding a field on the order of 1MV/cm-1), the photoluminescence (fluorescence) intensity decreases ∼5% and the probe−sampleprobe−sample distance (under shear-force feedback control) increases ∼7 Å. Opposite effects for both signals occur when the ITO is charged negative. The E-field effect on the near-field luminescence properties of thin films of ZnODEP is discussed in terms of the following physical mechanisms:  (i) direct field induced dissociation of excitons, (ii) exciton/charge carrier electron/hole transfer processes, and (iii) interfacial electron/hole transfer processes. The potential for using the observed effects as an indirect means of imaging charge injection efficiencies in organic thin film devices is explored.

A newly synthesized light emitting compound 9,10-dimethylsulfone-7,12-diphenylbenzo[k]fluoranthene (DSDPBF) and its synthetic intermediate 9, 10-dimethyl-7,12-diphenylbenzo[k]fluoranthene (DMDPBF) were studied to evaluate how the addition of weak electron donating methyl groups and the subsequent addition of an electron withdrawing sulfone group affect the photophysical and electrochemical properties as well as the rate of radical cation coupling of the parent compound, 7,12-diphenylbenzo[k]fluoranthene (DPBF). Although the photochemical and electrochemical properties of DSDPBF were more similar to the unsubstituted DPBF than to the DMDPBF, there was a substantial decrease in the quantum efficiency upon addition of the electronrich sulfone group which was not observed upon addition of the methyl groups. On the other hand, the rate of radical cation coupling or dimerization observed upon electrochemical oxidation varied significantly. The addition of the electron donating methyl groups decreased the reactivity of the radical cation resulting in a 40 times slower rate of dimerization than that observed for the unsubstituted benzo[k]fluoranthene, whereas the addition of the electron withdrawing sulfone group to the methyl groups increased the radical cation reactivity resulting in a rate of dimerization that was 3 times faster than the unsubstituted parent compound. As a result, the electrogenerated chemiluminescence emission spectrum obtained from the annihilation reaction between the radical anion and radical cations of DSDPBF was dominated by emission from the dimer at 589 and 621 nm instead of emission from the monomer at ca. 485 nm. † Part of the special issue "Noboru Mataga Festschrift".