Laccase, a blue copper oxidase, in view of its moderate redox potential can oxidise only phenolic compounds by electron-transfer. However, in the presence of ABTS (2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonate) as a redox mediator, laccase reacts with the more difficult to oxidise non-phenolic substrates, such as benzyl alcohols. The role of ABTS in these mediated oxidations is investigated. Redox interaction with laccase could produce in situ two reactive intermediates from ABTS, namely ABTS++ or ABTS*+. These species have been independently generated by oxidation with Ce(iv) or Co(iii) salts, respectively, and their efficiency as monoelectronic oxidants tested in a kinetic study towards a series of non-phenolic substrates; a Marcus treatment is provided in the case of ABTS++. On these grounds, intervention of ABTS++ as a reactive intermediate in laccase-ABTS oxidations appears unlikely, because the experimental conditions under which ABTS++ is unambiguously generated, and survives long enough to serve as a diffusible mediator, are too harsh (2 M H2SO4 solution) and incompatible with the operation of the enzyme. Likewise, ABTS*+ seems an intermediate of limited importance in laccase-ABTS oxidations, because this weaker monoelectronic oxidant is unable to react directly with many of the non-phenolic substrates that laccase-ABTS can oxidise. To solve this paradox, it is alternatively suggested that degradation by-products of either ABTS++ or ABTS*+ are formed in situ by hydrolysis during the laccase-ABTS reactions, and may be responsible for the observed oxidation of non-phenolics.

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We have synthesized molecular clips 1 comprising (i) two benzo[k]fluoranthene sidewalls and (ii) a dimethylene-connected benzene bridge that carries two acetoxy (1a), hydroxy (1b), or methoxy (1c) substituents in the para position. Their NMR spectra, single-crystal structures, and photophysical (fluorescence intensity, lifetime, depolarization) and electrochemical properties are discussed. For the purpose of comparison, similar compounds (2 and 3) containing only one benzo[k]fluoranthene unit have been prepared and studied. The strongly fluorescent clips 1 form stable complexes with electron-acceptor guests because of a highly negative electrostatic potential on the inner van der Waals surface of their cavity. The complexation constants in chloroform solution for a variety of guests, determined by NMR and fluorescence titration, are much larger than those of the corresponding anthracene and naphthalene clips (4 and 5), particularly in the case of extended aromatic guests. The effect of the substituents in the para position of the benzene spacer unit of clips 1 is discussed on the basis of the host-guest complex structures obtained by X-ray analysis and molecular mechanics simulations. In the case of 9-dicyanomethylene-2,4,7-trinitrofluorene (TNF) guest, complex formation with clip 1a causes dramatic changes in the photophysical and electrochemical properties: (i) a new charge-transfer band at 600 nm arises, (ii) a very efficient quenching of the strong benzo[k]fluoranthene fluorescence takes place, (iii) shifts of both the first oxidation (clip-centered) and reduction (TNF-centered) potentials are observed, and (iv) reversible disassembling of the complex can be obtained by electrochemical stimulation.

or inorganic [ 13,18 ] interlayers have been introduced to protect ultrathin molecular layers from invasive, vapor deposited contacts. These approaches represent a promising pathway toward robust molecular/polymer circuits; however they require an additional organic/inorganic layer that inevitably masks the intrinsic electrical response of the molecules under investigation. A possible solution has been proposed by McCreery and co-workers, involving molecular layers that are sandwiched between carbon and copper electrodes forming stable and highly reproducible molecular junctions. [ 19 ] Remarkably, these large area junctions show high yields, endurance, and temperature stability, even though the requirement of using pyrolytic carbon as a bottom electrode might limit their applicability.Here, we demonstrate that by integration of Fe II -terpyridine redox complex oligomers [20][21][22] into large area solid-state junctions, molecular thin-fi lm devices of outstanding mechanical and electrical robustness are realized. Notwithstanding the metallic crossbar junctions are deposited in a conventional thermal evaporation process, Fe II -terpyridine oligomers are operational over a period of more than two and a half years and resist to temperatures ranging from 150-360 K. The oligomer layers show a high electron mobility ( µ e = 0.1 cm 2 V −1 s −1 ) and, most remarkably, electrical transport follows an ideal RichardsonSchottky (RS) injection behavior, as demonstrated by means of complementary experimental and theoretical investigations.Bottom electrodes are prepared by thermal evaporation of an array of eight parallel Au electrodes (each 100 µm wide) on native silicon using a shadow mask. Subsequently, metal center oligomers (MCOs) are deposited by a stepwise sequential coordination reaction of a Fe II redox center by a conjugated 1,4-di(2;2′;6′;2″-terpyridine-4′-yl)benzene (TPT) ligand ( Figure 1 a), [ 21 ] as schematically depicted in Figure 1 b. In our work, oligomers of three different lengths have been assembled by incorporation of 15, 20, and 30 Fe II metal centers (MC), yielding MCO layers with a thickness of 15, 20, and 30 nm. This allows a detailed study of their electrical characteristics as a function of molecular length. A symmetric contact of the oligomers to both Au electrodes is established by using 4′-(4-mercaptophenyl)terpyridine (MPTP) as the fi rst and last ligands of the stepwise coordination.From density functional theory (DFT) calculations, a length of 1.55 nm is derived for the repeat unit of the MCO chain (Figure 1 a). A constant increment in fi lm thickness as a function of the coordination number is determined from AFM data (Figure 1 c), following a linear regression with a slope of ≈1.08 nm per coordination step. These data and the coordination effi ciency known for the stepwise coordination process [ 23 ]