We report on the first successful output of electrons directly from photosystem I (PSI) of thermophilic cyanobacteria to the gate of a field-effect transistor (FET) by bypassing electron flow via a newly designed molecular wire, i.e., artificial vitamin K(1), and a gold nanoparticle; in short, this newly manufactured photosensor employs a bio-functional unit as the core of the device. Photo-electrons generated by the irradiation of molecular complexes composed of reconstituted PSI on the gate were found to control the FET. This PSI-bio-photosensor can be used to interpret gradation in images. This PSI-FET system is moreover sufficiently stable for use exceeding a period of 1 year.

Electronic conductivity of molecular wires is a critical fundamental issue in molecular electronics. pi-Conjugated redox molecular wires with the superior long-range electron-transport ability could be constructed on a gold surface through the stepwise ligand-metal coordination method. The beta(d) value, indicating the degree of decrease in the electron-transfer rate constant with distance along the molecular wire between the electrode and the redox active species at the terminal of the wire, were 0.008-0.07 A(-1) and 0.002-0.004 A(-1) for molecular wires of bis(terpyridine)iron and bis(terpyridine)cobalt complex oligomers, respectively. The influences on beta(d) by the chemical structure of molecular wires and the terminal redox units, temperature, electric field, and electrolyte concentration were clarified. The results indicate that facile sequential electron hopping between neighboring metal-complex units within the wire is responsible for the high electron-transport ability.

Films of linear and branched oligomer wires of Fe(tpy)2 (tpy = 2,2':6',2''-terpyridine) were constructed on a gold-electrode surface by the interfacial stepwise coordination method, in which a surface-anchoring ligand, (tpy-C6H4N=NC6H4-S)2 (1), two bridging ligands, 1,4-(tpy)2C6H4 (3) and 1,3,5-(C[triple bond]C-tpy)3C6H3 (4), and metal ions were used. The quantitative complexation of the ligands and Fe(II) ions was monitored by electrochemical measurements in up to eight complexation cycles for linear oligomers of 3 and in up to four cycles for branched oligomers of 4. STM observation of branched oligomers at low surface coverage showed an even distribution of nanodots of uniform size and shape, which suggests the quantitative formation of dendritic structures. The electron-transport mechanism and kinetics for the redox reaction of the films of linear and branched oligomer wires were analyzed by potential-step chronoamperometry (PSCA). The unique current-versus-time behavior observed under all conditions indicates that electron conduction occurs not by diffusional motion but by successive electron hopping between neighboring redox sites within a molecular wire. Redox conduction in a single molecular wire in a redox-polymer film has not been reported previously. The analysis provided the rate constant for electron transfer between the electrode and the nearest redox-complex moiety, k1 (s(-1)), as well as that for intrawire electron transfer between neighboring redox-complex moieties, k2 (cm2 mol(-1) s(-1)). The strong effect of the electrolyte concentration on both k1 and k2 indicates that the counterion motion limits the electron-hopping rate at lower electrolyte concentrations. Analysis of the dependence of k1 and k2 on the potential gave intrinsic kinetic parameters without overpotential effects: (k1(0) = 110 s(-1), k2(0) = 2.6x10(12) cm2 mol(-1) s(-1) for [n Fe3], and k1(0) = 100 s(-1), k2(0) = 4.1x10(11) cm2 mol(-1) s(-1) for [n Fe4] (n = number of complexation cycles).

Ferrocene has many attractive features, such as excellent reversible redox properties, high solubility in organic media, and high modifiability with organic chemical methods, [1] and it remains a promising molecular fragment for molecular devices. Related to the redox properties, intramolecular mixed-valence interactions between multiple ferrocene sites have been regarded as a key to the realization of molecular electronics, such as molecular quantum cellular automata (QCA), [2] and the fundamental evaluation of their ability as molecular electronic wires. [3] Ferrocene exhibits an excellent affinity for organic p-bridge systems, with strong electronic coupling between the Fe d orbitals and the p orbitals of the cyclopentadienyl ring and p bridges. This mutual interaction can yield an intramolecular mixed-valence interaction [4] and a charge-transfer (CT) band in the visible region. [5][6][7] This CT transition from ferrocene d orbitals to the LUMO of either the acceptor group [5] or the p* orbital of the bridge [6] is key to the excellent nonlinear optical properties of ferrocene(donor)-acceptor combinations [5] and, for example, the green-light-induced trans-to-cis isomerization of the azobenzene moiety in ferrocenylazobenzenes. [6] To our knowledge, light-triggered electronic communication between ferrocenes has never been reported before. In the present study, we adopted an ethynylethene p framework [8] as a bridge fragment, which undergoes Z-E photoisomerization on the central CÀC double bond. The greatest benefit of introducing this class of photochromic compounds is the thermal stability of the Z and E isomers, [8] which is important in terms of their applications as, for example, molecular switching devices. Additionally, the possibility of modifying substituents on the central CÀC double bond is also likely to be important in terms of tuning the photoisomerization behavior and mixed-valence communication by the electronic perturbation of the p system. These properties of ethynylethene are superior to those of other photochromic species such as the azo group. Our attempts at quantitative analysis of the mixed-valence interaction in cis-azoferrocene have not been successful because of the low stability of the cis isomer. [9,10] Herein, we report two types of ferrocene-conjugated ethynylethenes, (E)-1 and (E)-2 (Scheme 1), which differ in the presence of a p or s substituent on the central double bond. Their photophysical properties also contrast with each other: (E)-1 showed visible-light photochromism, whereas (E)-2 did not show any photochromic behavior. Also discussed is the decrease in the strength of the mixed-valence interaction between the two ferrocene moities accompanying E!Z isomerization in 1. Compounds (E)-1 and (E)-2 were synthesized according to the procedure outlined in Scheme 1. The Z isomer of 1 was obtained as a minor by-product during the synthesis of (E)-1. [11] The absolute configurations of (E)-1 and (Z)-1 were confirmed by single-crystal X-ray analysis (Figure 1). [12] The c...

Tokyo, Hongo, Japan ͑Received 25 November 2002; accepted 13 January 2003͒We performed systematic low-temperature (Tϭ350 mK-15 K͒ magnetotransport measurements on the two-dimensional hole gas with various sheet carrier densities P s ϭ(0.57-2.1)ϫ1012 cm