Masatoshi Kozaki

Synthesis and preliminary testing of molecular wires and devices.

Presented here are several convergent synthetic routes to conjugated oligo(phenylene ethynylene)s. Some of these oligomers are free of functional groups, while others possess donor groups, acceptor groups, porphyrin interiors, and other heterocyclic interiors for various potential transmission and digital device applications. The syntheses of oligo(phenylene ethynylene)s with a variety of end groups for attachment to numerous metal probes and surfaces are presented. Some of the functionalized molecular systems showed linear, wire-like, current versus voltage (I(V)) responses, while others exhibited nonlinear I(V) curves for negative differential resistance (NDR) and molecular random access memory effects. Finally, the syntheses of functionalized oligomers are described that can form self-assembled monolayers on metallic electrodes that reduce the Schottky barriers. Information from the Schottky barrier studies can provide useful insight into molecular alligator clip optimizations for molecular electronics.

Evolution of Strategies for Self‐Assembly and Hookup of Molecule‐Based Devices

ABSTRACT: Strategies for self‐assembling molecule‐based devices are considered in terms of current chemical issues whose resolution appears critical to efficient connection and addressing of electronically active molecules between electrodes. We discuss issues related to the type and shape of the molecules, chemical bonding at junctions, molecular lengths and electrode gap matching, molecular alignment at electrodes, chemistry of deposited metal contacts, and the doping of molecular conductors. Examples of each of these aspects is given using fully conjugated molecules, constituted from rigid rod phenylene‐ethynylene units, self‐assembled onto metal and semiconductor surfaces.

Benzoxazinophenoxazines: neutral and charged species

Abstract A new electron-donor, benzoxazinophenoxazine 1 , was synthesized. It showed a low oxidation potential of +0.21∼+0.23 V versus SCE. The neutral molecule, its radical cation salts, and charge transfer complexes were synthesized and characterized.

Exchange interaction of bispyridinyl diradicals linked by σ-frames

1,1′-(Di-, tri-, tetramethylene, and trans-1,4-cyclohexanediyl)bis(2,4,6-triphenylpyridinyl) diradicals were prepared and their exchange interaction was studied. The exchange interaction was found to be considerably variable depending on the structure of the σ-framed linkers: a singlet ground state with ΔES-T > 1.7 kJ/mol for the dimethylene-, singlets with ΔES-T < 230 J/mol for the trimethylene- and tetramethylene-, and a triplet or a degenerate singlet with the triplet for trans-1,4-cyclohexandiyl-linked diradicals.

Preparation and Exchange Interaction of DPPH-Derived Polyradicals

Abstract A series of 1,1′-(benzene-1,3-diyl)bis(1-phenyl-2-picrylhydrazine) derivatives was prepared and oxidized to generate the corresponding bis-DPPH diradicals. No triplet species was observed for the parent compound in the ESR. Incorporation of substituents in both the central benzene ring and the N-phenyl groups resulted in the detection of triplet diradicals. Especially, the diradical with Me and t-Bu groups on the central benzene and the N-phenyl rings, respectively, was successfully purified and isolated at O °C as a purple solid. Temperature-dependence of the intensity of the ESR signal showed that the isolated radical had a triplet ground state.

Preparation and characterization of novel DPPH-based diradicals

Abstract A series of 1,1′-(2,4-di-X-benzene-1,3-diyl)bis[1-(4-Y-phenyl)-2-picrylhydrazine]s were prepared and oxidized to generate the corresponding bis- DPPH diradicals. No triplet species was observed for the compounds with X = H in the ESR measurement. Modification of the central benzene ring (X = Me) and N-phenyl group (Y = OMe, Ph, t -Bu) allowed the detection of their triplet diradicals. Especially, the diradical with X = Me, Y = t -Bu was successfully purified, isolated at 0 °C as a purple solid, and was shown to be in a triplet ground state.