Vibrational Cooling in Oligomeric Viologens of Different Sizes and Topologies.

Vibrational cooling was investigated in a set of homologous dimers and trimers with methyl viologen repeat units (MV). The rapid, <500 fs decay of the D excited state of monoreduced viologen (MV) via a conical intersection allows the preparation of a vibrationally hot D ground state with a large excess energy of 1.7 eV, which is equivalent to the initial effective temperature of ∼800 K.

Electrostatic Repulsion-Induced Desorption of Dendritic Viologen-Arranged Molecules Anchored on a Gold Surface through a Gold-Thiolate Bond Leading to a Tunable Molecular Template.

We investigated the adsorption and desorption behavior of self-assembled monolayers (SAMs) on gold derived from dendritic viologen-arranged molecules with an ω-mercaptodecyl group (A n, n (dendritic generation) = 0-3) at the apex of the dendritic structure in polar solvents. The adsorption of the dendritic molecules occurred quickly and saturated within a few minutes in an acetonitrile/ethanol (1/1, v/v) mixture at a concentration of 2 mM. Atomic force microscopy images of the SAMs showed flat surfaces regardless of the dendritic generation because the peripheral viologen units were closely packed at the surface of the molecular layer.

Generation Dependent Ultrafast Charge Separation and Recombination in a Pyrene-Viologen Family of Dendrons.

The ability of a dendritic network to intercept electrons and extend the lifetime of a short-lived photoinduced charge separated (CS) state was investigated in a homologous family of methyl viologen (MV(2+)) dendrons spanning four generations, G0 through G3. The CS state in the parent pyrene-methylene-viologen G0 system with a single acceptor exhibits an extremely short lifetime of τ = 0.72 ps.

Conical Gradient Junctions of Dendritic Viologen Arrays on Electrodes.

The three-dimensional construction of arrays of functional molecules on an electrode surface, such as organic semiconductors and redox-active molecules, is a considerable challenge in the fabrication of sophisticated junctions for molecular devices. In particular, well-defined organic layers with precise molecular gradients are anticipated to function as novel metal/organic interfaces with specific electrical properties, such as a space charge layer at the metal/semiconductor interface. Here, we report a strategy for the construction of a three-dimensional molecular array with an electrical connection to a metal electrode by exploiting dendritic molecular architecture.

Copolymers of vinyl-containing benzoxazine with vinyl monomers as precursors for high performance thermosets.

A benzoxazine containing a vinyl group (P-4va) was prepared by the reaction of phenol, 4-vinylaniline, and paraformaldehyde. A differential scanning calorimetry (DSC) study revealed that ring-opening polymerization of the benzoxazine and chain polymerization of the vinyl group occurred in the same temperature range. When 2,2'-azobisisobutyronitrile was added as a radical initiator to P-4va, however, only the vinyl groups were polymerized at lower temperature, giving oligo(P-4va) that contains pendent benzoxazine units.

Crystallization behavior of single isotactic poly(methyl methacrylate) chains visualized by atomic force microscopy.

We have, for the first time, successfully visualized the crystallization behavior of a single isolated polymer chain at the molecular level by atomic force microscopy (AFM). Previously, we found that isotactic poly(methyl methacrylate) (it-PMMA) formed two-dimensional folded chain crystals composed of double-stranded helices upon compression of its Langmuir monolayer on a water surface, and the molecular images of the crystals deposited on mica were clearly visualized by AFM (Kumaki, J.; et al.

Ketene-Based Route to rigid Cyclobutanediol Monomers for the Replacement of BPA in High Performance Polyesters.

Recently, polyesters based on the diol monomer 2,2,4,4-tetramethyl-1,3-cyclobutanediol (TMCBDO) have been shown to exhibit excellent thermal stability, mechanical properties, and optical clarity. In particular, the ability of TMCBDO to replace bisphenol A as a diol monomer in polycarbonates and polyesters has resulted in significant commercial and academic interest in these types of monomers. Herein, we report a versatile synthetic strategy based on the dimerization of ketenes derived from the thermal treatment of Meldrum's acid for the synthesis of structurally diverse cyclobutanediol (CBDO) monomers.

Separation of C70 over C60 and selective extraction and resolution of higher fullerenes by syndiotactic helical poly(methyl methacrylate).

A one-handed helical polymer, syndiotactic poly(methyl methacrylate) (st-PMMA), recognizes the size and chirality of higher fullerenes through an induced-fit mechanism and can selectively extract enantiomers of the higher fullerenes, such as C(76), C(80), C(84), C(86), C(88,) C(90), C(92), C(94), and C(96). This discovery will generate a practical and valuable method for selectively extracting the elusive higher fullerenes and their enantiomers and opens the way to developing novel carbon cage materials with optical activities.

Helix-sense-controlled synthesis of optically active poly(methyl methacrylate) stereocomplexes.

Optically active poly(methyl methacrylate) (PMMA) stereocomplexes were prepared through the helix-sense-controlled supramolecular inclusion of an isotactic (it) PMMA within the helical cavity of an optically active, fullerene-encapsulated syndiotactic (st) PMMA with a macromolecular helicity memory. The observed and calculated vibrational circular dichroism spectra revealed that the it-PMMA replaced the encapsulated fullerenes to fold into a double-stranded helix with the same handedness as that of the st-PMMA single helix through the formation of a topological triple-stranded helix.

Molecular weight recognition in the multiple-stranded helix of a synthetic polymer without specific monomer-monomer interaction.

Stereoregular isotactic and syndiotactic poly(methyl methacrylate)s (it- and st-PMMAs) are known to form a multiple-stranded complementary helix, so-called stereocomplex (SC) through van der Waals interactions, which is a rare example of helical supramolecular structures formed by a commodity polymer. In this study, we prepared SCs by using uniform it- and st-PMMAs and those with a narrow molecular weight distribution having different molecular weights and investigated their structures in detail using high-resolution atomic force microscopy as a function of the molecular weight and molecular weight distribution of the component PMMAs. We found that complementary it- and st-PMMAs with the longer molecular length determine the total length of the SC, and molecules of the shorter component associate until they fill up or cover the longer component.

Nanosphere and nanonetwork formations of [60]fullerene-end-capped stereoregular poly(methyl methacrylate)s through stereocomplex formation combined with self-assembly of the fullerenes.

We report a novel and versatile method for constructing a supramolecular nanosphere and nanonetwork based on isotactic and syndiotactic C60-end-capped poly(methyl methacrylate)s (it- and st-PMMA-C60's) through their stereocomplex formation combined with self-assembly of the terminal C60. The stereoregular PMMA-C60's with a precisely controlled structure including molecular weight, its distribution, tacticity, and the chain-end structure were synthesized by the stereospecific anionic living polymerizations of methyl methacrylate followed by end-capping with C60, and their structures were proven by size exclusion chromatography, NMR, UV-vis, and MALDI-TOF-MS analyses. The stereoregular PMMA-C60's self-assembled to form a core-shell aggregate with C60 as the core and the PMMA chains as the shell in H2O/CH3CN (1/9, v/v) due to the solvophobic interaction of the C60 units.

Synthesis, isolation via self-assembly, and single-molecule observation of a [60]fullerene-end-capped isotactic poly(methyl methacrylate).

We report the preparation and single-molecule observation of a high molecular weight C60-end-capped, stereoregular poly(methyl methacrylate) (PMMA-C60) with a precisely controlled structure. The highly isotactic PMMA-C60 (mm = 98%) with a narrow molecular weight distribution was synthesized by the stereospecific anionic living polymerization of tert-butyl methacrylate followed by end-capping with C60, hydrolysis of the pendant esters, and methylation with CH3I. Although the functionality of the C60 (fC60) of the as-prepared isotactic PMMA was imperfect (ca.

Two-dimensional folded chain crystals of a synthetic polymer in a Langmuir-Blodgett film.

Isotactic poly(methyl methacrylate) monolayers deposited from a water surface onto mica at different surface pressures were studied by atomic force microscopy, and their structure formation from single chains to two-dimensional folded chain crystals was clearly observed. Furthermore, gentle crystallization of the monolayer by slow compression on the water surface enabled the observation of crystals at a molecular level, thus visualizing the chain foldings and tie-chains for the first time. The resulting molecular level information will provide an important clue toward the understanding of polymer crystals not only in two dimensions but also in three dimensions.