20 research outputs found

    Intramolecular Electron-Transfer Studies as a Function of Bridge Topology: The Importance of Solvent-Mediated Donor-Acceptor Electronic Coupling

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    The donor-acceptor electronic coupling matrix elements, |V|, for photoinduced, intramolecular electron-transfer (ET) reactions in one linear and three C-shaped molecules have been determined from the temperature dependence of ET rate constants. The coupling matrix element in the linear molecule was found to be solvent-independent. By contrast, the coupling matrix elements in two of the three C-shaped molecules exhibit significant solvent dependence. Donor-acceptor coupling matrix elements were calculated for the linear and C-shaped molecules in the absence and presence of solvent molecules using the generalized Mulliken-Hush theory. Together, the experimental and theoretical results indicate that solvent molecules, and not the covalent bridge, mediate the electronic coupling in the C-shaped molecules. Preliminary studies of ET rate constants as a function of solvent bulk are also described

    Theoretical Study of Solvent Effects on the Electronic Coupling Element in Rigidly Linked Donor-Acceptor Systems

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    The recently developed generalized Mulliken-Hush approach for the calculation of the electronic coupling matrix element for electron-transfer processes is applied to two rigidly linked donor-bridge-acceptor systems having dimethoxyanthracene as the donor and a dicarbomethoxycyclobutene unit as the acceptor. The dependence of the electronic coupling matrix element as a function of bridge type is examined with and without solvent molecules present. For clamp-shaped bridge structures solvent can have a dramatic effect on the electronic coupling matrix element. The behavior with variation of solvent is in good agreement with that observed experimentally for these systems

    Shape-Directed Patterning and Surface Reaction of Tetra-diacetylene Monolayers: Formation of Linear and Two-Dimensional Grid Polydiacetylene Alternating Copolymers

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    Side chains containing two diacetylene units spaced by an odd number of methylene units exhibit pronounced “bumps” composed of 0.3 nm steps, in opposite directions, at odd and even side-chain positions. In densely packed self-assembled monolayers, the bis-diacetylene bumps stack into each other, similar to the stacking of paper cups. Bis-diacetylene side chain structure and associated packing constraints can be tailored by altering the bump width, direction, side-chain location, and overall side-chain length as a means to direct the identities and alignments of adjacent molecules within monolayers. Scanning tunneling microscopy (STM) at the solution–HOPG interface confirms the high selectivity and fidelity with which bis-diacetylene bump stacking directs the packing of shape-complementary side chains within one-component monolayers and within two-component, 1-D self-patterned monolayers. Drop cast or moderately annealed monolayers of anthracenes bearing two bis-diacetylene side chains assemble single domains as large as 10<sup>5</sup> nm<sup>2</sup>. Light-induced cross-linking of two-component, 1-D patterned monolayers generates linear polydiacetylene alternating copolymers (A-B-)<sub><i>x</i></sub> and 2-D grid polydiacetylene alternating copolymers (A<sub>‑B‑</sub><sup>‑B‑</sup>A<sub>‑B‑</sub><sup>‑B‑</sup>)<sub><i>x</i></sub> that covalently lock in monolayer structure and patterns

    Shape Amphiphiles in 2‑D: Assembly of 1‑D Stripes and Control of Their Surface Density

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    The morphology of monolayers assembled from mixtures of a shape-amphiphilic molecule, {33,19} = 1-((hentriaconta-14,16-diyn-1-yloxy)­methyl)-5-((heptadecyloxy)­methyl)­anthracene, and a symmetric molecule, {19<sub>2</sub>}, at the solution–HOPG interface depends strongly on the components’ solution concentrations and sample annealing history. The kinked alkadiyne side chain, {33}, packs optimally only with antiparallel aligned, {33} side chains. Thus, optimal packing of {33} side chains should assemble “{33} stripes” consisting of two adjacent {33,19} columns with interdigitated {33} chains. The aliphatic {19} side chain of {33,19} can pack with antiparallel aligned {19} side chains from {19<sub>2</sub>} or from {33,19}. Thus, {33} stripes can incorporate as “guests” within {19<sub>2</sub>} “host” monolayers. The composition and morphology of monolayers formed by drop casting solutions of {33,19} and {19<sub>2</sub>} at 19 °C are dominated by assembly kinetics. Short {33} strips are immersed haphazardly in monolayers comprised mostly of {19<sub>2</sub>}. Thermal annealing promotes fuller expression of {33,19}’s shape amphiphilicity and assembly of thermodynamically determined monolayers incorporating 1-D {33} stripes within a 2-D matrix of {19<sub>2</sub>}. Larger solution mole fractions of {19<sub>2</sub>} yield annealed monolayers with nearly constant {33} strip lengths, decreased {33} strip density, and increased {33} strip spacing

    Shape Amphiphiles in 2‑D: Assembly of 1‑D Stripes and Control of Their Surface Density

    No full text
    The morphology of monolayers assembled from mixtures of a shape-amphiphilic molecule, {33,19} = 1-((hentriaconta-14,16-diyn-1-yloxy)­methyl)-5-((heptadecyloxy)­methyl)­anthracene, and a symmetric molecule, {19<sub>2</sub>}, at the solution–HOPG interface depends strongly on the components’ solution concentrations and sample annealing history. The kinked alkadiyne side chain, {33}, packs optimally only with antiparallel aligned, {33} side chains. Thus, optimal packing of {33} side chains should assemble “{33} stripes” consisting of two adjacent {33,19} columns with interdigitated {33} chains. The aliphatic {19} side chain of {33,19} can pack with antiparallel aligned {19} side chains from {19<sub>2</sub>} or from {33,19}. Thus, {33} stripes can incorporate as “guests” within {19<sub>2</sub>} “host” monolayers. The composition and morphology of monolayers formed by drop casting solutions of {33,19} and {19<sub>2</sub>} at 19 °C are dominated by assembly kinetics. Short {33} strips are immersed haphazardly in monolayers comprised mostly of {19<sub>2</sub>}. Thermal annealing promotes fuller expression of {33,19}’s shape amphiphilicity and assembly of thermodynamically determined monolayers incorporating 1-D {33} stripes within a 2-D matrix of {19<sub>2</sub>}. Larger solution mole fractions of {19<sub>2</sub>} yield annealed monolayers with nearly constant {33} strip lengths, decreased {33} strip density, and increased {33} strip spacing
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