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

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

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

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 10⁵ nm². Light-induced cross-linking of two-component, 1-D patterned monolayers generates linear polydiacetylene alternating copolymers (A-B-)_<i>x</i> and 2-D grid polydiacetylene alternating copolymers (A_‑B‑^‑B‑A_‑B‑^‑B‑)_<i>x</i> that covalently lock in monolayer structure and patterns

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

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, {19₂}, 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 {19₂} or from {33,19}. Thus, {33} stripes can incorporate as “guests” within {19₂} “host” monolayers. The composition and morphology of monolayers formed by drop casting solutions of {33,19} and {19₂} at 19 °C are dominated by assembly kinetics. Short {33} strips are immersed haphazardly in monolayers comprised mostly of {19₂}. 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 {19₂}. Larger solution mole fractions of {19₂} 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

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, {19₂}, 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 {19₂} or from {33,19}. Thus, {33} stripes can incorporate as “guests” within {19₂} “host” monolayers. The composition and morphology of monolayers formed by drop casting solutions of {33,19} and {19₂} at 19 °C are dominated by assembly kinetics. Short {33} strips are immersed haphazardly in monolayers comprised mostly of {19₂}. 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 {19₂}. Larger solution mole fractions of {19₂} yield annealed monolayers with nearly constant {33} strip lengths, decreased {33} strip density, and increased {33} strip spacing