Polymerization of Physisorbed Molecular Monolayers via Overhanging Alkynyl Chains: Characterization of Polymerization Kinetics and Monolayer Durability.

Monolayers self-assembled by triphenyleneethynylene (TPE) compounds bearing two terminal alkynyl chains were polymerized by Glaser-Hay (G-H) alkyne coupling at the acetonitrile-HOPG interface. The alkynyl chains extend into the solution due to the monolayer's dense-packed morphology. Reacting substructures that have no morphology-determining roles is a potential strategy for preserving monolayer morphology throughout polymerization.

Reactive two-component monolayers template bottom-up assembly of nanoparticle arrays on HOPG.

Two triphenyleneethynylene derivatives, 1OH and 2, self-assemble a patterned monolayer (ML) at the solution-graphite (HOPG) interface. The four molecule unit cell of the ML, (1OH1OH22), spans 19 nm and contains adjacent columns of 1OH molecules spaced by 4.7 nm.

Zipping and unzipping monolayers: switchable monolayer oligomerization and adhesion via thiol-disulfide interconversion.

Triphenyleneethynylene (TPE) monolayers at the solution-HOPG interface are oligomerized by the oxidation of pendant thioethers to form disulfide cross-links. The oligomerized TPE monolayer adheres strongly to HOPG. Disulfide reduction unzips the oligomers to form a monomeric TPE monolayer with pendant thiols.

Tracking Invisible Transformations of Physisorbed Monolayers: LDI-TOF and MALDI-TOF Mass Spectrometry as Complements to STM Imaging.

Triphenyleneethynylene (TPEE) derivatives bearing one long aliphatic chain on each terminal aryl ring and two short aliphatic chains on the central aryl ring (core chains) self-assemble single component and 1-D patterned, two-component, crystalline monolayers at the solution-graphite interface. The monolayer morphology directs the core chains off the graphite, making them accessible for chemical reactions but invisible to imaging by scanning tunneling microscopy (STM). This precludes using STM to monitor transformations of the core chains, either by reaction or solution-monolayer exchange of TPEE molecules.

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.

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.

Odd or even? Monolayer domain size depends on diyne position in alkadiynylanthracenes.

1,5-(Alkadiynyl)anthracenes self-assemble single component and multicomponent monolayers at the solution-HOPG interface. An alkadiynyl chain's kinked shape constrains the molecular structures with which it can close-pack. This affords rudimentary molecular recognition that has been used to direct self-assembly of 1-D patterned, multicomponent monolayers.

Monolayer patterning using ketone dipoles.

The self-assembly of multi-component monolayers with designed patterns requires molecular recognition among components. Dipolar interactions have been found to influence morphologies of self-assembled monolayers and can affect molecular recognition functions. Ketone groups have large dipole moments (2.

Reactive capture of gold nanoparticles by strongly physisorbed monolayers on graphite.

Anthracene Diels Alder adducts (DAa) bearing two long side chains (H-(CH(2))(22)O(CH(2))(6)OCH(2)-) at the 1- and 5-positions form self-assembled monolayers (SAMs) at the phenyloctane-highly oriented pyrolytic graphite (HOPG) interface. The long DAa side chains promote strong physisorption of the monolayer to HOPG and maintain the monolayer morphology upon rinsing or incubation in ethanol and air-drying of the substrate. Incorporating a carboxylic acid group on the DAa core enables capture of 1-4 nm diameter gold nanoparticles (AuNPs) provided (i) the monolayer containing DAa-carboxylic acids is treated with Cu(2+) ions and (ii) the organic coating on the AuNP contains carboxylic acids (11-mercaptoundecanoic acid, MUA-AuNP).

Patterned monolayer self-assembly programmed by side chain shape: four-component gratings.

A molecular recognition strategy based on alkadiyne side chain shape is used to self-assemble a four-component, 1D-patterned monolayer at the solution-HOPG interface. The designed monolayer unit cell contains six molecules and spans 23 nm × 1 nm. The unit cell's internal structure and packing are driven by complementary shapes and lengths of six different alkadiyne side chains.

Tetris in monolayers: patterned self-assembly using side chain shape.

The "kinked" shapes of conjugated alkadiynes constrain chain packing in monolayers on HOPG. Centrally located diyne units permit assembly of 1,5-bis(alkadiyne)anthracene monolayers. Off-center diynes inhibit self-assembly.

Photo- and biophysical studies of lectin-conjugated fluorescent nanoparticles: reduced sensitivity in high density assays.

Lectin-conjugated, fluorescent silica nanoparticles (fNP) have been developed for carbohydrate-based histopathology evaluations of epithelial tissue biopsies. The fNP platform was selected for its enhanced emissive brightness compared to direct dye labeling. Carbohydrate microarray studies were performed to compare the carbohydrate selectivity of the mannose-recognizing lectin Concanavalin A (ConA) before and after conjugation to fluorescent silica nanoparticles (ConA-fNP).

Dipolar side chain control of monolayer morphology: symmetrically substituted 1,5-(mono- and diether) anthracenes at the solution-HOPG interface.

Scanning tunneling microscopy (STM) is used to determine the 2-D unit cell parameters of monolayers self-assembled by twelve symmetrical, 1,5-bis(linear aliphatic ether side chain) anthracenes at the solution-graphite interface. The standard morphology assembled by 1,5-bis(alkyloxymethyl) anthracenes consists of single-lamella domains containing columns of anthracene cores alternating with columns of interdigitated, aliphatic side chains. Adjacent side chains within the aliphatic columns adsorb in antiparallel orientations.

Self-assembly of patterned monolayers with nanometer features: molecular selection based on dipole interactions and chain length.

Patterned cocrystal monolayers self-assemble on HOPG in contact with solutions containing complementary pairs of 1,5-chain-substituted anthracene derivatives. Monolayer unit cells containing three or four molecules and spanning 9-11 nm are generated. The monolayers consist of alternating aromatic and aliphatic columns.

Photothermal readout of surface-arrayed proteins: attomole detection levels with gold nanoparticle visualization.

Transverse photothermal beam deflection (tPBD) is used to detect and quantify proteins arrayed on slides. The slides are "read" using an argon-ion excitation source. Optical absorption cross-sections of most proteins are too small for submonolayer coverages to produce thermal gradients of sufficient magnitude for detection using tPBD.

Nanowiring of a redox enzyme by metallized peptides.

A molecular assembly consisting of a redox enzyme, NADH peroxidase, a metallized double-helical peptide, and a gold nanoparticle immobilized onto a gold wire derivatized with a benzenedithiol compound, initiated and conducted redox signals in the presence of H(2)O(2) and NADH. The current generated by the binding of NADH, the electron donor, was transduced through the molecular assembly with apparently little loss of signal to the solution. The currents measured correlate to an electron transfer rate constant on the order of 3,000 s(-1) within each assembly.

Scanning tunneling microscopy of prochiral anthracene derivatives on graphite: chain length effects on monolayer morphology.

The morphology of monolayers formed upon adsorption of prochiral 1,5-substituted anthracene derivatives on highly oriented pyrolytic graphite is investigated using scanning tunneling microscopy at the liquid-solid interface. The adsorption orientation of these prochiral anthracene derivatives positions one of their enantiotopic faces in contact with the graphite. The molecules adsorb in rows with contact between adjacent anthracenes.

Dynamic nature of the intramolecular electronic coupling mediated by a solvent molecule: a computational study.

We present a combined Molecular Dynamics/Quantum Chemical study of the solvent-mediated electronic coupling between an electron donor and acceptor in a C-clamp molecule. We characterize the coupling fluctuations due to the solvent motion for different solvents (acetonitrile, benzene, 1,3-diisopropyl-benzene) for the charge separation and the charge recombination processes. The time scale for solvent-induced coupling fluctuation is approximately 0.

Hole transfer in a C-shaped molecule: conformational freedom versus solvent-mediated coupling.

The electronic coupling matrix elements attending the charge separation reactions of a C-shaped molecule containing an excited pyrene as the electron acceptor and a dimethylaniline as the donor are determined in aromatic, ether, and ester solvents. Band shape analyses of the charge-transfer emission spectra (CT --> S(0)) provide values of the reaction free energy, the solvent reorganization energy, and the vibrational reorganization energy in each solvent. The free energy for charge separation in benzene and toluene solvents is independently determined from the excited state equilibrium established between the locally excited pyrene S(1) state and the charge-transfer state.