Ordered Polyelectrolyte Multilayers: Unidirectional FRET Cascade in Nanocompartmentalized Polyelectrolyte Multilayers

Multifunctional polyelectrolyte (or layer‐by‐layer, LbL) multilayers consisting of a set of nanocompartments separated by impermeable ultrathin barriers, whereby the thickness of the compartments is tuned in the range 1–10 nm, are synthesized. Each compartment contains a different dye, introduced by co‐adsorption during multilayer deposition. Different LbL barriers are tested for impermeability towards dye diffusion while simultaneously allowing energy transfer to occur between the compartmentalized dyes. Cross‐linked LbL multilayers based on poly(acrylic acid) and poly(allyl amine) are shown to provide the desired impermeability for thicknesses as small as about 2.5 nm. A proof‐of‐concept system is then realized involving a cascade of two FRET processes, whereby the light energy is collected in a first nanocompartment containing pyranine, sent to a second nanocompartment loaded with fluorescein, before finally being transferred to a third, Nile blue‐filled compartment located at the external surface of the film. This demonstrates the possibility to fabricate complex light‐harvesting antenna systems by LbL assembly while controlling the architecture of the antenna down to a few nanometers.     

Internal Architecture and Adsorption Sites of Violet Lander Molecules Assembled on Native and KBr‐Passivated InSb(001) Surfaces

The adsorption of individual Violet Lander molecules self‐assembled on the c(8×2) reconstructed InSb(001) surface in its native form and on the surface passivated with one to three monolayers of KBr is investigated by means of low‐temperature scanning tunneling microscopy (STM). Preferred adsorption sites of the molecules are found on flat terraces as well as at atomic step edges. For molecules immobilized on flat terraces, several different conformations are identified from STM images acquired with submolecular resolution and are explained by the rotation of the 3,5‐di‐tert‐butylphenyl groups around σ bonds, which allows adjustment of the molecular geometry to the anisotropic substrate structure. Formation of ordered molecular chains is found at steps running along substrate reconstruction rows, whereas at the steps oriented perpendicularly no intermolecular ordering is recorded. It is also shown that the molecules deposited at two or more monolayers of the epitaxial KBr spacer do not have any stable adsorption sites recorded with STM. Prospects for the manipulation of single molecules by using the STM tip on highly anisotropic substrates are also explored, and demonstrate the feasibility of controlled lateral displacement in all directions.     

Twisted Morphologies and Novel Chiral Macroporous Films from the Self‐Assembly of Optically Active Helical Polyphosphazene Block Copolymers

A series of optically active helical polyphosphazene block copolymers of general formula R? [N?P(O₂C₂₀H₁₂)]_n‐b‐[N?PMePh]_m (R‐ 7 a – c ) was synthesized and characterized. The polymers were prepared by sequential living cationic polycondensation of N‐silylphosphoranimines using the mono‐end‐capped initiator [Ph₃P?N?PCl₃][PCl₆] ( 5 ) and exhibit a low polydispersity index (ca. 1.3). The temperature dependence of the specific optical activity ([α]_D) of R‐ 7 a , b relative to that for the homopolymers R‐[N?P(O₂C₂₀H₁₂)]_n (R‐ 8 a ) and the R/S analogues (R/S‐ 7 a , b ), revealed that the binaphthoxy–phosphazene segments induce a preferential helical conformation in the [N?PMePh] blocks through a “sergeant‐and‐soldiers” mechanism, an effect that is unprecedented in polyphosphazenes. The self‐assembly of drop‐cast thin films of the chiral block copolymer R‐ 7 b (bearing a long chiral and rigid R? [N?P(O₂C₂₀H₁₂)] segment) evidenced a transfer of helicity mechanism, leading to the formation of twisted morphologies (twisted “pearl necklace”), not observed in the nonchiral R/S‐ 7 b . The chiral R‐ 7 a and the nonchiral R/S‐ 7 a , self‐assemble by a nondirected morphology reconstruction process into regular‐shaped macroporous films with chiral‐rich areas close to edge of the pore. This is the first nontemplate self‐assembly route to chiral macroporous polymeric films with pore size larger than 50 nm. The solvent annealing (THF) of these films leads to the formation of regular spherical nanostructures (ca. 50 nm), a rare example of nanospheres exclusively formed by synthetic helical polymers.     

The effect of illumination on the depth profile of thermally annealed MEH‐PPV/dPS blends

Due to its simplicity and cost‐effectiveness, single solution casting of organic optoelectronics has grown in popularity for device fabrication to produce technologies such as organic photovoltaics and thin film transistors. In order to explore the structural evolution that occurs in the film formation of a blend composed of polystyrene and the benchmark conjugated polymer MEH‐PPV, we have performed a series of neutron reflectivity experiments focused on studying the film structure as it changes through the thermal annealing process both in the presence and absence of white light. Results indicate the formation of a nonhomogeneous blend upon casting, which becomes stratified with thermal annealing. More importantly, the extent of stratification varies with illumination, where exposure to white light increases stratification. This data suggests in situ illumination is a potential novel tool to manipulate device‐relevant morphologies of optoelectronic active layers throughout the fabrication process, offering a cheap nondestructive tool to effectively tune desired structural parameters. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1142–1149     

Self‐Assembly of a Low‐Symmetry Monodendron Containing Two Asymmetrically Linked Molecular Wedges

Herein, we describe the synthesis of a low‐symmetry monodendron, 3,4‐bis(dodecyloxy)‐5‐[3,4,5‐tris(dodecyloxy)benzyloxy]benzoic acid, following a simple route which starts from gallic acid ethyl ester and does not require any protecting groups. The self‐assembled structures formed by the compound in 3D and 2D were investigated by synchrotron X‐ray scattering and scanning force microscopy (SFM). In 3D, the compound forms a stable crystalline phase with an orthorhombic lattice in which the alkyl chains connected to different benzene rings form crystalline and amorphous domains. Upon cooling from the isotropic melt the compound exhibits a monotropic smectic mesophase. In 100‐nm‐thick films on a neutral substrate the structure loses its biaxiality, adopting a hexagonal columnar structure with the columns oriented parallel to the substrate. By contrast, in ultrathin films on graphite the SFM likely reveals two crystal orientations, which can develop due to the epitaxial adsorption on the substrate of the alkyl chains pertinent to different benzene rings.     

Deposition and characterization of Langmuir‐Blodgett films of cadmium arachidate/SWCNTs composites

The incorporation of single‐wall carbon nanotubes (SWCNTs) in cadmium arachidate film by means of the Langmuir‐Blodgett (LB) technique was investigated as a function of arachidic acid/SWCNT mass ratio at the air/water interface and in Langmuir‐Blodgett films. The behaviour at the air/water interface shows that SWCNTs act as an independent phase with respect to the cadmium arachidate. Deposition conditions are optimized when the weight ratio between the arachidic acid (AA) and SWCNTs is in the range 0.018:1 to 1:1. The general order of the LB multilayered structure was destroyed by the progressive density increase in SWCNT quantity as evidenced by X‐ray reflectivity (XRR) analysis. Scanning electron microscopy images indicated that when a multilayered structure was formed its layers consisted of SWCNT bundles stacked one over the other. Copyright © 2006 John Wiley & Sons, Ltd.     

Structure and dynamics of self-assembled poly(ethylene glycol) based coiled-coil nano-objects.

Herein we describe the structure and dynamics of self-assembled nano-objects generated from poly(ethylene glycol) based (PEG-ylated) coiled-coil hybrid block copolymers. Electron paramagnetic resonance (EPR) experiments on spin-labeled samples provided a strong indication for a parallel alignment of the peptide helices in at least the dimeric coiled-coil nano-object and indicated that the PEG chains are folded rather closely around the peptide core of the nano-objects. The EPR results were supported by AFM studies, which revealed the presence of discrete nanosized objects in thin, spin cast films of the block copolymers on mica substrates. Since their size and structure may be engineered via directed mutations in the amino acid sequence, these nano-objects may be interesting building blocks for the development of supramolecular materials with various potential applications.