Grafted carbazole-assisted electrodeposition of graphene oxide.

The electrodeposition of graphene oxide (GO) by covalently linked electroactive monomer, carbazole (Cbz) is first demonstrated herein. This is based on the electropolymerization and electrodeposition of covalently linked Cbz units when a potential is applied. During the electrochemical process, the Cbz groups electropolymerize and carry the GO nanosheets as it electrodeposits on the substrate. Moreover, the GO-Cbz sheets selectively deposit onto the conducting regions of the substrate, which demonstrates its promise for the fabrication of electropatterned graphene-based devices. In addition, GO-Cbz is a promising material for the fabrication of nanocomposite coatings for anticorrosion application. In as little as 1 wt % GO-Cbz loading, a protection efficiency as high as 95.4% was achieved.

A supramolecularly templated catenane initiator and a controlled ring expansion strategy.

We report the first synthesis of a catenated polymer via a ring-expansion strategy, which is based on a supramolecularly templated initiator. The high yielding synthesis and simple isolation method will enable the investigation and development of this unique polymer system for further applications.

Catenated PS-PMMA block copolymers via supramolecularly templated ATRP initiator approach.

A novel route to synthesize catenated macrocyclic PS-PMMA block copolymers is demonstrated via combination of supramolecular chemistry and controlled radical polymerization (CRP). Polymerization of styrene with bromopropionate ester initiator coupled with phenanthroline Cu(I) complex affords a four arm PS macroinitiator, which upon further chain extension by polymerization of MMA generates a four arm PS-PMMA block copolymer. Intramolecular coupling of PS-PMMA-Br arms via low temperature styrene-assisted atom transfer radical coupling (ATRC) leads to the formation of PS-PMMA catenand, which generates the metal-free catenated macrocyclic PS-PMMA block copolymer after removal of Cu metal. The interlocked structures of catenated block copolymers are confirmed by GPC, NMR, and AFM image analysis.

Conjugated polymer network films of poly(p-phenylene vinylene) with hole-transporting carbazole pendants: dual photoluminescence and electrochromic behavior.

A series of poly(p-phenylene vinylene) (PPV) copolymers functionalized with hole-transport and electrochemically active carbazole units as pendant moieties is reported. These polymers exhibit photoluminescence properties by virtue of the PPV analogous backbone. They were also designed as precursor polymer bearing the electroactive carbazole group to form conjugated polymer network (CPN) films by electrodeposition. The electrochemical polymerization of the pendant units eventually lead to a dual property electro-optically active thin film - photoluminescence (PL) behavior that can be attenuated with CPN formation, and a reversible doping and dedoping processes at controlled potentials that lead to an electrochromic behavior. This reveals the ability to incorporate complementary optical and electro-optical properties within the same film using the CPN approach. It should be possible to design and synthesize other PPV π-conjugated polymers with efficient pendant hole-transport groups exhibiting tunable PL and electrochromism with cross-linking.

Facile patterning of hybrid CdSe nanoparticle films by photoinduced surface defects.

The photopatterning of CdSe quantum dots (QDs) films is facilitated by preparing defect-rich QDs on selective sites on the film. A key step is UV irradiation in the presence of a polar solvent such as methanol in situ as a "developer" which readily dissolves trioctylphosphine oxide (TOPO) but not the QDs. This results in a dramatically reduced photopatterning time and irradiation intensity requirement. The optical property changes were examined by UV-vis and fluorescence spectroscopy. Furthermore, the photo-oxidized pattern of the CdSe QD film was readily observed by fluorescence microscopy. The chemical change due to attenuation of the P═O vibration of TOPO (due to its removal) could be detected by FT-IR imaging or FT-IR chemical mapping. Thus, the protocol is a simple yet effective way of patterning PL properties of QD films at much reduced exposure time compared to previously reported methods. It may find utility for a host of cell-based film assays and PL display device applications at various resolutions.

Permeability of anti-fouling PEGylated surfaces probed by fluorescence correlation spectroscopy.

The present work reports on in situ observations of the interaction of organic dye probe molecules and dye-labeled protein with different poly(ethylene glycol) (PEG) architectures (linear, dendron, and bottle brush). Fluorescence correlation spectroscopy (FCS) and single molecule event analysis were used to examine the nature and extent of probe-PEG interactions. The data support a sieve-like model in which size-exclusion principles determine the extent of probe-PEG interactions. Small probes are trapped by more dense PEG architectures and large probes interact more with less dense PEG surfaces. These results, and the tunable pore structure of the PEG dendrons employed in this work, suggest the viability of electrochemically-active materials for tunable surfaces.

Interfacial behavior of OEG-linear dendron monolayers: aggregation, nanostructuring, and electropolymerizability.

We report on the interesting interfacial behavior of oligoethylene glycol or OEGylated linear dendron monolayers at the air-water interface as a function of (a) carbazole dendron generation, (b) the length of the OEG units, and (c) the surface pressure applied upon compression. Surface pressure-area isotherms, hysteresis studies, and isobaric creep measurement revealed a structure-property relationship consistent with the hydrophilic-lipophilic balance of a linear dendron with the OEG group serving as the surface anchor to the water subphase. AFM studies revealed that all the OEGylated carbazole dendrons self-assemble into spherical morphology at low surface pressures but form ribbonlike structures as the surface pressure is increased. This nanostructuring is primarily imparted by the increase in van der Waals forces with increasing amount of carbazole units per dendron generation on a hydrophilic mica surface. Further, electrochemical cross-linking of the carbazole molecules by cyclic voltammetery (CV) on doped Si wafer has enabled the formation of an LB film monolayer with a secondary level of organization in the monolayer imparted by the inter- and intramolecular cross-linking among the carbazole units. This study should provide a basis for monolayer film materials based on combining the LB technique and electrochemical cross-linking for nanostructuring superstructures at the air-water interface.

Colloidally templated two-dimensional conducting polymer arrays and SAMs: binary composition patterning and chemistry.

A facile approach and strategy toward binary-composition, two-dimensional (2D) patterned surfaces of conducting polymer periodic arrays, together with thiol self-assembled monolayers (SAMs) is described. The method involved a Langmuir-Blodgett (LB)-like deposition of latex microsphere particles, electropolymerization via cyclic voltammetric (CV) techniques, and self-assembly of an amphiphile. The LB-like technique enabled the monolayer deposition of different sizes of polystyrene (PS) particles in hexagonal packing arrangement on planar substrates. Combining the LB-like method with CV electropolymerization is advantageous because it provides deposition control of a polymer interconnected network, controlled composition ratio of polymer and SAMs, and control of 2D size and spacing of the spherical void pattern. Electrochemical-quartz crystal microbalance (EC-QCM) in situ monitoring of the film deposition quantified a constant and linear growth rate, with varying viscoelastic behavior of the conducting polymer adsorption on planar and PS-templated substrates. The dual-patterned surface provided a good imaging contrast as observed by atomic force microscopy (AFM). Complementary analyses such as X-ray photoelectron spectroscopy (XPS), attenuated total internal reflection infrared (ATR IR) spectroscopy, ultraviolet-visible (UV-vis) spectroscopy, and static contact angle measurements were used to characterize the formation of the patterned surface. The versatility of the method enables the potential for making various types of quantitative binary compositions and patterned surfaces using different combinations of conducting polymer or functional SAMs, which can be extended in the future to polymer brushes and layer-by-layer assembly of various materials.

Electropolymerization molecularly imprinted polymer (E-MIP) SPR sensing of drug molecules: pre-polymerization complexed terthiophene and carbazole electroactive monomers.

A novel chemosensitive ultrathin film with high selectivity was developed for the detection of naproxen, paracetamol, and theophylline using non-covalent electropolymerized molecular imprinted polymers (E-MIP). A series of monofunctional and bifunctional H-bonding terthiophene and carbazole monomers were compared for imprinting these drugs without the use of a separate cross-linker. A key step is the fast and efficient potentiostatic method of washing the template, which facilitated enhanced real-time sensing by surface plasmon resonance (SPR) spectroscopy. Various surface characterizations (contact angle, ellipsometry, XPS, AFM) of the E-MIP film verified the templating and release of the drug from the cross-linked conducting polymer film.

Synthesis and electrografting of dendron anchored OEGylated surfaces and their protein adsorption resistance.

In this study, a series of electrochemically active oligo(ethylene glycol) (OEG) linear-dendrons have been synthesized and grafted onto electrode surfaces by cyclic voltammetry (CV) to improve protein resistance. Dendronized molecules with peripheral carbazole functionality and branching architecture enabled tethering of the poly(ethylene glycol) (PEG) or OEG group with a predictable number of electrochemical reactive groups affecting OEG distribution and orientation. It is possible that ample spacing between the OEG chains affects the intrinsic hydration of these layers and thus surface protein resistance. The films were characterized by CV, surface plasmon resonance (SPR), static contact angle measurements, and atomic force microscopy (AFM). This approach should enable improved nonbiofouling properties on biorelevant electrode surfaces (metal or metal oxides) by potentiostatic or potentiodynamic electrochemical methods, providing an alternative to the self-assembled monolayer (SAM) approach for anchoring PEG layers.

Nanoparticle formation and ultrathin film electrodeposition of carbazole dendronized polynorbornenes prepared by ring-opening metathesis polymerization.

We report on the synthesis, electropolymerization, and nanoparticle formation of a series of electroactive carbazole-terminated dendronized linear polynorbornenes prepared by living ring-opening metathesis polymerization (ROMP). The molecular weight (MW) of the dendronized polymers was controlled by varying the feed ratio between the dendronized monomer and first-generation Grubbs' catalyst. Ultrathin films were prepared by electrodeposition. The electrochemical behavior and viscoelastic properties of such films were found to be highly dependent on the dendron generation and linear polymer MW as studied by electrochemical quartz crystal microbalance (E-QCM). Moreover, nanoparticle formation and size/shape control were observed by tuning the surface wetting properties of the substrate during adsorption and by intramolecular cross-linking via chemical oxidation in solution.

Self-assembly and electrochemical oxidation of polyamidoamine-carbazole dendron surfmer complexes: nanoring formation.

We report a detailed and quantitative study on the supramolecular complexation of amine-functionalized polyamidoamine (PAMAM) dendrimer G(4)-NH(2) with carboxylic acid terminal dendrons containing peripheral electroactive carbazole groups of different generations (G(0)COOH, G(1)COOH, and G(2)COOH). While the focus is on a detailed understanding and mechanism of complex formation, subsequent electrochemical oxidation of the dendron surfmers resulted in the formation of nanoring structures electrodeposited on the conducting substrate. Complexation was confirmed by NMR, UV-vis, and IR measurements. Critical micelle concentration (CMC), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) studies revealed that the ringlike structures were formed during the equilibrium-decomplexation stage and that the electrochemical process did not destroy the complex but rather stabilized it. The different generations of the dendrons provided various structures and complex formation efficacy. This type of template polymerization combined with electrochemically anodic oxidation has not been previously reported.