We present a plasmon-active hybrid nanomaterial design with electrochemical tunability of the localized surface plasmon resonances. The plasmonic-active nanostructures are composed of silver nanocube aggregates embedded into an electrochromic polymer coating on an indium tin oxide electrode with the nanocube aggregation controlled by the surface pressure. Such polymer-nanocube hybrid nanomaterials demonstrated unique tunable plasmonic behavior under an applied electrochemical potential. A significant reversible experimental peak shift of 22 nm at an electrical potential of 200 mV has been achieved in these measurements. Finite-difference time-domain (FDTD) simulations show that, under full oxidation potential, a maximal spectral shift of ca. 80 nm can be potentially achieved, which corresponds to a high sensitivity of 178 nm per refractive index unit. Furthermore, FDTD modeling suggests that the electrochemically controlled tunability of plasmonic peaks is caused by reversible changes in the refractive index of the electrochromic polymer coating caused by oxidation or reduction reactions under external electrical potential. Consequently, we define the orthogonal plasmonic resonance shift as a shift that is orthogonal to the redox process responsible for the refractive index change. On the basis of these results, we suggest that the combination of anisotropic nanostructures and electrochromic matrix has the potential to reversibly electrically tune plasmonic resonances over the full visible spectrum.

Although metal free cycloadditions of cyclooctynes and azides to give stable 1,2,3-triazoles have found wide utility in chemical biology and material sciences, there is an urgent need for faster and more versatile bioorthogonal reactions. We have found that nitrile oxides and diazocarbonyl derivatives undergo facile 1,3-dipolar cycloadditions with cyclooctynes. Cycloadditions with diazocarbonyl derivatives exhibited similar kinetics compared to azides whereas the reaction rates of cycloadditions with nitrile oxides were much faster. Nitrile oxides could conveniently be prepared by direct oxidation of the corresponding oximes with BAIB and these conditions made it possible to perform oxime formation, oxidation and cycloaddition as a one-pot procedure. The methodology was employed to functionalize the anomeric center of carbohydrates with various tags. Furthermore, oximes and azides provide an orthogonal pair of functional groups for sequential metal free click reactions and this feature makes it possible to multi-functionalize biomolecules and materials by a simple synthetic procedure that does not require toxic metal catalysts.

Branched polyelectrolytes with cylindrical brush, dendritic, hyperbranched, grafted, and star architectures bearing ionizable functional groups possess complex and unique assembly behavior in solution at surfaces and interfaces as compared to their linear counterparts. This review summarizes the recent developments in the introduction of various architectures and understanding of the assembly behavior of branched polyelectrolytes with a focus on functional polyelectrolytes and poly(ionic liquid)s with responsive properties. The branched polyelectrolytes and poly(ionic liquid)s interact electrostatically with small molecules, linear polyelectrolytes, or other branched polyelectrolytes to form assemblies of hybrid nanoparticles, multilayer thin films, responsive microcapsules, and ion-conductive membranes. The branched structures lead to unconventional assemblies and complex hierarchical structures with responsive properties as summarized in this review. Finally, we discuss prospectives for emerging applications of branched polyelectrolytes and poly(ionic liquid)s for energy harvesting and storage, controlled delivery, chemical microreactors, adaptive surfaces, and ion-exchange membranes.

We demonstrate the electrically controlled and reversible plasmonic signature of hybrid polymer–metal nanostructures composed of core/shell nanostructures: gold nanocubes (AuNCs) coated with electrochromic polyaniline (PANI) shells. A reversible tuning of the localized surface plasmon resonance (LSPR) peak of the AuNC core was obtained by applying an electrical potential that caused a reversible oxidation state change in the electroactive PANI nanoshell. A significant shift of the main LSPR peak was achieved with high reversibility and electrochemical stability due to the interplay of the local decay of the electromagnetic field and the controlled thickness of the surrounding polymer shell. Here, the PANI shell acts as an electroactive medium as well as a physical spacer to prevent uncontrollable plasmonic coupling. The most efficient LSPR shift can be induced by the refractive index change of nanoscale PANI shell thickness lower than the electromagnetic field decay length of the given gold nanoparticles. Single particle studies showed that coupling of plasmon resonances of densely packed nanocubes with thicker PANI shells was prevented and the extinction signature of individual core/shell nanocubes remained mostly unchanged after their assembly into densely packed aggregates. Therefore, these core/shell structures could preserve the original plasmonic signature of individual nanostructure by damping plasmonic coupling between AuNC cores.

Multifunctional star-graft quarterpolymers PS n [P2VPb-(PAA-g-PNIPAM)] n with two different arm types, shorter PS arms and longer P2VP-b-PAA block copolymer arms with grafted PNIPAM chains, were studied in terms of their ability to form micellar structures at the air/water and air/solid interfaces. Because of the pH-dependent ionization of P2VP and PAA blocks, as well as thermoresponsiveness of PNIPAM chains, these multifunctional stars have multiple responsive properties to pH, temperature, and ionic strength. We observed that the molecular surface area of the stars is the largest at basic pH, when the PAA blocks are strongly charged and extended, and PNIPAM chains are spread at the interface. At acidic conditions, the molecular surface area is the smallest because the P2VP blocks submerge into the water subphase and the PAA blocks are contracted and form hydrogen bonding with grafted PNIPAM chains. The molecular surface area of the stars at the air/water interface gradually increases at elevated temperature. We suggest that the transition across lower critical solution temperature (LCST) results in the emerging of PNIPAM chains from the water subphase to the interface due to the hydrophilic to hydrophobic transition. Moreover, at higher surface pressure, the stars tend to form intermolecular micellar aggregates above LCST. The graft density of PNIPAM chains as well as the arm number was also found to have strong effects on the thermo-and pH-response. Overall, this study demonstrates that the star block copolymer conformation and aggregation are strongly dependent on the intramolecular interactions between different blocks and spatial distribution of the arms, which can be controlled by the external conditions, including pH, temperature, ionic strength, and surface pressure.