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International audience; Immobilization of well-defined homogenous (electro)catalysts onto conductive supports offers an attractive strategy for designing advanced functional materials for energy conversion. In this context, this study reports (i) the introduction of a pyrene anchoring group on a PNP-pincer Ir-I complex previously described as a selective catalyst for the electrodriven CO2 reduction (CO2RR) into CO in DMF/water mixtures, (ii) the comparison of its CO2RR activity in DMF/water mixtures with the ones of two pyrene-free reference complexes, and (iii) its activity in pure water after immobilization onto carbon nanotubes (CNTs). Surprisingly, in homogeneous conditions we find HCOO-, instead of CO, as the main CO2 reduction product for the three catalysts. After immobilization on CNTs, even if non-negligible competitive proton reduction reaction is observed in fully aqueous media, the complex is still able to drive CO2RR and produce HCOO- with a significantly lower overpotential with respect to solution studies.

International audience; Despite being the key metals supporting carbon dioxide reduction into formate, in natural systems, W and Mo are still rarely used for preparing synthetic electrocatalysts for CO2RR. Herein we investigate the activity of an original molybdenum(III) SCS-pincer complex for the electrodriven reduction of carbon dioxide. This system is able to promote the formation of formate with modest TON and faradaic efficiencies (TONHOO-) after 30 min of a controlled potential electrolysis at an applied potential of-2.30 V vs. ferrocene in 0.1 M [n-Bu4N]BF4 acetonitrile solution in the presence of phenol as a source of proton.

International audience; The covalent assembly between a cobalt diimine-dioxime complex and a fullerenic moiety results in enhanced catalytic properties in terms of overpotential requirement for H2 evolution. The interaction between the fullerene moiety and PCBM heterojunction further allows for the easy integration of the cobalt diimine-dioxime – fullerene catalyst with a poly-3-hexylthiophene (P3HT):[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojunction, yielding hybrid photoelectrodes for H2 evolution from near-neutral aqueous solutions.

Suitably functionalized porous matrices represent versatile platforms to support well-dispersed catalytic centers. In the present study, porous organic polymers (POPs) containing phosphine oxide groups were fabricated to bind transition metals and to be investigated for potential electrocatalytic applications. Cross-linking of mono- and di-phosphine monomers with multiple phenyl substituents was subject to the Friedel-Crafts (F-C) reaction and the oxidation process, which generated phosphine oxide porous polymers with pore capacity up to 0.92 cm

The cobalt tetraazamacrocyclic [Co(N4H)Cl2]+ complex is becoming a popular and versatile catalyst for the electrocatalytic evolution of hydrogen, because of its stability and superior activity in aqueous conditions. We present here a benchmarking of its performances based on the thorough analysis of cyclic voltammograms recorded under various catalytic regimes in non-aqueous conditions allowing control of the proton concentration. This allowed a detailed mechanism to be proposed with quantitative determination of the rate-constants for the various protonation steps, as well as identification of the amine function of the tetraazamacrocyclic ligand to act as a proton relay during H2 evolution., The mechanism of H2 evolution catalyzed by the [Co(N4H)Cl2]+ complex is elucidated with quantitative determination of the rate-constants for the various protonation steps, and the identification of the aliphatic amine to act as a proton relay.

International audience; Dye-sensitized photoelectrochemical cells (DSPECs) are a promising approach to produce solar fuels, e.g., by reduction of protons to molecular hydrogen. Her; we present functional NiO photocathodes sensitized with covalent organic dye-catalyst assemblies integrating a robust cobalt tetraazamacrocyclic complex. This catalyst proved to be decisive in improving the stability of these systems, with hydrogen being produced with a 26-fold increase in turnover numbers compared to similar photocathodes based on a cobaloxime catalyst, all other conditions being strictly identical otherwise. Transient absorption spectroelectrochemical (TA-SEC) measurements observed the catalytically competent Co-1 state in a functional dye-sensitized photocathode, with a lifetime of up to >1 ms, comparable to the timescale of catalysis. They also unveiled the lack of efficiency of the thermally activated electron transfer from the reduced dye to the catalyst, which first limits the photocurrent density for hydrogen production. A second consequence is the accumulation of photogenerated charges on the acceptor side of the dye, ultimately leading to its degradation, as observed in operando and post operando characterizations of the system. This study thus provides tracks to improve the performances of hydrogen-evolving dye-sensitized photocathodes toward their integration into functional DSPECs.

The cobalt tetraazamacrocyclic [Co(N4H)Cl-2](+) complex is becoming a popular and versatile catalyst for the electrocatalytic evolution of hydrogen, because of its stability and superior activity in aqueous conditions. We present here a benchmarking of its performances based on the thorough analysis of cyclic voltammograms recorded under various catalytic regimes in non-aqueous conditions allowing control of the proton concentration. This allowed a detailed mechanism to be proposed with quantitative determination of the rate-constants for the various protonation steps, as well as identification of the amine function of the tetraazamacrocyclic ligand to act as a proton relay during H-2 evolution. De två första författarna delar förstaförfattarskapet.

International audience; Ammonia (NH3) is a major feedstock of the chemical industry. The imperious need to decarbonize its production has stimulated a quest for efficient catalysts able to drive the direct electro-reduction of dinitrogen (N-2) into NH3. A large number of materials have now been proposed for this reaction, including bioinspired molybdenum sulfide derivatives. Here, we revisit the potential of amorphous molybdenum sulfide to drive the electrocatalytic reduction of N-2 and other substrates of nitrogenase. We find that this material exhibits negligible activity towards N-2 but achieves efficient reduction of inorganic azides.

International audience; The amplification effect of polyoxometalates (POMs) on the efficiency of dye-sensitized nano-ITO cathodes is disclosed. The use of hybrid polyoxometalates of the type [PW11O39{SnC6H4 C6H4F}](4-), F standing for a carboxylic group (POM-COOH) or a diazonium unit, allows control of the loading of the POMs on the electrode and investigation of key parameters. Even at very low loading, POM-COON has a substantial effect on the photocurrent response with up to 25-fold increase. Besides ensuring the stability toward leaching, the anchoring function of the POM hybrids was also found to play an intricate role in the competition between the multiple events involved.

Hydroxamic acids chelate metals with high affinity and form hydrolytically stable complexes with metal oxides such as TiO2. However, these appealing binding properties can cause problems during the preparation and application of metallocatalysts with appended hydroxamate anchoring groups. Here we show that the tetrahydropyran (THP) O-protected hydroxamate group can be cleaved in situ on a TiO2 surface at room temperature, leading to the surface-bound species. Surface-mediated deprotection has several advantages over direct surface functionalization including increased hydrolytic stability of the covalent interaction with the metal oxide surface and decreased aggregation of the surface species. Application of the surface-mediated chelation method for dye-sensitized photoelectrochemical cells (DSPC) was examined using the organic dye MK-2. Results show that the surface-mediated deprotection led to improved DSPC performance attributed to a decrease in dye aggregation relative to a DSPC prepared using standar...

We examine structure–function relationships in a series of N-phenylbenzamide (NPBA) derivatives by using computational modeling to identify molecular structures that exhibit both rectification and good conductance together with experimental studies of bias-dependent single molecule conductance and rectification behavior using the scanning tunneling microscopy break-junction technique. From a large number of computationally screened molecular diode structures, we have identified NPBA as a promising candidate, relative to the other structures that were screened. We demonstrate experimentally that conductance and rectification are both enhanced by functionalization of the NPBA 4-carboxamido-aniline moiety with electron donating methoxy groups, and are strongly correlated with the energy of the conducting frontier orbital relative to the Fermi level of the gold leads used in break-junction experiments.

A short, convenient, and scalable protocol for the one-pot synthesis of a series of fluorescent 7,8-dihalo-2,3-diaminophenazines is introduced. The synthetic route is based on the oxidative condensation of 4,5-dihalo-1,2-diaminobenzenes in aqueous conditions. The resulting diaminophenazines could be attractive intermediates for the preparation of polyfunctional phenazines and extended polyheteroacenes. We find that the undesired hydroxylation byproducts, typically obtained in aqueous conditions, are completely suppressed by addition of a stoichiometric amount of acetone during the oxidation step allowing for selective formation of 7,8-dihalo-2,2-dimethyl-2,3-dihydro-1H-imidazo[4,5-b]phenazine derivatives with good to excellent yields. Under reductive conditions, the imidazolidine ring can be hydrolyzed into the desired 7,8-dihalo-2,3-diaminophenazines. Furthermore, we report a selective route under highly reducing conditions to monohydrodeaminate the 2,3-di(methylamino) phenazine derivatives, which allows for further structural variations of these phenazine building blocks. All of these derivatives are luminescent, with measured fluorescence quantum-yields of up to 80% in ethanol for the more rigid structures, highlighting the potential of such materials to provide new fluorophores.

International audience; The energy needs of humankind has experimented a sharp increase since the beginning of the Anthropocene due to a large increase in population and the evolution of our society’s lifestyle. Recent projections suggest that it will likely lead to a major crisis due to environmental issues associated with the increasing use of fossil fuel as major energy source, as well as due to a rapid dwindling of the classical and easily accessible fossil-fuels stocks. These issues require a quick response if the lifestyle adopted by our societies shall be sustained. Several solutions have been envisioned to tackle these problems, of which, the development of Artificial Photosynthetic systems is one of the most appealing. The field of artificial photosynthesis takes Nature itself as a source of inspiration, to propose alternative energy harvesting and storage strategies. This field of research not only aims at mimicking the main processes that permitted photosynthetic organisms to thrive and become the most successful autotrophs on earth, but as well at improving and optimizing these processes using synthetic materials. In this chapter, the underlying mechanisms that enable photosynthetic organisms to convert (and store) solar energy into a directly usable chemical energy will be discussed. Then it will be explained how these concepts can be extended to artificial systems and ultimately used to our own benefit.

International audience; The association of different metals in stable, well-defined molecular assemblies remains a great challenge of supramolecular chemistry. In such constructs, the emergence of synergism, or cooperative effects between the different metal centers is particularly intriguing. These effects can lead to uncommon reactivity or remarkable physico-chemical properties that are not otherwise achievable. For example, the association of alkaline or alkaline-earth cations and transition metals is pivotal for the activity of several biomolecules and human-made catalysts that carry out fundamental redox transformations (water oxidation, nitrogen reduction, water-gas shift reaction, etc.). In many cases the precise nature of the interactions between the alkaline-earth cations and the redox-active transition metals remains elusive due to the difficulty of building stable molecular heterometallic assemblies that associate transition metals and alkaline or alkaline-earth cations in a controlled way. In this work we present the rational design of porphyrin-based ligands possessing a second binding site for alkaline-earth cations above the porphyrin macrocycle primary complexation site. We demonstrate that by using a combination of crown ether and carboxylic acid substituents suitably positioned on the periphery of the porphyrin, bitopic ligands can be obtained. The binding of calcium, a typical alkaline-earth cation, by the newly prepared ligands has been studied in detail and we show that a moderately large binding constant can be achieved in protic media using ligands that possess some degree of structural flexibility. The formation of Zn-Ca assemblies discussed in this work is viewed as a stepping stone towards the assembly of well defined molecular transition metal-alkaline earth bimetallic centers using a versatile organic scaffold.

A manganese complex covalently attached to a TiO2 electrode via a light-absorbing organic linker (L) was used in the photooxidation of 2′,7′-dihydrodichlorofluorescein (H2DCF). Significant and sustained photocurrent was observed upon visible-light illumination of the fully assembled anode in the presence of the substrate. The two-electron, two-proton oxidation of H2DCF yields the fluorescent compound, 2′,7′-dichlorofluorescein (DCF). Our studies suggest that the MnII–L–TiO2 architecture is an effective photoanode for multielectron chemistry, as production of DCF under visible-light illumination exceeds yields observed for bare TiO2 as well as ZnII–L–TiO2 anodes. The turn-on fluorescent behavior of H2DCF upon oxidation makes it an excellent substrate for the study of new photoanodes. The high fluorescence quantum yield of DCF allows for nanomolar sensitivity and real-time monitoring of substrate oxidation.

An efficient synthetic protocol to functionalize the cyanoacrylic acid anchoring group of commercially available MK-2 dye with a highly water-stable hydroxamate anchoring group is described. Extensive characterization of this hydroxamate-modified dye (MK-2HA) reveals that the modification does not affect its favorable optoelectronic properties. Dye-sensitized solar cells (DSSCs) prepared with the MK- 2HA dye attain improved efficiency (6.9%), relative to analogously prepared devices with commercial MK-2 and N719 dyes. The hydroxamate anchoring group also contributes to significantly increased water stability, with a decrease in the rate constant for dye desorption of MK-2HA relative to MK-2 in the presence of water by as much as 37.5%. In addition, the hydroxamate-anchored dye undergoes essentially no loss in DSSC efficiency and the external quantum efficiency improves when up to 20% water is purposefully added to the electrolyte. In contrast, devices prepared with the commercial dye suffer a 50% decline in efficiency under identical conditions, with a concomitant decrease in external quantum efficiency. Collectively, our results indicate that covalent functionalization of organic dyes with hydroxamate anchoring groups is a simple and efficient approach to improving the water stability of the dye–semiconductor interface and overall device durability

Mechanical responsiveness is essential to all biological systems down to the level of tissues and cells. The intra- and extracellular mechanics of such systems are governed by a series of proteins, such as microtubules, actin, intermediate filaments and collagen. As a general design motif, these proteins self-assemble into helical structures and superstructures that differ in diameter and persistence length to cover the full mechanical spectrum. Gels of cytoskeletal proteins display particular mechanical responses (stress stiffening) that until now have been absent in synthetic polymeric and low-molar-mass gels. Here we present synthetic gels that mimic in nearly all aspects gels prepared from intermediate filaments. They are prepared from polyisocyanopeptides grafted with oligo(ethylene glycol) side chains. These responsive polymers possess a stiff and helical architecture, and show a tunable thermal transition where the chains bundle together to generate transparent gels at extremely low concentrations. Using characterization techniques operating at different length scales (for example, macroscopic rheology, atomic force microscopy and molecular force spectroscopy) combined with an appropriate theoretical network model, we establish the hierarchical relationship between the bulk mechanical properties and the single-molecule parameters. Our results show that to develop artificial cytoskeletal or extracellular matrix mimics, the essential design parameters are not only the molecular stiffness, but also the extent of bundling. In contrast to the peptidic materials, our polyisocyanide polymers are readily modified, giving a starting point for functional biomimetic hydrogels with potentially a wide variety of applications, in particular in the biomedical field.

Helical structures play a vital role in nature, offering mechanical rigidity, chirality and structural definition to biological systems. Little is known about the influence of the helical architecture on the intrinsic properties of polymers. Here, we offer an insight into the nano architecture of helical polymers by measuring helical polyisocyanopeptides with single molecule force spectroscopy. An unprecedented large heterogeneity in the stiffness of the polymers was found. The heterogeneity persisted when the stiffness of these polymers was steered by: (1) enhancing the formation of the hydrogen bonding network along the polymer, (2) via pi-pi stacking interactions of aromatic perylenes, and (3) by changing the stereochemistry of the side chain. However, the heterogeneity was lost after completely disrupting the secondary structure by the addition of trifluoroacetic acid. Molecular dynamics simulations revealed three possible structural conformations which can account for the observed heterogeneity and their corresponding energy landscape is proposed.

The development of molecular components functioning as switches, rectifiers or amplifiers is a great challenge in molecular electronics. A desirable property of such components is functional robustness, meaning that the intrinsic functionality of components must be preserved regardless of the strategy used to integrate them into the final assemblies. Here, this issue is investigated for molecular diodes based on N-phenylbenzamide (NPBA) backbones. The transport properties of molecular junctions derived from NPBA are characterized while varying the nature of the functional groups interfacing the backbone and the gold electrodes required for break-junction measurements. Combining experimental and theoretical methods, it is shown that at low bias (

An efficient noncovalent assembly process involving high geometrical control was applied to a linear bis(imidazolyl zinc porphyrin) 7Zn, bearing C(18) substitutents, to generate linear multiporphyrin wires. The association process is based on imidazole recognition within the cavity of the phenanthroline-strapped zinc porphyrin. In chlorinated solvents, discrete soluble oligomers were obtained after (7Zn)(n) was end-capped with a terminal single imidazolyl zinc porphyrin derivative 4Zn. These soluble species, as well as their destabilization in the presence of protic solvents, were studied by UV-visible and time-resolved luminescence. In the solid state, assemblies as long as 480 nm, which corresponds to 190 iterative units or a total of 380 porphyrins, were observed by atomic force microscopy measurements on mica. The length and linearity of the porphyrin wires obtained illustrate the potential of phenanthroline-strapped porphyrins for the directional control of self-assembly processes.

Stable helical polymers with a preferred handedness are compounds that offer intriguing characteristics. This review describes the progress in the synthesis of helical polyisocyanides and the investigations to determine their structural properties, such as helical pitch and handedness, by spectroscopic measurements and high resolution AFM. This review is not intended to be comprehensive; its purpose is to highlight recent studies that allow a better understanding of the main aspects of helical polyisocyanides.

The straightforward syntheses of polyisocyanides containing the alanine-cysteine motif in their side chains have been achieved. Detailed characterization of the polymers revealed a well-defined and highly stable helical conformation of the polyimine backbone responsible for the formation of rodlike structures of over one hundred nanometers. The 4(1) helix is further stabilized by beta-sheet-like interactions between the peptide arms. As a result, the cysteine sulfur atoms are regularly aligned along the polymer axis, which provides a unique platform for the scaffolding of various entities by using versatile click-chemistry postmodification approaches. For instance, pyrene derivatives were introduced through thio-specific reactions involving either maleimide, iodoacetamide, or thioester groups, leading to arrays of stacked chromophores with excimer-like emission. A water-soluble cysteine-rich polyisocyanide was successfully biotinylated and coupled to streptavidin.

The design and synthesis of functional biomimetic water soluble polymers with a defined secondary structure has been developed using β-sheet polyisocyanopeptide scaffolds. Water soluble isocyanopolymers were prepared by random copolymerisation of the azido functionalized isocyanopeptides with nonfunctionalised methyl ester isocyanides derived from alanine. Upon saponification of the latter function a rigid rod water soluble polymer was obtained with an accessible azide for postfunctionalization. The potential of these biomimetic polymers was successfully demonstrated by using the click chemistry reaction of these polymers with an acetylene functionalised rhodamine dye.

Accessible and hindered phenanthroline-strapped Zn(II) porphyrin receptors exhibited suitable topography tailored to strongly and selectively bind N(1)-unsubstituted imidazoles and imidazoles appended to free-base porphyrins. Distal binding was clearly driven by the formation of strong bifurcated hydrogen bonds with the phenanthroline unit of the receptors. An extensive physicochemical study emphasized the influence of bulkiness of the substrate and of the porphyrin receptor on the binding and self-assembly mechanism. Knowledge of the corresponding spectroscopic, thermodynamic, and kinetic data were of fundamental importance to elucidate and to model the photoinduced properties which occur within the self-assembled porphyrin dyads.

Two self-complementary phenanthroline-strapped porphyrins bearing imidazole arms and C 12 or C 18 alkyl chains were synthesized, and their surface self-assembly was investigated by atomic force microscopy (AFM) on mica and highly ordered pyrrolitic graphite (HOPG). Upon zinc(II) complexation, stable porphyrin dimers formed, as confirmed by DOSY (1)H NMR and UV-visible spectroscopy. In solution, the dimers formed J-aggregates. AFM studies of the solutions dip-coated onto mica or drop-casted onto HOPG revealed that the morphologies of the assemblies formed were surface-tuned. On mica, fiber-like assemblies of short stacks of J-aggregates were observed. The strong influence of the mica's epitaxy on the orientation of the fibers suggested a surface-assisted assembly process. On HOPG, interactions between the alkyl chains and the graphite surface resulted in the stabilization and trapping of monomer species followed by their subsequent association into coordination polymers on the surface. Interdigitation of the alkyl chains of separate polymer strands induced lateral association of wires to form islands that grew preferentially upon drop-casting and slow evaporation. Clusters of laterally assembled wires were observed for the more mobile functionalized porphyrins bearing C 12 chains.

The thermal motion of polymer chains in a crowded environment is anisotropic and highly confined. Whereas theoretical and experimental progress has been made, typically only indirect evidence of polymer dynamics is obtained either from scattering or mechanical response. Toward a complete understanding of the complicated polymer dynamics in crowded media such as biological cells, it is of great importance to unravel the role of heterogeneity and molecular individualism. In the present work, we investigate the dynamics of synthetic polymers and the tube-like motion of individual chains using time-resolved fluorescence microscopy. A single fluorescently labeled polymer molecule is observed in a sea of unlabeled polymers, giving access to not only the dynamics of the probe chain itself but also to that of the surrounding network. We demonstrate that it is possible to extract the characteristic time constants and length scales in one experiment, providing a detailed understanding of polymer dynamics at the single chain level. The quantitative agreement with bulk rheology measurements is promising for using local probes to study heterogeneity in complex, crowded systems.

We report a systematic computational search of molecular frameworks for intrinsic rectification of electron transport. The screening of molecular rectifiers includes 52 molecules and conformers spanning over 9 series of structural motifs. N-Phenylbenzamide is found to be a promising framework with both suitable conductance and rectification properties. A targeted screening performed on 30 additional derivatives and conformers of N-phenylbenzamide yielded enhanced rectification based on asymmetric functionalization. We demonstrate that electron-donating substituent groups that maintain an asymmetric distribution of charge in the dominant transport channel (e.g., HOMO) enhance rectification by raising the channel closer to the Fermi level. These findings are particularly valuable for the design of molecular assemblies that could ensure directionality of electron transport in a wide range of applications, from molecular electronics to catalytic reactions.

International audience; The assembly of imidazole-functionalized phenan-throline-strapped zinc porphyrins (ZnPorphen)w ith alkyl or polyethylene glycol (PEG) side chains was studied in solution and by AFM after casting on highly oriented pyrolytic graphite (HOPG) or mica. The natureo ft he solvent and its evaporation time influenced the morphology of the objectso b-served.O nH OPG, short rods of about 100 nm were observed after fast evaporation of solutions of the alkyl derivatives in CHCl 3 ,T HF,o rp yridine, whereas islands of aligned rows of longer wires were obtained from methylcyclohexane (MCH). Slow evaporation of MCH led to at hree-dimensional assembly. The PEG porphyrin assembled into short wires on HOPG or fibers on mica after slow evaporation of solutions in THF.T his study shows the role of surface–molecule interactions in the interfacial assembly of ZnPorphen derivatives and contributes to understanding the parameters that control their noncovalent assembly into molecular wires on as urface.

Current molecular water-oxidation photoelectrocatalytic cells have substantial kinetic limitations under normal solar photon flux where electron–hole recombination processes may outcompete charge buildup on the catalytic centers. One method of overcoming these limitations is to design a system where multiple light-harvesting dyes work cooperatively with a single catalyst. We report a porphyrin monomer/dyad array for analysis of lateral hole transfer on a SnO2 surface consisting of a free-base porphyrin that functions to absorb light and initiate charge injection into the conduction band of SnO2, which leaves a positive charge on the organic moiety, and a free-base porphyrin/Zn-porphyrin dyad molecule that functions as a thermodynamic trap for the photoinduced holes. By using transient absorption spectroscopy, we have determined that the holes on the surface-bound free-base porphyrins are highly mobile via electron self-exchange between close-packed neighbors. The lateral charge-transfer processes were modelled by treating the system statistically with a random-walk method that utilizes experimentally derived kinetic parameters. The results of the modelling indicate that each self-exchange (hop) occurs within 25 ns and that the holes are efficiently transferred to the Zn-porphyrin. This hole-harvesting scheme provides a framework for enhancing the efficiency of multielectron photoelectrocatalytic reactions such as the four-electron oxidation of water.

A highly soluble phenanthroline strapped porphyrin is prepared on multigram scale by appropriate functionalization with C 12 chains after the cyclization of the tetrapyrrolic macrocycle.

This contribution describes the synthesis and full characterization of oligo(ethylene glycol) functionalized polyisocyanopeptides. The thermal behavior of the resulting semi-flexible polymers was investigated in diluted aqueous conditions and features a tunable Lower Critical Solution Temperature (LCST). In line with previously described oligo(ethylene glycol) decorated polymers, the LCST of the materials shows a very small hysteresis effect and directly correlates with the oligo(ethylene glycol) side-chains length; short oligo(ethylene glycol) substituents are associated with lower LCST. In contrast with poly[oligo(ethylene glycol) methacrylate], a significant effect of the degree of polymerization (DP) of the poly(isocyanopeptide) core on the LSCT of the materials was observed. Most remarkably, poly(isocyanopeptide)-graft-oligo(ethylene glycol) chains of high DP lead to the reversible formation of strong hydrogels above the transition temperature, even at very low polymer concentration (0.1 wt.%). AFM studies point towards the formation of a highly organized fibrillar network in the gel-state, reminiscent of structures observed for low molecular weight gelators, polysaccharides, and protein-based (hydro)gels. It is proposed that the stiff and well-defined helical poly(isocyanopeptide) backbone avoids the collapse of the chains into globules at the transition temperature as usually observed for more flexible systems. Thus, above a critical DP the semi-flexible non-linear PEGs chains are getting kinetically trapped in an extended fibrillar network, when the oligo(ethylene glycol) corona hydrophilicity is lowered at higher temperature. As a result these polymers exhibit a strong ability to gel water at extremely low polymer concentrations.

A new class of antibody-functionalized, semi-flexible and filamentous polymers (diameter 5–10 nm, length ∼200 nm) with a controlled persistence length, a high degree of stereoregularity and the potential for multiple simultaneous receptor interactions has been developed. We have decorated these highly controlled, semi-stiff polymers with T cell activating anti-CD3 antibodies and analyzed their application potential as simple synthetic mimics of dendritic cells (sDCs). Our sDCs do not only activate T cells at significantly lower concentrations than free antibodies or rigid sphere-like counterparts (PLGA particles) but also induce a more robust T cell response. Our novel design further yields sDCs that are biocompatible and non-toxic. The observed increased efficacy highlights the importance of architectural flexibility and multivalency for modulating T cell response and cellular function in general.

International audience; In view of the many potential applications for functional hybrid interfaces, the controlled assembly of sophisticated structures on surfaces is a current challenge for chemists. Applications can be foreseen in fields such as molecular electronics, spintronics, sensors, catalysis and even synthesis. Independent of their functional nature, the characterization of nano-objects usually involves their deposition on surfaces. Whereas the formation of 2D networks on a surface corresponds to the association of scaffolds of the same dimensionality, 1D and 3D self-organized materials clearly differ from the 2D nature of the support. Unless necessary, organized 2D networks will not be examined in detail, as this subject has been periodically reviewed elsewhere. In this review, concepts originating from the 2D organization, but leading to the surface-assisted production of organized 1D and 3D self-assemblies will be examined and illustrated by selected recent examples from the literature. Three roles can be played by the surface. First, the surface can simply serve as an inert foundation for the organization of the functional layer, which is controlled by molecule-molecule interactions only. Second, the surface can be considered as a template by adding specific constraints to the assembly of the building blocks, restricting their conformational freedom and thus confining the growth in a surface plane or directing the growth of the nanostructures along specific symmetry axes (epitaxy) or surface defects and heterogeneities (step edges). This case seems the most conceptually advanced and has already led to integration of self-assembled materials into devices by using preferred orientations of the surface to align molecules in given directions, for example between interdigitated electrodes. Third, the surface itself can be a source of constituents, or adatoms, of the assembly and can alter the electronic structure of the building blocks, thus directly participating in the assembly process and final function of the structures. The latter case is more scarcely spread over different explorative works in which the major road maps are the successive growth of layers into three dimensions from a preorganized two dimensional (molecular) adlayer, as well as surface-induced reactions within an organized layer.

This review focuses on the strategies available for the construction of persistent linear species from monomers. The scope is mostly restricted to wires, but also includes some selected examples illustrating the fast developing area of fibers and tubular structures, given that their linearity is governed by supramolecular interactions. Strategies are primarily limited to those that are based on noncovalent assembly obtained by iterative interactions that range from coordination bonds to π-interactions and hydrogen bonding. Each approach is illustrated by a selection of either pioneering or recent examples. The use of supramolecular templates to assemble molecules into linear wires, whose structures are sometimes covalently locked, is also briefly presented. Keywords: self-assembly; hydrogen bonding; π-interactions; molecular wires; molecular fibers

Rigid rod polyisocyanopeptides bearing phthalocyanines as pendant groups have been synthesised through CuAAC of polyisocyanopeptides containing acetylene groups with zinc(II) phthalocyanine azide. As confirmed by UV/Vis, fluorescence, and circular dichroism spectroscopies, the phthalocyanines are arranged in a helical fashion along the polymer backbone, forming the longest reported well-defined phthalocyanine assembly described to date.

We report on the synthesis and detailed photo-physical investigation of four model chromophore side chain polyisocyanopeptides: two homopolymers of platinum-porphyrin functionalized polyisocyanopeptides (Pt-porphyrin-PIC) and perylene-bis(dicarboximide) functionalized polyisocyanopeptides (PDI-PIC), and two statistical copolymers with different ratios of Pt-porphyrin and PDI molecules attached to a rigid, helical polyisocyanopeptide backbone. (1)H NMR and circular dichroism measurements confirm that our model compounds retain a chiral architecture in the presence of the chromophores. The combination of Pt-porphyrin and PDI chromophores allows charge- and/or energy transfer to happen. We observe the excitation and relaxation pathways for selective excitation of the Pt-porphyrin and PDI chromophores. Studies of photoluminescence and transient absorption on nanosecond and picosecond scales upon excitation of Pt-porphyrin chromophores in our multichromophoric assemblies show similar photophysical features to those of the Pt-porphyrin monomers. In contrast, excitation of perylene chromophores results in a series of energy and charge transfer processes with the Pt-porphyrin group and forms additional charge-transfer states, which behave as an intermediate state that facilitates electronic coupling in these multichromophoric systems.

Self-trapping of NH-stretch vibrational excitations in synthetic beta-sheet helices is observed using femtosecond infrared pump-probe spectroscopy. In a dialanine-based beta-sheet helix, the transient-absorption change upon exciting the NH-stretch mode exhibits a negative absorption change at the fundamental frequency and two positive peaks at lower frequencies. These two induced-absorption peaks are characteristic for a state in which the vibrational excitation is self-trapped on essentially a single NH-group in the hydrogen-bonded NH center dot center dot center dot OC chain, forming a small (Holstein) vibrational polaron. By engineering the structure of the polymer we can disrupt the hydrogen-bonded NH center dot center dot center dot OC chain, allowing us to eliminate the self-trapping, as is confirmed from the NH-stretch pump-probe response. We also investigate a trialanine-based beta-sheet helix, where each side chain participates in two NH center dot center dot center dot OC chains with different hydrogen-bond lengths. The chain with short hydrogen bonds shows the same self-trapping behavior as the dialanine-based beta-sheet helix, whereas in the chain with long hydrogen bonds the self-trapping is too weak to be observable.

Polyisocyanopeptides have been synthesised containing acetylene groups on the side arms as scaffolds for multifunctional derivatisation by the copper-catalysed click reaction with a variety of azides. By using ethylene glycol azide and perylene azide chromophoric water-soluble polymeric nanowires (Mw 1–2 million Daltons) were formed. The potential to incorporate multiple chromophores was also demonstrated by the reaction of the acetylene-containing polymers with perylene azide and azidocoumarin dyes. In the latter case a blue-shifted emission of the coumarin was observed due to the interaction with the coupled perylene molecules. In particular the ability to form water-soluble dye-containing polymers, which can be modified by the addition of biomolecules, such as antibodies, proteins and peptides, give materials that are very promising as novel biomarker materials.

[structure: see text] Based on the high affinity of phenanthroline-strapped porphyrins for imidazoles, building blocks for self-assembled, linear porphyrin architectures have been designed. Their synthesis is reported, and the assembly principle is illustrated by the formation of the shortest possible scaffold. Only one type of assembly is observed, and the stepwise energy transfer from the boron dipyrrylmethane (BODIPY) input to the free base output is highly efficient.

Three self-assembled photonic dyads comprising a zinc porphyrin donor and a free base acceptor have been studied by time-resolved fluorescence spectroscopy. The driving force of the assembly is the site selective binding of an imidazole connected to a free base porphyrin. Three spacers have been incorporated between the imidazole connector and the free base porphyrin, providing three different distances separating the donor and the acceptor. The high efficiencies and the rates of energy transfer in the set of dyads is consistent with the Forster energy transfer mechanism. Evidence for Forster back transfer has been obtained, and its efficiency and rate have been quantitatively evaluated for the first time.

The unique recognition properties of phenanthroline-strapped zinc porphyrin 1, which displays extremely high affinity for N-unsubstituted imidazoles, has been used as the driving force for the assembly of a photochemical dyad involving a zinc(II) porphyrin as energy donor and a free base porphyrin as energy acceptor. The synthesis of the imidazole-substituted porphyrin is described together with the assembly of the dyad. (1)H NMR titrations confirm the formation of a 1/1 complex between 1 and 6, as well as insertion of the imidazole of the acceptor within the phenanthroline strap of the donor. Preliminary fluorescence quenching measurements show that efficient energy transfer occurs between the self-assembled components.