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The assembly of donor–acceptor molecules via charge transfer (CT) interactions gives rise to highly ordered nanomaterials with appealing electronic properties. Here, we present the synthesis and bulk co-assembly of pyrene (Pyr) and naphthalenediimide (NDI) functionalized oligodimethylsiloxanes (oDMS) of discrete length. We tune the donor–acceptor interactions by connecting the pyrene and NDI to the same oligomer, forming a heterotelechelic block molecule (NDI-oDMSPyr), and to two separate oligomers, giving Pyr and NDI homotelechelic block molecules (Pyr-oDMS and NDI-oDMS). Liquid crystalline materials are obtained for binary mixtures of Pyr-oDMS and NDI-oDMS, while crystallization of the CT dimers occurred for the heterotelechelic NDI-oDMS-Pyr block molecule. The synergy between crystallization and phase-segregation coupled with the discrete length of the oDMS units allows for perfect order and sharp interfaces between the insulating siloxane and CT layers composed of crystalline CT dimers. We were able to tune the lamellar domain spacing and donor–acceptor CT interactions by applying pressures up to 6 GPa on the material, making the system promising for soft-material nanotechnologies. These results demonstrate the importance of the molecular design to tune the CT interactions and stability of a CT material., A robust, soft material held together by charge transfer interactions is developed. The nanostructure dimensions and material properties can be tuned by molecular design or pressure.

Narrowly dispersed, 10 micron-sized, liquid crystalline elastomer polymer actuators were first prepared via thiol–ene dispersion polymerization and then embedded and stretched in a polyvinyl alcohol film, followed by photopolymerization of the residual acrylate groups. Prolate micro spheroids in which the mesogens are aligned parallel to the long axis were obtained and showed reversible thermally driven actuation owing to nematic to isotropic transition of the liquid crystal molecules. The particles were also compressed to form disk-shaped oblate microactuators in which the mesogens are aligned perpendicular to the short axis, demonstrating that the reported method is a versatile method to fabricate liquid crystal elastomer microactuators with programmable properties.

The effect of the length of solubilizing alkyl side chains, ranging from hexyl to pentadecyl, on the formation and structure of two distinct semi-crystalline semiconductor phases, ß1and ß2, of a single conjugated polymer is investigated for a low band gap poly(diketopyrrolopyrrole-alt-quaterthiophene). Compared to ß1, the ß2phase exhibits a distinct redshifted absorption and an associated near infrared photoluminescence. The length of the alkyl side chains controls the formation of the ß1and ß2phases. Intermediate length alkyl side chains (nonyl and dodecyl) can selectively provide the ß1or ß2phase in solution and in semi-crystalline thin films, depending on the nature of the solvent used. For short side chains (hexyl) the ß2phase forms more readily while for long side chains (pentadecyl) the ß1phase is predominant. The kinetics of ß2phase formation is investigated and reveals a reduced growth rate when long alkyl side chains are present. X-ray diffraction reveals a closer p-p stacking distance for ß2than for ß1, consistent with its redshifted absorption and its higher mobility in field-effect transistors. The polymer with hexyl side chains adopts an edge-on orientation in thin films, while the longer alkyl chains induce a face-on orientation. Photovoltaic devices exhibit an additional near infrared spectral contribution to the photocurrent for the ß2phase. The study shows that the formation of the two polymorphs ß1and ß2is controlled by the alkyl side chains and the solubility that arises from them. Shorter side chains (lower solubility) favor ß2and longer side chains (higher solubility) ß1, and at intermediate lengths both phases can be formed.

We report on the epitaxial growth of photoresponsive alkyl-substituted azobenzene fibres on top of uniaxially oriented polyethylene (PE) films. In these fibres, the alkyl chains are oriented parallel with regard to the drawing direction of PE, whereas the azobenzene moieties pack into a roughly 60° angle. The bilayer films act as a light responsive actuator generating an actuation stress of about 3 MPa.

The effect of gradually replacing the branched alkyl side chains of a diketopyrrolopyrrole (DPP) conjugated polymer by linear side chains containing branched siloxane end groups on the photovoltaic performance of blends of these polymers with a common fullerene acceptor is investigated. With an increasing proportion of siloxane side chains, the molecular weight and solubility of the polymers decreases. While the siloxane containing polymers exhibit a higher hole mobility in field-effect transistors, their performance in solar cells is less than the polymer with only alkyl sides chains. Using grazing-incidence wide-angle X-ray scattering, transmission electron microscopy, and fluorescence spectroscopy we identify two main reasons for the reduced performance of siloxane containing polymers in solar cells. The first one is a somewhat coarser phase-separated morphology with slightly wider polymer fibers. This is unexpected as often the fiber width is inversely correlated with polymer solubility. The second one is stronger non-radiative decay of the pristine polymers containing siloxane side chains. G. H. L. Heintges acknowledges the Agency for Innovation by Science and Technology in Flanders (IWT). This project has further received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 747422, from the European Research Council under the European Union's Seventh Framework Programme (FP/2007-2013)/ERC Grant Agreement No. 339031 and from the Ministry of Education, Culture and Science (Gravity program 024.001.035).

Self-supporting polymer thin films were obtained by the polymerization of an AB3-type hydrogen-bonded complex in the plastic columnar phase. Porous polymers with pore diameters of ≈1.1 and ≈1.6 nm lined with either -COOH or -COONa groups were fabricated from the polymer thin films. Both the pore size and pore collapse influence the adsorption of cations.

Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is frequently used as hole transport layer in planar p-i-n perovskite solar cells. Here we show that processing of a metal halide perovskite layer on top of PEDOT:PSS via spin coating of a precursor solution chemically reduces the oxidation state of PEDOT:PSS. This reduction leads to a lowering of the work function of the PEDOT:PSS and the perovskite layer on top of it. As a consequence, the solar cells display inferior performance with a reduced open-circuit voltage and a reduced short-circuit current density, which increases sublinearly with light intensity. The reduced PEDOT:PSS can be re-oxidized by thermal annealing of the PEDOT:PSS/perovskite layer stack in the presence of oxygen. As a consequence, thermal annealing of the perovskite layer in air provides solar cells with increased open-circuit voltage, short-circuit current density and high efficiency.

The majority of organic semiconductors have a low relative dielectric constant (ϵr < 6), which is an important limitation for organic solar cells (OSCs). A high dielectric constant would reduce the exciton binding energy, reduce charge carrier recombination losses, and thereby enhance the overall device performance of OSCs. However, the development of organic/polymeric semiconductors with higher relative dielectric constants (ϵr > 6) has attracted a very limited attention. Moreover, high performance OSCs based on high dielectric constant photovoltaic materials are still in their infancy. Herein, we report an oligoethylene oxide side chain-containing non-fullerene acceptor (ITIC-OE) with a high relative dielectric constant of ϵr ≈ 9.4, which is two times larger than that of its alkyl chain-containing counterpart ITIC. Encouragingly, the OSCs based on ITIC-OE show a high power conversion efficiency of 8.5%, which is the highest value for OSCs that employ high dielectric constant materials. Nevertheless, this value is lower than those of ITIC-based control devices. The less phase-separated morphology in blend films due to the reduced crystallinity of ITIC-OE and the too good miscibility between PBDB-T and ITIC-OE are responsible for the lower device performance. This work suggests additional prerequisites to make high dielectric constants play a significant role in OSCs.

Oligomers of methacrylic acid containing a propenyl ω-endgroup (i.e. MAA-macromonomers) were synthesized by cobalt-mediated catalytic chain transfer polymerization and used as precursors to stabilizers in emulsion polymerization. It was found that only in those polymerizations in which these precursors were sufficiently quickly converted into amphiphilic molecules, via a type of polymerization induced self-assembly (PISA) mechanism, stable emulsion polymerization could be carried out. This process was too slow in the emulsion polymerization of methyl methacrylate (MMA) and in order to obtain stable latexes, the addition of a conventional surfactant (sodium dodecyl sulphate, SDS) was necessary. In the emulsion polymerization of butyl acrylate, however, reactions with the macromonomers were faster and because of the more hydrophobic nature of BA (as compared to MMA), stabilizers were sufficiently quickly formed in situ and stable latexes were produced without the need for additional SDS. Also the emulsion polymerization of butyl methacrylate (BMA), which reacts via the same "sulfur-free RAFT" mechanism as MMA, could be carried out in the absence of SDS because of the greater hydrophobicity of the monomer. Copolymerizations of MMA with >30% of BA or 85% BMA also resulted in stable latexes without the addition of SDS. The synthesized macromonomers and in situ formed copolymers were characterized by means of size exclusion chromatography (SEC), 1H NMR spectroscopy and MALDI-ToF MS.

Integration of a third component into a single-junction polymer solar cell (PSC) is regarded as an attractive strategy to enhance the performance of PSCs. Although binary all-polymer solar cells (all-PSCs) have recently emerged with compelling power conversion efficiencies (PCEs), the PCEs of ternary all-PSCs still lag behind those of the state-of-the-art binary all-PSCs, and the advantages of ternary systems are not fully exploited. In this work, we realize high-performance ternary all-PSCs with record-breaking PCEs of 9% and high fill factors (FF) of over 0.7 for both conventional and inverted devices. The improved photovoltaic performance benefits from the synergistic effects of extended absorption, more efficient charge generation, optimal polymer orientations and suppressed recombination losses compared to the binary all-PSCs, as evidenced by a set of experimental techniques. The results provide new insights for developing high-performance ternary all-PSCs by choosing appropriate donor and acceptor polymers to overcome limitations in absorption, by affording good miscibility, and by benefiting from charge and energy transfer mechanisms for efficient charge generation.

We demonstrate that diblock copolymers comprising hydrophobic polystyrene and hydrophilic poly(acrylic acid) blocks connected by an off-center anthracene-maleimide Diels-Alder adduct mechanophore are mechanochemically active when sonicated in the form of micelles. Non-crosslinked and crosslinked hairy poly(butyl acrylate) latex particles were synthesized using amphiphilic block copolymers as stabilizers in emulsion polymerization. Both non-crosslinked and crosslinked hairy particles can be mechanically activated by sonication, which means that the "hairs" on the surface of particles can be selectively cleaved. The sensitivity to mechanical force enhanced with increasing crosslinking of the PBA particles, but it may also lead to particle degradation. The mechanoresponsive hairy latex particles may facilitate the design of stress-sensing probes in aqueous systems.

We report off-white circularly polarized luminescence (CPL) from supramolecular aggregates formed by a chiral carboxylic acid-functionalized naphthalene diimide. The self-assembly behaviour and the stability of the aggregates in solution were assessed by variable-temperature UV-Vis and electronic circular dichroism experiments. The observed 200 nm-wide emission band is unusual for a single chromophore and is a consequence of the supramolecular ordering due to a combination of π-stacking and H-bonding interactions, leading to excimer formation. High emission anisotropy factors glum, around |1-2| × 10-2, were observed over the whole spectrum in chlorinated/hydrocarbon solvent mixtures, as well as in thin films. These values are one order of magnitude higher than those of most chiral self-assembled fluorophores and other common small organic emitters.

We report the synthesis and self-assembly behavior of a chiral C3-symmetrical benzene-tricarboselenoamide. The introduction of the selenoamide moiety enhances the dipolar character of the supramolecular interaction and confers a remarkable thermal stability to the supramolecular polymers obtained.

Understanding the self-assembly of small molecules in water is crucial for the development of responsive, biocompatible soft materials. Here, a family of benzene-1,3,5-tricarboxamide (BTA) derivatives that comprise a BTA moiety connected to an amphiphilic chain is synthesised with the aim to elucidate the role of hydrophobic and hydrogen-bonding interactions in the self-assembly of these BTAs. The amphiphilic chain consists of an alkyl chain with a length of 10, 11, or 12 methylene units, connected to a tetraethylene glycol (at the periphery). The results show that an undecyl spacer is the minimum length required for these BTAs to self-assemble into supramolecular polymers. Interestingly, exchange studies reveal only minor differences in exchange rates between BTAs containing undecyl or dodecyl spacers. Additionally, IR spectroscopy provides the first experimental evidence that hydrogen-bonding is operative and contributes to the stabilisation of the supramolecular polymers in water.

Photoelectrochemical water splitting is demonstrated in an organic artificial leaf composed of a triple junction polymer solar cell for light absorption and charge generation and low-overpotential catalytic electrodes for hydrogen and oxygen evolution. For small area solar cells (

New alternating copolymers based on benzo[1,2-b:4,5-b′]dithiophene and thieno[3,4-d]thiazole derivatives have been synthesized by using different combinations of side chains and spacers in order to study their effect on the optical, electrochemical and photovoltaic properties. Optical and electrochemical characterization were performed and the resulting copolymers exhibit optical bandgaps ranging from 1.66 to 1.80 eV, HOMO energy levels between −5.19 and −5.30 eV and LUMO energy levels between −3.60 and −3.72 eV. Photovoltaic devices were fabricated and characterized after a careful optimization of the active layer fabrication by using different solvents, additives and acceptors. Following this process, PCEs up to 4.4% were obtained.

Four different thiazole-flanked diketopyrrolopyrrole-based polymers were applied as an electron acceptor in bulk heterojunction solar cells with poly(3-hexylthiophene) as an electron donor. Power conversion efficiencies of 1.5% to 3.0% were achieved with a spectral response from 350 to 950 nm.

A water-soluble benzene-1,3,5-tricarboxamide (BTA) derivative that self-assembles into one-dimensional, helical, supramolecular polymers is functionalised at the periphery with one L-proline moiety. In water, the BTA-derivative forms micrometre long supramolecular polymers, which are stabilised by hydrophobic interactions and directional hydrogen bonds. Furthermore, we co-assemble a catalytically inactive, but structurally similar, BTA with the L-proline functionalised BTA to create co-polymers. This allows us to assess how the density of the L-proline units along the supramolecular polymer affects its activity and selectivity. Both the supramolecular polymers and co-polymers show high activity and selectivity as catalysts for the aldol reaction in water when using p-nitrobenzaldehyde and cyclohexanone as the substrates for the aldol reaction. After optimisation of the reaction conditions, a consistent conversion of 92 ± 7%, deanti of 92 ± 3%, and eeanti of 97 ± 1% are obtained with a concentration of L-proline as low as 1 mol%.

The interplay of Phe-Gly-Gly (FGG)-tagged proteins and bivalent FGG-tagged penta(ethylene glycol) as guest molecules with cucurbit[8]uril (Q8) hosts is studied to modulate the supramolecular assembly process. Ring structure formation of the bivalent guest molecule with Q8 leads to enhanced binding properties and efficient inhibition of protein assemblies. Graphical abstract: Cucurbit[8]uril templated supramolecular ring structure formation and protein assembly modulation

Supramolecular chemistry provides an attractive entry to generate dynamic and well-controlled bioactive surfaces. Novel host–guest systems are urgently needed to provide a broader affinity and applicability portfolio. A synthetic strategy to carborane–peptide bioconjugates was therefore developed to provide an entry to monovalent supramolecular functionalization of ß-cyclodextrin coated surfaces. The ß-cyclodextrin·carborane–cRGD surfaces are formed efficiently and with high affinity as demonstrated by IR-RAS, WCA, and QCM-D, compare favourable to existing bio-active host–guest surface assemblies, and display an efficient bioactivity, as illustrated by a strong functional effect of the supramolecular system on the cell adhesion and spreading properties. Cells seeded on the supramolecular surface displaying bioactive peptide epitopes exhibited a more elongated morphology, focal adhesions, and stronger cell adhesion compared to control surfaces. This highlights the macroscopic functionality of the novel supramolecular immobilization strategy.

In this work, antimicrobial glycosylated block copolymers were successfully immobilized onto polymeric surfaces by using them as surfactants in butyl methacrylate emulsion polymerization. In particular several amphiphilic block copolymers of various compositions were employed, all consisting of a poly(butyl methacrylate) hydrophobic segment and a statistical copolymer containing quaternized trimethylaminoethyl methacrylate and 2-(D-glucosamin-2-N-yl)carbonylethyl methacrylate glycomonomer as a hydrophilic block. The influence of the antimicrobial polymeric surfactant structure and solid content on the emulsion polymerization was investigated in detail. It was demonstrated that the efficiency of the surfactant is highly dependent on the hydrophilic/hydrophobic balance; in general the surface-active properties get worse with an excess of hydrophilicity. Monodisperse and stable latexes stabilized with an antimicrobial polymeric surfactant were successfully obtained and then employed to form active films. The film formation process under thermal treatments was followed and confirmed by AFM. The surface functionality of the films was tested by analyzing the interaction of glycounits of the surface with Concanavalin A lectin by fluorescence spectroscopy. In addition, the antimicrobial capability of these films against Gram-positive bacteria and yeast was demonstrated whereas the leaching of the surfactants to the media was discarded. Graphical abstract: Functional surfaces obtained from emulsion polymerization using antimicrobial glycosylated block copolymers as surfactants

Herein, we present a facile strategy to controllably build up dendrimicelles by self-assembly of anionic PAMAM dendrimers with cationic–neutral diblock copolymers. We present a systematic study incorporating a full decade (0–9) of dendrimer generations, tracing the gradual variation from aggregates (G0 and G1) to self-assembled micelles (G2–G8), and an unidendrimer micelle structure (G9) by different scattering techniques (light and X-ray). The formed micelles (G2–G9) are spherical in shape with a hydrodynamic radius of about 25 nm. Interestingly, the micellar size, structure and number of incorporated block copolymers are independent of the dendrimer generation (for G2 to G9), while the aggregation number of the dendrimers decreases from 108 to 1, and the stability of the micelles increases upon an increase in the dendrimer generation. Moreover, the micelles with lower generation dendrimers transform from spherical into worm-like structures upon an increase in the positive charge fraction (excess polymers) or ionic strength, while micelles with higher generation dendrimers do not show such a transition. This differential behavior is in-line with a change from a flexible configuration into rigid globular nanoparticles with increasing dendrimer generation. The reported systematic investigation of dendrimicelles comprising a full decade of dendrimer generations provides the basis for versatile strategies focused on building up new (multi)functional materials, e.g. by packing multiple types of dendrimers with different functional groups or encapsulated cargos controllably within one micelle.

Supramolecular hydrogels formed by decorating benzene-1,3,5-tricarboxamide (BTA) units with amphiphilic ethylene glycol-based side chains are presented; careful selection of the substituents of the BTAs allows for the tuning of the self-assembly behaviour and hence the mechanical properties of the resultant hydrogel.

Engineering of anisotropic tissues demands extracellular matrix (ECM) mimicking scaffolds with an asymmetric distribution of functionalities. We here describe a convenient, modular approach based on supramolecular building blocks to form electrospun bilayered scaffolds with tailorable properties. Polymers and peptides functionalized with hydrogen-bonding ureido-pyrimidinone (UPy) moieties can easily be mixed-and-matched to explore new material combinations with optimal properties. These combinatorial supramolecular biomaterials, processed by electrospinning, enable the formation of modular fibrous scaffolds. We demonstrate how UPy-functionalized polymers based on polycaprolactone and poly(ethylene glycol) enable us to unite both cell-adhesive and non-cell adhesive characters into a single electrospun bilayered scaffold. We furthermore show that the non-cell adhesive layer can be bioactivated and made adhesive for kidney epithelial cells by the incorporation of 4 mol% of UPy-modified Arg-Gly-Asp (RGD) peptide in the electrospinning solution. These findings show that the UPy-based supramolecular biomaterial system offers a versatile toolbox to form modular multilayered scaffolds for tissue engineering and regenerative medicine applications such as the formation of membranes for a living bioartificial kidney.

The controlled self-assembly of multiple molecules into predefined architectures requires highly directional and controllable non-covalent interactions with a high association constant. Here, we introduce the self-complementary ureido-benzoic acid (UBA) quadruple hydrogen-bonding motif. The dimerization constant is of the order of 109 M-1 in chloroform, which makes it an excellent candidate for supramolecular chemistry in dilute conditions. The self-complementary quadruple hydrogen bonding was confirmed in the solid state by a crystal structure. The applicability of the motif in supramolecular polymers was evaluated by bis-UBA telechelic poly(ethylene-butylene) polymers, which showed a dramatic increase in mechanical properties upon functionalization. The potential of the UBA motif in supramolecular chemistry was further evaluated in solution. One of the synthesized UBA molecules revealed hydrogen bonding to NaPy at high concentrations in chloroform. However, upon dilution, the UBA:NaPy hydrogen bonding is disrupted and UBA homodimers are obtained. This shows the potential of NaPy as a supramolecular protective group for the UBA molecule, which can be deprotected upon dilution. Furthermore, the dimerization of the UBA motif was reversibly switched between the 'off' and 'on' states using base and acid, demonstrating an alternative method of influencing the UBA dimerization. Switching of a UBA molecule in the presence of UPy revealed that UBA dimerization can be selectively switched 'off' and 'on' in the presence of UPy dimers. These results show the applicability and great potential of the self-complementary quadruple hydrogen-bonding UBA motif for supramolecular chemistry. © 2014 the Partner Organisations.

The synthesis, characterization and functionalization of DNA-grafted supramolecular polymers are described. Cargo loading of the helical supramolecular assemblies with gold nanoparticles is demonstrated.

There has been tremendous progress towards the development of responsive polymers that are programmed to respond to an external stimulus such as light, pH and temperature. The unique combination of molecular packaging followed by slow, controlled release of molecular cargo is of particular importance for self-healing materials and the controlled release of drugs. While much focus and progress remains centred around synthetic carriers, viruses and virus-like particles can be considered ideal cargo carriers as they are intrinsically designed to package, protect and deliver nucleic acid cargo to host cells. Here, we report the encapsulation of a stimuli-responsive self-immolative polymer within virus-like assemblies of Cowpea Chlorotic Mottle Virus. Upon photo-irradiation, the self-immolative polymer undergoes a head-to-tail depolymerization into its monomeric subunits, resulting in the slow release of the molecular cargo. We propose that the liberated monomers are small enough to diffuse through the pores of the virus capsid shell and offer an alternative strategy for the controlled loading and unloading of the molecular cargo using viruses as cargo carriers.

Antibody-based molecular recognition plays a dominant role in the life sciences ranging from applications in diagnostics and molecular imaging to targeted drug delivery and therapy. Here we report a generic approach to introduce protease sensitivity into antibody-based targeting by taking advantage of the intrinsic ability of antibodies to engage in multivalent interactions. Bivalent peptide ligands with dsDNA as a rigid linker were shown to effectively bridge the relatively large distance between the two antigen binding sites within the same antibody, yielding exclusively the cyclic 1 : 1 antibody–ligand complex. Size exclusion chromatography and small angle X-scattering were used to study the types of complexes formed between a model antibody and peptide–dsDNA conjugates displaying 1 or 2 peptide ligands and different linker lengths. Competitive binding assays using fluorescence anisotropy revealed that the interaction between bivalent peptide–dsDNA conjugate and antibody is 500-fold stronger than that of the monovalent peptide, allowing effective blocking of the antigen binding sites in a non-covalent manner. Cleavage of the linker between the peptide epitope and the DNA by matrix metalloprotease 2 disables this strong bivalent interaction and was shown to effectively restore the binding activity of the antibody in an in vitro binding assay. The approach presented here is broadly applicable, because it takes advantage of the Y-shaped multivalent presentation of antigen binding sites common to all antibodies and could be extended to control antibody activity by other input signals.

Using Stille and Suzuki polymerization reactions we incorporate thienoisoindigo (TII) as an acceptor co-monomer into a series of alternating p-conjugated copolymers with combinations of benzene, thiophene and carbazole as donor co-monomers. By changing the nature and length of the donor segments, the optical band gap of these soluble TII copolymers can be varied over a large range from 1.52 eV down to 0.87 eV. The semiconducting properties of the TII copolymers were established in bottom-gate bottom-contact field-effect transistors that provide hole mobilities for these materials in the range of 10-3 to 10-2 cm2 V-1 s-1.

N,N′,N′′-Trialkylbenzene-1,3,5-tricarboxamides (BTAs) cooperatively self-assemble into one-dimensional, helical supramolecular polymers in apolar alkane solutions. Previous studies revealed that the position and configuration of the methyl group on the aliphatic side-chain gives rise to an ‘odd–even effect’ both in the shape and the sign of the CD-effect. In this study, we elucidate the molecular origin of this odd–even effect by a combination of TD-DFT calculations and spectroscopic experiments. In addition, we observed a pronounced effect of the molecular structure of the alkane solvent on the shape of the Cotton effects and the thermodynamic parameters describing the cooperative supramolecular polymerization. The results revealed a different ability of solvent molecules governed by the shape of their structure to intercalate into the helical stacks, which influences the conformation of the monomer within the supramolecular polymer. The solvent affects the dihedral angle (θ) between the CO group and the benzene central core of the BTA molecule. These findings help to increase a molecular-level understanding of how the solvent controls the conformation of repeating units in a supramolecular system.

An in depth investigation of the fine structure adopted by the helical stacks of C3-discotics 1 incorporating three 3,3'-diamino-2,2'-bipyridine units is described. In the bulk the molecules display liquid crystalline behaviour in a temperature window of >300 K and an ordered rectangular columnar mesophase (Colro) with an inter-disc distance of 3.4 Å is assigned. X-Ray diffraction on aligned samples has also revealed a helical superstructure in the liquid crystalline state, and a rotation angle of 13–16° between consecutive discs. The proposed superstructure in the bulk phase has been further substantiated by a combination of quantum-chemical calculations and solid-state NMR spectroscopy. Dilute solution NMR spectroscopy and elaborate CD spectroscopy on aggregated samples have revealed an isodesmic growth pattern of the C3-discotics. From the combined results it has become evident that the fine tuning interaction responsible for the highly ordered helical architectures is not weak intermolecular hydrogen bonding, but rather rigidification, due to propeller formation after preorganisation by p–p interactions. Although all the techniques used underpin the structural features proposed, none of them individually is able to point to a unique structure. However, together the techniques give very strong evidence for a confined ship-screw arrangement in which all amidic carbonyl oxygens point in one direction.

Solid-state NMR experiments as well as extensive Car–Parrinello Molecular Dynamics simulations are used to study the dependence of supramolecular self-organization of benzene-1,3,5-tricarboxamides (BTA) on the local orientation of the amide functionality. Unlike the known symmetric co-planar helical arrangement of CO-centered BTAs found in supramolecular architectures like supramolecular polymers in gels, N-centered BTAs adopt an asymmetric helical arrangement in the solid-state. The resulting tilt angle between the aromatic cores of neighboring BTA molecules leads to a breaking of the three-fold molecular symmetry and thus causes a splitting of 1H MAS NMR signals. At elevated temperatures, motional averaging of the split 1H MAS NMR signals is observed, which can be attributed to certain dynamics on the ms time scale of individual BTA molecules in the columnar packing arrangement.

Three copolymers of thieno[3,2-b]thiophene (TT) and diketopyrrolo[3,4-c]pyrrole (DPP) with a varying number of interconnecting thiophene units (nT) were synthesized by Suzuki polymerization. The PDPPnT-TT polymers display optical band gaps in the range of 1.33 to 1.52 eV and show ambipolar charge transport when applied in a field-effect transistor (FET) with hole and electron mobilities up to 3 × 10-2 and 2 × 10-3 cm2 V-1 s-1, respectively. Organic solar cells based on the PDPPnT-TT polymers as donors and the fullerene derivative [60]PCBM as acceptor achieve power conversion efficiencies up to 3.4% when the layer is deposited with the use of a co-solvent. The co-solvent strongly affects the morphology of the active layer and improves the performance. For these polymers the LUMO–LUMO offset with [60]PCBM correlates with the photocurrent and the maximum external quantum efficiency.

A series of four small band gap polymers have been synthesized and have been incorporated into bulk heterojunction solar cells. The polymers were prepared via Yamamoto coupling and consist of alternating electron-rich dithiophene and electron-deficient bisquinoxaline or thienopyrazine units. In the thin solid films the optical band gaps (Eg) vary from 1.38 eV for the bisquinoxaline to 1.21 eV for thienopyrazine containing polymers. All polymers provide a photovoltaic response when blended with a methanofullerene as electron acceptor in the near infrared region up to the optical band gap. The best cells reach an efficiency of ¿ = 1.5% under estimated standard solar light conditions (AM1.5G, 100 mW/cm2).

Novel core-functionalized dendritic oligothiophenes (DOT) bearing pyridine or methylpyridinium acceptors have been synthesized up to the third generation. A bathochromic shift in the absorption of the functionalized dendritic oligothiophenes and the appearance of new absorption bands were noticed issuing from an intramolecular charge transfer process. These novel donor-acceptor systems are, due to their broad absorption, promising materials for optoelectronic applications such as organic solar cells. By electrochemical measurements HOMO/LUMO energy levels have been determined and two compounds could be identified with almost ideal energy levels for application in bulk heterojunction solar cells (BHJSC) with fullerene PC61BM as acceptor.

This tutorial review serves as an introduction to helical self-assembled systems, illustrated by a specific class of helical aggregates: helical nanofibers. The common ways by which these systems are designed, prepd., and characterized will be presented. [on SciFinder (R)]

The thermotropic behaviour of a series of hydrogen bonded chiral and achiral oligo(p-phenylenevinylenes) (OPVs) has been investigated. The liquid crystalline properties are studied as a function of their molecular design that is based on hydrogen bonding units, the lengths of the π-conjugated and flexible segments and the branching of the side chains. Two-dimensional wide-angle X-ray scattering experiments indicate self-assembly of all OPVs into columnar superstructures which is the result of hydrogen bonds formed by the diaminotriazine or ureidotriazine units and π-stacking interactions accompanied by a local phase separation between the alkoxy side chains and the aromatic rods. The phase behaviour of the compounds bearing the diaminotriazine functionality depends on the length of the OPV segment. OPV trimers are already liquid crystalline at ambient conditions, while longer OPV tetramers are in a well-organized crystalline state at that temperature. In the liquid crystalline phase the intracolumnar order decreases due to molecular motion as confirmed by solid-state NMR studies. Interestingly, the introduction of branched (S)-2-methylbutoxy side chains increases significantly the π-stacking distance while the dimensions of the hexagonal unit cell decrease. The hydrogen bonding ureidotriazine groups decrease the thermal stability and lower the degree of order in comparison with the diaminotriazine derivatives. This low degree of order is probably the result of the ureidotriazine units that form hydrogen bonded dimers while the diaminotriazine arrays form hydrogen bonded hexameric rosettes. In the latter case a more densely packed columnar structure is formed.

We discuss the materials challenges for increasing cell efficiencies of polymer solar cells via the route of stacking several cells on top of each other in multi-junction solar cells. For such cells, the recombination layer between the two sub cells is crucial. Typically, the recombination layer consists of a semi-transparent n- and p-type semiconductor bilayer. Several options for the recombination layer will be discussed. Furthermore, we discuss how the workfunction and the conductivity of the semi-transparent semiconductors may influence the performance of the cells. We also discuss requirements for accurate measurements of spectral response and efficiency. Keywords: tandem, polymer film, multi-junction solar cell

Three C3-symmetrical discotics containing a 1,3,5-benzenetricarboxamide unit functionalized with pi-conjugated oligo(p-phenylenevinylene)s (OPV)s have been synthesized and fully characterized. For the two amide OPV discs a two-step transition from helical stacks to molecularly dissolved species was observed and surprisingly, the topology of the amide determines the stability and helicity of the fibers in solution and the length of the fibrils at a surface. In case of the bipyridine disc, aggregates were formed that show little chiral ordering while the stacks remain present over a large temperature range. At a surface, completely disordered structures exist probably as a result of competing types of pi-pi stacking interactions that differ in strength and orientation. The results show that the design of functional self-assembled architectures based on hydrogen bonding and pi-pi stacking interactions is an extremely delicate matter and reveal that special demands have to be taken into account to balance the topology, directionality and strength of multiple secondary interactions.

Biology often uses hierarchical self-assembly to produce complex functional structures from smaller components. At each level of this stepwise process, non-covalent interactions bring together the subunits of a lower level of complexity, using the information encoded in their structures. Applying this approach to synthetic systems represents a formidable challenge, because it requires a high degree of command of non-covalent interactions. In this tutorial review, recent developments in the hierarchical self-assembly of discrete columnar aggregates are discussed.

Heterosupramolecular assemblies of TiO2 nanoparticles (

The formation of supramolecular polymers in water through rational design of a benzene-1,3,5-tricarboxamide (BTA) motif is presented. Intermolecular hydrogen bonding and hydrophobic effects cooperate in the self-assembly into long fibrillar aggregates. Minimal changes in molecular structure significantly affect the internal packing of the aggregates.

The interaction of an acid-functionalized oligo(p-phenylene vinylene) (OPV3-COOH) with nanocryst. TiO2 was studied as a model for semiconducting polymer-inorg. material hybrid solar cells. Langmuir adsorption studies show that the monolayer coverage of OPV3-COOH on nc-TiO2 results in 35% filling of the nanopores. Photoluminescence quenching and near steady-state photoinduced absorption spectroscopy demonstrate that an efficient forward photoinduced electron transfer occurs from OPV3-COOH to TiO2. Photovoltaic cells based on OPV3-COOH/nc-TiO2, and a liq. electrolyte as a medium for hole transport, provide an incident photon-to-electron conversion efficiency of 55%, comparable to the values obtained with the best Ru dyes. The results demonstrate that the majority of the photogenerated charges can be collected. [on SciFinder (R)]

Small changes in the alkane solvent structure in combination with temperature effects lead to four different conformations of stereoselectively deuterated benzene-1,3,5-tricarboxamides in the aggregated state, affecting the expression of the supramolecular chirality and highlighting the role of the solvent structure in self-assembly processes.

The [FeFe] hydrogenase is a highly sophisticated enzyme for the synthesis of hydrogen via a biological route. The rotated state of the H-cluster in the [FeIFeI] form was found to be an indispensable criteria for an effective catalysis. Mimicking the specific rotated geometry of the [FeFe] hydrogenase active site is highly challenging as no protein stabilization is present in model compounds. In order to simulate the sterically demanding environment of the nature's active site, the sterically crowded meso-bis(benzylthio)diphenylsilane (2) was utilized as dithiolate linker in an [2Fe2S] model complex. The reaction of the obtained hexacarbonyl complex 3 with 1,2-bis(dimethylphosphino)ethane (dmpe) results three different products depending on the amount of dmpe used in this reaction: [{Fe2(CO)5{μ-(SCHPh)2SiPh2}}2(μ-dmpe)] (4), [Fe2(CO)5(κ2-dmpe){μ-(SCHPh)2SiPh2}] (5) and [Fe2(CO)5(μ-dmpe){μ-(SCHPh)2SiPh2}] (6). Interestingly, the molecular structure of compound 5 shows a [FeFe] subsite comprising a semi-rotated conformation, which was fully characterized as well as the other isomers 4 and 6 by elemental analysis, IR and NMR spectroscopy, X-ray diffraction analysis (XRD) and DFT calculations. The herein reported model complex is the first example so far reported for [FeIFeI] hydrogenase model complex showing a semi-rotated geometry without the need of stabilization via agostic interactions (Fe⋯H-C). This journal is