Mathieu Surin

Thermal annealing-induced enhancement of the field-effect mobility of regioregular poly(3-hexylthiophene) films

Polymer field-effect transistors with a field-effect mobility of μ≈0.3cm2s−1V−1 have been demonstrated using regioregular poly(3-hexylthiophene) (rr-P3HT). Devices were fabricated by dip coating the semiconducting polymer followed by annealing at 150°C for 10min. The heat annealed devices exhibit an increased field-effect mobility compared with the as-prepared devices. Morphology studies and analysis of the channel resistance demonstrate that the annealing process increases the crystallinity of rr-P3HT and improves the contact between the electrodes and the P3HT films, thereby increasing the field-effect mobility of the films.Polymer field-effect transistors with a field-effect mobility of μ≈0.3cm2s−1V−1 have been demonstrated using regioregular poly(3-hexylthiophene) (rr-P3HT). Devices were fabricated by dip coating the semiconducting polymer followed by annealing at 150°C for 10min. The heat annealed devices exhibit an increased field-effect mobility compared with the as-prepared devices. Morphology studies and analysis of the channel resistance demonstrate that the annealing process increases the crystallinity of rr-P3HT and improves the contact between the electrodes and the P3HT films, thereby increasing the field-effect mobility of the films.

Relationship between the microscopic morphology and the charge transport properties in poly(3-hexylthiophene) field-effect transistors

We fabricate field-effect transistors (FETs) by depositing a regioregular poly(3-hexylthiophene) (RR-P3HT) active layer via different preparation methods. The solvent used in the polymer film deposition and the deposition technique determine the film microstructure, which ranges from amorphous or granular films to a well-defined fibrillar texture. The crystalline ordering of RR-P3HT into fibrillar structures appears to lead to optimal FET performances, suggesting that fibrils act as efficient “conduits” for the charge carrier transport. Treating the silicon oxide gate insulator with hexamethyldisilazane enhanced the FET performance.

Multicolour Self-Assembled Fluorene Co-Oligomers: From Molecules to the Solid State via White-Light-Emitting Organogels

Five fluorene-based co-oligomers have been prepared to study their self-assembly in a wide range of concentrations, from dilute solutions to the solid state. Subtle changes to the chemical structures, introduced to tune the emission colours over the entire visible range, induce strong differences in aggregation behaviour. Only two of the fluorescent co-oligomer derivatives self-assemble to form soluble fibrils from which fluorescent organogels emerge at higher concentrations. In contrast, the other compounds form precipitates. Mixed fluorescent co-oligomer systems exhibit partial energy transfer, which allows the creation of white-light-emitting gels. Finally, a mechanism for the hierarchical self-assembly of this class of materials is proposed based on experimental results and molecular modelling calculations.

A dynamic supramolecular polymer with stimuli-responsive handedness for in situ probing of enzymatic ATP hydrolysis.

Design of artificial systems, which can respond to fluctuations in concentration of adenosine phosphates (APs), can be useful in understanding various biological processes. Helical assemblies of chromophores, which dynamically respond to such changes, can provide real-time chiroptical readout of various chemical transformations. Towards this concept, here we present a supramolecular helix of achiral chromophores, which shows chiral APs responsive tunable handedness along with dynamically switchable helicity. This system, composing of naphthalenediimides with phosphate recognition unit, shows opposite handedness on binding with ATP compared with ADP or AMP, which is comprehensively analysed with molecular dynamic simulations. Such differential signalling along with stimuli-dependent fast stereomutations have been capitalized to probe the reaction kinetics of enzymatic ATP hydrolysis. Detailed chiroptical analyses provide mechanistic insights into the enzymatic hydrolysis and various intermediate steps. Thus, a unique dynamic helical assembly to monitor the real-time reaction processes via its stimuli-responsive chiroptical signalling is conceptualized.

Self-assembly of tetrathiafulvalene derivatives at a liquid/solid interface—compositional and constitutional influence on supramolecular ordering

The self-assembly of a series of tetrathiafulvalene (TTF) derivatives at the interface between non-volatile organic solutions and the graphite surface has been studied by scanning tunnelling microscopy (STM). The TTFs have been prepared such that they bear none, one, two (in different constitutions) or four alkyl chains of different lengths and different functional groups. The STM images reveal that the packing of the TTF cores can effectively be controlled by changing the substitution pattern on the heterocycle. Several structures are seen at the interphase—parquet-type packing, single and double core tapes, and even isolated molecules—all of which have the TTF core essentially coplanar with the surface. Molecular modelling has shown that several orientations of the molecules are practically equal in energy on the graphite, which explains the polymorphous packing of some of the molecules. Solvent effects also play a role in determining the 2D structures.

Surface-controlled self-assembly of chiral sexithiophenes

We report on the self-assembly of two enantiomeric sexithiophenes in solution and on surfaces. Circular dichromism of aggregated sexithiophenes and drop-cast films reveals, as expected, mirror image spectra for both enantiomers. The aggregation in thin deposits from sexithiophenes molecularly dispersed in a solution on different types of substrates was investigated by atomic force microscopy (AFM). On graphite, one-dimensional objects (nanowires) are formed while on mica platelets are generated. Remarkably, we found that both enantiomers form left-handed helices on silicon. This observation depends on the hydrophilicity of the silicon. Furthermore, the achiral sexithiophene did not form helical aggregates suggesting that the stereocenter is required to obtain chirality in the fibers.

Nanoscale investigation of the electrical properties in semiconductor polymer–carbon nanotube hybrid materials

The morphology and electrical properties of hybrids of a semiconducting polymer (namely poly(3-hexylthiophene) P3HT) and carbon nanotubes are investigated at the nanoscale with a combination of Scanning Probe Microscopy techniques, i.e., Conductive Atomic Force Microscopy (C-AFM) and time-resolved Current Sensing Force Spectroscopy Atomic Force Microscopy (CSFS-AFM, or PeakForce TUNA™). This allows us to probe the electrical properties of the 15 nm wide P3HT nanofibers as well as the interface between the polymer and single carbon nanotubes. This is achieved by applying controlled, low forces on the tip during imaging, which allows a direct comparison between the morphology and the electrical properties at the nanometre scale.

A Rigid Dinuclear Ruthenium(II) Complex as an Efficient Photoactive Agent for Bridging Two Guanine Bases of a Duplex or Quadruplex Oligonucleotide

The rigid dinuclear [(tap)(2)Ru(tpac)Ru(tap)(2)](4+) complex (1) (TAP=1,4,5,8-tetraazaphenanthrene, TPAC=tetrapyridoacridine) is shown to be much more efficient than the mononuclear bis-TAP complexes at photodamaging oligodeoxyribonucleotides (ODNs) containing guanine (G). This is particularly striking with the G-rich telomeric sequence d(T(2)AG(3))(4). Complex 1, which interacts strongly with the ODNs as determined by surface plasmon resonance (SPR) and emission anisotropy experiments, gives rise under illumination to the formation of covalent adducts with the G units of the ODNs. The yield of photocrosslinking of the two strands of duplexes by 1 is the highest when the G bases of each strand are separated by three to four base pairs. This corresponds with each Ru(tap)(2) moiety of complex 1 forming an adduct with the G base. This separation distance of the G units of a duplex could be determined thanks to the rigidity of complex 1. On the basis of results of gel electrophoresis, mass spectrometry, and molecular modelling, it is suggested that such photocrosslinking can also occur intramolecularly in the human telomeric quadruplex d(T(2)AG(3))(4).

Fiber-Optic SPR Immunosensors Tailored To Target Epithelial Cells through Membrane Receptors

We report, for the first time, the use of a surface plasmon resonance (SPR) fiber-optic immunosensor for selective cellular detection through membrane protein targeting. The sensor architecture lies on gold-coated tilted fiber Bragg gratings (Au-coated TFBGs) photoimprinted in the fiber core via a laser technique. TFBGs operate in the near-infrared wavelength range at ∼1550 nm, yielding optical and SPR sensing characteristics that are advantageous for the analyses of cellular bindings and technical compatibility with relatively low-cost telecommunication-grade measurement devices. In this work, we take consider their numerous assets to figure out their ability to selectively detect intact epithelial cells as analytes in cell suspensions in the range of 2-5 × 10(6) cells mL(-1). For this, the probe was first thermally annealed to ensure a strong adhesion of the metallic coating to the fiber surface. Its surface was then functionalized with specific monoclonal antibodies via alkanethiol self-assembled monolayers (SAMs) against extracellular domain of epidermal growth factor receptors (EGFRs) and characterized by peak force tapping atomic force microscopy. A differential diagnosis has been demonstrated between two model systems. The developed immunosensors were able to monitor, in real time, the specific attachment of single intact cells in concentrations from 3 × 10(6) cells mL(-1). Such results confirm that the developed probe fits the lab-on-fiber technology and has the potential to be used as a disposable device for in situ and real-time clinical diagnosis.

Functional polymers: scanning force microscopy insights

Scanning force microscopy (SFM) and related techniques make it possible to visualize polymer systems with a molecular resolution. Beyond imaging, they also enable the unveiling of a variety of (dynamic) physico-chemical properties of both isolated polymer chains and their supramolecular architectures, including structural, mechanical and electronic properties. This article reviews recent progress in the use of SFM on polymers, with a particular emphasis on the mechanical properties of copolymers and single polymer chains, as well as on the bottom-up fabrication of supramolecular polymeric (helical) nanostructures in particular based upon pi-conjugated macromolecules as building blocks for nanoelectronics. Through a detailed understanding of the polymer behavior, we propose solutions for the generation of organic functional (nano)systems.