A Modular Strategy for Fully Conjugated Donor–Acceptor Block Copolymers

A novel strategy for the synthesis of fully conjugated donor–acceptor block copolymers, in a single reaction step employing Stille coupling polymerization of end-functional polythiophene and AA + BB monomers, is presented. The unique donor–acceptor structure of these block copolymers provides a rich self-assembly behavior, with the first example of a fully conjugated donor–acceptor block copolymer having two separate crystalline domains being obtained

Modulating structure and properties in organic chromophores: influence of azulene as a building block

The properties of isomeric azulene derivatives, substituted through the 5-membered ring, were examined using a combination of experimentation and theoretical calculations for a series of well-defined electroactive oligomers. The substitution pattern was shown to dramatically influence solid-state, electronic, and optical properties of the oligomers with acid-responsive materials only being observed when the azulenium cation could be directly stabilized by substituents on the 5-membered ring. In addition, the absorption maxima and optical band-gaps of the azulenium cations can be tuned by the substitution position of the azulene ring by the chromophore

Linking vertical bulk-heterojunction composition and transient photocurrent dynamics in organic solar cells with solution-processed MoOx contact layers

It is demonstrated that a combination of microsecond transient photocurrent measurements and fi lm morphology characterization can be used to identify a charge-carrier blocking layer within polymer:fullerene bulk-heterojunction solar cells. Solution-processed molybdenum oxide (s-MoO x ) interlayers are used to control the morphology of the bulk-heterojunction. By selecting either a low- or high-temperature annealing (70 C or 150 C) for the s-MoO x layer, a well-performing device is fabricated with an ideally interconnected, high-efficiency morphology, or a device is fabricated in which the fullerene phase segregates near the hole extracting contact preventing efficient charge extraction. By probing the photocurrent dynamics of these two contrasting model systems as a function of excitation voltage and light intensity, the optoelectronic responses of the solar cells are correlated with the vertical phase composition of the polymer:fullerene active layer, which is known from dynamic secondary-ion mass spectroscopy (DSIMS). Numerical simulations are used to verify and understand the experimental results. The result is a method to detect poor morphologies in operating organic solar cells

A Modular Strategy for Fully Conjugated Donor–Acceptor Block Copolymers

A novel strategy for the synthesis of fully conjugated donor–acceptor block copolymers, in a single reaction step employing Stille coupling polymerization of end-functional polythiophene and AA + BB monomers, is presented. The unique donor–acceptor structure of these block copolymers provides a rich self-assembly behavior, with the first example of a fully conjugated donor–acceptor block copolymer having two separate crystalline domains being obtained

A Facile Route to Poly(acrylic Acid) Brushes Using Atom Transfer Radical Polymerization

We report the preparation of a poly(acrylic acid) polymer brush from a flat silica substrate using a surface-initiated atom transfer radical polymerization of tert-butyl acrylate. Significantly, we use a chemical free deprotection strategy through pyrolysis of the tert-butyl esters to the corresponding carboxylic acids. This eliminates the possibility of loss of the polymer brush from the surface via acidolysis of the ester group in the surface bound initiator. We have verified the formation of the poly(acrylic acid) brush through ATR-FTIR, ellipsometry, water contact angle analysis, and XPS. We also demonstrate the stimuli-responsive nature of these brushes with respect to pH and added electrolyte concentration

Effect of Relative Humidity On the Young\u27s Modulus of Polyelectrolyte Multilayer Films and Related Nonionic Polymers

We have measured the Young\u27s modulus and thickness of ultrathin polyelectrolyte multilayer (PEM), polystyrene (PS), and poly(methyl methacrylate) (PMMA) films as a function of relative humidity. We demonstrate that PEMs undergo substantial swelling and plasticization in the presence of ambient water and that both the choice of polyelectrolytes and the pH of the deposition baths influence the response of a PEM film to changes in humidity. These responses were roughly linear in two of the PEM systems tested; however, a third system demonstrated evidence of anti plasticization and an abrupt swelling transition at intermediate humidity. This behavior is attributed to an internal structure rich in hydrogen-bonding sites. Overall, our results suggest that the chemical composition and molecular architecture of PEMs are responsible for differences in the environmental responsiveness of these materials. Both PS and PMMA films exhibited comparatively small but measurable swelling and plasticization in the presence of water; these effects were more pronounced in the case of the more hydrophilic PMMA. Our results offer insight into the material structure and internal chemical interactions that determine the properties and responsiveness of PEM systems

Diels-Alders adducts of C-60 and esters of 3-(1-indenyl)-propionic acid:alternatives for [60]PCBM in polymer:fullerene solar cells

A series of new, easily synthesized C-60-fullerene derivatives is introduced that allow for optimization of the interactions between rr-P3HT and the fullerene by systematic variation of the size of the ester group. Two compounds gave overall cell efficiencies of 4.8%, clearly outperforming [60]PCBM which gives 4.3% under identical conditions

Polyampholyte Terpolymers of Amphoteric, Amino Acid-Based Monomers With Acrylamide and (3-Acrylamidopropyl)trimethyl Ammonium Chloride

Low-charge-density amphoteric copolymers and terpolymers composed of acrylamide, (3-acrylamidopropyl)trimethyl ammonium chloride, and the amino acid derived monomers (e.g., N-acryloyl valine, N-acryloyl alanine, and N-acryloyl aspartate) were prepared via free-radical polymerization in aqueous media to yield terpolymers with random charge distributions and homogeneous compositions. Sodium formate (NaOOCH) was employed as a chain transfer agent during the polymerization to suppress gel effects and broadening of the molecular weight distribution. Terpolymer compositions were determined by C-13 and H-1 NMR spectroscopy. Terpolymer molecular weights and polydispersity indices were obtained via size exclusion chromatography/multi-angle laser light scattering, and hydrodynamic diameter values were obtained via dynamic light scattering. The solution properties of low-charge-density amphoteric copolymers and terpolymers have been studied as a function of solution pH, ionic strength, and polymer concentration. The low-charge-density terpolymers display excellent solubility in deionized (DI) water with no phase separation. The charge-balanced terpolymers exhibit antipolyelectrolyte behavior at pH values \u3e=(6.5 +/- 0.2). As solution pH is decreased, these charge-balanced terpolymers become increasingly cationic because of the protonation of the anionic repeat units. Charge-imbalanced terpolymers generally demonstrate polyelectrolyte behavior, although the effects of intramolecular electrostatic interactions (e.g., polyampholyte, effects) on the hydrodynamic volume are evident at certain values of solution pH and salt concentration. The aqueous solution behavior (i.e., globule-to-coil transition at the isoelectric point in the presence of salt and globule elongation with increasing charge asymmetry) of the terpolymers in the dilute regime correlates well with that predicted by the polyampholyte solution theories of Dobrynin and Rubinstein as well as Kantor and Kardar. Examination of comonomer charge density, hydrogen-bonding ability, and spacer group (e.g., the moiety separating the ionic group from the polymer chain) indicates that conformational restrictions of the amino acid comonomers result in increased chain stiffness and higher solution viscosities in DI water and brine solutions. (c) 2006 Wiley Periodicals, Inc