The molecular organization and electronic properties of dithiocarbamate (DTC) anchored self-assembled monolayers (SAMs) linked to Au(111) substrates are studied by a combination of X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and state-of-the-art density functional theory calculations. For that, several piperidine/piperazine precursors with different architecture and substitution patterns are selected. The presented data show that the DTC anchor provides a useful building block for monomolecular self-assembly on coinage metals with both sulfur atoms bonded to the substrate in a way similar to what is usually observed for the more commonly applied thiolate docking group. The combination of the DTC group with the quite flexible piperidine/piperazine cyclic linkers results in a dense molecular packing with an upright orientation of the terminal moieties. The latter comprise phenyl rings bearing various substituents, which enables tuning the interfacial dipole over a wide range. Simulations on two prototypical DTC-docked SAMs help to better understand the experimental observations and provide insight into the local origin of the SAM-induced shifts in the electrostatic energy. In particular, a comparison of measured and simulated XP spectra reveals the significant contribution of the DTC group to the interfacial dipole.

Its inherent strong tendency to aggregate in solution is used in the following study to prepare highly anisotropic films of the n-type copolymer poly{[N,N'-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (P(NDI2OD-T-2)). Solvent vapor annealing (SVA) allows to tune the size of oriented domains in spherulite-like superstructures with alignment up to several hundreds of micrometers. Blade coating (BC), on the other hand, yields square centimeter large perfectly oriented films with dichroic ratios of 18 and charge transport anisotropies up to 14. On the nanometer scale highly oriented fibers of form I are visible in the oriented areas with the fiber long axis parallel to the chain direction. We give experimental evidence that structure formation does involve liquid crystal (LC) mesophases at high solution concentrations which are frozen upon solvent removal. Temperature post-treatment of the oriented films gives, on the other hand, evidence for a classical semicrystalline nature of this polymer with spherulites consisting of crystalline and amorphous domains. These findings point to a different growth behavior than previously discussed for the well-studied p-type polymer poly(3-hexylthiophene) and suggests that the definition and distinction between liquid-crystalline and semicrystalline nature might need to be reassessed.

Both electrochemical and chemical doping of the n-type regioregular polymer poly{[N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithio-phene)} (P(NDI2OD-T-2)) and its regioirregular counterparts are presented. Electrochemical doping clearly shows that a 2-fold reduction with maximum conductivity in the radical-anion state is possible with the polymers. Chemical doping with the state-of-the-art high-performance dopants 4-(2,3-dihydro-1,3-dimethyl-1H-benzimidazol-2-yl)-N,N-dimethylbenzeneamine (N-DMBI) and tetrakis(dimethylamino)ethylene (TDAE) gives conductivity values between 10(-4) and 10(-3) S cm(-1) for as-cast films with clear involvement of the radical-anion species. Anisotropic conductivities of vapor-doped blade-coated films give up to 6 times higher values along the polymer chain direction compared with the perpendicular direction, both in face-on and edge-on oriented chains in the bulk of the films. The polymorph concomitantly changes from a mixed stacking of naphthalenediimide and bithiophene units (form II) to a segregated stacking mode (form I), indicating a strong effect of the dopant on the overall film structure. Maximum achievable conductivity along the chain is 8 x 10(-3) S cm(-1). Our study underlines that regardless of regioisomerism and film preparation, higher maximum conductivity seems not to be achievable with P(NDI2OD-T-2), at least with the herein used chemical dopants. Reasons might include the following: (1) strong localization of charges on the NDI units and (2) too low reduction potentials of the dopants, both evidenced by electrochemistry; (3) another factor is the high volatility of TDAE, which is elucidated by transmission electron microscopy, electron diffraction experiments, and spectroscopy.

In this article we highlight the importance of film deposition conditions on the electrochemical behaviour of the work horse of the organic electronics community, namely poly(3-hexylthiophene) (P3HT). While a huge number of publications have dealt with the influence of morphology on optical, electronic and opto-electronic properties, the effect on the electrochemical response has been less addressed. Electrochemistry is often only used as convenient tool in this community to determine the energy levels or more specifically the HOMO level of P3HT. This is performed by measuring oxidation onset potentials and introducing correction factors which relate the electrochemical with the Fermi scale. Here we want to stress out that this procedure should be performed with great care in order to get meaningful data. We demonstrate that film deposition conditions can strongly alter the oxidation behaviour of the polymers which makes the determination of the oxidation onset potentials and energy levels very difficult. We compare state-of-the-art of electropolymerisation and solution deposition of chemically synthesized polymers of defined regioregularity with our own expertise on deposition and controlling crystallisation in films. (C) 2018 Elsevier Ltd. All rights reserved.

We highlight the influence of processing conditions on polymorphism and structure formation on the mesoscale for the family of PCPDTBT polymers with branched alkyl side chains. Direct correlations of morphology to the chemical structure and to transistor device performance are established. We found that up to four different packing motifs could be realized depending on the polymer derivative and the processing conditions: amorphous, pi-stacked, crosshatched and dimer-containing polymorphs. While C- and F-PCPDTBT display similar packing behavior organizing in pi-stacked and dimer-like structures, Si-PCPDTBT gives rise to cross-hatched structures upon simple deposition from solution. The observed differences in chain packing for C-/F-PCPDTBT versus Si-PCPDTBT are attributed to differences in backbone conformations and aggregation behavior in solution. The effect of polymorphism on charge transport is probed using field-effect transistors, in which both pi-stacked and cross-hatched polymer chain arrangements yield the highest hole mobilities. Mesoscopic morphology and mobility simulations rationalize our experimental findings by relating mobility to distributions of electronic coupling elements between the chains.

We report on the controlled synthesis of naphthalenediimide-bithiophene copolymers with varying ratios of 2,6- and 2,7-linkage (parent polymer: poly{[N,N'-bis (2-octyldodecyl)-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} P(NDI2OD-T-2)). Monomers with different ratios of 2,6- and 2,7-regioisomers could be isolated, leading to n-type polymers with tunable regioregularity. With increasing content of 2,7-linkage in the polymer backbone the aggregation tendency can be drastically reduced. Both the reduction behavior and the electron transport properties are very similar for all systems. For the regioregular system we find mobility values of 3 x 10(-1) cm(2)/(V s); the regioirregular systems become comparable with values as high as 7 x 10(-2) cm(2)/(V s) when temperature annealing is employed. This means that regioregularity seems to have an overall lower effect in comparison to classical systems such as poly(3-hexylthiophene). Tuning regioregularity in such systems therefore provides a powerful tool to optimize processing without deteriorating device performance. We even find that device performance of bulk-heterojunction solar cells with a polythiophene derivative as donor strongly improves upon use of the regioirregular systems.

Zeolites ZSM-5, ZSM-11, and ZSM-22 (n(si)/n(Al) = 20-1000) were applied as methanol-to-olefin conversion (MTO) catalysts and optimized for high propene selectivities at high methanol conversions, high weight hourly space velocities, and for long catalyst lifetimes. On zeolites ZSM-5 and ZSM-11 with optimized Bronsted acid site densities of 0.13 and 0.15 mmol/g, propene selectivities of 51 and 52%, respectively, at a reaction time of 25 h were reached. In contrast, zeolite ZSM-22 with an optimized acid site density of 0.30 mmol/g showed a maximum propene selectivity of 38% only and a significantly shorter lifetime. Under these conditions, no aromatics could be detected by in situ UV-vis spectroscopy and on-line GC. Thus, an optimized acid site density can suppress the aromatic-based reaction mechanisms by hindering intermolecular hydrogen transfer reactions. Therefore, the acid site optimization could be a promising way for tuning the product selectivity of MTO catalysts on significantly different pore systems. (C) 2015 Elsevier B.V. All rights reserved.

This manuscript provides the first systematic characterization of the electrochemical properties of the high mobility n-type polymer poly{[N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis (dicarboximide)-2,6-diyl]-alt-5,5'(2,2'-bithiophene)} (P(NDI2OD-T2)) and its corresponding monomer 2,6-bis(2-bromothien5-yl) naphthalene-1,4, 5,8-tetracarboxylic-N,N'-bis(2-octyldodecyl) diimide (Br-NDI2OD-T2-Br) by cyclic voltammetry and in situ spectroelectrochemistry. Both monomer and polymer reveal a 2-fold reduction to the dianion via a radical anion species. The comparison between monomeric and polymeric species allows the explanation of the electrochemical behavior of P(NDI2OD-T2) according to redox polymers with localization of charges on the naphthalene bisimide unit. Measurements with electrolyte gated transistors suggest electron hopping transport according to mixed valence conductivity. In the last section of this paper we discuss a sigthficant first cycle effect upon electrochemical reduction which had not been reported for n-type polymers before. The effect is even more pronounced for samples with controlled morphology, that is, high aggregation in the films: In agreement with solution experiments we attribute the appearance of the signal at -1.04 V (E-1/2 = -1.00 V) to the radical anion form of the solvated species.

A versatile convergent synthesis route to side chain pi-extended, highly regioregular polythiophenes is presented. The implementation of beta-conjugated alkyl thiophene branches in linear polythiophenes is used as synthetical tool for energy level engineering, with branched alkyl chains being introduced for solubility reasons. While the length of the branched alkyl side chains does not influence the functional properties, the aggregation behavior in solution does vary from highly aggregated to fully dissolved at room temperature. Temperature-dependent UV-vis spectroscopy highlights the differences in the aggregation behavior in solution and thin films. The aggregation behavior in solid state is further studied using DSC temperature-dependent Raman spectroscopy and temperature-dependent XRD. Finally, controlled crystallization conditions via solvent vapor annealing are applied to allow the formation of spherulite-like structures which reveal a face-on orientation of the polymer backbone with respect to the substrate.

This study describes the impact of a single fluorine atom substitution in the conjugated backbone of poly(cyclopentadithiophene-alt-benzothiadiazole) on the structure and the polymorphism of the polymer bearing 2-ethylhexyl side chains. Controlled growth of the nonfluorinated and fluorinated polymers by solvent vapor annealing (SVA), melt-crystallization on oriented poly(tetrafluoroethylene), and high-temperature rubbing yield highly crystalline and/or oriented films of a thermodynamically stable polymorph called form I. The single-crystal hk0 and the oriented fiber patterns are obtained in films prepared by SVA and aligned films, respectively. Form I involves a high-symmetry packing of four chains in an orthorhombic cell (Pan space group) with pseudohexagonal symmetry. The chains are paired into dimers with a 3.6-3.8 angstrom interchain pi-stacking distance and a segregated mode of stacking of cyclopentadithiophene and benzothiadiazole (BT). A single H/F substitution on the BT unit modifies the orientation of the dimers in the unit cell of form I. Absorption and structural properties of this new polymorph are discussed with respect to the classical pi-stacking structure obtained from solvent-additive processed films. Evidence of yet another polymorph (form II) highlights the polymorphism of these alternated donor-acceptor copolymers.

PCPDTBT, a marginally crystallizable polymer, is crystallized into a new crystal structure using solvent-vapor annealing. Highly ordered areas with three different polymer-chain orientations are identified using TEM/ED, GIWAXS, and polarized Raman spectroscopy. The optical and structural properties differ significantly from films prepared by standard device preparation protocols. Bilayer solar cells, however, show similar performance.