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Two new polymer systems, poly(3-phenylenevinylene)thiophene (P3PVT) and poly(3-phenyl)thiophene (P3PT), were designed with the aim of obtaining a helical conjugated polymer via a living polymerization. The polymerization proceeded without transfer and termination reactions via the Kumada catalyst transfer condensative polymerization (KCTCP) mechanism, confirming the living nature of the polymerization. Solvatochroism and circular dichroism (CD) experiments showed the helical nature of P3PVT and the stacking behavior of P3PT in poor solvent conditions. Block copolymers of 3-alkyl-substituted polythiophenes and helical P3PVT were prepared to determine the aggregation behavior of such systems. Solvatochroism, CD, and AFM measurements showed that the blocks influence each other's behavior. If the P3AT block stacks before the helical P3PVT block organizes, one-handed helix formation is hindered. If helix formation occurs first, the stacking behavior is not influenced. [ABSTRACT FROM AUTHOR]

The internal structure and cross-sectional geometry of fiber-like poly(3-hexylthiophene)-based block copolymer micelles has been determined using small- and wide-angle X-ray scattering (SAXS and WAXS, respectively) techniques alongside electron and atomic force microscopies. WAXS of concentrated micellar solutions demonstrated that the block copolymers form crystalline-core micelles in solvents selective for the corona-forming block. Furthermore, by generating macroscopic fibers from micellar solutions, it was possible to align the micelles and discern the type and orientation of the unit cell within the core. Using the unit cell information gained from the wide-angle measurements, in conjunction with the structural insights gained from the microscopy techniques, it was possible to form a complete picture of the cross-sectional geometry of the micelles, whereby the polymer chains lie perpendicular to the long axis of the micelle core and do not undergo chain folding. Finally, this information was used to propose a self-assembly mechanism and to construct and validate a model for the small-angle scattering data, revealing the inherent flexibility of the micelles. [ABSTRACT FROM AUTHOR]

Molecular p-doping of the conjugated polymer poly(3-hexylthiophene) (P3HT) with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) is a widely studied model system. Underlying structure-property relationships are poorly understood because processing and doping are often carried out simultaneously. Here, we exploit doping from the vapor phase, which allows us to disentangle the influence of processing and doping. Through this approach, we are able to establish how the electrical conductivity varies with regard to a series of predefined structural parameters. We demonstrate that improving the degree of solid-state order, which we control through the choice of processing solvent and regioregularity, strongly increases the electrical conductivity. As a result, we achieve a value of up to 12.7 S cm-1 for P3HT:F4TCNQ. We determine the F4TCNQ anion concentration and find that the number of (bound + mobile) charge carriers of about 10-4 mol cm-3 is not influenced by the degree of solid-state order. Thus, the observed increase in electrical conductivity by almost 2 orders of magnitude can be attributed to an increase in charge-carrier mobility to more than 10-1 cm2 V-1 s-1. Surprisingly, in contrast to charge transport in undoped P3HT, we find that the molecular weight of the polymer does not strongly influence the electrical conductivity, which highlights the need for studies that elucidate structure-property relationships of strongly doped conjugated polymers. [ABSTRACT FROM AUTHOR]

We report a directly photopatternable polythiophene derivative PToNB with o-nitrobenzyl (oNB)-functionalized side chains. PToNB has unique phototunable solubilities programmed through three stages: (i) organic-soluble/aqueous-insoluble, (ii) organic-insoluble/aqueous-insoluble, and (iii) organic-insoluble/aqueous soluble. The capability to control conjugated polymer solubility with spatiotemporal precision and orthogonal developer solvents through three stages allows for direct patterning of this conjugated polymer and provides flexibility to choose between positive and negative tone photolithography. This approach to photomodulate solubility also enables all-solution processing of multilayer stacked conjugated polymer films; we demonstrate here direct two-layer photopatterning with this novel conjugated polymer photoresist. [ABSTRACT FROM AUTHOR]

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-T2)). 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 × 10-1 cm²/(V s); the regioirregular systems become comparable with values as high as 7 × 10-2 cm²/(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. [ABSTRACT FROM AUTHOR]

The stiff backbones of conjugated polymers can lead to a rich phase behavior that includes both crystalline and liquid crystalline phases, making measurements of the glass transition challenging. In this work, the glass transitions of regioregular poly(3-hexylthiophene-2,5-diyl) (RR P3HT), regiorandom (RRa) P3HT, and poly((9,9-bis(2-octyl)-fluorene-2,7-diyl)-alt-(4,7-di(thiophene-2-yl)-2,1,3-benzothiadiazole)-5',5"-diyl) (PFTBT) are probed by linear viscoelastic measurements as a function of molecular weight. We find two glass transition temperatures (Tg's) for both RR and RRa P3HT and one for PFTBT. The higher Tg, Tα, is associated with the backbone segmental motion and depends on the molecular weight, such that the Flory-Fox model yields Tα = 22 and 6 °C in the long chain limit for RR and RRa P3HT, respectively. For RR P3HT, a different molecular weight dependence of Tα is seen below Mn = 14 kg/mol, suggesting this is the typical molecular weight of intercrystal tie chains. The lower Tg (TαPE ≈ -100 °C) is associated with the side chains and is independent of molecular weight. RRa P3HT exhibits a lower Tα and higher TαPE than RR P3HT, possibly due to a different degree of nanophase separation between the side chains and the backbones. In contrast, PFTBT only exhibits one Tg above -120 °C, at 144 °C in the long chain limit. [ABSTRACT FROM AUTHOR]

A new family of thieno[3,4-b]thiophene-benzodithiophene terpolymers (PBTClx) have been designed and synthesized, in which the chlorine/fluorine content has been adjusted and optimized. As the content of chlorine is increased in polymers, the twist angle between the donor and acceptor is increased, which leads to a diminishment in the planarity and conjugation. As a result, the UV-vis absorption is continuous blue-shifted, and the band gap increases from 1.57 to 2.04 eV when the chlorinated moieties increased from 0 to 100%. The highest occupied molecular orbital (HOMO) levels of those polymers are decreased by increasing the content of chlorinated moiety, which opens a window to constantly modify the Voc values and eventually meets a balance point for optimized solar energy conversion. The highest power conversion efficiency of 8.31% is obtained by using PBTCl25 as the donor and PC71BM as the acceptor in polymer solar cells (PSCs), in which the Voc increased from 0.79 to 0.82 V after 25% chlorinated monomer involved in copolymerization. Herein, the chlorine replacement could be a good method to further pump the solar conversion by increasing the open circuit voltage without reducing other factors of the polymer solar cells. [ABSTRACT FROM AUTHOR]

By using different polysaccharide and polysulfonylimide type polyelectrolytes for the synthesis of aqueous PEDOT:polyelectrolyte dispersions, the influence of the polyelectrolyte backbone and of the anionic groups on the properties of the resulting PEDOT:polyelectrolyte complex has been studied. The obtained PEDOT:polyelectrolyte systems were characterized regarding the doping and the morphology of the complexes in dispersion as well as regarding the optoelectronic properties and the morphology of the dry PEDOT:polyelectrolyte films. Polyelectrolytes with high molar mass, a rigid backbone, and strongly acidic functionalities resulted in highly conducting PEDOT:polyelectrolyte films, while polyelectrolytes with flexible backbones and weakly acidic groups resulted in insulating PEDOT:polyelectrolyte systems. These findings could help to develop a palette of new PEDOT:polyelectrolyte systems, which correspond better to the specific requirements of different applications. [ABSTRACT FROM AUTHOR]

Multiscale assembly of poly(3-alkylthiophene)s complexed with various alkyl-chain surfactant architectures has been investigated in dilute and concentrated solutions by means of ultraviolet-visible absorption and fluorescence spectroscopy, polarized optical microscopy, small-angle X-ray scattering, and four-point probe conductivity measurements. Supramolecular complexation occurs via ionic interactions between poly(3-alkylthiophene)s electrolytes and ionic surfactants. In dilute solutions, the supramolecular complex undergoes a coil-to-rod conformational transition as evidenced by a time-dependent chromism. Spectroscopic studies on transition kinetics reveal an inverse first-order rate law. While surfactant architectures significantly affect the persistence length of the complexes, the inverse first-order rate law is maintained. When concentrated above a critical value, the supramolecular complex exhibits an isotropic-to-liquid crystalline transition yielding hexagonally ordered microstructures. The liquid crystalline phase boundaries are largely dependent on polymer and surfactant architectures. The correlations between the intrinsic rigidity of conjugated polymers, optoelectronic properties, and liquid crystalline formation are presented. The dried films made from the sheared liquid crystalline solutions inherit liquid crystalline monodomains and display four times faster charge transport along the backbone alignment direction than the perpendicular direction. [ABSTRACT FROM AUTHOR]

We systematically varied the degree of fluorination along the backbone of a series of highly regioregular 3-hexylthiophene-based polymers, P3HT-50F, P3HT-33F, and P3HT-25F, in which 50%, 33%, and 25% of the thiophene units within the polymer chain contain fluorine atoms in the available 4-position, respectively. These materials were homopolymerized using the Kumada catalyst transfer polycondensation method from a set of mono-fluorinated bi-, ter-, and quarterthiophenes to ensure high polymer regioregularity and evenly spaced fluorine atoms along the conjugated thiophene backbone. The monomers were obtained from a synthetic route consisting of iterative Migita-Stille couplings of fluorinated and non-fluorinated 3-hexylthiophenes. The effect of the fluorine atoms on both polymer structure and properties is presented, with supporting quantum mechanical calculations that rationalize the intrinsic conformation preferences of the three P3HT derivatives. P3HT-50F (M̅ n = 34 kg/mol, 98.5% rr), P3HT-33F (M̅ n = 46 kg/mol, 98% rr), and P3HT-25F (M̅ n = 53 kg/mol, 95% rr) displayed HOMO levels of -5.34, -5.26, and -5.24 eV, bandgaps of 1.98, 1.98, and 1.97 eV, and average field-effect transistor hole mobilities of 4.5 × 10-3, 2.7 × 10-2, and 1.2 × 10-2 cm² V-1 s-1, respectively. [ABSTRACT FROM AUTHOR]

The photophysical properties of films of alkyl-substituted polythiophenes are governed by a subtle interplay between intra- and interchain electronic couplings. The intramolecular properties, however, are still not entirely clear because polythiophenes possess a strong tendency to form π-stacked aggregate structures with appreciable interchain couplings. Here we employ low-temperature single-molecule photoluminescence spectroscopy on isolated regioregular poly(3-hexylthiophene), P3HT, chains with different, but well-defined molecular weights to reveal the intrachain properties of their emitting sites. We find that the inhomogeneous distribution function of the zero-phonon lines (ZPL) is very narrow (<480 cm-1, 60 meV), which indicates a low degree of torsional disorder of the P3HT backbone on length scales of the emitting sites (despite a large mean dihedral angle). Moreover, the single-chain ZPLs are exclusively located in the high energy tail of the corresponding spectrum of a disordered ensemble. Using concentration-dependent measurements in combination with time-dependent density functional theory, we show that this spectral shift stems from aggregation-induced partial planarization and concomitant electronic coupling between segments of neighboring P3HT chains. [ABSTRACT FROM AUTHOR]

We report the synthesis of all-conjugated branched poly(thiophenes) with a control over the degree of nonlinearity via two different routes. In the first approach a branched monomer is polymerized using three different catalysts which differentiate in the degree of association to the π-system of the polymer backbone. In the second approach a copolymerization is performed with the branched and a linear monomer. In a next step the influence of the different degrees of nonlinearity on the optoelectronic properties is investigated by UV-vis and fluorescence spectroscopy. Finally, the thermal behavior, the morphology, and the electrical properties at the nanoscale of the material in solid state are studied using DSC and AFM techniques. [ABSTRACT FROM AUTHOR]

Charge carrier mobilities in conjugated semicrystalline polymers depend on morphological parameters such as crystallinity, crystal orientation, and connectivity between ordered regions. Despite recent progress in the development of conducting polymers, the complex interplay between the aforementioned parameters and their impact on charge transport is not fully understood. By varying the casting solvents and thermal annealing, we have systematically modulated the crystallization of poly(3-hexylthiophene-2,5-diyl) (P3HT) and poly[2,5-bis(3-hexadecylthiophen-2-yl)thieno(3,2-b)thiophene] (PBTTT) thin films to examine the role of microstructure on charge mobilities. In particular, we achieve equal crystallinities through different processing routes to examine the role of structural parameters beyond the crystallinity on charge mobilities. As expected, a universal relationship does not exist between the crystallinity in either P3HT and PBTTT active layers and the charge mobility in devices. In P3HT films, higher boiling point solvents yield longer conjugation lengths, an indicator of stronger intracrystalline order, and therefore higher device mobilities. In contrast, the charge mobilities of PBTTT devices depend on the interconnectivity between crystallites and intercrystalline order in the active layer. [ABSTRACT FROM AUTHOR]

We have investigated how the addition of 1,8-diiodooctane (DIO) alters the formation of disordered and ordered phases in a film of poly(3-hexyl-thiophene-2,5-diyl) (P3HT). By combining in situ time-resolved absorption spectroscopy with 60 ms time resolution, optical and transmission electron microscopy and spatially resolved photoluminescence spectroscopy, we show that, in addition to the excitonic coupling, the film formation process during spin-coating as well as the subsequent long-time film drying process differ significantly when DIO is added to a solution of P3HT. During spin-coating, the addition of DIO reduces the actual time for transformation from disordered to ordered phase, even though it increases the time until the disorder-order transition sets in. In place of a solidification front, we observe an all-over solidification throughout the entire film. The phase separation between nonaggregated and aggregated phase increases when using DIO, with compositional variation in the content of aggregated phase on a micrometer scale. [ABSTRACT FROM AUTHOR]

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) is a material consisting of two oppositely charged polymers and is available as aqueous dispersions. Various annealing and doping methods dramatically enhance PEDOT:PSS conductivity, rendering it competitive with inorganic conductors like indium tin oxide. Yet a comprehensive understanding of PEDOT:PSS conductivity enhancement remains elusive. To unravel the chief physical interactions at play, we explore aspects of solution-state PEDOT:PSS through light scattering, X-ray scattering, rheological measurement, and the construction of a partial phase diagram. We show these features in neat water and with the addition of several conductivity enhancement agents: dimethyl sulfoxide, ethylene glycol, 1-ethyl-3-methylimidazolium tetrafluoroborate, or sodium chloride. We find that PEDOT:PSS solutions exist as a dispersion of charged, many-chain microgels with structural features and dynamics strongly influenced by electrostatic interactions. Two distinct phase transitions occur with high sensitivity to ionic strength: a coexistence of a dilute and a concentrated PEDOT:PSS phase and a physical gelation. Despite the rich solution properties uncovered here, we find no connection between them and the enhancement of film conductivity. [ABSTRACT FROM AUTHOR]

The large majority of semiconducting polymers based on poly(alkylthiophene)s with either linear or branched alkyl side chains are reported to p-stack in their crystalline phases. In regioregular poly(3-(2,5-dioctylphenyl)thiophene) (PDOPT), however, p-p interactions are absent due to the presence of the bulky 2,5-dioctylphenyl side groups. In this work, high levels of crystallinity and orientation are created in thin films of PDOPT aligned on substrates of naphthalene by slow directional epitaxial crystallization of the side chains. Depending on molecular weight, both edge-on and flat-on lamellar crystals are obtained. As for poly(3-hexylthiophene) (P3HT), electron microscopy imaging reveals a transition from extended to folded chain crystallization in PDOPT for Mn ~12.7 kDa. The high orientation and crystallinity result in high anisotropy in UV-vis absorption and photoluminescence with well-defined vibronic structures. The single-crystal-like electron diffraction patterns are further used to refine a structural model of PDOPT (a = 29.09 Å, b = 10.45 Å, c = 7.72 Å, a = ß = γ = 90°, and space group P21/c). Uniquely, crystalline PDOPT features perfectly planarized chains despite the absence of p-stacking between polythiophene backbones. The octyl side chains are interdigitated and crystallize in a dense subcell which is compared to that of other semiconducting polythiophenes, e.g. form I poly(3-hexylthiophene) and poly(2,5-bis(3-dodecyl-2-yl)thieno[3,2-b]thiophene), to draw a trend between overall crystallinity and density of the side chain packing. [ABSTRACT FROM AUTHOR]

We present a strategy for tuning physical properties of P3HT-based copolymers by incorporating a fluorinated thiophene repeat unit. The synthesis and characterization of a series of fluorinated polythiophene P(3HT-co-3H4FT) materials are described, where the percentage of fluorinated repeat units in the polymer backbone is systematically varied from 0 to 100%. These P(3HT-co-3H4FT)s (P0, P25, P50, P75, and P100) were synthesized via direct arylation polymerization (DArP) methods. By varying the feed ratio of the two monomers, the percent of fluorinated repeat units (3H4FT) could be precisely controlled. As fluorination is increased, there is a strong effect on the electronic properties of the polymers, evidenced by a 0.4 eV drop in the EHOMO level for P100 when compared to P0. GIWAXS and TEM were used to determine the crystallinity and morphology. TEM analysis of thin film polymer/PCBM bulk-heterojunction blends indicates that increased fluorination does not result in stronger phase separation. Organic photovoltaic devices were fabricated to evaluate changes in device performance as a result of fluorination. [ABSTRACT FROM AUTHOR]

Here, taking a polythiophene derivative (PBDD4T) as a starting polymer, we tried to increase the rotation barrier and hence stabilize its backbone conformation by introducing fluorine into the β- and β'-position of the α-linked bithiophene segments and then synthesized a new polymer named as PBDD4T-2F. Our results demonstrate that the rotation barrier between the α-linked bithiophene significantly increases after the fluorination, so PBDD4T-2F has a more stable backbone conformation than PBDD4T. Compared to PBDD4T, PBDD4T-2F shows stronger aggregation effect in solution state and more compact π-π stacking in solid thin film and also possesses deeper HOMO level. These properties make PBDD4T-2F being an ideal donor material in PSCs. When blended with PC71BM, a fullerene acceptor, the PBDD4T-2F-based device showed a power conversion efficiency (PCE) of 9.04%, which is 38% higher than that of the PBDD4T-based device; when blended with ITIC, a non-fullerene acceptor, the PBDD4T-2F-based device showed a PCE of 8.69%, which is almost 20 times higher than that of the PBDD4T-based device. What is more, the tandem cell, in which the blend of PBDD4T-2F:PC61BM was used for making the front subcell, exhibited a high PCE of 10.12%. The photovoltaic results indicate that the fluorination is an effective method to enhance interchain π-π interaction for the polythiophene and hence to tune its photovoltaic properties in PSCs, especially for the fullerene-free device based on ITIC. [ABSTRACT FROM AUTHOR]

A family of coil-rod-coil ABA triblock copolymers containing poly(3-hexylthiophene) (P3HT) and poly(hexadecyloxyallene) (PHA) were facilely synthesized in one-pot via three sequential living polymerizations of hexadecyloxyallene, 2-bromo-3-hexyl-5-chloromagnesiothiophene, and hexadecyloxyallene using the π-allylnickel complex as a single catalyst. Although the different monomers were polymerized under distinct polymerization mechanisms, the one-pot block copolymerization were revealed to proceed in a living/controlled chain-growth manner, affording well-defined PHA-b-P3HT-b-PHA triblock copolymers in high yields with controlled molecular weights and tunable compositions. The isolated triblock copolymers were found to self-assemble into well-defined supramolecular helical polymers with equivalent of right- and left-handedness. The helicity of the assemblies can be facilely tuned through the induction of chiral cholesteryl pendants introduced on the polyallene segments. Moreover, by using this synthetic method, amphiphilic P3HT triblock copolymers containing hydrophobic P3HT and hydrophilic poly(triethylene glycol allene) (PTA) were readily prepared. Such water-soluble PTA-b-P3HT-b-PTA triblock copolymer exhibited multiresponsiveness including solvent, pH, and temperature. [ABSTRACT FROM AUTHOR]

Polythiophenes bearing a siloxane moiety in a substituent at the 3-position are prepared by deprotonative polycondensation of 2-bromo-3-substituted-thiophene with a bulky magnesium amide chloromagnesium 2,2,6,6-tetramethylpiperidine-1-yl lithium chloride salt (TMPMgCl•LiCl) catalyzed by a nickel complex. Deprotonation takes place at 60 °C for 1 h to form the corresponding thiophene magnesium species, which is subjected to the polymerization by addition of 0.1-5 mol % NiCl2(PPh3)IPr (IPr: 1,3-bis(2,6-diisopropylphenyl)imidazole-2-yl). Polymerization proceeds in a highly regioregular manner, and the molecular weight of the thus-obtained polymer is controllable by the ratio of monomer feed/catalyst loading to indicate Mn of up to 280 000 with narrow molecular weight distribution. Chlorothiophenes are also found to induce polymerization in a deprotonative manner with TMPMgCl•LiCl or nBuLi (the Murahashi coupling polymerization). The obtained polymers bearing a siloxane moiety in the substituent is revealed to be dissolved in a hydrocarbon allowing formation of thin film from hexane. [ABSTRACT FROM AUTHOR]

The aggregation kinetics of negatively charged borate-stabilized silver nanoparticles (NPs) induced by the cationic regioregular polythiophene polyelectrolyte poly{3-[6-(1-methylimidazolium-3-yl)hexyl]thiophene-2,5-diyl bromide} (PMHT-Br) and the morphology of formed aggregates have been investigated via ultraviolet-visible light (UV-vis) spectroscopy, transmission electron microscopy (TEM), zeta (ζ) potential measurements, dynamic light scattering (DLS), and time-resolved small-angle X-ray scattering (SAXS). Two or three populations of NPs are formed within milliseconds upon mixing the components, which differ in the mean size, extent of polymer coating, and time stability. These characteristics are primarily controlled by the PMHT-Br to Ag-NPs ratio. Population of single NPs of a mean size of ~5 nm is present in every system and is mostly stable for a long time. At low ratios, the single NPs are most probably almost free of polymer chains and the second population includes slow, but in a limited extent, growing NPs in which single NPs might be interconnected by polymer chains. At the ratios corresponding to the charge balance in the system (ca. zero ζ-potential of NPs), the NPs aggregate, forming a second population that continuously grows in size, and finally undergo sedimentation. At the high ratios, three long-time stable populations of NPs are observed, having mean sizes of ca. 5, 13, and 35 nm; all NPs should be fully coated with PMHT-Br, giving them a positively charged stabilizing shell. [ABSTRACT FROM AUTHOR]

We report the synthesis of well-defined poly(3,3‴-didodecyl-2,2′:5′,2″:5″,2‴-quaterthiophene) (PQT12) from a direct heteroarylation polymerization (DHAP) of 5-bromo-3,3‴-didodecyl-2,2′:5′,2″:5″,2‴-quaterthiophene (monomer A) and 5-bromo-3′,4″-didodecyl-2,2′:5′,2″:5″,2‴-quaterthiophene (monomer B). Experiments with different catalysts, ligands, additives, and solvents have revealed that the utilization of Herrmann-Beller catalyst and P(o-NMe2Ph)3 can lead to selective thiophene-thiophene couplings. In this regard, solid-state optical and thermal measurements were particularly useful to detect the presence of β-branching and indicate that minor molecular defects can induce important changes within the supramolecular organization. We also highlight the fact that steric protection around unsubstituted β-positions of α-bromothiophene units is needed to obtain a good selectivity of the cross-couplings at the α-positions. This can be achieved by the presence of a substituent at an adjacent β-position or the utilization of a bulky acidic additive (i.e., neodecanoic acid) in the catalytic system. These synthetic procedures applied to both monomers have led to PQT12 samples showing essentially the same optical and thermal properties and are comparable to those observed with their analogues prepared from chemical oxidation or Stille coupling. [ABSTRACT FROM AUTHOR]

This study describes the impact ofa single fluorine atom substitutionin the conjugated backbone of poly(cyclopentadithiophene-alt-benzothiadiazole) on the structure and thepolymorphism of the polymer bearing 2-ethylhexyl side chains. Controlledgrowth of the nonfluorinated and fluorinated polymers by solvent vaporannealing (SVA), melt-crystallization on oriented poly(tetrafluoroethylene),and high-temperature rubbing yield highly crystalline and/or orientedfilms of a thermodynamically stable polymorph called form I. The single-crystal hk0 and the oriented fiber patterns are obtained in filmsprepared by SVA and aligned films, respectively. Form I involves ahigh-symmetry packing of four chains in an orthorhombic cell (Pccnspace group) with pseudohexagonal symmetry. The chainsare paired into dimers with a 3.6–3.8 Å interchain π-stackingdistance and a segregated mode of stacking of cyclopentadithiopheneand benzothiadiazole (BT). A single H/F substitution on theBT unit modifies the orientation of the dimers in the unit cell ofform I. Absorption and structural properties of this new polymorphare discussed with respect to the classical π-stacking structureobtained from solvent-additive processed films. Evidence of yet anotherpolymorph (form II) highlights the polymorphism of these alternateddonor–acceptor copolymers. [ABSTRACT FROM AUTHOR]

We have introduced a facile syntheticroute for well-defined [poly(3-dodecylthiophene)]2poly(methylmethacrylate) miktoarm star copolymer (P3DDT2PMMA) by usinga click reaction. For this purpose, PMMA withtwo ethynyl groups (PMMA-(≡)2) and ω-azidopropyl-P3DDTwere synthesized. We found that the use of alkyl linker (here, propylgroup) between P3DDT and azido group is very essential to minimizethe steric hindrance arising from bulky side group in P3DDT duringthe click reaction. When we employed a slightly excess amount of theω-azidopropyl-P3DDT, we obtained a well-defined P3DDT2PMMA with a narrow molecular weight distribution (polydispersityindex <1.20) after selective removal of the unreacted ω-azidopropyl-P3DDTin a crude product by using column chromatography. We also investigatedself-assembled structure of P3DDT2PMMA by small-angle X-rayscattering (SAXS) and transmission electron microscopy (TEM). P3DDT2PMMA with weight fraction of P3DDT block (wP3DDT) of 0.33 had lamellar microdomains, while a lineardiblock copolymer (P3DDT-b-PMMA) with wP3DDT= 0.37 showed cylindrical microdomains. Also, P3DDT2PMMA with wP3DDT= 0.59 showedthe HEX cylindrical microdomains of PMMA in the P3DDT matrix, whereasP3DDT-b-PMMA with wP3DDT= 0.56 exhibited lamellar microdomains. More interestingly, P3DDT2PMMA with wP3DDTof 0.76 showedhexagonally packed PMMA cylinders in the P3DDT matrix at molten state,and this morphology was maintained even after crystallization of theP3DDT block. This behavior is quite different from linear P3DDT-b-PMMA diblock with the same weight fraction of P3DDT becausethe latter shows fibril structures after P3DDT crystallization. Theseresults imply that controlling the molecular architecture is an effectiveway to tune the morphology of P3AT-containing block copolymers. [ABSTRACT FROM AUTHOR]

The optoelectronic properties oforganic electronic materials aresignificantly affected by their molecular packing and local environments.Herein, atomic force microscopy (AFM) is used to characterize nanowhiskersof poly(3-hexylthiphene) (P3HT). The P3HT nanowhiskers form layeredstructures with distinctive heights that increase over time, suggestingthat layered structures are more thermodynamically favored in solution.Further inspection reveals that the monolayer (ML) nanowhiskers areconsistently wider than double-layered (DL) ones. The width disparityis likely due to the sliding of π–π stacked motifswithin ML nanowhiskers evident by the rougher edges of ML nanowhiskers.Conversely, the interfacial interactions between two P3HT monolayersmay inhibit the sliding of conjugated motifs inside the DL nanowhiskers,leading to much narrower and tightly packed structures. Kelvin probeforce microscopy (KPFM) measurements are carried out to investigatethe influence of ML and DL nanowhiskers’ morphologies and localenvironments on their electronic properties. Curved, vertically stacked,and overlapped regions show higher contact potential differences (CPD)resulting from a combined effect of irregular molecular packing andlocal environmental impacts. [ABSTRACT FROM AUTHOR]

In an endeavor to correlate the optoelectronic properties of π-conjugated polymers with their structural properties, we investigated the aggregation of P3HT in THF solution within a temperature range from 300 to 5 K. By detailed steady-state, site-selective, and time-resolved fluorescence spectroscopy combined with Franck–Condon analyses, we show that below a certain transition temperature (265 K) aggregates are formed that prevail in different polymorphs. At 5 K, we can spectroscopically identify two H-type aggregates with planar polymer backbones yet different degree of order regarding their side chains. Upon heating, the H-character of the aggregates becomes gradually eroded, until just below the transition temperature the prevailing “aggregate” structure is that of still phase-separated, yet disordered main and side chains. These conclusions are derived by analyzing the vibrational structure of the spectra and from comparing the solution spectra with those obtained from thin films that were cooled slowly from the melting temperature to room temperature and that had been analyzed previously by various X-ray techniques. In addition, site selectively recorded fluorescence spectra show that there is dependent on temperatureenergy transfer from higher energy to lower energy aggregates. This suggests that they must form clusters with dimensions of the exciton diffusion length, i.e., several nanometers in diameter. [ABSTRACT FROM AUTHOR]

A new derivative of 3,4-propylenedioxyselenophene bearing naphthalenylmethyl appeandages on the bridge, called 3,4-dihydro-3,3-bis((naphthalen-2-yl)methyl)-2H-selenopheno[3,4-b][1,4]dioxepine (ProDOS-Np2), was synthesized and polymerized via potentiostatic and potentiodynamic methods. The electrochemically obtained polymer film (PProDOS-Np2) is pure blue at the neutral state and highly transparent at the oxidized state. An increase in the size of the substituents on the bridge resulted in an increase in the optical contrast ratio. Upon moving from naked bridge to benzyl and to naphthalenylmethyl substituents on the bridge center, the optical contrast changed from 51% to 65% and finally to 84%, which is the second highest reported optical contrast ratio in polyselenophene family. When compared to polythiophene analogue, the PProDOS-Np2 has lower oxidation potential and band gap, higher optical contrast ratio, coloration efficiency, robustness, and stability. The polymer film preserved its properties even after thousands of cycles under ambient conditions. [ABSTRACT FROM AUTHOR]

In order to tune the optical propertiesof poly(3-alkylthiophene)s,varying amounts of phenyl groups were incorporated more or less randomlyalong the backbone of this polymer. Because a living random copolymerizationof thiophene and phenyl monomers is not possible in standard conditions,a specially designed biaryl monomer was used. The degree of randomnessof this incorporation could be estimated by an in-depth 1H NMR analysis. The effect on the bandgap was remarkable, since alinear relation between the bandgap and the percentage of introducedphenyl rings was observed. This enables the synthesis of conjugatedpolymers with tunable and predictable bandgaps. Aggregation and crystallizationbehavior were also affected by the introduction of phenyl rings. Aggregationwas still possible with 20% of phenyl rings, albeit to a small extent,while crystallization was already completely inhibited at that point. [ABSTRACT FROM AUTHOR]

A series of fully conjugated graftcopolymers containing poly(3-hexylthiophene)(P3HT) side chains and a p-type carbazole-diketopyrrolopyrrole (CbzDPP)donor–acceptor backbone were synthesized via a graft throughSuzuki polymerization. The macromonomers were formed by externallyinitiating P3HT growth from a boronic ester-functionalized carbazolevia Kumada catalyst transfer polycondensation. Subsequently, thismacromonomer was copolymerized with a DPP monomer via a graft throughSuzuki polymerization to yield the final graft copolymers. The graftcopolymers exhibit optical and electronic properties of both P3HTand the CbzDPP polymers independently due to the break in conjugationbetween the carbazole unit and P3HT chain. Moreover, these propertiesreflect the relative proportion of P3HT and CbzDPP polymers; shorterP3HT chain lengths lead to graft copolymers that possess more CbzDPPcharacter and vice versa. The macromonomers were characterized bygel permeation chromatography, mass spectrometry, and UV–visiblespectroscopy. The graft copolymers were further investigated usinggel permeation chromatography, UV–visible spectroscopy, cyclicvoltammetry, differential scanning calorimetry, and atomic force microscopy.Finally, organic field effect transistors were fabricated using thegraft copolymers and compared to an analogous linear CbzDPP copolymer.Ultimately, the graft copolymers with the longest P3HT chains (ca.75 repeat units) exhibited almost exclusively P3HT characteristics,possessing a small CbzDPP internal charge transfer (ICT) peak andonly p-type conductivity (μh∼ 6 × 10–4cm2V–1s–1). Conversely, the graft copolymers with the shortest P3HT chains(ca. 10 repeat units) showed significant CbzDPP character, includinga strong ICT peak and ambipolar mobilities (μh∼5 × 10–3cm2V–1s–1; μe∼ 7 × 10–4cm2V–1s–1). [ABSTRACT FROM AUTHOR]

Simply prepared π-allylnickelcomplexes were used as external initiators for promoting the polymerizationof 2-bromo-3-hexyl-5-chloromagnesiothiophene in a living/controlledchain growth manner to afford regioregular poly(3-hexylthiophene)with an allyl terminus. The nickel species on the other chain endcan initiate the block copolymerization of hexadecyloxylallene and2-bromo-3-hexyl-5-chloromagnesiothiophene to give a well-defined triblockcopolymer containing poly(3-hexylthiophene) and poly(hexadecyloxylallene)segments in one pot via mechanically distinct, sequential living polymerization.Furthermore, such π-allylnickel(II) complexes can also catalyzethe polymerization of a range of vinyl monomers, including styrene,1-methoxy-4-vinylbenzene, and 1-chloro-4-vinylbenzene as well as tert-butyl acrylate, in living/controlled fashion. The activenickel unit at the growing chain end of these vinyl polymers can alsoinitiate the block copolymerization of 2-bromo-3-hexyl-5-chloromagnesiothiopheneto give a series of block copolymers containing vinyl polymer andpoly(3-hexylthiophene) segments. The new block copolymerizations havebeen demonstrated to proceed in living/controlled chain-extensionmanner. The well-defined conjugated block copolymers are isolatedin high yield with controlled molecular weight and tunable compositions. [ABSTRACT FROM AUTHOR]

The development of efficient multicomponenttandem polymerizationis attractive but challenging, owing to the limitations such as therequired strict stoichiometric balance, the poor solubility and lowmolecular weight of the polymer products, etc. In this work, an efficientone-pot three-component polymerization of alkyne, carbonyl chlorideand ethyl 2-mercaptoacetate was reported. The polymerization of aromaticdiyne (1), diaroyl chloride (2), and ethyl2-mercaptoacetate (3) catalyzed by Pd(PPh3)2Cl2/CuI proceeded smoothly under mild conditionsat room temperature without strict stoichiometric balance of the monomers,affording poly(arylene thiophenylene) (P1) with highmolecular weights (Mwup to 156 000) inexcellent yields (up to 97%). Single crystal structure of model compound 4was obtained, aiding in verification of the complete transformationto the desired polymer product. The thiophene-containing conjugatedpolymer possesses good solubility in common organic solvents, goodfilm-forming ability and high thermal stability. Meanwhile, the polymershows typical aggregation-enhanced emission behavior: its solutionis weakly emissive, but turns to be highly emissive when nanoaggregatesor thin films are formed. Furthermore, thin film of P1shows high refractive indices (n= 1.9461–1.6668)in a wide wavelength region of 400–1000 nm, which can be furthermodulated by UV irradiation. Well-resolved fluorescent photopatterncan be generated by exposure of the thin film of P1underUV irradiation through a copper photomask. The polymer also servesas an efficient fluorescent chemosensor for Ru3+with highsensitivity and selectivity, and the quenching constants for the sensingare up to 8.8 × 105L mol–1. Thiswork provides a new polymerization concept and an efficient approachtoward functional conjugated polymer materials, overcoming the limitationsof multicomponent polymerization. [ABSTRACT FROM AUTHOR]

We demonstrate a method to determineabsolute crystallinity inhigh molar mass poly(3-hexylthiophene) (P3HT), as used in commerciallyrelevant organic photovoltaic devices, using enthalpy of fusion andmelting temperature values derived from differential scanning calorimetry(DSC) and 13C CPMAS NMR. By studying P3HT with molar massesranging from 3.6 to 49 kg/mol and using recent work on oligomeric3-hexylthiophene, we demonstrate several critical items. First, thatproper extrapolation to infinite chain lengths, i.e., crystal size,yields values for the equilibrium melting temperature Tm0of 272 ±6 °C and the enthalpy of fusion per crystalline repeat unit ΔHuof 49 ± 2 J/g for Form I crystals ofP3HT. Second, that a simple correction for crystal size using Tm0is critical for determining an accurate degree of crystallinityfrom enthalpy measurements because of finite crystal size effects.Furthermore, our results demonstrate that the ordered fraction ofP3HT measured from 13C NMR is indistinguishable from theDSC-determined crystalline fraction, once crystal size correctionsare properly implemented. The connection between crystal size andmelting temperature is affirmed by successive self-nucleation andannealing (SSA) measurements, which, when performed as a functionof molar mass, allowed us to identify the molar mass at which chainfolding occurs in P3HT in the melt, ≈11.5 kg/mol. [ABSTRACT FROM AUTHOR]

In situ growth of cadmium sulfide(CdS) quantum dots (QDs) was achieved directly through solvent-assistedgrafting in the self-assembled templates of amphiphilic all conjugateddiblock copolythiophene, poly(3-hexylthiophene)-b-poly(3-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)methylthiophene) (P3HT-b-P3TEGT) and gas–solid reaction. Such diblock polymertemplates allowed a desired amount of cadmium sulfide salt (Cd(Ac)2) to easily accomplish dispersion and self-assembly via controlledassembling block copolymers in selective solvents. After P3HT-b-P3TEGT polymer templates grafted with Cd2+precursor(P3HT-b-P3TEGT/Cd2+) reacting in hydrogensulfide (H2S) gas, one-dimensional core–shell nanobeamsnetwork P3HT-b-P3TEG/CdS (donor–acceptor)was formed with excellent phase separation between P3HT-b-P3TEGT crystalline domains and inorganic CdS QDs domains at nanoscales,which was driven by the interaction between oxygen atoms of ethyleneoxide side chains and Cd2+ions, and the thermodynamicequilibrium between polymer chains deformation. The one-dimensionalwire-like nanostructure were highly desirable for the active layersin photovoltaic devices as providing high carrier mobility, largeinterfacial area between electron donor and acceptor, and highly efficienttransport pathways to improve the power conversion efficiency (PCE)of hybrid bulk heterojunction solar cells. [ABSTRACT FROM AUTHOR]

The colloidal self-assembly of anew conjugated diblock copolymerof a polythiophene derivative, poly[3-(2,5,8,11-tetraoxatridecanyl)thiophene]-block-poly(ethylene glycol) (PTOTT-b-PEG),led to various well-defined assembly structures such as vesicles,sheets, and nanoribbons. A unique and technologically relevant nanoribbonstructure with a dimension reaching tens of micrometers was formedin water when polar protic solvents were used as initial cosolvents.Self-assembly of PTOTT-b-PEG in various solvent compositionsand polymer concentrations indicated that the hydrogen bonding betweenthe diblock copolymer and the self-assembly medium plays an importantrole in determining the self-assembly structure and that the finalassembly structure should be the result of a delicate interplay betweenhydrogen bonding and π–π interactions. This studydemonstrates that the addition of hydrogen bonding capability andamphiphilicity in the self-assembly of conjugated polymers can leadto many interesting well-defined assembly structures that are nottypically found in conjugated polymers. [ABSTRACT FROM AUTHOR]

Nanoimprintinghas been well explored to create nanostructures and to induce molecularorientation in conjugated polymer thin films. We demonstrate herethat large area poly(3-hexylthiophene) (P3HT) nanopillar arrays canbe fabricated by a simple, cost-effective nanoimprinting method ina solvent-swollen plasticized state at room temperature. In addition,the solvent-assistant room-temperature nanoimprinting induces face-onchain alignment in the P3HT nanopillars; i.e., the π–πstacking of P3HT is aligned normal to the substrate, favorable fororganic photovoltaic cell applications. The face-on chain alignmentsolely depends on the diameters of nanopores defined in the nanoimprintingmold, rather than on the initial chain orientation in unprocessedthin films. Furthermore, a critical dimension of ca. 85 nm in diameteris found to be essentially needed to induce the face-on chain alignmentwithin the nanopillars. [ABSTRACT FROM AUTHOR]

Wereport the use of solvent vapor swelling of ultrathin polymerfilms to determine Flory–Huggins solvent–polymer andpolymer–polymer interaction parameters (χi–j) for poly(3-hexylthiophene) (P3HT) andpolystyrene (PS) over a wide solvent composition range. From the calculatedinteraction parameters, we constructed a polymer/polymer/solvent phasediagram that was validated experimentally. χtetrahydrofuran–P3HT(1.04 ± 0.04) and χCHCl3–P3HT(0.99 ± 0.01) were determined through swelling of ultrathinP3HT films. Similar experiments using PS films gave χtetrahydrofuran–PS= 0.41 ± 0.02 and χCHCl3–PS= 0.39 ± 0.01, consistent with literature values. As expected,these χi–jparameters indicatedthat P3HT is less compatible than PS with either solvent. From δPS(17.9 ± 0.2 MPa1/2) and δP3HT(14.8 ± 0.2 MPa1/2), determined through regularsolution theory, we calculated χPS–P3HT=0.48 ± 0.06 at 23 °C. The resulting phase diagram was validatedby solution-based transmission measurements of PS/P3HT blends in o-xylene. Although we focused on PS/P3HT blends in thiswork, this approach is easily adaptable to other polymer/polymer combinationsof interest. [ABSTRACT FROM AUTHOR]

Highly oriented hybrid thin filmscomposed of rod-shaped CdSe nanocrystalsand poly(3-hexylthiophene) are prepared by mechanical rubbing. Theorientation distribution of both CdSe nanorods and crystalline P3HTdomains is determined by a combination of transmission electron microscopy(electron diffraction, low dose high-resolution TEM, and tomography),grazing incidence X-ray diffraction measurements, and UV–visspectroscopy. After rubbing, P3HT crystalline domains show a preferentialface-on orientation ((010) contact plane) and the chains align parallelto the rubbing direction. CdSe nanorods also align parallel to therubbing direction, but the level of alignment is a function of theirconcentration in the polymer matrix: the lower their concentration,the higher the level of in-plane orientation of both the nanorodsand the polymer chains. GIXD and electron diffraction suggest thatCdSe nanorods adopt a preferential contact plane on the substrateafter rubbing. The high in-plane alignment of the nanorods is mainlydue to the orientation of the surrounding P3HT matrix. In particular,low dose HR-TEM shows that the local orientation of individual NRsmatches the orientation of the surrounding π-stacked P3HT chains.For a high NR concentration, bundling of NRs into larger aggregatesprevents their efficient alignment by rubbing. [ABSTRACT FROM AUTHOR]

Polyelectrolytes are promising electronicallyinsulating layers for low-voltage organic field effect transistors.However, the polyelectrolyte–semiconductor interface is difficultto manufacture due to challenges in wettability. We introduce an amphiphilicsemiconducting copolymer which, when spread as a thin film, can changeits surface from hydrophobic to hydrophilic upon exposure to water.This peculiar wettability is exploited in the fabrication of polyelectrolyte-gatedfield-effect transistors operating below 0.5 V. The prepared amphiphilicsemiconducting copolymer is based on a hydrophobic regioregular poly(3-hexylthiophene)(P3HT) covalently linked to a hydrophilic poly(sulfonated)-based randomblock. Such a copolymer is obtained in a three-step strategy combiningGrignard metathesis (GRIM), atom transfer radical polymerization (ATRP)processes, and a postmodification method. The structure of the diblockcopolymer was characterized using FT-IR, 1H NMR spectroscopy,and gel permeation chromatography (GPC). [ABSTRACT FROM AUTHOR]

Theproperties of regioregular poly(3-hexylthiophene) (P3HT) thin layersprepared on silica surfaces are investigated by X-ray reflectivitymeasurements and a model-independent fitting approach. As P3HT isa semicrystalline polymer Bragg peaks, corresponding to the repeatingdistance of lamella sheets, are evident within the reflectivity curveswhich are not describable with simple one- or two-layer models withina reflectivity simulation minimizing the accuracy of the data evaluation.In this work a model-independent fitting approach is applied to beable to explain the entire reflectivity curve and to gain informationon the internal structure within thin films. The thin layers werespin-coated from various chloroform solutions; solution concentrations(c) from 0.2 to 6.3 g/L resulted in P3HT layers withthicknesses (d) ranging from 3.7 to 64 nm with thelayer thickness following a d∼ c0.84dependence. The model-independent fitting approachreveals directed lamella order is present within the samples preparedfrom low concentrated solutions while for higher concentrations disorderwithin the electron density profile is observed. [ABSTRACT FROM AUTHOR]

We report the increased crystallizationof poly(3-hexylthiophene)(P3HT) in the donor–acceptor mixture of [6,6]-phenyl-C61-butyricacid methyl ester (PCBM) with P3HT by the addition of a block copolymer,P3HT-b-PI, where PI refers to polyisoprene. The photovoltaicperformance of devices created using this blend is markedly improvedby the addition of the diblock copolymer. We have characterized thestructure of thin films of the P3HT-b-PI containingmixtures using optical microscopy, scanning force microscopy, UV–visabsorption spectroscopy, neutron reflectometry, and grazing incidenceX-ray diffraction (GIXD). The GIXD data provide the information onthe crystallinity of the films, the absorption data were used to confirmthat the addition of the diblock was responsible for the increasein crystallization, neutron reflectometry data reveal a PCBM-richregion near the hole injection layer, and the two microscopy techniquesrevealed the structural effect of the crystallization at the surfaceof the films. [ABSTRACT FROM AUTHOR]

Hydrogen bond interactions between a dye adsorbed atthe interface of TiO2nanorods and functionalized P3HTwas used to control nanorod dispersion, increase interfacial area,and improve efficiency in solution-processable hybrid bulk heterojunctionsolar cells. A series of poly(3-hexylthiophene-b-ethyleneglycol) (P3HT-b-PEG) copolymers were prepared bya combination of Grignard metathesis polymerization and click chemistry.The short PEG segments in P3HT-b-PEG serve as a hydrogenbond acceptor. TiO2nanorods functionalized with N3-dyebearing multiple COOH groups function as both the electron acceptorand hydrogen bond donor. The strong preferential H-bonding interactionbetween TiO2nanorods and the PEG chain limits the aggregationof the TiO2nanorods and affords homogeneously dispersionof the nanorods within the polymer matrix to form an interpenetratingnetwork. This structure provides large interfacial area between electrondonor and acceptor and highly efficient transport pathways withinthe composite. Hybrid devices constructed from copolymers with 10wt % PEG and N3-dye TiO2nanorods exhibit power conversionefficiency ∼50% higher than that of conventional P3HT homopolymerand N3-dye TiO2nanorods. [ABSTRACT FROM AUTHOR]

Thieno[3,2-b]thiophenes (TT), having para-substituted phenyl groups at C-3, have been synthesizedthrougha ring closure reaction, using P4S10, in moderateto high yields. Their absorbance studies displayed that the TT, havingnitrophenyl group had the most red shift absorbance at 365 nm, whichalso showed the lowest optical band gap of 2.92 eV; the rest of theTTs had the absorbance between 300 and 302 nm. Cyclic voltammetrystudies indicated that while all the TTs had the oxidation potentialsabove 1.0 V, the TT with dimethylaminophenyl group had the lowestoxidation potential of 1.33 V. The rest had the oxidation potentialsbetween 1.6 and 1.99 V. The TTs were both electropolymerized and copolymerizedwith thiophene through Suzuki coupling reaction. Electropolymerizedpolymers indicated that while the polymer having strong electron donatingdimethylaminophenyl group had the lowest oxidation potential of 0.97V, the rest of the polymers displayed the potentials between 1.09and 1.39 V. Their electronic band gaps varied between 1.86 and 2.46eV. The CV–UV studies of the polymers, electro-deposited onITO, showed absorbance maxima between 431 and 468 nm, and the lowestoptical band gap was observed with the polymer having methoxyphenylgroup (1.99 eV). The rest of the polymers had the optical band gapsbetween 2.05 and 2.19 eV. Regarding the copolymers, the one with methoxyphenylgroup had the lowest oxidation potential of 0.75 V. They displayedabsorption and emission maxima between 325 and 445 and 454–564nm, respectively. Their optical and electronic band gaps varied between2.0 and 2.5 eV. As the copolymer having strong electron donating methoxyphenylgroup had the highest quantum yield, 0.64 eV, the one with strongelectron withdrawing nitrophenyl group had the lowest quantum yieldof 0.003 eV. [ABSTRACT FROM AUTHOR]

A new D–A copolymer, poly(thieno[3,2-b]thiophene-alt-bithiazole) (PTTBTz),based on thieno[3,2-b]thiophene donor unit and bithiazoleacceptor unit, wassynthesized by the Pd-catalyzed Stille-coupling reaction for the applicationas donor material in polymer solar cells (PSCs). PTTBTzfilm possesses high thermal stability with 5% weight-loss temperatureat 450 °C, a lower-lying HOMO energy level at −5.20 eV,a higher hole mobility of 6.45 × 10–3cm2/(V s), and a crystalline structure. Photovoltaic performanceof the polymer was investigated with [6,6]-phenyl-C71-butyricacid methyl ester (PC70BM) or indene-C60bisadduct(ICBA) as acceptor and with 3% DIO additive. The power conversionefficiency (PCE) of the PSC based on PTTBTz:ICBA (1:1w/w) reached 5.35% with a high Vocof1.03 V, a Jscof 8.55 mA/cm2, and an FF of 0.608, whereas the PCE of the PSC based on PTTBTz:PC70BM (1:1 w/w) was 4.57% with a Vocof 0.82 V, a Jscof 9.89 mA/cm2, and an FF of 0.563, under the illumination of AM1.5, 100mW/cm2. PTTBTzis one of the D–A copolymersthat shows better photovoltaic performance with ICBA as acceptor thanPC70BM. PTTBTz/ICBA could be a promising frontactive layer for high-efficiency tandem PSC because of its high Voc. [ABSTRACT FROM AUTHOR]

We report on a convenient and simple process to preparehighly regioregular poly(thiophene)-based multiblock copolymers bya novel thermally induced coupling reaction. Diblock copolymers of3-hexylthiophene (3HT) and 2,5-dibromo-3-(2-(2-tetrahydropyranyl-2-oxy)ethyl)thiophene(THPET) end-capped by a nickel complex (Br-P3HT-b-PTHPET-Ni(dppp)Br) are first prepared using Ni(dppp)Cl2as catalyst at 30 °C by Grignard metathesis polymerization(GRIM process). The coupling of these α-bromo, ω-Ni(dppp)Brtelechelic diblock copolymers then occurs by heating the solutionof the copolymer at 80 °C for a few hours without adding anyadditional reagent. Reactions are complete in only 10 min when heatingthe copolymer at 120 °C using microwaves. The deprotection ofthe alcohol groups of PTHPET blocks allows further modifications suchas the incorporation of acrylates by esterification. AFM analysison thin films shows the influence of the nature of side chains (protectedalcohol or acrylate), the molecular weight, and the architecture (diblockor multiblock) of the copolymer on the supramolecular organizationof the polythiophene chains. [ABSTRACT FROM AUTHOR]

3-Alkynyl-substituted terthiophenes and polythiopheneswere synthesized,and their properties and behavior toward hydroboration with Mes2BH were investigated. The alkynyl-substituted terthiophenewas found to crystallize in an intriguing layered structure that mimicsan interdigitated polymer wherein the terthiophenes form tightly π-stackedlinear pseudopolymer strands. The heptynyl side chains of neighboringstacks interlock ideally, almost completely filling the void in-betweensubstituents and thus allowing for minimal spacing between neighboringpseudopolymer strands. Poly(3-alkynylthiophene)s were accessed throughGrignard metathesis polymerization (GRIM) of 2,5-dibromo-3-heptynylthiophene,which yielded polymers of moderate molecular weights (Mn= 6.3; PDI = 1.73) in yields of up to 82%. Further modificationby hydroboration with Mes2BH resulted in a material thatis partially functionalized with vinylborane groups and as a resultexhibits charge transfer bands in the UV–vis spectra. A single-crystalX-ray structure of the corresponding hydroborated terthiophene speciesshows extensive intermolecular interactions, resulting in π-stacksof π-dimers, despite the steric bulk of the dimesitylboranemoieties. [ABSTRACT FROM AUTHOR]

The mixing behavior of the hole- and electron-transportingmaterials in bulk heterojunction (BHJ) organic photovoltaic (OPV)blends plays a key role in determining the nanoscale morphology, whichis believed to be a decisive factor in determining device performance.We present a systematic investigation of the mixing behavior betweenpoly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methylester (PCBM) in model multilayer structures. The bilayer structuresare composed of amorphous PCBM that is mechanically laminated to differentP3HT layers with varying degrees of crystallinity. We find that mixingis significantly decreased as the crystallinity of P3HT is increased.The mixing behavior can be explained as resulting from (1) nearlycomplete miscibility of PCBM with amorphous P3HT (based on our resultsfrom regiorandom P3HT) and (2) the existence of tie chains betweencrystalline P3HT domains that restrain the swelling of the P3HT layerby PCBM. We also introduce a unique PCBM–P3HT–PCBM trilayerstructure where one of the PCBM layers is highly crystalline. Thecrystalline PCBM dramatically alters the mixing behavior. Initialmixing of the amorphous PCBM into P3HT is followed by rapid cold crystallizationat the crystalline PCBM layer, which depletes the PCBM in the P3HTlayer. These bilayer and trilayer experiments illustrate that mixingof P3HT and PCBM is influenced by multiple factors, such as the semicrystallinenature of P3HT (overall crystallinity, characteristics of amorphouschains) and phase (amorphous or crystalline) of the PCBM. [ABSTRACT FROM AUTHOR]

The impact of thermal annealing on the growth of crystallinenanodomainsof poly(3-alkylthiophene) (P3AT) in thin films (15–20 nm thick)was investigated as a function of length of alkyl side chain by combinedlow-dose high-resolution transmission electron microscopy (HR-TEM)and grazing incidence X-ray diffraction (GIXD). Statistical analysisof the data yields the characteristic dimensions of the face-on orientedP3AT nanocrystals, i.e., average stem length lcalong backbones and lateral dimension perpendicular to thestems laalong side chains. The followingtrends were identified: (i) in as-spin-coated films, the proportionof face-on oriented nanocrystals increases with the number of carbonatoms in the side chain, (ii) annealing favors the lateral in-planegrowth of the nanocrystals along the side chain direction (aP3ATaxis), (iii) for a given P3AT, the proportion offace-on oriented domains increases with annealing temperature, (iv)lateral growth along the aP3ATaxis is mostefficient for the longer octyl side chains, and (v) thermal annealinginduces only modest lamellar thickening which is limited by the poorslide diffusion of π-stacked P3AT chains as opposed to lateralgrowth favored by weak van der Waals interactions between layers of n-alkyl side chains. The increase in the population of face-onoriented crystallites, observed when the length of the side chainincreases, coincides with a corresponding decrease in the field effectmobility in annealed P3AT thin films. [ABSTRACT FROM AUTHOR]

Unsubstituted polythiophene (PT) with defined and knownhigh molecularmass (up to ca. 36 000 g mol–1(Mw)) and low structural defects (ca. 3.6 mol %) as highlyattractive semiconducting material is presented. The new syntheticstrategy for this polymer is based on the combination of Stille-typepolycondensation reactions, ultrasound-assisted dispersion technique,and microwave-assisted ring-closure reactions. The use of Stille-typepolycondensation produces a diketal prepolymer with good solubilityand prescient and controllable degree of polymerization (DP) for thefinal insoluble PT. Ultrasonication preserves a high interfacial area,while microwave provides fast and effective heating for the last heterophasering-closure reaction. The characterization of the final product bysolid-state NMR, TEM, UV–vis absorption and fluorescence emissionspectroscopy, XRD, TGA, andconductivity measurements exhibits significant features for electronicand photoelectronic applications, such as broadened absorption, relativelyhigh crystallinity, high thermal stability, and typical semiconductingproperties. [ABSTRACT FROM AUTHOR]

We have synthesized photo-cross-linkable azide-functionalizedpoly(3-hexylthiophene)to explore improvements in the thermal stability of bulk heterojunctionsolar cells. Exposing blends of photo-cross-linkable polythiopheneand [6,6]-phenyl-C61-butyric acid methyl ester to ultravioletlight preferentially cross-linked the polythiophene without degradingits optical or electrical properties. X-ray scattering measurementsshowed that cross-linking slightly compacted the polythiophene chainlamellar stacking while increasing the polymer crystal coherence lengthby 20%. Optimized solar cells having cross-linked active blend layersretained 65% of their initial photovoltaic power conversion efficiencyafter 40 h of thermal annealing at 110 °C, while devices usingun-cross-linked commercial polythiophene underwent significant phaseseparation and retained less than 30% of their initial efficiencyafter annealing. [ABSTRACT FROM AUTHOR]

Two new conjugated side-chain isolated polythiophenederivatives, PT4TVand PT4TV-C, were designedand synthesizedby copolymerization of thiophene unit with thienylene–vinylene(TV) conjugated side chain and unsubstituted terthiophene unit. Thedifference of the two polymers is an additional carbonyl group onthe conjugated TV side chain in PT4TV-C. Compared toprevious reported conjugated side chain polythiophenes (CSC-PTs) withconcentrated side chains, PT4TVand PT4TV–Cshowed red-shifted and enhanced π–π*transition absorption of the polymer backbone along with the shoulderpeak and steep absorption edge, indicating ordered polymer main chainsand well-packed side chains. PT4TVpossessed an absorptionedge of 663 nm and a HOMO energy level at −5.21 eV. The introducingof electron deficient carbonyl group in PT4TV–Cled to 17 nm red-shifted absorption and a down-shifted HOMOenergy level at −5.26 eV, but aroused the issue of poorer planarityof the polymer backbone. The more ordered structure in PT4TVtranslated into better hole mobility and better photovoltaic properties.The polymer solar cell based on PT4TVas donor and indene–C60bisadduct as acceptor displayed a power conversion efficiencyof 3.05% with a high open circuit voltage of 0.93 V, under the illuminationof AM1.5G, 100 mW/cm2. The results indicate that the sidechain isolated CSC-PTs could be promising high performance photovoltaicpolymers. [ABSTRACT FROM AUTHOR]