Random copolymers consisting of dithienylcyclopentadienone, thiophene and benzothiadiazole for bulk heterojunction solar cells

Novel random copolymers containing dithienylcyclopentadienone, thiophene and benzothiadiazole were synthesized and photovoltaic properties of these materials were evaluated. Thermal, structural, optical and electrochemical characterization of the synthesized copolymers was carried out. These thermally stable copolymers are solution processable unlike the homopolymer. The absorption spectra indicated that with the incorporation of alkyl chains in the thiophene moiety, the onset of absorption increases and hence band gap decreases (1.47 eV to 1.41 eV). Bulk heterojunction solar cells were fabricated with the blend of copolymer and phenyl-C61-butyric acid methyl ester (PCBM) as the active material and device parameters were extracted. The copolymer consists of alkyl thiophene exhibit higher open circuit voltage than the copolymer consisting of thiophene moiety. (c) 2012 Elsevier B.V. All rights reserved.

Molecular topology of three ring nematogens from C-13-H-1 dipolar couplings

Molecules in their liquid crystalline phase undergo rotational motion about the long axis of the molecule and the shape adopted by the rotating molecule plays an important role in influencing the mesophase morphology. In this context, obtaining the topology and the relative orientation of the different sub-units are important steps. For studying the liquid crystalline phase, C-13 NMR spectroscopy is a convenient method and for certain specifically designed nematogens, 2-dimensional separated local field (2D-SLF) NMR spectroscopy provides a particularly simple and straightforward means of arriving at the molecular topology. We demonstrate this approach on two three ring based nematogens designed with a phenyl or a thiophene ring at one of the termini. From the C-13-H-1 dipolar couplings of the terminal carbon obtained using the 2D-SLF NMR technique, the order parameter of the local symmetry axis of the terminal phenyl ring as well as of the long molecular axis could be easily estimated. For the thiophene nematogen, the lack of symmetry of the thiophene moiety necessitates some additional computational steps. The results indicate that the thiophene unit has its local ordering axis oriented away from the long molecular axis by a small angle, consistent with a bent structure expected in view of the thiophene geometry. The experiment also demonstrates the ability of 2D-SLF NMR to provide high resolution spectra by separation of several overlapped resonances in terms of their C-13-H-1 dipolar couplings. The results are consistent with a rod-like topology of the core of the investigated mesogens. The investigation demonstrates the potential of 2D-SLF NMR C-13 spectroscopy for obtaining atomistic level information and its utility for topological studies of different mesogens.

Formation of a self-assembled monolayer of 2-mercapto-3-n-octylthiophene on gold

Monolayer assembly of 2-mercapto-3-n-octylthiophene (MOT) having a relatively large headgroup onto gold surface from its dilute ethanolic solutions has been investigated by electrochemistry. An electrochemical capacitance measurement on the permeability of the monolayer to aqueous ions, as compared with its alkanethiol counterpart [CH3(CH2)(9)SH (DT)] with a similar molecular length, shows that the self-assembled monolayers (SAMs) of MOT can be penetrated by aqueous ions to some extent. Furthermore, organic molecular probes, such as dopamine, can sufficiently diffuse into the monolayer because a diffusion-limited current peak is observed when the dopamine oxidation reaction takes place, showing that the monolayer is loosely packed or dominated by defects. But the results of electron transfer to aqueous redox probes (including voltammetry in Fe(CN)(6)(3-/4-) solutions and electrochemical ac impedance spectrum) confirm that the monolayer can passivate the gold electrode surface effectively for its very low ratio of pinhole defects. Moreover, a heterogeneous patching process involving addition of the surfactants into the SAMs provides a mixed or hybrid membrane that has superior passivating properties. These studies show that the MOT monolayer on the electrode can provide an excellent barrier for hydrated ionic probe penetration but cannot resist the organic species penetration effectively. The unusual properties of the SAMs are attributed to the entity of the relatively large thiophene moiety between the carbon chain and the thiol group.

Novel nicotinamide adenine dinucleotide analogues as selective inhibitors of NAD-dependent enzymes

Three novel dinucleotide analogues of nicotinamide adenine dinucleotide (NAD+) have been synthesised from -ribonolactone. These compounds incorporate a thiophene moiety in place of nicotinamide and are hydrolytically stable. They have been evaluated as inhibitors of adenosine diphosphate ribosyl cyclase, glutamate dehydrogenase and Sir2 acyltransferase activities. Enzyme specificity and a high level of inhibition was observed for the dehydrogenase.

Materials design for ambipolar devices: tuning orbital energetics in oligothiophene-naphthalimides semiconductors

Ambipolar organic field-effect transistors (OFETs), which can efficiently transport both holes and electrons, using a single type of electrode, are currently of great interest due to their possible applications in complementary metal oxide semiconductor (CMOS)-like circuits, sensors, and in light-emitting transistors. Several theoretical and experimental studies have argued that most organic semiconductors should be able to transport both types of carrier, although typically unipolar behavior is observed. One factor that can compromise ambipolar transport in organic semiconductors is poor solid state overlap between the HOMO (p-type) or LUMO (n-type) orbitals of neighboring molecules in the semiconductor thin film. In the search of low-bandgap ambipolar materials, where the absence of skeletal distortions allows closer intermolecular π-π stacking and enhanced intramolecular π-conjugation, a new family of oligothiophene-naphthalimide assemblies have been synthesized and characterized, in which both donor and acceptor moieties are directly conjugated through rigid linkers. In previous works we found that oligothiophene-napthalimide assemblies connected through amidine linkers (NDI derivates) exhibit skeletal distortions (50-60º) arising from steric hindrance between the carbonyl group of the arylene core and the sulphur atom of the neighbored thiophene ring (see Figure 1). In the present work we report novel oligo- and polythiophene–naphthalimide analogues NAI-3T, NAI-5T and poly-NAI-8C-3T, in which the connections of the amidine linkage have been inverted in order to prevent steric interactions. Thus, the nitrogen atoms are directly connected to the naphthalene moiety in NAI derivatives while they were attached directly to the thiophene moiety in the previously investigated NDI-3T and NDI-5T. In Figure 1 is depicted the calculated molecular structure of NAI-3T together with that of NDI-3T showing how the steric interactions are not present in the novel NAI derivative. The planar skeletons in these new family induce higher degree of crystallinity and the carrier charge transport can be switched from n-type to ambipolar behaviour. The highest FET performance is achieved for vapor-deposited films of NAI-3T with mobilities of 1.95x10-4cm2V-1s-1 and 2.00x10-4cm2V-1s-1 for electrons and holes, respectively. Finally, these planar semiconductors are compared with their NDI derivates analogues, which exhibit only n-type mobility, in order to understand the origin of the ambipolarity in this new series of molecular semiconductors.

Influence of Side-Chain on Structural Order and Photophysical Properties in Thiophene Based Diketopyrrolopyrroles: A Systematic Study

In this work, we have synthesized a series of TDPP derivatives with different alkyl groups such as n-hexyl (-C6H13) 3a, 2-ethylhexyl (-(2-C2H5)C6H12) 3b, triethylene glycol mono methyl ether (-(CH2CH2O)(3c)H-3, TEG) 3c, and octadodecyl (-(8-C8H17)C12H22) 3d. N,N dialkylation of Othiophene-diketopyrrolopyrrole (TDPP, 1) strongly influences its solubility, solid state packing, and structural order. These materials allow us to explicitly study the influence of alkyl chain on solid state packing and photophysical properties. TDPP moiety containing two different alkyl groups 3e (TEG and 2-ethylhexyl) and 3f (TEG and n-hexyl) were synthesized for the first time. The absorption spectra of all derivatives exhibited a red shift in solid state when compared to their solution spectra. The type of alkyl chains leads to change in the optical band gaps in solid state. The fluorescence study reveals that TDPP derivatives have strong pi-pi interaction in the solid state and the extent of bathochromic shift is due to combination of intramolecular interaction and formation of aggregates in solid state. This behavior strongly depends on the nature of alkyl chain. The presence of strong C-H center dot center dot center dot O inter chain interactions and CH-pi interactions in solid state exhibits strong influence on the photophysical properties of TDPP chromophore.

Photophysical Investigations of Thiophene Azomethine Derivatives

Une série de dimères composés de thiophène-aniline encombrée stériquement a été synthétisée. Les différents processus de désactivation de l’état singulet excité ont été étudiés par UV-visible, fluorescence, phosphorescence, photolyse par impulsion laser et calculs théoriques. Les graphiques de Stern-Volmer obtenus à partir des expériences de désactivation des états singulet et triplet ont démontré l’efficacité de l’azométhine à désactiver les fluorophores. Les calculs semi-empiriques AM1 examinant l’effet des substituants encombrés ont démontrés que les groupements tert-butyls sur l’aniline ont moins d’influence sur la barrière de rotation N-aryl que les substitutions alkyles en ont sur la rotation de thiophène-C. Les calculs Rehm-Weller basés sur les potentiels d’oxydation et de réduction ont montré que l’autodésactivation de l’état excité des azométhines se fait par transfert d’électron photoinduit menant à une éradication complète de la fluorescence. Des complexes métalliques contenant des ligands azométhines ont aussi été préparés. Le ligand est composé d’une unité hydroxyquinoline lié à un cycle thiophène. Les données photophysiques de ces complexes indiquent un déplacement bathochromique aussi bien en absorbance qu’en fluorescence. Des dispositifs de détection d’ion métallique ont été préparés et un exemple à partir d’une solution de cuivre a montré un déplacement bathochromique.

Regioregular poly(3-hexyl-thiophene) helical self-organization on carbon nanotubes

Mixtures of Regioregular Poly(3-hexyl-thiophene) (rrP3HT) and multi wall carbon nanotubes have been investigated by Scanning Tunneling Microscopy in Ultra High Vacuum. Carbon nanotubes covered by rrP3HT have been imaged and analyzed, providing a clear evidence that this polymer self assembles on the nanotube surface following geometrical constraints and adapting its equilibrium chain-to-chain distance. Largely spaced covered nanotubes have been analyzed to investigate the role played by nanotube chirality in the polymer wrapping, evidencing strong rrP3HT interactions along well defined directions.

Poly(3-hexyl-thiophene) coil-wrapped single wall carbon nanotube investigated by scanning tunneling spectroscopy

Scanning Tunneling Spectroscopy was performed on a (15,0) single wall carbon nanotube partially wrapped by Poly(3-hexyl-thiophene). On the bare nanotube section, the local density of states is in good agreement with the theoretical model based on local density approximation and remarkably is not perturbed by the polymer wrapping. On the coiled section, a rectifying current-voltage characteristic has been observed along with the charge transfer from the polymer to the nanotube. The electron transfer from Poly(3-hexyl-thiophene) to metallic nanotube was previously theoretically proposed and contributes to the presence of the Schottky barrier at the interface responsible for the rectifying behavior.

Spectroscopic investigation of the polymerisation of pyrrole and thiophene within zeolite channels

The reaction of pyrrole and thiophene monomers with copper- or nickel-exchanged mordenite has been investigated using X-ray photoelectron (XPS) and photoacoustic infrared (PAIRS) spectroscopies. Because of the differing oxidising powers of the cations studied, polymerisation occurred only with copper-exchanged mordenite. PAIRS and XPS data indicated that both polypyrrole and polythiophene were partially oxidised when synthesised within the zeolite structure. IR spectra of polythiophene and polythiophene and polypyrrole showed intense bands typical of ring vibrations which could couple to the large dipole change induced by charges moving along the polythiophene chain. In addition it was noted that only vibrations typical of oxidised polymer structures were recorded, suggesting that the charge carrier was located within these segments. Furthermore, N 1s spectra contained a high binding energy peak at 402.5 eV which was attributed to a positively charged nitrogen species, in agreement with IR data. Significantly, C 1s spectra confirmed that molecular wires were formed within the confines of the zeolite lattice. Depth-profiling experiments suggested that polypyrrole was distributed throughout the entire zeolite host. By contrast, polythiophene may have been restricted to the uppermost zeolite channels owing to the ability of sulfur species to bond to CuI sites [produced by reduction of copper(II) ions during the polymerisation process], thus obstructing movement along the channels.

Charge transport study of high mobility polymer thin-film transistors based on thiophene substituted diketopyrrolopyrrole copolymers

In this paper, we report on the device physics and charge transport characteristics of high-mobility dual-gated polymer thin-film transistors with active semiconductor layers consisting of thiophene flanked DPP with thienylene-vinylene-thienylene (PDPP-TVT) alternating copolymers. Room temperature mobilities in these devices are high and can exceed 2 cm2 V-1 s-1. Steady-state and non-quasi-static measurements have been performed to extract key transport parameters and velocity distributions of charge carriers in this copolymer. Charge transport in this polymer semiconductor can be explained using a Multiple-Trap-and-Release or Monroe-type model. We also compare the activation energy vs. field-effect mobility in a few important polymer semiconductors to gain a better understanding of transport of DPP systems and make appropriate comparisons.

Design and modification of three-component randomly incorporated copolymers for high performance organic photovoltaic applications

In this study we report the molecular design, synthesis, characterization, and photovoltaic properties of a series of diketopyrrolopyrrole (DPP) and dithienothiophene (DTT) based donor-acceptor random copolymers. The six random copolymers are obtained via Stille coupling polymerization using various concentration ratios of donor to acceptor in the conjugated backbone. Bis(trimethylstannyl)thiophene was used as the bridge block to link randomly with the two comonomers 5-(bromothien-2-yl)-2,5-dialkylpyrrolo[3,4-c]pyrrole-1, 4-dione and 2,6-dibromo-3,5-dipentadecyl-dithieno[3,2-b;2′,3′-d] thiophene. The optical properties of these copolymers clearly reveal a change in the absorption band through optimization of the donor-acceptor ratio in the backbone. Additionally, the solution processability of the copolymers is modified through the attachment of different bulky alkyl chains to the lactam N-atoms of the DPP moiety. Applications of the polymers as light-harvesting and electron-donating materials in solar cells, in conjunction with PCBM as acceptor, show power conversion efficiencies (PCEs) of up to 5.02%.

A high mobility P-type DPP-thieno[3,2-b]thiophene copolymer for organic thin-film transistors

A copolymer comprising 1,4-diketopyrrolo[3,4-c]pyrrole (DPP) and thieno[3,2-b]thiophene moieties, PDBT-co-TT, shows high hole mobility of up to 0.94 cm2 V-1 s-1 in organic thin-film transistors. The strong intermolecular interactions originated from π-π stacking and donor-acceptor interaction lead to the formation of interconnected polymer networks having an ordered lamellar structure, which have established highly efficient pathways for charge carrier transport.

Poly(2,5-bis(2-octyldodecyl)-3,6-di(furan-2-yl)-2,5-dihydro-pyrrolo[3,4-c] pyrrole-1,4-dione-co-thieno[3,2-b]thiophene): A high performance polymer semiconductor for both organic thin film transistors and organic photovoltaics

A new diketopyrrolopyrrole (DPP)-containing donor-acceptor polymer, poly(2,5-bis(2-octyldodecyl)-3,6-di(furan-2-yl)-2,5-dihydro-pyrrolo[3,4-c] pyrrole-1,4-dione-co-thieno[3,2-b]thiophene) (PDBF-co-TT), is synthesized and studied as a semiconductor in organic thin film transistors (OTFTs) and organic photovoltaics (OPVs). High hole mobility of up to 0.53 cm 2 V -1 s -1 in bottom-gate, top-contact OTFT devices is achieved owing to the ordered polymer chain packing and favoured chain orientation, strong intermolecular interactions, as well as uniform film morphology of PDBF-co-TT. The optimum band gap of 1.39 eV and high hole mobility make this polymer a promising donor semiconductor for the solar cell application. When paired with a fullerene acceptor, PC 71BM, the resulting OPV devices show a high power conversion efficiency of up to 4.38% under simulated standard AM1.5 solar illumination.