Oligothiophene Derivatives Research Articles

Effect of End‐capping Functional Groups on the Optoelectronic Properties of Oligothiophene Derivatives

AbstractFive novel oligothiophene derivatives end‐capped by different functional groups (R=ethoxyl (EtOP3T), methylsulfanyl (MSP3T), acetyl (AcP3T), methylsulfonyl (MSO2P3T) and biphenyl (BP3T) groups) were synthesized. They were characterized by Hnuclear magnetic resonanceH (P1PH NMR), Hmass spectrometryH (MS) and Fourier transform Infra‐red spectra (IR). The relationship between end‐capping functional groups and optoelectronic properties of them was investigated. It was found that the compound with sulfonyl group in the molecular structure (MSOR2RP3T) shows the highest oxidation stability (also supported by theoretical calculations) and best thermal stability among the five compounds. The results of scanning electron microscope (SEM) interpret that MSOR2RP3T displays excellent ability of self‐film forming. This reveals that it could be a potential candidate for thin film material. The liquid crystal property of MSOR2RP3T was characterized by polarized optical microscopy analysis (POM) and X‐ray diffraction (XRD). The results of this paper provide useful information for the design of tailored oligothiophene derivatives for devices.

The fabrication and enhanced nonlinear optical properties of electrostatic self-assembled film containing water-soluble chiral polymers

An ultra-thin film containing a water-soluble chiral PPV derivative and oligo-thiophene derivative was fabricated through the electrostatic self-assembly technique. The PPV and thiophene derivatives are poly{(2,5-bis(3-bromotrimethylammoniopropoxy)-phenylene-1,4-divinylene)-alt-1,4-(2,5-bis((3-hydroxy-2-(S)-methyl)propoxy)phenylenevinylene) (BHP-PPV) and 4′,3″-dipentyl-5,2′:5′,2″:5″,2″′-quaterthiophene-2,5″′-dicarboxylic acid (QTDA), respectively. The circular dichroism (CD) spectrum of BHP-PPV cast film on quartz substrate proved the chirality of BHP-PPV. The UV–vis spectra showed a continuous deposition process of BHP-PPV and QTDA. The film structure was characterized by small angle X-ray diffraction (XRD) measurement and atomic force microscopy (AFM) images. The nonlinear optical (NLO) properties of BHP-PPV/QTDA ultra-thin film with different number of bilayers were investigated by the Z-scan technique with 8ns laser pulse at 532nm. The Z-scan experimental data were analyzed with the double-sided film Z-scan theory. The BHP-PPV/QTDA film exhibits enhanced reverse saturable absorption (RSA) and self-defocusing effects, which may be attributed to the conjugated strength, chirality and well-ordered film structure. The chirality may lead to the RSA of BHP-PPV/QTDA film contrary to the SA of the other electrostatic self-assembled films without chiral units. The self-defocusing effect should be due to the thermal effect.

Supramolecular Control of Photochemical and Electrochemical Properties of Two Oligothiophene Derivatives at the Air/Water Interface

Two geometric isomers of oligothiophene derivatives containing two crowned styryl fragments in 2- or 3-positions of thiophene rings are able to form stable monolayers on the water subphase. The organizing of crown-containing oligothiophenes in monolayers is guided by the π-stacking interaction of hydrophobic styrylthiophene fragments and interaction of hydrophilic macrocycles with the water subphase. The difference in structure of oligothiophene molecules leads to the formation of distinct monolayer architectures with various electrochemical and optical characteristics.

Preparation and Electrochromic Properties of Polythiophene Derivative Films Based on Oligothiophene Derivative Monomers

Preparation and Electrochromic Properties of Polythiophene Derivative Films Based on Oligothiophene Derivative Monomers

Pyrene end-capped oligothiophene derivatives for organic thin-film transistors and organic solar cells

We have demonstrated an efficient one-step synthesis of pyrene end-capped thiophene oligomers as active materials for organic thin-film transistors (OTFTs) and donor materials for organic solar cells (OSCs). In particular, the OTFT device based on 5,5′′-di(pyren-1-yl)-2,2′:5′,2′′-terthiophene (3s) exhibited a reasonable field effect mobility of 0.11 cm2 V−1 s−1, and a power conversion efficiency of 1.20% was achieved when 3s was used as active materials in OSCs. These pyrene end-capped thiophene oligomers are considered to be good organic semiconducting materials for OTFTs and OSCs.

Impact of dye end groups on acceptor–donor–acceptor type molecules for solution-processed photovoltaic cells

Two new oligothiophene derivatives of the acceptor–donor–acceptor type, incorporating double rhodanine or 1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione units as the terminal acceptor groups, D2R(8 + 2)7T and DTDMP7T, have been designed and synthesized for solution-processable small molecule BHJ solar cells. The impacts of these different end dye moieties on their optical, electrochemical properties, morphology, mobility and solar cell performance were studied. Both compounds exhibit broad and highly efficient solar absorption with low bandgaps of 1.70 and 1.62 eV for D2R(8 + 2)7T and DTDMP7T, respectively. The D2R(8 + 2)7T and DTDMP7T based BHJ solar cell devices achieved a PCE of 2.46% and 4.05%, respectively, under the illumination of AM.1.5, 100 mW cm−2.

Acenaphtho[1,2-b]quinoxaline based low band gap copolymers for organic thin film transistor applications

We report the synthesis of a novel class of low band gap copolymers based on an acenaphtho[1,2-b]quinoxaline core and oligothiophene derivatives acting as the acceptor and the donor moieties, respectively. The optical properties of the copolymers were characterized by ultraviolet-visible spectroscopy while the electrochemical properties were determined by cyclic voltammetry. The band gap of these polymers was found to be in the range 1.8–2.0 eV as calculated from the optical absorption band edge. X-ray diffraction measurements show weak π–π stacking interactions between the polymer chains. The hole mobility of the copolymers was evaluated using field-effect transistor measurements yielding values in the range 10−5–10−3 cm2/Vs.

Ultra-flat coplanar electrodes for controlled electrical contact of molecular films

Reliable measurement of electrical charge transport in molecular layers is a delicate task that requires establishing contacts with electrodes without perturbing the molecular structure of the film. We show how this can be achieved by means of novel device consisting of ultra-flat electrodes separated by insulating material to support the molecular film. We show the fabrication process of these electrodes using a replica technique where gold electrodes are embedded in a silicon oxide film deposited on the angstrom-level flat surface of a silicon wafer. Importantly, the co-planarity of the electrode and oxide areas of the substrate was in the sub-nanometer range. We illustrate the capabilities of the system by mapping the distribution of electrical transport pathways in molecular thin films of self-assembled oligothiophene derivatives using conductive atomic force microscopy. In comparison with traditional bottom contact non-coplanar electrodes, the films deposited on our electrodes exhibited contact resistances lower by a factor of 40 than that of the similar but non-coplanar electrodes.

Fabrication of Organic-Inorganic Nano-Hybrid Materials Containing Oligothiophene Derivatives

Oligothiophene derivatives, 4,4’-bis-(2-aminoethylthienyl)-3,4-ethylenedioxythiophene dihydrohalide (AET-EDOT·HX: X = I, Br), were synthesized by Grignard coupling reactions. The hybrid films of oligothiophene and lead halide were fabricated by casting and spin-coating methods. The effect of halogen species on the optical properties of the perovskites was investigated. The X-ray diffraction profiles of (AET-EDOT)PbX4 cast films indicated that the layered structures were formed by the self-organization. After hybridization of AET-EDOT·HX with PbX2, new absorption peaks due to the confined excitons were observed at 400 nm for (AET-EDOT)PbBr4 film, and at 395 nm for (AET-EDOT)PbI4 film. These results indicated that the diamino-type oligothiophenes were successfully incorporated into the organic-inorganic layered perovskites. AFM images of (AET-EDOT)PbX4 cast films showed polycrystalline grains, indicating that the polycrystalline structures covered on the substrate surface.

Influence of Morphology of Vacuum-Evaporated Oligothiophene Derivative Films on Oganic Photovoltaic Performance

In order to understand the influence of morphology of vacuum-evaporated conjugated organic thin film on organic photovoltaic performance, oligothiophene derivatives, 2,3,4,5-tetrathienylthiophene (X-5T) and 2,5-dithienyl-3,4-di ((2,2') bithiophene-5yl) thiophene (X-7T), were prepared. The thermal behaviour and morphologies of vacuum-deposited X-5T and X-7T films were examined by differential scanning calorimetry (DSC) and x-ray diffraction (XRD). The influence of morphologies of vacuum-evaporated X-5T and X-7T films on organic photovoltaic performance was hen investigated. It was found that vacuum-evaporated oligothiophene derivative films possessing crystalline morphology could be beneficial to improve organic photovoltaic performance of device by promoting forward interfacial electron transfer and transport.

Synthesis and Electrochromic Properties Based on Star-Shaped Oligothiophene Derivatives with Phenyl Core

For the purpose of developing novel electrochromic materials, star-shaped oligothiophene derivatives with phenyl core, 1,3,5-tris (2′-thienyl) benzene (3TB) and 1,3,5-tris (5′-(2,2′- bithienyl)) benzene (3BTTB) were synthesized, and their electrochromic properties were investigated. It was found that 3TB and 3BTTB as solid films showed reversible, clear color changes on electrochemical doping and dedoping. The two oligothiophene derivatives with phenyl core constitute a new class of potential electrochromic materials.

Thickness Dependence of the Ambipolar Charge Transport Properties in Organic Field-Effect Transistors based on a Quinoidal Oligothiophene Derivative

We examine the influence of film thickness on the optical and ambipolar field-effect transistor properties of solution-processed dicyanomethylene-substituted quinoidal oligothiophene [QQT(CN)4] thin films. Threshold voltages for both p- and n-channels show a linear thickness dependence due to an increase in the bulk conductance in thicker films. Electron mobility is found to increase gradually when decreasing film thickness. In contrast, hole mobility remains nearly unchanged except in films thinner than 50 nm. Film morphology is characterized by atomic force microscopy and X-ray diffraction techniques. Direct correlation between crystalline grain size and thickness dependence of the electron field-effect mobility is observed. This result can be attributed to a strong effect of the grain boundaries on the electron trapping properties and suggests the possibility to improve the charge transport properties of QQT(CN)4 thin films by controlling their morphology. The influence of contact resistance effects on the electron transport properties of the devices is also discussed. Devices with optimized structure show hole and electron mobilities in the saturation regime as high as 0.08 and 0.015 cm2/(V s), respectively. Overall, this study provides new important insight into the ambipolar charge transport properties of quinoidal oligothiophene derivatives for organic field-effect transistors.

Synthesis and Photovoltaic Properties of Donor–Acceptor Oligothiophene Derivatives Possessing Mesogenic Properties

For the purpose of developing novel photovoltaic materials and organic photovoltaic devices with good performance characteristics, 5-cyano-2,2′:5′,2″-terthiophene (3T-CN) and 5-cyano-2,2′:5′,2″:5″,2″′-tetrathiophene (4T-CN) were synthesized. The 3T-CN and 4T-CN were donor–acceptor oligothiophene derivatives possessing mesogenic properties. The photovoltaic properties of 3T-CN and 4T-CN were studied. The rigid and flexible photovoltaic devices were fabricated using 3T-CN, 4T-CN, and 3,4,9,10-perylenetertracarboxylic dianhydride (PTCDA). The results showed that the -CN group played an important role in increasing short circuit current density (I sc) and power conversion efficiency (PCE). Both rigid device glass-ITO/4T-CN/PTCDA/Al and flexible device PET-ITO (indium tin oxides coated with polyethylene terephthalate)/4T-CN/PTCDA/Al had greater I sc and PCE compared with rigid device glass-ITO/4T/PTCDA/Al. It was possible that the -CN group, with strong electron-withdrawing character, and mesogenic properties of 4T-CN enhanced the efficiency by promoting forward interfacial electron transfer.

Highly efficient semitransparent tandem organic solar cells with complementary absorber materials

We present highly efficient, semitransparent small molecule organic solar cells. The devices employ an indium tin oxide-free top contact, consisting of thin metal films. An additional organic layer is used to enhance light outcoupling. The solar cell incorporates two stacked subcells, each containing a donor:acceptor bulk heterojunction. The two subcells have complementary absorbers, with separate blue (C60), red (fluorinated zinc phthalocyanine), and green (dicyanovinyl oligothiophene derivative) absorbing molecules. A power conversion efficiency of 4.9 ± 0.2% is obtained for the device having an average transmission of 24% in the visible range.

ChemInform Abstract: Vacuum‐Processed Small Molecule Solar Cells Based on Terminal Acceptor‐Substituted Low‐Band Gap Oligothiophenes.

AbstractThe bis‐stannylation of terthiophene (I) and a subsequent Stille coupling reaction provides access to thiadiazolopyridine‐containing oligothiophene derivatives (V).

Flexible organic field-effect transistors and complementary inverters based on a solution-processable quinoidal oligothiophene derivative

We report on the fabrication and characterization of ambipolar organic field-effect transistors based on the solution-processable quinoidal oligothiophene [QQT(CN)4] and using a new fluorinated polymer (AL-X601) with a dielectric constant of 3.1 as dielectric material layer. As-prepared devices show ambipolar transport with hole and electron field-effect mobilities of 6 × 10 −2 and 5 × 10 −3 cm 2/V s respectively as well as an on and off state current ratio higher than 10 3. Influence of a thermal annealing on the device performances was investigated and was found to lead to a majority carrier type conversion from a p-type to an n-type dominant behavior. QQT(CN)4 based field-effect transistors and complementary inverters fabricated on flexible substrates and using Al-X601 as gate dielectric material show high performance and good mechanical stability.

Tuning Photoluminescent Wavelength of Water-Soluble Oligothiophene/Polymer Complex Film by Proton Bonding

Abstract We synthesized a new oligothiophene derivative with pyridine end groups and investigated their optical properties. Upon adding an aqueous polystyrene sulfonic acid solution, it forms homogeneous polymer complex films with protonated structure. Furthermore, reversible color change in photoluminescence in response to a base due to reversible protonation of pyridyl end groups in oligothiophene was demonstrated, which can be applied to acid sensors.

Length-dependent self-assembly of oligothiophene derivatives in thin films

Abstract

Nanoscale structure, dynamics and power conversion efficiency correlations in small molecule and oligomer-based photovoltaic devices.

Photovoltaic functions in organic materials are intimately connected to interfacial morphologies of molecular packing in films on the nanometer scale and molecular levels. This review will focus on current studies on correlations of nanoscale morphologies in organic photovoltaic (OPV) materials with fundamental processes relevant to photovoltaic functions, such as light harvesting, exciton splitting, exciton diffusion, and charge separation (CS) and diffusion. Small molecule photovoltaic materials will be discussed here. The donor and acceptor materials in small molecule OPV devices can be fabricated in vacuum-deposited, multilayer, crystalline thin films, or spin-coated together to form blended bulk heterojunction (BHJ) films. These two methods result in very different morphologies of the solar cell active layers. There is still a formidable debate regarding which morphology is favored for OPV optimization. The morphology of the conducting films has been systematically altered; using variations of the techniques above, the whole spectrum of film qualities can be fabricated. It is possible to form a highly crystalline material, one which is completely amorphous, or an intermediate morphology. In this review, we will summarize the past key findings that have driven organic solar cell research and the current state-of-the-art of small molecule and conducting oligomer materials. We will also discuss the merits and drawbacks of these devices. Finally, we will highlight some works that directly compare the spectra and morphology of systematically elongated oligothiophene derivatives and compare these oligomers to their polymer counterparts. We hope this review will shed some new light on the morphology differences of these two systems.

Molecular dynamics effects on luminescence properties of oligothiophene derivatives: a molecular mechanics–response theory study based on the CHARMM force field and density functional theory

CHARMM force field parameter values for a class of oligothiophene derivatives have been derived with reference to density functional theory/B3LYP potential energy surfaces. The force field parametrization of these luminescent conjugated polyelectrolytes includes the electronic ground state as well as the strongly light absorbing first excited state. In conjunction with quantum chemical response theory calculations of transition state properties, a molecular dynamical model of the Stokes shift is obtained. The theoretical model is benchmarked against experimental data recorded at room temperature which refer to sodium salts of p-HTAA and p-FTAA with distilled water as a solvent. For p-HTAA the theoretically predicted Stokes shift of 112 nm is in good agreement with the experimental result of 124 nm, given the approximations about exciton localization that were introduced to obtain a force field for the excited state.