Oligothiophene Moiety Research Articles

Light-Responsive Oligothiophenes Incorporating Photochromic Torsional Switches.

We present a quaterthiophene and sexithiophene that can reversibly change their effective π-conjugation length through photoexcitation. The reported compounds make use of light-responsive molecular actuators consisting of an azobenzene attached to a bithiophene unit by both direct and linker-assisted bonding. Upon exposure to 350 nm light, the azobenzene undergoes trans-to-cis isomerization, thus mechanically inducing the oligothiophene to assume a planar conformation (extended π-conjugation). Exposure to 254 nm wavelength promotes azobenzene cis-to-trans isomerization, forcing the thiophenic backbones to twist out of planarity (confined π-conjugation). Twisted conformations are also reached by cis-to-trans thermal relaxation at a rate that increases proportionally with the conjugation length of the oligothiophene moiety. The molecular conformations of quaterthiophene and sexithiophene were characterized by using steady-state UV-vis spectroscopy, X-ray crystallography and quantum-chemical modeling. Finally, we tested the proposed light-responsive oligothiophenes in field-effect transistors to probe the photo-induced tuning of their electronic properties.

Ring‐Strain‐Promoted Ultrafast Diaryltetrazole–Alkyne Photoclick Reactions Triggered by Visible Light

AbstractBy exploiting the scope of dipolarophiles, we discovered that endo‐bicyclo[6.1.0]non‐4‐yn‐9‐ylmethanol (BCN) is an appropriate chemical reporter for the 2,5‐diaryltetrazole (DATet) based photoclick reaction, which proceeds via an ultrafast cycloaddition rate (∼105 M−1 s−1). Introduction of a 2,6‐(CF3)2phenyl moiety on the C5‐position of the tetrazole core brings a significant improvement of the chemical selectivity toward BCN without loss of reactivity. The high selectivity benefits from a combination of the steric and the electrostatic sheltering effect of a nitrile imine (NI) intermediate generated from photolysis of the DATet. In the absence of BCN, the oligothiophene moiety on the N2‐position of the tetrazole was found to induce self‐quenching of the NI intermediate instead of nucleophilic addition by 10 mM glutathione, demonstrating the fidelity of the DATet reagent. We also investigated the bioorthogonality of the DATet‐BCN photoclick chemistry for covalent bioconjugation toward BCN tags on proteins with visible‐light illumination.

Nano Structures of Thin Films of Block Copolymers with Oligothiophene Side Chains

We synthesized polymers containing a liquid-crystalline (LC) oligothiophene moiety in the side chain. This oligothiophene shows LC behavior between 101°C and 194°C in its original form, while when incorporated into the side chains of a polymer, the resultant polymer showed a nematic phase in a much wider temperature range. Thin films of these polymers showed nano-phase-separated structures with domain sizes of 15–40 nm upon annealing.

Visible-Light-Induced Water Splitting Based on Two-Step Photoexcitation between Dye-Sensitized Layered Niobate and Tungsten Oxide Photocatalysts in the Presence of a Triiodide/Iodide Shuttle Redox Mediator

Water splitting into H2 and O2 under visible light was achieved using simple organic dyes such as coumarin and carbazole as photosensitizers on an n-type semiconductor for H2 evolution, a tungsten(VI) oxide (WO3) photocatalyst for O2 evolution, and a triiodide/iodide (I3(-)/I(-)) redox couple as a shuttle electron mediator between them. The results on electrochemical measurements revealed that the oxidized states of the dye molecules having an oligothiophene moiety (two or more thiophene rings) in their structures are relatively stable even in water and possess sufficiently long lifetimes to exhibit reversible oxidation-reduction cycles, while the carbazole system required more thiophene rings than the coumarin one to be substantially stabilized. The long lifetimes of the oxidized states enabled these dye molecules to be regenerated to the original states by accepting an electron from the I(-) electron donor even in an aqueous solution, achieving sustained H2 and I3(-) production from an aqueous KI solution under visible light irradiation when they were combined with an appropriate n-type semiconductor, ion-exchangeable layered niobate H4Nb6O17. The use of H4Nb6O17 loaded with Pt cocatalyst inside the interlayer allowed the water reduction to proceed preferentially with a steady rate even in the presence of a considerable amount of I3(-) in the solution, due to the inhibited access of I3(-) to the reduction site, Pt particles inside, by the electrostatic repulsion between the I3(-) anions and the negatively charged (Nb6O17)(4-) layers. It was also revealed that the WO3 particles coloaded with Pt and IrO2 catalysts exhibited higher rates of O2 evolution than the WO3 particles loaded only with Pt in aqueous solutions containing a considerable amount of I(-), which competitively consumes the holes and lowers the rate of O2 evolution on WO3 photocatalysts. The enhanced O2 evolution is certainly due to the improved selectivity of holes toward water oxidation on IrO2 cocatalyst, instead of undesirable oxidation of I(-). Simultaneous evolution of H2 and O2 under visible light was then achieved by combining the Pt/H4Nb6O17 semiconductor sensitized with the dye molecules having an oligothiophene moiety, which can stably generate H2 and I3(-) from an aqueous KI solution, with the IrO2-Pt-loaded WO3 photocatalyst that can reduce the I3(-) back to I(-) and oxidize water to O2.

Novel organic dyes incorporating a carbazole or dendritic 3,6-diiodocarbazole unit for efficient dye-sensitized solar cells

Four organic photosensitizers incorporating a carbazole or 3,6-diiodocarbazole unit as the electron donor, a benzene/thiophene or oligothiophene moiety as the conjugated spacer, and 2-cyanoacrylic acid as the electron acceptor have been synthesized. The photovoltaic performance data are quite sensitive to the structural modification of sensitizer. The introduction of the benzene/thiophene linker benefits from lower tendency to aggregate, but disfavors the electron transport between donor and acceptor. The addition of a thiophene unit in the bridge efficiently red-shifts the absorption response, however, organic dyes have some π–π aggregation. Incorporation of 3,6-diiodocarbazole as a dendritic donor unit not only enhances the molar extinction coefficients of the absorption but also suppresses the charge recombination with electrolyte.

Synthesis and Optical Properties of Pyrrolo[3,2-b]pyrrole-2,5(1H,4H)-dione (iDPP)-Based Molecules

We describe the synthesis and photophysical properties of a series of derivatives of pyrrolo[3,2-b]pyrrole-2,5(1H,4H)-dione-3,6-diyl (iDPP) linked to two oligothiophenes of variable length (nT). The iso-DPP-oligothiophenes (iDPPnTs) differ from the common pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-3,6-diyl-oligothiophene analogues (DPPnTs) by a different orientation of the two lactam rings in the bicyclic iDPP unit compared to DPP. In contrast to the highly fluorescent DPPnTs, the new isomeric iDPPnTs exhibit only very weak fluorescence. We demonstrate with the help of quantum-chemical calculations that this can be attributed to a different symmetry of the lowest excited state in iDPPnT (A in C2 symmetry) compared to DPPnTs (B) and the corresponding loss in oscillator strength of the lowest energy transition. Upon extending the oligothiophene moiety in the iDPPnTs molecules, the charge transfer character of the lowest A excited state becomes more pronounced. This tends to preclude high fluorescence quantum yields even in extended iDPPnTs systems.

Synthesis of Well-Defined Head-to-Tail-Type Oligothiophenes by Regioselective Deprotonation of 3-Substituted Thiophenes and Nickel-Catalyzed Cross-Coupling Reaction

Iterative growth of thiophene oligomers by single-step extensions has been realized by regioselective metalation of 3-substituted thiophenes with the Knochel-Hauser base (TMPMgCl·LiCl) and coupling with bromothiophene using a nickel catalyst. Treatment of 3-hexylthiophene with TMPMgCl·LiCl induces metalation at the 5-position selectively. Subsequent addition of 2-bromo-3-hexylthiophene and a nickel catalyst leads to the corresponding bithiophene. The obtained bithiophene is converted to the terthiophene and then to the quaterthiophene by repeating the similar protocol. A concise synthesis of MK-1 and MK-2, which are organic dye molecules bearing an oligothiophene moiety that are used in photovoltaic cells, has been achieved.

Simple Oligothiophene-Based Dyes for Dye-Sensitized Solar Cells (DSSCs): Anchoring Group Effects on Molecular Properties and Solar Cell Performance

Abstract Simple oligothiophene-based dyes with a cyanoacrylic acid anchor were synthesized and evaluated as a photosensitizer for dye-sensitized solar cells (DSSCs). Although the molecular properties of the dyes at a glance are quite similar to those of related oligothiophene dyes with a carboxylic acid anchor, the DSSC performance of the former (up to η = 4.8%) is fairly improved over the latter (≈1.2%). Absorption spectra of the oligothiophene dyes with the cyanoacrylic acid are red-shifted compared to those with the carboxylic acid, resulting in the improved photocurrent conversion efficiency at above 600 nm in the DSSCs. With the aid of theoretical calculations, electronic properties of the oligothiophene dyes were investigated, and it turned out that the excited states of the dyes are significantly affected by the anchoring groups. The cyanoacrylic acid anchor brings about a stabilized LUMO with localized electron density on the cyanoacrylic acid moiety, whereas the carboxylic acid dye has relatively a high-lying LUMO with delocalized electron density over the oligothiophene moiety. Thus, the difference in the DSSC performance is rationalized by the different electronic structure at the excited states caused by the anchoring groups on the oligothiophene cores.

Theoretical study of the electronic ground states and low-lying singlet excited states of thiophene-based spirofluorenes

The electronic structures and optical properties of oligothiophene substituted spirofluorenes are investigated theoretically with semi-empirical quantum chemical calculations. A theoretical investigation of the interaction between two perpendicular π-systems of various oligothiophene substituted spirofluorenes is conducted. The results demonstrate that the interaction between two perpendicular branches is reduced by oligothiophene substitutions. Photoexcitation induced relaxation is mainly located on one of the equivalent branches or the branch with longer conjugation length. In addition to these benefits brought by 9,9-spirobifluorene center, the specific oligothiophene moieties linked to the spiro center also have properties of significant merit, such as the ability to tune energy levels and emission colors by controlling the conjugation length.

Synthesis and Photovoltaic Properties of Solution Processable Small Molecules Containing 2-Pyran-4-ylidenemalononitrile and Oligothiophene Moieties

A series of solution processable small molecules (4TPM, 6TPM, and 8TPM) were synthesized with 2-pyran-4-ylidenemalononitrile (PM) as the electron-accepting unit and oligothiophene with different numbers as the electron-donating unit. Differential scanning calorimetry (DSC) measurement indicated that melting point and crystal temperature of molecules increased with the increase of thiophene number. UV−vis absorption demonstrated that the combination of PM with oligothiophene resulted in an enhanced intramolecular charge transfer (ICT) transition, which led to an extension of the absorption of the molecules. Cyclic voltammetry investigation displayed that the highest occupied molecular orbital (HOMO) energy levels of the three molecules were relatively low, which promised good air stability and high open circuit voltage (Voc) for photovoltaic application. Theoretical calculations revealed that the variation laws of HOMO and the lowest unoccupied molecular orbital (LUMO) energy levels are well consistent wit...

Electronic Processes in Conjugated Diblock Oligomers Mimicking Low Band-Gap Polymers: Experimental and Theoretical Spectral Analysis

Conjugated oligomers containing a common central thienothiophene unit symmetrically connected to two identical thiophene oligomers were studied as model systems for a series of low bandgap organic diblock copolymers. The oligothiophene side chain fragments were varied in length as a means to tune the electronic coupling between the thienothiophene and oligothiophene moieties. The fragment length dependence of both the ground- and excited-state electronic and structural properties of a series of diblock oligomers were investigated in detail. The charge transfer character in these diblock oligomers, revealed by their optical absorption and fluorescence spectra, is responsible for their low band gap and energy gap tunability compared with their homooligomer counterparts. The electronic spectra and theoretical analysis indicate a partially localized central charge in the first excited state. Using experimental results and comparing them with theoretical calculations, we estimate that the electronic effects from a single thienothiophene unit spreads over seven to nine adjacent units through π-conjugation along the oligomers.

Synthesis and characterization of perylene-based donor–acceptor copolymers containing triple bonds

Two donor–acceptor copolymers containing perylene diimide and oligothiophenes linked through triple bonds have been designed and synthesized by palladium catalyzed Sonogashira coupling reaction. The introduction of the triple bond spacer between the electron acceptor perylene moieties and the electron donating oligothiophene moieties produces an extended conjugation along the main chain, and produces soluble and high molecular weight copolymers.The thermal, optical and electrochemical properties of these copolymers were examined. The HOMO–LUMO energy levels of these copolymers, along with the quenching of their photoluminescence in 1:1 (w/w) blends with poly(3-hexylthiophene) (P3HT), indicate that they are suitable materials for application as electron acceptor and n-type components in bulk heterojunction solar cells with P3HT.

Organic Dyes Incorporating the Dithieno[3,2-b:2′,3′-d]thiophene Moiety for Efficient Dye-Sensitized Solar Cells

New dipolar compounds incorporating a dithieno[3,2-b:2',3'-d]thiophene unit as the electron donor, an oligothiophene moiety as the conjugated spacer, and 2-cyanoacrylic acid as the electron acceptor have been synthesized. These nonarylamine type metal-free organic compounds have been successfully used as the sensitizers of dye-sensitized solar cells (DSSCs). The conversion efficiencies of the DSSCs range from 3.54 to 5.15% under AM 1.5 G irradiation. The best efficiency reached approximately 70% of the ruthenium dye N719-based standard cell fabricated and measured under similar conditions.

Oxidation of Unsymmetrically Substituted Quaterthiophene with Two Terminal Ferrocenyl Groups

Abstract An unsymmetrically substituted quaterthiophene with two terminal ferrocenyl groups was prepared as a long π-conjugated system. Electrochemical and spectroscopic studies were carried out to evaluate the electronic and/or electrostatic communication between the two terminals. The one-electron oxidation would occur at one ferrocene moiety specified due to the unsymmetry of the oligothiophene moiety. The one-electron oxidizing species extended into the oligothiophene moiety apparently interacts with the other terminal ferrocene moiety.

Highly stable sensitizer dyes for dye-sensitized solar cells: role of the oligothiophene moiety

The photostability of five sensitizer dyes with and without an oligothiophene moiety was studied by means of spectroscopic techniques to determine the dyes' suitability for dye-sensitized solar cells. We examined the effect of light irradiation on the dyes adsorbed on nanocrystalline TiO2 films under ambient conditions and found that the dyes containing an oligothiophene moiety showed high stability. The results of transient absorption measurements suggest that the location of holes on the oligothiophene moieties was responsible for this observed high stability.

Synthesis and characterization of donor-acceptor perylene based copolymers

AbstractTwo donor-acceptor copolymers containing perylene diimide and oligothiophenes linked through triple bonds have been designed and synthesized by palladium catalyzed Sonogashira coupling reaction. The introduction of the triple bond spacer between the electron-acceptor perylene moieties and the electron donating oligothiophene moieties produces an extended conjugation along the main chain, and produces soluble and high molecular weight copolymers.The thermal, optical and electrochemical properties of these copolymers were examined. The HOMO-LUMO energy levels of these copolymers, along with the photoinduced charge transfer process, probed by photoluminescence quenching and by FTIR photoinduced absorption spectroscopy, in blends with poly(3-hexylthiophene) (P3HT), indicate that they are suitable materials for application as electron acceptor and n-type components in bulk heterojunction solar cells with P3HT.

Tetrahedral Oligothiophenes; Synthesis, X‐ray Analysis, and Optoelectronic Properties of Highly Symmetrical, 3D‐Branched Oligothiophenes

Tetrakis(bithienyl)methane and tetrakis(terthienyl)methane have been synthesized from tetrakis(2-thienyl)methane by use of Suzuki-Miyaura coupling as a key reaction. Their trimethylsilyl (TMS) derivatives are also synthesized. X-ray analysis reveals that each oligothiophene moiety tends to adopt anti-conformations and show relatively small torsion angles between the adjacent thiophene rings. While the longest absorption maxima of these tetrakis(oligothienyl)methanes exhibit only a slight bathochromic shift compared to the corresponding linear oligothiophene derivative, tetrakis(bithienyl)methane and its TMS derivative exhibit an appreciable red-shift in their fluorescence spectra. The intramolecular interaction between thienyl groups of tetrakis(2-thienyl)methane is supported by DFT calculation.

π-Dimer Formation in an Oligothiophene Tweezer Molecule

An oligothiophene tweezer molecule, which has two quaterthiophene moieties connected to create an electrochemically activated hinge, has been synthesized. Two-electron oxidation of the tweezer molecule produces an intramolecular pi-dimer between the two oligothiophene moieties at room temperature as confirmed by UV-vis absorption, electrochemistry, and EPR experiments.

A Chiroptical Study of Chiral Λ- and X- Type Oligothiophenes Toward Modelling the Interchain Interactions of Chiral Conjugated Polymers

A variety of chiral Λ-type and X-type oligothiophenes (MDC 1–10) was synthesized and studied by means of UV–vis and CD spectroscopy in order to model the chiral interchain interactions of conjugated polymers with optically active side chains in both neutral and oxidized state. It was found that, within the class of chiral Λ-type oligothiophenes, the interchain chiral exciton coupling was only present when using an electronwithdrawing imine linkage between the oligothiophene and the chiral unit (MDC 7–9). Together with the observed decrease in g-value (dissymmetry factor for absorption) by extending the oligothiophene moiety, these linkage and elongation restrictions impose crucial drawbacks on chiral Λ-type oligothiophenes as study model in both neutral and oxidized state. Therefore, a new chiral X-type oligothiophene (MDC 10) was developed that combines chiral exciton coupling in neutral state with the additional ability of oxidation.

Oxidized states of methoxy- and hexyl-oligothiophenes with ferrocenyl groups

Quater-, quinque-, and sexithiophene with two ferrocennyl groups were prepared as model compounds for molecular wires attached terminals. The oligothiophenes, wire moieties, were substituted with methoxy and/or hexyl groups for the purpose of increase in the oxidized ability and the solubility, respectively. The oxidation processes and the oxidized states of the compounds were investigated by cyclic voltammetry, coulometry, and electronic absorption spectroscopy. The electrochemical measurements of quinque- and sexithiophene derivatives show that the oxidized species produced in a ferrocene moiety, terminal, interacts with other ferrocene moiety. The electronic absorption spectra of the one-electron-oxidized oligothiophenes indicate that the oxidized species are spread in the oligothiophene moiety.