3-substituted Thiophene Research Articles

Influence of Chemical Structure on the Charge Transfer State Spectrum of a Polymer:Fullerene Complex

Charge transfer (CT) state properties at the donor:acceptor interface in organic photovoltaic materials are widely regarded as crucial in determining the charge separation efficiency of organic photovoltaic devices. In this work, we use time dependent density functional theory (TDDFT) with B3LYP/6-31g* to study the influence of chemical structure on excitation energies, oscillator strengths, and electronic structure. We vertically excite states in a series of polymer:fullerene blends, modeling each blend as an oligomer:fullerene pair in vacuo. Our method reproduces experimentally observed trends in CT state energy with chemical structure as measured by electroluminescence. For oligothiophene:PCBM (PCBM = [6,6]-phenyl C61-butyric acid methyl ester), we find that Coulomb binding tends to reduce in higher excited CT states. In the case of several isoindigo and diketopyrrolopyrrole (DPP) based donors, we find that the first excited state of the pair lies close in energy to the first singlet of the oligomers, and low excited states have hybrid, or incomplete charge transfer, character. The natures and energies of these states are dependent on the fullerene position. We discuss the effect of thiophene substitution in a DPP polymer on charge generation in terms of the calculated CT state properties and rationalize the observed charge separation efficiency of corresponding experimental systems in terms of these calculations.

Photoalignment Studies on Azo Containing Thiophene Based Acrylates

The photoalignment properties of thin films made from several azo-containing thiophene-based acrylate with respect to the commercially available nematic liquid crystal (MLC 6873-100; ε>o) is reported. As observed, the photoalignment ability of these films is influenced by the number and disposition of fluoro-substituents and the position of attachment of the terminal thiophene moiety. Inclusion of a lateral fluoro-substituent (s) provides excellent photo alignment ability whereas the non-fluorinated counterpart tends to give unsatisfactory alignment quality. The performed study showed also that 2-substituted thiophenes give better photoalignment quality.

Murahashi Coupling Polymerization: Nickel(II)–N-Heterocyclic Carbene Complex-Catalyzed Polycondensation of Organolithium Species of (Hetero)arenes

Revisiting Murahashi coupling, we found that it effectively allows polymerization of lithiated (hetero)arenes by nickel(II)-catalyzed polycondensation. Deprotonative polymerization of 2-chloro-3-substituted thiophene with n-butyllithium gave head-to-tail-type poly(3-substituted thiophene). Poly(1,4-arylene)s were obtained by the reaction of the corresponding dibromides through lithium-bromine exchange. A lithiated thiophene derivative obtained via deprotonative halogen dance also underwent polymerization to afford a bromo-substituted polythiophene.

Facile Preparation of Poly(3-substituted thiophene) Block Copolymers by Nickel-catalyzed Deprotonative Polycondensation without External Generation of Thiophene Organometallic Species

Abstract Thiophene-based block copolymers are synthesized by addition of bromothiophene and the Knochel–Hauser base (TMPMgCl·LiCl). Nickel-catalyzed deprotonative C–H coupling polycondensation of 3-substituted-thiophenes proceeds to give head-to-tail-type poly(3-substituted thiophen-2,5-diyl) bearing nickel at the polymer end. Block copolymers of thiophene derivatives are obtained by successive addition of 2-bromo-3-alkylthiophene and magnesium amide to a living polythiophene end. The use of nickel catalyst bearing an o-tolyl group gives the tolyl-group-terminated thiophene diblock copolymers in high efficiency. Triblock copolymer is also synthesized by the iterative addition of bromothiophene and TMPMgCl·LiCl.

Deprotonative Metalation of Chlorothiophene with Grignard Reagents and Catalytic cis-2,6-Dimethylpiperidine under Mild Conditions

Deprotonative metalation of chlorothiophene takes place with a catalytic amount of cis-2,6-dimethylpiperidine (DMP) and an alkyl Grignard reagent at room temperature for three hours to give the corresponding thienyl Grignard reagent. Polymerization leading to head-to-tail-type poly(3-substituted thiophene) with the thus metalated chlorothiophene proceeds in the presence of a nickel catalyst bearing an N-heterocyclic carbene (NHC) ligand. Palladium-catalyzed cross-coupling reaction with aryl bromides also gives arylated thiophenes in good to excellent yields while the C–Cl bond remains intact.

Synthesis and Characterization of Polythiophene With Liquid Crystalline Azobenzene as Side Chains

In this study a series of azobenzene-functionalized liquid crystalline (LC) polythiophene derivatives: poly{2-[N-ethyl-N- [4-[4′-(nitrophenyl)azo]phenyl]amino]ethyl-3-thiophene acetate}, Poly(Th3AA-RedI), poly{2-[N-ethyl-N-[4-[4′-(nitrophenyl)azo]-phenyl]amino]ethyl-3-thiophene acetate-co-thiophene}, Poly(Th3 AA-RedI-co-Th), poly{2-[N-ethyl-N-[4-[4′-(nitrophenyl)azo]-phenyl]amino]ethyl-3-thiophene acetate-co-pyrrole}, Poly(Th3 AA-RedI-co-py) were synthesized. Novel 3-substituted thiophene with liquid crystalline side chain (Th3AA-RedI) was synthesized by the direct reaction of thiophene -3-acetic acid with 2-[N-ethyl-N-[4-[4′-(nitrophenyl)azo]-phenyl]amino]ethanol (RedI). Chemical polymerization of (Th3AA-RedI), and its copolymerization with thiophene and pyrrole were carried out, by using ferric perchlorate as oxidation agent. The composition, structure and thermal property of these LC polythiophene derivatives were fully characterized by FTIR, 1H,13C-NMR, and UV-Visible spectroscopic methods, and its LC behavior and photoresponsive property were also investigated by polarized optical microscope and differential scanning calorimeter (DSC). The results show that Poly(Th3AA-RedI) exhibited the smecticC (SC) and nematic (N) liquid crystalline behavior. Conclusion shifted phase transition temperatures of the poly(Th3AA-RedI) in the heating process are as follows: C → Sc (108°C), Sc → N (200°C), and N → I (261°C). Electrical conductivity of polymer [poly(Th3AA-RedI)] and of two its copolymers [poly(Th3AA-RedI-co-Th) and poly(Th3AA-RedI-co-Py)], has been studied by four probe methods and produced 3.6 × 10−6, 4.9 × 10−3, and 7.5 × 10−3 Scm−1 conductivities, respectively.

Azo containing thiophene based prop-2-enoates for photoalignment of a nematic liquid crystal

The ability of suitably derived prop-2-enoates from 3-(thiophen-2-yl)- and 3-(thiophen-3-yl)-prop-2-enoic acid and appropriately fluorinated and non-fluorinated 4-[(4-alkoxyphenyl)diazenyl]phenols to promote excellent photoalignment of a bulk commercial nematic liquid crystal is reported. The performed study showed that the photoalignment of the liquid crystal is influenced by the number and disposition of fluoro-substituents and the position of attachment of the terminal thiophene moiety, either 2- or 3-substituted, in the molecular structure of the alignment material. Inclusion of a lateral fluoro-substituent(s) induces an excellent photoalignment whereas the non-fluorinated counterpart tends to give an unsatisfactory alignment. 3-Substituted thiophenes give a better photoalignment than their 2-substituted isomeric counterparts. A prototype display, which contains an alignment layer made from one of the proposed materials, possessing good alignment ability, is presented in order to demonstrate the application potential of these materials in LCDs.

Concise Synthesis of Well‐Defined Linear and Branched Oligothiophenes with Nickel‐Catalyzed Regiocontrolled Cross‐Coupling of 3‐Substituted Thiophenes by Catalytically Generated Magnesium Amide

The synthesis of linear and branched oligothiophenes of well-defined structures is performed with regioselective deprotonation of 3-substituted thiophenes and nickel-catalyzed cross-coupling of the thus formed metalated species with a bromothiophene. The reaction of 3-hexylthiophene with EtMgCl and 2,2,6,6-tetramethylpiperidine (TMP-H, 10 mol%) induces the metalation selectively at the 5-position by use of the catalytically generated hindered magnesium amide (TMPMgCl) and the subsequent reaction of a 2-halo-3-hexylthiophene (bromide or chloride) in the presence of a nickel catalyst affords a head-to-tail (HT)-type dimer. By repeating the same sequence, the linear oligothiophene up to a 4-mer is synthesized in good yield. The reaction of 3-hexylthiophene with 2,3-dibromothiophene also takes place to afford a branched oligothiophene 3-mer in quantitative yield. The obtained 3-mer is also metalated at the sterically less-hindered position in a regioselective manner furnishing a 7-mer in >99% yield after a further coupling reaction with 2,3-dibromothiophene. These dendrimers react with several multifunctionalized organic electrophiles, leading to a variety of branched oligothiophenes.

Dizincation of a 2‐Substituted Thiophene: Constructing a Cage with a [16]Crown‐4 Zincocyclic Core

Metal detector: a bowl-shaped nanomolecule (see picture; S yellow, C gray, Zn blue) containing an unprecedented 16-atom [ZnC(3)](4) "anti-crown" ring has been unearthed by isolating a dizincated 2-substituted thiophene intermediate that would normally be hidden in tandem functionalization methodology.

Dizincation of a 2‐Substituted Thiophene: Constructing a Cage with a [16]Crown‐4 Zincocyclic Core

Dizincation of a 2‐Substituted Thiophene: Constructing a Cage with a [16]Crown‐4 Zincocyclic Core

Gold(I)‐Catalyzed Rearrangement of 3‐Silyloxy‐1,5‐enynes: An Efficient Synthesis of Benzo[b]thiophenes, Dibenzothiophenes, Dibenzofurans, and Indole Derivatives

With the IPr ligand (IPr=1,3-bis-(2,6-diisopropylphenyl)imidazol-2-ylidene) on gold(I) excellent yields in the benzanellation of 2-substituted thiophenes, benzothiophenes, pyrroles, benzofurans, and indoles were achieved. The 1-siloxybut-3-ynyl side chains, incorporated in the anellation, are easily accessible by the addition of a propargyl metal reagent to a formyl group and silylation of the alcohol. This conveniently allows an anellation at the position of the formyl group under mild conditions. All reactions involve a 2,3-shift of the side chain in the anellation step and thus, provide an easy access to specific substitution patterns. Only in the case of 2-substituted indoles with their highly nucleophilic 3-position a direct hydroarylation without shift is observed. On the other hand, 3-substituted indoles give the same products as 2-substituted indoles. Then, a 3,2-shift in the indole ring system has to be involved.

ChemInform Abstract: Transition Metal‐Catalyzed Bond‐Forming Reactions at the C—H Bond of Heteroaromatic Compounds

AbstractReview: ca. 50 refs.

Thiocyanate-free cyclometalated ruthenium sensitizers for solar cells based on heteroaromatic-substituted 2-arylpyridines

The first examples of thiocyanate-free thiophene-substituted Ru(II) cyclometalated complexes, based on thiophene-derived 2-(2,4-difluorophenyl)pyridine ligands, are presented and investigated as photosensitizers in DSCs. Upon thiophene substitution the complexes presented enhanced optical properties compared to the reference dye with no thiophene substitution. DSCs based on the dithienyl-derived dye showed power conversion efficiencies up to 5.7%, more than twice that containing the complex without the thiophene substitution.

Design of benzodithiophene-diketopyrrolopyrrole based donor–acceptor copolymers for efficient organic field effect transistors and polymer solar cells

Three low-band-gap donor–acceptor (D–A) copolymers containing benzo(1,2-b:4,5-b′)dithiophene (BDT), 3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (TDP) or 3,6-di(furan-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (FDP) were designed and synthesized. Their thermal stability, optical and electrochemical properties, device performances for organic field effect transistors (OFETs) and polymer solar cells were systematically investigated. The device performances were significantly enhanced by the introduction of conjugated alkylthienyl side chains to the BDT core and the substitution of thiophene with furan moieties in polymer backbone. Compared to alkoxy side chains, conjugated alkylthienyl chains resulted in higher coplanarity, increased thermal stability (Td increased from 364 °C to 417 °C) and a lower HOMO level (from −5.10 eV to −5.24 eV). The incorporation of furan evidently improved the polymer solubility, leading to a finer phase separation morphology as proved by atomic force microscopy and transmission electron microscopy. After optimization, the designed polymer showed excellent performance in both OFETs and PSCs with an optimal hole mobility of 0.16 cm2 V−1 s−1 and a high power conversion efficiency of 5.54%.

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.

Regioselective Oxidative Couplings of 3-Substituted Thiophenes

This work discloses the oxidative coupling of different arylboronic acids at the C4 position of 3-substituted thiophenes. High regio­selectivities are achieved regarding substitution at C4 vs. C2- or C5-substitution. Due to elevated stability under oxidative conditions, the phosphonates lead to superior product yields than the acetate-substituted thiophenes.

Palladium-Catalysed C2 or C5 Direct Arylation of 3-Substituted Thiophenes with Aryl Bromides

The Pd(OAc)2/dppb system was found to be an efficient catalyst for the direct arylation of 3-substituted thiophene derivatives. The regioselectivity of the arylation strongly depends on the thiophene substituent and also on the nature of the aryl bromide. When using 3-formyl, 3-cyano, 3-methyl, 3-hydroxymethyl or 3-bromothiophene, the 2-arylated thiophenes were obtained with 76-95% regioselectivity; whereas, the arylation of 3-formylthiophene diethylacetal or 3-acetylthiophene gave the 5-arylated thiophenes with 52-90% regioselectivity. The use of congested aryl bromides favours the arylation at C5. These reactions were performed using only 0.1 mol% of catalyst. Moreover, this procedure has been found to be tolerant to a variety of functional groups on the aryl bromide such as formyl, propionyl, benzoyl, nitrile, and nitro.

Regioselective Oxidative Coupling Reactions of 3-Substituted Thiophenes with Arylboronic Acids

Under optimized conditions, 3-substituted thiophenes (EWG = COOEt, PO(OEt)(2)) undergo a facile and regioselective oxidative coupling reaction at carbon atom C4. The reactions were performed with various aryl boronic acids as nucleophiles in the presence of silver oxide (2.0 equiv), cesium trifluoroacetate (tfa) (1.0 equiv), benzoquinone (BQ) (0.5 equiv), and catalytic amounts of Pd(tfa)(2) (10 mol %) employing trifluoroacetic acid (TFA) as the solvent.

Nickel-catalyzed Dehydrobrominative Polycondensation for the Practical Preparation of Regioregular Poly(3-substituted thiophene)s

Abstract Poly(3-hexylthiophene) was synthesized by the polycondensation of 2-bromo-3-hexylthiophene with a nickel catalyst and (2,2,6,6-tetramethylpiperidin-1-yl)magnesium. The polymerization proceeded at room temperature in a highly regioregular manner.

Synthesis and characterization of new 3-substituted thiophene copolymers

This work reports the synthesis of three polymers and two new copolymers based on 3-substituted polythiophene derivatives, all of them demonstrated photoluminescent properties. All polymers synthesized, i.e., poly(3-methoxythiophene) (PMOT), poly(3-thiopheneethanol) (PTE), poly(3-thiophenemethanol) (PTM), poly(3-methoxythiophene-co-3-thiopheneethanol) (PMOT-co-TE) and poly(3-methoxythiophene-co-3-thiophenemethanol) (PMOT-co-TM), were characterized by FT IR, UV-Vis, photoluminescence (PL), thermal analysis (TG and DSC) and X-ray diffraction (XRD). All materials emitted light in the orange region of the visible spectrum. Spectrometric analysis in the infrared region demonstrated the successful synthesis of polymers and copolymers by the presence of characteristic bands. Thermal analysis showed that the obtained materials had good thermal stability.