Palladium-catalyzed Stille Coupling Reaction Research Articles

Synthesis, Photophysical properties and OFET application of thienothiophene and benzothiadiazole based Donor-π-Acceptor-π (D-π -A-π) type conjugated polymers

Novel conjugated donor- π -acceptor- π (D- π -A- π) type polymers (P1-P3), possessing thieno[3,2-b]thiophene (TT) with different aromatic substituents as donors, benzo[1–3]thiadiazole (BT) as an acceptor and thiophene as a π -linker, were designed and synthesized via palladium-catalyzed Stille coupling reaction. Their electronic, optical and thermal properties were investigated using UV–vis and fluorescence spectroscopies, cylic voltammetry, and thermal gravimetric analysis. Photophysical characterizations of these novel polymers showed a remarkable mega Stokes shift, reaching up to 130 nm and optic/electronic band gaps between 1.70 and 2.00 eV, as well as good thermal stability of degradation temperature at around 260 °C. To study the effect of electron donating and withdrawing groups on the electronic properties of the π -extended polymers, their organic field-effect transistors (OFETs) were fabricated and charge transport characteristics were investigated. While all three polymers showed a p-type field-effect behaviour, dimethylamine substituted P3 exhibited the highest average saturated hole mobility, μsat, 0.04 cm2 V−1 s−1, on/off current ratio, Ion/Ioff = 3.0 × 103, and the smallest subthreshold swing, SS, 250 mV dec-1, outperforming similar p-type D- π -A- π semiconducting polymers reported in the literature. The results presented in this work corroborate that the three novel TT-BT polymers have promising potential for electronic and optoelectronic applications, in particular where the tunability of field-effect behaviour is essential for performance.

Synthesis and characterization of D-A type electrochromic polymers based on planar monomers: Cyclopenta[2,1-b;3,4-b′]dithiophene and tris(thienothiophene) as electron donors, diketopyrrolopyrrole as electron acceptor

In this work, starting from cyclopenta[2,1-b;3,4-b′]dithiophene (CPDT) and tris(thienothiophene) (3TT) as donor units, and diketopyrrolopyrrole (DPP) as the acceptor unit, three new solution-processable donor-acceptor conjugated copolymers (P1, P2, P3) were successfully synthesized through the palladium-catalyzed Stille coupling reaction. The monomer molar feeding ratios (CPDT:DPP:3TT) of the three polymers are 3:2:1, 2:1:1, 3:1:2, respectively, which are named as PCPT-1, PCPT-2, and PCPT-3. For comparison purpose, we also synthesized the binary copolymers between CPDT and DPP (PCP), CPDT and 3TT (PCT), and compared their properties with the ternary copolymers. The optical band gaps of the five polymers were all lower than 1.9 eV, and they all showed abundant color changes. During the oxidation process, PCPT-1 changed from purple to cyan-gray and turned to earthy brown finally, PCPT-2 changed from purple in a neutral state to blue-gray in an oxidized state. Similarly, PCPT-3 turned from purple to cement gray and finally oxidized to light blue. PCP polymer changed from dark green in a neutral state to cement gray in an oxidized state, PCT polymer changed from purple in a neutral state to Light gray purple in an oxidized state. The electrochromic kinetic performance study showed that the response time of the five polymers was about 1 s within a 4-second interval. In the dynamic stability test of 750 cycles (6000 s), the five polymers demonstrated good stability. The contrast retention of polymer PCPT-2 at 570 nm reached to as high as 96.17%.

Energy-Level Manipulation in Novel Indacenodithiophene-Based Donor–Acceptor Polymers for Near-Infrared Organic Photodetectors

Organic photodetectors (OPDs) are promising candidates for next-generation digital imaging and wearable sensors due to their low cost, tuneable optoelectrical properties combined with high-level performance, and solution-processed fabrication techniques. However, OPD detection is often limited to shorter wavelengths, whereas photodetection in the near-infrared (NIR) region is increasingly being required for wearable electronics and medical device applications. NIR sensing suffers from low responsivity and high dark currents. A common approach to enhance NIR photon detection is lowering the optical band gap via donor-acceptor (D-A) molecular engineering. Herein, we present the synthesis of two novel indacenodithiophene (IDT)-based D-A conjugated polymers, namely, PDPPy-IT and PSNT-IT via palladium-catalyzed Stille coupling reactions. These novel polymers exhibit optical band gaps of 1.81 and 1.27 eV for PDPPy-IT and PSNT-IT, respectively, with highly desirable visible and NIR light detection through energy-level manipulation. Moreover, excellent materials' solubility and thin-film processability allow easy incorporation of these polymers as an active layer into OPDs for light detection. In the case of PSNT-IT devices, a photodetection up to 1000 nm is demonstrated with a peak sensitivity centered at 875 nm, whereas PDPPy-IT devices are efficient in detecting the visible spectrum with the highest sensitivity at 660 nm. Overall, both OPDs exhibit spectral responsivities up to 0.11 A W-1 and dark currents in the nA cm-2 range. With linear dynamic ranges exceeding 140 dB and fast response times recorded below 100 μs, the use of novel IDT-based polymers in OPDs shows great potential for wearable optoelectronics.

Novel narrow bandgap polymer donors based on ester-substituted quinoxaline unit for organic photovoltaic application

Two narrow bandgap conjugated polymers, PTT-EFQX and PT-DFBT-T-EFQX, comprising a novel bis(2-alkyl) 5,8-dibromo-6,7-difluoroquinoxaline-2,3-dicarboxylate (EF-Qx) unit, are designed and synthesized through palladium-catalyzed Stille coupling reaction. The ester groups and difluorine substituents are introduced into the EF-Qx unit to improve the electron affinity. The polymers containing EF-Qx unit exhibit a relatively narrow bandgap of around 1.6 eV. To optimize the effects of solubility and molecular packing, D-A structure and D-A1-D-A2 structure synthesis strategies are adopted in this work and the structure-property relationship is systematically studied. The results morphology characterizations indicate that the active layer based on D-A structure polymer PTT-EFQX has a superior morphology compared to active layer based on D-A1-D-A2 structure polymer PT-DFBT-T-EFQX, which helps PTT-EFQX-based polymer solar cells (PSCs) to obtain better PCEs of up to 5.4%. Our work demonstrates that the effective design strategy for development of quinoxaline-based polymer donor is necessary for controlling the morphology and thus achieving high-performance PSCs.

Simultaneously enhancing the dielectric constant, photo-response and deepening HOMO levels of benzo[1,2-b;4,5-b']dithiophene derivatives-based conjugated polymers

An alternating conjugated polymer (CPs) named as PBDT-TS-DPP, derived from 2-ethylhexylthiothiophen-2-yl-flanked (TS) benzo[1,2-b;4,5-b']dithiophene (BDT-TS) and diketopyrrolopyrrole derivatives (DPP), was prepared by Palladium-catalyzed Stille coupling reaction. The comparison investigations of the opto-electronic properties and aggregation characteristics between the PBDT-TS-DPP and PBDT-T-DPP, which was derived from 2-ethylhexylthiophen-2-yl-flanked (T) benzo[1,2-b;4,5-b']dithiophene (BDT-T) and DPP, were implemented. The results indicated that the PBDT-TS-DPP not only presented narrower optical band gap, deeper HOMO energy levels, similar charger transporting and aggregation characteristics etc., but also held enhanced relative dielectric constant (εr) in relative to that for the PBDT-T-DPP. To our knowledge, it is firstly to verify that the replacement of T with TS flanks would result in the enhancing εr besides the deepening HOMO energy levels and broadening the light response range for the BDT based CPs. Beyond that, the inverted photovoltaic cells (i-OPVs) with power conversion efficiencies (PCEs) of 5.48% and 4.78%, open circuit voltage (VOC) of 0.78 V and 0.74 V, short current density (JSC) of 11.52 mA/cm2 and 9.46 mA/cm2, fill factors (FF) of 61.0% and 68.3%, were respectively presented in PBDT-TS-DPP and PBDT-T-DPP based i-OPVs. Meanwhile, it has also been certified that the i-OPVs from PBDT-TS-DPP exhibited higher exciton dissociation probability, charge carrier density, charger carriers lifetime, and lower recombination rate co-efficiency etc., which might be attributed to the higher dielectric constant of PBDT-TS-DPP as compared with PBDT-T-DPP, thus devote to the additional improvement of the PCEs, VOC and JSC for the PBDT-TS-DPP based i-OPVs, except that the improvement of the these parameters were compensated from the deepening HOMO energy level and broadening light response of the PBDT-TS-DPP.

Synthesis and electropolymerization of a donor-acceptor-donor trimeric monomer containing 3,4-Propylenedioxythiophene and dithienosilole units

A new dithienosilole and 3,4-propylenedioxythiophene based monomer, namely 2,6-bis(3,3-didecyl-3,4-dihydro-2H-thieno[3,4–b][1,4]dioxepin-6-yl)-4,4-dioctyl-4H-silolo[3,2-b:4,5-b']dithiophene, was synthesized via palladium catalyzed Stille Coupling Reaction and then polymerized electrochemically in an electrolyte solution of 0.1 M lithium perchlorate dissolved in a mixture of dichloromethane and acetonitrile (1:1, v:v). Due to the presence of long alkyl chains on donor and acceptor units, the corresponding polymer was soluble in common organic solvents like tetrahydrofuran, toluene, hexane and dichloromethane. Polymer has both fluorescent and electrochromic properties. Fluorescent polymer emits a reddish pink at 585 nm when excited at 480 nm and the quantum yield was found as 14%. On the other hand, the electrochromic polymer film changed its color from purple to transmissive cyan with 0.65 s switching time upon moving from neutral state to oxidized state and the film has a coloration efficiency of 501 cm2/C as well as 60% optical contrast. The optical band gap of the polymer was also calculated as 1.83 eV with a maximum wavelength at 577 nm.

Synthesis of Pyridinothienogermoles as Unsymmetrically Condensed Germoles

Pyridinothienogermoles (PyTGs) were prepared by the reaction of dilithiopyridylthiophene with dichlorodi(n-octyl)germane and dichlorodiphenylgermane, and their electronic states were investigated by optical measurements and density functional theory (DFT) calculations. Bromination of trimethylsilyl-substituted PyTG with N-bromosuccinimide gave PyTG bromide, and palladium-catalyzed Stille coupling reactions of bromide with diphenyl[(trimethylstannyl)phenyl]amine and N-[(trimethylstannyl)phenyl]carbazole provided donor–acceptor compounds with pyridine as the acceptor and triphenylamine or phenylcarbazole as the donor. These compounds showed clear solvatochromic properties in the photoluminescence (PL) spectra. Bi(pyridinothienogermole) was prepared by the Stille coupling of DPyG bromide and trimethylstannyl-substituted DPyG. The Lewis basicity of the pyridine ring made it possible to use these DPyG derivatives as ligands for complex formation. Protonation and complex formation of the PyTG pyridine unit with...

Synthesis and characterization of a low band gap polymer based on cyclopentadithiophene and thieno[3,4-b]thiophene

ABSTRACTA low band gap polymer based on thieno[3,4-b]thiophene (TT) and cyclopentadithiophene (CPDT), named as P-TT, was synthesized through palladium-catalyzed Stille coupling reaction. Due to the strong electron-donating property of CPDT and quinoidal structural TT, P-TT exhibited narrow band gap (1.30 eV). Optical and thermal properties of P-TT had been investigated.

A low band gap diketopyrrolopyrrole-based polymer: Synthesis, thermal and optical properties

ABSTRACTIn this work, P-DPP, which was a low band gap polymer based on diketopyrrolopyrrole (DPP) and cyclopentadithiophene (CPDT), was synthesized through palladium-catalyzed Stille coupling reaction. Due to the strong electron-donating property of CPDT and strong withdrawing property of DPP, P-DPP exhibited narrow band gap of 1.29 eV. The thermal and optical properties of P-DPP had been carefully investigated.

Growth of thiophene based oligomers using Stille and direct arylation methods for optoelectronic applications

Palladium catalyzed Stille coupling reactions are extensively used for the preparation of functionalised thiophene based polymers. In addition, polycondensation via direct C-H arylation produces alternating copolymers in moderate yields. In the present work, we report the synthesis and optoelectronic properties of thiophene based compounds having rigid cycloalkanone and a novel hexhydro-2H-indazole spacers in between. X-ray diffraction analysis shows the semi-crystalline nature of the synthesized materials with extensive side chain crystallinity. Band-gap energy of the synthesized materials has been obtained experimentally via optical and electrochemical methods and theoretically via computational studies. Open aperture Z-Scan results confirm the competence of these materials as optical limiters (NLO) while the photoluminescence emission characteristics and Schottky diode characteristics indicate their application prospects in Polymer Light Emitting Diodes (PLEDs). Polymers having hexhydro-2H-indazole spacers appear to be promising candidates for optoelectronic applications.

Low-bandgap conjugated polymers based on alkylthiothienyl-substituted benzodithiophene for efficient bulk heterojunction polymer solar cells

Three two-dimensional (2D) conjugated polymers, named PBDTSDPP-1, PBDTSDPP-2, and PBDTSDPP-3, based on benzo[1,2-b:4,5-b’]dithiophene (BDT) donor unit with conjugated alkylthiothiophene side chain and diketopyrrolopyrrole (DPP) acceptor unit, were designed and synthesized via palladium-catalyzed Stille-coupling reaction. The resulting polymers exhibited good thermal stability with a high decomposition temperature over 350 °C and a broad absorption in the range from 400 to 900 nm. The HOMO energy levels of the polymers are deeper than −5.39 eV and the LUMO energy levels of them are higher than −4.09 eV. The field effect transistors prepared from PBDTSDPP-1, PBDTSDPP-2 and PBDTSDPP-3 provide a hole mobility of 3.52 × 10−3, 3.85 × 10−4 and 4.36 × 10−3 cm2 V−1 s−1, respectively. The photovoltaic properties of the polymer as donor was investigated with an inverted structure of ITO/PEIE/polymer:PC71BM/MoO3/Ag. As a preliminary result, PBDTSDPP-1, PBDTSDPP-2, and PBDTSDPP-3 showed power conversion efficiency (PCE) of 4.75%, 3.56%, and 5.28%, respectively. The short-circuit current density (JSC) and PCE value of PSCs based on PBDTSDPP-3 are higher than those of the other two polymers because of better morphology, higher and more balanced charge-carrier mobilities, leading to less recombination loss.

Synthesis of a selenium and germanium containing random copolymer as an acceptor for all‐polymer solar cells

For the need of electron‐transporting and electron‐affinity materials, n‐type polymers (as acceptor) have gained a lot of attention recently. We have synthesized a selenium and germanium containing copolymer as the acceptor for all‐polymer solar cells (all‐PSCs). The copolymer has larger p‐orbital selenium and germanium atoms for more electron transition from pi to pi* to enlarge light harvest of polymer. To prepare the copolymer, a monomer containing d‐orbital atom, selenium, was first synthesized from low‐cost starting materials. A random copolymer was prepared from the monomer with a commercial germanium containing monomer via palladium catalyzed Stille coupling reaction. Taking the side‐chain effect into account, we incorporated dodecyloxy group to increase the solubility of the polymer and also increase the coplanarity by oxygen–sulfur (S–O) interaction. Despite the low short‐circuit current density (Jsc) value, the random copolymer with 3d‐orbital electrons has the potential to be the candidate for n‐type material. In comparison, we also fabricated P3HT/PffBT4T‐2OD all‐PSCs, acquiring PCE of about 0.5% without any additive. POLYM. ENG. SCI., 58:387–394, 2018. © 2017 Society of Plastics Engineers

Highly selective palladium-catalyzed Stille coupling reaction toward chlorine-containing NIR electroluminescent polymers

Chlorine-containing conjugated polymers were obtained by the optimized Stille coupling reaction; non-doped PLEDs of the polymers exhibited NIR emission.

Design, synthesis and photovoltaic properties of two π-bridged cyclopentadithiophene-based polymers

Two fluorinated D–A type conjugated polymers, PCPDT-DTFBT (P1) and PCPDT-DTDFBT (P2) with an extended π-bridge, were synthesized through the palladium-catalyzed Stille coupling reaction. Both P1 and P2 exhibit a narrow band gap (1.63 eV for P1 and 1.60 eV for P2) and low lying energy level with the highest-occupied molecular orbital (HOMO) of −5.16 and −5.19 eV, respectively. Because of the insertion of the 4-hexylthiophene π-bridge between the donor and acceptor units, P1 and P2 exhibit excellent solubility in common organic solvents. Particularly for P2, the improved solubility was conducive to the film forming ability with a root-mean-square roughness (RMS) value of 3.60 nm and a nanoscale bicontinuous interpenetrating network in the active layer. As a result, a short-circuit current (JSC) of 13.58 mA cm−2, an open circuit voltage (VOC) of 0.70 V, and a fill factor (FF) of 61.6% were obtained, giving a high energy conversion efficiency (PCE) of 5.85% after device optimization.

Two-dimensional benzodithiophene and benzothiadiazole based solution-processed small molecular organic field-effect transistors & solar cells

Benzodithiophene (BDT) and benzothiadiazole (BT) based small molecules have been synthesized through palladium-catalyzed Stille coupling reactions. The molecules with and without the conjugated thiophene side-chain were named as DRTBTTBDTT (2D) and DRTBTTBDT (1D), respectively. These molecules exhibited an optical band gap of around 1.8 eV. Solution-processed thin films of 1D and 2D showed that the conjugated thiophene side-chain oriented to produce a uniform 2D structure, which led to a relatively high hole mobility of 0.016 cm2 V−1 s−1, and this was one of the highest values for solution-processed small-molecule donors in organic solar cells (OSCs). With proper engineering of energy levels, the organic solar cells based on DRTBTTBDTT (2D) as donors exhibited a high Voc of around 0.9 V.

Synthesis, photophysics, and photovoltaic properties of low-band gap conjugated polymers based on thieno[3,4-c]pyrrole-4,6-dione: a combined experimental and computational study

Four novel donor–acceptor (D–A) alternating copolymers were designed and successfully synthesized by the palladium-catalyzed Stille coupling and Suzuki coupling reactions. Utilizing thieno[3,4-c]pyrrole-4,6-dione (TPD) as an acceptor comonomer coupled with dialkoxybithiophene or cyclopentadithiophene as the donor gave polymers PTBT and PTCT. Employing carbazole as the donor and the dithiophene-substituted TPD serving as the acceptor monomers yielded polymers PTC1 and PTC2. Owing to the various strengths of electronic coupling between the donors and the acceptor unit, the band gaps of these polymers can be adjusted from 1.57 to 1.90 eV. Due to the different electron-donor ability of dialkoxybithiophene, cyclopentadithiophene, and carbazole, the HOMO energy levels of polymers were tuned from −5.34 to −5.67 eV, while LUMO levels remained relatively unchanged. The theoretical calculations provided insight to the observed photophysical properties of these polymers. Theoretically estimated band gaps and oxidation potentials correlate well with the experimental data. Carrier mobility and photovoltaic properties of TPD polymers were also investigated for which 1.3% power conversion efficiency was obtained from a blend of PTCT:PC71BM (1:2) bulk-heterojunction device.

Synthesis and Properties of Soluble and Stable Silyl End-capped Bis-thienylanthracene Oligomers

A series of new organic semiconductors dimethyl-n-octylsilyl end-capped thiophene-anthracene oligomers containing 9,10-anthracene moiety in the center have been synthesized using palladium-catalyzed Stille coupling reactions. The synthesized bis-silylated thiophene-anthracene oligomers were characterized by 1 H-NMR, 13 C-NMR and high-resolution mass spectroscopy, and are observed to have remarkably high solubility in common organic solvents. Their optical, thermal and electrochemical properties were measured. UV-vis absorption and emission spectral data on bis-silylated-, di-hexylated- and unsubstituted-thiophene-anthracene oligomers indicate that their absorption maxima are independent upon the presence of the kind of substitution in dilute solution while end-capped long-alkyl chain containing silyl groups enhance conjugation of arene backbone of the oligomers in solid film states. Absorption maxima of bis-quarterthienylanthracene in solution is closer to those obtained α,ω-dihexylsexithiophene (DH-6T). For oligomer bis-bithienylanthracene, bis-terthienylanthracene and bis-quarterthienylanthracene the main endothermic peaks are detected at 84 °C, 120 °C and 194 °C, respectively which indicate that the end-capped silyl groups lead to decrease about 100 °C comparing to the corresponding end-capped hexyl groups. Electrochemical measurements indicate that bis-silylated thiophene-anthracene oligomers have better oxidation stability than the corresponding oligothiophenes without anthracene core. Bis-quarterthienylanthracene 3 still has low HOMO level in spite that it contains totally nine arene rings in the oligomeric molecules.

Dibenzothiophene derivatives as new prototype semiconductors for organic field-effect transistors

New prototype semiconductor materials based on dibenzothiophene (DBT) derivatives were successfully synthesized by a convergent approach using palladium catalyzed Stille coupling reactions. Thermogravimetric analysis, UV-vis spectra and electrochemistry results indicated these materials had good thermal and photooxidation stability. X-Ray diffraction measurements of the vacuum-evaporated films showed enhanced crystalline order with increasing substrate deposition temperature. The ordered vacuum-evaporated films with charge carrier mobility as high as 7.7 × 10−2 cm2 V−1 s−1 and an on/off ratio of nearly 1 × 107 had been achieved with 3,7-bis(5′-hexyl-thiophen-2′-yl)-dibenzothiophene (3,7-DHTDBTT). These results suggest that the 3,7-substituted DBT system is a good prototype for new type organic semiconductors and will play a more important role in organic semiconductors.

A Novel Heteroditopic Terpyridine-Pincer Ligand as Building Block for Mono- and Heterometallic Pd(II) and Ru(II) Complexes

A palladium-catalyzed Stille coupling reaction was employed as a versatile method for the synthesis of a novel terpyridine-pincer (3, TPBr) bridging ligand, 4'-{4-BrC6H2(CH2NMe2)2-3,5}-2,2':6',2' '-terpyridine. Mononuclear species [PdX(TP)] (X = Br, Cl), [Ru(TPBr)(tpy)](PF6)2, and [Ru(TPBr)2](PF6)2, synthesized by selective metalation of the NCNBr-pincer moiety or complexation of the terpyridine of the bifunctional ligand TPBr, were used as building blocks for the preparation of heterodi- and trimetallic complexes [Ru(TPPdCl)(tpy)](PF6)2 (7) and [Ru(TPPdCl)2](PF6)2 (8). The molecular structures in the solid state of [PdBr(TP)] (4a) and [Ru(TPBr)2](PF6)2 (6) have been determined by single-crystal X-ray analysis. Electrochemical behavior and photophysical properties of the mono- and heterometallic complexes are described. All the above di- and trimetallic Ru complexes exhibit absorption bands attributable to (1)MLCT (Ru --> tpy) transitions. For the heteroleptic complexes, the transitions involving the unsubstituted tpy ligand are at a lower energy than the tpy moiety of the TPBr ligand. The absorption bands observed in the electronic spectra for TPBr and [PdCl(TP)] have been assigned with the aid of TD-DFT calculations. All complexes display weak emission both at room temperature and in a butyronitrile glass at 77 K. The considerable red shift of the emission maxima relative to the signal of the reference compound [Ru(tpy)2]2+ indicates stabilization of the luminescent 3MLCT state. For the mono- and heterometallic complexes, electrochemical and spectroscopic studies (electronic absorption and emission spectra and luminescence lifetimes recorded at room temperature and 77 K in nitrile solvents), together with the information gained from IR spectroelectrochemical studies of the dimetallic complex [Ru(TPPdSCN)(tpy)](PF6)2, are indicative of charge redistribution through the bridging ligand TPBr. The results are in line with a weak coupling between the {Ru(tpy)2} chromophoric unit and the (non)metalated NCN-pincer moiety.

Synthesis and photovoltaic properties of mono-substituted quaterthiophenes bearing strong electron-withdrawing group

We report here on the synthesis and properties of a monosubstituted quaterthiophene derivative asymmetrically functionalized by an electron-withdrawing group using the palladium-catalyzed Stille's coupling reaction. The UV–vis absorption spectrum evidences a strong intramolecular charge transfer transition. Thus oligothiophenes act as electron donors and substituent group as acceptor. The diodes in which monosubstituted quaterthiophenes behave as organic semiconductors, exhibit a rectifying behavior. Photovoltaic measurements show moderate power conversion efficiency.