Synthesis of Poly(3‐hexylthiophene) with a Narrower Polydispersity

Summary: The polymerization of 2‐bromo‐3‐hexyl‐5‐iodothiophene ( 1 ) with isopropylmagnesium chloride and Ni(dppp)Cl₂ was quenched with 5 M hydrochloric acid instead of water to yield head‐to‐tail poly(3‐hexylthiophene) (HT‐P3HT) with a very low polydispersity. The of the polymer was controlled by the feed ratio of 1 to Ni(dppp)Cl₂. Quenching with 5 M hydrochloric acid seemed to promote protonolysis of HT‐P3HT‐Ni complexes before the coupling reaction between HT‐P3HT.

GPC profiles of HT‐P3HT obtained after quenching with water and 5 M hydrochloric acid, respectively.     

Precision Synthesis of Poly(3‐hexylthiophene) from Catalyst‐Transfer Suzuki−Miyaura Coupling Polymerization

^tBu₃ PPd(Ph)Br ( 1 )‐catalyzed Suzuki‐Miyaura coupling polymerization of 2‐(4‐hexyl‐5‐iodo‐2‐thienyl)‐4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolane ( 2 ) was investigated. Monomer 2 was polymerized with 1 at 0 °C in the presence of CsF and 18‐crown‐6 in THF containing a small amount of water to yield P3HT with a narrow molecular weight distribution and almost perfect head‐to‐tail regioregularity. The values increased up to 11 400 g · mol⁻¹ in proportion to the feed ratio of 2 to 1 . The MALDI‐TOF mass spectra showed that P3HT with moderate molecular weight uniformly had a phenyl group at one end and a hydrogen atom at the other, indicating involvement of a catalyst‐transfer mechanism. Successive 1 ‐catalyzed polymerization of fluorene monomer 3 and then 2 yielded a well‐defined block copolymer of polyfluorene and P3HT.

     

Regioregular Poly(3‐hexylthiophene) in a Novel Conducting Amphiphilic Block Copolymer

Regioregular poly(3‐hexylthiophene) has been successfully incorporated into a novel amphiphilic block copolymer. The amphiphilic nature of poly(3‐hexylthiophene)‐block‐poly(acrylic acid) has been investigated using spectroscopic methods and has yielded solvatochromic behavior in several solvents of varying polarity. Evidence suggests that a supramolecular, long range ordering of block copolymer occurs in polar solvents, resulting in the formation of aggregates. Despite relatively large amounts of non‐conductive blocks, the poly(3‐hexylthiophene) diblock copolymer yields a high conductivity of 1 S · cm⁻¹, and atomic force microscopy shows the formation of a highly organized nanofibrilar morphology in the solid state.

     

Balanced Ambipolar Poly(diketopyrrolopyrrole‐alt‐tetrafluorobenzene) Semiconducting Polymers Synthesized via Direct Arylation Polymerization

The synthesis of an ambipolar π‐conjugated copolymer consisting of alternating diketopyrrolopyrrole and tetrafluorobenzene via direct arylation polymerization (DAP) is reported. Two different combinations of monomers are investigated under various catalytic conditions for DAP. The target polymer obtained under an optimized catalytic condition shows minimal structural defects, a number‐average molecular weight of 33.2 kDa, and balanced electron and hole mobility of 1 × 10⁻² cm² V⁻¹ S⁻¹ in the organic field‐effect transistors fabricated and tested under ambient conditions.

     

Synthesis and Characterization of a Block Copolymer Containing Regioregular Poly(3‐hexylthiophene) and Poly(γ‐benzyl‐L‐glutamate)

Poly(3‐hexylthiophene)‐b‐poly(γ‐benzyl‐L ‐glutamate) (P3HT‐b‐PBLG) rod–rod diblock copolymer was synthesized by a ring‐opening polymerization of γ‐benzyl‐L ‐glutamate‐N‐carboxyanhydride using a benzylamine‐terminated regioregular P3HT macroinitiator. The opto‐electronic properties of the diblock copolymer have been investigated. The P3HT precursor and the P3HT‐b‐PBLG have similar UV–Vis spectra both in solution and solid state, indicating that the presence of PBLG block does not decrease the effective conjugation length of the semiconducting polythiophene segment. The copolymer displays solvatochromic behavior in THF/water mixtures. The morphology of the diblock copolymer depends upon the solvent used for film casting and annealing results in morphological changes for both films deposited from chloroform and trichlorobenzene.

     

Optimization of direct arylation polymerization conditions for the synthesis of poly(3‐hexylthiophene)

Direct arylation polymerization (DArP) is an emerging alternative to Stille and Suzuki polymerizations. This method is attractive as it allows preparation of high‐molecular‐weight conjugated polymers in good yield without the need to metallate monomers. Despite this promise, for poly(3‐hexylthiophene) (P3HT) and related polymers that have β‐protons on the thiophene ring, DArP is known to produce β‐defects, which make the polymer properties different from polymers produced by traditional methods. Here, we demonstrate that DArP conditions based on simple, inexpensive, and bench‐stable reagents can be tuned to limit the amount of defects and produce P3HT with properties remarkably similar to Stille P3HT. Specifically, lowering the reaction temperature, lowering the amount of catalyst, and using a bulkier carboxylate ligand is critical. Optimized conditions include reacting 2‐bromo‐3‐hexylthiophene with 0.25 mol % of Pd(OAc)₂, 1.5 equivalents of K₂CO₃, and 0.3 equivalents of neodecanoic acid in N,N‐dimethylacetamide at 70 °C and give DArP P3HT with ～60% yield, regioregularity of 93.5%, molecular weight of 20 kDa, polydispersity of 2.8, and melting point of 217 °C, providing a very close match to Stille P3HT, which is obtained with 70–80% yield, 91–94% regioregularity, molecular weight of 15–25 kDa, polydispersity of 2.5–2.8, and melting point of 214–221 °C. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2660–2668     

The effect of amide solvent structure on the direct arylation polymerization (DArP) of 2‐Bromo‐3‐hexylthiophene

In this work, we investigate the influence of the amide solvent chemical structure on the properties of poly(3‐hexylthiophene) (P3HT) prepared via direct arylation polymerization (DArP). Our findings indicate that for successful polymerization the amide must possess an acyclic aliphatic structure since cyclization of an amide results in a complete shutdown of DArP reactivity as evidenced by failed polymerization in N‐methylpyrrolidone, whereas the presence of an aromatic motif renders the amide solvent susceptible to C? H activation and leads to incorporation of the solvent structure into the P3HT backbone, as demonstrated on the example of N,N‐diethylbenzamide. Additionally, we observed that the steric bulk of alkyl substituents on both the nitrogen atom and the carbonyl group within the amide structure has to be delicately balanced for optimal DArP reactivity. In the optimal cases, P3HT is obtained in high yield, with high molecular weight and contains a minimal amount of structural defects. The obtained polymer samples were comprehensively studied in terms of their chemical structure, optical, thermal and solid‐state properties in thin films using GPC analysis, ¹H NMR, MALDI, UV–vis, GIXRD spectroscopy, and DSC. We additionally note a drastic difference of the amide solvent effect between DArP and Stille polymerization. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2494–2500     

Synthesis of π‐Conjugated Polymer Consisting of Pyrrole and Fluorene Units by Ru‐Catalyzed Site‐Selective Direct Arylation Polycondensation

Polycondensation of 1‐(2‐pyrimidinyl)pyrrole with 2,7‐dibromo‐9,9‐dioctylfluorene via Ru‐catalyzed direct arylation gives the corresponding conjugated polymer with a molecular weight of 19 800 in 86% yield. The introduction of directing group, 2‐pyrimidinyl substituent, into the pyrrole monomer induces ortho‐metalation and provides the site‐selective direct arylation polycondensation at the α‐position of pyrrole unit without the protection of β‐position. The removal of 2‐pyrimidinyl substituent on the pyrrole unit proceeds efficiently and results in the enhancement of coplanarity along the main chain of the polymer.

     

Pd‐Catalyzed Synthesis of α‐Aryl Vinylphosphonates via Suzuki Arylation of α‐Phosphonovinyl Nonaflates

The first palladium‐catalyzed method for the arylation of α‐phosphonovinyl nonaflates is described. Using a catalyst comprised of Pd(OAc)₂ and SPhos, terminal and internal α‐aryl vinylphosphonates could be efficiently accessed under mild conditions. The reaction features a broad coupling partner scope and tolerates many functional groups.     

Biocompatibility Studies of Functionalized Regioregular Poly(3‐hexylthiophene) Layers for Sensing Applications

There is a significant medical and biological need for cheap disposable analytical sensing devices, which can be used in clinical settings or medical research. Organic electronics based on polymeric materials, being suitable for large‐area, low‐cost, flexible, and maybe even disposable electronics, could satisfy this need in a very elegant way. Unfortunately, the ensurance of biocompatibility and biofunctionalization of conducting and semiconducting polymers is still often lacking. In the present study, we concentrate on one of the most promising polymeric materials, regioregular poly(3‐hexylthiophene) (P3HT), being both a reasonably conducting and optically active polymer. To overcome biocompatibility problems, protein‐based coatings and oxygen‐plasma treatments are performed to enable growth of adherent living cells on those modified surfaces. For our studies, the polymer material is spun or casted onto glass substrates under an inert nitrogen atmosphere. The toxic solvents are removed by thermal treatment with subsequent application of the coating or functionalizing materials. Cell‐growth studies and adhesion experiments on the modified P3HT thin‐film layers are carried out with mouse fibroblasts. This work demonstrates the biocompatibility and biofunctionalization of an active semiconducting organic polymer, hence opening new possibilities in the realization of biomedical test systems based on organic biosensors in life sciences.

     

Pd‐Catalysed Direct Arylation Polymerisation for Synthesis of Low‐Bandgap Conjugated Polymers and Photovoltaic Performance

Low‐bandgap conjugated copolymers based on a donor–acceptor structure have been synthesised via palladium‐complex catalysed direct arylation polymerisation. Initially, we report the optimisation of the synthesis of poly(cyclopentadithiophene‐alt‐benzothiadiazole) (PCPDTBT) formed between cyclopentadithiophene and dibromobenzothiadiazole units. The polymerisation condition has been optimised, which affords high‐molecular‐weight polymers of up to M _n = 70 k using N‐methylpyrrolidone as a solvent. The polymers are used to fabricate organic photovoltaic devices and the best performing PCPDTBT device exhibits a moderate improvement over devices fabricated using the related polymer via Suzuki coupling. Similar polymerisation conditions have also been applied for other monomer units.     

Copper(I)‐Catalyzed Intramolecular Direct C‐Arylation of Azoles with Aryl Bromides

A concise route to access 5H‐imidazo[2,1‐a]isoindole heterofused compounds by copper(I)‐catalyzed intramolecular coupling of non‐activated aryl bromides with azoles is reported. With CuI as catalyst, 1,10‐phenanthroline as ligand, and K₃PO₄ as base, the reactions of 1‐(2‐bromobenzyl)‐1H‐imidazoles in DMF/o‐xylene (1:1, V:V) at 145°C afford the corresponding substituted 5H‐imidazo[2,1‐a]isoindoles in high yields via intramolecular C‐arylation.     

Stille Catalyst‐Transfer Polycondensation Using Pd‐PEPPSI‐IPr for High‐Molecular‐Weight Regioregular Poly(3‐hexylthiophene)

A commercially available palladium N‐heterocyclic carbene (Pd‐NHC) precatalyst is used to initiate chain‐growth polymerization of 2‐bromo‐3‐hexyl‐5‐trimethylstannylthiophene. The molecular weight of the resultant poly(3‐hexylthiophene) can be modulated (7 to 73 kDa, Đ = 1.14 to 1.53) by varying the catalyst concentration. Mass spectrometry data confirm control over the polymer end groups and ¹H NMR spectroscopy reveals that the palladium catalyst is capable of “ring‐walking”. A linear relationship between M_n and monomer conversion is observed. Atomic force microscopy and X‐ray scattering verify the regioregular nature of the resultant polythiophene.

     

Palladium‐Catalyzed α‐Arylation of Arylketones at Low Catalyst Loadings

A general catalytic protocol for the α‐arylation of aryl ketones has been developed. It involves the use of a preformed, bench‐stable Pd–N‐heterocyclic carbene pre‐catalyst bearing IHept as an ancillary ligand, and allows the coupling of various functionalized coupling partners at very low catalyst loading. Careful choice of the solvent/base system was crucial to obtain optimum catalyst performance. The pre‐catalyst was also successfully tested in the synthesis of an industrially relevant compound.     

Minimization of the auxiliary reagent loading for direct arylation polymerization (DArP) of 2‐bromo‐3‐hexylthiophene

In this work, we present a powerful set of synthetic strategies aimed at minimization of auxiliary reagent loading for direct arylation polymerization (DArP) of 2‐bromo‐3‐hexylthiophene. As such, we report efficient lowering of Pd(OAc)₂ catalyst loading as well as loading of other auxiliary reagents, such as neodecanoic acid and N,N‐dimethylacetamide. Unprecedented low loadings of catalyst down to 0.0313% (313 ppm) were achieved, while producing polymer in high yield (91% after Soxhlet extraction), with a high molecular weight (24.2 kDa) and carefully controlled chemical structure thus making the optimized DArP protocol significantly more cost‐effective, convenient, sustainable, and environmentally friendly. The resulting polymer samples were thoroughly investigated in terms of their chemical structure as well as optical, thermal, chain ordering and electronic properties using GPC analysis, ¹H NMR, MALDI, UV–vis, GIXRD spectroscopy, DSC, and SCLC hole mobility measurements. The results demonstrate that the reagent lowering strategies increase the polymer regioregularity from 94.6 to 96.5% as evidenced by ¹H NMR spectra and corroborated by GIXRD, DSC, and UV–vis measurements. Additionally, polymer samples obtained at low reagent loading are more uniformly proton‐terminated as evidenced by ¹H NMR and MALDI end‐group analysis. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1492–1499     

Functional syndiotactic poly(β‐hydroxyalkanoate)s via stereoselective ring‐opening copolymerization of rac‐β‐butyrolactone and rac‐allyl‐β‐butyrolactone

The copolymerization of racemic β‐butyrolactone (rac‐BL^Me) with racemic “allyl‐β‐butyrolactone” (rac‐BL^allyl) in toluene, catalyzed by the discrete amino‐alkoxy‐bis(phenolate) yttrium‐amido complex 1 , gave new poly(β‐hydroxyalkanoate)s with unsaturated side chains. The poly(BL^Me‐co‐BL^allyl) copolymers produced have a highly syndiotactic backbone structure (P_r = 0.80–0.84) with a random enchainment of monomer units, as evidenced by ¹³C NMR, and high molecular weight (M_n up to 58,000 g mol^?1) with a narrow polydispersity (M_w/M_n = 1.07–1.37), as determined by GPC. The comonomer incorporation (5–50 mol % rac‐BL^allyl) was a linear function of the feed ratio. The pendant vinyl bond of the side‐chains in those poly(BL^Me‐co‐BL^allyl) copolymers allowed the effective introduction of hydroxy or epoxy groups via dihydroxylation, hydroboration‐oxidation or epoxidation reactions. NMR studies indicated that all of these transformations proceed in an essentially quantitative conversion and do not affect the macromolecular architecture. Some thermal properties (T_m, ΔH_m, T_g) of the prepared polymers have been also evaluated. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3177–3189, 2009     

Palladium(II)‐N‐Heterocyclic Carbene Complexes: Efficient Catalysts for the Direct C‐H Bond Arylation of Furans with Aryl Halides

This paper contains the synthesis and characterization of the seven new benzimidazolium salts and their corresponding new palladium(II)‐NHC complexes with the general formula [PdX₂(NHC)₂], (NHC = N‐heterocyclic carbene, X = Cl or Br), and also their catalytic activity in direct C‐H bond arylation of 2‐substituted furan derivatives with aryl bromides and aryl chlorides. Under the optimal conditions, these palladium(II)‐NHC complexes showed the good catalytic performance for the direct C‐H bond arylation of 2‐substituted furans with (hetero)aryl bromides, and with readily available and inexpensive aryl chlorides. The C‐H bond arylation regioselectively produced C5‐arylated furans by using 1 mol% of the palladium(II)‐NHC catalysts in moderate to high yields.     

Synthesis and spectroscopic investigation of π‐conjugated (E)‐enyne polycarbazole with different organo‐metallic catalysts from 3,6‐diethynyl‐9‐(2‐ethylhexyl)carbazole

In the present study, a new (E)‐rich‐enyne π‐conjugated polymer containing a carbazole was designed and synthesized. Two different synthesis methods of poly[N‐(2‐ethylhexyl)‐3,6‐carbazolyleneethynylene‐(E)‐vinylene] (PCZEV) have been prepared from 3,6‐diethynyl‐9(2‐ethylhexyl)carbazole by using the palladium‐carbene‐catalyzed reaction and/or by using the organolanthanide‐catalyzed reaction leading to well‐defined polymer, and their general properties were studied. Compared to poly[N‐(2‐ethylhexyl)‐3,6‐carbazolyleneethynylene] (PCE), the UV‐vis absorption and photoluminescence of the PCZEV was red‐shifted, which indicates the extension of conjugation length. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2434–2442, 2009