Mixed-Ligand Approach to Palladium-Catalyzed Direct Arylation Polymerization: Effective Prevention of Structural Defects Using Diamines

Halogen-, oxidant- and directing group-free synthesis of donor-acceptor type conjugated polymers

An intermolecular hydrogen migration from dibutadienylpyridine to dialkynylthiophene catalysed by [Ru(η6-naphthalene)(η4-oxa-bnd)] (oxa-bnd = 9-oxabicyclo[3.3.1]nona-2,6-diene) produces poly(dialkynylthiophene-alt-dibutadienylpyridine). The exact alternating copolymerisation nature is shown by MALDI-TOF MS.

Ru(0)-catalysed cross-dimerisation and -trimerisation of alkynyl- with butadienylheteroarenes

Ru(0)-catalysed cross-dimerisation and -trimerisation give a series of di- and triheteroaryl compounds cross-linked by π-conjugated trienyl groups. Their photochemical behaviour is studied using UV-visible absorption spectra, fluorescence emission spectra, and TD-DFT calculations. The cross-trimer prepared from 2,5-dialkynylthiophene with 2 equiv. of 2-butadienylpyridine shows a longer wavelength shift in the absorption maximum than the cross-trimer prepared from dialkynylbenzene with 1-phenylbutadiene. The solvent effect and the TD-DFT calculations suggest that the planarity of the π-conjugated system contributes more than spontaneous polarization. Namely, in the 5-membered thiophene ring, the conjugated trienyl group extends in the same plane (dihedral angle: -4.0°) as the thienyl group, whereas in the 6-membered benzene ring, the planarity is reduced due to steric hindrance (dihedral angle: -24.1°). Thus, the cross-trimers with a 5-membered heteroaryl centre contribute to longer wavelengths of absorption and fluorescence emission due to the increased planarity of the conjugated trienyl groups.

Direct Heteroarylation Guidelines for Well-Defined Thiophene-Based Conjugated Molecules

Direct (hetero)arylation polymerization (DHAP) shows great promise for simple, low cost, and benign preparation of conjugated polymers. However, coupling selectivity has always posed a problem. Herein, direct (hetero)arylation was studied on small molecule models to develop suitable conditions for C-C couplings between 2-methylthiophene acting as an electron-donating moiety and 2-thiophenecarbonitrile acting as an electron-withdrawing moiety, when one of the partners is brominated. We observed that the best conditions are obtained when the electron-withdrawing moiety is halogenated.

Synthesis of Conjugated Polymers via Transition Metal Catalysed C-H Bond Activation

Transition metal catalysed C-H bond activation chemistry has emerged as an exciting and promising approach in organic synthesis. This allows us to synthesize a wider range of functional molecules and conjugated polymers in a more convenient and more atom economical way. The formation of C-C bonds in the construction of pi-conjugated systems, particularly for conjugated polymers, has benefited much from the advances in C-H bond activation chemistry. Compared to conventional transition-metal catalysed cross-coupling polymerization such as Suzuki and Stille cross-coupling, pre-functionalization of aromatic monomers, such as halogenation, borylation and stannylation, is no longer required for direct arylation polymerization (DArP), which involve C-H/C-X cross-coupling, and oxidative direct arylation polymerization (Ox-DArP), which involves C-H/C-H cross-coupling protocols driven by the activation of monomers' C(sp² )-H bonds. Furthermore, poly(annulation) via C-H bond activation chemistry leads to the formation of unique pi-conjugated moieties as part of the polymeric backbone. This review thus summarises advances to date in the synthesis of conjugated polymers utilizing transition metal catalysed C-H bond activation chemistry. A variety of conjugated polymers via DArP including poly(thiophene), thieno[3,4-c]pyrrole-4,6-dione)-containing, fluorenyl-containing, benzothiadiazole-containing and diketopyrrolopyrrole-containing copolymers, were summarized. Conjugated polymers obtained through Ox-DArP were outlined and compared. Furthermore, poly(annulation) using transition metal catalysed C-H bond activation chemistry was also reviewed. In the last part of this review, difficulties and perspective to make use of transition metal catalysed C-H activation polymerization to prepare conjugated polymers were discussed and commented.

Thieno[3,4-c]pyrrole-4,6-dione-based conjugated polymers for organic solar cells

Thieno[3,4-c]pyrrole-4,6-dione (TPD) based conjugated polymers as an electron donor, acceptor and single-component for application in organic solar cells in the past ten years have been intensively reviewed in this Feature Article.

Theoretical Calculations for Highly Selective Direct Heteroarylation Polymerization: New Nitrile-Substituted Dithienyl-Diketopyrrolopyrrole-Based Polymers

Direct Heteroarylation Polymerization (DHAP) is becoming a valuable alternative to classical polymerization methods being used to synthesize π-conjugated polymers for organic electronics applications. In previous work, we showed that theoretical calculations on activation energy (E_a) of the C–H bonds were helpful to rationalize and predict the selectivity of the DHAP. For readers’ convenience, we have gathered in this work all our previous theoretical calculations on E_a and performed new ones. Those theoretical calculations cover now most of the widely utilized electron-rich and electron-poor moieties studied in organic electronics like dithienyl-diketopyrrolopyrrole (DT-DPP) derivatives. Theoretical calculations reported herein show strong modulation of the E_a of C–H bond on DT-DPP when a bromine atom or strong electron withdrawing groups (such as fluorine or nitrile) are added to the thienyl moiety. Based on those theoretical calculations, new cyanated dithienyl-diketopyrrolopyrrole (CNDT-DPP) monomers and copolymers were prepared by DHAP and their electro-optical properties were compared with their non-fluorinated and fluorinated analogues.

Performance Comparisons of Polymer Semiconductors Synthesized by Direct (Hetero)Arylation Polymerization (DHAP) and Conventional Methods for Organic Thin Film Transistors and Organic Photovoltaics

C-C bond forming reactions are central to the construction of π-conjugated polymers. Classical C-C bond forming reactions such as the Stille and Suzuki coupling reactions have been widely used in the past for this purpose. More recently, direct (hetero)arylation polymerization (DHAP) has earned a place in the spotlight with an increasing number of π-conjugated polymers being produced using this atom-economic and more sustainable chemistry. As semiconductors in organic electronics, the device performances of the polymers made by DHAP are of great interest and importance. This review compares the device performances of some representative π-conjugated polymers made using the DHAP method with those made using the conventional C-C bond forming reactions when they are used as semiconductors in organic thin film transistors (OTFTs) and organic photovoltaics (OPVs).

Synthesis of a 1,2-Dithienylethene-Containing Donor-Acceptor Polymer via Palladium-Catalyzed Direct Arylation Polymerization (DArP)

This paper reports the synthesis of D-A polymers containing 1,2-dithienylethene (DTE) units via palladium-catalyzed direct arylation polymerization (DArP). The reaction of dibromoisoindigo (1-Br) and DTE (2-H), in the presence of Pd₂(dba)₃·CHCl₃ (0.5 mol%), P(2-MeOC₆H₄)₃ (L1) (2 mol%), pivalic acid (1 equiv) as catalyst precursors, and Cs₂CO₃ (3 equiv) as a base affords poly(1-alt-2) with a high molecular weight (Mn up to 44,900). Although, it has been known that monomers, with plural C⁻H bonds, tend to form insoluble materials via direct arylation at undesirable C⁻H positions; the reaction of 1-Br and 2-H cleanly proceeds without insolubilization. The resulting polymer has a well-controlled structure and exhibits good charge transfer characteristics in an organic field-effect transistor (OFET), compared to the polymer produced by Migita⁻Kosugi⁻Stille cross-coupling polymerization. The DArP product displays an ideal linear relationship in the current⁻voltage curve, whereas the Migita⁻Kosugi⁻Stille product shows a VG-dependent change in the charge mobility.

Facile green synthesis of isoindigo-based conjugated polymers using aldol polycondensation

A green and efficient synthetic protocol suitable for the preparation of isoindigo-based polymer was developed using aldol polymerization.

To branch or not to branch: C–H selectivity of thiophene-based donor–acceptor–donor monomers in direct arylation polycondensation exemplified by PCDTBT

The possibility for unselective C–H activation of a thiophene-based, donor–acceptor–donor monomer during direct arylation polycondensation is investigated.

A General Protocol for the Polycondensation of Thienyl N-Methyliminodiacetic Acid Boronate Esters To Form High Molecular Weight Copolymers

Thienyl di-N-methyliminodiacetic acid (MIDA) boronate esters are readily synthesized by electrophilic C–H borylation producing bench stable crystalline solids in good yield and excellent purity. Optimal conditions for the slow release of the boronic acid using KOH as the base in biphasic THF/water mixtures enables the thienyl MIDA boronate esters to be extremely effective homo-bifunctionalized (AA-type) monomers in Suzuki–Miyaura copolymerizations with dibromo-heteroarenes (BB-type monomers). A single polymerization protocol is applicable for the formation of five alternating thienyl copolymers that are (or are close analogues of) state of the art materials used in organic electronics. The five polymers were produced in excellent yields and with high molecular weights comparable to those produced using Stille copolymerization protocols. Therefore, thienyl di-MIDA boronate esters represent bench stable and low toxicity alternatives to highly toxic di-trimethylstannyl AA-type monomers that are currently ubiquitous in the synthesis of these important alternating copolymers.

Direct arylation of fluoroarenes toward linear, bent-shaped and branched π-conjugated polymers: polycondensation post-polymerization approaches

A direct arylation polycondensation of fluoroarenes with 2,7-dibromo-9,9-dioctylfluorene,F8, was achieved in a low polar solvent, toluene.