Direct Hetero Arylation Polymerization Research Articles

Synthesis of 1,4‐dihydropyrrolo[3,2‐b]pyrrole‐containing donor–acceptor copolymers and their optoelectronic properties

AbstractDonor–acceptor (D–A)‐conjugated polymers have achieved promising performance metrics in numerous optoelectronic applications that continue to motivate studying structure–property relationships and discovering new materials. Here, the materials toolbox is expanded by synthesizing D–A copolymers where 1,4‐dihydropyrrolo[3,2‐b]pyrrole (DHPP) is directly incorporated into the main chain of D–A copolymers for the first time via direct heteroarylation polymerization. Notably, the synthetic complexity of DHPP‐containing polymers coupled with thieno[3,2‐b]pyrrole‐4,6‐dione (TPD) or 3,6‐bis(2‐thienyl)‐2,5‐dihydropyrrolo[3,4‐c]pyrrole‐1,4‐dione (Th2DPP) comonomers is calculated to be lower compared to many common conjugated polymers synthesized via direct arylation. The electron‐rich nature of DHPPs when coupled with TPD or DPP enables optoelectronic properties to be manipulated, evident by measuring distinctly different absorbance and redox properties. Additionally, these D–A copolymers demonstrate their potential in organic electronic applications, such as electrochromics and organic photovoltaics. The reported DHPP‐alt‐Th2DPP copolymer is the first DHPP‐based colored‐to‐transmissive electrochrome and achieves power conversion efficiencies of ~2.5% when incorporated into bulk heterojunction solar cells. Overall, the synthetic accessibility of DHPP monomers and their propensity to participate in robust polymerizations highlights the value of establishing structure–property relationships of an underutilized scaffold. These fundamental attributes serve to inform and advance efforts in the development of DHPP‐containing copolymers for various applications.

Electrochromic conjugated polymers containing benzotriazole and thiophene performing sub-second response time and 916 cm2 C−1 superb coloration efficiency

In pursuit of high-performance electrochromic conjugated polymers (ECPs), three benzotriazole-thiophene ECPs employing benzotriazole as acceptor and different thiophene repeating units as donors, namely, PBTz-T, PBTz-BT, and PBTz-TT, were synthesized via direct (hetero)arylation polymerization (DHAP). Meanwhile, following the above ECPs model, we investigated the effect of corresponding conjugated chain length of monomers on their optical, electrochemical and electrochromic properties. The results showed that along with the increase of the numbers of thiophene in the repeating unit of ECPs, the electronic and optical band gaps decreased, the UV–Vis absorption and fluorescence spectra showed significant bathochromic shift, and the electrochemical cycle stability gradually improved. PBTz-T exhibited giant coloration efficiency (916 cm2 C−1 at 530 nm), which is one of the best results in the visible region. And higher coloration efficiency means less energy consumption, which holds great potential for various applications, including electrochromic back covers of smartphones. PBTz-BT displayed the highest transmittance (28% at 550 nm), and BTz-TT illustrated the fastest switching time (0.6 s/0.5 s for doping/dedoping process). Flexible electrochromic device (ECD) fabricated employed PBTz-T as functional layer gradually changed from red (reduction) to dark green (oxidation), and maintained good cycling stability.

Toward Defect Suppression in Polythiophenes Synthesized by Direct (Hetero)Arylation Polymerization

In this study, we have investigated different reaction conditions for defect suppression in polythiophene derivatives synthesized by direct (hetero)arylation polymerization (DHAP). The well-known PQT12 polymer was used as a model due to its simple structure which facilitated analysis. 2-Bromo-3,4′-didodecyl-2:2′,5′:2″,5″:2‴-quaterthiophene and 2-bromo-3″,4‴-didodecyl-2:2′,5′:2″,5″-2‴-quaterthiophene monomers allowed the analysis of both homocoupling defects and β-branching defects due to their asymmetric structure as well as the effect of β-protection. The properties of the resulting polymers were analyzed using size-exclusion chromatography, differential scanning calorimetry, UV–visible absorption spectroscopy, and 1H NMR spectrometry. Some model compounds were synthesized to help with end-groups analysis, revealing debromination as the main obstacle to chain growth. The highest quality polymer was obtained when using toluene as a solvent, Pd2dba3 as a palladium(0) catalyst, neo-decanoic acid (NDA) as a carboxylic acid additive, and a dual-ligand system with diamine TMEDA and phosphine P(o-OMePh)3. This study also revealed the importance of the choice of the monomers for the preparation of well-defined conjugated polymers.

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.

Exploring SiliaCat Pd-DPP as a recyclable heterogeneous catalyst for the multi-batch direct heteroarylation polymerization for P(NDI2OD-T2)

Direct heteroarylation polymerization (DHAP) has been achieved for P(NDI2OD-T2) with a consistent molar mass using a modified A-B-A monomer and a recyclable heterogeneous SiliaCat Pd-DPP catalyst, for up to four consecutive reuses.

Structure-property insights into chiral thiophene copolymers by direct heteroarylation polymerization

Chiral thiophene copolymers with fluorene as co monomer are designed having N-Boc-L-glutamic acid-1-tert-butyl ester as a chiral substituent located either on the thiophene unit or the fluorene unit with varying spacer length. The atom-economic direct heteroarylation polymerization (DHAP) method is utilized for the polymerization. Gibb’s free energy (ΔG) for polymerization determined using DFT calculations indicate difficulty in achieving high molar mass when the bulky chiral substituents are attached through short spacer to the backbone. The experimental observations are in agreement with the theoretical calculations with no polymerization or very low molar mass sticky compounds obtained for reactions with predicted + ΔG values. Structure-property relationship are compared for two chiral polymers - P4 and P5 having the chiral substitution on thiophene and fluorene units respectively. No CD signal is observed in THF-a good solvent where the polymers are molecularly dissolved. Intense bisignated CD signal is observed for both polymers upon addition of methanol – a poor solvent, to their THF solution. The bisignate CD signal with maxima at lower wavelength and inflection point associated with the π-π* absorption band is characteristic of exciton coupling between polymer chains in a left handed helical orientation. Small differences are observed in the intensity of the CD signal for the polymers P4 and P5 highlighting the impact of steric hindrance of bulky pendant groups on polymer conformation. DHAP is an atom economic polymerization procedure that can be gainfully utilized for developing chiral conjugated polymers.

Molecular weight and linking position (2,7 vs 3,6) effects on electrochromic properties of alternating carbazole-EDOT copolymers obtained by direct (hetero) arylation polymerization

Two carbazole-EDOT electrochromic conjugated polymers (ECPs), namely P(2,7-Cbz-E)-HW and P(3,6-Cbz-E) have been developed by direct (hetero)arylation polymerization (DHAP). The effects of molecular weight and linked position on electrochromic properties for the above ECPs were investigated in detail. The 2,7-linked high molecular weight ECPs of P(2,7-Cbz-E)-HW exhibited excellent optical contrast and electrochemical stability. Meanwhile, both P(2,7-Cbz-E)-LW and P(2,7-Cbz-E)-HW performed short response times at 450 nm (<1 s) and P(2,7-Cbz-E)-LW showed outstanding coloration efficiency (up to 370 cm2 C−1 at 450 nm). However, 3,6-linked ECPs of P(3,6-Cbz-E), whose conjugation are sort of interruption, resulted in a low molecular weight and presented a highly blue-shifted absorption edge and unsatisfactory electrochromic performance compared with 2,7-linked ECPs. Further, flexible and patterned electrochromic devices (ECDs) were presented employing 2,7-linked ECPs, which achieved a reversible color change between yellow and dark blue with acceptable optical contrast (26% for P(2,7-Cbz-E)-LW and 32% for P(2,7-Cbz-E)-HW both at 605 nm). The research indicates that the molecular weight and linked position are crucial to achieve high-performance electrochromism, which provides guidance for designing ECPs and flexible ECDs.

Direct heteroarylation polymerization of a π-conjugated polymer with degradable 1,2,4-oxadiazole linkers

The synthesis of π-conjugated polymers containing a degradable 1,2,4-oxadiazole linker by direct heteroaryl polymerization (DHAP) is reported.

Low-Defect, High Molecular Weight Indacenodithiophene (IDT) Polymers Via a C–H Activation: Evaluation of a Simpler and Greener Approach to Organic Electronic Materials

The development, optimization, and assessment of new methods for the preparation of conjugated materials is key to the continued progress of organic electronics. Direct C–H activation methods have emerged and developed over the last 10 years to become an invaluable synthetic tool for the preparation of conjugated polymers for both redox-active and solid-state applications. Here, we evaluate direct (hetero)arylation polymerization (DHAP) methods for the synthesis of indaceno[1,2-b:5,6-b′]dithiophene-based polymers. We demonstrate, using a range of techniques, including direct visualization of individual polymer chains via high-resolution scanning tunneling microscopy, that DHAP can produce polymers with a high degree of regularity and purity that subsequently perform in organic thin-film transistors comparably to those made by other cross-coupling polymerizations that require increased synthetic complexity. Ultimately, this work results in an improved atom economy by reducing the number of synthetic steps to access high-performance molecular and polymeric materials.

New narrow bandgap polymers containing 10-(4-((2-ethylhexyl)oxy)phenyl)-10H-phenothiazine/phenoxazine and 3,6-di(2-thienyl)pyrrolo[3,4-c]pyrrole-1,4-dione)-based units: synthesis and photovoltaic properties

Diketopyrrolopyrrole (DPP) is one of the most used moieties in D–A conjugated polymers for high-performance π-extended conjugated polymer-based organic solar cells. The combination of 1,4-diketo-3,6-dithienylpyrrolo[3,4-c]pyrroles (DTDPPs) and the donor moieties 10-(4-((2-ethylhexyl)oxy)phenyl)-10H-phenothiazine (M1), 10-(4-((2-ethylhexyl)oxy)phenyl)-10H-phenoxazine (M2), has not been reported yet. In this report, novel low-bandgap D–A conjugated polymer derivatives including DTDPP, phenothiazine and phenoxazine were successfully synthesized via direct (hetero) arylation polymerization with in the yields of 40.94–60.77%. The obtained D–A conjugated polymers named poly(3,6-Di(2-thienyl)pyrrolo[3,4-c]pyrrole-1,4-dione)-alt-(10-(4-((2-ethylhexyl)oxy) phenyl)-10H-phenothiazine) (P1) and poly(3,6-Di(2-thienyl)pyrrolo[3,4-c]pyrrole-1,4-dione)-alt-(10-(4-((2-ethylhexyl)oxy) phenyl)-10H-phenoxazine) (P2) exhibited a wide range of absorption spectrum in visible light region and have a low bandgaps of 1.4–1.5 eV, as well as thermal stabilities, these D–A conjugated polymers are very promising as activated polymeric materials for organic solar cells (OSCs).

Water Compatible Direct (Hetero)arylation Polymerization of PPDT2FBT: A Pathway Towards Large‐Scale Production of Organic Solar Cells

AbstractThe interest in organic solar cells (OSCs) has grown exponentially over the last few years and devices are approaching a symbolic power conversion efficiency (PCE) of 20%. However, many challenges related to scaling‐up several processes must be addressed before this technology can reach the production scale. In order to facilitate the scaled‐up production of OSCs, the synthesis of an efficient and cost‐effective conjugated polymer, PPDT2FBT, was adapted to a water‐based method of direct (hetero)arylation polymerization (DHAP). This aqueous DHAP method yields molecular weights (Mn) between 20 and 80 kg mol−1, which can be controlled by manipulating the polymerization time and temperature. The varying polymer molecular weights were used for the fabrication of OSCs with PC61BM and air‐processed in non‐halogenated solvents. When the 40 kg mol−1 PPDT2FBT:PC61BM active layer is slot‐die coated, PCEs of 8.15% were attained under standard one sun illumination. The temporal stability of the devices under constant illumination showed a 80% PCE loss after 220 hours (TS80), after the initial ‘‘burn‐in’’.

Synthesis of 1,6‐didecylnaphtho[1,2‐b:5,6‐b']difuran‐based copolymers by direct heteroarylation polymerization

AbstractThe use of direct CH arylation cross‐coupling polymerization was evaluated for the synthesis of donor–acceptor conjugated co‐polymers using the novel donor 1,6‐didecylnaphtho[1,2‐b:5,6‐b']difuran and either thieno[3,4‐c]pyrrole‐4,6‐dione (TPD) or 1,4‐diketopyrrolo[3,4‐c]pyrrole (DPP) as the acceptor. Thiophene and furan moieties were used to flank the DPP group and the impact of these heterocycles on the polymers' properties was evaluated. The alkyl chains on the diketopyrrolopyrrole monomers were varied to engineer the solubility and morphology of the materials. All of the polymers have similar optoelectronic properties with narrow optical band gaps around 1.3 eV, which is ideal for solar energy harvesting. Unfortunately, these polymers also had high‐lying highest occupied molecular orbital levels of −4.8 to −5.1, and as a result bulk‐heterojunction photovoltaic cells fabricated using the soluble fullerene derivative PC71BM as the electron‐acceptor and these polymers as donor materials exhibited poor performance due to limited Voc values. An examination of the films from these blends indicates that film‐thickness and morphology were also a major hindrance to performance and a potential point of improvement for future materials.

Optimized synthesis of fluorinated dithienyl-diketopyrrolopyrroles and new copolymers obtained via direct heteroarylation polymerization

Optimized synthesis of fDT-DPP and related 3-fluorothiophene comonomers and application in highly fluorinated polymers obtained via direct heteroarylation polymerization.

Synthesis via direct (hetero)arylation polymerization, electrochemical and optical properties of poly (3,4-disubstituted)thiophenes

Some poly (3,4-disubstituted)thiophenes bearing both cyano and alkoxy or thioalkoxy groups have been synthesized by direct (hetero)arylation polymerization (DHAP) of 2-iodo-3,4-disubstituted thiophenes. The electron donor and acceptor properties of substituents in positions 3 and 4 allow to adjust the HOMO and LUMO levels. On the other hand, in order to avoid the polymer solubility problems, long branched or unbranched alkyl chains have also been introduced. Thus polymers with alkoxy groups have led to complete absorption in the wavelength range of the visible spectrum whereas in the presence of thioalkoxy groups, the absorption of the visible spectrum is only partial. Theoretical calculations have shown that sulphur creates torsions leading to a non-planar polymer chain.

Direct (hetero)arylation polymerization: toward defect-free conjugated polymers

In a very short time, direct (hetero)arylation polymerization (DHAP) has established itself as a valuable and atom-economical alternative to traditional cross-coupling methods such as the Migita–Stille and Suzuki-Miyaura polymerizations for the synthesis of low cost and efficient conjugated polymers for organic electronics. Because of sustained research efforts combining in-depth theoretical calculations, the development of new ligands and the careful fine-tuning of polymerization conditions, selectivity and reactivity issues should be soon a thing of the past. This focus review highlights the recent advances that lead to defect-free polymeric semiconductors and conductors and the current limitations and challenges of DHAP as it moves toward simultaneously becoming an industrially feasible, environmentally friendly, and synthetically powerful polymerization technique. The implementation of Direct Heteroarylation Polymerization (DHAP) in the synthesis of well-defined and defect-free materials for organic electronics is still in its early stages but giant leaps have been made over the past few years to improve and stir the selectivity of the reaction to avoid unwanted side-reaction such as β-branching or homocoupling. DHAP has proven to be an efficient, cost-effective, green and scalable polymerization method now competing or even surpassing well-established Suzuki-Miyaura or Migita–Stille cross-coupling polymerization methods. This focus review puts emphasis on the synthetic strategies that made DHAP successful.

A Fruitful Usage of a Dialkylthiophene Comonomer for Redox Stable Wide-Gap Cathodically Coloring Electrochromic Polymers

A series of conjugated polymers are prepared via direct heteroarylation polymerization with the goal of yielding wide-gap, yellow and orange switching to transmissive cathodically coloring electrochromic polymers (ECPs). The polymers are based on repeat units of dialkylthiophene (DAT) in alternation with dioxythiophenes (DOTs) with various side chains to induce differing levels of inter-ring strain yielding 3,4-ethylenedioxythiophene (DAT-EDOT), 3,4-propylenedioxythiophene (DAT-ProDOT), 3,4-(1,3-dimethylpropylene)dioxythiophene (DAT-DMP), and 3,4-dimethoxythiophene (DAT-DMOT) structured polymers. Examination of the optoelectronic properties via UV–vis–NIR spectroscopy, differential pulse voltammetry, and spectroelectrochemistry shows that while increasing the inter-ring strain induced by the side chain of the DOT unit leads to an increased oxidation potential ranging from −122 to +288 mV relative to Fc/Fc+, this does not decrease the accessibility of the extreme charge states. Through subtle steric intera...

Mechanistic Origin of β-Defect Formation in Thiophene-Based Polymers Prepared by Direct (Hetero)arylation

A computational study of the direct arylation reaction was undertaken to understand the origin of nonselective β-couplings observed in thiophene-based polymers prepared by direct (hetero)arylation polymerization (DHAP). The reactivities and selectivities of C–H bond activations were studied for the concerted metalation–deprotonation mechanism on model thiophene substrates using density functional theory (DFT) and domain-based local pair natural orbital coupled cluster with singles, doubles, and perturbative triples (DLPNO-CCSD(T)). Substituent effects are shown to control experimentally observed regioselectivities. Electron-rich or -deficient thiophene substrates with multiple C–H bonds possess an intrinsic selectivity for bond activation at the α-position, while halogens in the α-position substantially reduce coupling selectivities by activating the adjacent Cβ–H bonds. Therefore, the halogenated monomer is responsible for the reported poor selectivities in DHAP. The effect of the substrate undergoing ox...

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 (Ea) 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 Ea 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 Ea 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.

Pyromellitic Diimide-Based Copolymers and Their Application as Stable Cathode Active Materials in Lithium and Sodium-Ion Batteries

Organic molecules are emerging candidates for the next generation of cost-effective active materials of Li-ion batteries. Small diimide building blocks such as pyromellitic diimide (PMDI) have attracted much attention because of their high theoretical capacity. Many strategies have been undertaken to limit the well-known phenomenon of dissolution of the active material in the electrolyte. Such strategies include the preparation of salts and the synthesis of polyimides or macrocycles. Since dibromopyromellitic dimiide exhibits almost no sp2 cross-coupling polymerization reaction by conventional synthetic routes (Suzuki–Miyaura or Migita–Stille), we used PMDI as an aromatic C–H bond-bearing unit for direct (hetero)arylation polymerization (DHAP) with 1,4-dibromobenzene as comonomer as a new stabilization strategy. DHAP proved to be an effective tool in the preparation of this polymer, yielding a number-average molecular weight of up to 31 kDa. We studied the effect of side-chain engineering using variable c...

Poly(naphthalene diimide-alt-bithiophene) Prepared by Direct (Hetero)arylation Polymerization for Efficient All-Polymer Solar Cells

A high molecular weight alternating naphthalene diimide–bithiophene copolymer (poly{[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} (PNDIOD-T2)) has been prepared by direct (hetero)arylation polymerization (DHAP). Its structure and properties were investigated in comparison with the Stille-prepared commercial analog, N2200. It was found that the new DHAP-derived PNDIOD-T2 and known N2200 have similar optical absorption spectra and HOMO/LUMO energy levels but slightly different 1H NMR spectra. Inverted all-polymer solar cells using PNDIOD-T2 as the acceptor and PCE12 or PCE10 as the donor polymer showed slightly superior performances compared to similar N2200 devices. All-polymer solar cells with 7.3% efficiency could be achieved with PNDIOD-T2 blends without the use of a processing additive. These results demonstrate that low-cost and eco-friendly DHAP-based n-type semiconducting polymers are promising for developing high performance all-polymer sola...