Robust Direct (Hetero)arylation Polymerization in Biphasic Conditions

The synthesis of conjugated polymers from direct (hetero)­arylation polymerization (DHAP) has been achieved for the first time using biphasic water/toluene conditions. This protocol is robust enough to form polymers even when air is introduced in the system. General reactivity is demonstrated for a single set of polymerization conditions with thienyl- or phenyl-based substrates, whether they are electron-rich or electron-poor. Complete characterization from differential scanning calorimetry and ¹H NMR and UV–vis–NIR spectroscopies is presented, demonstrating this DHAP protocol offers comparable or better properties than the very best values published thus far. High molecular weights are obtained, showcasing the perfect equilibrium of reactivity and selectivity attained with this method. Moreover, this efficient and versatile methodology, which also uses low-cost, “wet” reagents, is scalable and done at ambient pressure

En Route to Defect-Free Polythiophene Derivatives by Direct Heteroarylation Polymerization

We report the synthesis of well-defined poly­(3,3‴-didodecyl-2,2′:5′,2″:5″,2‴-quaterthiophene) (PQT12) from a direct heteroarylation polymerization (DHAP) of 5-bromo-3,3‴-didodecyl-2,2′:5′,2″:5″,2‴-quaterthiophene (monomer <b>A</b>) and 5-bromo-3′,4″-didodecyl-2,2′:5′,2″:5″,2‴-quaterthiophene (monomer <b>B</b>). Experiments with different catalysts, ligands, additives, and solvents have revealed that the utilization of Herrmann–Beller catalyst and P­(<i>o</i>-NMe₂Ph)₃ can lead to selective thiophene–thiophene couplings. In this regard, solid-state optical and thermal measurements were particularly useful to detect the presence of β-branching and indicate that minor molecular defects can induce important changes within the supramolecular organization. We also highlight the fact that steric protection around unsubstituted β-positions of α-bromothiophene units is needed to obtain a good selectivity of the cross-couplings at the α-positions. This can be achieved by the presence of a substituent at an adjacent β-position or the utilization of a bulky acidic additive (<i>i.e</i>., neodecanoic acid) in the catalytic system. These synthetic procedures applied to both monomers have led to PQT12 samples showing essentially the same optical and thermal properties and are comparable to those observed with their analogues prepared from chemical oxidation or Stille coupling

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

A high molecular weight alternating naphthalene diimide–bithiophene copolymer (poly­{[<i>N</i>,<i>N</i>′-bis­(2-octyldodecyl)-naphthalene-1,4,5,8-bis­(dicarboximide)-2,6-diyl]-<i>alt</i>-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 solar cells

Liquid-Phase Exfoliation of Graphite in a Low-Boiling-Point Solvent Using 2,6-Azulene-Based Conjugated Copolymers as Stabilizers

In the present study, we report a procedure of liquid-phase exfoliation (LPE) of pristine graphite in chloroform using azulene-based copolymers. The resulting dispersions were prepared using tip sonication for only 2 h and were stable over months. Sonication parameters and their impact on the graphene concentration have been studied. Atomic force microscopy, Raman spectroscopy, and transmission electron microscopy revealed that the exfoliated material consists of multiple layers of graphene with an average thickness ranging from 10 to 35 nm. The presence of the polymer not only enables the exfoliation process and stabilizes the dispersions but also improves the processability of the solution. G/PAz films were prepared, and conductivity values of up to 1.9 S·cm–1 were measured

Low-Cost Synthesis and Physical Characterization of Thieno[3,4‑<i>c</i>]pyrrole-4,6-dione-Based Polymers

The improved synthesis of thieno­[3,4-<i>c</i>]­pyrrole-4,6-dione (TPD) monomers, including Gewald thiophene ring formation, a Sandmeyer-type reaction, and neat condensation with an amine, is presented. This protocol enables faster, cheaper, and more efficient preparation of TPD units in comparison to traditional methods. Furthermore, a series of TPD homo- and pseudohomopolymers bearing various alkyl chains was synthesized via a direct heteroarylation polymerization (DHAP) procedure. UV–visible absorption and powder X-ray diffraction measurements revealed the relationship between the ratio of branched to linear alkyl chains and the optoelectronic properties of the polymers as well as their packing in the solid state

Intensity Dependent Femtosecond Dynamics in a PBDTTPD-Based Solar Cell Material

PBDTTPD is a conjugated polymer with high power conversion efficiency if used in organic solar cells together with fullerene derivatives. We have investigated for the first time the excited state dynamics of pristine PBDTTPD thin film as well as the ultrafast evolution of charge carriers in PBDTTPD:PCBM bulk heterojunction blend using femtosecond transient absorption spectroscopy. In the latter, charges appear within the time resolution of the experiment (<100 fs), but clean spectral signatures allowed to directly follow slower ∼1 ps charge separation. Only the slower quenching component competes with exciton–exciton and exciton–charge annihilation, leading to a reduced yield of charge carriers at high laser fluence. Our excellent measuring sensitivity made it possible to reduce pump power to a point where annihilation is quasi suppressed. In this case >80% of charges survive after 1 ns; the rest recombines (most probably geminately) on the 200 ps time scale

Thiocarbonyl Substitution in 1,4-Dithioketopyrrolopyrrole and Thienopyrroledithione Derivatives: An Experimental and Theoretical Study

A series of new 1,4-dithioketopyrrolopyrrole and thienopyrrolodithione derivatives have been synthesized and characterized by spectroscopy and electrochemistry measurements. The replacement of carbonyl by thiocarbonyl has a direct effect on the optical gap and on the ionization potential and electron affinity energies. For example, the optical gaps have been lowered by 0.5 eV, a fact that has been correctly predicted by density functional theory and time-dependent density functional theory calculations. A theoretical analysis on the stability of the new molecules is also presented

Conjugated Polymers à la Carte from Time-Controlled Direct (Hetero)Arylation Polymerization

Direct (hetero)­arylation polymerization (DHAP) shows great promise for simple, cheap, and environmentally benign preparation of conjugated polymers, but seems to involve a lack of selectivity when different aromatic C–H bonds are present. We report that some time-controlled DHAP reactions can yield well-defined and processable semiconducting polymers. Following these procedures, various aromatic compounds have been efficiently polymerized, including 2,7-dibromofluorene, 2,7-dibromocarbazole, 1,4-dibromobenzene, bithiophene, dithienyl-benzothiadiazole, and diketopyrrolopyrrole derivatives. All resulting polymers have shown comparable, if not slightly better, properties than their Stille- and Suzuki-synthesized analogs. These findings (re)­open the door for the low-cost production of many conjugated polymers for plastic electronics

Qualitative Analysis of Bulk-Heterojunction Solar Cells without Device Fabrication: An Elegant and Contactless Method

The enormous synthetic efforts on novel solar cell materials require a reliable and fast technique for the rapid screening of novel donor/acceptor combinations in order to quickly and reliably estimate their optimized parameters. Here, we report the applicability of such a versatile and fast evaluation technique for bulk heterojunction (BHJ) organic photovoltaics (OPV) by utilizing a steady-state photoluminescence (PL) method confirmed by electroluminescence (EL) measurements. A strong relation has been observed between the residual singlet emission and the charge transfer state emission in the blend. Using this relation, a figure of merit (FOM) is defined from photoluminescence and also electroluminescence measurements for qualitative analysis and shown to precisely anticipate the optimized blend parameters of bulk heterojunction films. Photoluminescence allows contactless evaluation of the photoactive layer and can be used to predict the optimized conditions for the best polymer–fullerene combination. Most interestingly, the contactless, PL-based FOM method has the potential to be integrated as a fast and reliable inline tool for quality control and material optimization

Langmuir–Blodgett Films of Amphiphilic Thieno[3,4‑<i>c</i>]pyrrole-4,6-dione-Based Alternating Copolymers

The synthesis of four amphiphilic thieno­[3,4-<i>c</i>]­pyrrole-4,6-dione (TPD)-based alternating copolymers and their behavior at the air–water interface are reported. Homogeneous and stable monolayers of TPD-based copolymers were prepared. Brewster angle microscopy (BAM) was utilized to characterize the morphology and topography of these Langmuir films. UV–vis absorption spectroscopy as well as atomic force microscopy has revealed a regular transfer of some copolymers on glass substrates. It was possible to obtain homogeneous Langmuir–Blodgett films of up to 30 layers. Infrared dichroic measurements revealed an edge-on orientation. These Langmuir–Blodgett films made of conjugated polymers are therefore good candidates for organic field-effect transistors (OFETs)