Synthesis Of Π-conjugated Polymers Research Articles

Synthesis and Characterization of Vanillin-Based π-Conjugated Polyazomethines and Their Oligomer Model Compounds.

The synthesis of π-conjugated polymers via an environmentally friendly procedure is generally challenging. Herein, we describe the synthesis of divanillin-based polyazomethines, which are derived from a potentially bio-based monomer. The polymerization is performed in 5 min under microwave irradiation without any metallic catalyst, with water as the only by-product. The vanillin-based polyazomethines were characterized by SEC, TGA, and UV-Vis spectroscopy. Model compounds were designed and characterized by X-ray diffraction and UV-Vis spectroscopy. The structure/properties study of vanillin-based azomethines used as models allowed us to unequivocally confirm the E configuration and to highlight the cross-conjugated nature of divanillin-based polymers.

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.

Synthesis of π-Conjugated Polymers Containing Benzotriazole Units via Palladium-Catalyzed Direct C-H Cross-Coupling Polycondensation for OLEDs Applications.

Four D-π-A conjugated polymers, namely P1–P4, which contain benzotriazole building blocks in their backbone as acceptor, are synthesized via palladium-catalyzed direct C-H cross-coupling polycondensation of 5,6-difluorobenzotriazole with different thiophene derivatives, including 3-octylthiophene, 2,2’-bithiophene, thieno[3,4-b][1,4]dioxine, and 4,4-dioctyl-4H-silolo-[3,2-b:4,5-b’]dithiophene as donor units, respectively. Taking the polymer P1 as an example, the chemical structure of the polymer is demonstrated by 1H and 19F NMR spectra. The optical, electrochemical, and thermal properties of these polymers are assessed by UV–vis absorption and fluorescence spectroscopy, cyclic voltammetry (CV), and thermal gravimetric analysis (TGA), respectively. DFT simulations of all polymers are also performed to understand their physicochemical properties. Furthermore, P1 and P2, which have relatively higher molecular weights and better fluorescent quantum efficiency than those of P3 and P4, are utilized as lighting emitters for organic light-emitting diodes (OLEDs), affording promising green and red luminescence with 0.07% and 0.14% of maximum external quantum efficiency, respectively, based on a device with an architecture of ITO/PEDOT:PSS/PTAA/the polymer emitting layer/TPBi/LiF/Al.

High-Performance Ambient-Condition-Processed Polymer Solar Cells and Organic Thin-Film Transistors.

Large-scale commercial synthesis of bulk-heterojunction (BHJ) solar cell materials is very challenging and both time and energy consuming. Synthesis of π-conjugated polymers (CPs) with uniform batch-to-batch molecular weight and low dispersity is a key requirement for better reproducibility of high-efficiency polymer solar cells. Herein, a conjugated polymer (CP) PTB7-Th, well known for its high performance, has been synthesized with high molecular weight and low dispersity in a closed microwave reactor. The microwave reaction procedure is known to be more controlled and consumes less energy. The precursors were strategically reacted for different reaction time durations to obtain the optimum molecular weight. All different CPs were well characterized using 1H NMR, gel permeation chromatography (GPC), UV–vis, photoluminescence (PL), electron spin resonance (ESR), and Raman spectroscopy, whereas the film morphology was extensively studied via atomic force microscopy (AFM) and grazing incidence X-ray diffraction (GIXRD) techniques. The effect of molecular weight on a conventional BHJ solar cell with PC71BM acceptor was investigated to derive systematic structure–property relationships. The CP obtained after 35 min of reaction time and integrated into BHJ devices under ambient conditions provided the best performance with a power conversion efficiency (PCE) of 8.09%, which was quite similar to the results of CPs synthesized via a thermal route. An enhanced PCE of 8.47% was obtained for the optimized polymer (35 min microwave reaction product) when device fabrication was carried out inside a glovebox. The organic thin-film transistor (OTFT) device with the microwave-synthesized CP displayed better hole mobility (0.137 cm2 V–1 s–1) as compared to that with the thermally synthesized CP. This study also proved that the device stability and reproducibility of the microwave-synthesized CP were much better and more consistent than those of the thermally developed CP.

Transition-Metal-Free Synthesis of 1,3-Butadiene-Containing π-Conjugated Polymers.

This work describes the synthesis of π-conjugated polymers possessing arylene and 1,3-butadiene alternating units in the main chain by the reaction of α,β-unsaturated ester/nitrile containing γ-H with aromatic/heteroaromatic aldehyde compound. By using 4-(4-formylphenyl)-2-butylene acid ethyl ester as a model monomer, the different polymerization conditions, including catalyst, catalyst amount, and solvent, are optimized. The polymerization of 4-(4-formylphenyl)-2-butylene acid ethyl ester is carried out by refluxing in ethanol for 72 h with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as a catalyst to give a 1,3-butadiene-containing π-conjugated polymer, poly(phenylene-1,3-butadiene), in 84.3% yield with M¯n and M¯w/M¯n (PDI) estimated as 6172 and 1.65, respectively. Based on this new methodology, a series of π-conjugated polymers containing 1,3-butadiene units with different substituents are obtained in high yields. A possible mechanism is proposed for the polymerization through a six-membered ring transition state and then a 1,5-H shift intermediate.

Metal-Free, Multicomponent Synthesis of Pyrrole-Based π-Conjugated Polymers from Imines, Acid Chlorides, and Alkynes.

Multicomponent coupling reactions (MCRs) are becoming increasingly used in the synthesis of macromolecules, as they can allow the rapid generation of libraries of materials as a method to tune properties. MCRs could prove particularly useful in the synthesis of π-conjugated polymers in which structural changes are necessary for fine-tuning of electronic properties. We describe here the first metal-free multicomponent approach to conjugated polymers. This reaction exploits the coupling of imines, acid chlorides, and (catechyl)PPh to generate phospha-münchnone-containing polymers, which can be converted to poly(pyrroles) via cycloaddition. The platform allows for the efficient synthesis of families of high molecular weight polymers in one step from readily available monomers.

C–H Arylation in the Synthesis of π-Conjugated Polymers

C-H activation reactions have allowed us to react traditionally chemically inert bonds in molecules to develop new methods for cross-coupling reactions. This type of reactivity can be applied to conjugated polymer materials in an effort to improve existing synthetic difficulties including harsh reaction conditions, multiple monomer functionalization steps, and organometallic reagent waste. In this Viewpoint, we highlight some of the encouraging advances in direct arylation polymerization (DArP) as well as ongoing challenges for future improvement and utility.

Selectivity of Reaction Sites for Direct Arylation Polycondensation in Bithiophene Derivatives

Direct arylation polycondensation has recently emerged as the method for the synthesis of π-conjugated polymers. In developing this methodology, site selectivity of the reacting C-H bonds is one of the most important issues. Herein, we investigate the direct arylation polycondensation of bithiophene and dialkylbithiophenes to assess site selectivity. We found that low temperature was a key factor for high selectivity in bithiophene, and that 4,4′-dicyclohexylbithiophene exhibited the highest selectivity among the tested dialkylbithiophenes reaction sites.

Synthesis of π-Conjugated Polymers Containing Dibenzosilepin Moieties with Pentacoordinate Silicon

Abstract Benzo[h]quinolyldibenzo[b,f]silepin containing pentacoordinate silicon was incorporated into π-conjugated polymers. Substituent effects were investigated from UV–vis absorption and photoluminescence spectra. The extension of π-conjugation involving pentacoordinate silicon was suggested from the characteristic absorption and emission bands through the polymer chain at meta-positions toward silicon in the silepin rings. The polymers containing the fluorinated silicon showed bathochromic shift compared to that from the methylated silicon-containing polymers. Polymerization at para-positions toward silicon resulted in the formation of short conjugation length. Finally, the emission band from the charge-transfer transition was observed in photoluminescence spectra of the fluorinated polymer.

Synthesis of π-Conjugated Polymers Containing Benzodipyrrole Moieties in the Main Chain through Cleavage of C-H Bonds in 1,4-Bis(acetylamino)benzene.

Rhodium-catalyzed copolymerization between 1,4-bis(acetylamino)benzene and diynes through C-H bond cleavage afforded π-conjugated polymers containing benzodipyrrole moieties. The polymers with substituted benzene units exhibited nearly the same absorption peaks and HOMO levels. Fluorenone and benzothiadiazole moieties can be also introduced as electron-acceptor units to the main chain by polymerization in tert-amyl alcohol and tetrahydropyran as mixed solvent, leading to absorption at longer wavelength.

Synthesis of π-Conjugated Polymers Containing Phosphole Units in the Main Chain by Reaction of an Organometallic Polymer Having a Titanacyclopentadiene Unit.

A regioregular organometallic polymer possessing titanacyclopentadiene units in the main chain, which was obtained by the reaction of terminal diyne and a low-valent titanium complex, was subjected to the reaction with dichlorophosphines to give π-conjugated polymers with phosphole or phosphole oxide units in the main chain. For example, a phenylphosphole-containing polymer was obtained in 76% yield by the reaction with dichlorophenylphosphine, whose number-average molecular weight (Mn) and molecular weight distribution (Mw/Mn) were estimated to be 6100 and 1.9, respectively, by GPC. The polymer was found to have an extended π-conjugated system, and its lowest unoccupied molecular orbital (LUMO) energy level was remarkably low (-3.28 eV) as supported by its UV-vis absorption spectrum and cyclic voltammetric (CV) analysis. Also, the polymer exhibits orange photoluminescence with an emission maximum (Emax) of 595 nm and a quantum yield (Φ) of 0.10.

Synthesis of π-Conjugated Polymers Containing Organoboron Benzo[h]quinolate in the Main Chain

Synthesis of π-Conjugated Polymers Containing Organoboron Benzo[<i>h</i>]quinolate in the Main Chain