Novel Brush-Type Copolymers Bearing Thiophene Backbone and Side Chain Quinoline Blocks. Synthesis and Their Use as a Compatibilizer in Thiophene−Quinoline Polymer Blends

Post-polymerisation approaches for the rapid modification of conjugated polymer properties

Post-polymerisation functionalisation provides a facile and efficient way for the introduction of functional groups on the backbone of conjugated polymers. Using post-polymerisation functionalisation approaches, the polymer chain length is usually not affected, meaning that the resulting polymers only differ in their attached functional groups or side chains, which makes them particularly interesting for investigating the influence of the different groups on the polymer properties. For such functionalisations, highly efficient and selective reactions are needed to avoid the formation of complex mixtures or permanent defects in the polymer backbone. A variety of suitable synthetic approaches and reactions that fulfil these criteria have been identified and reported. In this review, a thorough overview is given of the post-polymerisation functionalisations reported to date, with the methods grouped based on the type of reaction used: cycloaddition, oxidation/reduction, nucleophilic aromatic substitution, or halogenation and subsequent cross-coupling reaction. Instead of modifications on the aliphatic side chains of the conjugated polymers, we focus on modifications directly on the conjugated backbones, as these have the most pronounced effect on the optical and electronic properties. Some of the discussed materials have been used in applications, ranging from solar cells to bioelectronics. By providing an overview of this versatile and expanding field for the first time, we showcase post-polymerisation functionalisation as an exciting pathway for the creation of new conjugated materials for a range of applications.

Mild and efficient copper-catalyzed oxidative cyclization of oximes with 2-aminobenzyl alcohols at room temperature: synthesis of polysubstituted quinolines

A simple and efficient ligand-free Cu-catalyzed protocol for the synthesis of polysubstituted quinolines via oxidative cyclization of oxime acetates with 2-aminobenzyl alcohols at room temperature has been developed. The presented approach provides a new synthetic pathway leading to polysubstituted quinolines with good functional group tolerance under mild conditions. Moreover, this transformation can be applied for the preparation of quinolines on a gram scale. Oxime acetates serve as the internal oxidants in the reactions, thus making this method very attractive.

All-conjugated P3HT donor PCDTBT acceptor graft copolymers synthesised via a grafting through approach

A generally applicable synthetic method for all-conjugated graft copolymers is presented.

Synthesis of Polythiophene⁻Fullerene Hybrid Additives as Potential Compatibilizers of BHJ Active Layers

Perfluorophenyl functionalities have been introduced as side chain substituents onto regioregular poly(3-hexyl thiophene) (rr-P3HT), under various percentages. These functional groups were then converted to azides which were used to create polymeric hybrid materials with fullerene species, either C₆₀ or C₇₀. The P3HT–fullerene hybrids thus formed were thereafter evaluated as potential compatibilizers of BHJ active layers comprising P3HT and fullerene based acceptors. Therefore, a systematic investigation of the optical and morphological properties of the purified polymer–fullerene hybrid materials was performed, via different complementary techniques. Additionally, P3HT:PC₇₀BM blends containing various percentages of the herein synthesized hybrid material comprising rr-P3HT and C₇₀ were investigated via Transmission Electron Microscopy (TEM) in an effort to understand the effect of the hybrids as additives on the morphology and nanophase separation of this typically used active layer blend for OPVs.

Compatibilization of All-Conjugated Polymer Blends for Organic Photovoltaics

Compatibilization of an immiscible binary blend comprising a conjugated electron donor and a conjugated electron acceptor polymer with suitable electronic properties upon addition of a block copolymer (BCP) composed of the same building blocks is demonstrated. Efficient compatibilization during melt-annealing is feasible when the two polymers are immiscible in the melt, i.e. above the melting point of ∼250 °C of the semicrystalline donor polymer P3HT. To generate immiscibility at these high temperatures, the acceptor polymer PCDTBT is equipped with fluorinated side chains leading to an increased Flory-Huggins interaction parameter. Compatibilization in bulk and thin films is demonstrated, showing that the photovoltaic performance of pristine microphase separated and nanostructured BCPs can also be obtained for compatibilized blend films containing low contents of 10-20 wt % BCP. Thermodynamically stable domain sizes range between several tens of microns for pure blends and ∼10 nm for pure block copolymers. In addition to controlling domain size, the amount of block copolymer added dictates the ratio of edge-on and face-on P3HT crystals, with compatibilized films showing an increasing amount of face-on P3HT crystals with increasing amount of compatibilizer. This study demonstrates the prerequisites and benefits of compatibilizing all-conjugated semicrystalline polymer blends for organic photovoltaics.

Studies of Luminescence Performance on Carbazole Donor and Quinoline Acceptor Based Conjugated Polymer

We report on the synthesis of conjugated polymer (CV-QP) containing carbazole (donor) and quinoline (acceptor) using Wittig methodology. The structural, optical and thermal properties of the polymer were investigated by FT-IR, NMR, GPC, UV, PL, cyclic voltammetry, atomic force microscopy (AFM) and thermogravimetric analysis (TGA). The polymer exhibits thermal stability upto 200 °C and shows good solubility in common organic solvents. The polymer has optical absorption band in a thin film at 360 nm and emission band formed at 473 nm. The optical energy band gap was found to be 2.69 eV as calculated from the onset absorption edge. Fluorescence quenching of the polymer CV-QP was found by using DMA (electron donor) and DMTP (electron acceptor). AFM image indicated that triangular shaped particles were observed and the particle size was found as 1.1 μm. The electrochemical studies of CV-QP reveal that, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the CV-QP are 6.35 and 3.70 eV, which indicated that the polymers are expected to provide charge transporting properties for the development of polymer light-emitting diodes (PLEDs).

Molecular reorganization of selected quinoline derivatives in the ground and excited states—Investigations via static DFT

Quinoline derivatives are interesting objects to study internal reorganizations due to the observed excited-state-induced intramolecular proton transfer (ESIPT). Here, we report on computations for selected 12 quinoline derivatives possessing three kinds of intramolecular hydrogen bonds. Density functional theory was employed for the current investigations. The metric and electronic structure simulations were performed for the ground state and first excited singlet and triplet states. The computed potential energy profiles do not show a spontaneous proton transfer in the ground state, whereas excited states exhibit this phenomenon. Atoms in Molecules (AIM) theory was applied to study the nature of hydrogen bonding, whereas Harmonic Oscillator Model of aromaticity index (HOMA) provided data of aromaticity evolution as a derivative of the bridge proton position. The AIM-based topological analysis confirmed the presence of the intramolecular hydrogen bonding. In addition, using the theory, we were able to provide a quantitative illustration of bonding transformation: from covalent to the hydrogen. On the basis of HOMA analysis, we showed that the aromaticity of both rings is dependent on the location of the bridge proton. Further, the computed results were compared with experimental data available. Finally, ESIPT occurrence was compared for the three investigated kinds of hydrogen bridges, and competition between two bridges in one molecule was studied.

Functionalized Poly(3-hexylthiophene)s via Lithium-Bromine Exchange

Poly(3-hexylthiophene) (P3HT) is one of the most extensively investigated conjugated polymers and has been employed as the active material in many devices including field-effect transistors, organic photovoltaics and sensors. As a result, methods to further tune the properties of P3HT are desirable for specific applications. Herein, we report a facile postpolymerization modification strategy to functionalize the 4-position of commercially available P3HT in two simple steps–bromination of the 4-position of P3HT (Br–P3HT) followed by lithium−bromine exchange and quenching with an electrophile. We achieved near quantitative lithium–bromine exchange with Br–P3HT, which requires over 100 thienyl lithiates to be present on a single polymer chain. The lithiated-P3HT is readily combined with functional electrophiles, resulting in P3HT derivatives with ketones, secondary alcohols, trimethylsilyl (TMS) group, fluorine, or an azide at the 4-position. We demonstrated that the azide-modified P3HT could undergo Cu-catalyzed or Cu-free click chemistry, significantly expanding the complexity of the structures that can be appended to P3HT using this method.

N-heterocyclic carbene (NHC)-modulated Pd/Cu cocatalyzed three-component synthesis of 2,6-diarylquinolines

An efficient NHC-modulated Pd/Cu cocatalyzed three-component coupling reaction for the synthesis of 2,6-diarylquinolinesviaoxidation, cyclization and Suzuki reactions.

Interfacial self-assembly and characterization of chiral coordination polymer multilayers with bidentate ligands of hydroquinine anthraquinone-1,4-diyl diether as linkers

Chiral coordination polymers (CPs) have been prepared at the air-water interface by using the ligand of 1,4-bis(9-O-dihydroquininyl)anthraquinone [(DHQ)2AQN] and its enantiomer of 1,4-bis(9-O-dihydroquinidinyl)anthraquinone [(DHQD)2AQN] as linkers and AgNO3 as the connector. Surface pressure-area isotherms indicated that both ligands could form insoluble monomolecular layers on the pure water and AgNO3 subphase surfaces. Compared with the average molecular area on the pure water surface, that of the ligand increased about 10% when its monolayer was formed on the AgNO3 subphase surface due to the formation of Ag-(DHQ)2AQN and Ag-(DHQD)2AQN chiral CPs. These monolayers were deposited on the quartz, Si, and indium tin oxide (ITO) substrate surfaces via the Langmuir-Blodgett (LB) method. The as-prepared LB films were characterized by using UV-vis absorption and fluorescence spectroscopy, circular dichroism and X-ray photoelectron spectroscopy, as well as by using a scanning electron microscope and atomic force microscope. Broad fluorescence emissions were measured at about 365 and 525 nm for the ligands in the methanol solutions. The second emission red shifted to about 555 nm in the LB films of both pure ligands and their Ag-directed CPs. A couple of well-reversible redox waves were recorded and centered at about -0.2 ~ -0.3 V (vs Ag/AgCl) for the ITO electrode covered by the LB films of (DHQ)2AQN, (DHQD)2AQN, or of the Ag(+)-directed CPs, which were designated to one electron transfer process of the ligands. Small aggregates were observed for the LB films prepared at the lower surface pressures, which were compressed to form more uniform two-dimensional layers at the higher surface pressures.

Brush Polymers Containing Semiconducting Polyene Backbones: Graft-Through Synthesis via Cyclopolymerization and Conformational Analysis on the Coil-to-Rod Transition

Using a grafting-through strategy, brush polymers containing semiconducting polyene backbones were efficiently synthesized by cyclopolymerization for the first time. Macromonomers containing poly(l-lactide) and poly(ε-caprolactone), prepared by living ring-opening polymerization, were polymerized using the Grubbs-Hoveyda catalyst to produce high molecular weight (>0.5 M Da) brush polymers. The brush polymers underwent a unique coil-to-rod transition during the aging of the polymer solution, and this conformational change was supported by UV-vis and size-exclusion chromatography (SEC)-viscometry analysis. In addition, the extended conformation of single chains of the brush polymers could be visualized by atomic force microscopy.

Block copolymer as a nanostructuring agent for high-efficiency and annealing-free bulk heterojunction organic solar cells

The addition of a block copolymer to the polymer/fullerene blend is a novel approach to the fabrication of organic solar cells. The block copolymer (P3HT-b-P4VP) is used as nanostructuring agent in the active layer. A significant enhancement of the cell efficiency is observed, in correlation with morphology control, both before (as-cast) and after the annealing process.

Effects of PPV-g-PSFu Graft Copolymer on Morphology and Power Conversion Efficiency of Bulk Heterojunction Solar Cell Base on P3HT/C60 Blends

This research work concerns a study on the effect of donor-acceptor graft copolymer, namely poly-p-phenylene vinylene grafted with polystyrene fullerene (PPV-g-PSFu), on morphology and power conversion efficiency of bulk heterojunction solar cells (BHJ) based on P3HT/C60. The aim of this work is to investigate the effect of the graft copolymers content (10, 20 and 40 pph) on morphology and efficiency of the solar cells. The copolymer was mixed with P3HT and C60, by using a solution blending technique. The blend film was fabricated by using a spin coating technique. Power conversion efficiency of the cells was determined by using current density-voltage (J-V) measurements. From the results, it was found that power conversion efficiency (PCE) of various BHJ cells increased from 0.07 x10-4 % to 1.45 x10-4 % after the copolymer (20 pph) was added. The above change was discussed in the light of some changes in morphology of the P3HT/C60 blend. Atomic force micrographs (AFM) the various blends showed that, by adding the graft copolymer, the domain size decreased and finer dispersed particle morphology was obtained.

Morphology control of a polythiophene-fullerene bulk heterojunction for enhancement of the high-temperature stability of solar cell performance by a new donor-acceptor diblock copolymer

A well defined diblock copolymer (P3HT-b-C(60)) based on regioregular poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) was synthesized via two controlled polymerization steps and used as a compatibilizer for the P3HT/PCBM blend, which has widely been used as an active layer in bulk heterojunction polymer solar cells. The addition of a small amount of P3HT-b-C(60) results in not only the reduction of phase size of P3HT/PCBM blend but also the suppression of macrophase separation for long-time thermal annealing owing to the preferential location of the diblock copolymers at the interface between P3HT and PCBM phases. The morphology change with the annealing time is closely related to the change of the power conversion efficiency (PCE) of solar cells: the PCE of P3HT/PCBM greatly decreases with increasing annealing time while the addition of P3HT-b-C(60) significantly reduces the decrease of PCE for long-time thermal annealing.

The role of intrachain and interchain interactions of regioregular poly(3-octylthiophene) chains on the optical properties of a new amphiphilic conjugated random copolymer in solution

The synthesis of a random copolymer through free radical copolymerization of a properly vinyl monofunctionalized regioregular poly(3-octylthiophene) (rrP3OT) macromonomer and N,N'-dimethylacrylamide (DMAM) is presented. The optical properties of the copolymer in water and in several organic solvents of varying polarity, as well as in THF/water and THF/methanol mixtures, were explored using UV-vis and photoluminescence spectroscopy. It is demonstrated that the rrP3OT chains adopt a coil conformation in solvents such as tetrahydrofuran (THF) and chloroform with the appearance of the absorption and emission maxima at 439 and 565 nm, respectively. On the contrary, the rrP3OT chains are organized on a single chain packing form (intrachain interactions) in polar solvents such as ethanol and methanol, as it is verified with the observation of the characteristic three vibronic features of the absorption spectra of the copolymer with maxima at 513, 550, and 603 nm and emission maxima at 560 nm. However, when water is used as solvent, the rrP3OT chains self-assemble into a stacklike structure due to the increased interchain interactions, as confirmed by the different aggregation process of the rrP3OT chains in the THF/water mixture, the broader absorption spectrum in water compared to those recorded in ethanol and methanol, and the 80 nm red-shifted emission maximum, centered at 640 nm.

Conductive Polymer Brushes of Regioregular Head-to-Tail Poly(3-alkylthiophenes) via Catalyst-Transfer Surface-Initiated Polycondensation

We describe a new method to grow conductive polymer (CP) brushes of regioregular head-to-tail poly(3-alkylthiophenes) (P3AT) via surface-initiated polycondensation of 2-bromo-5-chloromagnesio-3-alkylthiophene. A simple procedure for the preparation of the Ni(II) macroinitiator by the reaction of Ni(PPh3)4 with photocross-linked poly-4-bromostyrene films was developed. Exposure of the initiator layers to the monomer solution leads to selective chain growth polycondensation of the monomer from the surface, resulting in P3AT brushes in a very economical way. In contrast to the P3AT films prepared by traditional solvent casting methods, our approach leads to mechanically robust CP films, stable against delamination. We believe that our approach will be helpful in the fabrication of all-plastic devices.