Structure Of Conjugated Polymers Research Articles

Tuning the Mechanical and Electric Properties of Conjugated Polymer Semiconductors: Side‐Chain Design Based on Asymmetric Benzodithiophene Building Blocks

AbstractUnderstanding molecular design rules for stretchable polymer semiconductors is important for enabling next generation stretchable electronic circuits. To simultaneously improve both electrical properties and mechanical stretchability, a design strategy is reported in introducing conjugated rigid fused‐rings with bulky side groups in semiconducting polymers. In this work, the understanding of this design concept is improved by systematically investigating the effect of different types of bulky side groups asymmetrically substituted on conjugated polymer semiconductor backbones. Specifically, four types of side groups are investigated, including naphthalene (NaPh), biphenyl (PhPh), thienylphenyl (ThPh), and alkylphenyl (C4Ph), asymmetrically substituted on benzodithiophene units, namely asy‐BDT. With the four types of side groups installed on BDT‐containing conjugated polymers in an asymmetrical fashion, it is observed that they reduced the polymer chain aggregation and film crystallinity, hence improving the film stretchability. Furthermore, the fully conjugated polymer backbone allows maintenance of good charge carrier mobilities. Specifically, polymer PDPP‐C4Ph (with C4Ph side groups) shows the highest mobility in the fully stretchable transistor and maintained its mobility even after being subjected to hundreds of stretching‐releasing cycles at 25% strain. Overall, the results provide anunderstanding of the use of asymmetrically substituted fused‐ring conjugated polymer structures to tune mechanical and charge transport properties.

Boosting Electrocatalytic CO 2 Reduction with Conjugated Bimetallic Co/Zn Polyphthalocyanine Frameworks

Boosting Electrocatalytic CO ₂ Reduction with Conjugated Bimetallic Co/Zn Polyphthalocyanine Frameworks

Variety of Ordered Patterns in Donor-Acceptor Polymer Semiconductor Films Crystallized from Solution.

A huge challenge is to control the nucleation of crystallites/aggregates in the solution during polymer film formation to generate desired structures. In this work, we investigate crystallization of P(NDI2OD-T2), a donor–acceptor polymer semiconductor, with controlled solution flow along the contact line between the drying film and solution through a seesaw-like pivoting of samples during polymer drying. By controlling the pivoting frequency/amplitude, various types of line patterns can be observed: (I) an array of fishbone-like stripes oriented in the film-growth direction; (II) the pinning–depinning of contact line (PDCL)-mechanism-defined patterned wires along the contact line; and (III) periodic twined crystalline line pattern oriented in the direction of the contact line. The rich variety of pattern formation observed is attributed to the distinctiveness of the donor–acceptor conjugated polymer structure. The result measured from thin-film transistors made of the generated films/structures showed that the charge mobility of P(NDI2OD-T2) does not change much with the film morphology, which supports recent controversy over the charge-transportation mechanism of some donor–acceptor polymer semiconductors.

Poly(Pyridinium Salt)s Containing 2,7-Diamino-9,9'-Dioctylfluorene Moieties with Various Organic Counterions Exhibiting Both Lyotropic Liquid-Crystalline and Light-Emitting Properties.

A series of poly(pyridinium salt)s-fluorene main-chain ionic polymers with various organic counterions were synthesized by using ring-transmutation polymerization and metathesis reactions. Their chemical structures were characterized by Fourier Transform Infrared (FTIR), proton (1H), and fluorine 19 (19F) nuclear magnetic resonance (NMR) spectrometers. These polymers showed a number-average molecular weight (Mns) between 96.5 and 107.8 kg/mol and polydispersity index (PDI) in the range of 1.12–1.88. They exhibited fully-grown lyotropic phases in polar protic and aprotic solvents at different critical concentrations. Small-angle X-ray scattering for one polymer example indicates lyotropic structure formation for 60–80% solvent fraction. A lyotropic smectic phase contains 10 nm polymer platelets connected by tie molecules. The structure also incorporates a square packing motif within platelets. Thermal properties of polymers were affected by the size of counterions as determined by differential scanning calorimetry and thermogravimetric analysis measurements. Their ultraviolet-visible (UV-Vis) absorption spectra in different organic solvents were essentially identical, indicating that the closely spaced π-π* transitions occurred in their conjugated polymer structures. In contrast, the emission spectra of polymers exhibited a positive solvatochromism on changing the polarity of solvents. They emitted green lights in both polar and nonpolar organic solvents and showed blue light in the film-states, but their λem peaks were dependent on the size of the counterions. They formed aggregates in polar aprotic and protic solvents with the addition of water (v/v, 0–90%), and their λem peaks were blue shifted.

Open-Shell and Closed-Shell Quinoid-Aromatic Conjugated Polymers: Unusual Spin Magnetic and High Charge Transport Properties.

While quinoidal moieties are considered as emerging platforms showing efficient charge transport and interesting open-shell diradical characteristics, whether these properties could be changed by extension to the conjugated polymer structure remains as a fundamental question. Here, we developed and characterized two conjugated polymers incorporating quinoids with different lengths, which have a stable close- and open-shell diradical character, respectively, namely, poly(quinoidal thiophene-thienylene vinylene) (PQuT-TV) and poly(quinoidal bithiophene-thienylene vinylene) (PQuBT-TV). A longer length of a quinoidal core led to enhanced diradical characteristics. Therefore, the longer core length of QuBT was favorable for the formation of an open-shell diradical structure in its monomer and in the quinoidal polymer. PQuBT-TV exhibited high spin characteristics observed by the strong ESR signal, a low band gap, and improved electrochemical stability. On the other hand, as QuT maintained a closed-shell quinoid structure, PQuT-TV exhibited high backbone coplanarity and strong intermolecular interaction, which was beneficial for charge transport and led to high hole mobility (up to 2.40 cm2 V-1 s-1) in organic field-effect transistors. This work successfully demonstrated how the control of the closed/open-shell character of quinoidal building blocks changes charge transport and spin properties of quinoidal conjugated polymers via quinoid-aromatic interconversion.

One-dimensional micro-scale patterned conjugated polymer structures in bilayer architecture and light emitting diode application

To maximize luminescent brightness in organic light-emitting diode (OLED) systems, charge transport dynamics of emissive layer is needed to be controlled. Herein, we pattern aligned micrometer scale conjugated polymer structures using a solution based processing method. Super yellow (SY)-polyethylene oxide (PEO) nanofibers were electrospun using simple uniaxial electrospinning method. A hybrid bilayer of SY-PEO fiber and poly (9,9-dioctylfluorene) derivative PFO film was formed by the sequential deposition of the electrospun fiber and spin-coated film. The maximum brightness of hybrid LED devices was increased over 1.7 fold to that of film-film bilayer device possessing same average film thickness. Besides, optical properties such as absorption/luminescence of SY were modulated by the rapid crystallization and solvent evaporation during electrospinning process compared to the spin-coated film. The electroluminescence enhancement and color control was attributed to balanced charge transport and enhanced Förster resonance energy transfer (FRET). A patterned hybrid bilayer was formed by the combination of the SY-PEO fiber and PFO thin film via solution based sequential deposition methods, including electrospinning and spin-coating. Thanks to the molecular packing and increment of conjugation length in electrospun SY-PEO nanofibers, such nanofibers exhibited distinct optical properties in comparison with SY thin film. Micro-dimensional alignment of conjugated polymer fiber-film bilayer device exhibited superior electroluminescent brightness besides color tunability of constructed LED device. Such enhancements were attributed to balanced charge transport and enhanced Förster resonance energy transfer in fiber-film hybrid emissive bilayer. • Aligned conjugated polymer fibers by electrospinning process. • Electrospun super yellow -polyethylene oxide nanofibers. • One-dimensional conjugated polymer microstructures in fiber-film hybrid bilayer architecture. • Utilization of conjugated polymer nanofibers in light emitting devices.

The development of conjugated polymers as the cornerstone of organic electronics

The expansion of the field of organic electronics has hinged upon structural and fundamental developments in the field of conjugated polymers. Conjugated polymers allow for the manufacture of low-cost, light-weight, flexible organic electronic devices, with notable applications in organic photovoltaics (OPV), organic field effect transistors (OFET), and organic light emitting diodes (OLED). This extraordinary breadth of applications is due to the remarkable diversity of structure, an extensive understanding of structure-function relationships, and the relative ease of structural tuning. Important advancements and the development of such applications is largely due to the evolution of polymer structure, enabled by a broad range of synthetic methods for the tailoring of structures and the development of improved polymerization conditions to limit defects. This perspective provides background from the early days of concerted and focused conjugated polymer research (1970s-1990) to the present, and describes how the tailoring of conjugated polymer structure has now become closely tied to application. A significant focus is also directed to how polymerization methods have evolved from the aggressive, unselective conditions used for oxidative polymerizations to finely tuned transition-metal catalyzed polymerizations that can provide incredibly high structural-fidelity and can proceed through C–H activation. Areas for future work and emerging areas are also discussed, such as high-performing polymers without added structural and synthetic complexity, identifying polymer structures with improved environmental stability, flexible and transient or bioresorbable conjugated polymers, mixed-ion conductors, and photocatalytic and select biological applications.

New Donor-Acceptor polymers with a wide absorption range for photovoltaic applications

For conjugated polymers of interest in photovoltaic applications, control of the bandgap as well as the energy levels of the molecules are of great importance to improve the efficiency and performance of the resulting polymer solar cells. A general tactic for adjusting these properties via modification of the conjugated polymer structure is by using different and chosen molecular groups for copolymerization. This communication presents the synthesis of conjugated donor–acceptor type polymers that have the same benzotrithiophene (BTT) donor and different acceptor units, i.e. DPP and fluoro-carbazole substituted thieno[3,4-b]pyrazine (FCTP) denoted as P(BTT-DPP) (P1) and P(BTT-FCTP) (P2), respectively, and their photovoltaic performance using as donor, and non-fullerene acceptor (PDIF) in the bulk heterojunction active layer. The bandgaps as well as the HOMO and LUMO energy levels are effectively tuned. The P(BTT-FCTPZ) structure exhibits a smaller bandgap as compared to P(BTT-DPP) that results from the lower LUMO energy and higher HOMO energy due to the FCTP unit. Having optimized the active layers, the PSCs that were based on P(BTT-DPP) and P(BTT-FCTPZ gave an overall power conversion efficiency of about 9.77% and 10.97%, respectively, using a wide bandgap PDIF non-fullerene acceptor, and 8.38% and 9.05, respectively, using PC71BM as electron acceptor.

Fabrication of 3D conjugated polymer structures via vat polymerization additive manufacturing

Conjugated polymers are a class of electroactive active material that have been studied for their potential in advanced sensing and actuation technologies. Conventional methods to fabricate conjugated polymer transducers produce devices with planar morphologies that limit fabricated devices to simplistic linear or bending modes of operation. To overcome this limitation, this work develops a photosensitive polypyrrole formulation and light-based additive manufacturing method capable of realizing three-dimensional conjugated polymer structures with micro-scale features. The electroactivity and strain sensing properties of the photosensitive polymer formulation are reported to show the early development of this method towards new sensing and actuation technologies.

12.1: Invited Paper: Polarization control and optical efficiency improvement of light emitted from OLED using liquid crystalline luminophores

Highly circularly polarized (CP) light is generated by using a twisted conjugated polymer structure with a small amount of chiral molecules as the light emitting layer of the OLED. It is confirmed that the luminous efficiency is increased by 60% compared to the conventional OLED structure.

Thermally Activated in Situ Doping Enables Solid-State Processing of Conducting Polymers.

Free-standing bulk structures encompassing highly doped conjugated polymers are currently heavily explored for wearable electronics as thermoelectric elements, conducting fibers, and a plethora of sensory devices. One-step manufacturing of such bulk structures is challenging because the interaction of dopants with conjugated polymers results in poor solution and solid-state processability, whereas doping of thick conjugated polymer structures after processing suffers from diffusion-limited transport of the dopant. Here, we introduce the concept of thermally activated latent dopants for in situ bulk doping of conjugated polymers. Latent dopants allow for noninteractive coprocessing of dopants and polymers, while thermal activation eliminates any thickness-dependent diffusion and activation limitations. Two latent acid dopants were synthesized in the form of thermal acid generators based on aryl sulfonic acids and an o-nitrobenzyl capping moiety. First, we show that these acid dopant precursors can be coprocessed noninteractively with three different polythiophenes. Second, the polymer films were doped in situ through thermal activation of the dopants. Ultimately, we demonstrate that solid-state processing with a latent acid dopant can be readily carried out and that it is possible to dope more than 100 μm-thick polymer films through thermal activation of the latent dopant.

Advances in Conjugated Polymer Lasers.

This paper provides a review of advances in conjugated polymer lasers. High photoluminescence efficiencies and large stimulated emission cross-sections coupled with wavelength tunability and low-cost manufacturing processes make conjugated polymers ideal laser gain materials. In recent years, conjugated polymer lasers have become an attractive research direction in the field of organic lasers and numerous breakthroughs based on conjugated polymer lasers have been made in the last decade. This paper summarizes the recent progress of the subject of laser processes employing conjugated polymers, with a focus on the photoluminescence principle and excitation radiation mechanism of conjugated polymers. Furthermore, the effect of conjugated polymer structures on the laser threshold is discussed. The most common polymer laser materials are also introduced in detail. Apart from photo-pumped conjugated polymer lasers, a direction for the future development of electro-pumped conjugated polymer lasers is proposed.

Thermal annealing-induced structural reorganization in polymeric photocatalysts for enhanced hydrogen evolution.

Herein, a facile reorganization of a triazine-based conjugated polymer structure was adopted to optimize the optical, electronic, and photocatalytic properties of the polymer. The optimal photocatalyst presents enhanced performance as compared to the pristine photocatalyst by a factor of 3. This demonstration provides a new strategy for the optimization of conjugated polymers for various photoredox applications.

Superresolution mapping of energy landscape for single charge carriers in plastic semiconductors

The performance of conjugated polymer devices is largely dictated by charge transport processes. However, it is difficult to obtain a clear relationship between conjugated polymer structures and charge transport properties, due to the complexity of the structure and the dispersive nature of charge transport in conjugated polymers. Here, we develop a method to map the energy landscape for charge transport in conjugated polymers based on simultaneous, correlated charge carrier tracking and single-particle fluorescence spectroscopy. In nanoparticles of the conjugated polymer poly[9,9-dioctylfluorenyl-2,7-diyl)-co-1,4-benzo-{2,1′-3}-thiadiazole)], two dominant chain conformations were observed, a blue-emitting phase (λmax = 550 nm) and a red-emitting phase (λmax = 595 nm). Hole polarons were trapped within the red phase, only occasionally escaping into the blue phase. Polaron hopping between the red-emitting traps was observed, with transition time ranging from tens of milliseconds to several seconds. These results provide unprecedented nanoscale detail about charge transport at the single carrier level.

Synthesis and characterization of a polyacetylene derivative: Poly(N-methylpropargylamine)

ABSTRACTThe polymerization of N-methylpropargylamine was carried out by var-ious transition metal catalysts. The polymerizations of N-methylpropar-gylamine using the Pd, Pt, and Ru chlorides proceeded well in mild homogeneous manner to give the corresponding polymers in moderate yields. The chemical structure of poly(N-methylpropargylamine) was characterized by such instrumental methods as NMR (1H-, 13C-), IR, UV-visible spectroscopies, and elemental analysis to have the designed conjugated polymer structure. The photoluminescence peak of poly(N-methylpropargylamine) was observed at 444 nm, which is corresponded to the photon energy of 2.79 eV. The electrochemical properties were also measured and discussed.

Parallelized biocatalytic scanning probe lithography for the additive fabrication of conjugated polymer structures.

Scanning probe lithography (SPL) offers a more accessible alternative to conventional photolithography as a route to surface nanofabrication. In principle, the synthetic scope of SPL could be greatly enhanced by combining the precision of scanning probe systems with the chemoselectivity offered by biocatalysis. This report describes the development of multiplexed SPL employing probes functionalized with horseradish peroxidase, and its subsequent use for the constructive fabrication of polyaniline features on both silicon oxide and gold substrates. This polymer is of particular interest due to its potential applications in organic electronics, but its use is hindered by its poor processability, which could be circumvented by the direct in situ synthesis at the desired locations. Using parallelized arrays of probes, the lithography of polymer features over 1 cm2 areas was achieved with individual feature widths as small as 162 ± 24 nm. The nature of the deposited materials was confirmed by Raman spectroscopy, and it was further shown that the features could be chemically derivatized postlithographically by Huisgen [2 + 3] "click" chemistry, when 2-propargyloxyaniline was used as the monomer in the initial lithography step.

Tunable intrinsic semiconducting properties of diketopyrrolopyrrole-based copolymers with electron donating thiophene and electron accepting thiazole moieties

The p- and n-type semiconducting characteristics of four conjugated polymers, P(DPPBT), P(DPPBTz), P(TzDPPBT), and P(TzDPPBTz) with molecular energy levels that were systematically varied in a cascade manner, was investigated. The four polymers were synthesized using 3,6-bis(5-bromothiophen-2-yl)-2,5-bis(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione or 3,6-bis(5-bromothiazol-2-yl)-2,5-bis(2-octyldodecyl)pyrrolo [3,4-c]pyrrole-1,4(2H,5H)-dione monomers coupled with bithiophene or bithiazole monomers. By replacing the electron-rich thiophene with electron-deficient thiazole, the energy levels of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) were significantly lowered. Thin film transistors (TFTs) based on the four polymers were investigated to observe the effect of the polymer energy levels. The results demonstrate that DPP-based polymers have the potential to exhibit p-type or n-type semiconducting properties based on the number of thiazole units incorporated into the conjugated polymer structure.

Conjugated Polymer Nanoparticles in Aqueous Media by Assembly with Phospholipids via Dense Alkyl Chain Packing

Revealing the nature of chain packing in conjugated polymer nanoparticles (CPNs) is one of the important issues to polymer physics research. Surfactant-stabilized CPNs in water show significantly enhanced luminescence intensity in comparison to small molecular organic dyes and single polymer chains dissolved in solvents. The importance of the conjugated polymer structure in nanomaterials is undoubted. However, details of the relationship between alignment of conjugated polymer backbone in CPNs and its luminescent property have not been established. Furthermore, there are yet no methods that can predict the atom-resolved structure of conjugated polymer in the CPNs. Herein, we employ coarse-grained (CG) molecular dynamic simulations to investigate the structure of phase-separated film and the film shattering process for a mixture of poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) and 1,2-dioctanoyl-sn-glycero-3-phosphocholine (D8PC). The π...

The role of incident light intensity, wavelength, and exposure time in the modification of conjugated polymer structure in solution

Our recent investigations indicate that simple white light exposure holds intriguing potential to alter the structure of conjugated polymer chains. To provide further insight into how to rationally control this process, we have employed small angle neutron scattering to investigate structural changes occurring in solutions of poly(3-hexylthiophene-2,5-diyl) upon exposure to white light. Our previous results indicate significant change in the structure of the polymer upon illumination, an effect we attribute to an alteration in the thermodynamic interactions of the polymer with the surrounding solvent. This work provides additional information to further refine our understanding of this phenomenon by studying the relationship between the magnitude of exciton creation and subsequent structural changes through a series of exposure time, light intensity, and wavelength sensitive experiments. The results demonstrate a clear and consistent relationship between the number of absorbable photons available to the conjugated polymer chain and more powerful alterations in polymer structural parameters, indicating that net exciton generation provides the fundamental driving force for this phenomenon. This points towards the feasibility of employing light exposure protocols as a powerful unobtrusive in-situ method for precise tailoring of optoelectronic active layers over a wide range of organic electronic device fabrication procedures.

π共役系高分子構造制御を指向した直接的アリール化反応

π共役系高分子構造制御を指向した直接的アリール化反応