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We report a Forster resonance energy transfer (FRET)-based imaging ensemble for the visualization of membrane potential in living cells. A water-soluble poly(fluorene-cophenylene) conjugated polyelectrolyte (FsPFc10) serves as a FRET donor to a voltage-sensitive dye acceptor (FluoVolt™ ). We observe FRET between FsPFc10 and FluoVolt™ , where the enhancement in FRET-sensitized emission from FluoVolt™ is measured at various donor/acceptor ratios. At a donor/acceptor ratio of 1, the excitation of FluoVolt™ in a FRET configuration results in a three-fold enhancement in its fluorescence emission (compared to when it is excited directly). FsPFc10 efficiently labels the plasma membrane of HEK 293T/17 cells and remains resident with minimal cellular internalization for ~ 1.5 h. The successful plasma membrane-associated colabeling of the cells with the FsPFc10-FluoVolt™ donor-acceptor pair is confirmed by dual-channel confocal imaging. Importantly, cells labeled with FsPFc10 show excellent cellular viability with no adverse effect on cell membrane depolarization. During depolarization of membrane potential, HEK 293T/17 cells labeled with the donor-acceptor FRET pair exhibit a greater fluorescence response in FluoVolt™ emission relative to when FluoVolt™ is used as the sole imaging probe. These results demonstrate the conjugated polyelectrolyte to be a new class of membrane labeling fluorophore for use in voltage sensing schemes.

The synthesis of conjugated polymers with ionic substituents directly bound to their main chain repeat units is a strategy for generating strongly electron-accepting conjugated polyelectrolytes, as demonstrated through the synthesis of a series of ionic azaquinodimethane (iAQM) compounds. The introduction of cationic substituents onto the quinoidal para-azaquinodimethane (AQM) core gives rise to a strongly electron-accepting building block, which can be employed in the synthesis of ionic small molecules and conjugated polyelectrolytes (CPEs). Electrochemical measurements alongside theoretical calculations indicate notably low-lying LUMO values for the iAQMs. The optical band gaps measured for these compounds are highly tunable based on structure, ranging from 2.30 eV in small molecules down to 1.22 eV in polymers. The iAQM small molecules and CPEs showcase the band gap reduction effects of combining the donor-acceptor strategy with the bond-length alternation reduction strategy. As a demonstration of their utility, the iAQM CPEs so generated were used as active agents in photothermal therapy.

An eco-friendly n-type water/alcohol-soluble conjugated polyelectrolyte PFEO SO3 Li was synthesized and applied as a cathode interfacial layer in organic solar cells. The π-delocalized polyfluorene backbone has an intimate connection with the hydrophobic active layer, and the side chain with lithium ion may move toward the ZnO layer through the self-assembly property of conjugated polyelectrolytes. UV photoelectron spectroscopy indicated that modification with PFEO SO3 Li dramatically lowers the work function of indium-doped tin oxide (ITO)/ZnO and may form strong interfacial dipoles between ZnO and the active layer. Meanwhile, introduction of lithium ions as spectator cations may contribute to reduction of the intrinsic surface defects of ZnO. The green emission in the photoluminescence spectrum of ZnO disappeared after modification with PFEO SO3 Li. In addition, the roughness of ZnO barely changed after coating with PFEO SO3 Li, and the surface became more hydrophobic, which demonstrates that the thin conjugated polyelectrolyte layer exhibits good adhesion with both ZnO and the active layer. These phenomena indicate that the introduction of PFEO SO3 Li makes ITO/ZnO an efficient cathode. As a result, inverted organic solar cell devices with ZnO/PFEO SO3 Li double-interlayers exhibit high efficiencies of 11.7 and 10.6 % for PBDB-T:IT-M and PBDB-T:ITIC blend systems, respectively.

Phosphonium-based polythiophene conjugated polyelectrolytes (CPEs) with three different counterions (dodecylsulfate, octylsulfate and perfluorooctane sulfonate) are synthesized to determine how the nature of the counterion affects the thermal properties, the self-assembly in thin films and the performance as the cathode interfacial layer in polymer solar cells (PSCs). The counterion has a significant effect on the thermal properties of the CPEs, affecting both their glass transition and crystalline behaviour. Grazing-incidence wide-angle X-ray scattering studies also indicate that changing the nature of the counterion influences the microstructural organization in thin films (face-onversusedge-on orientation). The affinity of the CPEs with the underlying photoactive layer in PSCs is highly correlated with the counterion species. Finally, in addition to an increase of the power conversion efficiency ofca15% when using these CPEs as cathode interfacial layers in PSCs, a higher device stability is noted, compared to a reference device with a calcium interlayer. (c) 2020 Society of Industrial Chemistry This work was supported by the CNRS and the Universite de Montpellier. This work was also supported in part by the Science Foundation Ireland under grant no. 12/IP/1608. Research in Mons is supported by FNRS-FRFC (2Dto3D project - EOS programme) and Region Wallonne (OPTI2MAT excellence programme). The University of Mons and Hasselt University co-authors are grateful for financial support by the Science Policy Office of the Belgian Federal Government (BELSPO; PAI/IAP 7/05). JK is a postdoctoral fellow of the Research Foundation - Flanders (FWO Vlaanderen). NVdB thanks the Vrije Universiteit Brussel for a post-doctoral grant. The HINT COST action MP1202 and French-Irish programme 'Hubert Curien Ulysses' (31998ZF) are also acknowledged for support. This research has also been supported by the European Commission under the 7th Framework Programme through the 'Research Infrastructures' action of the 'Capacities' programme (contract no. CP-CSA_INFRA-2008-1.1.1 Number 226507-NM13). We further thank the Diamond Light Source for beamtime at the I07 beamline (experiment SI13868) and TA Instruments for the RHC equipment. Clement, S (corresponding author), Univ Montpellier, ENSCM, CNRS, ICGM, Montpellier, France. sebastien.clement1@umontpellier.fr

Conducting polymer hydrogels (CPHs) are an attractive class of materials that synergize the electrical properties of organic semiconductors with the physical properties of hydrogels. Of particular interest is the implementation of CPHs as electrode materials for electrochemical energy storage by taking advantage of redox-tunable conjugated backbones and the large electroactive surface area. Herein, the use of 2D electrolytes as an effective post-polymerization additive to enhance the pseudocapacitive performance of CPHs, is demonstrated. By using the self-doped conjugated polyelectrolyte CPE-K hydrogel as a model system, improvements in cycling stability, specific capacitance and working voltage window upon addition of the 2D electrolytes, are shown. Furthermore, positively charged 2D electrolytes to be more effective than their negatively charged counterparts are revealed. Rheology measurements and SEM imaging indicate that the 2D electrolytes serve as non-covalent cross-linkers that help in forming a mechanically more robust and highly percolated conducting network. These results provide a new and simple to execute post-polymerization strategy to optimize the electrochemical performance of CPH-based pseudocapacitors. National Research Foundation (NRF) This work was supported by the National University of Singapore start up grant R143-000-A97-133 and the Medium-Sized Centre (MSC) grant from the National Research Foundation (NRF) of Singapore, Prime Minister's Office. G.Q. acknowledges funding from the President's Graduate Fellowship (PGF) under the National University of Singapore.

Conjugated polyelectrolytes (CPEs) are characterized by an electronically delocalized backbone bearing ionic functionalities. These features lead to properties relevant for use in energy-storing pseudocapacitor devices, including ionic conductivity, water processability, gel-formation, and formation of polaronic species stabilized by electrostatic interactions. In this Perspective, the basis for evaluating the figures of merit for pseudocapacitors is provided, together with the techniques used for their evaluation. The general utility and challenges encountered with neutral conjugated polymers are then discussed. Finally, recent advances on the use of CPEs in pseudocapacitor devices are reviewed. The article is concluded by discussing how their miscibility in aqueous media permits the incorporation of CPEs in living materials that are capable of switching function from extraction of energy from bacterial metabolic pathways to pseudocapacitor energy storage.

In the past two decades, bulk heterojunction-organic photovoltaic devices (BHJ-OPVs) have emerged as attractive candidates for solar energy conversion due to their light-weight design and potential for low-cost high-throughput, solution-phase processability. Interfacial engineering is a proven efficient approach to achieve OPVs with high power conversion efficiencies (PCEs). This mini-review provides an overview of the key structural considerations necessary when undertaking the molecular design of conjugated polyelectrolytes (CPEs), for application as interfacial layers (ILs). The different roles of ILs are outlined, together with the advantages and disadvantages of competing classes of IL materials. Particular emphasis is placed on the design and synthesis of water-soluble polythiophene-based IL materials and the influence of their structural characteristics on their performance as a promising class of IL materials. Finally, the challenges and opportunities for polythiophenes as IL materials for OPVs and other solution-processed solar cell technologies (e.g. perovskite solar cells) are discussed.

Molecular weights of seven poly(phenylene ethynylene)-based water-soluble conjugated polyelectrolytes (CPEs) obtained through Sonogashira coupling are determined by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). A standard sample preparation protocol is developed to characterize the seven CPEs using 2,5-dihydroxybenzoic acid as the matrix (M) and AgTFA as the cationization reagent (CR). High-quality MALDI mass spectra are obtained at volume mixing ratios (CPE/M/CR) of 5/5/1 for anionic polymers (P1–P4) and 5/50/1 for cationic polymers (P5–P7). Molecular weight, molecular weight distribution, and end-group information are analyzed. The effects of molecular weight of CPEs on optical and quenching properties are also studied. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017

Synthesis of fluorene-based conjugated polyelectrolytes was achieved via Suzuki polycondensation in water and completely open to air. The polyelectrolytes were conveniently purified by dialysis and analysis of the materials showed properties expected for fluorene-based conjugated polyelectrolytes. The materials were then employed in solar cell devices as an interlayer in conjunction with ZnO. The double interlayer led to enhanced power conversion efficiency of 10.75 % and 15.1 % for polymer and perovskite solar cells, respectively.

Ionic polythiophenes are important conjugated polymers because of their excellent optical properties and water solubility. They are classified as cationic, anionic and zwitterionic conjugated polyelectrolytes. This review article describes concisely their biological and analytical applications. The specific detection of different negatively charged biomolecules such as DNA and adenosine triphosphate, anions like halides and toxic pseudo-halide (CN−) and environmental pollutants, e.g. surfactants, is discussed. The conformational changes of cationic polythiophenes (CPTs) induced by various analytes due to formation of ionic conjugates and the cooperative responses of all segments cause dominant signal amplification even in the presence of a small perturbation. In addition, reactive oxygen scavenging, antimicrobial photosensitizing and cell imaging applications of CPTs are documented. Use of anionic polythiophenes for sensing of protamine and cations like Cu2+ and Ca2+ is also discussed. Finally, sensing of DNA, peptides and surfactants by zwitterionic polythiophenes is included. The concluding part discusses future prospects. © 2016 Society of Chemical Industry

Red and near infrared (NIR) fluorescent conjugated polyelectrolytes (CPEs) have attracted increasing attention in the past few years due to their potential applications in biomedical fields. Specifically, red and NIR fluorescent CPEs with special functionalities exhibit great promises in targeted tumor cell imaging and detection of disease-related biomarkers. In addition, smart agents combining image and therapeutic actions have also been successfully demonstrated for some red and NIR emissive CPEs. In this mini review, we attempt to offer a brief description of the synthetic methods for red and NIR CPEs, and focus predominantly on the rationale behind the molecular design and their applications in biomedical research. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016

Organic solar cells (OSCs) based on nonfullerene acceptors (NFAs) have made significant breakthrough in their device performance, now achieving a power conversion efficiency of ≈18% for single junction devices, driven by the rapid development in their molecular design and device engineering in recent years. However, achieving long‐term stability remains a major challenge to overcome for their commercialization, due in large part to the current lack of understanding of their degradation mechanisms as well as the design rules for enhancing their stability. In this review, the recent progress in understanding the degradation mechanisms and enhancing the stability of high performance NFA‐based OSCs is a specific focus. First, an overview of the recent advances in the molecular design and device engineering of several classes of high performance NFA‐based OSCs for various targeted applications is provided, before presenting a critical review of the different degradation mechanisms identified through photochemical‐, photo‐, and morphological degradation pathways. Potential strategies to address these degradation mechanisms for further stability enhancement, from molecular design, interfacial engineering, and morphology control perspectives, are also discussed. Finally, an outlook is given highlighting the remaining key challenges toward achieving the long‐term stability of NFA‐OSCs.

In the following report, a conjugated polyelectrolyte (CPE) blend has been introduced for the first time as a fluorescent probe of membrane organization. Insertion of the blend into the lipid doubl ...

In this work, a multifunctional platform based on the versatile function of cationic poly(p-phenylene vinylene) (PPV) derivative has been developed for white light-enhanced siRNA delivery in a remote control manner. Conjugated polyelectrolyte PPV, which possesses cationic and amphipathic features, can effectively self-assemble with siRNA and deliver siRNA into living cells. More importantly, PPV can sensitize surrounding oxygen into reactive oxygen species (ROS) upon exposure to white light and disrupt the endosomal membrane, and the resulting enhanced endosomal escape increases the gene silencing ability of siRNA. Besides, due to high fluorescent emission, PPV can also be used to image the siRNA delivery and intracelluar location. Therefore, by taking full advantage of PPV, this strategy provides a new enhanced siRNA delivery in a non-invasive and spatiotemporal photochemical manner.

Conjugated polyelectrolytes (CPEs) are macromolecules with highly delocalized π-conjugated backbones and charged side chains, which are unique types of active materials, with wide applications in optoelectronics, sensing, imaging, and therapy. By attaching specific groups (e.g., recognition elements, magnetic resonance (MR) contrast agents, gene carriers, and drugs) to the side chain or backbone of CPEs, functionalized CPEs have been developed and used for specific biological applications. In this account, we summarize the recent progress of functionalized CPEs with respect to their synthesis and biomedical applications. Future perspectives are also discussed at the end.

Alkoxy side-chain tethered polyfluorene conjugated polyelectrolyte (CPE), poly[(9,9-bis((8-(3-methyl-1-imidazolium)octyl)-2,7-fluorene)-alt-(9,9-bis(2-(2-methoxyethoxy)ethyl)-fluorene)] dibromide (F8imFO4), is utilized to obtain CPE-hybridized ZnO nanoparticles (NPs) (CPE:ZnO hybrid NPs). The surface defects of ZnO NPs are passivated through coordination interactions with the oxygen atoms of alkoxy side-chains and the bromide anions of ionic pendent groups from F8imFO4 to the oxygen vacancies of ZnO NPs, and thereby the fluorescence quenching at the interface of yellow-emitting poly(p-phenylene vinylene)/CPE:ZnO hybrid NPs is significantly reduced at the CPE concentration of 4.5 wt%. Yellow-emitting polymer light-emitting diodes (PLEDs) with CPE(4.5 wt%):ZnO hybrid NPs as a cathode interfacial layer show the highest device efficiencies of 11.7 cd A−1 at 5.2 V and 8.6 lm W−1 at 3.8 V compared to the ZnO NP only (4.8 cd A−1 at 7 V and 2.2 lm W−1 at 6.6 V) or CPE only (7.3 cd A−1 at 5.2 V and 4.9 lm W−1 at 4.2 V) devices. The results suggest here that the CPE:ZnO hybrid NPs has a great potential to improve the device performance of organic electronics.

Three types of cationic polyfluorenes with a different number of ionic groups are synthesized to modulate their solubility in water and the interactions with anionic oligonucleotide probes (DNA-C). Increasing the charge density improves the water-solubility of conjugated polyelectrolytes (CPEs) but decreases its optical antenna effect in the electrostatic sensory platform (CPE/DNA-C), resulting in low fluorescence resonance energy transfer (FRET) signal. With increasing charge density in CPE, the concentration of conjugated units in CPE/DNA-C decreases at [+]:[−] = 1:1, after which little driving force is expected to bring positive CPEs and negative DNA-C into close proximity for efficient FRET. CPF2 with 2 ionic groups (per repeat unit) and hydrophilic polyether side-chains exhibits good water-solubility and a higher FRET signal with an enhanced signal on/off ratio. In addition, the charge density in CPEs modulates the range of sensory responses by forming a tighter or weaker electrostatic CPE/DNA-C complex, which perturbs the probe-target binding interactions.

PCPDTBT-SO3 K (CPE-K), a conjugated polyelectrolyte, is presented as a mixed conductor material that can be used to fabricate high transconductance accumulation mode organic electrochemical transistors (OECTs). OECTs are utilized in a wide range of applications such as analyte detection, neural interfacing, impedance sensing, and neuromorphic computing. The use of interdigitated contacts to enable high transconductance in a relatively small device area in comparison to standard contacts is demonstrated. Such characteristics are highly desired in applications such as neural-activity sensing, where the device area must be minimized to reduce invasiveness. The physical and electrical properties of CPE-K are fully characterized to allow a direct comparison to other top performing OECT materials. CPE-K demonstrates an electrical performance that is among the best reported in the literature for OECT materials. In addition, CPE-K OECTs operate in the accumulation mode, which allows for much lower energy consumption in comparison to commonly used depletion mode devices.

A series of anionic conjugated polyelectrolytes (CPEs) is synthesized based on poly(fluorene-co-phenylene) by varying the side-chain ionic density from two to six per repeat units (MPS2-TMA, MPS4-TMA, and MPS6-TMA). The effect of MPS2, 4, 6-TMA as interlayers on top of a hole-extraction layer of poly(bis(4-phenyl)-2,4,6-trimethylphenylamine (PTAA) is investigated in inverted perovskite solar cells (PeSCs). Owing to the improved wettability of perovskites on hydrophobic PTAA with the CPEs, the PeSCs with CPE interlayers demonstrate a significantly enhanced device performance, with negligible device-to-device dependence relative to the reference PeSC without CPEs. By increasing the ionic density in the MPS-TMA interlayers, the wetting, interfacial defect passivation, and crystal growth of the perovskites are significantly improved without increasing the series resistance of the PeSCs. In particular, the open-circuit voltage increases from 1.06 V for the PeSC with MPS2-TMA to 1.11 V for the PeSC with MPS6-TMA. The trap densities of the PeSCs with MPS2,4,6-TMA are further analyzed using frequency-dependent capacitance measurements. Finally, a large-area (1 cm2 ) PeSC is successfully fabricated with MPS6-TMA, showing a power conversion efficiency of 18.38% with negligible hysteresis and a stable power output under light soaking for 60 s.

Interface engineering is an effective means to enhance the performance of thin‐film devices, such as perovskite solar cells (PSCs). Herein, a conjugated polyelectrolyte, poly[(9,9‐bis(3′‐((N,N‐dimethyl)‐N‐ethyl‐ammonium)‐propyl)‐2,7‐fluorene)‐alt‐2,7‐(9,9‐dioctylfluorene)]di‐iodide (PFN‐I), is used at the interfaces between the hole transport layer (HTL)/perovskite and perovskite/electron transport layer simultaneously, to enhance the device power conversion efficiency (PCE) and stability. The fabricated PSCs with an inverted planar heterojunction structure show improved open‐circuit voltage (Voc), short‐circuit current density (Jsc), and fill factor, resulting in PCEs up to 20.56%. The devices maintain over 80% of their initial PCEs after 800 h of exposure to a relative humidity 35–55% at room temperature. All of these improvements are attributed to the functional PFN‐I layers as they provide favorable interface contact and defect reduction.

An optical nanoruler system based on a conjugated polyelectrolyte-silver nanoprism pair is developed for label-free protein detection by taking advantage of the metal-enhanced fluorescence effect of silver nanostructures. Antibody-antigen interactions induce a change in the metal-fluorophore distance, followed by the response of a fluorescent signal of the conjugated polyelectrolyte. The system is used to detect target antigens sensitively and selectively.

The spontaneous, catalyst free polymerization of four monomers of the bis(pyridyl)acetylene and bis[(pyridyl)ethynyl]benzene types containing either 2-pyridyl or 4-pyridyl groups via activation with benzyl bromide leads to ionic π-conjugated polyacetylene-type polyelectrolytes (CPEs). All polymers are characterized by means of NMR, IR, UV/vis and photoluminescence spectroscopies, thermogravimetric analysis (TGA) and matrix assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS). The position of the pyridyl groups in the monomer influences the degree of quaternization and the extent of conjugation of CPEs. Monomers with 4-pyridyl groups provide CPEs with a low extent of quaternization [N+/(N+ + N) = 0.27–0.34] and high extent of conjugation. On the other hand, the CPEs derived from 2-pyridyl-containing monomers are highly quaternized [N+/(N+ + N) = 0.77–1.00], however, possess lower conjugation of the main chains. The mechanism assuming quaternization and polymerization as competitive reactions is proposed to explain the difference in the extent of quaternization of CPEs. Prepared CPEs i) are well soluble in polar solvents, e.g., water, methanol, dimethyl sulfoxide, and dimethylformamide, ii) exhibit photoluminescence (emission in the violet to yellow region), and iii) possess high thermal stability.

An easy and efficient approach to achieve a large-area cathode interlayer with controlled film composition, uniformity, and thickness under a nanometer scale is reported by using an electrostatic layer-by-layer (eLbL) self-assembly process. The eLbL films provide a new means for preparing efficient interlayers for polymer solar cells (PSCs) and also represent a potential candidate for use in high-performance large-area PSC modules in the future.

The applications of conjugated polyelectrolytes in biosensing and bioimaging have attracted more and more research interests due to their excellent photophysical properties. In this work, a new series of conjugated polyelectrolytes containing long-lived phosphorescent Ir(III) complexes is designed and synthesized, which can be used for ratiometric and lifetime-based sensing of heparin utilizing the electrostatic interaction between cationic polymers and anionic heparin. By changing the ligand structures of Ir(III) complexes, the sensing performances of phosphorescent-conjugated polyelectrolytes (PCPEs) are optimized. In addition, the application of PCPEs in cellular imaging is carried out. These polymers can be applied for specific staining of cell membrane. Importantly, utilizing the long emission lifetime of phosphorescent signal of Ir(III) complexes, time-gated luminescent imaging is carried out, which can eliminate the short-lived background fluorescence interferences from the environment or biological samples.

Two novel anionic conjugated copolyelectrolytes PSDPPPV and PSDPPPE were synthesized via Heck/Sonogashira coupling reactions and characterized by FT-IR, 1H NMR, UV-vis, and PL spectroscopy. The two polymers are respectively constituted of 2,5-diethoxy-1,4-phenyleneethynylene (DPV) and 2,5-diethoxy-1,4-phenyleneethynylene (DPE) with 1,4-diketo-2,5-bis(4-sulfonylbutyl)-3,6-diphenylpyrrolo[3,4-c]pyrrole (SDPP) which is a novel water soluble diketopyrrolopyrrole derivative. PSDPPPV and PSDPPPE show broad absorption band in visible region and they exhibit strong fluorescence quenching in aqueous solution. The fluorescence of their aqueous solutions can be enhanced in the presence of cationic surfactant or polymer nonionic surfactant. Fluorescence enhancement by introduction of polyvinylpyrrolidone (PVP) shows linear response. This result provides a controllable method to increase fluorescence intensity of dipyrrolopyrrole-based conjugate polyelectrolytes in aqueous phase. The optical properties suggested that PSDPPPV and PSDPPPE which are negatively charged conjugated polymers can assemble with positively charged photovoltaic materials to form ionic photoactive layer. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 739–751

PCPDTBTSO3 K, an anionic, narrow-band-gap conjugated polyelectrolyte, was found to be doped after dialysis. The proposed doping mechanism involves protonation of the polymer backbone, followed by electron transfer from a neutral chain, to generate radical cations, which are stabilized by the pendant sulfonate anions. Formation of polarons is supported by spectroscopy and electrical-conductivity measurements.

A new potassium ion detection assay was developed using a dye-labeled aptamer and conjugated polyelectrolyte (CPE) as a signaling platform via 1-step and 2-step fluorescence resonance energy transfer. Guanine-rich K+-specific aptamers were designed as K+ ion recognition species with 6-carboxyfluorescein (6-FAM) and 6-carboxytetramethylrhodamine (6-TAMRA) at both termini. In the presence of K+ ions, the aptamers undergo a conformational change from an unfolded to folded form by forming a G-quadruplex with K+, bringing two dyes in proximity. FRET-induced 6-TAMRA emission was proportional to [K+] in a range of 22.5 μm–100 mm in water without interference by the presence of excess Na+ ions (100 mm). Upon the addition of CPE, a two-step FRET process from CPE to 6-TAMRA via 6-FAM was enabled, showing an intensified 6-TAMRA signal with K+ ions. The dynamic detection range and limit of detection (LOD) was fine-tuned from ∼millimolar to ∼nanomolar concentrations of K+ by modulating the signal amplification effect of CPE. The LOD was determined to be ≈3.0 nm. This detection assay also showed high selectivity against other metal ions. This sensing scheme can be extended to the detection of a wide range of target materials by simply modifying the recognition aptamer sequence.

Despite the excellent work function adjustability of conjugated polyelectrolytes (CPEs), which induce a vacuum level shift via the formation of permanent dipoles at the CPE/metal electrode interface, the exact mechanism of electron injection through the CPE electron transport layer (ETL) remains unclear. In particular, understanding the ionic motion within the CPE ETLs when overcoming the sizable injection barrier is a significant challenge. Because the ionic functionality of CPEs is a key component for such functions, a rigorous analysis using highly controlled ion density (ID) in CPEs is crucial for understanding the underlying mechanism. Here, by introducing a new series of CPEs with various numbers of ionic functionalities, energy level tuning at such an interface can be determined directly by adjusting the ID in the CPEs. More importantly, these series CPEs indicate that two different mechanisms must be invoked according to the CPE thickness. The formation of permanent interfacial dipoles is critical with respect to electron injection through CPE ETL (≤ 10 nm, quantum mechanical tunneling limit), whereas electron injection through thick CPE ETL (20–30 nm) is dominated by the reorientation of the ionic side chains under a given electric field.

A hybrid complex composed of an anionic conjugated polyelectrolyte (PFB-SO3Na) and a cationic phosphorescent Ir(III) oligomer is formed through electrostatic interaction by simple physical mixing in aqueous media. Due to their opposite charges and their effective spectral overlap, fluorescence resonance energy transfer occurs from the blue-emissive PFB-SO3Na to the red-emissive phosphorescent Ir(III) complex, which allows ratiometric and colorimetric Hg2+ sensing in aqueous solution with good selectivity, sensitivity, as well as visible detection. Time-resolved photoluminescence is applied for Hg2+ detection, which can effectively eliminate the background interference and improve the sensing sensitivity and signal-to-noise ratio in complicated media.

This study concentrates on the potential application of conjugated polyelectrolytes (CPEs) to cell imaging and DNA delivery. Four different types of polyfluorene copolymers, namely, PAHFP-Br, PAEFP-Br, PAHFbT-Br, and PSBFP-Na, which have the same π-conjugated backbone but different side chains, were synthesized. For cytotoxicity testing, L-929 fibroblastic cells were treated with increasing concentrations (0-50 µM) of each CPE and then cell viability was determined by WST-8 assay. Cellular uptake of CPEs into cultured L-929 cells was observed by fluorescence microscopy. To examine DNA delivery by CPEs, the cells were incubated for 1 H with PAHFP-Br/fluorescein (Fl)-labeled single-stranded DNA (ssDNA-Fl) complex and then visualized by fluorescence microscopy. Cytotoxicity of CPEs was increased in a dose-dependent manner but at lower than 10 µM, PAHFP-Br, PAEFP-Br, and PSBFP-Na did not show any cytotoxic effects on the cells. When added to cell cultures at 1 µM, PAHFP-Br/ssDNA-Fl complex was delivered and then dissociated into PAHFP-Br and ssDNA-Fl within the cells. This result implies that PAHFP-Br can enable cell imaging and DNA delivery into fibroblastic cells. Therefore, it is suggested that PAHFP-Br with various advantages such as low cytotoxicity and high fluorescence efficiency can be extensively used as a potential agent for cell imaging and gene delivery.

Understanding the cellular entry pathways of synthetic biomaterials is highly important to improve overall labeling and delivery efficiency. Herein, cellular entry mechanisms of conjugated polymer nanoparticles (CPNs) are presented. CPNs are intrinsic fluorescent materials used for various biological applications. While CPNs cause no toxicity, decreased CPN uptake is observed from cancer cells pretreated with genistein, which is an inhibitor of caveolae-mediated endocytosis (CvME). CvME is further confirmed by high co-localization with caveolin-1 proteins found in the caveolae and caveosomes. Excellent photophysical properties, non-toxicity, and non-destructive delivery pathways support that CPNs are promising multifunctional carriers minimizing degradation of contents during delivery.

In the field of polymer solar cells, improving photovoltaic performance has been the main driver over the past decade. To achieve high power conversion efficiencies, a plethora of new photoactive donor polymers and fullerene derivatives have been developed and blended together in bulk heterojunction active layers. Simultaneously, further optimization of the device architecture is also of major importance. In this respect, we report on the use of specific types of electron transport layers to boost the inherent I-V properties of polymer solar cell devices, resulting in a considerable gain in overall photovoltaic output. Imidazolium-substituted polythiophenes are introduced as appealing electron transport materials, outperforming the currently available analogous conjugated polyelectrolytes, mainly by an increase in short-circuit current. The molecular weight of the ionic polythiophenes has been identified as a crucial parameter influencing performance.

The application of a time-resolved photoluminescence technique and fluorescence lifetime imaging microscopy for biosensing and bioimaging based on phosphorescent conjugated polyelectrolytes (PCPEs) containing Ir(III) complexes and polyfluorene units is reported. The specially designed PCPEs form 50 nm nanoparticles with blue fluorescence in aqueous solutions. Electrostatic interaction between the nanoparticles and heparin improves the energy transfer between the polyfluorene units to Ir(III) complex, which lights up the red signal for naked-eye sensing. Good selectivity has been demonstrated for heparin sensing in aqueous solution and serum with quantification ranges of 0–70 μM and 0–5 μM, respectively. The signal-to-noise ratio can be further improved through time-resolved emission spectra, especially when the detection is conducted in complicated environment, e.g., in the presence of fluorescent dyes. In addition to heparin sensing, the PCPEs have also been used for specific labeling of live KB cell membrane with high contrast using both confocal fluorescent cellular imaging and fluorescence lifetime imaging microscopies. This study provides a new perspective for designing promising CPEs for biosensing and bioimaging applications.

Conjugated polyelectrolytes (CPEs) are a kind of π-conjugated polymers (CPs) containing side chains with ionic functionality [1]. CPEs can be divided into two categories according to the charge of their side chains: cationic conjugated polyelectrolytes (CCPEs) and anionic conjugated polyelectrolytes (ACPEs). Typical cationic groups of CCPEs include quaternary ammonium (NR3 ) and pyridinium, while anionic groups of ACPEs include carboxylate (CO2 ), phosphonate (PO 2− 3 ), and sulfonate (SO3 ). The solubility of CPEs in polar solvents (e.g., water and methanol) is not only dependent on the ionic side groups but also affected by the hydrophobic aromatic backbones [2]. During the past 20 years, a variety of CPEs have been synthesized, most typically via carbon–carbon bond-forming reactions using organometallic catalysts. The most widely used polymerization methods are shown in Scheme 1.1, which include FeCl3-catalyzed or electrochemical oxidization; the Yamamoto and Suzuki coupling reactions for poly(arylene)s [3]; the Wittig, Gilch, Wessling, and Heck reactions for poly(arylene vinylene)s [4]; and the Sonogashira coupling reactions for poly(arylene ethynylene)s [5]. Through these well-established reactions, CPEs can be obtained directly or via postpolymerization strategy. Another example is the ring-opening metathesis polymerization of cyclooctatetraenes, which is described in more detail in Chapter 3. Among these reactions, palladium-catalyzed coupling methods (the Suzuki, Heck, and Sonogashira methods) are the most popular ones because of their tolerance to various functional groups, mild reaction conditions, and capability to produce different backbone structures. This chapter summarizes the design and synthesis of various CPEs. The sections are organized according to the backbone structures of CPEs. The chapter starts with poly(arylene)s, which is followed by poly(arylene ethynylene)s and poly(arylene vinylene)s. In addition, reported physical properties of CPEs including solubility, absorption (λabs) and emission (λem) maxima, and fluorescence quantum yields ( F) are summarized in Tables 1.1–1.3, respectively. However, it should be noted

Herein is reported the synthesis of gadolinium ion (Gd(III))-chelated hyperbranched conjugated polyelectrolyte (HCPE-Gd) and its application in fluorescence and magnetic resonance (MR) dual imaging in live animals. The synthesized HCPE-Gd forms nanospheres with an average diameter of ∼42 nm measured by laser light scattering and a quantum yield of 10% in aqueous solution. The absorption spectrum of HCPE-Gd has two maxima at 318 and 417 nm, and its photoluminescence maximum centers at 591 nm. Confocal laser scanning microscopy studies indicate that the HCPE-Gd is internalized in MCF-7 cancer cell cytoplasm with good photostability and low cytotoxicity. Further fluorescence and MR imaging studies on hepatoma H22 tumor-bearing mouse model reveal that HCPE-Gd can serve as an efficient optical/MR dual-modal imaging nanoprobe for in vivo cancer diagnosis.

Conjugated polyelectrolyte-antibody hybrid materials promise to enhance the utility of conjugated polymers in bioimaging field. Polymer-antibody conjugates that are biologically safe and highly sensitive and selective to cells are designed to image human T or B lymphocytes. In the clear state, the observed efficiency of luminescence is superior to that of commercially available FITC-antibody probe.