Π-conjugated Polymer Poly Research Articles

Conjugated polymer-encapsulation-manipulated aggregation-induced electrochemiluminescence of tetraphenylethylene for sensitive malathion analysis

Tetraphenylethylene (TPE) and its derivatives with tunable structure and excellent photoelectric performance have aroused great concern in the field of electrochemiluminescence (ECL), but improving their ECL efficiency remains an enormous challenge in ECL bioanalysis. Herein, an encapsulation-manipulated aggregation-induced ECL (EM-AIECL) strategy was explored to effectively boost the ECL efficiency of TPE. Large π-conjugated polymer poly[2,5-dioctyl-1,4-phenylene] (PDP) was creatively developed as encapsulation matrix to envelop TPE molecules via hydrophobic interactions. The resulting complex TPE@PDP nanoparticles (NPs) not only restricted the molecule motion of TPE due to space limitation, but also inhibited the aggregation-caused quenching effect caused by TPE crystals featuring dense aggregation structure. Furthermore, the robust electronic coupling between PDP and TPE aggregates enabled superior charge transport within TPE@PDP NPs, thus yielding strong AIECL. As compared to TPE crystals, TPE@PDP NPs showcased 3.87-fold enhancement of ECL intensity. Impressively, TPE@PDP NPs coupled a three-dimensional DNA walker-assisted multiple rolling circle amplification strategy to construct an ECL sensing platform for malathion analysis, and a wide linear range of 5.0 fM ∼ 0.5 μM and low limit of detection of 0.9 fM were obtained. EM-AIECL strategy provides a new idea for designing organic AIECL luminophors, and opens an avenue for detecting pesticides specifically and sensitively.

Different PEG-PLGA Matrices Influence In Vivo Optical/Photoacoustic Imaging Performance and Biodistribution of NIR-Emitting π-Conjugated Polymer Contrast Agents.

The π-conjugated polymer poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b0]-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) with deep-red/near-infrared (NIR) absorption and emission has been investigated as a contrast agent for in vivo optical and photoacoustic imaging. PCPDTBT is encapsulated within poly(ethylene glycol) methyl ether-block-poly(lactide-co-glycolide) (PEG2kDa -PLGA4kDa or PEG5kDa -PLGA55kDa ) micelles or enveloped by the phospholipid, 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] (PEG2kDa -DPPE), to investigate the formulation effect on imaging performance, biodistribution, and biocompatibility. Nanoparticles that meet the quality requirements for parenteral administration are generated with similar physicochemical properties. Optical phantom imaging reveals that both PEG-PLGA systems exhibit a 30% higher signal-to-background ratio (SBR) than PEG2kDa -DPPE. This trend cannot be observed in a murine HeLa xenograft model following intravenous administration since dramatic differences in biodistribution are observed. PEG2kDa -PLGA4kDa systems accumulate more rapidly in the liver compared to other formulations and PEG2kDa -DPPE demonstrates a higher tumor localization. Protein content in the "hard" corona differs between formulations (PEG2kDa -DPPE < PEG2kDa -PLGA4kDa < PEG5kDa -PLGA55kDa ), although this observation alone does not explain biodistribution patterns. PEG2kDa -PLGA4kDa systems show the highest photoacoustic amplitude in a phantom, but also a lower signal in the tumor due to differences in biodistribution. This study demonstrates that formulations for conjugated polymer contrast agents can have significant impact on both imaging performance and biodistribution.

Control of Intrachain Morphology in the Formation of Polyfluorene Aggregates on the Single-Molecule Level.

Controlling the morphology of π‐conjugated polymers for organic optoelectronic devices has long been a goal in the field of materials science. Since the morphology of a polymer chain is closely intertwined with its photophysical properties, it is desirable to be able to change the arrangement of the polymers at will. We investigate the π‐conjugated polymer poly(9,9‐dioctylfluorene) (PFO), which can exist in three distinctly different structural phases: the α‐, β‐, and γ‐phase. Every phase has a different chain structure and a unique photoluminescence (PL) spectrum. Due to its unique properties and the pronounced spectral structure‐property relations, PFO can be used as a model system to study the morphology of π‐conjugated polymers. To avoid ensemble averaging, we examine the PL spectrum of single PFO chains embedded in a non‐fluorescent matrix. With single‐molecule spectroscopy the structural phase of every single chain can be determined, and changes can be monitored very easily. To manipulate the morphology, solvent vapor annealing (SVA) was applied, which leads to a diffusion of the polymer chains in the matrix. The β‐ and γ‐phases appear during the self‐assembly of single α‐phase PFO chains into mesoscopic aggregates. The extent of β‐ and γ‐phase formation is directed by the solvent‐swelling protocol used for aggregation. Aggregation unequivocally promotes formation of the more planar β‐ and γ‐phases. Once these lower‐energy more ordered structural phases are formed, SVA cannot return the polymer chain to the less ordered phase by aggregate swelling.

Stable and Efficient Organo-Metal Halide Hybrid Perovskite Solar Cells via π-Conjugated Lewis Base Polymer Induced Trap Passivation and Charge Extraction.

High-quality pinhole-free perovskite film with optimal crystalline morphology is critical for achieving high-efficiency and high-stability perovskite solar cells (PSCs). In this study, a p-type π-conjugated polymer poly[(2,6-(4,8-bis(5-(2-ethylhexyl) thiophen-2-yl)-benzo[1,2-b:4,5-b'] dithiophene))-alt-(5,5-(1',3'-di-2-thienyl-5',7'-bis(2-ethylhexyl) benzo[1',2'-c:4',5'-c'] dithiophene-4,8-dione))] (PBDB-T) is introduced into chlorobenzene to form a facile and effective template-agent during the anti-solvent process of perovskite film formation. The π-conjugated polymer PBDB-T is found to trigger a heterogeneous nucleation over the perovskite precursor film and passivate the trap states of the mixed perovskite film through the formation of Lewis adducts between lead and oxygen atom in PBDB-T. The p-type semiconducting and hydrophobic PBDB-T polymer fills in the perovskite grain boundaries to improve charge transfer for better conductivity and prevent moisture invasion into the perovskite active layers. Consequently, the PSCs with PBDB-T modified anti-solvent processing leads to a high-efficiency close to 20%, and the devices show excellent stability, retaining about 90% of the initial power conversion efficiency after 150 d storage in dry air.

Macroscopic Structural Compositions of π-Conjugated Polymers: Combined Insights from Solid-State NMR and Molecular Dynamics Simulations.

Molecular dynamics simulations are combined with solid-state NMR measurements to gain insight into the macroscopic structural composition of the π-conjugated polymer poly(2,5-bis(3-tetradecyl-thiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT). The structural and dynamical properties, as established by the NMR analyses, were used to test the local structure of three constitutient mesophases with (i) crystalline backbones and side chains, (ii) lamellar backbones and disordered side chains, or (iii) amorphous backbones and side chains. The relative compositions of these mesophases were then determined from the deconvolution of the 1H and 13C solid-state NMR spectra and dynamic order parameters. Surprisingly, on the basis of molecular dynamics simulations, the powder composition consisted of only 28% of the completely crystalline mesophase, while 23% was lamellar with disordered side chains and 49% amorphous. The protocol presented in this work is a general approach and can be used for elucidating the relative compositions of mesophases in π-conjugated polymers.

Exceptional gain for the stimulated resonant Raman scattering in the π-conjugated polymer poly(dioctylfluorene).

Stimulated resonant Raman scattering (SRRS) is observed in slab waveguides formed in thin films of the π-conjugated polymer poly(dioctylfluorene) (PFO). The presence of two distinct morphological phases with different electronic bandgaps in these films allows the output frequency of this process to be observed over a much broader range than in other organic materials. In particular, the SRRS peak is pronounced when it is spectrally located in the vicinity of the amplified spontaneous emission bands of the films, which peak at 449 and 463 nm, respectively, for the two different phases, allowing selective tuning in the range of 440-470 nm. Furthermore, the superposition of the SRRS spectral location with that of electronic gain produces an overall gain of 269 cm(-1), making this material extremely attractive for use as an active material in compact Raman lasers.

Morphology dependent amplified spontaneous emission in π-conjugated polymer

Abstract The amplified spontaneous emission (ASE) spectra of a π-conjugated polymer Poly [2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) are studied in as-cast film, annealed film, 1 mg/ml solution and 2.5 mg/ml solution, respectively, using a 10 ns pulsed laser as an excitation source. We found that for annealed film (420 K), the ASE is hardly achieved compared to the as-cast film, which is consistent with the formation of the aggregation; whereas the film's temperature had much less effect on its ASE threshold. In solution, the ASE spectra show both 0–0 peak and 0–1 peak in 1 mg/ml solution, but only 0–1 peak in 2.5 mg/ml one. When the temperature of solution increases slightly from 300 K to 330 K, the ASE threshold increases dramatically in 1 mg/ml solution but slightly in 2.5 mg/ml one. Our results show the important role the morphology played in the ASE spectra in both film and solution. Therefore, controlling the interchain interaction in PCPs may be the key factor for performance of the organic lasers.

THE EFFECT OF LIGHT-INDUCED METASTABLE DEFECTS ON THE MAGNETO-CONDUCTANCE OF POLY(PHENYLENE-VINYLENE) DIODES

We studied the changes in the magneto-conductance (MC) response in bipolar and unipolar organic diodes based on the π-conjugated polymer poly[2-methoxy-5-(2-ethylhexyl-oxy)-1,4-phenylene-vinylene] (MEH-PPV), upon prolonged illumination of light in the Visible–UV range. We found that the MC response in the hole-unipolar device gradually changes sign from negative to positive upon illumination, caused by the photogeneration of metastable donor-like defects in the MEH-PPV layer. This conclusion is supported by photoinduced absorption spectroscopy of pristine MEH-PPV film. In contrast, we found very little change in the MC response upon illumination of electron-unipolar devices; however, the MC response substantially increases in bipolar devices. We interpret the sign change in the MC response of hole-unipolar devices as due to illumination induced change in the spin-pairs that participate in the MC, from spin pairs of same charge to spin pairs of opposite charges.

Characterization of photoluminescence spectra from poly allyl diglycol carbonate (CR-39) upon excitation with the ultraviolet radiation of various wavelengths

The induced photoluminescence (PL) from the π-conjugated polymer poly allyl diglycol carbonate (PADC) (CR-39) upon excitation with the ultraviolet radiation of different wavelengths was investigated. The absorption and attenuation coefficients of PADC (CR-39) were recorded using a UV–visible spectrometer. It was found that the absorption and attenuation coefficients of the PADC (CR-39) exhibit a strong dependence on the wavelength of ultraviolet radiation. The PL spectra were measured with a Flormax-4 spectrofluorometer (Horiba). PADC (CR-39) samples were excited by ultraviolet radiation with wavelengths in the range from 260 to 420 nm and the corresponding PL emission bands were recorded. The obtained results show a strong correlation between the PL and the excitation wavelength of ultraviolet radiation. The position of the fluorescence emission band peak was red shifted starting from 300 nm, which was increased with the increase in the excitation wavelength. The PL yield and its band peak height were increased with the increase in the excitation wavelength till 290 nm, thereafter they decreased exponentially with the increase in the ultraviolet radiation wavelength. These new findings should be considered carefully during the use of the PADC (CR-39) in the scientific applications and in using PADC (CR-39) in eyeglasses.

A New Supramolecular Hole Injection/Transport Material on Conducting Polymer for Application in Light‐Emitting Diodes

A new DNA-mimetic π-conjugated polymer poly(triphenylamine-carbazole) (PTC-U) has been prepared which exhibits high thermal stability, non-corrosion, excellent hole injection and electron-blocking abilities in the solid state owing to the uracil induced physical cross-linking. In addition, a trilayer device with PTC-U as a hole injection/transport layer is approximately 1.6 times higher than that of the commercial product PEDOT:PSS-based devices.

Fluorescence Decrease of Conjugated Polymers by the Catalytic Activity of Horseradish Peroxidase and Its Application in Phenolic Compounds Detection

We report the fluorescence decrease of the water-soluble π-π-conjugated polymer poly(2-methoxy-5-propyloxy sulfonate phenylene vinylene, MPS-PPV) by the catalytic activity of horseradish peroxidase in the presence of H(2)O(2). MPS-PPV acts as a donor substrate in the catalytic cycle of horseradish peroxidase where the electron-deficient enzymatic intermediates compounds I and II can subtract electrons from the polymer leading to its fluorescence decrease. The addition of phenolic drug acetaminophen to the former solution favors the decrease of the polymer fluorescence, which indicates the peroxidase-catalyzed co-oxidation of MPS-PPV and acetaminophen. The encapsulation of horseradish peroxidase within polyacrylamide microgels allows the isolation of intermediates compound I and compound II from the polymer, leading to a fluorescence decrease that is only due to the product of biocatalytic acetaminophen oxidation. This system could be used to develop a new device for phenolic compounds detection.

Prussian blue nanoparticles protected by the water-soluble π-conjugated polymer PEDOT-S: synthesis and multiple-color pH-sensing with a redox reaction

Prussian blue nanoparticles (PB NPs), stabilized for the first time by the pi-conjugated polymer poly(4-(2,3-dihydrothieno[3,4-b][1,4]dioxin-2yl-methoxy-1-butanesulfonic acid, potassium salt) (PEDOT-S), demonstrated a novel multiple-color pH-sensing function with a redox reaction based on the electronic interaction between the PB nano-core and the PEDOT-S shell.

Photoelectrical behavior of perylene derivative/π-conjugated polymer system

Organic photovoltaic (PV) cells composed of a perylene derivative, N, N′-di(pentan-3-yl)-perylene-3,4:9,10-bis(dicarboximide), PTCDI, acting as an acceptor and a π-conjugated polymer poly{1-phenyl-2-[4-(trimethylsilyl)phenyl]acetylene}, PDPA, acting as a donor of photogenerated free electrons are presented. Two types of starting double-layer samples were prepared: samples I composed of a spin-cast PDPA thin film bottom layer and a PTCDI upper layer deposited by the vacuum sublimation, and samples II composed of a spin-cast mixed PDPA/PTCDI layer and a vacuum-sublimation deposited PTCDI upper layer. The samples were treated with toluene vapors to induce changes in the morphology of heterojunctions due to recrystallization of PTCDI, which have been monitored by the optical absorption spectra and AFM images, and the influence of the morphology changes on photovoltaic characteristics of the samples has been studied. A short-time (2–5 min) toluene-vapor treatment positively influences the PV efficiency of system I due to a formation of larger PTCDI crystals, which improves the collection efficiency of the upper layer. However, a longer-time treatment of a system I results in a decrease in its PV efficiency owing to a significant decrease in the PDPA–PTCDI interfacial area accompanying further growth of PTCDI crystals, which lowers the photogeneration efficiency of the system. A combination of molecularly dissolved (in PDPA) and crystalline PTCDI in the system II has been proved to provide better PV efficiency due to a combination of improved free charge carrier photogeneration in the composite bottom layer and the collection efficiency of charge carriers of the upper layer.

Influence of the morphology of organic heterojunction on the photovoltaic cell performance

We present a series of organic photovoltaic (PV) cells based on the bulk-distributed heterojunction where π-conjugated polymer poly[1-(4-trimethylsilylphenyl)-2-phenylvinylene], PSDPhV, acts as the donor upon photoexcitation and the substituted perylene based low-molecular-weight compound: N,N'-di(pent-3-yl)-perylene-3,4:9,10-bis(dicarboximide), DPe-PTCDI, as the acceptor of photogenerated electrons. According to both absorption spectra and AFM images of the thin films spin-coated from solution of DPe-PTCDI and PSDPhV in toluene, the DPe-PTCDI is molecularly dissolved in conjugated polymer matrix. Upon exposition of layers to toluene vapors, microcrystals of DPe-PTCDI are progressively formed. The influence of the morphology of DPe-PTCDI inside the polymer matrix on PV cell performance is investigated.

Comparing small molecules and polymer for future organic spin-valves

We report spin polarized injection and transport in organic spin-valves made from both organic small molecules and polymers. The devices with the structure La 0.67Sr 0.33MnO 3 (LSMO)/organic spacer/Co showed inverse magnetoresistance and low temperature operation with the vacuum evaporated π-conjugated small molecule 8-hydroxyquinoline aluminium (Alq 3) while normal MR and high temperature operation was observed in devices with the π-conjugated polymer poly(3-hexylthiophene). Due to the proximate values of the work functions of LSMO and Co with the highest occupied molecular orbital (HOMO) energy of the polymers, spin polarized carrier injection is much more efficient in the polymeric spin-valves compared to the organic spin-valves with Alq 3 where carrier injection is hindered due to greater barrier height. Efficient spin transport is also observed in polymeric spin-valves and can be attributed to longer conjugation in the polymeric chains compared to the small molecules.

Synthesis and properties of poly(3,9-carbazole) and low-molar-mass glass-forming carbazole compounds

The novel π-conjugated polymer poly(3,9-carbazole) was prepared by Ullmann polycondensation reaction of 3-iodo-9 H-carbazole. The polymer has a number-average molecular weight of ca. 2400 with a molecular weight distribution of 2.15. The dimer model compound and the carbazole trimer 3,6-di(carbazolyl)alkylcarbazole have been synthesized by stepwise reactions. All these compounds have been found to form glasses with glass transition temperatures in the range 35–157 °C as characterized by differential scanning calorimetry. The ionization potentials of these compounds range from 5.45 to 5.97 as determined by the electron photoemission method. Time of flight experiment showed that hole drift mobilities of the low-molar-mass glasses were in the range 10 −5–10 −3 cm 2 V −1 s −1.

Photoluminescence, Electroluminescence, Nonlinear Optical, and Humidity Sensitive Properties of Poly(p-diethynylbenzene) Prepared with a Nickel Acetylide Catalyst

The π-conjugated polymer poly(p-diethynylbenzene) (PDEB) has potential applications in electronics and optics; however, its poor solubility and processability have limited its usefulness. The new synthesis reported here makes use of a novel nickel catalyst, and gives rise to PDEB with good solubility and excellent thermal stability characteristics. The polymer exhibits fair photoluminescence and electroluminescence, a large third-order nonlinear optical susceptibility, and good humidity sensitivity, while doped PDEB shows semiconductor characteristics.

Selective excitation of the luminescence of a polymer film at room temperature

Selective laser excitation of the luminescence of a thin film of the π-conjugated polymer poly(p-phenylene) at room temperature is achieved. Monochromatic excitation is selective only for excitation in the long-wavelength wing of the absorption spectrum. This is manifested as a shift of the luminescence spectrum with excitation frequency. The experimental results are interpreted on the basis of model calculations.