Phenylene Vinylene Research Articles

The effect of cross-linking yield of PVK on the vibrational and emissive properties of new copolymer based on vinylcarbazole and phenylene-vinylene units

The Phenylene-Vinylene (PV) unit’s was successfully incorporated in the Vinylarbazole (VC) skeleton using the oxidative way via an anhydrous FeCl3. Dramatic changes in the vibrational and emissive properties are founded by varying the FeCl3 amount in the synthesis way due to the cross-linking of PVK units. SEM analysis showing a modified morphology structures of three compounds. However the percentage of the oxidant account induces the modulation of copolymer properties particularly theirs emissive proprieties. A red shifting of the maximum of photoluminescence, a quenching of luminescence and a fast decay time was observed with increasing of the oxidation yields.

Macromol. Rapid Commun. 10/2016

Front Cover: Geometric squeezing of the poly(phenylene vinylene) repeating units from conventional para-connectivity to the ortho isomeric state induces considerable perturbation of the delocalized π–electron system. Shortened conjugation lengths and significant blue-shifts of UV-vis absorption and photoluminescence characteristics are the consequences. Creative graphic support in catchy visualization of that squeezing effect provided by Mr. Christian Krupp, WKC project, is gratefully acknowledged. Further details can be found in the article by V. Rittscher, S. Kuch, and M. Rehahn* on page 814.

Sequence Effects in Conjugated Donor-Acceptor Trimers and Polymers.

To investigate the sequence effect on donor-acceptor conjugated oligomers and polymers, the trimeric isomers PBP and BPP, comprising dialkoxy phenylene vinylene (P), benzothiadiazole vinylene (B), and alkyl endgroups with terminal olefins, are synthesized. Sequence effects are evident in the optical/electrochemical properties and thermal properties. Absorption maxima for PBP and BPP differ by 41 nm and the electrochemical band gaps by 0.1 V. The molar emission intensity is five times greater in PBP than BPP. Both trimers are crystalline and the melting points differ by 17 °C. The PBP and BPP trimers are used as macromonomers in an acyclic diene metathesis polymerization to give PolyPBP and PolyBPP. The optical and electrochemical properties are similar to those of their trimer precursors-sequence effects are still evident. These results suggest that sequence is a tunable variable for electronic materials and that the polymerization of oligomeric sequences is a useful approach to introducing sequence into polymers.

Simulated Dilatometry and Static Deformation Prediction of Glass Transition and Mechanical Properties of Polyacetylene and Poly(para‐phenylene vinylene)

Thermophysical and mechanical properties of two conjugated polymers, poly(p‐phenylene vinylene) (PPV) and polyacetylene (PA), are predicted using molecular dynamics simulations and compared with results obtained from differential scanning calorimetry, nanoindentation, and dynamic mechanical analysis experiments. Glass transition temperature (Tg) is calculated from the changes in the slopes of the specific volume versus temperature and cohesive energy density versus temperature plots, obtained from constant pressure and constant temperature simulations (NPT ensemble). The effects of temperature on the torsion angle distributions and characteristic ratio are analyzed. PPV is found to have a Tg of 416 ± 8 K. PA does not exhibit a glass transition in the temperature range of 120 to 500 K. Using the static deformation method, the values of Young's modulus are calculated to be 1.81 ± 0.34 GPa for PA and 9.20 ± 0.57 GPa for PPV at 298 K. These values are in good agreement with the experimental measurements, validating the suitability of these techniques in the prediction of the polymer properties. image

Preparation of Reactive Oligo(p-Phenylene Vinylene) Materials for Spatial Profiling of the Chemical Reactivity of Intracellular Compartments.

An oligo(p-phenylene vinylene) derivative (OPV-pfp) functionalized with pentafluorophenol active ester is designed and synthesized. The high reactivity of OPV-pfp with biological small molecules or macromolecules containing amino groups under physiological conditions leads to spectral changes of OPV-pfp; thus, spatial reactivity discrimination for different subcellular structures inside cells is realized by triggering and imaging the fluorescence signal change of the OPV-pfp.

Photoinduced Gilch Polymerization: A Basically New Access to Poly(p-phenylene vinylenes) (PPVs) of Exciting Constitutional Homogeneity.

A novel procedure has been developed for the Gilch reaction leading to poly(p-phenylene vinylenes) (PPVs). In the first step, selective activation of the starting material is achieved at low temperature. Subsequently, controlled chain growth is induced by lighting the α-halo-p-quinodimethane monomer. In contrast to the thermal Gilch polymerization, the photoinduced process allows adjusting crucial parameters such as intensity and energy of light. The progress of PPV formation can be followed visually or by in situ UV-vis spectroscopy. If the polymers are formed under appropriate conditions, they show very high molar masses, polydispersities in the common range, and higher constitutional homogeneity than thermally grown PPVs.

A Thermo- and Mechanoresponsive Cyano-Substituted Oligo(p-phenylene vinylene) Derivative with Five Emissive States.

Multiresponsive materials that display predefined photoluminescence color changes upon exposure to different stimuli are attractive candidates for advanced sensing schemes. Herein, we report a cyano-substituted oligo(p-phenylene vinylene) (cyano-OPV) derivative that forms five different solvent-free solid-state molecular assemblies, luminescence properties of which change upon thermal and mechanical stimulation. Single-crystal X-ray structural analysis suggested that tolyl groups introduced at the termini of solubilizing side-chains of the cyano-OPV play a pivotal role in its solid-state arrangement. Viewed more broadly, this report shows that the introduction of competing intermolecular interactions into excimer-forming chromophores is a promising design strategy for multicolored thermo- and mechanoresponsive luminescent materials.

Synthesis and Photophysical and Electroluminescent Properties of Poly(1,4-phenylene-ethynylene)-alt-poly(1,4-phenylene-vinylene)s with Various Dissymmetric Substitution of Alkoxy Side Chains.

The synthesis and characterization of a set of conjugated polymers, poly(1,4-phenylene–ethynylene)-alt-poly(1,4-phenylene–vinylene)s (PPE–PPVs), with a dissymmetrical configuration (partial or total) of alkoxy side chains is reported. Five new polymers bearing octyloxy and/or octadecyloxy side chains at the phenylene–ethynylene and phenylene–vinylene segments, respectively, were obtained. Two symmetrical substituted polymers were used for comparison. Polymers with weight-average molecular weight, Mw, up to 430 000 g/mol and degree of polymerization between 17 and 322 were obtained by a Horner–Wadsworth–Emmons olefination polycondensation reaction of the respective luminophoric dialdehydes and bisphosphonates. As expected, identical conjugated backbones in all polymers results in very similar photophysical response in dilute solution, with high fluorescence quantum yields between 50% and 80%. In contrast, the thin film properties are dependent on the combinatorial effects of side chain configuration, molecular weight, and film thickness parameters, which are the basis of the resulting comparison and discussion.

Dynamics of charge migration in poly(para-phenylene vinylene) films and nanocomposites with single walled carbon nanotubes

We present in this paper a comprehensive study of the migration dynamics of the charges underlying transient photoluminescence (PL) processes in poly(para–phenylene vinylene) (PPV) samples from room temperature to 13 K. In order to interpret experimental data, we have modelled the long–time PL decays (from 100 to 1000 ps) using a time function proportional to in which the parameter α is evaluated in a Monte Carlo simulation on polymeric chains. The one dimensional chains (2000 sites long) are formed by random sequences of long and short conjugated segments whose bimodal distributions have been elaborated in previous works in order to reproduce the PL band shapes and peak positions. Intra-chain and inter-chain dynamics are taken into account in the migration of the photogenerated charges from short to long conjugated segments. The statistical analysis is performed by averaging over a total of 106 trials for each initial conditions. The values of α have been determined for pristine PPV films and PPV composite films with single-walled carbon nanotubes. This theoretical analysis is in good agreement with experimental data and provides a coherent description for the migration of the photogenerated charges in such inhomogeneous polymeric systems.

White light emitting diode based on quantum dots and MEH-PPV

The white light emitting diode (LED) devices, in which blue-emitting quantum dots doped in the polymer of poly [2-methoxy-5-(2-ethylhexyloxy)-1, 4-phenylene vinylene] (MEH-PPV) serve as the active layer, have been fabricated in a nitrogen-filled glove box; the devices have the structure of ITO/PEDOT/MEH-PPV:QDs(B)/LiF/Al. After a systematical investigation, we report the effect of different quantum dots (QDs) doping concentration (mass fraction) on the electroluminescent spectrum, current density, brightness, CIE coordinates of the devices and atomic force microscopy (AFM) characterizations of the emitting layer. With the increase of QDs doping concentration, we find that the QDs luminance intensity of the controlling devices continues to grow. When the QDs doping concentration is 40%, the normal white light emission is obtained in the devices. The CIE coordinates of the white QD-LED are (0.35, 0.32), which are close to the balanced white coordinates. Besides, we also fabricate the non-doped devices, in which the structure is ITO/PEDOT/MEH-PPV/QDs(B)/LiF/Al. After finishing the active layer's preparation, the morphology of the films are investigated by AFM. By comparing the analysis, the doped system has a lower level on the root mean squared roughness. In addition, the doped devices demonstrate a superior performance, and exhibit a low turn-on voltage and a high maximum value of luminance.

Alkyl substituted [2.2]paracyclophane-1,9-dienes.

[2.2]Paracyclophane-1,9-dienes substituted with n-octyl chains have been synthesised from the corresponding dithia[3.3]paracyclophanes using a benzyne induced Stevens rearrangement. The use of 2-(trimethylsilyl)phenyl trifluoromethanesulfonate and tetra-n-butylammonium fluoride as the in situ benzyne source gave significantly improved yields over traditional sources of benzyne and enabled the preparation of n-octyl substituted [2.2]paracyclophane-1,9-dienes on a multi-gram scale.

Excitons in poly(para phenylene vinylene): a quantum-chemical perspective based on high-level ab initio calculations.

Excitonic effects play a fundamental role in the photophysics of organic semiconductors such as poly(para phenylene vinylene) (PPV). The emergence of these effects is examined for PPV oligomers based on high level ab initio excited-state calculations. The computed many-body wavefunctions are subjected to our recently developed exciton analysis protocols to provide a qualitative and quantitative characterization of excitonic effects. The discussion is started by providing high-level benchmark calculations using the algebraic-diagrammatic construction for the polarization propagator in third order of perturbation theory (ADC(3)). These calculations support the general adequacy of the computationally more efficient ADC(2) method in the case of singly excited states but also reveal the existence of low-energy doubly excited states. In a next step, a series of oligomers with chains of two to eight phenyl rings is studied at the ADC(2) level showing that the confinement effects are dominant for small oligomers, while delocalized exciton bands emerge for larger systems. In the case of the largest oligomer, the first twenty singlet and triplet excited states are computed and a detailed analysis in terms of the Wannier and Frenkel models is presented. The presence of different Wannier bands becomes apparent, showing a general trend that exciton sizes are lowered with increasing quasi-momentum within the bands.

Phenylene vinylene macrocycles as artificial transmembrane transporters.

A series of rigid phenylene vinylene macrocycles and phenylene ethynylene macrocycles with various substituents have been investigated as transmembrane ion channels. The length and polarity of the substituents have a significant effect on the ion channel formation and the mass transport efficiency. Macrocycles with strong aggregation facilitate ion passage across lipid bilayers.

A phenylene–vinylene terpyridine conjugate fluorescent probe for distinguishing Cd2+ from Zn2+ with high sensitivity and selectivity

A blue light emitting phenylene–vinylene functionalized terpyridine conjugate was developed as a ‘turn-on’ fluorescent probe exhibiting a high selectivity towards toxic Cd2+ without interference by other competing metal ions in submicromolar level. The specific response towards Cd2+ and the ability in discriminating Zn2+ offer an opportunity to develop on-site test paper kit for practical utility to detect toxic Cd2+.

Photoelectrochemical properties of ZnO nanocrystals/MEH-PPV composite: The effects of nanocrystals synthetic route, film deposition and electrolyte composition

This paper reports a study on the photoelectrochemical processes occurring at the interface of ZnO nanocrystals/MEH-PPV composites. Colloidal chemical routes were used to obtain size controlled non-hydrolytic ZnO nanocrystals (NCs) dispersible in organic solvents, while a low molecular weight poly[2-methoxy-5-(2′-ethyl-hexyloxy)phenylene vinylene] (MEH-PPV), characterized by high degree of structural order, was synthesized via an organometallic method. The optical properties of the nanocomposite material were comprehensively investigated on solution and on films deposited by spin coating. Remarkably, a significant fluorescence quenching of the polymer at the MEH-PPV/ZnO junction was observed. Photoelectrochemical measurements demonstrated that the photoactivity of the composite material was significantly improved in the case of non-hydrolytic NCs with respect to hydrolytic route prepared ZnO. Moreover, the effective role of the organic/inorganic blend to improve the charge transfer with respect to the double layer hetero-junction was confirmed, thanks to the extended interfaces which enable an effective electron transfer between the hetero-junction components. The system was also studied at different film thicknesses and electrolyte compositions. The results indicated that film photoactivity increased with film thickness up to 300nm due to the presence of a large number of interfaces, while the change of cation size influenced the ionic conductivity through the nanocomposite film. It was shown that efficient photoconductivity requires not only efficient charge separation, but also efficient transport of the carriers to the electrodes without recombination.

Synthesis of Phenylene Vinylene Macrocycles through Acyclic Diene Metathesis Macrocyclization and Their Aggregation Behavior

A series of phenylene vinylene macrocycles (PVMs) bearing substituents with various sizes and electronic properties have been synthesized through a one-step acyclic diene metathesis macrocyclization approach and their aggregation behaviors have been investigated. In great contrast to the aggregation of the analogous phenylene ethynylene macrocycles, which aggregate only when substituted with electron-withdrawing groups, these PVMs undergo exceptionally strong aggregation, regardless of the electron-donating or -withdrawing characters of the substituents. The unusual aggregation behavior of the PVMs is further investigated with thermodynamic and computer modeling studies, which show a good agreement with the recently proposed direct through-space interaction model, rather than the polar/π model. The high aggregation tendency of PVMs suggests the great potential of this novel class of shape-persistent macrocycles in a variety of applications, such as ion channels, host-guest recognition, and catalysis.

Origin of the positive spin-12photoluminescence-detected magnetic resonance in π-conjugated materials and devices

The spin-$1/2$ single-modulation (SM) and double-modulation (DM) photoluminescence (PL) detected magnetic resonance (PLDMR) in poly(2-methoxy-5-(2\ensuremath{'}-ethyl)--hexoxy-1,4- phenylene vinylene) (MEH-PPV) films and poly(3-hexylthiophene) (P3HT) films is described, analyzed, and discussed. In particular, the models based on spin-dependent recombination of charge pairs (SDR) and triplet-polaron quenching (TPQ) are evaluated. By analyzing the dependence of the resonance amplitude on the microwave chopping (modulation) frequency using rate equations, it is demonstrated that the TPQ model can well explain the observed resonance behavior, while SDR model cannot reproduce the results of the observed DM-PLDMR. Thus the observed spin-$1/2$ PLDMR is assigned to TPQ rather than SDR, even though the latter may also be present.

Continuous Synthesis and Thermal Elimination of Sulfinyl‐Route Poly(p‐Phenylene Vinylene) in Consecutive Flow Reactions

AbstractContinuous synthesis of multistep polymerizations at microscale is made available by coupling two microstructured chip reactors in a single reactor setup. Conjugated [2‐methoxy‐5‐(3′,7′‐dimethyloctyloxy)]‐1,4‐phenylenevinylene (MDMO‐PPV) is synthesized via the radical sulfinyl precursor route. Reactions are carried out in separate reactors and optimization of the elimination of polymer can be effectively performed in a defined temperature range, allowing for full polymer conversion within minutes and formation of conjugated materials. The combination of both processes in a single coupled reactor setup permits total monomer‐to‐conjugated‐MDMO‐PPV conversions while retaining its pristine optical properties. Polymer characteristics are comparatively good and the reduction in yield due to the lower initial monomer concentrations is compensated by the much shorter reaction times required in the flow process.

A Supramolecular Antibiotic Switch for Antibacterial Regulation.

A supramolecular antibiotic switch is described that can reversibly "turn-on" and "turn-off" its antibacterial activity on demand, providing a proof-of-concept for a way to regulate antibacterial activity of biotics. The switch relies on supramolecular assembly and disassembly of cationic poly(phenylene vinylene) derivative (PPV) with cucurbit[7]uril (CB[7]) to regulate their different interactions with bacteria. This simple but efficient strategy does not require any chemical modification on the active sites of the antibacterial agent, and could also regulate the antibacterial activity of classical antibiotics or photosensitizers in photodynamic therapy. This supramolecular antibiotic switch may be a successful strategy to fight bacterial infections and decrease the emergence of bacterial resistance to antibiotics from a long-term point of view.

A Supramolecular Antibiotic Switch for Antibacterial Regulation

AbstractA supramolecular antibiotic switch is described that can reversibly “turn‐on” and “turn‐off” its antibacterial activity on demand, providing a proof‐of‐concept for a way to regulate antibacterial activity of biotics. The switch relies on supramolecular assembly and disassembly of cationic poly(phenylene vinylene) derivative (PPV) with cucurbit[7]uril (CB[7]) to regulate their different interactions with bacteria. This simple but efficient strategy does not require any chemical modification on the active sites of the antibacterial agent, and could also regulate the antibacterial activity of classical antibiotics or photosensitizers in photodynamic therapy. This supramolecular antibiotic switch may be a successful strategy to fight bacterial infections and decrease the emergence of bacterial resistance to antibiotics from a long‐term point of view.