Emission Of Poly Research Articles

Inducing Multicolour emission in MEH-PPV/TiO2 nanocomposites

Fluorescence-based polymers have a wide variety of applications such as light-emitting diodes, optoelectronics, and biosensors. The present study endeavors towards the effect of TiO2 nanoparticles (calcined at various temperature) on the emission of Poly [2-methoxy-5-(2-ethylhexyloxy)-1, 4-phenylenevinylene] (MEH-PPV) and to induce multicolor emission. The TiO2 nanoparticles synthesized by sol-gel method were calcined at 400°C and 600°C. In situ polymerization was adopted to synthesize MEH-PPV / TiO2 nanocomposites and the structural characteristics of the nanocomposites were studied using Fourier transformed Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The photo-physical characteristics of the nanocomposites were investigated using UV-Visible spectroscopy, Photoluminescence spectroscopy, and Fluorescence microscopy. TiO2 nanoparticles calcined at 400°C demonstrates anatase phase, whereas the particles calcined at 700°C exhibits mixed phase of rutile and anatase. The study reveal that calcination temperature has a strong impact on the morphology of the synthesized nanoparticles. The photoluminescence spectra reveal that the incorporation of TiO2 nanoparticles enhances the red orange emission intensity of MEH-PPV, additionally exhibits emission at multiple wavelengths. Fluorescence microscopy evidences multiple colour emission from MEH-PPV/TiO2 nanocomposites. The multiple emission in the polymer nanocomposite is arised from the oxygen vacancies present in anatase and rutile phases of TiO2 nanoparticle.

Ultra-long room temperature phosphorescence, intrinsic mechanisms and application based on host-guest doping systems

To construct efficient room-temperature phosphorescence (RTP) doping systems by simple doping methods, isomers 2-(2-(9H-carbazol-9-yl)benzyl)malononitrile (o-CzCN), 2-(3-(9H-carbazol-9-yl)benzyl)malononitrile (m-CzCN) and 2-(4-(9H-carbazol-9-yl)benzyl)malononitrile (p-CzCN) were designed and synthesized by choosing commercial carbazole. Based on the structure-function relationships of three isomers and excellent compatibility between carbazole and benzocarbazole, 2-(3-(9H-carbazol-9-yl)benzyl)malononitrile (Lm-CzCN) and 2-(3-(5H-benzo[b]carbazol-5-yl)benzyl)malononitrile (m-BCzCN) were prepared by self-made carbazole and 2-naphthylamine. Then, Lm-CzCN/m-BCzCN was constructed and optimized by dissolution and rapid evaporation, as well as tuning the mass ratios between Lm-CzCN and m-BCzCN. Lm-CzCN shows excitation dependent RTP and afterglow lifetimes, as well as concentration dependent RTP emission in poly(vinyl alcohol) (PVA) films, while 1% m-BCzCN@PVA film emits bright green afterglow, with RTP and afterglow lifetimes of 2.303 and 17 s in turn, as well as RTP quantum yield of 0.22. More importantly, Lm-CzCN/m-BCzCN presents ultra-long room temperature phosphorescence, with RTP and afterglow lifetimes of 597.58 ms and 8 s, respectively. Moreover, crystals m-CzCN and p-CzCN, as well as Lm-CzCN/m-BCzCN can be excited by visible light of 440 nm, showing yellow afterglow of 1–4 s. Noteworthy, polymorphism o-CzCNY and o-CzCNB were found, whose different emission was investigated by molecular conformation, intermolecular arrangement and stacking patterns. Finally, multiple encryptions were successfully constructed based on the different luminescent properties.

Copolymerization induced emission of poly[(methylenelactide)-co-(2-vinylpyridine)

Copolymerization is a facile and effective approach to develop functional polymers from two or more types of monomers.

Cyclometalated Platinum Complexes with Aggregation-Induced Phosphorescence Emission Behavior and Highly Efficient Electroluminescent Ability

Aggregation-induced emission (AIE) materials can exhibit intense luminescence in the aggregated or solid state, which are highly desirable for OLED application. However, only limited research results on developing AIE-active PtII complexes in electroluminescence (EL) application have been reported so far. Herein, a series of AIE-active PtII(C^N)(N-donor ligand)Cl complexes have been developed. Their chemical structures have been determined by NMR, MS, and X-ray crystallography characterization. Theoretical results including the frontier molecular orbitals, the simulated UV–vis spectra, and natural transition orbitals (NTO) have been employed to insightfully interpret their photophysical properties. It has also been found that a much higher degree of molecular aggregation in these PtII complexes should be required to induce phosphorescent AIE than that for the fluorescent AIE behavior. These AIE-active PtII complexes can exhibit very strong emission in poly(methyl methacrylate) (PMMA) films with the phosph...

Controlling Morphology and Aggregation in Semiconducting Polymers: The Role of Solvents on Lasing Emission in Poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene-vinylene

Systematic experiments were performed to investigate solvent-dependent morphology and aggregation of the semiconducting polymer film poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene-vinylene] (MEH-PPV), which was span-cast from nonaromatic strong polarity solvents tetrahydrofuran (THF), trichloromethane (TCM) and aromatic weak polarity solvents chlorobenzene (CB), toluene, and p-xylene. The results indicated that the conformation of the spin-cast MEH-PPV films with weak aggregation such as THF and TCM demonstrated excellent lasing emission performances because of inhibiting the fluorescence quenching induced by bi-molecule process. The Atomic Force Microscope (AFM) images confirmed the distinct morphologies of the spin-cast MEH-PPV films. The amplified spontaneous emission (ASE) was investigated in a simple asymmetric slab planar waveguide structure by methods of variable stripe length (VSL) and shifting excitation stripe (SES). The amplified spontaneous emission (ASE) experiments confirmed the distinct polymer chain conformation. The conformation, which preserved from the spin-cast process, indicated the distinct interactions between solvents and MEH-PPV polymer chains. The pure film spectra were performed to confirm the effect of distinct conformation on the material energy level. This work provides insights into the morphology and aggregation effect of the spin-cast polymer films on the performances of lasers.

Stable pure‐blue emission of poly(9,9‐dioctylfluorene) via suppression of the green emission

ABSTRACTStable pure‐blue electroluminescence (EL) is obtained from polymer light‐emitting devices by dispersing poly(9,9‐dioctylfluorene) (PFO) into a wide band‐gap mixed‐matrix of poly(9‐vinylcarbazole) (PVK):2‐(4‐biphenylyl)‐5‐(4‐tert‐butylphenyl)‐1,3,4‐oxadiazole (PBD). From the EL spectra of the PFO‐doped films, we find that the additional green emission observed in the EL spectra of the pure PFO devices was significantly suppressed in the PFO‐doped devices. The spectral stability was also improved through evaluating the EL spectra of the PFO‐doped films annealed at different temperatures (from 80 to 150 °C). These results demonstrate that doping of PFO into a matrix to weaken the aggregate and oxidation of the PFO molecules is a simple strategy to suppress the green emission. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44950.

Emission of poly and perfluoroalkyl substances, UV-filters and siloxanes to air from wastewater treatment plants

The potential of wastewater treatment plants (WWTPs) to act as sources of poly and perfluoroalkyl substances (PFASs), volatile methyl siloxanes (VMSs) and organic UV-filters to the atmosphere was investigated. Target compounds included: PFASs (fluorotelomer alcohols (FTOHs), perfluorooctane sulfonamides/sulfonamidoethanols (FOSAs/FOSEs), perfluroalkyl sulfonic acids (PFSAs) and perfluroalkyl carboxylic acids (PFCAs)), cyclic VMSs (D3 to D6), linear VMSs (L3 to L5) and eight UV-filters. Emissions to air were assessed at eight WWTPs using paired sorbent-impregnated polyurethane foam passive air samplers, deployed during summer 2013 and winter 2014. Samplers were deployed on-site above the active tank and off-site as a reference. Several types of WWTPs were investigated: secondary activated sludge in urban areas (UR-AS), secondary extended aeration in towns (TW-EA) and facultative lagoons in rural areas (RU-LG). The concentrations of target compounds in air were ∼1.7–35 times higher on-site compared to the corresponding off-site location. Highest concentrations in air were observed at UR-AS sites while the lowest were at RU-LG. Higher air concentrations (∼2–9 times) were observed on-site during summer compared to winter, possibly reflecting enhanced volatilization due to higher wastewater temperatures or differences in influent wastewater concentrations. A significant positive correlation was obtained between concentrations in air and WWTP characteristics (influent flow rate and population in the catchment of the WWTP); whereas a weak negative correlation was obtained with hydraulic retention time. Emissions to air were estimated using a simplified dispersion model. Highest emissions to air were seen at the UR-AS locations. Emissions to air (g/year/tank) were highest for VMSs (5000–112,000) followed by UV-filters (16–2000) then ΣPFASs (10–110).

Nano graphite platelets enhanced blue emission in alternating current field induced polymer based electroluminescence devices using Poly (9,9-dioctylfluorenyl-2,7-diyl) as the emitter

We report a simple way of enhancing blue emission in Poly (9,9-dioctylfluorenyl-2,7-diyl) (PFO) based alternating current field driven electroluminescence devices by mixing graphite nano platelets in the emission layer. Significantly strong and well resolved blue peaks at 437nm and 470nm are observed both in the devices’ electroluminescence and photoluminescence spectra with the presence of graphite nano platelets. The origin of this strong blue emission has been identified as the PFO’s beta-phase formation confirmed by transmission electron microscopy images and UV–Vis absorption spectra. The nano platelets loading in PFO solution can be controlled by the dispersion time in organic solvents. When the loading increases, the green emission in the electroluminescence spectrum can be reduced. This technique has been found useful in the generation of bright white light when illuminating through down conversion phosphor.

Charge transfer excitons in low band gap polymer based solar cells and the role of processing additives

Organic semiconductor blends yielding efficient charge generation and transport are key components for the development of high performance organic bulk-heterojunction solar cells. In this paper the effect of the processing additive octane-dithiol on the charge transfer emission in 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 [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) is investigated. Despite the fact that blends processed with and without additive show a ground state charge transfer optical absorption only the blend processed without additive shows a corresponding charge transfer emission. The presented experimental data show that the nano-morphology of the bulk-heterojunction blends plays an important role for the formation of emissive charge transfer excitons, and that it is a loss channel in the studied solar cells.

Synthesis and characterization of poly(fluorene vinylene) copolymers containing thienylene–vinylene units

AbstractNarrow‐band‐gap 2,5‐thienylene‐divinylene (ThV) units were incorporated into the poly(fluorene vinylene) backbone via a Gilch reaction as an energy trap with various feed ratios; this yielded pronounced changes in the electrochemical and optical properties of the material. The energy levels of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the polymers {poly(9,9‐di‐iso‐octylfluorene vinylene) [poly(fluorene vinylene‐co‐thiophene vinylene (FV))], C1, and C2} were estimated to be −5.53 to −5.10 eV and −2.98 to −2.84 eV, respectively, by cyclic voltammetry measurements. In comparison with poly(FV), the HOMO energy levels of polymers poly(fluorene vinylene‐co‐thiophene vinylene (FV) (90 : 10) (C1) and poly(fluorene vinylene‐co‐thiophene vinylene (FV) (80 : 20) (C2) were significantly increased, but their LUMO energy levels were slightly decreased. The optical properties were investigated by absorption and emission spectra of the polymers. The good spectral overlap between the emission of poly(FV) and the absorption of polymers C1 and C2 revealed a sufficient energy transfer from the majority of 9,9‐di‐iso‐octylfluorene vinylene units to the minority of ThV units. The reduction of self‐absorption losses of polymers C1 and C2 due to spectral separation caused by the incorporation of ThV units could be indirectly confirmed by nonlinear optical (NLO) properties. The result of the NLO properties of the polymers showed that the third‐order NLO coefficients of poly(FV), C1, and C2 were 8.1 × 10−10, 1.35 × 10−9, and 1.51 × 10−9 esu, respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Charge Carrier Formation in Polythiophene/Fullerene Blend Films Studied by Transient Absorption Spectroscopy

We report herein a comparison of the photophysics of a series of polythiophenes with ionization potentials ranging from 4.8 to 5.6 eV as pristine films and when blended with 5 wt % 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]C61 (PCBM). Three polymers are observed to give amorphous films, attributed to a nonplanar geometry of their backbone while the other five polymers, including poly(3-hexylthiophene), give more crystalline films. Optical excitation of the pristine films of the amorphous polymers is observed by transient absorption spectroscopy to give rise to polymer triplet formation. For the more crystalline pristine polymers, no triplet formation is observed, but rather a short-lived (approximately 100 ns), broad photoinduced absorption feature assigned to polymer polarons. For all polymers, the addition of 5 wt % PCBM resulted in 70-90% quenching of polymer photoluminescence (PL), indicative of efficient quenching of polythiophene excitons. Remarkably, despite this efficient exciton quenching, the yield of dissociated polymer+ and PCBM- polarons, assayed by the appearance of a long-lived, power-law decay phase assigned to bimolecular recombination of these polarons, was observed to vary by over 2 orders of magnitude depending upon the polymer employed. In addition to this power-law decay phase, the blend films exhibited short-lived decays assigned, for the amorphous polymers, to neutral triplet states generated by geminate recombination of bound radical pairs and, for the more crystalline polymers, to the direct observation of the geminate recombination of these bound radical pairs to ground. These observations are discussed in terms of a two-step kinetic model for charge generation in polythiophene/PCBM blend films analogous to that reported to explain the observation of exciplex-like emission in poly(p-phenylenevinylene)-based blend films. Remarkably, we find an excellent correlation between the free energy difference for charge separation (deltaG(CS)rel) and yield of the long-lived charge generation, with efficient charge generation requiring a much larger deltaG(CS)rel than that required to achieve efficient PL quenching. We suggest that this observation is consistent with a model where the excess thermal energy of the initially formed polaron pairs is necessary to overcome their Coulombic binding energy. This observation has important implications for synthetic strategies to optimize organic solar cell performance, as it implies that, at least devices based on polythiophene/PCBM blend films, a large deltaG(CS)rel (or LUMO level offset) is required to achieve efficient charge dissociation.

Blue Emission of a Soluble Poly(p‐phenylene) with a Cross‐Conjugated Bisimidazole‐Based Chromophore

AbstractA novel poly(p‐phenylene) (6) has been synthesized by a cruciform combination of a polyphenylene backbone with 2,2′‐(p‐phenylene)‐bis(4,5‐diphenylimidazole) (5) as an additional, orthogonal chromophore. Polymer 6 showed in solution and in the solid state, a blue‐green emission, which is obviously arising from the second bisimidazole‐based chromophore. UV‐Vis spectroscopy, and cyclic voltammetry revealed that the optical and electronic properties of 6 were fully determined by the incorporated 2,2′‐(1,4‐phenylene)bisimidazole structure. The bisimidazole unit led to high solubility and, despite the steric demand of the substituents, at the same time to the blue‐green emission of the poly(p‐phenylene) (6). In addition, the oxidation of 6 with potassium ferricyanide yielded a low bandgap polymer with a quinoid‐type structure and a bandgap of 1.6 eV.magnified image

Effect of interchain interactions on the absorption and emission of poly(3-hexylthiophene)

The absorption spectrum of polythiophene and its derivative poly(3-hexylthiophene) (P3HT) is usually described in terms of an intrachain exciton coupled to a single phonon mode. We show that this model is too simplistic for highly ordered, regioregular P3HT and that, analogous to the case of charged polarons in this material, interchain interactions must be taken into account to correctly describe the absorption spectrum. We show that the lowest energy feature in the $\ensuremath{\pi}\ensuremath{-}{\ensuremath{\pi}}^{*}$ region of the absorption spectrum is associated with an interchain absorption, the intensity of which is correlated with the degree of order in the polymer. Correspondingly, we show that the emission from P3HT also exhibits contributions from both interchain and intrachain states, in a manner similar to that recently shown for poly(phenylenevinylene). Having reinterpreted the physical origin of the features in the absorption and emission spectra of P3HT, we then model these spectra and show how they evolve as the degree of order in the polymer is changed by varying several physical parameters including temperature and regioregularity of the polymer.

Photoluminescence and excimer emission of functional groups in light‐emitting polymers

AbstractNear‐UV and blue‐light‐emitting polymers were synthesized with luminescent functional groups in the side chains or in the polymer main chain. The unsubstituted fluorophores, 2,5‐diphenylfuran, 2‐phenylbenzoxazole, and triphenylamine, do not form excimers in solution; however, in the case of polymers, excimer emission was negligible only with 2‐phenylbenzoxazole derivatives. The monomers as well as the polymers, poly(2‐(4‐vinylphenyl)‐benzoxazole), poly{N‐(4‐benzoxazol‐2‐yl‐phenyl)‐N′‐[2‐(methacryloyloxy)ethyl]urea}, and the polyurea of 2‐(4‐aminophenyl)‐5‐aminobenzoxazole with 1,5‐diisocyanato‐2‐methylpentane, were strong blue emitters; photoluminescence shifted to longer wavelengths than that of 2‐phenylbenzoxazole. Light‐emitting polymers containing 2,5‐diphenylfuran derivatives, including poly[2‐(4‐vinylphenyl)‐5‐phenylfuran], poly[2‐(4‐vinylphenyl)‐5‐(4‐tert‐butylphenyl)furan], and poly(N‐[2‐(methacryloyloxy)ethyl]‐N′‐{4‐[5‐(4‐tert‐butylphenyl)‐2‐furyl]phenyl}urea), particularly in solid films, exhibited a strong blue excimer emission. The emission characteristics of polymers with triphenylamine side chains were influenced by the mode of attachment of the luminescent group. A longer spacer group between the lumophore and the polymer main chain successfully minimized excimer emission in poly{N‐[2‐(methacryloyloxy)ethyl]‐N′‐[4‐(N,N‐diphenylamino)phenyl]urea}, showing near UV/violet photoluminescence. Polymers with a shorter connecting group, such as poly[4‐(N,N‐diphenylamino)benzyl acrylate], displayed blue excimer emission. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1634–1645, 2003

Stimulated emission in poly( p-phenylene–vinylene) films

Excitonic emission has been studied in films of poly( p-phenylene–vinylene) (PPV) derivatives. At high excitation intensities we found an unusual stimulated emission regime characterized by a finely structured spectrum having features as narrow as 0.1 nm.

Interaction of naphthalene-labeled poly(hydrochloride quaternized 2-norbornene-5-methyleneamine) with O/W microemulsion droplets

Interaction between naphthalene-labeled poly(hydrochloride quaternized 2-norbornene-5-methyleneamine), poly(HCQNBMA)/NA (luminophore), and quencher, emulsifier or coemulsifier in the aqueous or microemulsion media was studied by using steady-state fluorescence measurements. Fluorescence experiments were carried out with poly(HCQNBMA)/NA dissolved in the aqueous solutions of ionic and nonionic emulsifiers, emulsifier/n-hexane/water microemulsion (A) and emulsifier/n-hexane/1-pentanol/water microemulsion (B), respectively. The intensity of fluorescence emission of poly(HCQNBMA)/NA was much higher in the aqueous phase than in microemulsion. Furthermore, the aqueous solution of ionic emulsifier increased the monomer emission. The increase in the monomer emission can be ascribed to the shielding of the naphthalene (NA) groups by SDS micelles. This separates NA groups from each other, which depresses the deactivation of excited states. The strong decrease in monomer emission within the microemulsion media probably results from the elongated conformation structure of the polymer molecule, and higher conformation freedom of NA groups, which increases interaction between the probe and the quencher. The formation of nonfluorescence clusters is not ruled out. The quenching of NA emission by nitromethan (NM) is much stronger in microemulsion than in the aqueous phase, and the quenching is more pronounced for the low molecular weight 2-norbornene-5-methoxylnaphthalene (NBMNA) than for its polymer. The extent of penetration of reactants into the interfacial layer governs quenching of hydrophobic NA probe by hydrophilic quencher. Furthermore, the quenching events are connected with the thickness and density of the interfacial layer, as well as its charge. The addition of coemulsifier (1-pentanol) increases the total surface area of the microdroplets, the entry rate of reactants into the microdroplets, and the interaction of hydrophobic and hydrophilic reactants. The quenching events are more pronounced in the close packed o/w interfacial layer than in the loosely packed one. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 101–114, 2001

An ultrafast spectroscopy study of stimulated emission in poly(9,9-dioctylfluorene) films and microcavities

We report measurements of stimulated emission in poly(9,9-dioctylfluorene). We find a gain coefficient of 1.2×104 cm−1 for 100 nm-thick films at an excitation energy density of 9.9 mJ/cm2. Using ultrafast pump–probe measurements, we have studied the effect of cavity optical confinement. A strong shift of the cavity resonance due to nonlinear refraction is observed.

Tunable emission in poly(4-vinylpyridine)-based gel

We have discovered a new class of smart-gels, poly(4-vinylpyridine) (PVPy) swollen with pyridine (Py), that following photoexcitation (395, 455, 557 nm) emits three independent colors: blue, green, and red (477, 527, 585 nm, respectively). These excitation wavelengths also induced large reversible changes in pH and electrical conductivity. The primary photoexcitation paths within this photo-active gel are singlet-excitons. The origin of this phenomenon is attributed to the combined properties of weak coupling via hydrogen-bonding and high polarizability. Our preliminary model suggests, that C—H ⃛N based Py associates are formed during the gelation process. Photoexcitation leads to proton transfer within three different kinds of assemblies and to a solid-state-like electronic behavior of the gel. This system, i. e. a photoconducting transparent organic gel with multiple color emission, is very attractive for a wide range of promising applications in the field of optoelectronic devices such as organic LED's and 3D holography.

Tunable emission in poly(4-vinylpyridine)-based gel

Tunable emission in poly(4-vinylpyridine)-based gel

Solid-state-concentration effects on the optical absorption and emission of poly(p-phenylene vinylene)-related materials.

We present measurements of the optical absorption and emission properties of poly(p-phenylene vinylene) (PPV) -related materials focusing on the differences between molecules isolated by dispersion in an inert host and concentrated molecular films. Optical absorption spectra, photoluminescence (PL) spectra, PL efficiency, and time-resolved PL spectra of dilute blends of PPV oligomers with 2--5 phenylene-phenyl rings are compared with those of dense oligomer and polymer films. In dilute oligomer-poly(methyl methacrylate) (PMMA) blends with high PL efficiency, the PL decay is exponential, independent of both temperature and oligomer length. This implies that the fundamental radiative lifetime of PPV oligomers is essentially independent of oligomer length. Concentrated spin-cast oligomer films and polymers have a faster and strongly temperature-dependent PL decay that approaches that of the dilute oligomer results at low temperature. The differences in PL decay correspond to changes in PL efficiency. The efficiency of the oligomer-PMMA blend is high and only weakly temperature dependent, whereas that of concentrated films is lower and strongly temperature dependent, decreasing by more than a factor of 3 from 10 to 350 K. The quenching of the PL efficiency in concentrated films is due to migration to extrinsic, impurity related centers as opposed to an intrinsic intermolecular recombination process. The PL spectrum of a dilute oligomer blend redshifts substantially, both as the excitation energy is decreased and as the emission time increases. This spectral redshift is due to disorder-induced site-to-site variation and not to diffusion to lower-energy sites. In contrast, no spectral shift with excitation energy or emission time was observed for dense oligomer films. \textcopyright{} 1996 The American Physical Society.