Showing papers on "Fluorenone published in 2006"

On‐Chain Fluorenone Defect Emission from Single Polyfluorene Molecules in the Absence of Intermolecular Interactions

Abstract: The emission of semiconducting polyfluorenes is often accompanied by an undesired feature in the green spectral region. Whereas a number of previous investigations have argued in favor of a monomolecular origin of the emission species based on ketonic defects, recent experimental results suggested the necessity of excimer formation between individual fluorenone units. We provide a range of new evidence supporting the monomolecular origin of green band emission in polyfluorenes. Most importantly, we succeed in performing single-molecule spectroscopy on fluorenone-containing polyfluorene model compounds. Whereas most fluorenone-containing molecules exhibit both blue backbone and green fluorenone emission independent of fluorenone concentration, it is the relative intensities of the two species which correlate strongly with the fluorenone concentration on the single-molecule level. Furthermore, we consider a novel model compound with a bifacial arrangement of two fluorenone units. This compound does not provide any signatures of enhanced intramolecular excimer formation but does strongly indicate that concentration quenching effects occur once fluorenone units can interact electronically. The ability to detect on-chain defect emission in a single polymer molecule demonstrates that photochemical reactions in conjugated polymers can be monitored by fluorescence spectroscopy down to the level of a few atoms, constituting an unprecedented degree of materials characterization.

Synthesis and properties of conjugated oligomers containing fluorene, fluorenone, thiophene and cyclopentadithiophenone units

Abstract: Conjugated oligomers based on fluorene, fluorenone and thiophene derivatives have been prepared by parallel synthesis using the Suzuki cross-coupling reaction. These oligomers can be used as models of the corresponding fluorene copolymers and their structures were correlated with the observed optical and electrochemical behaviour. The long wavelength absorption bands observed for oligomers that contain fluorenone or cyclopentadithiophene units were assigned to an allowed π–π* transition associated with the carbonyl containing monomer unit. In addition the photoluminescence efficiency and the concentration dependence of the long wavelength emission band (>525 nm) for these materials strongly suggests that it can be attributed to emission involving fluorenone-based excimers.

Stable Blue Emission from a Polyfluorene/Layered‐Compound Guest/Host Nanocomposite

Abstract: In this study a blue-light-emitting conjugated polymer, poly(9,9-dioctylfluorene), is confined to the interlayer space of inorganic, layered metal dichalcogenide materials, metallic MoS2, and semiconducting SnS2. The nanocomposites are prepared through Li intercalation into the inorganic compound, exfoliation, and restacking in the presence of the polymer. X-ray diffraction and optical absorption measurements indicate that a single conjugated polymer monolayer, with an overall extended planar morphology conformation, is isolated between the inorganic sheets, so that polymer aggregation or p–p interchain interactions are significantly reduced. Photoluminescence (PL) measurements show that the appearance of the undesirable green emission observed in pristine polymer films is suppressed by incorporating the polymer into the inorganic matrix. The blue emission of the intercalated polymer is stable for extended periods of time, over two years, under ambient conditions. Furthermore, the green emission is absent in the PL spectra of nanocomposite films heated at 100°C for 7 h in air with direct excitation of the keto defect. Finally, no green emission was observed in the electroluminescence spectrum of light-emitting devices fabricated with a polymer-intercalated SnS2 nanocomposite film. These results support the proposed hypothesis that fluorenone defects alone are insufficient to generate the green emission and that interchain interactions are also required.

Effect of Fluorenone Units on the Property of Polyfluorene and Oligofluorene Derivatives: Synthesis, Structure−Properties Relationship, and Electroluminescence

Abstract: A series of well-defined 9,9‘-dihexylfluorene-co-fluorenone copolymers with various fluorenone contents and a set of monodisperse oligofluorenes in the chain center have been developed through the palladium-catalyzed Suzuki coupling reaction. The structure−property relationships, especially the effect of fluorenone moieties on the photophysical and electroluminescent properties of these materials, are systematically investigated to elucidate the exact origin of the low-energy emission in polyfluorenes. On the basis of our substantial studies of the steady-state photoluminescence (PL) and PL decay dynamics of the fluorenone-containing oligomers and copolymers both in dilute solutions and in thin films, the origin of the controversial low-energy emission band might be due to the interaction between intrachain fluorenone moieties in polyfluorenes instead of the intermolecular aggregates or excimers. We further show that fluorene pentamer with a central fluorenone unit (oligomer 2) is more appropriate to repr...

White light from polymer light-emitting diodes: Utilization of fluorenone defects and exciplex

Abstract: A white light polymer light-emitting diode was demonstrated with a double layer configuration: poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (poly-TPD) blended with poly(N-vinylcarbazole) as both hole-transporting layer and electron-blocking layer, blue-emissive poly(9,9-dihexylfluorene-alt-co-2,5-dioctyloxy-para-phenylene) (PDHFDOOP) blended with green-emissive poly[6,6′-bi-(9,9′-dihexylfluorene)-co-(9,9′-dihexylfluorene-3-thiophene-5′-yl)] as an emissive layer. By annealing the emissive layer at a relatively high temperature, fluorenone defects were generated into PDHFDOOP, which formed an exciplex with poly-TPD, as a red emitter. The devices exhibit a maximum brightness of ∼4800cd∕m2 and a maximum luminous efficiency of ∼3cd∕A. Moreover, the Commission Internationale de L’Eclairage coordinates of the emitted light is close to that of pure white light and is insensitive to the applied voltages.

Fast and Slow Time Regimes of Fluorescence Quenching in Conjugated Polyfluorene−Fluorenone Random Copolymers: The Role of Exciton Hopping and Dexter Transfer along the Polymer Backbone

Abstract: The luminescence decay kinetics of polyfluorene copolymers containing fluorenone units randomly distributed along the polymer chain have been studied by steady-state and time-resolved fluorescence techniques in toluene solution. The typical green emission from polyfluorenes containing 9-fluorenone moieties is only observed if the 9-fluorenone group is covalently attached to the polymer. Small-angle neutron scattering (SANS) measurements indicate that, independent of the 9-fluorenone fraction, all the studied copolymers adopt an open wormlike conformation. This prevalent 1-dimensional arrangement confirms that the green emission observed with polyfluorenes is not the result of excimer formation in the typical sandwich-like conformation. Analysis of time-resolved fluorescence decays by the maximum entropy method (MEM) collected at the polyfluorene emission (415 nm) and by global analysis of decays collected at 415 and 580 nm (the 9-fluorenone defect emission wavelength) clearly indicates two different time regimes in the population of the fluorenone defect: one occurring in the time interval of 10 to 30 ps and a second one occurring in the time range from 70 to 200 ps. While the slower process shows a linear dependence with the 9-fluorenone fraction, compatible with a hopping migration process along the polymer chain, the faster process does not show such a dependence and instead suggests a short-range Dexter mechanism. These findings are in agreement with our previous work where the presence of a faster component was suggested.

Modeling of molecular packing and conformation in oligofluorenes

Abstract: We describe the application of molecular modeling to study problems related to the packing and conformation of oligofluorene molecules in the solid state. First of all, we describe an improved force field for oligofluorenes. The model is based on the MM3 force field for the intramolecular degrees of freedom, but it relies on ab initio calculations for the torsion potential between two monomers and the electrostatic interactions. We also report ab initio calculations of the interaction potentials between fluorene and fluorenone units. The force field has been tested on the crystal structures of a fluorene monomer, a dimer, and a pentamer containing a fluorenone at the center. It has then been employed to study conformational defects of the chains, both in vacuo and in the bulk. We find that certain modes of inversion from right-handed to left-handed helices are also possible within the constraining environment of the crystals. The effect of the presence of two different types of side chains has been also addressed. Finally, the possibility of having two fluorene units parallel and close to each other has been investigated as a model of a ground-state precursor of an excimer. Our simulations show that this configuration is sterically and energetically unfavorable so that formation of an excimer following optical excitation appears to be unlikely.

Polyfluorene Terpolymers Containing Phenothiazine and Fluorenone: Effects of Donor and Acceptor Moieties on Energy and Intrachain Charge Transfer Processes in the Photoluminescence and Electroluminescence of Multichromophore Copolymers

Abstract: Five new conjugated terpolymers containing 9,9-dihexylfluorene, 10-hexylphenothiazine (HPT) donor, and 9-fluorenone (FLO) acceptor were synthesized by Suzuki copolymerization and used to study the effects of competing energy and intramolecular charge transfer processes on the photoluminescence (PL) and electroluminescence (EL) of multichromophore copolymers. The HPT and FLO moieties were found to act as emissive exciton traps on the terpolymer chains, leading new blue-green (475−485 nm) and green (520−525 nm) emission bands in addition to the blue (415 nm) emission of the fluorene segments. Additional charge transfer excited states and associated nonradiative decay channels resulting in factors of 2−4 decrease in the solution PL quantum yields of the terpolymers emerged due to the HPT moieties. As the emissive materials in light-emitting diodes (LEDs), the terpolymers showed green to yellow EL with luminances of 1900−8970 cd/m2 and efficiencies of 0.5−3.5 cd/A that varied with terpolymer composition. As a...

The Interplay of Inverted Redox Potentials and Aromaticity in the Oxidized States of New π-Electron Donors: 9-(1,3-Dithiol-2-ylidene)fluorene and 9-(1,3-Dithiol-2-ylidene)thioxanthene Derivatives

Abstract: Derivatives of 9-(1,3-dithiol- 2-ylidene)fluorene (9) and 9-(1,3-di- thiol-2-ylidene)thioxanthene (10) have been synthesised using Horner-Wads- worth-Emmons reactions of (1,3-di- thiol-2-yl)phosphonate reagents with fluorenone and thioxanthen-9-one. X- ray crystallography, solution electro- chemistry, optical spectroscopy, spec- troelectrochemistry and simultaneous electrochemistry and electron para- magnetic resonance (SEEPR), com- bined with theoretical calculations per- formed at the B3P86/6-31G** level, elucidate the interplay of the electronic and structural properties in these mole- cules. These compounds are strong two-electron donors, and the oxidation potentials depend on the electronic structure of the oxidised state. Two, single-electron oxidations (E ox E ox ) resulting in a single, two- electron oxidation process. The latter is due to the aromatic structure of the thioxanthenium cation (formed on the loss of a second electron), which stabil- ises the dication state (10 2 + ) compared with the radical cation. This contrasts with the nonaromatic structure of the fluorenium cation of system 9 .T he two-electron oxidation wave in the thioxanthene derivatives is split into two separate one-electron waves in the corresponding sulfoxide and sulfone derivatives 27-29 owing to destabilisa- tion of the dication state.

Surface modification of nylon 6,6 using a carbene insertion approach

Abstract: The diazirine functionalised fluorenone, 3-[3-(trifluoromethyl)diazirin-3-yl]phenyl-9-oxo-9H-fluorene-2-carboxylate was synthesised to act as a model compound capable of modifying a wide variety of polymeric substrates. Photochemical activation of the diazirine moiety of the fluorenone derivative was utilised to afford highly reactive carbenes capable of insertion into or addition to a wide variety of functionalities. In this paper the photoinduced attachment of a fluorenone derivative to nylon 6,6 has been studied using UV-visible spectroscopic analysis. Incorporation of the fluorenone chromophore onto the backbone of nylon at different loading levels and after different coating cycles has been investigated and is detailed in this paper.

Effect of meta-linkages on the photoluminescence and electroluminescence properties of light-emitting polyfluorene alternating copolymers

Abstract: Alternating copolymers poly[9,9-dihexylfluorene-alt-(1,3-phenylene)x(1,4-phenylene)1−x] (x = 0, 0.05, 0.1, 0.25, 0.5, 0.75, 1.0) were prepared, and the absorption spectra showed the expected hypsochromic shift with increasing meta linkages. In the solution photoluminescence (PL) emission spectra, all but the all-meta polymer (x = 1) showed a spectrum similar to the all-para polymer, indicating rapid intrachain energy transfer to para-linked segments. Similar spectra were observed from thin films in which inter-chain energy transfer is also available. Annealing of the thin films in air above the Tg of the polymer for several hours led to an increase in long wavelength emission, but the increase was smaller for the polymers containing more meta linkages. IR experiments confirmed the formation of fluorenone defects during the annealing process. For those polymers with high meta-linkage incorporation (i.e. 75% and 100% meta) the long wavelength emission is suppressed. This suggests that when the conjugation length of the polymer is reduced then energy transfer to fluorenone defects is less likely, due to lower exciton delocalisation and mobility. The long wavelength emission was more prominent in the electroluminescence (EL) spectra of devices prepared from the polymer, and, while initially less intense in the high meta linkages polymers, became dominant even for the all-meta linked polymer after a few minutes of operation. In summary, the meta linkages had a beneficial effect in suppressing the undesirable long wavelength emission in both the PL and EL output.

Nanoscale aryleneethynylene oligomers incorporating fluorenone units as electron-dopable molecular wires

Abstract: The first general synthetic procedures to obtain fluorenone-containing aryleneethynylene oligomers have been developed. The strategy involves stepwise Sonogashira cross-coupling methodology, with 2,7-diethynylfluorenone and 1,4-diiodo-2,6-di(hexyloxy)benzene as key building blocks, with terminal benzenethiol functionality protected as cyanoethyl derivatives. A second family of compounds contains a central 9-[(4-pyridyl)methylene]fluorene or 9-[di(4-pyridyl)methylene]fluorene unit in the backbone. UV-Vis absorption studies in solution establish that the increase of molecular lengths from ca. 4 nm (compounds 15 and 16) to ca. 7 nm (compounds 17, 27 and 28) results in only a very small red shift, with the effective conjugation length slightly longer than that of the 1,4-di(phenylethynyl)benzene (PEPEP) subunits. The pyridyl groups in 27 and 28 are only weakly conjugated to the π-electron backbone (UV-Vis data) which is consistent with the twisted conformation observed in the X-ray crystal structures of model compounds 20 and 24. Cyclic voltammetric studies reveal that the reduction waves of the fluorenone, 9-[(4-pyridyl)methylene]fluorene and 9-[di(4-pyridyl)methylene]fluorene units endow these oligomers with n-doping characteristics, with reversible reduction waves being observed for some compounds. The new aryleneethynylene oligomers have potential applications as molecular wires in practical devices.

Spectroscopic properties of anion radicals studied using pulse radiolysis

Abstract: The anion radicals of benzophenone, amino derivatives of benzophenone, fluorenone, furil and antharcene have been generated by pulse radiolysis in acetonitrile solution and their spectroscopic and kinetic properties have been characterized. The G-value for generation of anion radicals in acetonitrile has been measured to be 1.01 ± 0.1 per 100 eV. We have also investigated the electron-transfer reactions from anion radicals of one kind of solutes to the ground state of another solute. This study has demonstrated that pulse radiolysis can be a useful technique for generation and characterization of anion radicals and for studying electron-transfer reactions using acetonitrile as solvent.

Synthesis and optical properties on a series of polyethers incorporating terfluorene segments and methylene spacers

Abstract: A series of polyethers consisting of a modified terfluorenediol connected with a nonconjugated spacer were synthesized and characterized in respect to their thermal, electrochemical, optical and morphological properties. The polymers were further investigated as thin deposits with the use of the FT‐IR technique after thermal (200°C for 30 min) and photo‐oxidation treatment. After thermal treatment no generation of the carbonyl stretching mode of the fluorenone moiety is observed, while after photo‐oxidation in various times (between 5 to 30 min) the appearance of the fluorenone unit is well established. Furthermore, the length of the flexible spacer used influenced the optical properties of the polyethers after thermal treatment. In particular, odd ones showed more intensely the low energy emission band at 520 nm after the thermal treatment in contrast to even ones.

Method for oxidizing fluorene to 9-fluorenone

Abstract: The invention discloses a method to prepare 9-fluorenone with fluorene. Wherein, using dimethyl sulfoxide as solvent, sodium hydroxide as catalyst, oxygen as oxidant and tower filling reactor; cooling and filtering the reacted liquid to obtain 93% coarse fluorenone; distilling liquid and recycling 94% solvent and some coarse fluorenone; refining with oriented crystallization method and obtaining yellow piece 99.8% fluorenone. This method is simple, needs short reaction time, produces no waste water, and convenient to produce in industry.

Degradation of poly(terphenylenephthalide) at high temperatures

Abstract: The thermal and thermooxidative degradation of poly(terphenylenephthalide) has been studied by thermal analysis, IR and UV spectroscopy, and mass spectrometry. On the basis of the spectral data and the chemical composition of degradation products, it has been shown that both the thermal and thermooxidative degradations of poly(terphenylenephthalide) are characterized by intramolecular cyclization reactions. Depending on the mode of closure of intermediates generated in the course of thermal decomposition of neighboring phthalide groups (head-to-head or head-to-tail), either phenyl-substituted anthraquinones, fluorenones, and fluorenes or symmetric and nonsymmetric dicyclic compounds containing end anthraquinone, fluorenone, and fluorene groups may be formed. The oxidation of poly(terphenylenephthalide) likewise gives rise to cyclic products—the compounds of xanthone and dibenzofuran series.

Multifunctional Block Copolymers for Organic Photorefractive Materials

Abstract: Photorefractive active block copolymers were successfully synthesized via an atom transfer radical polymerization of acrylate containing liquid crystalline moiety and hole transporting carbazole moiety. Resulting copolymers were characterized by gel permeation chromatography, NMR, and DSC. Copolymers afforded the transparent films showing birefringent nature. Photorefractive characteristics of copolymers with 2 wt% of trinitro- fluorenone as a photosensitizer were investigated by four wave mixing and two-beam coupling methods with a He-Ne laser. For the block copolymer, higher diffraction efficiency and larger coupling gain were observed compared with the corresponding statistical random copolymer.

Method for producing fluorenone

Abstract: PROBLEM TO BE SOLVED: To provide a method for producing in high yield a fluorenone useful as a raw material for pharmaceuticals, agrochemicals, macromolecular compounds for electronic materials, dyes, pigments, photosensitizers, etc. by oxidizing the corresponding fluorene with molecular oxygen. SOLUTION: The method for producing the fluorenone comprises oxidizing the corresponding fluorene such as a (substituted) fluorene with molecular oxygen in an organic solvent such as toluene or a xylene in the presence of a phase-transfer catalyst such as a quaternary ammonium salt and a solid alkali metal hydroxide at 30-100°C. COPYRIGHT: (C)2007,JPO&INPIT

Single Molecule Studies of a 2,7-Bis-(Phenylethenyl)fluorenone: Implications for Green-Emission Bands in Fluorene-Based OLEDs

Abstract: The color purity of blue polyfluorene fluorescence emission is often adversely contaminated by green emission bands. The origin of this green emission has been attributed to various factors including on-chain oxidation of fluorene leading to monomeric fluorenone emission and inter/intra-chain interaction between segments of fluorenone units leading to excimer formation on the polyfluorene backbone. We report here emission properties at the bulk and single molecule level of a molecular fluorene derivative and compare them to those of its oxidative fluorenone derivative. Whereas the bulk fluorescence emission of 2,7-bis(3,4,5-trimethoxyphenylethenyl)-9,9-diethyl-9H-fluorene (OFPV) exhibits a blue to blue-green emission at about 480 nm, 2,7-bis(3,4,5-trimethoxyphenylethenyl)-9,9-diethyl-9H-fluorenone (OFOPV) shows red luminescence with a peak centered at about 630 nm. However, the peak position for OFOPV shifts to higher energies (∼540 nm) upon dilution or dispersion in polymer matrices like PMMA or Zeonex. Single molecule measurements of OFOPV show fluorescence spectra dominated by peaks around 540 nm, with a small minority at longer wavelengths that are attributed to emission from dimers or higher aggregates. This distribution indicates that monomeric emission of OFOPV is green, consistent with green emission bands seen in polyfluorenes.