Fluorene Copolymers Research Articles

Facile synthesis of a variety of triarylamine-based conjugated polymers and tuning of their optoelectronic properties

An alternating copolymer of fluorene and aniline (P1) was prepared by Suzuki–Miyaura coupling polymerization. P1 was used as a precursor for post-functionalization of the aniline moiety by Buchwald–Hartwig amination to give successfully P2–P4, having triarylamine units with a variety of substituents at the para-position of the aromatic ring introduced. The optical properties of P1–P4 were studied by UV–vis and photoluminescence (PL) analyses both in solution and in the film state, showing characteristic absorption and emission behaviors depending on their structures. The electrochemical behavior of the polymers in the thin-film state was also investigated by cyclic voltammetry to exhibit the reversible oxidation/re-reduction couples.

Fluorescent π‐Conjugated Polymer Dots versus Self‐Assembled Small‐Molecule Nanoparticles: What’s the Difference?

Fluorescent nanoparticles based on π-conjugated small molecules and polymers are two different classes of π-conjugated systems that have attracted much interest. To date, both emerging classes have only been studied separately and showed no clear differences in their properties. Herein these nanoparticles are compared on the basis of a fluorene co-polymer and its corresponding small molecule. Both systems formed nanoparticles with the same diameter, whereas the fluorescence properties clearly differed. In case of the polymer the fluorescence diminished, whereas for the small molecules the fluorescence increased. In addition, the capability of encapsulation and release of a hydrophobic dye from the fluorescent nanoparticles was studied. For the polymer system, encapsulation was highly efficient and no release was observed, whereas for the small molecule system encapsulation was less efficient and release of the dye was observed. These studies show a clear difference between small molecules and polymers which has important implications for the design of fluorescent nanoparticles.

Efficient Single-Layer White Light-Emitting Devices Based on Silole-Containing Polymers

Efficient white-light-emitting polymers were developed through the incorporation of narrow-bandgap green-emitting and red-emitting siloles moieties into the blue-emitting fluorene and carbazole copolymers backbone. By carefully controlling the concentrations of the green- and red-emitting species in the resulting copolymers, a white-light emission was achieved due to the simultaneous emission from all three colors. EL devices based on the copolymers exhibited luminance efficiencies of 4.87 cd/A with color coordinates of (0.30, 0.31) that was very close to the ideal CIE chromaticity coordinates for pure white light of (0.33, 0.33). After thermal treatment under 160 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C, the devices showed the best luminous properties with external quantum yield of 3.39%, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ELmax</sub> of 6.78 cd/A and color coordinate of (0.29, 0.30). Furthermore, the color coordinates remained almost unchanged over the range of operating potentials. The main operating process involve in the white electroluminescent process can be attributed to the direct charge trapping on the narrow band gap units and partial energy transfer from the blue-emitting segments to the green- and red-emitting siloles moieties.

The Marriage of Metallacycle Transfer Chemistry with Suzuki–Miyaura Cross-Coupling To Give Main Group Element-Containing Conjugated Polymers

A versatile and general synthetic route for the synthesis of conjugated main group element-based polymers, previously inaccessible by conventional means, is reported. These polymers contain five-membered chalcogenophene rings based on S, Se, and Te, and we demonstrate that optoelectronic properties can be readily tuned via controlled atom substitution chemistry. In addition, regioregular hybrid thiophene-selenophene-tellurophene and selenophene-fluorene copolymers were synthesized to provide a further illustration of the scope of the presented metallacycle transfer/cross-coupling polymerization method.

Ambipolar Low-bandgap Copolymers Consisting of Dithienoketopyrrole for All-Polymer Solar Cells

The new low-band gap copolymers containing electron-accepting thienoisoindigo (TIDG) exhibit the low-lying lowest unoccupied molecular orbital (LUMO) at -3.8 eV. This envisions their use as n-type polymer in combination with typical p-type regioregular poly(3-hexylthiophene) (P3HT) towards all-polymer organic photovoltaics (OPV). The alternating fluorene and TIDG copolymer, PFTIDG, shows the electronic absorption maximum at 744 nm in the film states, of which spectrum is complementary to that of P3HT and thus advantageous for covering the wide solar spectrum. The laser and Xe-flash time-resolved microwave conductivity (TRMC) evaluations were performed for screening the effects of p/n blend ratio and thermal annealing in bulk heterojunction framework. The power conversion efficiency of 0.06% was obtained for pre-annealed P3HT:PFTIDG = 1:1 together with a high open circuit voltage of 0.92 V, which is suggestive of ambipolar characteristics of PFTIDG.

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芴与联噻吩发光共聚物的合成与发光特性

Cyclopentadithiophene–Fluorene Copolymer for Organic Solar Cells and Light Emitting Diodes

Synthesis of a conjugated copolymer PF8CPDT10 comprising cyclopentadithiophene and fluorene units, investigation of its optical and electrochemical properties and evaluation of this material in organic bulk heterojunction solar cells and light emitting diodes are reported.

Micro X-ray diffraction mapping of a fluorene copolymer fibre

Using raster-scanning wide-angle X-ray scattering, we investigate oriented fibres of the low bandgap conjugated polymer, poly[2,7-(9,9-dioctylfluorene)-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (F8TBT), that was developed in particular for polymer solar cells. For the first time, structural data are provided for F8TBT. Our results demonstrate that the nano-scale structure of this polymer is closely related to the externally observable features of the fibre, and thus emphasise the importance of having full control over the local molecular conformation. Liquid-crystalline phases are observed at elevated temperatures, and the molecular alignment in the drawn fibres yields scattering patterns that are dominated by broad peaks of equatorial diffuse scattering. The significant degree of preferred orientation facilitates the analysis, leading to estimates of (average) nearest-neighbour packing distances and coherence length of this macromolecule. In particular, we observe a pronounced broad signal assigned to packing of the conjugated backbone with an approximate spacing of 4.00–4.39 Å that is coherent over 5-6 polymer segments.

Introducing a new triazoloquinoxaline‐based fluorene copolymer for organic photovoltaics: Synthesis, characterization, and photovoltaic properties

AbstractA new donor‐acceptor copolymer consisting of triazoloquinoxaline and 9,9‐dialkylfluorene units on the main chain has been synthesized, characterized and evaluated as donor material in bulk heterojunction solar cells using PC61BM as an acceptor. The resulting polymer PTQF showed good thermal stability and solubility in common organic solvents. Cyclic Voltammetry measurements showed that the PTQF has HOMO–LUMO energy levels of −5.13 and −3.62 eV, respectively. DFT calculations revealed that the HOMO is delocalized all over the thiophene and fluorene units and the LUMO is localized mainly on the triazole and pyrazine units. PTQF absorbs broadly in the visible region and exhibits a bandgap of 1.4 eV. Photovoltaic devices exhibited 1.7% efficiency for 1:2 PTQF:PC61BM blend ratio using Ca/Ag electrodes. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Performance of fluorene and terthiophene copolymer in bilayer photovoltaic devices: The role of the polymer conformations

We report experiments using fluorene and terthiophene copolymer as the active layer in bilayer devices with C60. The highest short circuit current, open circuit voltage and power conversion efficiency upon AM1.5 illumination were 6.8mA/cm2, 0.68V and 2.33%, respectively. Density functional theory analysis was used to identify the most stable configurations of the terthiophene moieties in the polymer: the most stable form has the thiophene rings in the alternate configuration (anti) and the second conformation has the thiophene rings pointing to the same direction (syn). Comparing theoretical results with measurements of absorbance, X-ray diffraction, and X-ray reflectometry experiments, we conclude that the annealing treatment produces conformational anti to syn transition along the backbone of poly[9,9′-n-dihexyl-2,7-fluorene-alt-2,5-terthiophene] (LaPPS45). The syn segments of the chain condensed then in a lamellar ordered structure which increases the degree of crystallinity of the annealed samples and improve the light harvest at long wavelengths. From absorption measurements of films submitted to different annealing temperatures and with the help of theoretical calculations we propose a “wave-like” aggregation pattern to the syn segments in those lamellas.

Biotin-functionalized semiconducting polymer in an organic field effect transistor and application as a biosensor.

This report presents biotin-functionalized semiconducting polymers that are based on fluorene and bithiophene co-polymers (F8T2). Also presented is the application of these polymers to an organic thin film transistor used as a biosensor. The side chains of fluorene were partially biotinylated after the esterification of the biotin with corresponding alcohol-groups at the side chain in F8T2. Their properties as an organic semiconductor were tested using an organic thin film transistor (OTFT) and were found to show typical p-type semiconductor curves. The functionality of this biosensor in the sensing of biologically active molecules such as avidin in comparison with bovine serum albumin (BSA) was established through a selective decrease in the conductivity of the transistor, as measured with a device that was developed by the authors. Changes to the optical properties of this polymer were also measured through the change in the color of the UV-fluorescence before and after a reaction with avidin or BSA.

Dielectric and electrical properties of an organic device containing benzotriazole and fluorene bearing copolymer

AbstractDielectric and electrical properties of a benzotriazole and fluorene copolymer were investigated using current‐voltage (I–V), capacitance‐voltage (C–V), and conductance–voltage (G/w–V) measurements at room temperature. The electrical parameters, barrier height (φBo), and ideality factor (n) obtained from the forward bias LnI‐V plot were found as 0.453 eV and 2.08, respectively. The Rs values were found as 2.20, 2.12, 1.90 Ω using dV/dLnI versus I, H(I) versus I and F(V)‐V plots, respectively. The dielectric constant (ε′), the dielectric loss (ε″), and the ac electrical conductivity ( σac) are a strong function of voltage and frequency. Decrease in ε′ and ε″ values with increasing frequency was observed. On the other hand, the increase of σac with increasing frequency was observed. Experimental results show that the conjugated copolymer plays an important role in the values of barrier height, ideality factor, series resistance, and dielectric parameters. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Tunable Fluorescent/Phosphorescent Platinum(II) Porphyrin–Fluorene Copolymers for Ratiometric Dual Emissive Oxygen Sensing

A series of new platinum(II) 5,15-bis(pentafluorophenyl)-10,20-bis(phenyl)porphyrin-9,9-dioctylfluorene copolymers, in which the relative intensities of the blue fluorescence and red phosphorescence can be easily tuned by the initial feed ratio of the two monomers or energy transfer between the fluorescent and phosphorescent units, have been designed and prepared for the application in ratiometric dual emissive oxygen sensing. To the best of our knowledge, this is the first example of a ratiometric oxygen sensor based on dual fluorescent/phosphorescent polymers or copolymers containing transition-metal complexes. It also provides an alternative and easy way to achieve dual emissive oxygen sensing.

Highly Charged Conjugated Polymers with Polyphenylene Backbones and Poly(acrylic acid) Side Chains

A synthetic strategy to prepare various amphiphilic, conjugated graft copolymers by means of the grafting onto technique via click coupling reaction is described. In particular, amphiphilic, conjugated polyelectrolyte brush copolymers based on 2,7-linked carbazole–fluorene copolymers as main chains and pH-sensitive, highly charged poly(acrylic acid) side chains (PAA) are presented. The main chain is obtained by a Suzuki polycondensation of dibromo- and diboronic ester of fluorene and carbazole monomers, resulting in conjugated polyphenylene-type copolymers with both alternating and statistical carbazole–fluorene structures. In order to vary the amphiphilicity of the graft copolymers, 9,9-disubstituted fluorene derivatives with different polarities, induced by branched alkyl as well as by methoxytetra(ethylene glycol) (TEG) groups, were used. To graft the side chains on the conjugated backbone, the carbazole units are, first, N-functionalized by pentynyl groups. These units are reacted in a click reaction ...

Fluorescent nanoparticles from self-assembly of β-cyclodextrin-functionalized fluorene copolymers for organic molecule sensing and cell labeling

Bromide-bearing conjugated fluorene copolymers were prepared by Suzuki coupling polymerization of 2,7-dibromo-9,9-bis(6′-bromohexyl)fluorene and 2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-dihexylfluorene. Thiol-functionalized β-cyclodextrin was subsequently grafted to the bromoalkyl side chains of the fluorene copolymers via the thio-bromo ‘click’ reaction. The resulting fluorene copolymers can self-assemble into fluorescent nanoparticles surrounded by a β-cyclodextrin outer layer in an aqueous medium. Host–guest interactions of the β-cyclodextrin moieties of nanoparticles with the organic guest molecules in the aqueous medium gave rise to variations in the emission intensity of the nanoparticles. The low cytotoxicity of the fluorescent nanoparticles was revealed by incubation with KB cells, a cell line derived from carcinoma of the nasopharynx, in 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assays in vitro. The biocompatible and fluorescent nanoparticles were further used as effective fluorescence labels for KB cells.

Effect of the Temperature of Annealing on the Performance of Fluorene and Bithiophene Copolymer in Bilayer Solar Cells

ABSTRACTWe have investigated the effect of temperature annealing on bilayer heterojunction solar cells based on poly[9,9’-hexyl-fluorene-alt-bithiophene] as active layer. Film morphology for different temperature annealing was probed by atomic force microscopy (AFM) and the values of roughness range from 0.59 up to 2.15 nm. The best photovoltaic performance was found for devices with active layer annealed at 200°C with power conversion efficiency (η) of 2.8 % while devices without annealing presented only 0.4%. This performance enhancement is attributed to the reduction of traps and increased hole mobility after the thermal annealing.

Synthesis and application of poly(fluorene-alt-naphthalene diimide) as an n-type polymer for all-polymer solar cells

A new alternating copolymer of fluorene and naphthalene diimide, PF-NDI, was synthesized and characterized. The highest power conversion efficiency of all-polymer solar cells based on P3HT:PF-NDI reached 1.63% with a relatively high fill factor of 0.66 by using 1,8-diiodooctane as a solvent additive to optimize the mixing morphology.

2-(2,3,4,5,6-Pentafluorophenyl)-1H-benzo[d]imidazole, a fluorine-rich building block for the preparation of conjugated polymer donors for organic solar cell applications

We have introduced the pentafluorophenyl substituted benzimidazole as a building block of conjugated polymers for optoelectronic applications. We present the synthesis of a copolymer bearing fluorene as the comonomer. A detailed characterization of the novel material including structural, electrochemical and optical (using absorption, emission and time-resolved photoluminescence techniques) properties as well as computational modeling is described. The polymer exhibits highly efficient photoluminescence quenching when blended with fullerene derivatives (PCBM). The experimental results are compared with the alternating fluorene copolymer (APFO-3) in order to identify structure and property relations with the novel synthesized conjugated polymer. Early photovoltaic performance data are presented and compared with the well established APFO-3 : PCBM material system.

Spectroscopic studies of energy transfer in fluorene co-polymer blend nanoparticles

Nanoparticles of poly(9,9-dioctylfluorene-co-bis-N,N-(4-butylphenyl)-bis-N,N-phenyl-1,4-phenylenediamine) [PFB] and poly(9,9-dioctylfluorene-co-benzothiadiazole) [F8BT] (1:1 w/w) were studied using scanned probe and single particle spectroscopy techniques. Photoluminescence (PL spectra of ∼58 and ∼100nm PFB/F8BT nanoparticles show efficient energy transfer from the PFB (donor) component to the F8BT (acceptor) component that is independent of particle size. We propose that nanoparticles are phase segregated into discrete PFB/F8BT nanodomains on the order of ∼20–40nm for both particle sizes. Pressure-dependent nanoparticle PL spectra support this assignment where lineshape maxima of each component red-shift in a similar manner due to increased interchain packing within the single nanodomains.

A novel fluorescent nanoparticle composed of fluorene copolymer core and silica shell with enhanced photostability

A variety of fluorescent nanoparticles have been developed for demanding applications such as optical biosensing and fluorescence imaging in live cells. Silica-based fluorescent nanoparticles offer diverse advantages for biological applications. For example, they can be used as labeling probes due to their low toxicity, high sensitivity, resolution, and stability. In this research, a new class of highly fluorescent, efficient nanoparticles composed of a newly synthesized poly[di(2-methoxy-5-(2-ethylhexyloxy))-2,7-(9,9-dioctyl-9 H-fluorene)] (PDDF) core and a silica shell (designated as PDDF@SiO 2) were prepared using a simple reverse micelle method, and their fluorescent properties were evaluated using methods such as single-dot photoluminescence measurements. The enhanced photostability of the particles and their potential applications for bioanalysis are discussed in this article. The morphology, size, and fluorescent properties for prepared PDDF@SiO 2 nanoparticles were characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM) and photoluminescence spectroscopy. The prepared particles size, which was approximately 60 nm, resulted in an excellent colloidal stability in a physiological environment. The photobleaching dynamics, total numbers of emitted photons (TNEP) and statistical measurements of individual nanoparticles were observed using laser scanning fluorescence microscopy to assess the structure and photostability of PDDF@SiO 2 nanoparticles. Additionally, PDDF@SiO 2 nanoparticles were used in cell toxicity and permeation tests for biological analyses, demonstrating a great potential for use as powerful, novel materials within the emerging fields of biosensing and biomedical engineering.