Fluorene Backbone Research Articles

Amplified Chirality Transfer to Aromatic Molecules through Non-specific Inclusion by Amorphous, Hyperbranched Poly(fluorenevinylene) Derivatives.

Optically active, hyperbranched, poly(fluorene-2,4,7-triylethene-1,2-diyl) [poly(fluorenevinylene)] derivatives bearing a neomenthyl group and a pentyl group at the 9-position of the fluorene backbone at various ratios acted as a chirality donor (host polymers) efficiently included naphthalene, anthracene, pyrene, 9-phenylanthracene, and 9,10-diphenyanthracene as a chirality acceptor (guest molecules) in their interior space in film as well as in solution, with the guest molecules exhibiting intense circular dichroism through chirality transfer with chirality amplification. The efficiency of the chirality transfer was much higher with higher-molar-mass polymers than lower-molar-mass ones as well as with hyperbranched polymers compared to the analogous linear ones. The hyperbranched polymers include the small molecules in their complex structure without any specific interactions at various stoichiometries. The included molecules may have ordered intermolecular arrangement that may be somewhat similar to those of liquid crystals. Naphthalene, anthracene, and pyrene included in the polymer exhibited efficient circularly polarized luminescence, where the chirality was remarkably amplified in excited states, and anthracene exhibited especially high anisotropies in the emission on the order of 10-2 .

Amplified Chirality Transfer to Aromatic Molecules through Non‐specific Inclusion by Amorphous, Hyperbranched Poly(fluorenevinylene) Derivatives

AbstractOptically active, hyperbranched, poly(fluorene‐2,4,7‐triylethene‐1,2‐diyl) [poly(fluorenevinylene)] derivatives bearing a neomenthyl group and a pentyl group at the 9‐position of the fluorene backbone at various ratios acted as a chirality donor (host polymers) efficiently included naphthalene, anthracene, pyrene, 9‐phenylanthracene, and 9,10‐diphenyanthracene as a chirality acceptor (guest molecules) in their interior space in film as well as in solution, with the guest molecules exhibiting intense circular dichroism through chirality transfer with chirality amplification. The efficiency of the chirality transfer was much higher with higher‐molar‐mass polymers than lower‐molar‐mass ones as well as with hyperbranched polymers compared to the analogous linear ones. The hyperbranched polymers include the small molecules in their complex structure without any specific interactions at various stoichiometries. The included molecules may have ordered intermolecular arrangement that may be somewhat similar to those of liquid crystals. Naphthalene, anthracene, and pyrene included in the polymer exhibited efficient circularly polarized luminescence, where the chirality was remarkably amplified in excited states, and anthracene exhibited especially high anisotropies in the emission on the order of 10−2.

Non-uniform Self-folding of Helical Poly(fluorenevinylene) Derivatives in the Solid State Leading to Amplified Circular Dichroism and Circularly Polarized Light Emission.

An unprecedented non-uniform self-folding of artificial polymer chains composed of turn moieties and stretched segments is presented through the design of a set of optically active poly(fluorene-2,7-diylethene-1,2-diyl) (poly(fluorenevinylene)) derivatives bearing a neomenthyl group and a pentyl group attached at the 9-position of fluorene backbone at various ratios. The folded structure is formed and stabilized through inter-chain interactions in the solid state, leading to remarkably enhanced chiroptical properties (chirality amplification) in terms of circular dichroism (CD) and circularly polarized light (CPL) emission. This phenomenon is rationalized by experimental and theoretical CD and CPL spectral analyses. The polymer arrangements in the solid state were further assessed through transmission electron microscopic observations combined with enhanced sampling molecular dynamics simulations in the solid state revealing the thin film organizations.

Non‐uniform Self‐folding of Helical Poly(fluorenevinylene) Derivatives in the Solid State Leading to Amplified Circular Dichroism and Circularly Polarized Light Emission

AbstractAn unprecedented non‐uniform self‐folding of artificial polymer chains composed of turn moieties and stretched segments is presented through the design of a set of optically active poly(fluorene‐2,7‐diylethene‐1,2‐diyl) (poly(fluorenevinylene)) derivatives bearing a neomenthyl group and a pentyl group attached at the 9‐position of fluorene backbone at various ratios. The folded structure is formed and stabilized through inter‐chain interactions in the solid state, leading to remarkably enhanced chiroptical properties (chirality amplification) in terms of circular dichroism (CD) and circularly polarized light (CPL) emission. This phenomenon is rationalized by experimental and theoretical CD and CPL spectral analyses. The polymer arrangements in the solid state were further assessed through transmission electron microscopic observations combined with enhanced sampling molecular dynamics simulations in the solid state revealing the thin film organizations.

Development of highly alkaline stable anion conductive polymers with fluorene backbone for water electrolysis

AbstractAnion exchange membrane water electrolysis (AEMWE) is currently paying attention as a new hydrogen (H2) production method since it can operate at high current densities using inexpensive nonnoble metal catalysts. However, the significant problems of AEMs, including their insufficient anion conductivity and alkaline stability, prevent the practical usage of AEMWE. We show a novel anion conductive polymer, alkyl trimethylammonium‐substituted polyfluorene (TMA‐PF), bearing no heteroatom bonds in the main chain. The TMA‐PF membrane possesses higher anion conductivity than conventional AEMs due to the increased flexibility and mobility of the alkylammonium side chains of TMA‐PF. The TMA‐PF membrane shows high‐alkaline stability and maintains the initial ion conductivity after immersion in an aqueous NaOH solution (8 mol L−1) at 80°C for 48 h. In the water electrolysis evaluation, the cell using the TMA‐PF membrane exhibits a higher current density (400 mA cm−2 at 2.03 V) than the cell using the conventional AEM at the same potential, indicating that the novel AEM has a high potential to generate H2 effectively. Green hydrogen produced by AEMWE using renewable energy will be an environmentally benign energy source without CO2 emissions.

Highly efficient and stable blue quantum-dot light-emitting diodes based on polyfluorenes with carbazole pendent groups as hole-transporting materials

Highly efficient and stable blue quantum-dot light-emitting diodes (QD-LEDs) have been realized by using poly (9,9-bis(N-(2′-ethylhexyl)-carbazole-3-yl)-2,7-fluorene) (PFCz) as hole-transporting layers (HTLs). Due to the carbazole units as substituents at the 9-position of polyfluorene, PFCz shows higher hole mobility and better electrochemical stability than poly (N-vinlycarbazole) (PVK). As a result, the maximum current efficiency (CE) and external quantum efficiency (EQE) of the blue QD-LEDs increased from 4.32 cd A−1 to 7.9% for PVK HTL to 7.38 cd A−1 and 12.61% for PFCz HTL, respectively. Furthermore, the PFCz-based blue QD-LED exhibited lower turn-on voltage and longer device lifetime than the PVK-based device. The improvement performance of blue QD-LED should be attributed to the conjugated fluorene backbone and the substituents of the carbazole active sites, thus enhancing hole mobility and electrochemical stability. This result demonstrates that polyfluorenes with pendent carbazole groups is a promising hole-transporting materials for improving performance of blue QD-LEDs.

Enantiomeric Separation of Semiconducting Single-Walled Carbon Nanotubes by Acid Cleavable Chiral Polyfluorene.

Helical wrapping by conjugated polymer has been demonstrated as a powerful tool for the sorting of single-walled carbon nanotubes (SWCNTs) according to their electronic type, chiral index, and even handedness. However, a method of one-step extraction of left-handed (M) and right-handed (P) semiconducting SWCNTs (s-SWCNTs) with subsequent cleavage of the polymer has not yet been published. In this work, we designed and synthesized one pair of acid cleavable polyfluorenes with defined chirality for handedness separation of s-SWCNTs from as-produced nanotubes. Each monomer contains a chiral center on the fluorene backbone in the 9-position, and the amino and carbonyl groups in the 2- and 7-positions maintain the head-to-tail regioselective polymerization resulting in polyimines with strictly all-(R) or all-(S) configuration. The obtained chiral polymers exhibit a strong recognition ability toward left- or right-handed s-SWCNTs from commercially available CoMoCAT SWCNTs with a sorting process requiring only bath sonication and centrifugation. Interestingly, the remaining polymer on each single nanotube, which helps to prevent aggregation, does not interfere with the circular dichroism signals from the nanotube at all. Therefore, we observed all four interband transition peaks (E11, E22, E33, E44) in the circular dichroism (CD) spectra of the still wrapped optically enriched left-handed and right-handed (6,5) SWCNTs in toluene. Binding energies obtained from molecular dynamics simulations were consistent with our experimental results and showed a significant preference for one specific handedness from each chiral polymer. Moreover, the imine bonds along the polymer chains enable the release of the nanotubes upon acid treatment. After s-SWNT separation, the polymer can be decomposed into monomers and be cleanly removed under mild acidic conditions, yielding dispersant-free handedness sorted s-SWNTs. The monomers can be almost quantitatively recovered to resynthesize the chiral polymer. This approach enables high selective isolation of polymer-free s-SWNT enantiomers for their further applications in carbon nanotube (CNT) devices.

Light-Assisted Catalytic Hydrogenation of Carbon Dioxide at a Low Pressure by a Dinuclear Iridium Polyhydride Complex

A dinuclear iridium pentahydride complex bearing a diphosphine ligand with a fluorene backbone was synthesized and characterized for use as a photocatalyst for CO2 hydrogenation. The complex can be...

Covalent triazine-based framework-grafted functionalized fibrous silica sphere as a solid-phase microextraction coating for simultaneous determination of fenthion and chlorpyrifos by ion mobility spectrometry.

A novel covalent triazine-based framework (CTF)-grafted phenyl-functionalized fibrous silica nanosphere, KCC-1 (named as RS-2) was synthesized via a simple and effective Friedel-Crafts approach. The microporous CTF with fluorene backbone was coupled and grown uniformly on the surface of phenyl-functionalized KCC-1 to prepare a hybrid extended porous framework. The prepared materialswere characterized, and FE-SEM and TEM images revealed a flower-like structure for RS-2. The synthesized RS-2 showed excellent thermal stability, so the weight loss was about 30% at 800°C. RS-2 was applied as a new coating in the solid-phase microextraction procedure to extract chlorpyrifos and fenthion pesticides fromwater, wastewater, and fruit samples, before determining by corona discharge-ion mobility spectrometry. Some experimental factors affecting the extraction yield of the analytes, including ionic strength, stirring rate, sample pH, extraction temperature, and extraction time, were investigated. Under optimum conditions, the linear dynamic ranges were 0.1-10μgL-1 and 1.0-70μgL-1, and the limits of detection were 0.05 and 0.55μgL-1 for chlorpyrifos and fenthion, respectively. The proposed method showed recovery values in the range 86-117% with a precision of 3.0-7.1% for real samples. Covalent triazine-based framework (CTF)-grafted phenyl-functionalized fibrous silica nanosphere (named as RS-2) was synthesized. RS-2 was applied as a sorbent for solid-phase microextraction (SPME) of chlorpyrifos and fenthion from fruit and water samples followed by corona discharge ionization ion mobility spectrometry (CD-IMS).

Synthesis, characterization and device application of a novel blue-emitting copolymer incorporating fluorene and benzothiazole backbone units

Utilizing benzothiazole (BTz) combined with fluorene as backbone units, we designed and synthesized a novel blue-emitting copolymer poly[(9,9-dioctyl-9H-fluorene)-alt-(2-heptylbenzo[d]thiazole)] (PF-BTz). PF-BTz shows excellent thermal stability with the 5% weight-loss decomposition temperature above 410 °C. According to the molecular geometry analyzed by density functional theory (DFT) calculations, PF-BTz should possess clearly twisted backbone and weak molecule coplanarity. The photophysical properties of PF-BTz were discussed, and particularly the photoluminescence (PL) spectra of PF-BTz in solution and film both display the blue emission with peaks wavelength of 420 nm and 429 nm, respectively. Then the polymer light-emitting diodes (PLEDs) was fabricated by using PF-BTz as emitting layer, and the PF-BTz-based device also shows the blue emission with CIEx,y of (0.23, 0.25) and a maximal luminous efficiency (LEmax) of 0.25 cd/A. The results indicate that the PF-BTz copolymer incorporating fluorene and benzothiazole backbone units would be a promising blue emitter for high-performance PLEDs.

A simple fluorescent film probe for the detection of fluoride anion in organic solution

The detection of fluoride anion (F−) in an organic solution using a fluorescent film sensor has always been a challenge. In this investigation, a small fluorescent molecule, DPP-DWCZ, which is consisting of diketopyrrolopyrrole (DPP), fluorene backbone and the impendent carbazole side chains was designed and synthesized. Given the high electro-activity of carbazole, electropolymerization (EP) was used to prepare the cross-linking DPP-DWCZ films. The DPP-DWCZ EP films were further used as a fluorescence-quenching type sensor for the detection of F− in organic solution with the limit of detection to 4.1 × 10−8 M. The deprotonation of amide moiety caused by F− is responsible for the fluorescence quenching. This study provides a feasible way to the detection of F− in an organic solution with high sensitivity, remarkably higher anti-interference and prominent reusability.

Mesoscale Ordering and Charge-Transport of Crystalline Spiro-OMeTAD Organic Semiconductors

The mesoscale ordering and charge-transport of crystalline spiro-OMeTAD, a hole-transporting material extensively used in perosvkite and dye-sensitized solar cell applications, were explored using molecular dynamics and hole mobility calculations. Morphologies were evaluated through conformational changes, nematic order and paracrystallinity at various temperatures. Charge transport is predicted with electronic structure methods employing a hopping mechanism. Our calculations show that along with strong fluorene backbone packing, phenylenes in the methoxyphenyl–amine substituents of spiro-OMeTAD are an integral part of the material performance. Backbone and substituent paracrystallinity predictions showed highly ordered crystalline phase. The methoxyphenyl substituents have multiple conformations in the unit-cell scale, but interphenylene electronic-coupling remain nearly constant. A thermal increase in positional disorder results in a systematic increase in energetic disorder and a decrease in hole mobil...

A series of chiral metal–organic frameworks based on fluorene di- and tetra-carboxylates: syntheses, crystal structures and luminescence properties

A series of optically pure carboxylate ligands based on a fluorene backbone were synthesized and used for the elaboration of four chiral metal–organic frameworks (6, 7, 8, and 9) containing Cu-based paddle-wheels. The positions and numbers of coordinating carboxylate functions on the ligand core govern the resulting MOF topologies, leading to a 1D framework (8), 2D grids with (7) or without interpenetration (6), and a 3D (9) framework and showing calculated porosities ranging from 8 to 47% of the unit-cell volumes. Ligands as well as corresponding MOFs possess luminescence properties with blue emission. The most porous MOF (9), made of a tetracarboxylate ligand, exhibits a BET apparent surface area of 467 m2 g−1 and methane and carbon dioxide storage capacities of 26.5 cm3 g−1 and 129 cm3 g−1, respectively, at 303 K and 30 bar.

New Red-Emitting Conjugated Polyelectrolyte: Stabilization by Interaction with Biomolecules and Potential Use as Drug Carriers and Bioimaging Probes.

The design and development of fluorescent conjugated polyelectrolytes (CPEs) emitting in the red region of the visible spectrum is at present of great interest for bioimaging studies. However, despite the wide variety of CPEs available, stable bright red-emitters remain scarce due to their low solubility and instability in aqueous media, consequently limiting their applications. In this work, we have synthesized and characterized a new red-emitting cationic conjugated polyelectrolyte copoly-{[9,9-bis(6'-N,N,N-trimethylammonium)hexyl]-2,7-(fluorene)-alt-1,4-(naphtho[2,3c]-1,2,5-thiadiazole)} bromide (HTMA-PFNT), based on the incorporation of naphtha[2,3c][1,2,5] thiadiazole on fluorene backbone to increase the bathochromic emission, extending the conjugation length in the polymer backbone. Water stabilization was achieved by binding the polyelectrolyte to two different biological systems which are currently used as nanocarriers: human serum albumin (HSA) and lipid vesicles. Using both systems, stable nanostructures of different composition were obtained and their properties were characterized. The properties of the protein-based nanoparticles are consistent with polyelectrolyte aggregates covered with HSA molecules, while the liposome system is composed of lipid vesicles coated with polyelectrolyte chains partially inserted in the bilayer. Both protein and vesicle structural integrity were not affected after their interaction with HTMA-PFNT, as well as the carrier properties, allowing for the binding and transport of ligands. In addition, the nanoparticles displayed the ability of labeling the cell membrane of living cells. All these results extend the potential applications of these novel multifunctional nanoparticles as therapeutic carriers and bioimaging probes.

Benzocyclobutene resin with fluorene backbone: a novel thermosetting material with high thermostability and low dielectric constant

A new benzocyclobutene monomer with a fluorene backbone was synthesized, which can be thermally converted to a cross-linked network with low dielectric constant and high thermostability.

Influence of structure-selective fluorene-based polymer wrapping on optical transitions of single-wall carbon nanotubes

To understand how fluorene-based polymers selectively extract specific semiconducting single-wall carbon nanotubes (SWCNTs), we compared the optical transitions of SWCNTs wrapped with poly(9,9-dioctylfluorene-alt-pyridine) (PFOPy), i.e., structure-selective polymers, with those wrapped with poly(9,9-di-n-dodecylfluorene) (PFD), i.e., non-selective polymers, in organic solvents by using photoluminescence (PL) excitation spectroscopy. Two (n,m) species of PFOPy-wrapped SWCNTs with intermediate chiral angles exhibited blue-shifted emissions compared with the PFD-wrapped SWCNTs. The shifts in the peaks of PL signals cannot be explained in terms of the dielectric screening effect, but can plausibly be explained in terms of the strains of specific SWCNTs due to the PFOPy wrapping. Moreover, the emissions of specific SWCNTs wrapped with PFOPy were not blue-shifted as much when the solvent was changed from toluene to p-xylene, and this result could be accounted for by a change in the rigidity of the fluorene backbone. Moreover, using p-xylene instead of toluene lowered the selectivity of the SWCNT extraction, thereby suggesting the importance of having a rigid fluorene backbone for selective extraction of SWCNTs.

Synthesis and Characterization of Red Electrophosphorescent Polymers Containing Pendant Iridium(III) Complex Moieties

A series of fluorene-carbazole copolymers containing the pendant phosphor chromophore <TEX>$Ir(absn)_2(acac)$</TEX> (absn: 2-(1-naphthyl)benzothiazole; acac: acetylacetone) were designed and synthesized via Yamamoto coupling. In the film state, these copolymers exhibited absorption and emission peaks at approximately 389 and 426 nm, respectively, which originated from the fluorene backbone. However, in electroluminescent (EL) devices, a significantly red-shifted emission at approximately 611 nm was observed, which was attributed to the pendant iridium(III) complex. Using these copolymers as a single emission layer, polymer light-emitting devices with ITO/PEDOT:PSS/polymer:DNTPD/TmPyPb/LiF/Al configurations exhibited a saturated red emission at 611 nm. The attached iridium(III) complex had a significant effect on the EL performance. A maximum luminous efficiency of 0.85 cd/A, maximum external quantum efficiency of 0.77, maximum power efficiency of 0.48 lm/W, and maximum luminance of 883 <TEX>$cd/m^2$</TEX> were achieved from a device fabricated with the copolymer containing the iridium(III) complex in a 2% molar ratio.

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.

A Detailed Experimental and Theoretical Study into the Properties of C60 Dumbbell Junctions

A combined experimental and theoretical investigation is carried out into the electrical transport across a fullerene dumbbell one-molecule junction. The newly designed molecule comprises two C60 s connected to a fluorene backbone via cyclopropyl groups. It is wired between gold electrodes under ambient conditions by pressing the tip of a scanning tunnelling microscope (STM) onto one of the C60 groups. The STM allows us to identify a single molecule before the junction is formed through imaging, which means unambiguously that only one molecule is wired. Once lifted, the same molecule could be wired many times as it was strongly fixed to the tip, and a high conductance state close to 10(-2) G0 is found. The results also suggest that the relative conductance fluctuations are low as a result of the low mobility of the molecule. Theoretical analysis indicates that the molecule is connected directly to one electrode through the central fluorene, and that to bind it to the gold fully it has to be pushed through a layer of adsorbates naturally present in the experiment.

Synthesis and Photophysical Properties of a Blue Light-Emitting Hyperbranched Poly(fluorene)

A novel hyperbranched conjugated poly(fluorene) (Hyper-PDHF) was obtained through the Suzuki coupling polymerization. Hyper-PDHF has good solubility in common organic solvents and showed good thermal stability up to 428°C with less than 5 wt% weight loss. The photophysical properties of Hyper-PDHF in solution and net solid film are inspected and compared with poly(di-n-hexylfluorene) (PDHF) having linear structure. An absorption maximum of Hyper-PDHF film was determined at 334 nm which was far blue shifted than that of linear PDHF film (381 nm). Hyper-PDHF showed absolute blue photoluminescence (PL) peak at 418 nm with 394 and 444 nm as shoulder peaks. Hyper-PDHF showed also high fluorescence quantum yield as about Φsol = 0.81. In addition, Hyper-PDHF film exhibited almost no longer wavelength emission peaks even the film was annealed at 80°C for 1 hr with illuminating UV (365 nm) in air condition. The high PL efficiency and no aggregate or excimer emission of Hyper-PDHF results from the inhibition of intramolecular or intermolecular interaction by the introduction of the hyperbranched network into the poly(fluorene) backbone.