Fluorenone Units Research Articles

Phenothiazine dyes bearing fluorenone unit for dye-sensitized solar cells

Three N-phenylphenothiazine dyes were synthesized with fluorenone linked with aryl rings as π-bridges and cyanoacrylic acid as the electron acceptor. Their photophysical properties, electrochemical properties and photovoltaic performance were evaluated. Dyes with furan and thiophene bridges show longer ICT absorption wavelength and display distinctly broader and higher light absorption range on TiO2 film. Dye with benzene bridge has an inferior molecular planarity due to the larger dihedral angle between the fluorenone unit and benzene ring, which blueshifts its ICT absorption but favors its antiaggregation. Thus, dye with thiophene bridge achieves the highest JSC while dye with benzene bridge achieves the highest VOC. However, DSSC based on dye with furan bridge obtains the optimal photoelectric conversion efficiency due to better JSC and VOC and the highest ff. Compared with their carbazole counterpart, these phenothiazine dyes show the improved JSC and VOC, therefore, achieve higher photovoltaic conversion efficiency.

A class of electron-deficient units: fluorenone imide and its electron-withdrawing group-functionalized derivatives.

This study describes the development of a series of strong electron-deficient acceptor units, namely, fluorenone imide (FOI) and its derivatives, functionalized with various electron-withdrawing groups, which are developed via functionalization of the fluorenone unit with an imide group and then systematic variation of the attached electron-withdrawing groups at the bridgehead benzylic position.

Switchable Supramolecular Jalousie Constructed from a Fluorenone Macrocycle

Organic crystal engineering is a promising strategy to construct functional materials. Herein, we demonstrate that the marriage of organic crystal engineering and macrocyclic chemistry yields a supramolecular jalousie that can be reversibly opened and closed in crystals. The synchronous rotation of fluorenone units in macrocycles triggered by toluene/phenylmethanol vapor contributes to such motions. This supramolecular jalousie is assembled from a trimeric fluorenone macrocycle, which is synthesized in 46% yield by the condensation of a 2,7-bis(2,4-dimethoxyphenyl)fluorenone monomer with paraformaldehyde. Mechanistic studies indicate that the large size (∼1.6 nm) and the rigid skeleton of the trimeric fluorenone macrocycle provide enough space for the rotation of fluorenone units as well as the encapsulation of guests in the solid state. Moreover, the bistable conformations and induced-fit structural adjustment guarantee such switchable single-crystal-to-single-crystal transformations.

A Two‐Photon Pumped Supramolecular Upconversion Microresonator

AbstractA two‐photon pumped non‐linear optical (NLO) Fabry‐Pèrot (F‐P) type organic micro‐crystal resonator useful for a myriad of upconversion‐based light technologies is presented. The resonator is parallelepiped‐shaped and composed of a self‐assembled donor‐acceptor‐donor type molecule namely, 9,9,9”,9”‐tetramethyl‐9H,9’H,9”H‐[2, 2’:7,2”‐terfluoren]‐9’‐one (TTO). X‐ray crystal structure of an orange‐yellow TTO micro‐crystal reveals C−H⋅⋅⋅O type weak intermolecular hydrogen bond between the oxygen atom of the fluorenone unit and fluorine hydrogen atom. For one‐ and two‐photon excitation the micro‐crystals exhibit F‐P type modes in their photoluminescence signal. The fundamental frequency‐dependent NLO intensity shows a continuous increase as the fundamental wavelength is decreasing down to 770 nm. The two‐photon luminescence signals from these micro‐resonators are several orders of magnitude higher than the thin films of similar thickness.

D-A-D-type orange-light emitting thermally activated delayed fluorescence (TADF) materials based on a fluorenone unit: simulation, photoluminescence and electroluminescence studies.

The design of orange-light emitting, thermally activated, delayed fluorescence (TADF) materials is necessary and important for the development and application of organic light-emitting diodes (OLEDs). Herein, two donor–acceptor–donor (D–A–D)-type orange TADF materials based on fluorenone and acridine, namely 2,7-bis(9,9-dimethylacridin-10(9H)-yl)-9H-fluoren-9-one (27DACRFT, 1) and 3,6-bis(9,9-dimethylacridin-10(9H)-yl)-9H-fluoren-9-one (36DACRFT, 2), were successfully synthetized and characterized. The studies on their structure–property relationship show that the different configurations have a serious effect on the photoluminescence and electroluminescence performance according to the change in singlet–triplet splitting energy (ΔEST) and excited state geometry. This indicates that a better configuration design can reduce internal conversion and improve triplet exciton utilization of TADF materials. Importantly, OLEDs based on 2 exhibited a maximum external quantum efficiency of 8.9%, which is higher than the theoretical efficiency of the OLEDs based on conventional fluorescent materials.

Fluorene-based novel highly emissive fluorescent molecules with aggregate fluorescence change or aggregation-induced emission enhancement characteristics

A series of luminogens containing formamide or fluorenone units, based on fluorene, have been synthesized and characterized by NMR spectroscopy, mass spectrometry and elemental analysis. Their aggregate fluorescence change and aggregation-induced emission enhancement (AIEE) characteristics were investigated by luminescence and UV/Vis spectroscopies. The results indicate that luminogens 1d and 2d, containing formamide units, exhibit significant fluorescence color changing upon aggregate formation, which is a newly observed uncommon and interesting aggregation-induced emission phenomenon. Although the luminogen 3d, with one fluorenone unit and one fluorene unit, was weakly emissive in solution, it was highly fluorescent in the aggregated state and demonstrates typical AIEE characteristics. In comparison with 3d, the luminogen 4d with one fluorenone unit and two fluorene units showed weaker AIEE behavior. In thin-films and in the solid state, luminogen 1d shows intense yellow-green emission, and other luminogens show strong yellow emitting. Among these luminogens, 4d exhibits the highest solid-state emission quantum yield.

Synthesis and photophysical properties of 2′-deoxyguanosine derivatives labeled with fluorene and fluorenone units: toward excimer probes

In this study we prepared two fluorescent nucleosides, GFL and GFO, comprising 2′-deoxyguanosine units covalently bound to 2-ethynylfluorene and 2-ethynyl-9-fluorenone moieties, respectively. The photophysical properties (fluorescence emission shifts and emission intensities) of these fluorescent nucleosides are solvent-dependent. Most notably, GFO, which bears a guanine nucleobase as its electron-donating group, displays an excimer emission in nonpolar solvents; accordingly, we used excimer emission titration to determine the binding constants for the interactions between GFO and nucleobases.

Incorporating a stable fluorenone unit into D–A–π–A organic dyes for dye-sensitized solar cells

Two new organic dyes based on a donor–acceptor–π–bridge–acceptor/anchor (D–A–π–A) configuration, HIQF1 and HIQF2, were synthesized, characterized, and successfully employed in dye-sensitized solar cells. The incorporation of the weakly electron-withdrawing fluorenone group as an additional acceptor enhanced the dyes' properties for solar energy conversion in several ways. First, the absorption spectra of the dyes were broadened, covering a large range of sunlight. Second, the absorption spectra observed upon dye adsorption on TiO2 were only slightly blue-shifted as compared to the spectra of the dyes in solution. Third, the orbital energy levels and electron distributions of the D–A–π–A backbone were ideal for highly efficient electron transport and injection. The incorporation of long electron-donating alkoxy groups in the donor unit of HIQF1 further increased the dye's short-circuit photocurrent density (Jsc), open-circuit voltage (Voc), and overall conversion efficiency (η), but had little negative effect on the fill factor (FF). Solar cells sensitized with HIQF1 showed excellent current–voltage characteristics; the Jsc, Voc, and FF values were 12.26 mA cm−2, 0.70 V, and 0.73, corresponding to a η value of 6.26%.

Electrochemical Tuning of the Optoelectronic Properties of a Fluorene-Based Conjugated Polymer

The electrochemical reduction of a fluorene-based conjugated polymer, poly(9-fluorenone-alt-9,9-dioctylfluorene), was investigated for the first time. The carbonyl group in the fluorenone unit was selectively and quantitatively converted to the methylene group, as determined by (1)H NMR, IR, and energy-dispersive X-ray (EDX) analysis. The optical and electrochemical properties of the polymers were studied by UV-vis, photoluminescence (PL), and cyclic voltammetry (CV) measurements and were found to be tunable by varying the reduction level.

Synthesis of copolyfluorenes with high fluorenone contents and its application in electroluminescent device by simple blending

Poly(fluorene-co-fluorenone)s containing high contents of fluorenone chromophore were synthesized by the Suzuki coupling reaction to study their electroluminescent (EL) properties. The copolymers are thermally stable below 430°C (Td) in nitrogen atmosphere. In film state, their absorption and photoluminescence spectra (peaked at 373–382 nm and 562–564 nm, respectively) are mainly originated from fluorenone units, because of its efficient energy transfer. Both LUMO and HOMO energy levels, estimated from their cyclic voltammograms, are lowered slightly (−3.17−3.23 eV, −5.84−5.89 eV) with increasing contents of electron-withdrawing fluorenone units. Double-layer EL devices, using the copolyfluorenes or their blends with poly(9,9-dihexylfluorene) (PF) as emitting layer, show exclusive emission originated from fluorenone chromophore (565 nm) when its content is high. Blending 0.02–5 wt % of PF-33 (fluorenone fraction: 0.37) with PF greatly enhances device performance (610 cd m−2 4400 cd m−2 and 0.45 cd A−1 1.52 cd A−1). Our results demonstrate that the copolyfluorenes are promising emitting materials for EL devices by simple blending. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Synthesis and characterization of red-emission PPV copolymers containing fluorenone unit

Two soluble copolymers of fluorenone and dioctoxylbenzene (PFN) or anthracene (PFNAn) were synthesized through Heck polymerization, and were characterized by gel permeation chromatography (GPC), FT-IR, 1H-NMR, elemental analysis and thermogravimetric analysis. The polymers possess good solubility in common organic solvents and high thermal stability with the onset decomposition temperature at higher than 410 °C. The photophysical properties of the polymers were investigated in both solutions and spin-coated films. Cyclic voltammetry results revealed that the copolymers possess higher electron affinity and reversible reduction/re-oxidation processes. Their electroluminescent properties were further investigated. PFN and PFNAn show stable and saturated red light emission with high thermal stability and high electron injection ability. This type of conjugated polymers may be promising for the applications as electron acceptors in polymer photovoltaic cells and electron transporting materials.

Fluorenone‐Based Molecules for Bulk‐Heterojunction Solar Cells: Synthesis, Characterization, and Photovoltaic Properties

AbstractA series of four conjugated molecules consisting of a fluorenone central unit symmetrically coupled to different oligothiophene segments are conceptually designed and synthesized to provide new electroactive materials for application in photovoltaic devices. The combination of electron‐donating oligothiophene building blocks with an electron‐accepting fluorenone unit results in the emergence of a new band assigned to an intramolecular charge transfer transition that gives rise to the extension of the absorption spectral range of the resulting molecules. Detailed spectroscopic and voltammetric investigations show that all studied molecules have highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) level positions, which make them good candidates for the application as electron‐donors in bulk‐heterojunction photovoltaic cells, with (6,6)‐phenyl‐C61‐butyric acid methyl ester (PCBM)‐C60 as electron acceptor component. Moderate device performances, with power conversion efficiencies (PCEs) comprised between 0.3 and 0.6%, were obtained with rigid molecules, containing either the bridging units between the thiophene rings, i.e., (2,7‐bis(4,4′‐dioctyl‐cyclopenta[2,1‐b:3,4‐b′]dithiophen‐2‐yl)‐fluoren‐9‐one (SCPTF) and 2,7‐bis(4‐(dioctylmethylene)‐cyclopenta[2,1‐b:3,4‐b′]dithiophen‐5‐yl)‐fluoren‐9‐one (MCPTF) or a vinylene unit 2,7‐bis(5‐[(E)‐1,2‐bis(3‐octylthien‐2‐yl)ethylene])‐fluoren‐9‐one (TVF), whereas with (2,7‐bis‐(3,3‴‐dioctyl‐[2,2′;5′,2″;5″,2‴]quaterthiophen‐5‐yl)‐fluoren‐9‐one (QTF) PCE up to 1.2% (under AM 1.5 illumination, 100 mW cm−2, active area 0.28 cm2) was obtained. The strong π‐stacking interactions in the solid state for this oligomer leading to improved morphology could explain the good performances of QTF‐based devices, which rank among the highest recorded for non‐polymeric materials. Consequently, fluorenone‐based non‐polymeric molecules constitute highly attractive materials for solution‐processable solar cell applications.

The Orientation and Photophysical Properties of Conjugated Polymers in Oriented Films

AbstractHighly oriented light‐emitting blend films containing poly(9,9‐dioctylfluorene) (PFO), PFO with one fluorenone unit (PFF), and ultrahigh‐molecular‐weight polyethylene (U‐PE) are prepared by using a tensile deformation technique. A high dichroic ratio of 36 in photoluminescence from the oriented film is obtained. The photophysical properties of the PFF/PFO blend are investigated in the blend films. In particular, the origin of the green band (‘g‐band’) that often undesirably appears from PFO used in air, is discussed in such a highly oriented circumstance. The experimental results powerfully demonstrate that the g‐band originates from the mono‐chain fluorenone moieties, rather than the fluorenone‐based excimer.magnified image

Conjugated alternating copolymer of dialkylquaterthiophene and fluorenone: synthesis, characterisation and photovoltaic properties

New π-conjugated alternating copolymers containing thienylene and fluorenone units, namely poly[(5,5‴-dioctyl-[2,2′;5′,2″;5″,2‴]quaterthiophene)-alt-(2,7-fluoren-9-one)] (PQTF8), as well as its analogue without fluorenone groups (PQT8), have been synthesized. Absorption studies carried out both in solution and in thin films indicate that the presence of fluorenone chromophores in PQTF8 leads to a significant extension of the absorption spectrum in the visible range as compared to PQT8. The redox properties of both polymers, in particular their LUMO and HOMO levels, have been characterized by cyclic voltammetry and have been found suitable for potential use of these systems in organic solar cells. Finally, these materials have been tested as donor components in bulk-heterojunction-type photovoltaic cells using PCBM as an electron acceptor. We demonstrate a strong effect of the polymer's molecular weight on crucial cell parameters, such as the short-circuit current density Jsc, and therefore on the overall cell efficiency. This effect is particularly pronounced for PQTF8-based cells leading to power conversion efficiencies up to 1.5% for the highest molecular weights.

Control of electron transport through Fano resonances in molecular wires

Using a first principles approach, we study the electron transport properties of two molecules of length 2.5nm which are the building blocks for a new class of molecular wires containing fluorenone units. We show that the presence of side groups attached to these units leads to Fano resonances close to the Fermi energy. As a consequence electron transport through the molecule can be controlled either by chemically modifying the side group, or by changing the conformation of the side group. This sensitivity, which is not present in Breit-Wigner resonances, opens up new possibilities for novel single-molecule sensors.

Exploring a series of monoethynylfluorenes as alkynylating reagents for mercuric ion: Synthesis, spectroscopy, photophysics and potential use in mercury speciation

New luminescent mononuclear mercury(II) mono- and dialkynylated complexes containing substituted fluorene and fluorenone units [R–C C–HgCH 3] and [R–C C–Hg–C C–R] (R = 9,9-dialkylfluorene-2-yl and fluoren-9-one-2-yl; alkyl = H, ethyl, hexyl, octyl, hexadecyl) were prepared in good yields by mercuration of terminal acetylene R–C CH with CH 3HgCl and HgCl 2 at room temperature via the dehydrohalogenation reaction. The structures of these organomercurial compounds were characterized by IR and NMR spectroscopies, elemental analysis and FAB mass spectrometry. Their optical and photoluminescence spectra were also studied. The structural features of one complex was elucidated by X-ray crystallography in which there is an indication of weak mercuriophicity among the molecules in the solid state. A new protocol is developed for derivatization of inorganic mercury(II) ion into dialkynyl mercury(II) compounds followed by the ready extraction into dichloromethane, which can be analyzed by HPLC technique using UV detection. These results have important implications in the development of analytical procedures for the determination of mercuric ion in aqueous solutions.

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

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 represent the actual chromophore responsible for the green emission in the copolymers. The green emission of the copolymers in the solid states is well described by single-exponential decay and has a lifetime ranging from 4.21 to 8.15 ns, depending on fluorenone content. The substantially enhanced intensity of the green emission with increasing the intermolecular interaction in solid states results from the contribution of both the intramolecular and the more efficient intermolecular energy transfer from the fluorene segments to fluorenone moieties. We also find that the emission wavelength and the lifetime of the green emission for the copolymer with the lowest fluorenone content (PHF-FO0.1) in solid states are very similar to those of the emerging low-energy emission for poly(9,9‘-dihexylfluorene) (PDHF) after high-temperature thermal annealing in air. Bright yellow electroluminescence (EL) is achieved from double-layer LEDs based on these materials with an emission peak of 540−579 nm that steadily red-shifted with increasing fluorenone contents. The better luminance and external quantum efficiencies are probably due to improved electron injection and carrier transporting as well as efficient charge trapping and recombination at the fluorenone sites.

Modeling of Molecular Packing and Conformation in Oligofluorenes

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.

Synthesis and Optical Properties on a Series of Polyethers Incorporating Terfluorene Segments and Methylene Spacers

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.

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

AbstractThe 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.