Fluorene Molecules Research Articles

Computational study of substituent effects on molecular structure, vibrational and electronic properties of fluorene molecule using density functional theory

Density functional theory (DFT) provides a powerful tool for investigating the effects of halogen (F, Cl and Br) substitution on the electronic and structural properties of fluorene. The B3LYP/6-31G (d,p) protocol is a commonly used method in DFT calculations for the optimisation of molecular structures and the calculation of various molecular properties by Gaussian 09 W program. In the case of the fluorene molecule with halogen substitutions, (TD–DFT) calculations can be used to predict its UV–Vis spectrum. The B3LYP density functional model with a 6-31G(d,p) basis set is a common choice for performing (TD–DFT) calculations on molecules. The results showed a decrease in gap energies when electron-withdrawing groups were present in the molecule. A decrease in the gap energy indicates that the molecule is less stable and more reactive.

C-H-activated Csp2-Csp3 diastereoselective gridization enables ultraviolet-emitting stereo-molecular nanohydrocarbons with mulitple H···H interactions

Gridization is an emerging molecular integration technology that enables the creation of multifunctional organic semiconductors through precise linkages. While Friedel-Crafts gridization of fluorenols is potent, direct linkage among fluorene molecules poses a challenge. Herein, we report an achiral Pd-PPh3-cataylized diastereoselective (>99:1 d.r.) gridization based on the C-H-activation of fluorene to give dimeric and trimeric windmill-type nanogrids (DWGs and TWGs). These non-conjugated stereo-nanogrids showcase intramolecular multiple H…H interactions with a low field shift to 8.51 ppm and circularly polarized luminescence with high luminescent dissymmetry factors (|gPL | = 0.012). Significantly, the nondoped organic light-emitting diodes (OLEDs) utilizing cis-trans-TWG1 emitter present an ultraviolet electroluminescent peak at ~386 nm (CIE: 0.17, 0.04) with a maximum external quantum efficiency of 4.17%, marking the highest record among nondoped ultraviolet OLEDs based on hydrocarbon compounds and the pioneering ultraviolet OLEDs based on macrocycles. These nanohydrocarbon offer potential nanoscafflolds for ultraviolet light-emitting optoelectronic applications.

Synthesis of N/P co-doped monolithic hierarchical porous carbon for zinc-ion hybrid capacitors with boosted energy density in ZnSO4/ZnI2 redox electrolyte

Zinc-ion hybrid capacitors (ZHCs) are of great potential as a new type of energy storage device, yet how to increase the energy density remains a challenge, which is greatly restricted by cathode materials and electrolytes. Herein, we report on the synthesis of N/P co-doped monolithic hierarchical porous carbon (NPMC) materials from fluorene molecules via template-guided growth coupled with in situ activation strategy. The as-prepared NPMCs feature 3D carbonaceous framework with good electron conduction, well-developed macro/meso/micropores for ion transfer and tunable N/P species with additional pseudocapacity. Meanwhile, the introduction of ZnI2 into aqueous ZnSO4 electrolyte helps to significantly increase the capacity of ZHC due to the redox reactions. It has been demonstrated that the Zn//ZnSO4/ZnI2//NPMC ZHC with NPMC as cathode material delivers an ultrahigh energy density of 324.8 Wh kg−1, which is 3.5 times higher than Zn//ZnSO4//NPMC ZHC. The mechanisms for this superb performance have been explored in terms of the Zn2+ cations deposition/stripping, SO42−/I− anions adsorption/desorption, Zn4SO4(OH)6·0.5H2O precipitation/dissolution and the redox reactions (3I−/I3−, 2I−/I2). This novel work may pave a way to the exploration of high-energy ZHCs.

Giant dipole plasmon resonance in fluorene (C13H10) molecules

We report the observation of the giant dipole plasmon resonance in the fluorene molecule $({\mathrm{C}}_{13}{\mathrm{H}}_{10})$, a polycyclic aromatic hydrocarbon, upon collisions with H-like silicon ions. An idea of using highly charged ions to create a large perturbation strength is exploited to observe the plasmon state effectively in the electron double-differential distribution. The signature of plasmon excitation is observed directly as a characteristic broad peak in the electron double-differential spectrum. Such an excited state could not be observed for the same molecule when the low charged ions having lower perturbation were used. This is explained by a model based on dipole approximation and linear response theory for the giant plasmon resonance. The angular distribution of these electrons is modeled using the photoelectron angular distribution for an oscillating dipole superimposed with the postcollision interaction due to the long-range Coulomb interaction between the plasmon electrons and the receding projectile ions.

Developing Rationally Designed Small Molecules to Inhibit SARS‐CoV‐2 Spike Protein‐Human ACE2 Receptor Interactions

Targeting the binding domain of SARS‐CoV‐2 spike protein (S protein) with rationally designed small molecules is expected to disrupt S protein‐human ACE2 (hACE2) interactions. First, we set out to establish a small molecule library using traditional structure‐based drug design strategies and various computational tools. Small molecule design began by utilizing FTMap to identify “hotspots” on the S protein binding domain (Chain B), which has been shown to interact with the hACE2 receptor (PDB file 6LZG). A hotspot was identified in the S protein‐hACE2 binding domain. Within the probe cluster for this hotspot, the phenol probe was found to have strong interactions with the surrounding amino acids and thus selected as the initial scaffold. Based on the residues surrounding the hotspot, additional substituents were added to the scaffold to improve binding affinity to the S protein. AutoDock was used to sequentially evaluate the binding affinity of each small molecule to assess the effects of various substituents and geometries, thereby refining the small molecule library. Over 200 unique small molecules were rationally designed, which revealed two preferred substructures: fluorene and naphthalene‐based molecules. The lead molecule from the fluorene substructure had a binding affinity of ‐9.1 kcal/mol (jmol156), and the lead molecule from the naphthalene substructure had a binding affinity of ‐8.5 kcal/mol (tmol35) (Figure 1). These molecules most strongly interact with Tyr505 via pi‐stacking and Asn501, Gly496, Tyr453 and Gln493 via hydrogen bonding (Figure 2). Additionally, Tyr453 of the S protein, which participates in binding with hACE2, is partially blocked by both lead molecules. Overall, the jmol156 and tmol35 molecules show two preferred substructures that can be used for future drug design and demonstrate potential to serve as a starting point for in vitro testing.

3D hierarchical carbons composed of cross-linked porous carbon nanosheets for supercapacitors

3D hierarchical porous carbons with good electric conductivity and excellent physicochemical stability are of great potential as electrode materials for supercapacitors. Herein, we report a directing-confinement-template strategy for synthesis of 3D hierarchical carbons composed of cross-linked porous carbon nanosheets from fluorene molecules. The 3D cross-linked networks serve as highways for electron conduction while the multi-level pore structures function as channels for fast ion transport with abundant active sites for ion adsorption. Benefiting from the above merits, the hierarchical carbons manifest a high gravimetric capacitance of 344 F g−1 at 0.05 A g−1, a superb rate capability with the capacitance up to 278 F g−1 even at 100 A g−1 and an outstanding cycle stability with only 0.7% decay after 50,000 cycles in alkaline electrolyte. Remarkably, hierarchical carbon-based capacitor displays a high energy density of 31.9 Wh kg−1 in 3 M ZnSO4 neutral electrolyte owing to the wide voltage window of 2.2 V. This work opens up a new avenue for designing hierarchical carbons via directing and confinement template approach from small aromatic molecules for high-performance energy storage devices.

Electron emission from fluorene molecule in collisions with 3.5 MeV/u Si8+ ions

SynopsisWe present measured absolute double differential cross section (DDCS) of electron emission from fluorene (C13H10) molecule upon 3.5 MeV/u Si8+ ion impact. We have compared the energy and angular distributions of the DDCS with CB1 (Ist Born with correct boundary conditions) calculations. The e-DDCS shows an indication of collective excitation peak in low energy part of the spectrum at a few backward angles. The shape of the distribution has also been compared with that for a smaller molecule i.e. CH4.

Ionization and fragmentation of fluorene in collisions with 50-300 keV proton

SynopsisIn this report, we present the study of ionization and fragmentation of fluorene (C13H10) molecule upon intermediate energy proton impact. We have measured the TOF spectra of fluorene molecule to identify various fragmentation channels. We have also measured the projectile energy dependence of single and double ionization of fluorene molecule.

Energy selective time of flight spectrometer to study low energy dissociation channels of PAHs

SynopsisDissociation channels induced by sequential UV multiphoton absorption of vapour phase fluorene cation is investigated using energy selective ToF mass spectrometer. Neutral fluorene molecule is ionized by resonantly enhanced multiphoton absorption and dissociated in the same photon field. The main goal of this experiment is to determine the rate constants of statistical dissociation channels of PAH cations for a wide range of internal energies.

Deep Blue Light Amplification from a Novel Triphenylamine Functionalized Fluorene Thin Film.

The development of high performance optically pumped organic lasers operating in the deep blue still remains a big challenge. In this paper, we have investigated the photophysics and the optical gain characteristics of a novel fluorene oligomer functionalized by four triphenylamine (TPA) groups. By ultrafast spectroscopy we found a large gain spectral region from 420 to 500 nm with a maximum gain cross-section of 1.5 × 10−16 cm2 which makes this molecule a good candidate for photonic applications. Amplified Spontaneous Emission measurements (ASE) under 150 fs and 3 ns pump pulses have revealed a narrow emission at 450 nm with a threshold of 5.5 μJcm−2 and 21 μJcm−2 respectively. Our results evidence that this new fluorene molecule is an interesting material for photonic applications, indeed the inclusion of TPA as a lateral substituent leads to a high gain and consequently to a low threshold blue organic ASE.

Synthesis and fluorescence on/off switching of hyperbranched polymers having diarylethene at the branching point

We designed and synthesized hyperbranched polymers (HBPs) having diarylethene (DE) at branching points and having fluorene (FL) and DE derivatives between branching points in order to investigate the effect of the polymer structure to fluorescence on/off switching efficiency induced by the photochromic reaction of DE. First, HBP was synthesized by polymerization of an FL monomer (FL-St) in the presence of a DE monomer with reversible addition-fragmentation chain transfer unit (St-DE-RAFT) in the feed ratio of [FL-St]/[St-DE-RAFT] = 10. The fluorescence intensity of the resulting HBP decreased linearly as a function of the photocyclization conversion of DE. The change in the fluorescence intensity accompanied by the photochromic reactions indicates that one DE closed-ring isomer can quench 16.9 neighboring FL moieties. However, the switching rate and on/off contrast of fluorescence were relatively low because the number of FL in the polymer chain is much larger than that of DE. Therefore, we synthesized two types of HBPs having DE positioned not only at the branching points but also integrated in the polymer chains with different branching degrees. The fluorescence intensity of FL for such HBPs showed a non-linear dependence on the photocyclization conversion of DE, and a significant emission decrease with high on/off contrast even in low conversion was demonstrated. One DE closed-ring isomer quenched 5.4–6.4 F L moieties, whereas the fluorescence quantum yield in the “on” state was found to be around 0.15. The quenching of FL molecules is more pronounced for higher branching degrees in the polymers, indicating that DE closed-ring isomer can quench efficiently FL molecules when located within the polymer chains as well as at the branching points of the polymer.

An Optical Power Limiting and Ultrafast Photophysics Investigation of a Series of Multi-Branched Heavy Atom Substituted Fluorene Molecules

A common molecular design paradigm for optical power limiting (OPL) applications is to introduce heavy atoms that promote intersystem crossing and triplet excited states. In order to investigate this effect, three multi-branched fluorene molecules were prepared where the central moiety was either an organic benzene unit, para-dibromobenzene, or a platinum(II)–alkynyl unit. All three molecules showed good nanosecond OPL performance in solution. However, only the dibromobenzene and Pt–alkynyl compounds showed strong microsecond triplet excited state absorption (ESA). To investigate the photophysical cause of the OPL, especially for the fully organic molecule, photokinetic measurements including ultrafast pump–probe spectroscopy were performed. At nanosecond timescales, the ESA of the organic molecule was larger than the two with intersystem crossing (ISC) promoters, explaining its good OPL performance. This points to a design strategy where the singlet-state ESA is balanced with the ISC rate to increase OPL performance at the beginning of a nanosecond pulse.

From fluorene molecules to ultrathin carbon nanonets with an enhanced charge transfer capability for supercapacitors.

It is a big challenge to synthesize ultrathin carbon nanonets with an enhanced charge transfer capability for high-performance energy storage devices. Herein, ultrathin carbon nanonets (UCNs) were successfully synthesized for the first time from fluorene, a typical aromatic molecule, by a template strategy for supercapacitors. The formation mechanism of UCNs was determined using Density Functional Theory and Materials Studio, in which the fluorene-derived radicals were assembled into UCNs in the template-confinement space with the assistance of KOH. The as-made UCNs feature interconnected high-conductivity net-like architectures with enhanced charge transfer capability, evidenced by their high capacitance, excellent rate performance and cycling stability for symmetrical supercapacitors in a KOH electrolyte. This finding may provide a significant step forward in understanding the formation mechanism of graphene-like materials from more complicated aromatic hydrocarbon molecules, and our work may draw wide attention in the fields of aromatic chemistry and carbon-based energy storage materials.

Fluorene, pyrene, and thiophene-based donor-acceptor asymmetric small molecules for solution-processable memory performance

In this paper, two new asymmetric donor-bridge-acceptor molecules (PFTCH and PFTCE) containing the same electron donor (pyrene group) and bridge (fluorene group) but different terminal electron acceptors (cyanoacetic acid for PFTCH and ethyl cyanoacetate for PFTCE) have been synthesized and characterized by NMR, HR-MS etc. Their photophysical properties including Uv-vis absorption and emission spectra were studied. They were further used as the memory active materials and the ITO/PFTCH or PFTCE/Al sandwich memory devices were prepared, in which the organic films were obtained by solution process. The I-V measurements display satisfactory memory performance; they have a low threshold voltage, high ON/OFF ratio (106) and a low current value (10−4 A) at the ON state. Although the electron-withdrawing ability of the cyanoacetic acid group is stronger than that of the ethyl cyanoacetate group, the two memory devices (ITO/PFTCH/Al or Au and ITO/PFTCE/Al or Au) display different memory behaviors (volatile DRAM for ITO/PFTCH/Al or Au devices and nonvolatile WORM for ITO/PFTCE/Al or Au devices). The mechanism is speculated and the different memory behaviors can be tentatively attributed to the different migration processes of the charge carriers under the influence of an electric field. This can offer a new idea for the molecular design of materials with volatile memory.

Differential electron emission from polycyclic aromatic hydrocarbon molecules under fast ion impact

Interaction between polycyclic aromatic hydrocarbon (PAH) molecule and energetic ion is a subject of interest in different areas of modern physics. Here, we present measurements of energy and angular distributions of absolute double differential electron emission cross section for coronene (C24H12) and fluorene (C13H10) molecules under fast bare oxygen ion impact. For coronene, the angular distributions of the low energy electrons are quite different from that of simpler targets like Ne or CH4, which is not the case for fluorene. The behaviour of the higher electron energy distributions for both the targets are similar to that for simple targets. In case of coronene, a clear signature of plasmon resonance is observed in the analysis of forward-backward angular asymmetry of low energy electron emission. For fluorene, such signature is not identified probably due to lower oscillator strength of plasmon compared to the coronene. The theoretical calculation based on the first-order Born approximation with correct boundary conditions (CB1), in general, reproduced the experimental observations qualitatively, for both the molecules, except in the low energy region for coronene, which again indicates the role of collective excitation. Single differential and total cross sections are also deduced. An overall comparative study is presented.

Synthesis and characterization of copolymers composed of 3-hexylthiophene and fluorene via chemical oxidation with FeCl3

A series of conducting copolymers including fluorene (F) and 3-hexylthiophene (3HT) were synthesized in chloroform via chemical oxidative polymerization with FeCl3. The incorporation of 3HT and fluorene units into the resultant polymer main chain was verified via proton nuclear magnetic resonance (1H NMR) and matrix-assisted laser desorption/ionization mass spectrometry. During copolymerization, the molar ratios of fluorene and thiophene changed (0 to 100%). Thus, the fluorene content in the copolymers was proportional to that of the fluorene fed into the polymerization reaction mixture. Ultraviolet–visible (UV–Vis) and fluorescence spectra indicated that the absorption and emission peak wavelengths of the resulting copolymer were significantly affected by the fluorene content. The quantum yield determined using the relative method increased from 0.26 to 0.73 with an increase in the fluorene content. The thermal stability of the copolymers also improved with the presence of fluorene. A series of conducting copolymers including fluorene (F) and 3-hexylthiophene (3HT) were synthesized in chloroform by chemical oxidative polymerization with FeCl3, and the incorporation of fluorene and 3HT units into the resultant copolymer main chain was clarified. The quantum yield value of obtained copolymers determined by relative method increased by the amount of incorporated fluorene molecules in the resulting copolymer backbone. In addition, fluorene was demonstrated to play an important role in enhancing the thermal stability of the copolymers.

Copper–Fluorenephosphonate Cu­(PO3‐C13H9)·H2O: A Layered Antiferromagnetic Hybrid

AbstractA Cu(PO3‐C13H9)·H2O hybrid compound has been synthesized by a hydrothermal method from Cu(NO3)2·3H2O and 9H‐fluorene‐2‐phosphonic acid [C13H9PO(OH)2]. Its structure was determined by X‐ray diffraction performed on a single crystal. The compound crystallizes in the monoclinic centrosymmetric space group P21/a [a = 7.4977(5), b = 7.5476(5), c = 22.3702(16) Å, β = 97.794(3)°, V = 1254.23(15) Å3, Z = 4]. Its lamellar structure consists of alternating organic and inorganic layers. Its organic sub‐network is made up of a double layer of fluorene molecules, and its inorganic layer is composed of copper(II) dimers connected to phosphonate groups. In the structure, the neighbouring fluorenyl planes are almost orthogonal to each other, which indicates the absence of π stacking. A study of its magnetic properties, performed on a polycrystalline powder sample, showed antiferromagnetic interactions between the spin carriers without any ordering down to 1.8 K. The interactions between the two copper(II) species within the dimers were evaluated at J = –6.13(5) cm–1 with respect to the spin Hamiltonian H = –JSCu1SCu2. A fluorescence study under excitation at 266 nm showed the disappearance of fluorescence emission in the solid state. This has been attributed to fluorescence quenching by the metallic counterpart.

Sorption and desorption of fluorene on five tropical soils from different climes

The main processes controlling soil–polycyclic aromatic hydrocarbon interaction is sorption–desorption as influenced by the soil physicochemical conditions. Sorption–desorption phenomena can influence translocation, persistence and bioavailability. Hence, laboratory batch experiments were undertaken to investigate the sorption characteristics of fluorene on five tropical soils from varying tropical agro-ecological zones having different physicochemical properties. Fluorene concentrations used for the study ranged from 20 to 100μg/L, and results showed that fluorene sorption equilibria were attained usually within 24h. Increase in pH had a negative effect on fluorene sorption. Fluorene sorption was concentration dependent and exothermic. The sorbed fluorene molecules were distributed between surface adsorption sites and phases in soil. Sorption was controlled by weak hydrophobic forces, such as the π–π interactions and Van der Waal's forces. Desorption hysteresis were most pronounced in soils with high organic matter contents than lower ones. The sorption was characterized as multiple reaction phenomena composed of several linear and non-linear isotherms. The physicochemical conditions of the soil must be understood in order to predict the fate and bioavailability of fluorene in soil.

Indeno[2,1-c]fluorene: A New Electron-Accepting Scaffold for Organic Electronics

A new class of fully conjugated indenofluorenes has been synthesized and confirmed by solid-state structure analysis. These indeno[2,1-c]fluorene molecules, containing an antiaromatic as-indacene core (in red), possess high electron affinities and show a broad absorption that reaches into the near-IR region of the electromagnetic spectrum. All of the featured compounds reversibly accept up to two electrons. Their electronic properties make this class of compounds attractive for applications in organic electronic devices.

The Influence of Spin-Labeled Fluorene Compounds on the Assembly and Toxicity of the Aβ Peptide

BackgroundThe deposition and oligomerization of amyloid β (Aβ) peptide plays a key role in the pathogenesis of Alzheimer's disease (AD). Aβ peptide arises from cleavage of the membrane-associated domain of the amyloid precursor protein (APP) by β and γ secretases. Several lines of evidence point to the soluble Aβ oligomer (AβO) as the primary neurotoxic species in the etiology of AD. Recently, we have demonstrated that a class of fluorene molecules specifically disrupts the AβO species.Methodology/Principal FindingsTo achieve a better understanding of the mechanism of action of this disruptive ability, we extend the application of electron paramagnetic resonance (EPR) spectroscopy of site-directed spin labels in the Aβ peptide to investigate the binding and influence of fluorene compounds on AβO structure and dynamics. In addition, we have synthesized a spin-labeled fluorene (SLF) containing a pyrroline nitroxide group that provides both increased cell protection against AβO toxicity and a route to directly observe the binding of the fluorene to the AβO assembly. We also evaluate the ability of fluorenes to target multiple pathological processes involved in the neurodegenerative cascade, such as their ability to block AβO toxicity, scavenge free radicals and diminish the formation of intracellular AβO species.ConclusionsFluorene modified with pyrroline nitroxide may be especially useful in counteracting Aβ peptide toxicity, because they posses both antioxidant properties and the ability to disrupt AβO species.