Fluorenone Molecule Research Articles

Proton Activity and Pathway in Aqueous Organic Redox Flow Battery Electrolyte

Aqueous soluble organic (ASO) redox-active materials have recently shown great promise as alternatives to transition metal ions employed as energy-bearing active materials in redox flow batteries for large-scale energy storage because of their structural tunability, cost-effectiveness, availability, and safety features. However, development so far has been limited to a small palette of organics that are aqueous soluble. This presentation will use fluorenone as an example to showcase how a natively redox-inactive molecule can be tuned to possess two-electron redox reversibility through hydrogenation and dehydrogenation. The modified fluorenone molecules demonstrated high energy density and recorded stable cycling. Furthermore, research has shown the unique chemical-electrochemical coupled redox reactions mechanism; thus, the system rate capabilities can be improved by incorporating suitable hydrogen acceptors that regulate the proton pathway for faster kinetics.Reference:Feng et al., Science 372, 836–840, 2021Feng et al., Joule 7, 1–14, 2023

Proton Activity and Pathway in Aqueous Organic Redox Flow Batteries

Aqueous soluble organic (ASO) redox-active materials have recently shown great promise as alternatives to transition metal ions employed as energy-bearing active materials in redox flow batteries for large-scale energy storage because of their structural tunability, cost-effectiveness, availability, and safety features. However, development so far has been limited to a small palette of organics that are aqueous soluble. This presentation will use fluorenone as an example to showcase how a natively redox-inactive molecule can be tuned to possess two-electron redox reversibility through hydrogenation and dehydrogenation. The modified fluorenone molecules demonstrated high energy density and recorded stable cycling. Furthermore, research has shown the kinetics of the redox reactions; thus, the system rate capabilities can be improved by incorporating suitable hydrogen acceptors that regulate the proton pathway for a faster redox reaction.Reference: Feng et al., Science 372, 836–840 (2021), Feng et al., submitted, 2022

Halogen-bonded building block for 2D self-assembly: Triggered by hydrogen-bonding motifs relative to the terminal functions of the side chains

Owning to the excellent applications of halogen bonds in supramolecular chemistry, the recognition of halogen bonds is of significance during molecular self-assembly process. The 2D self-assembly of fluorenone molecules (BEDF, BCDF, and BHDF) characterized by different terminal groups have been studied at the 1-phenyloctane/HOPG interface. The H-bonding motifs relative to the terminal groups determine the bonding motifs of the conjugated cores and serve as the trigger of halogen bonds. The COOC2H5-terminated groups of BEDF sever as hydrogen bond acceptors to bond with the cores, giving rise to the dimer configuration of cores linked by CH···Br hydrogen bonds. By contrast, the COOH-terminated groups of BCDF and the OH-terminated groups of BHDF act as both the electrophile and nucleophile interacted with the cores. On account of the secondary hydrogen bond distinct in strength and the different intersection of the aggregates, the type-I bonds (Br···Br) and halogen bonds (Br···OC and Br···Br) are observed in the networks of BCDF and BHDF, respectively. The types of halogen bonds could be further modified by changing the concentrations. The work clearly demonstrates that an appreciation of terminal functions is critical to the recognition of halogen bonds, thus establishing the controllable self-assembly morphology.

Tailoring of the self-assembled structures and optical waveguide behaviour of arylaminofluorenone derivatives

In this work, the fluorenone molecule was symmetrically difunctionalised in the 3,6-positions with four different arylamine moieties. Using slow evaporation, the four fluorenone derivatives (FO1-4) exhibit good ability to arrange into microstructures in the solid state. The electronic and steric effects of arylamine substituents influence both optical features and aggregation processes, as evidenced by photophysical and XRD characterization. SEM investigations have shown that the four FO1-4 derivatives arrange in four different microstructures. More specifically, the self-assembled 1D microribbon – shaped structure of FO1 exhibited an excellent optical loss coefficient (α) as low as 0.006 dBμm−1, suggesting a potential use of these materials in the field of optical waveguide.

Fluorenone Based Anolyte for an Aqueous Organic Redox-Flow Battery

Here we present the first aqueous organic redox-flow battery based on a fluorenone anolyte. The use of polar carboxylic acid functional groups on the core fluorenone molecule enables good solubility under alkaline conditions. Three isomers of carboxyl functionalized fluorenone were screened, with the most promising, 9-fluorenone-2-carboxylic acid, achieving a maximum solubility of 0.8M in 1M KOH with a redox potential of -690 mV vs SHE. When paired with a ferro/ferricyanide redox couple, an open cell potential of 1.18 V was achieved. However, during charge/discharge cycling significant capacity loss was observed within the first few cycles. In addition, flow-battery tests showed low limiting current densities and peak power densities. Subsequent analysis revealed that the redox reversibility of the fluorenone molecules is strongly dependent on pH and potential, which can lead to undesired irreversible redox reactions.

Chemical mechanism of surface-enhanced Raman scattering via charge transfer in fluorenone–Ag complex

The intermolecular interaction between fluorenone (FN) and silver surfaces was investigated experimentally and theoretically. The structural, electronic and optical properties of the FN–Ag complex indicate that the carbonyl group O atom in FN molecules is the adsorbed position site to attach the silver substrate through the weak bond O…Ag. The analysis of vibrational modes and Raman activity of the largely enhanced Raman peaks using two FN–Ag4-x (x = l, s) complex models reveals that only the a1 vibrational modes with C2v symmetry are selectively enhanced, from the point view of the change of dipole moment and polarizability induced by the interaction between FN and Ag4 substrate. Furthermore, the direct visualized evidence of the surface-enhanced Raman scattering (SERS) chemical enhancement mechanism for the FN–Ag complex is presented. The results reveal that only the intermolecular charge transfer with π–π transition characterization between FN and an Ag4 cluster facilitates the resonance Raman process and is directly responsible for chemical enhancement of Raman scattering of the FN–Ag complex.

Direct observation of slow intersystem crossing in an aromatic ketone, fluorenone.

Direct measurements of Single vibronic Level InterSystem Crossing (SLISC) have been performed on the fluorenone molecule in the gas phase, by time resolved photoelectron and photoion spectroscopy. Vibronic transitions above the S1 nπ* origin were excited in the 432-420 nm region and the decay of S1 and growth of T1(3)ππ* could be observed within a 10 ns time domain. The ionization potential is measured as 8.33 ± 0.04 eV. The energy of the first excited triplet state of fluorenone, T1 has been characterized directly at 18 640 ± 250 cm(-1). The internal conversion of S1 to S0 is found to amount to ∼15% of the population decay, thus ISC is the dominant electronic relaxation process. ISC, although favored by the S1(1)nπ*-T1(3)ππ* coupling scheme, is 3 orders of magnitude less efficient than in the similar molecule benzophenone. Thus, the planarity of the fluorenone molecule disfavors the exploration of the configuration space where surface crossings would create high ISC probability, which occurs in benzophenone through surface crossings. The time evolution of S1 fluorenone is well accounted for by the statistical decay of individual levels into a quasi-continuum of T1 vibronic levels.

Photodetachment spectroscopy of fluorenone radical anions microsolvated with methanol: rationalizing the anomalous solvatochromic behavior due to hydrogen bonding.

The attribution of the extraordinary blue shift for the intramolecular charge-transfer absorption band of fluorenone radical anion solvated in protic media was investigated by means of photodetachment spectroscopy of the gas-phase anions microsolvated with methanol, in conjunction with quantum chemical calculations based on density functional theory. Sequential shifts of the vertical detachment energy as a function of the cluster size are consistent with theoretical predictions, where up to two methanol molecules can directly attach to the carbonyl group. In the photodetachment excitation spectra as alternatives to the photoabsorption spectra, with increasing cluster size, a new absorption band grows in the higher-energy region, which coincides with the blue-shifted band in protic media. Spectral simulations using time-dependent density functional theory with the CAM-B3LYP functional reproduced the feature of the phenomenon. Analyses on the electronic configuration elucidated that the extraordinarily blue shifts originate from energy-level repulsion due to solvation-induced resonant coupling with another electronic state. The orbital transition for the counterpart state corresponds to the first absorption band of the neutral fluorenone molecule, which has small oscillator strength from the ground state. It was found that correction of long-range electron exchange correlation is important for the spectral simulation involving the electronic-state coupling.

Close-Packed Dye Molecules in Zeolite Channels Self-Assemble into Supramolecular Nanoladders

A tough challenge in nanomaterials chemistry is the determination of the structure of multicomponent nanosystems. Dye–zeolite L composites are building blocks of hierarchically organized multifunctional materials for technological applications. Supramolecular organization inside zeolite L nanochannels, which governs electronic properties, is barely understood. This is especially true for confined close-packed dye molecules, a regime not investigated in applications yet and that might have great potential for future development in this field. Here we realize for the first time composites of zeolite L with maximally packed fluorenone molecules and elucidate their structure by integrated multitechnique analyses. By IR spectroscopy, thermogravimetric analysis, and X-ray diffraction, we establish the maximum degree of dye loading obtained (1.5 molecules per unit cell), and by modeling we reveal that at these conditions fluorenone molecules form quasi 1-D supramolecular nanoladders running along the zeolite cha...

Picosecond Pulse Radiolysis Study of Dynamics of Solvation of Electron and Fluorenone Anion in Primary Alcohols

We have studied the dynamics of solvation of electron injected directly into primary alcohols as well as that of fluorenone anion using pulse radiolysis technique with the time resolution of about 15 ps. Unlike in the previous reports, we observe nonexponential dynamics of both electron and anion solvation. While the ultrafast component, τ1 (<15 ps) representing the inertial time scale of the dynamics is faster than the time resolution of the spectrometer, the slower component, τ2, has been assigned to the translational motion leading to structural changes of the hydrogen bonding network of the solvent in the inner solvation cell or alcohol cluster. τ2 agrees well with the electron solvation times reported by the earlier authors. τ3 is associated with the restructuring of the hydrogen bond network structure of the solvent in the region outside the solvation cell. Nonexponential solvation dynamics of the fluorenone anion has been described well by a two-component process. The most important observation in this work is that the lifetime of the shorter component, τ1, determined in four alcoholic solvents, is much longer than the electron solvation time in the corresponding solvents determined in this work or anion solvation time reported earlier. The lifetime of this component is nearly comparable with the average dipolar solvation time but shorter than the longitudinal relaxation time of the solvent. In the case of anion, τ1 has been assigned to the restructuring of the first solvation shell by breakage of solvent hydrogen bonds of the fluorenone molecule and formation of hydrogen bonds with the anion. In this case, too, the longer component, τ2, with the lifetime of a few nanoseconds, has been assigned to reorganization of hydrogen bonds in the solvent hydrogen bond network structure.

Theoretical Insights into Intermolecular Hydrogen-Bonding Strengthening in Fluorenone-Methanol Complexes Induced by Electronic Excitation and Bulk Solvent Effect

This work presents a theoretical insight into the variation of the site-specific intermolecular hydrogen-bonding (HB), formed between C=O group of fluorenone (FN) and O—H groups of methanol (MeOL) molecules, induced by both the electronic excitation and the bulk solvent effect. Through the calculation of molecular ground- and excited-state properties, we not only demonstrate the characters of HB strengthening induced by electronic excitation and the bulk solvent effect but also reveal the underlying physical mechanism which leads to the HB variation. The strengthening of the intermolecular HB in electronically excited states and in liquid solution is characterized by the reduced HB bond-lengths and the red-shift IR spectra accompanied by the increasing intensities of IR absorption corresponding to the characteristic vibrational modes of the O—H and C=O stretching. The HB strengthening in the excited electronic states and in solution mainly arises from the charge redistribution of the FN molecule induced by the electronic excitation and bulk solvent instead of the intermolecular charge transfer. The charge redistribution of the solute molecule increases the partial dipole moment of FN molecule and the FN-MeOL intermolecular interaction, which subsequently leads to the HB strengthening. With the bulk solvent effect getting involved, the theoretical IR spectra of HBed FN-MeOL complexes agree much better with the experiments than those of gas-phase FN-MeOL dimer. All the calculations are carried out based on our developed analytical approaches for the first and second energy derivatives of excited electronic state within the time-dependent density functional theory.

Heteroatom Effects on Electronic Excited State Hydrogen Bonding of Fluorenone-Based Molecular Materials

In this work, the geometry optimizations in the ground state and electronic excitation energies and corresponding oscillation strengths of the low-lying electronically excited states for the isolated fluorenone (FN) and FN-based molecular monomers, the relatively hydrogen-bonded dimers, and doubly hydrogen-bonded trimers, are calculated by the density functional theory and time-dependent density functional theory methods, respectively. We find the intermolecular hydrogen bond CO···HO is strengthened in some of the electronically excited states of the hydrogen-bonded dimers and doubly hydrogen-bonded trimers, because the excitation energy in a related excited state decrease and electronic spectral redshift are induced. Similarly, the hydrogen bond CO···HO is weakened in other excited states. On this basis, owing to the important difference of electronegativity, heteroatoms S, Se, and Te that substitute for the O atom in the carbonyl group of the FN molecule have a significant effect on the strength of the hydrogen bond and the spectral shift. It is observed that the hydrogen bond CTe···HO is too weak to be formed. When the CS and CSe substitute for CO, the strength of the hydrogen bonds and electronic spectra frequency shift are significantly changed in the electronic excited state due to the electron transition type transformation from the ππ* feature to σπ* feature. © 2013 Wiley Periodicals, Inc. Heteroatom Chem 24:153–162, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/hc.21075

First-principles simulation of the absorption bands of fluorenone in zeolite L

The absorption spectrum of fluorenone in zeolite L is calculated from first-principles simulations. The broadening of each band is obtained from the explicit treatment of the interactions between the chromophore and its environment in the statistical ensemble. The comparison between the simulated and measured spectra reveals the main factors affecting the spectrum of the chromophore in hydrated zeolite L. Whereas each distinguishable band is found to originate from a single electronic transition, the bandwidth is determined by the statistical nature of the environment of the fluorenone molecule. The K(+)···O=C motif is retained in all conformations. Although the interactions between K(+) and the fluorenone carbonyl group result in an average lengthening of the C[double bond, length as m-dash]O bond and in a redshift of the lowest energy absorption band compared to gas phase or non-polar solvents, the magnitude of this shift is noticeably smaller than the total shift. An important factor affecting the shape of the band is fluorenone's orientation, which is strongly affected by the presence of water. The effect of direct interactions between fluorenone and water is, however, negligible.

Single‐Molecule Studies of a Model Fluorenone

Single-molecule fluorescence measurements of 2,7-bis(3,4,5-trimethoxyphenylethenyl)fluorenone (OFOPV) reveal narrow emission spectra concentrated around 540 nm, with weak emission at longer wavelengths. The wide scattering of emission-maximum wavelengths is attributed to varying molecular environments, with dimers or higher-order aggregates contributing to the low-energy emission. This spectral distribution indicates that emission from monomers of this model fluorenone is mostly green, which is consistent with contaminant emission (g-bands) often observed in fluorene- and polyfluorene-based organic light emitting diode (OLED) devices. A histogram of center wavelengths from 118 single-molecule spectra shows good agreement with the green emission previously observed in thermally stressed 2,7-bis(3,4,5-trimethoxyphenylethenyl)-9,9-diethylfluorene (OFPV). Whereas bulk OFPV exhibits blue fluorescence at about 480 nm, OFOPV bulk thin film measurements reveal red luminescence shifted to 630 nm. This unexpected peak position for bulk OFOPV shifts to higher energies (ca. 540 nm) upon dilution in a solid-state matrix, suggesting that the bulk red emission finds its origins in interactions between fluorenone molecules. Explanations for this red emission include aggregate or excimer formation or intermolecular energy transfer between fluorenone molecules.

Photochemistry and photopolymerization activity of novel perester derivatives of fluorenone: a conventional and laser flash photolysis study

The photochemistry of three novel t-butylperester derivatives of fluorenone was examined and compared with unsubstituted fluorenone and a mono- t-butylperester of benzophenone using both conventional microsecond and nanosecond laser flash photolysis. On conventional microsecond flash photolysis in 2-propanol, all four fluorenone compounds gave transient absorption in the region 300–400 nm due to a ketyl radical formed from the abstraction of a hydrogen atom from the solvent by the upper excited triplet n—π* state of the fluorenone chromophore. This assignment was confirmed by a pH-dependent study on the transient absorption spectra. The nitro- t-butylperester derivative of fluorenone gave additional absorption above 400 nm due to species associated with the nitro group. No evidence for benzoyloxy radical formation could be found in non-hydrogen-atom-donating solvents with microsecond flash photolysis which is associated with homolysis of the perester groups. On nanosecond laser flash photolysis of the fluorenone compounds at 355 nm excitation in acetonitrile and hexa-fluorobenzene, transient absorptions were observed in the region 320–640 nm due to the corresponding triplet states. All the t-butylperester derivatives showed residual absorbances at longer time delays which were tentatively assigned to the corresponding benzoyloxy radicals produced by homolysis of the perester groups. In contrast, the mono- t-butylperester of benzophenone, included for comparison only, showed very weak transient absorption in the region 320–640 nm compared with that of the strong triplet of benzophenone under the same excitation conditions. The triplet absorptions and lifetimes of the fluorenone compounds were correlated with their photopolymerization activities in bulk methylmethacrylate monomer. In oxygenated solutions, the triplet absorptions of fluorenone and benzophenone were effectively quenched; however, long-lived transient growths were observed for all the t-butylperester derivatives. The intensities of these novel transient absorptions appear to correlate with the total number of t-butylperester groups in the fluorenone molecule and tentative assignments are discussed.

Relaxation processes from highly-excited vibrational levels of fluorenone molecules

Relaxation processes from highly-excited vibrational levels of fluorenone molecules

Spectroscopic Properties of the Lower-Lying Excited States of Fluorenone

The spectroscopic properties of the lower-lying electronically excited states of fluorenone have been investigated. A test for n—π* transitions, based upon the effect of oxime formation on the absorption spectra, is discussed. Application of the oxime test to fluorenone, in conjunction with an examination of the emission properties, the solvent effects on the absorption spectrum, the vibrational structure of the fluorescence spectrum, the absorption spectra of related molecules, and the results of MO calculations clearly establish that the lowest excited singlet state of fluorenone is a (π, π*) state, rather than an (n, π*) state, as previously assigned. The principal emission observed from fluorenone in solution at room temperature and at 77°K, and from crystalline fluorenone, is demonstrated to be fluorescence. Both the fluorescence spectrum and the quantum yield for fluorescence were found to be solvent and temperature dependent. At room temperature in solution, the fluorescence quantum yield is about 1% and increases to about 12% upon cooling to 77°K. The fluorescence quantum yield from fluorenone crystals is nearly temperature independent, but decreases by a factor of 14 when the crystal is melted. The relation between the quenching of the fluorescence in fluid solutions and the concommitant shift of the emission spectra is discussed in terms of the interaction between excited state fluorenone molecules and polar solvent molecules. Very weak delayed fluorescence is observed from concentrated rigid-glass solutions and zone-refined crystals of fluorenone. In fluorenone crystals doped with 3.7×10−2 mole/mole pyrene, the delayed fluorescence is considerably stronger than in the ``pure'' crystals, and strong pyrene phosphorescence is observed. Normal phosphorescence from fluorenone could not be observed from thoroughly purified material, but estimates of the singlet—triplet splitting, combined with the pyrene-doping experiments and solution absorption spectra obtained using heavy-atom solvents, indicate that the lowest triplet state of fluorenone is located near 560 to 570 mμ. Anomalous phosphorescence (τ=3.6 sec, λ0–0=435 mμ, Φ≃0.01) has been observed, but only upon excitation of the fluorenone to a high-lying excited singlet state (&amp;lt;330 mμ). It is proposed that this anomalous phosphorescence originates from some new chemical species which is produced photochemically in its excited triplet state from fluorenone.