Showing papers on "Fluorenone published in 1997"

Quenching Processes in Hydrogen-Bonded Pairs: Interactions of Excited Fluorenone with Alcohols and Phenols

Abstract: In order to clarify mechanisms of excited state interactions in hydrogen-bonded pairs, we have studied the kinetics of dynamic quenching of singlet and triplet fluorenone by a series of alcohols, phenols, and related compounds, in which hydrogen-bonding power, redox potential, and acidity are systematically varied. In addition, effects of solvent basicity or polarity and deuteration help identify the role of hydrogen-bonding in physical or chemical quenching processes. Alcohols and weak acids, with high oxidation potentials, do not quench the triplet, but quench the singlet at rates which parallel hydrogen-bonding power. This is attributed to a physical mechanism, involving vibronic coupling to the ground state via the hydrogen bond. This is much stronger in the excited state than in the ground state, and provides efficient energy dissipation in the radiationless transition. Phenols, with hydrogen-bonding power comparable to that of the alcohols but with much lower oxidation potentials, quench both single...

Photophysical characterization of fluorenone derivatives

Abstract: The photophysics of several fluorenone derivatives was studied using fluorescence and laser-induced optoacoustic spectroscopy. Electron-donating substituents increase the energy of the key upper triplet state (T 3 ) which, for the parent compound, is responsible for the increased intersystem crossing quantum yield in non-polar solvents. Electron-withdrawing substituents decrease the energy of T 3 , and an increase in the intersystem crossing rate constant is observed. Halogen substitution leads to a heavy-atom effect, which is partially compensated by a decrease in the intersystem crossing rate constant due to changes in the energy gap between S 1 and T 3 . For most compounds, an increase in the internal conversion rate constant is observed. The magnitude of this increase is a function of the nature of the substituent and its position on the fluorenone ring.

Ultraviolet-visible and Fourier transform infrared diffuse reflectance studies of benzophenone and fluorenone adsorbed onto microcrystalline cellulose

Abstract: Benzophenone and fluorenone, which have a nonrigid and a rigid structure, respectively, were used as probes to study the nature of the adsorption process onto microcrystalline cellulose. Diffuse reflectance techniques were used in the UV−vis and infrared regions. Luminescence studies revealed that whenever fluorenone or benzophenone are entrapped into the natural polymer chains and in close contact with the substrate, a strong quenching effect exists for both probe's luminescence at room temperature. For fluorenone, the fluorescence quantum yields (ΦF) determined were about 0.10 when dichloromethane, cyclohexane, and benzene (solvents which do not swell cellulose) were used for sample preparation, while for dioxane, acetone, ethanol, and methanol (solvents which efficiently swell cellulose) ΦF was approximately 0.01. These values are about 1 order of magnitude higher than those obtained in solution, showing the importance of the rigid dry matrix in reducing the nonradiative pathways of deactivation of the...

Formation and Rearrangement of a 2,2-Dimethoxyoxirane from Dimethoxycarbene and Fluorenone

Abstract: Thermolysis of 2,2-dimethoxy-5,5-dimethyl-Δ3-1,3,4-oxadiazoline (1) at 110 °C in the presence of 9-fluorenone (3) yielded 9-(dimethoxymethylene)fluorene oxide (4) and methyl 9-methoxyfluorene-9-carboxylate (5), which are the result of the addition of dimethoxycarbene (2) to the carbonyl group of 9-fluorenone. While the epoxide 4 is most likely generated from direct [2 + 1] cycloaddition, the ester 5 is the result of subsequent rearrangement of the oxirane. Thermolysis of the trideuteriomethoxy oxadiazoline 1-d3 in the presence of fluorenone showed that 5 is not formed by an intermolecular process because evidence for crossover of the label in the product 5 was not found. The rearrangement of 4 to 5 does not proceed by ring opening and intramolecular methyl transfer either but, instead, by ring opening and intramolecular methoxy transfer. Thus, as predicted by the Baldwin rules, the strained intramolecular 5-endo-tet methyl transfer is avoided in favor of another process.

Structures of dibenzocycloheptenylidene‐ and fluorenylidene‐(2,4,6‐tri‐t‐butylphenyl)phosphines and their reactions with sulfur

Abstract: Dibenzocycloheptenylidene(2,4,6-tri-t-butylphenyl)-phosphine and fluorenylidene(2,4,6-tri-t-butylphenyl)-phosphine were prepared by the reactions of lithium silylphosphide with benzosuberenone and fluorenone, respectively. The reactions of the phosphines with sulfur were carried out to compare the results with those of the corresponding diphenyl derivative, and the new findings are discussed in terms of steric hindrance based on the results of the X-ray crystallographic analyses for dibenzocycloheptenylidenephosphine and its sulfide and the computational structure for the fluorenyl derivative. © 1997 John Wiley & Sons, Inc. Heteroatom Chem 8: 375–382, 1997

Method for production of fluorenone

Abstract: A method for the production of fluorenone for the vapor-phase catalytic oxidation of fluorene with a molecular oxygen-containing gas, which including adjusting the molar ratio of fluorene to molecular oxygen in a feed raw material gas composed of fluorene as a raw material and a molecular oxygen-containing gas in the range of 1:1 to 0.13:1, or keeping the sulfur content in a raw material fluorene at or below 0.15% by weight.

Description of solvent effect on the visible absorption spectrum of fluorenone radical anion

Abstract: The solvatochromic shift of the most intensive band of fluorenone radical anion (FN*-) in the visible region has been examined in 10 polar formally aprotic media. It has been found that this shift depends on the solvent acceptor number (AN) and static dielectric constant (D) according to planar regression: It is suggested that the ground state of FN*- is relatively stabilized in a solvent with a high acceptor number and the dipole moment of the solute increases during an excitation.

Photophysical properties of 3-azafluorenone

Abstract: Photophysical properties of 3-azafluorenone have been studied in acetonitrile at room temperature (296 K). Its fluorescence quantum yield and fluorescence lifetime were found to be lower than those of fluorenone due to the higher rate of nonradiative processes.

Fluorene compound and its production

Abstract: PROBLEM TO BE SOLVED: To obtain a new compound useful as a photoconductive raw material for electrophotography. SOLUTION: This fluorene compound is represented by formula I [R1 and R2 are each fluoroalkoxycarbonyl; (m) and (n) are each 0-4; Z is OC(X) (Y) or N(W); X and Y are each H, cyano, an alkyl, an aryl, an alkoxycarbonyl, an aryloxycarbonyl or heterocyclic ring; and W is an alkyl, an aryl or heterocyclic ring], e.g. 9-fluoreone-1-(2,2,2)-trifluoroethoxycarboxylic acid ester. The compound of formula I is obtained by reacting a fluorenone compound of formula II with an amine compound of the formula, H2 N-W. The compound of formula I is especially useful as an electron charge transporting substance in a functional separation type electrophotographic photoreceptor. The compound is optically and chemically sensitized by a sensitizer such as a dye or a Lewis acid.

Production of 9,9-bis(hydroxyaryl)fluorene

Abstract: PROBLEM TO BE SOLVED: To obtain the subject compound in high safety and without use of an excess amount of a phenolic compound by oxidation of fluorene with oxygen and reaction of the produced fluorenone with the phenolic compound in respectively specific solvents. SOLUTION: First, fluorene is made to react with oxygen preferably at 25-60 deg.C in the presence of a caustic alkali (e.g. sodium hydroxide), and a phase- transfer catalyst (preferably a quaternary ammonium salt such as tetramethylammonium chloride) in a high-boiling solvent (preferably an aromatic hydrocarbon of boiling point within the range of 150-230 deg.C) to obtain fluorenone, and subsequently the fluorenone is made to react with a phenolic compound in the presence of an acid (preferably sulfuric acid) and a mercaptocarboxylic acid in an inert organic solvent (preferably benzene or the like) preferably at 50-60 deg.C. It is preferable to use the caustic alkali as an aqueous solution of alkali concentration ranging from 20 to 50wt.%.

Production of fluorenone

Abstract: PROBLEM TO BE SOLVED: To obtain fluorenone at a high conversion and a high selectivity by subjecting fluorenone to a catalytic gas phase oxidation. SOLUTION: The objective fluorenone is obtained by subjecting fluorene and a molecular oxygen-containing gas to a catalytic gas phase oxidation at 250-480 deg.C and 100-10,000/hr space velocity in the presence of a catalyst. In the reaction, a molar ratio of fluorene/molecular oxygen in a supplying raw material gas comprising raw material fluorene and a molecular oxygen-containing gas is adjusted to be 1-0.13. Vanadium, titanium oxide and an alkali metal sulfate are preferably used as the catalyst and an atomic ratio of the alkali metal to vanadium is 0.8-8, especially a catalyst carrying the catalyst-activating component on an inert carrier such as silicon carbide or alumina is preferably used. By the process, a high selectivity can be obtained with keeping a high fluorene invert ratio near 100%.