Core-Shell Architecture in Poly(3-hexylthiophene) Nanoparticles: Tuning of the Photophysical Properties for Enhanced Neuronal Photostimulation.

This study shows that entirely thiophene-based core@shell nanoparticles, in which the shell is made of the oxidized form of the core polymer (P3HT@PTDOx NPs), result in a type II interface at the particle surface. This enables the development of advanced photon nanotransducers with unique chemical-physical and biofunctional properties due to the core@shell nanoarchitecture. We demonstrate that P3HT@PTDOx NPs present a different spatial localization of the excitation energy with respect to the nonoxidized NPs, showing a prevalence of surface states as a result of a different alignment of the HOMO/LUMO energy levels between the core and shell. This allows for the efficient photostimulation of retinal neurons. Indeed, thanks to the stronger and longer-lived charge separation, P3HT@PTDOx NPs, administered subretinally in degenerate retinas from the blind Royal College of Surgeons rats, are more effective in photostimulation of inner retinal neurons than the gold standard P3HT NPs.

The Chemistry of Short-Lived α-Fluorocarbocations.

The present study of the chemistry of short-lived α-fluorocarbocations reveals that even inactive methyl carbons can serve as nucleophiles, attacking a cationic center. This, in turn, facilitates the synthesis of a cyclopropane ring in certain triterpene backbones. We report the synthesis of compounds similar to 2, containing a bridgehead cyclopropane, and compounds of type 3 with an 11 membered bicyclic ring consisting of two bridgehead double bonds (anti-Bredt) within a triterpene skeleton. The synthesis involves three unconventional chemical processes: (a) a methyl group serving as a nucleophile; (b) the unexpected and unprecedented synthesis of a strained system in the absence of an external neighboring trigger; and (c) the formation of an 11-membered bicyclic diene ring within a triterpenoid skeleton. An α-fluorocarbocation mechanism is proposed and supported by density functional theory calculations.

[All]-S,S-dioxide Oligo-Thienylenevinylenes: Synthesis and Structural/Electronic Shapes from Their Molecular Force Fields.

Oligo-S,S-dioxothienylenevinylenes have been prepared by transferring oxygen atoms to the sulfur atoms using the HOF⋅CH3 CN complex. Their photophysical properties are presented in comparison with their thiophenevinylene congeners. Together with their vibrational properties and molecular force fields, this study allows for the interpretation of the alteration of aromaticity and inter-ring exocyclic π-conjugation in this series.

Synthesis of N,N-Dioxopyridazines.

Despite many efforts, one of the smallest heterocycles containing two nitrogen atoms, pyridazine, could not be converted to its N,N-dioxide (see, however, Nakadate et al. Chem. Pharm. Bull. 1970 , 18 , 1211 - 1218 ). HOF·CH3CN, made easily from diluted fluorine, was able to accomplish this task in a fast reaction with good yields.

Poly(3-hexylthiophene) Nanoparticles Containing Thiophene-S,S-dioxide: Tuning of Dimensions, Optical and Redox Properties, and Charge Separation under Illumination.

We describe the preparation of poly(3-hexylthiophene-S,S-dioxide) nanoparticles using Rozen's reagent, HOF·CH3CN, either on poly(3-hexylthiophene) (P3HT) or on preformed P3HT nanoparticles (P3HT-NPs). In the latter case, core-shell nanoparticles (P3HT@PTDO-NPs) are formed, as confirmed by X-ray photoelectron spectroscopy measurements, indicating the presence of oxygen on the outer shell. The different preparation modalities lead to a fine-tuning of the chemical-physical properties of the nanoparticles. We show that absorption and photoluminescence features, electrochemical properties, size, and stability of colloidal solutions can be finely modulated by controlling the amount of oxygen present. Atomic force microscopy measurements on the nanoparticles obtained by a nanoprecipitation method from preoxidized P3HT (PTDO-NPs) display spherical morphology and dimensions down to 5 nm. Finally, Kelvin probe measurements show that the coexistence of p- and n-type charge carriers in all types of oxygenated nanoparticles makes them capable of generating and separating charge under illumination. Furthermore, in core-shell nanoparticles, the nanosegregation of the two materials, in different regions of the nanoparticles, allows a more efficient charge separation.

General synthesis of trifluoromethyl selenides utilizing selenocyanates and fluoroform.

Trifluoromethylated selenoethers are quite rare despite their potential and the interest that they generate. A series of trifluoromethylseleno derivatives, either primary and secondary aliphatic or aromatic and heterocyclic, is described herein by the reaction of easily prepared organic selenocyanates and CuCF3. Another beneficial feature of this reaction is the use of fluoroform as a source for the CF3 group, a compound whose chemistry is currently being intensively researched because it is a potent greenhouse gas that should not be released into the atmosphere.

Fluorination of flavones and chromones using elemental fluorine.

Flavonoids are abundant micronutrients in our diet, possessing various biological activities. Fluorine was successfully added across the double bond of various flavones and chromones. The difluoro derivative products were easily dehydrofluorinated to form the corresponding 3-fluoroflavones and 3-fluorochromones.

HOF·CH3CN: probably the best oxygen transfer agent organic chemistry has to offer.

The complex HOF·CH3CN is readily obtained by bubbling dilute fluorine into aqueous acetonitrile solution. It does not have to be purified or isolated, and its solution can react as is, after the concentration has been establish by any iodometric method. It is the only reagent possessing a distinctive positive oxygen species. This enables electrophilic oxygen transfer with results no other reagent can match. HOF·CH3CN demonstrates its ability in epoxidations that either could not be performed before or could only obtained 5 orders of magnitude slower. This complex is also an excellent tool for oxygenation of compounds at the α position of a carbonyl, including the synthesis of some hard-to-come-by indanediones, which are important for fingerprint visualization on paper. HOF·CH3CN proves itself as a very efficient reagent for oxygenating tertiary nitrogen atoms both in aliphatic (including azides) and in aromatic amines, which could not be accomplished despite many attempts in the last 50 years. Oxygenation of two tertiary nitrogen atoms in the same molecule also becomes feasible as demonstrated for various phenanthrolines, bipyridines, diazafluorenones, and quinoxalines. It was also used to oxygenate primary amines, and because of the exceptionally mild conditions, it could transform vicinal aliphatic diamines to vicinal dinitro derivatives as well as amino acids to the corresponding nitro ones, practically unknown transformations before. Its ability to react with azines and hydrazones and convert them to the original carbonyls helped to establish these groups as good protecting tools for a variety of carbonyls. HOF·CH3CN excels in oxygenation of various sulfur and selenium compounds that could not be oxygenated in the past. The selectivity of the oxidation is quite good, and if there are alcohols, double bonds, and sulfides in the same molecule, usually the sulfur atom will be attacked first. Of special interest is the reaction with oligothiophenes resulting at will in either [all]-S,S-dioxooligothiophenes or in partially oxygenated ones. Some of these last derivatives have the narrowest HOMO-LUMO gap of all oligothiophenes tested, a very desirable feature. This reagent can also oxidize thiols or disulfides to either sulfonic or sulfinic acids at will, all in seconds and in very high yields. Since the oxygen atom of HOF·CH3CN originates in water, it is very easy and relatively inexpensive to introduce the heavy oxygen isotope in many sites of a variety of molecules, some of them quite important. The (18)O tirapazamine and any desirable alcohol, R(Ar)(18)OH, are two examples.

Fluorination of aryl boronic acids using acetyl hypofluorite made directly from diluted fluorine.

Aryl boronic acids or pinacol esters containing EDG were converted in good yields and fast reactions to the corresponding aryl fluorides using the readily obtainable solutions of AcOF. In reactions with aryl boronic acids containing EWG at the para position, there are two competing forces: one directing the fluorination to take place ortho to the boronic acid and the other, toward an ipso substitution. With EWG meta to the boronic acid, substitution ipso to the boron moiety takes place in good yields.

The first general route for efficient synthesis of 18O labelled alcohols using the HOF·CH3CN complex.

A mild and very efficient method for converting boronic acids to alcohols has been developed using the acetonitrile complex of hypofluorous acid HOF·CH3CN. Employing (18)O-labeled water results in alcohols containing a heavy oxygen isotope. The reactions were performed at room temperature, within a few minutes and in excellent yields.

New conjugated oligothiophenes containing the unique arrangement of internal adjacent [all]-S,S-oxygenated thiophene fragments.

The quest for obtaining conjugated oligothiophene-containing molecules with narrower HOMO-LUMO gaps and higher oxidation and reduction potentials is the subject of this study. Molecules containing the bithiophene tetraoxide (2) and the terthiophene hexaoxide (3) moieties were prepared and studied. They were obtained by transferring oxygen atoms to the corresponding dibromo oligothiophenes with the HOF⋅CH3CN complex and then cross-coupling them with either thiophene- or acetylene tin derivatives. The photophysical and electrochemical studies of the products revealed that this particular class of mixed thiophenes is characterized by significantly smaller frontier orbital gaps and higher oxidation and reduction potentials compared with any other arrangement of oligothiophenes including various [all]-S,S-oxygenated thiophene derivatives.

Pyridine•BrF3, the missing link for clean fluorinations of aromatic derivatives.

This work demonstrates the unique features of the never used before Py•BrF(3) complex in the field of aromatic organic fluorinations. The main disadvantage of the noncomplexed BrF(3) is the fact that usually, in addition to the desired fluorination, a parallel electrophilic aromatic bromination takes place as well. Use of the Py•BrF(3) complex reduces this electrophilic bromination, which is observed with most reagents based on fluorine and bromine [BrF].

Activation of a CH bond in polypyridine systems by acetyl hypofluorite made from F2.

Activation of the relatively inactive polypyridine backbone with strong electrophilic fluorine, originating from acetyl hypofluorite (AcOF) enables attack of the acetoxy moiety at the α position to the heteroatom. Derivatives of bipyridine, phenanthroline and terpyridine systems have been acetoxylated or oxygenated within a few minutes usually in very good yields.

all-S,S-dioxygenated star oligothiophenes.

Star-shaped oligothiophenes are promising materials for applications in the organic electronics field. For the first time, a range of star-oligothiophenes was oxidized to the corresponding all-S,S-dioxides by using the HOF·CH(3)CN complex. These materials exhibit considerable thermal stability and red-shift absorptions in the UV/vis relative to the parent compounds.

Synthesis of oxidized thienopyrroles using HOF·CH3CN.

An efficient transformation of the sulfur atoms to the sulfonyl group in a range of thienopyrroles was achieved by using the HOF·CH(3)CN complex. Mild conditions, high yields, and easy purification are the main features of this novel route. Most new materials exhibit considerable red-shift absorptions in the UV/visible range relative to the parent compounds.

Synthesis of difluoroaryldioxoles using BrF3.

A novel synthesis of different aromatic and heteroaromatic difluorodioxole derivatives has been developed. The starting materials were catechols, which, after treatment with thiophosgene, formed at 0 °C the respective thiodioxoles. The latter were reacted for a short time with commercially available bromine trifluoride, producing potentially biologically important difluoroaryldioxoles in moderate to high yields.

The oxygenation of thieno[2,3-b]thiophenes.

Members of thieno[2,3-b]thiophenes were oxidized using the HOF.CH(3)CN complex, transforming the sulfur atom to the corresponding sulfonyl group in high yield and under very mild conditions.

Do [all]-S,S'-dioxide oligothiophenes show electronic and optical properties of oligoenes and/or of oligothiophenes?

A comprehensive photophysical and spectroscopic (electronic and Raman) study guided by density functional theory, DFT, CIS, and correlated ab initio calculations has been performed on a series of fully oxidized oligothiophenes with variable chain length, and up to four rings. A comparison with the properties of oligoenes and oligothiophenes is proposed. Absorption, fluorescence, lifetimes, flash-photolysis, phosphorescence, two-photon absorption, Raman, resonance Raman, and thermospectroscopy data are collected and interpreted according to the obtained theoretical results. The interest is focused on the ground electronic state and in the low-lying excited electronic states. Full oxygenation of the sulfur atoms of oligothiophenes results in: (i) restricted inter-ring isomerization such as observed from the absorption spectra; (ii) an effective quenching of fluorescence, and (iii) the appearance of dual emission. The emission features are explained by the interference of a dipole-allowed and a dipole-forbidden singlet excited states leading to simultaneous lighting from a local Frenkel and an intramolecular charge transfer photon-releasing configurations. These two excited states contribute to the broadening of the light emission spectrum. These properties highlight the similarity of these samples to that of oligoenes with comparable number of pi-electrons.

The tetrazole 3-N-oxide synthesis.

An efficient procedure for transferring an oxygen atom to the 1- or 2-substituted 5-alkyl or aryl tetrazole ring, resulting, for the first time, in the corresponding N-oxides, was developed using HOF.CH(3)CN. This novel route features mild conditions and high yields. X-ray structure analysis and (15)N NMR experiments indicate that the preferred position for the incorporation of the oxygen is on the N-3 atom.

Toward the synthesis of the rare N-(trifluoromethyl)amides and the N-(difluoromethylene)-N-(trifluoromethyl)amines [RN(CF3)CF2R'] using BrF3.

A synthesis of a wide range of different aliphatic, aromatic, and heterocyclic N-(trifluoromethyl)amides along with aromatic N-(difluoromethylene)-N-(trifluoromethyl)amine derivatives has been developed. The starting materials are the easily available isothiocyanates, and the fluorinating reagent is the commercially available bromine trifluoride. The reaction is performed under mild conditions, and the fluorinated amides and amines are produced in moderate to high yields.