Additions of Azomethine Ylides to Fullerene C₆₀ Assisted by a Removable Anchor

The addition of nitrile oxides to [60]fullerene, leading to isoxazolinofullerenes, can be reversed using reducing agents such as Mo(CO)6 or DIBALH. Thus, this reaction can be used, in principle, for protection/deprotection of [60]fullerene or for solubilization purposes. The tether-controlled tandem addition of nitrile oxides and azomethine ylides provides mainly cis-1 patterns. The determination of the structure of bisadducts was obtained by NMR spectroscopy with the help of HMQC, HMBC, and NOEDS techniques. The isoxazoline moiety could be removed using Mo(CO)6 leaving a fulleropyrrolidine derivative

Impact of the Interlayer Distance between Graphene and MoS₂ on Raman Enhancement

Two-dimensional (2D) materials and their van der Waals (vdW) heterostructures, particularly graphene and graphene/MoS2, have attracted intense attention due to their potential application in surface-enhanced Raman spectroscopy (SERS). Herein, we report how to modulate the SERS response of 2D materials. First, we demonstrate that SERS based on graphene materials is inversely proportional to the functionalization degree. The covalent functionalization interrupts the conjugation of the graphene π-system, inhibiting the charge transfer between graphene and the probe molecule (Rhodamine 6G), thus reducing Raman enhancement. For graphene/MoS2 vdW heterostructures, the SERS enhancement is dominated by the vdW interaction between graphene and MoS2. A shorter interlayer distance, with stronger vdW interactions, improves the dipole–dipole interaction and the charge transfer, increasing the Raman enhancement. Moreover, the SERS intensity of graphene/MoS2 vdW heterostructures varies rapidly when the interlayer distances are less than 0.6 nm, while it varies less at interlayer distances longer than 0.6 nm. This study not only demonstrates the Raman enhancement dependence on the functionalization degree of graphene materials and the interlayer distance in graphene/MoS2 vdW heterostructures but also opens the door for controlling and predicting the SERS intensity based on 2D materials

Photoinduced Cascade Reactions of 2‑Allylphenol Derivatives toward the Production of 2,3-Dihydrobenzofurans

A light-driven protocol for the synthesis of 2,3-dihydrobenzofurans under mild conditions is reported. Specifically, the cascade process is initiated by the photochemical activity of allyl-functionalized phenolate anions, generated in situ upon deprotonation of the corresponding phenols. The reaction proceeds rapidly with reaction times as low as 35 min, delivering a wide range of densely functionalized products (20 examples, yields up to 69%). Mechanistic studies have also been performed providing convincing evidence for the photochemical formation of carbon-centered radical species. A cascade reaction pathway involving a tandem atom transfer radical addition (ATRA) and an intramolecular nucleophilic substitution (SN) process is proposed to occur

A Three-Level Luminescent Response in a Pyrene/Ferrocene Rotaxane

A solvent switchable rotaxane equipped with a pyrene stopper and with two ferrocenyl units on the macrocycle is reported, in which three different states, two nondegenerate and one degenerate, can be obtained in different solvents at room temperature. This is accompanied by high contrast changes in fluorescence intensity of the pyrene stopper by the presence of the ferrocenyl moieties on the macrocycle, which quench the emission of pyrene more efficiently with proximity

[60]Fullerene−Pyrrolidine-<i>N</i>-oxides

Eight members of a new family of fullerene derivatives, [60]fulleropyrrolidine-N-oxides, have been synthesized and characterized. Facile oxidation, by a peracid, of the parent [60]fulleropyrrolidine gave clean conversions into the product molecules, in which the tertiary amine is transformed into a quaternary amine bearing an oxygen atom. The reaction is very selective, favoring the nitrogen atom of the pyrrolidine ring in preference to epoxidation of the fullerene cage. The 1H NMR shows an AB quartet splitting pattern, characteristic of nonequivalent hydrogens in the pyrrolidine ring and at a chemical shift displacement of 0.8 ppm downfield. Other methods of characterization are described, including MS, differential scanning calorimetry, thermogravimetric analysis, HPLC, UV/vis, and IR. Conclusive evidence for the formation of an N-oxide moiety is provided by the synthesis, oxidation, and NMR characterization of a novel [60]fulleropyrrolidine containing a 15N isotope, showing an 85 ppm downfield heteroatom chemical shift. Preliminary details of the effects of substitution on the reactivity of the pyrrolidine ring are also reported

Organic Functionalization and Optical Properties of Carbon Onions

We report, for the first time, the organic functionalization of carbon onions. The functionalization was achieved via 1,3-dipolar cycloaddition of azomethine ylides to a mixture of amorphous carbon and concentric fullerenes. Once functionalized, the onions become soluble in organic solvents and it is possible to purify them from the rest of carbon. Their nonlinear optical properties have been studied in solution for application as broadband optical limiters. It was found that the functionalized onions are an example of soluble material that functions equally well in both the visible and the NIR regions

Easy Access to Water-Soluble Fullerene Derivatives via 1,3-Dipolar Cycloadditions of Azomethine Ylides to C₆₀

Easy Access to Water-Soluble Fullerene Derivatives via 1,3-Dipolar Cycloadditions of Azomethine Ylides to C60</sub

Phenanthrene-Extended Phenazine Dication: An Electrochromic Conformational Switch Presenting Dual Reactivity

The synthesis and isolation of one of the few examples of a π-extended diamagnetic phenazine dication have been achieved by oxidizing a phenanthrene-based dihydrophenazine precursor. The resulting dication was isolated and fully characterized, highlighting an aromatic distorted structure, generated by the conformational change upon the oxidation of the dihydrophenazine precursor, which is also correlated with a marked electrochromic change in the UV–vis spectrum. The aromaticity of the dication has also been investigated theoretically, proving that the species is aromatic based on all major criteria (structural, magnetic, and energetic). Moreover, the material presents an intriguing dual reactivity, resulting in ring contraction to a π-extended triarylimidazolinium and reduction to the dihydrophenazine precursor, depending on the nature of the nucleophile involved. This result helps shed light on the yet largely unexplored reactivity and properties of extended dicationic polycyclic aromatic hydrocarbons (PAHs). In particular, the fact that the molecule can undergo a reversible change in conformation upon oxidation and reduction opens potential applications for this class of derivatives as molecular switches and actuators