Two-fold addition reaction of silylene to C60: structural and electronic properties of a bis-adduct.

The addition reaction of C60 with silylene 1, a silicon analog of carbene, yielded the corresponding bis-adduct 3. The structure of 3 was determined by single-crystal X-ray structure analysis, representing the first example of a crystal structure of a silirane (silacyclopropane) derivative of fullerenes. Electrochemical measurements confirmed that the redox potentials of 3 are shifted cathodically compared to those of the parent mono-adduct 2. Density functional theory (DFT) calculations provided the basis for the electronic properties of compound 3.

Perspectives on push-pull chromophores derived from click-type [2 + 2] cycloaddition-retroelectrocyclization reactions of electron-rich alkynes and electron-deficient alkenes.

Various push-pull chromophores can be synthesized in a single and atom-economical step through [2 + 2] cycloaddition-retroelectrocyclization (CA-RE) reactions involving diverse electron-rich alkynes and electron-deficient alkenes. In this review, a comprehensive investigation of the recent and noteworthy advancements in the research on push-pull chromophores prepared via the [2 + 2] CA-RE reaction is conducted. In particular, an overview of the physicochemical properties of the family of these compounds that have been investigated is provided to clarify their potential for future applications.

Controlling the reactivity of La@C82 by reduction: reaction of the La@C82 anion with alkyl halide with high regioselectivity.

Endohedral metallofullerenes have excellent redox properties, which can be used to vary their reactivity to certain classes of molecules, such as alkyl halides. In this study, the thermal reaction of the La@C2v-C82 anion with benzyl bromide derivatives 1 at 110 °C afforded single-bonded adducts 2-5 with high regioselectivity. The products were characterized by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and visible-near infrared spectroscopy. The reaction of La@C2v-C82 with alkyl halides using the same conditions showed no consumption of La@C2v-C82, indicating that the reactivity of La@C2v-C82 toward alkyl halides was effectively increased by one-electron reduction. Single-crystal X-ray diffraction analysis of the single-bonded adduct 3a revealed the addition site of the p-methoxybenzyl group on La@C2v-C82. Theoretical calculations indicated that the addition site carbons in neutral La@C2v-C82 have high spin density, whereas those in the La@C2v-C82 anion do not have high charge densities. Thus, the reaction is believed to occur via electron transfer, followed by the radical coupling of La@C2v-C82 and benzyl radicals, rather than by bimolecular nucleophilic substitution reaction of La@C2v-C82 anion with 1.

Control of functionalized single-walled carbon nanotube photoluminescence via competition between thermal rearrangement and elimination.

We conducted the chiral separation of functionalized single-walled carbon nanotubes (SWNTs) with dibromopropane derivatives. Depending on their chirality and diameter, the thermal treatment of functionalized SWNTs leads to a shift in the emission radiation to longer wavelengths owing to rearrangement reaction in competition with elimination reaction.

Selective emergence of photoluminescence at telecommunication wavelengths from cyclic perfluoroalkylated carbon nanotubes.

Chemical functionalisation of semiconducting single-walled carbon nanotubes (SWNTs) can tune their local band gaps to induce near-infrared (NIR) photoluminescence (PL). However, tuning the PL to telecommunication wavelengths (>1300 nm) remains challenging. The selective emergence of NIR PL at the longest emission wavelength of 1320 nm was successfully achieved in (6,5) SWNTs via cyclic perfluoroalkylation. Chiral separation of the functionalised SWNTs showed that this functionalisation was also effective in SWNTs with five different chiral angles. The local band gap modulation mechanism was also studied using density functional theory calculations, which suggested the effects of the addenda and addition positions on the emergence of the longest-wavelength PL. These findings increase our understanding of the functionalised SWNT structure and methods for controlling the local band gap, which will contribute to the development and application of NIR light-emitting materials with widely extended emission and excitation wavelengths.

Stepwise Functionalization of Single-Walled Carbon Nanotubes with Subsequent Molecular Conversion to Control Photoluminescence Properties.

Functionalization of single-walled carbon nanotubes (SWCNTs) has attracted interest because it alters the near-infrared (NIR) photoluminescence (PL) wavelength and emission efficiency. These modifications depend on the binding configuration and degree of functionalization. Excessive functionalization reduces the emission efficiency as the integrity of the conjugated π system decreases; thus, controlling the degree of functionalization is essential. Because the binding configurations and degree of functionalization are affected by the reagent structure, a stepwise approach combining SWCNTs functionalization and subsequent reactions to introduce functional groups into the addenda could effectively control their PL properties and functionalities. We studied this approach by implementing the reductive alkylation of SWCNTs by using bromoalkanes with t-butyl carbamate (Boc)-protected amino groups and subsequent deprotection and amidation reactions. The reaction products were analyzed based on absorption, PL, and Raman spectroscopy and the Kaiser test. Depending on the structure of the reagent, deprotection and amidation reactions competed with the elimination reaction of addenda, altering the PL properties of the SWCNTs. Furthermore, the elimination reaction was inhibited in the adducts functionalized using dibromoalkane with Boc-protected amino groups, demonstrating that the use of appropriate reagents enables the molecular conversion of the functional groups of SWCNT adducts without affecting their PL properties.

Synthesis and Conformational Analysis of Fullerene Torsion Balances for Assessing the Contribution of Dispersion and Anionic Character in Non-Covalent Arene-Fullerene Interactions.

We employ a molecular torsion balance displaying bifurcated conformational isomerism to quantitatively evaluate the non-covalent interactions between the fullerene surface and substituted arene moieties containing elements with high atomic numbers, as well as the thermodynamic processes involved in the folding equilibrium using nuclear magnetic resonance spectroscopy. The interaction between fullerene and haloaryl groups was stronger in cases where the introduced halogen had a higher atomic number, indicating that dispersion forces play a significant role in the interaction between fullerenes and 4-haloaryl groups. The dispersion term also significantly contributed to the interaction between fullerene and the 4-mercaptophenyl group. Moreover, the addition of an appropriate base to the 4-mercaptophenyl-appended torsion balance formed the corresponding thiophenolate anion, resulting in a large negative change in the folding free energy in CDCl3 . Detailed analysis suggested that the observed attractive anionic arene-fullerene interactions predominantly originated from solvation effects.

Unraveling the Nature and Strength of Non-Covalent Interactions on the Surface of Fullerenes.

The nature and strength of the noncovalent intermolecular interactions on the surface of fullerenes must be understood for the application of these molecules in pharmaceuticals and materials chemistry. Consequently, experimental and theoretical evaluations of such weak interactions have been conducted in parallel. Nevertheless, the nature of these interactions remains a topic of ongoing debate. In this context, this concept article summarizes recent advances in experimental and theoretical efforts aimed at characterizing the nature and strength of non-covalent interactions on fullerene surfaces. Specifically, this article summarizes recent studies conducted on host-guest chemistry based on various macrocycles and on catalyst chemistry based on conjugated molecular catalysts composed of fullerenes and amines. In addition, conformational isomerism analyses performed using fullerene-based molecular torsion balances and state-of-the-art computational chemistry are reviewed. These studies have enabled a comprehensive evaluation of the contributions of electrostatic, dispersion, and polar interactions on the surface of fullerenes.

Photoluminescence Properties of Single-Walled Carbon Nanotubes Influenced by the Tether Length of Reagents with Two Reactive Sites.

The functionalization of single-walled carbon nanotubes (SWNTs) is an effective method for controlling a local band gap, resulting in photoluminescence (PL) in the near-infrared region. Herein, SWNTs were functionalized using a series of bromoalkanes and dibromoalkanes to evaluate the effects of their length on the nanotube PL properties. When bromoalkanes (Cn H2n+1 Br) or dibromoalkanes (Cn H2n Br2 ) with tether lengths of six or more were utilized for six different semiconducting SWNTs, the obtained SWNT adducts exhibited two new PL peaks, whereas dibromoalkanes with tether lengths of 3-5 (Cn H2n Br2 : n=3-5) produced single peaks. Combined with theoretical calculations, the results suggested that the tether length of reagents changes the formation mechanism of functionalized adducts, that is, Cn H2n Br2 (n=3-5) tends to result in kinetic products.

Understanding the Nature and Strength of Noncovalent Face-to-Face Arene-Fullerene Interactions.

Face-to-face noncovalent arene-fullerene interactions are important in several research fields such as synthetic chemistry, materials chemistry, and medicinal chemistry; however, their nature and strength are still poorly understood. In this study, we prepare a fullerene-based torsion balance containing thioanisole, phenol, naphthalene, azulene, and pyrene moieties as a unimolecular model system. Moreover, we compare the folding free energies between the folded and the unfolded conformers of a series of the molecular torsion balances to quantify noncovalent interactions between arenes and the fullerene surface. This work demonstrates that the contributions of polarizabilities, anionic charges, electronic dipole moments, and the number of arene rings to the interactions can be experimentally measured by analyzing the folding equilibrium of the molecular torsion balances.

Non-Fasting Hypertriglyceridemia as an Independent Risk Factor for Coronary In-Stent Restenosis after Primary Bare Metal Stent Implantation in Patients with Coronary Artery Disease.

After a percutaneous coronary intervention (PCI) in patients with coronary artery disease (CAD), in-stent neoatherosclerosis may pose a risk of in-stent restenosis (ISR). To clarify whether non-fasting hypertriglyceridemia contributes to ISR, we examined the relationship between non-fasting hypertriglyceridemia (i.e., triglyceride (TG) level ≥ 200 mg/dL) and ISR after stenting with a bare metal stent (BMS) post-primary PCI in patients with CAD by means of a single-site retrospective analysis. A total of 1,039 patients with CAD were enrolled, and 86 patients (112 lesions) were evaluated for BMS-ISR 3-6 months post-primary PCI. The percentage of patients with non-fasting hypertriglyceridemia was significantly higher in the ISR (+) group than in the ISR (-) group (P < 0.009). The follow-up period and number of patients in the ISR (+) group were significantly smaller than those in the ISR (-) group (P < 0.001). There were no significant between-group differences in the other baseline patient characteristics before the primary PCI or at the time of the follow-up coronary angiography. However, at the follow-up period, the ISR (+) group had significantly lower diastolic blood pressure and high-density lipoprotein cholesterol levels (P = 0.015) and significantly higher TG levels (P = 0.012) than the ISR (-) group. A multiple logistic regression analysis demonstrated that non-fasting hypertriglyceridemia and a follow-up period of ≥ 6 months were independent risk factors for ISR after primary PCI in patients with BMS implantation for stenotic CAD (P = 0.006), with an adjusted odds ratio of 8.232 (1.201-56.410) and 0.006 (95% confidence interval < 0.001-0.045), respectively. Non-fasting hypertriglyceridemia may be an additional independent risk factor for BMS-ISR after primary PCI in patients with CAD.

Li@C60 thin films: characterization and nonlinear optical properties.

Organic materials have attracted considerable attention in nonlinear optical (NLO) applications as they have several advantages over inorganic materials, including high NLO response, and fast response time as well as low-cost and easy fabrication. Lithium-containing C60 (Li@C60) is promising for NLO over other organic materials because of its strong NLO response proven by theoretical and experimental studies. However, the low purity of Li@C60 has been a bottleneck for applications in the fields of solar cells, electronics and optics. In 2010, highly purified Li@C60 was finally obtained, encouraging further studies. In this study, we demonstrate a facile method to fabricate thin films of Li@C60 and their strong NLO potential for high harmonic generation by showing its comparatively strong emission of degenerate-six-wave mixing, a fifth-order NLO effect.

New Horizons in Chemical Functionalization of Endohedral Metallofullerenes.

This overview explains some new aspects of chemical functionalization of endohedral metallofullerenes (EMFs) that have been unveiled in recent years. After differences in chemical reactivity between EMFs and the corresponding empty fullerenes are discussed, cage-opening reactions of EMFs are examined. Then, the selective bisfunctionalization of EMFs is explained. Finally, single-bonding derivatization of EMFs is addressed. The diversity and applicability of the chemical functionalization of endohedral metallofullerenes are presented to readers worldwide.

A Fullerene-Based Molecular Torsion Balance for Investigating Noncovalent Interactions at the C60 Surface.

To investigate the nature and strength of noncovalent interactions at the fullerene surface, molecular torsion balances consisting of C60 and organic moieties connected through a biphenyl linkage were synthesized. NMR and computational studies show that the unimolecular system remains in equilibrium between well-defined folded and unfolded conformers owing to restricted rotation around the biphenyl C-C bond. The energy differences between the two conformers depend on the substituents and is ascribed to differences in the intramolecular noncovalent interactions between the organic moieties and the fullerene surface. Fullerenes favor interacting with the π-faces of benzenes bearing electron-donating substituents. The correlation between the folding free energies and corresponding Hammett constants of the substituents in the arene-containing torsion balances reflects the contributions of the electrostatic interactions and dispersion force to face-to-face arene-fullerene interactions.

Copper-Mediated Cascade Synthesis of Open-Cage Fullerenes.

An open-cage fullerene bearing an eight-membered ring orifice has been synthesized in one pot by the reaction of C60 with propargylic phosphate in the presence of CuCl. The reaction cascade involves the transformation of the phosphate to the 1,3-dienyl phosphate, which enables the reaction with C60 by [4 + 2] cycloaddition to form the cyclohexene-annulated intermediate, and subsequent intramolecular syn-elimination of the phosphodiester affords the cyclohexadiene-annulated fullerene derivative as the precursor for the open-cage fullerene.

Sonochemical reaction to control the near-infrared photoluminescence properties of single-walled carbon nanotubes.

The effect of ultrasonic irradiation on the optical properties of single-walled carbon nanotubes (SWNTs) was investigated. Upon sonication in D2O in the presence of sodium dodecylbenzene sulfonate (SDBS) under air, red-shifted photoluminescence (PL) peaks at ∼1043 and ∼1118 nm were observed from the aqueous suspensions of (6,4) and (6,5)SWNTs, accompanied by a decrease in the intensity of the intrinsic PL peaks. Upon sonication with SDBS under an Ar atmosphere, the rate of spectral change increased with the sonication time and new PL peaks emerged at 1043, 1118, and 1221 nm. Meanwhile, upon the addition of 1-butanol, the PL peaks emerged only at 1043 nm and 1118 nm, while the emergence of the peak at 1221 nm was inhibited. On the other hand, a suspension with highly dispersed SWNTs was obtained upon sonication in the presence of sodium cholate without any change in the intrinsic optical properties of SWNTs. These experimental results reveal that the PL characteristics of SWNTs can be controlled by controlling the sonication conditions such as the type of surfactant used, the concentration of SWNTs, reaction environment, and the presence of an inhibitor such as 1-butanol.

Thermodynamic control of quantum defects on single-walled carbon nanotubes.

Single-walled carbon nanotubes with designed quantum defects are prepared and characterized. The photoluminescence (PL) of the nanotubes can be modified by thermal treatment from 1215-1224 to 1249-1268 nm. Theoretical calculations suggest that the change in the PL spectra by thermal treatment can be explained by isomerization from kinetic to thermodynamic products.

Synthesis of Fullerene-Fluorene Dyads through the Platinum-Catalyzed Reactions of [60]Fullerene with 9-Ethynyl-9H-fluoren-9-yl Carboxylates.

The single-step regio- and stereoselective platinum-catalyzed reactions of [60]fullerene with a series of 9-ethynyl-9H-fluoren-9-yl carboxylates afforded fullerene-fluorene dyads in their [2 + 2] cycloaddition forms. The presented reactions represent the first examples of the use of easily accessible fluorenyl carboxylates as fluorenylideneallene precursors. In addition, the single-crystal X-ray structure of one of the dyads reveals a distorted cyclobutane ring. Furthermore, the dyad forms a layered structure with close-packed arrays of C60 spheres in its crystals.

Influence of local strain caused by cycloaddition on the band gap control of functionalized single-walled carbon nanotubes.

Fine control of the band gap of single-walled carbon nanotubes (SWNTs) has been achieved by the functionalization with dibromoalkanes, namely, 1,3-dibromopropane (1a), 1,4-dibromobutane (1b), 1,5-dibromopentane (1c), and 1,8-bis(bromomethyl)naphthalene (1d). Red-shifted photoluminescence (PL) peaks observed at 1215-1242 nm were assigned to the local band gaps of the chemically functionalized SWNTs 2a, 2b, 2c, and 2d, respectively. Density functional theory (DFT) and time-dependent DFT calculations for 2a-2d suggest that "local strain" induced by cycloaddition plays an important role in tuning the local band gap energies of functionalized SWNTs.

Control of near infrared photoluminescence properties of single-walled carbon nanotubes by functionalization with dendrons.

Single-walled carbon nanotubes (SWNTs) were functionalized by reacting them with sodium naphthalenide and dendrons to control their photoemission in the near-IR region. The functionalized SWNTs were characterized by absorption, Raman, and photoluminescence (PL) spectroscopy. The degree of functionalization of the SWNTs decreased with the increasing bulkiness of the dendrons used. After functionalization, new red-shifted PL peaks could be observed at ∼1110 and ∼1210 nm where the intensities were drastically enhanced by the thermal treatment. The relative peak intensity of to that of increased with the increasing bulkiness of the dendrons. Density functional theory (DFT) calculations of the functionalized SWNTs with dendrons suggest that the adducts with less bulky hydroalkylated substitution are stable in Clar structures and the addition positions predominantly determine the PL peak positions.