Do Carbon Nano‐onions Behave as Nanoscopic Faraday Cages? A Comparison of the Reactivity of C 60 , C 240 , C 60 @C 240 , Li + @C 60 , Li + @C 240 , and Li + @C 60 @C 240

Diels-Alder Cycloaddition of Cyclopentadiene to C60 and Si60 and Their Endohedral Li+ Counterparts

Both silicon and carbon are elements located in group 14 on the periodic table. Despite some similarities between these two elements, differences in reactivity are important, and whereas carbon is a central element in all known forms of life, silicon is barely found in biological systems. Here, we investigate the Diels-Alder cycloaddition reaction of cyclopentadiene (CP) and cyclopentasildiene (CPSi) with fullerenes C60, Li+@C60, Si60, and Li+@Si60 using density functional theory methods. The results reveal distinct kinetic and thermodynamic trends that govern the reactivity and selectivity. For C60, the [6,6] pathway is kinetically and thermodynamically favored, whereas for Si60, the [5,6] pathway is preferred thermodynamically but not kinetically. The introduction of lithium cations increases the reactivity of both C60 and Si60. Energy decomposition analysis (EDA) unveils the importance of the components of the interaction energy between CPSi and the corresponding fullerenes. The findings provide insights into the interplay of electronic structure, substrate reactivity, and fullerene electrophilicity in cycloaddition reactions.

Magnetic response properties of carbon nano-onions

The magnetic response of a number of double- and triple-layer carbon nano-onions (CNOs) is analyzed by calculating the magnetically induced current density and the induced magnetic field using the pseudo-π model. Qualitatively the same magnetic response was obtained in calculations at the all-electron level. The calculations show that the CNOs exhibit strong net diatropic (paratropic) ring currents when the external magnetic field points perpendicularly to one of the six-membered (five-membered) rings. They are deshielded inside and shielded outside the CNO; the latter dominates for larger CNOs. The magnetic response originates from a combination of spherical paratropic current densities on the inside of each carbon layer and diatropic current densities on the outside of them. The quantitative differences in the aromaticity of the CNOs as compared to single fullerenes are discussed in terms of ring-current strengths. The magnetic response of some of the CNOs is approximately the sum of the magnetic response of the individual layers, whereas deviations are significant for CNOs containing C₈₀. For the largest CNOs, the deviation from the sum of the fullerene contributions is larger, especially when the external magnetic field is perpendicular to a six-membered ring.

Designing stable binary endohedral fullerene lattices

Nanoparticle lattices and endohedral fullerenes have both been identified as potential building blocks for future electronic, magnetic and optical devices; here it is proposed that it could be possible to combine those concepts and design stable nanoparticle lattices composed from binary collections of endohedral fullerenes. The inclusion of an atom, for example Ca or F, within a fullerene cage is known to be accompanied by a redistribution of surface charge, whereby the cage can acquire either a negative (Ca) or positive (F) charge. From calculations involving a combination of van der Waals and many-body electrostatic interactions, it is predicted that certain binary combinations, for example a metal (A) and a halogen (B), could result in the formation of stable nanoparticle lattices with the familiar AB and AB₂ stoichiometries. Much of the stability is due to Coulomb interactions, however, charge-induced and van der Waals interactions, which always enhance stability, are found to extend the range of charge on a cage over which lattices are stable. Some lattice types are shown to be three or four times more stable than an equivalent neutral C₆₀ structure. An extension of the calculations to the fabrication of structures involving endohedral C₈₄ is also discussed.

External Electric Field to Control the Diels-Alder Reactions of Endohedral Fullerene

The present work investigates the role of the External Electric Field (EEF) on a Diels-Alder reaction of endohedral fullerene by means of chemical kinetics and quantum chemical calculations. The investigation...

Quantification of the electric field inside protein active sites and fullerenes

While electrostatic interactions are exceedingly accountable for biological functions, no simple method exists to directly estimate or measure the electrostatic field in protein active sites. The electrostatic field inside the protein is generally inferred from the shift in the vibrational stretching frequencies of nitrile and thionitrile probes at the active sites through several painstaking and time-consuming experiments like vibrational Stark effect spectroscopy (VSS). Here we present a simple, fast, and reliable methodology, which can efficiently predict the vibrational Stark tuning rates (VSRs) of a large variety of probes within 10% error of the reported experimental data. Our methodology is based on geometry optimization and frequency calculations in the presence of an external electric field to predict the accurate VSR of newly designed nitrile/thionitrile probes. A priori information of VSRs is useful for difficult experiments such as catalytic/enzymatic study and in structural biology. We also applied our methodology successfully to estimate the electric field inside fullerenes and nano-onions, which is encouraging for researchers to adopt it for further applications in materials science and supramolecular chemistry.

[10]CPP-Based Inclusion Complexes of Charged Fulleropyrrolidines. Effect of the Charge Location on the Photoinduced Electron Transfer

A number of non-covalently bound donor-acceptor dyads, consisting of C60 as the electron acceptor and cycloparaphenylene (CPP) as the electron donor, have been reported. A hypsochromic shift of the charge transfer (CT) band in polar medium has been found in [10]CPP⊃Li+ @C60 . To explore this anomalous effect, we study inclusion complexes [10]CPP⊃Li+ @C60 -MP, [10]CPP⊃C60 -MPH+ , and [10]CPP⊃C60 -PPyMe+ formed by fulleropyrrolidine derivatives and [10]CPP using the DFT/TDDFT approach. We show that the introduction of a positively charged fragment into fullerene stabilizes CT states that become the lowest-lying excited states. These charge-separated states can be generated by the decay of locally excited states on a nanosecond to picosecond time scale. The distance of the charged fragment to the center of the fullerenic cage and its accessibility to the solvent determine the strength of the hypsochromic shift.

Two-dimensional two-photon absorptions and third-order nonlinear optical properties of Ih fullerenes and fullerene onions

The third order nonlinear optical properties of I_h symmetry fullerenes increase exponentially with fullerene size. The two-dimensional two-photon absorption spectra for C₆₀ and C₂₄₀ have strong self-phase modulation responses.