Spin density distribution in paramagnetic azafullerene

Hyperfine coupling (HFC) constants for ¹⁴N and ¹³C nuclei in azafullerene C₅₉N (1) were calculated. The HFC constants for the ¹H and ¹³C nuclei in the ^·CH₃ radical were calculated as functions of the pyramidal distortion of the angles at the carbon atom. Using this angular dependence, the spin density distribution of the unpaired -electron in 1 was determined. The spin density of the unpaired -electron in 1 is mainly localized around the nitrogen atom.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2372–2374, November, 2004.     

Axially Substituted Silicon Phthalocyanine as Electron Donor in a Dyad and Triad with Azafullerene as Electron Acceptor for Photoinduced Charge Separation

The synthesis of a donor–acceptor silicon phthalocyanine (SiPc)‐azafullerene (C₅₉N) dyad 1 and of the first acceptor–donor–acceptor C₅₉N‐SiPc‐C₅₉N dumbbell triad 2 was accomplished. The two C₅₉N‐based materials were comprehensively characterized with the aid of NMR spectroscopy, MALDI‐MS as well as DFT calculations and their redox and photophysical properties were evaluated with CV and steady‐state and time‐resolved absorption and photoluminescence spectroscopy measurements. Notably, femtosecond transient absorption spectroscopy assays revealed that both dyad 1 and triad 2 undergo, after selective photoexcitation of the SiPc moiety, photoinduced electron transfer from the singlet excited state of the SiPc moiety to the azafullerene counterpart to produce the charge‐separated state, with lifetimes of 660 ps, in the case of dyad 1 , and 810 ps, in the case of triad 2 . The current results are expected to have significant implications en route to the design of advanced C₅₉N‐based donor–acceptor systems targeting energy conversion applications.     

The structure of shock fronts in various gases

The optical reflectivity of shock fronts in A, N₂, O₂, CO, CO₂, N₂O, CH₄, Cl₂ and HCl have been studied. The thickness of shock fronts in A up to the Mach number M = 1·55 is in agreement with the theory of Gilbarg and Paolucci. The rotational relaxation time is about 5·5 collisions in N₂ and equal to or less than that in the other gases. However, for stronger shocks N₂ does not appear to reach rotational equilibrium in the shock front and a qualitative theoretical discussion of this phenomenon is presented. In HCl there appears to be over-excitation of rotation in the shock front. There is no vibrational excitation of any of the gases.     

Azafullerene C59N in Donor–Acceptor Dyads: Synthetic Approaches and Properties

Energy conversion schemes have attracted considerable attention in recent years. A large amount of research effort has focused on fullerenes, particularly C₆₀ and its derivatives, as suitable electron acceptors, owing to their outstanding properties. In this context, C₅₉N‐based donor–acceptor systems have lately attracted attention, owing to their exceptional energy‐and electron‐transfer properties. As a result, chemical derivatization of C₅₉N plays an important role in the realization of the aforementioned systems. The current Minireview aims to familiarize researchers with the main aspects of azafullerene synthesis, chemistry, and photophysical properties, while it mainly focuses on the synthetic methodologies employed for as well as on energy conversion schemes of azafullerene‐based donor–acceptor systems.     

Chloro Derivatives of Azafullerenes C59NCl5 and Non‐Classical C97NCl21

High‐temperature chlorination of HPLC fullerene fractions containing mainly C₉₂/C₉₄ and C₁₀₂/C₁₀₄ resulted in the isolation and X‐ray structural characterization of chloro derivatives of azafullerenes, C₅₉NCl₅ and C₉₇NCl₂₁. It was assumed that formation of azafullerenes in the arc‐discharge synthesis of fullerenes occurred due to air leakage into the reactor. The molecule of C₅₉NCl₅ contains an isolated aromatic pyrrole ring on the fullerene cage and possesses C _5v symmetrical shape typical of other known C₅₉NR₅ derivatives. The molecule of non‐classical (NC ) C₉₇N(NC )Cl₂₁ contains an NC₆ heptagon on the azafullerene cage that assumes its formation by a C₂ loss from C₉₉N in the course of chlorination. The chlorination pattern is characterized by the presence of stabilizing isolated aromatic systems and isolated double C=C bonds on the C₉₇N(NC ) azafullerene cage.     

Organic–Inorganic Azafullerene‐Gold C59N‐Au Nanohybrid: Synthesis,Characterization, and Properties

Azafullerene (C₅₉N) was functionalized using a Mannich‐type reaction and then subsequently condensed with lipoic acid to yield dithiolane‐modified C₅₉N. In the following step, the extended dithiolane moiety from the C₅₉N core was utilized to decorate the azafullerene sphere with gold nanoparticles (Au NPs). The latter were initially stabilized with dodecanothiol (DT ? Au) and then integrated on azafullerene through a ligand exchange reaction with the dithiolane‐functionalized C₅₉N to produce the C₅₉N/DT ? Au nanohybrid. The nanohybrid was fully characterized by spectroscopy and microscopy, revealing the formation of spherical nanoparticles with a diameter in the range of 2–5 nm, as imaged by HR‐TEM. In the electronic absorption spectrum of C₅₉N/DT ? Au nanohybrid, the characteristic surface plasmon band (SPB) of Au NPs was observed, however, it was redshifted compared with that of DT ? Au. The redshift of the SPB is indicative of closer interparticle proximity of Au NPs, in accordance with the formation of aggregated NPs as observed by TEM, in C₅₉N/DT ? Au nanohybrid. Excited‐state interactions in C₅₉N/DT ? Au were probed by photoluminescence assays. It was found that the weak emission of C₅₉N at 819 nm was blueshifted by 14 nm in C₅₉N/DT ? Au, but was stronger in intensity, thus suggesting energy transfer to C₅₉N, within the organic–inorganic C₅₉N/DT ? Au nanohybrid. Finally, with the aid of pump–probe measurements and transient absorption spectroscopy, the formation of the singlet excited state of C₅₉N was identified.     

Chemical bond inside a fullerene cage: is it possible?

The geometries, electronic structures, and hyperfine coupling constants of azafullerene C₅₉N (a π-electron radical) and its derivatives, C₅₉NH and endofullerene H@C₅₉N, were calculated at the B3LYP level of the density functional theory. Analysis of calculated potential energy profiles along trajectories of the motion of encapsulated hydrogen atom from the center of the fullerene sphere toward different atoms of C₅₉N revealed formation of a chemical bond between the H atom and a carbon atom that is involved in the 6,6-bond with the N atom and bears the most part of the π-electron spin density. The C—H endo-bond length is 1.12 Å, the bond dissociation energy being equal to 26.4 kcal mol⁻¹. The C—H exo-bond involving the same carbon atom is 0.02 Å shorter than the endo-bond, the bond dissociation energy being much higher (78.4 kcal mol⁻¹).__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 51–54, January, 2005.