Fullerene size controls the selective complexation of [11]CPP with pristine and endohedral fullerenes.

The ability of the carbon nanoring [11]cycloparaphenylene ([11]CPP) for coordinating fullerenes has been tested using a series of hosts, including the pristine fullerenes C60, C70, C76 and C78, the clusterfullerene Sc3N@C80, monometallic endofullerenes Y@C82 and Tm@C82, and dimetallic endofullerenes Y2@C82 and Lu2@C82. A systematic theoretical study employing dispersion corrected density functional methods has been carried out in order to explore the characteristics of the complexes and the strength of the interaction. Depending on the dimer, complexation energies span from around -36 kcal mol-1 with C60 to -53 kcal mol-1 with the C82 derivatives. Dispersion is the main stabilizing contribution in these dimers, so the molecules arrange to maximize the number of close interatomic contacts. Since most fullerenes can properly fill the cavity of the nanoring the stability of the complexes is pretty similar, with the exception of the smallest fullerenes. The complexes with endohedral fullerenes show similar stabilities in all cases studied, with no noticeable dependence on the nature of the endohedral species. The results obtained suggest that fullerenes larger than C76 could be selectively encapsulated by [11]CPP compared to smaller fullerenes.

A theoretical study of complexes between fullerenes and concave receptors with interest in photovoltaics.

The complexation of the pristine fullerenes C60 and C70 and the endohedral fullerenes Sc3N@C80 and Sc3N@C68 has been tested using a series of hosts of different nature, including the buckybowls corannulene and sumanene, a zinc porphyrin, a chloro boron subphthalocyanine, and a corannulene pentasubstituted with nitrile groups. A systematic theoretical study has been carried out in order to explore both the strength of the interaction and the feasibility for electron transfer of the dimers. Dispersion is the main stabilizing contribution in these dimers, so both molecules orientate so as to maximize the number of close contacts among atoms. As a consequence, all host molecules interact with C70 by the long axis. C60 and Sc3N@C80 are more spherically shaped, so there is no clear preference for the position of the host molecule, though endohedral fullerenes are encapsulated preferentially by the face without contacts with the inner cluster. Complexation energies increase with the contact surface between molecules in the complex. The most stable complexes with fullerenes are formed by the subphthalocyanine and the CN-pentasubstituted corannulene. Depending on the dimer, complexation energies span from around -15 kcal mol-1 of C60 with corannulene to -24 kcal mol-1 of Sc3N@C80 with the subphthalocyanine. Some of the dimers seem to be capable of acting as a donor-acceptor pair, leading to charge transfer states with a neat separation of charge, thus being candidates for organic photovoltaic devices. Endohedral fullerenes are less prone to these donor-acceptor transitions, with charge transfer taking place from the carbon cage to the endohedral cluster. cora5CN, with its inverted polarity, also shows charge transfer upon excitation but with the fullerene acting as a donor and the buckybowl as an acceptor.

Ab initio and DFT study of the aromaticity of some Fulvalenes derived from Methylidenecyclopropabenzene.

Methylidencyclopropabenzene (MCPB) 1 and Fulvalenes 2-4 are molecules of special interest due to the relation between structure and aromaticity. The aim of this work was to analyze this relation and to quantify the aromaticity in 1-4 using different methods. Magnetic properties are directly related with aromaticity; here we studied the magnetic susceptibility and the anisotropy of the magnetic susceptibility. Nucleus indepedent chemical shift (NICS) and the anisotropy of the induced current density (ACID) were also employed. Tools of very different nature, geometric indexes HOMA and Bird, were determinated too for 1-4. All of these measures were found to be in agreement.

A comparative theoretical study of the pericyclic-pseudopericyclic character in a group of cyclizations of dienylketenes to cyclohexadienones.

A comprehensive B3LYP/6-31+G* study of the nature of 6pi electrocyclizations of four different dienylketenes (2-furanyl, 2-pyrrolyl, cyclopenta-1,3-dienyl, and 2-thiophenyl-substituted ketenes) to corresponding cyclohexadienones was carried out. An analogous system ((3Z)-4-(3H-pyrrol-2-yl)buta-1,3-dien-1-one) was also analyzed. For this purpose, the complete pathways were determined (reactants, products, transition states, and the IRC connecting reactants and products), and changes in different magnetic properties (magnetic susceptibility, chi, magnetic susceptibility anisotropy, chi anis, and the nucleus-independent chemical shifts, NICS) were monitored along the reaction profiles with a view to estimating the aromatization associated to the processes. We have also applied the ACID (anisotropy of the current-induced density) method with the same intention. The deep analysis of the results indicates a pericyclic character of the processes for the dienylketenes despite the relatively small NICS values in the transition states. Only the reaction of (3Z)-4-(3H-pyrrol-2-yl)buta-1,3-dien-1-one presents pseudopericyclic character due to the in-plane attack of the lone pair on nitrogen.