Abstract
Over the last years, carbon nano-onions (CNOs) have been in focus in material science research. Apart from its prospective use in solar cells, the number of potential applications of CNOs have grown in the last decades. Among them, we can mention their application in gas storage processes, solid lubrication, or heterogeneous catalysis, and also as electrode materials in capacitors, anode materials in lithium-ion batteries, catalyst support in fuel cells, or electro-optical devices. From the analysis of the polarizability of CNOs, it was concluded that CNOs behave as near perfect nanoscopic Faraday cages.[1] If CNOs behave as ideal Faraday cages, the reactivity of the C240 cage should be the same in Li+@C240 and Li+@C60@C240. In the first part of this work, we have analyzed the Diels-Alder reaction of cyclopentadiene to the free C240 cage and the C60@C240 CNO together with their Li+-doped counterparts using density functional theory. We find that in all cases the preferred cycloaddition is on bond [6,6] of type B of the C240 cage. From the comparison between the reactivity of Li+@C240 and Li+@C60@C240, we conclude that C60@C240 does not act as a perfect Faraday cage.[2] In the second part of this work, we perform a systematic study of excited state properties of six double-layered Li+ doped fullerenes of Ih symmetry: [Li@C60@C240]+, [Li@C60@C540]+, [Li@C60@C960]+, [Li@C240@C540]+, [Li@C240@C960]+ and [Li@C540@C960]+. On the basis of TDDFT calculations, we show that the long-wave absorption by the Li+ doped species leads to charge transfer (CT) between the inner and the outer shells unlike their neutral double-layered precursors. The CT energy depends strongly on the size of the concentric fullerenes and it can easily be tuned by varying both the encapsulated metal ion and the size of the shells. Two types of low-lying excited states are identified (1) capacitor-like structures, as Li+@C60-@C240+, with alternating positive and negative charges, and (2) states, where the positive charge is delocalized over the outer shell, as in Li@C240@C540+.[3]
References
[1] R. R. Zope, J. Phys. B: At. Mol. Opt. Phys. 41 (2008) 41, 085101; [b] R. R. Zope, S. Bhusal, L. Basurto, T. Baruah and K. Jackson, J. Chem. Phys. 143 (2015) 084306.
[2] A. J. Luque-Urrutia, A. Poater and M. Solà. Submitted for publication.
[3] A. J. Stasyuk, O. A. Stasyuk, M. Solà and A. A. Voityuk. J. Phys. Chem. C 123 (2019) 16525-16532.
Figure 1