Photoinduced charge separation in the carbon nano-onion C60@C240

The double-shell fullerene C60@C240 formed by inclusion of C60 into C240 is the smallest stable carbon nano-onion. In the paper, we analyze in detail the character of excited states of C60@C240 in terms of exciton localization and charge transfer between the inner and outer shells. The unique structure of the buckyonion leads to a large electrostatic stabilization of charge-separated (CS) states in the C60@C240. As a result, the CS states C60+@C240 lie in the same region of the electronic spectrum (2.4-2.6 eV) as strongly absorbing locally excited states, and therefore, can be effectively populated. The CS states C60 @C240+ are found to be by 0.5 eV higher in energy than the states C60+@C240 . Unlike the situation observed in donor-acceptor systems, the energy of the CS states in C60@C240 does not practically depend on the environment polarity. This leads to exceptionally small reorganization energies for electron transfer between the shells. Electronic couplings for photoinduced charge separation and charge recombination processes are calculated. The absolute rate of the formation of the CS states C60+@C240 is estimated at ~ 4 ps-1. The electronic features found in C60@C240 are likely to be shared by other carbon nano-onionsWe are grateful for financial support from the Spanish Ministerio de Economía y Competitividad (MINECO) (Projects CTQ2014-54306-P and CTQ2015-69363-P), the Catalan DIUE (Project 2014SGR931, ICREA Academia 2014 Award to MS, and Xarxa de Referència en Química Teòrica i Computacional), and the FEDER fund (UNGI10-4E-801