Carbon Nano-onions as Photosensitizers: Stacking-Induced Red-Shift

We have investigated the double-layered
carbon nano-onions (CNOs)
C20@C60, C20@C80, C60@C180, C60@C240, C80@C240, and C240@C540 as well as
their triple-layered analogues C60@C240@C540 and C80@C240@C540 with
high-level electronic structure calculations. We were able to show
that earlier work, which showed the free rotation of the inner fullerene
in a CNO, does not extend to multilayered CNOs. We show that the likely
reason for this immobility of the outer layers is the superadditivity
of the interaction energies between individual shells, i.e., the total
interaction energy of all shells is larger than the sum of all individual
interaction energies between pairs of shells. We also show how the
electronic states of individual fullerenes are polarized but essentially
preserved in CNOs and how charge-transfer excitations between layers
arise, which are significantly red-shifted to lower absorption energies
compared to those of the free fullerenes. This allows CNOs to be utilized
as photosensitizers in nanotechnology applications.