Theoretical prediction of the host-guest interactions between novel photoresponsive nanorings and C60: a strategy for facile encapsulation and release of fullerene.

A series of photoresponsive-group-containing nanorings hosts with 12∼14 Å in diameter is designed by introducing different number of azo groups as the structural composition units. And the host-guest interactions between fullerene C60 and those nanoring hosts were investigated theoretically at M06-2X/6-31G(d)//M06-L/MIDI! and wB97X-D/6-31G(d) levels. Analysis on geometrical characteristics and host-guest binding energies revealed that the designed nanoring molecule (labeled as 7) which is composed by seven azo groups and seven phenyls is the most feasible host for encapsulation of C60 guest among all candidates. Moreover, inferring from the simulated UV-vis-NIR spectroscopy, the C60 guest could be facilely released from the cavity of the host 7 via configuration transformation between trans-form and cis-form of the host under the 563 nm photoirradiation. Additionally, the frontier orbital features, weak interaction regions, infrared, and NMR spectra of the C60@7 host-guest complex have also been investigated theoretically.