Second-Order Nonlinear Optical Response of Electron Donor - Acceptor Hybrids Formed between Corannulene and Metallofullerenes

A charge transfer (CT) complex was formed between C20H10 and Li+@C-60 in the ground state by the concave-convex pi-pi CT interaction. Herein, the structures, binding interactions, electronic absorption spectra, and first hyperpolarizabilities of a series of Li+ and Li atom in contact with C-60 have been explored with density functional theory methods. It is found that independent of the doping position, doping Li atom can significantly narrow the wide gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) (E-gap = 2.82 eV) of the pure C20H10/C-60 in the range of 0.86-0.99 eV. Among them, the Li-doped outer isomer C20H10/LiC60 can exhibit the intriguing n-type characteristic, where a high energy level containing the excess electron is introduced as the new HOMO orbital in the original gap of C20H10/C-60. Furthermore, the diffuse excess electron also brings C20H10/C-60 the considerable first hyperpolarizability, which is 3.53 X 10(-29) esu. When Li+ and Li were encapsulated into the C-60 cage, inner complexes C20H10/Li+@C-60 and C20H10/Li+@C-60 of enhanced static first hyperpolarizabilities (5.39 and 2.13 X 10(-29) esu, respectively) are also delivered due to that encapsulated Li+@C-60 and Li@C-60 show enhanced electron acceptability as compared to pristine C-60, leading to more obvious intermolecular CT transitions. From a certain point of view, such systems can be considered as high-performance NLO materials that combine the basic characteristics of a classical donor-acceptor superstructure and systems with cations and easily polarizable excess electrons.