Dimerization of Metallofullerenes to Obtain Materials with Enhanced Nonlinear Optical Properties.

In this work, we theoretically designed a new class of fullerene derivatives, metallofullerene heterodimers, through cross dimerization of metallofullerene monomers Li@C60 , Y@C82 and Y2 @C80 . The molecular structures, electronic structures, linear and nonlinear optical properties of the heterodimers were studied by using density functional theory calculations. We found that two fullerene cages are connected through a relatively weak carbon-carbon single bond. Inter-cage electron transfer takes place in the heterodimers because of the different electron accepting abilities of the metallofullerene moieties. The first hyperpolarizability of the metallofullerenes increases remarkably as a result of dimerization. Time-dependent density functional theory calculations reveal that the enhanced first hyperpolarizability of the dimer is associated with charge-transfer transitions. This study demonstrates that covalent dimerization is an efficient means to improve the nonlinear optical response of metallofullerenes.