| It has become a hot research topic to looking for high performance nonlinear optical(NLO) materials due to their application in fields of optics, electronics and medicine. In recentyears, many scientists dedicated to exploring methods to improve the nonlinear opticalresponse of material. The fullerene is fascinating molecule with lots of conjugated doublebonds. At present, scientists focus on studying moderate size of fullerene such as C60-C84,because its interior has a large cavity can be embedded atomic, molecular and metal clustersforming kinds of endohedral fullerene. Fullerene stability is determined by the IPR rule, whenthe fullerene with adjacent pentagons is contrary to IPR rule, their structure is unstable.Therefore, it is very necessary to stabilize non-IPR fullerene through the appropriatemodification. In addition, chemical modification of fullerene also can improve their physicaland chemical properties, which can expand the application of fullerene derivatives. Whenappropriate groups are in added fullerene molecule, the symmetry of fullerene derivativeschange, charge redistribute and nonlinear optical response significantly improve. In this work,the quantum chemistry calculation methods were used to study the geometry of fullerenederivatives, molecular interaction and nonlinear optical properties.In this paper, a series of fullerene derivatives with special physical and chemicalproperties were designed in theory, and they can be divided into two aspects, as follows:1. C2v-C60and halide C60Cl8system were chosen for this study, we research the electronicproperties, the NBO charge and the first hyperpolarizabilities (βtot) of C60(C2v) and C60Cl8(C2v).After the Stone–Wales transformation and chlorine addition reaction, the βtotvalues slightlyincrease from0for C60(Ih) to60au for C60(C2v) and502au for C60Cl8(C2v), respectively. Tofurther enhance the first hyperpolarizability, the endohedral fullerene derivative Li@C60Cl8,which was formed by encapsulating a lithium (Li) atom inside the C60Cl8, has been designed.Interestingly, the electron transfer between Li and C60Cl8leads to an extremely large βtotvalueof25569au, which is larger (51times) than the502au of C60Cl8. It shows that theencapsulated Li plays an important role in enhancing the first hyperpolarizability. we hope theLi@C60Cl8can be considered as a candidate for high-performance nonlinear optical materials. 2. Cs-C72(10528) is a non-IPR fullerene with two pairs of adjacent pentagon, and the Sc2Sis a V-shaped polar molecule, which is unable and cannot exist under laboratory conditions.However, when the Sc2S molecule was encapsulated into Cs-C72(10528), a stable endohedralfullerene Sc2S@Cs-C72(10528) was obtained. Then, we focus on the interaction between thepolar molecule M2N with C72, and which properties of will be influenced by this interaction.Thus, four encapsulated metallic fullerenes (EMFs) M2N@C72(M=Sc, Y and N=S, O) alongwith pristine Cs-C72(10528) were investigated by quantum chemistry methods. The resultsshow that the the Egap(3.01-3.14eV) of M2N@C72are greater than that of pristine Cs-C72(10528)(2.34eV). It indicates that the stabilities of these EMFs increase by encapsulatingV-shaped polar molecule into the fullerene. Furthermore, the natural bond orbital (NBO)charge analysis indicates electron transfer from M2N to C72cage, which plays a crucial role inenhancing first hyperpolarizability (βtot). The βtotvalues follow this order:1174au (Y2O@C72)≈1179au (Sc2O@C72)>886au (Y2S@C72)≈864au (Sc2S@C72)>355au (C72). It means thatthe βtotof M2N@C72is more remarkable than that of pristine Cs-C72(10528) due to theinduction effect of the encapsulated molecule. Compared with sulfide cluster fullerenes(Y2S@C72and Sc2S@C72), oxide cluster fullerenes (Sc2O@C72and Y2O@C72) show muchlarger βtotdue to the small ionic radius and large electronegative of oxygen. |
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