Magnetism,Fluorescence And Photochemical Reaction Study Of Novel Endohedral Metallofullerenes

Endohedral metallofullerenes(EMFs)are fullerene molecules with atoms,molecules,or atomic clusters encapsulatedinside the cage cavity.The electron transfer and interactions between the encaged species and carbon eage endow EMFs with unique magnetic and fluorescence properties,which give EMFs great potential in the application on the quantum computing,high-density information storage,molecular devices and biomedicine research field.At present,a variety of EMFs have been successfully isolated and characterized.Systematic investigation on their structures have been carried on,while the properties of novel EMFs,especially their single molecule magnetism and fluorescence properties,needs to be further explored.The fluorescence properties of EMFs have been rarely reported and it was generally believed that EMFs do not demonstrate fluorescence in the visible region.Moreover,the current study of single molecule magnetism focus mainly on the nitride cluster EMFs,other types of EMFs remained to be further explored.Herein,in this work,the synthesis,photochemical reactions,molecular magnetism and fluorescence properties of several new types of EMFs were investigated from the following aspects:(1)Utilizing Dy2O3 as a metal source and CO2 as an oxygen source,a series of novel dysprosium-oxide cluster fullerenes DyZO@C2n(2n=72,74,80,82,88)were successfully synthesized by a modified DC arc discharge method.The molecular strutures of Dy2O@C2n(2n=72,74,80,82,88)were determined by single crystal X-ray diffraction,cyclic voltammetry,UV-vis-NIR and mass spectrometry.Compared with the reported compounds containing Dy-O bonds,the crystallographic analysis unambiguously elucidated that the Dy-O bond length in Dy2O@C2n(2n=72,74,80,82)were shorter than these reported compounds.In particular,Dy2O@Cs(6)-C82 and Dy2O@C2v(9)-C82(1.941 and 1.944 A respectively)are the shortest Dy-O bond length discovered so far.The magnetism study of Dy2O@C2n(2n=72,74,80,82)found that the size and symmetry of the carbon cage can affect the bending degree of the hysteresis loop of Dy2O cluster at 1-1.5 T and the zero-field quantum tunneling effect of Dy2O cluster.A combined study of structure,magnetism and theoretical calculation of three isomers of Dy2O@Cs2 indicated that the compact geometry of Dy2O clusters in oxide clusterfullerenes lead to both strong axial ligand field and unprecedentedly strong antiferromagnetic exchange coupling between Dy ions.(2)By using ThO2 as the metal source,a series of novel mono-metal fullerenes Th@C2n(2n=80,82,86)were successfully synthesized by DC arc discharge method,and characterized by fluorescence,UV-vis-NIR,cyclic voltammetry and mass spectrometry.The experimental results indicated that Th@C2n(2n=80,82,86)could emit fluorescence in the visible region.The positions and shapes of the fluorescence peaks of Th@C80,Th@Qv(8)-C82 and Th@C86 resemble each other,but the fluorescence intensity of them varies greatly.The fluorescence of Th@C80 are the strongest,followed by Th@C86,and then Th@C3v(8)-C82.Comparing fluorescence spectra of Th@C3v(8)-Cg2 and Th@Cg2(?,?),it was found that the fluorescence peak position and shape of Th@C3v(8)-Cs2 were different from Th@Cs2(?,?).This indicates that metal coordination environment of Th-EMFs(the change of size and configuration of carbon cage)has a great influence on their fluorescence properties.(3)For the first time,chemical derivatives of actinide based EMFs Th@C82Ad,were papered by radical photochemical reactions of Th@C3v(8)-C82 and 2-amantadine-2,3-[3H]-diazirine(C10H14N2,AdN2).These derivative are mono-addition products with three isomers,Th@C82Ad(?,?,?).Th@C82Ad(I)is a thermodynamically stable product,and Th@C82Ad(?)and Th@Cs2Ad(?)were thermodynamically not stable and would eventually isomerize into Th@C82Ad(?).Th@C82Ad(?,?,?)were characterized by UV?vis-NIR,eyclic voltammetry,mass spectrometry,X-ray diffraction and fluorescence spectra.The experimental results indicated that the addition of Ad groups on different sites have different effects on the distribution of the electron density of the carbon cage,which further affects the electronic structure of the molecule and the interaction between metal and carbon cage.The crystallographic analysis of Th@C82Ad(?)unambiguously elucidated that the interaction between Th atoms and the carbon cage becomes weaker after addition of Ad groups to the carbon cage,while Th atoms become completely ordered.The fluorescence spectra of Th@C82Ad(?,?,?)showed that the fluorescence peak value of Th@C82Ad(?,?,?)did not change compared with Th@C3v(8)-C82.But the fluorescence intensity of the three isomers enhanced one or two orders of magnitude respectively as the coordination environment of Th atoms is different from Th@C3v(8)-C82.