Theoretical Study On Structure And Nonlinear Optical Properties Of Isomeric Molecules With Different Bond

The structure of molecule is dramatically entwined with the properties.Therefore,the change of structure of molecule present a dramatically influence for the bonding,the structure of electronic and so on.Furthermore,affect the properties of molecules.In my work,we employed density functional theory(DFT)to investigated their structures,bonding,electronic and NLO properties.The main contributions are as follows:1.In 2006,the interesting ?-stacks diradical 1,1?-bis(verdazyl)ferrocene(20)with two-electron multicenter(2e/mc)bonding were synthesized and investigated(J.Am.Chem.Soc.2006,128,690-691).Excepting the 20(with two facing radicals),two attractive isomeric complexes(319 and 4144)are obtained by a piece of radical rotating along iron-Cp axis about 19° and 144°,respectively.Among these three diradicals,due to the overlap of SOMOs of the two pieces of radicals,a unique two-electron eight-center(2e/8c)?–? bonding is obtained in the 20,the 319 has a ?-covalent bonding,and two separate radicals are shown in the 4144.Further,the UV-visible absorption spectrum of 20 and 319 arise a new absorption feature at 566 and 530 nm,respectively.However,this absorption feature not exist in experimental UV-visible absorption spectrum.Fortunately,the UV-visible absorption spectrum of 4144 is similar to experimental results,which demonstrate that the 20 with 2e/8c bonding may transform to be 4144 with two separate radicals in solution.These work demonstrate that three diradicals may transform to each other in some environment,which is beneficial to understanding their magnetic properties in solution and crystal and designing new complexes with excellent magnetic property.2.In 2009,the interesting photochromic complex [Au{4,5-bis(2,5-dimethylthien-3-yl)-1,3-dimethylimidazol-2-ylidene}(cbz)](o-Me CN)and its isomeric close form(c-Me CN)were synthesized and investigated(J.Am.Chem.Soc.2009,131,912-913),which would transform to each other according to the characterization of UV and visible irradiation.Based on this work,we optimized its structure in acetonitrile solvent.Superisingly,we found that The first hyperpolarizability(?tot)of c-Me CN is about 12 times as large as that of o-Me CN,which provide a basis for NLO switch.Further,the UV-visible absorption spectrum of c-Me CN arise a new absorption feature at 569 nm,which may be assigned to photochromic process gives a more extended ?-conjugation,and this absorption feature is well corresponding to experimental results.Therefore,the UV-visible absorption spectrum can confirm that the remarkable ?tot values for c-Me CN are mainly attributed to the charge transfer induced by the photocyclization.Significantly,we investigate the solvent effect on NLO switch.Results show that the ?tot values reduced with the increasing of dielectric constant ? of the solvent,and the differences of ?tot values between the open and close form,present a regularly change in different solvents.Therefore,changing solvent is effective to regulate the strength of NLO switch.This reversible photochromic process and solvent effect may open up new opportunities for the discovery of attractive NLO switch.