| In recent years,nonlinear optics(NLO)materials have been widely used in alloptical switching,signal processing and ultra-fast optical communication due to their remarkable optical nonlinear properties and short response time.In particular,the research of organic NLO materials with ?-conjugated molecules with a clear structure has attracted more and more attention.This is not only because of their high NLO performance,but also because of their flexible design and unique functional molecular structure.The combination of donor-acceptor(D-A)molecular crystals and physical/chemical properties of material has been widely developed for its application in NLO.Azobenzene as the terminal electron donor(D)and acceptor(A),different types of push-pull electron groups were introduced into the benzene ring of azobenzene by design to connect to the ?-conjugation system to form the D-?-A structure,and this class of organics would exhibit more excellent nonlinear performance.In addition,azobenzene is a common photosensitive group,which can undergo reversible cis-trans isomerization under the irradiation of specific wavelengths of ultraviolet light.This may alter the electron cloud distribution in the compound,thereby affecting its thirdorder NLO properties.The metal-organic complex is a new type of inorganic and organic hybrid material,which has the characteristics of large NLO coefficient,short optical response time,easy combination and cutting of organic compounds and good thermal stability of inorganic materials.If the designed and synthesized azobenzene organics are combined with metal ions to synthesize new metal-organic complexes,it will be one of the excellent candidates for the study of third-order NLO.The main research contents of this paper are as follows:(1)We synthesized three one-dimensional chain coordination compounds([Mn(L)(H2O)4]n(1),[Zn(L)(H2O)2)]n(2)and[(Cd(L)(H2O)4]n(3))using an organic ligand containing azophenyl groups for third-order NLO tests.Z-scan results show that they all have good third-order NLO performance.Due to their relatively similar structures,we discussed the influence of metal ions on the third-order NLO performance.The introduction of metal ions can effectively reduce the energy gap and promote the electron delocalization of the whole molecule,so that the nonlinear response signal of complex 1 is the strongest,and that of complex 3 is the weakest.The results of DFT calculation show that complex 1 has the narrowest energy band,larger electron delocalization,and the best third-order NLO performance.Through the study and comparison of the third-order NLO properties of the three complexes,a new idea is provided for the design and synthesis of NLO complex materials.(2)A novel photoresponsive compound 5-((4-(phenyldiazenyl)phenoxy)methyl)isophthalic acid(H2L)was synthesized.Four coordination compounds were designed and synthesized by hydrothermal synthesis using the ligand H2L,which were[ZnL]n(4),[CdL(H2O)(DMF)]n(5),[CdL(H2O)(DMA)]n(6)and[CuL(4,4'-azobpy)]n(7),respectively.And all compounds were prepared into PVA based film materials.Interestingly,the third-order NLO properties of the compounds are different in solution and films,which is consistent with our prediction.The dynamic dihedral angle between azobenzene and phenoxy group plays a promin ent role in the RSA of the com pound,while the restricted dihedral angle gives the SA of the film material compounds.The effect of dihedral angle is also reflected in the NLO properties of light response:compounds still show RSA and conver sion to self-defocusing effect,while th ose of thin film materials still show SA and conversion to self-defocusing effect.T his study not only provides a new idea for exploring the generation mechanism of third-order NLO properties,but also greatly expands the application fields of NLO materials. |
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