Preparation And Properties Of Azo Organic Thin Films And Single Crystals

Nonlinear optical?NLO?materials are significant for the development in the field of optical switching due to their large third-order nonlinearity and short response time,which has attracted the attention of researchers.With the study of nonlinear materials,it has been found that azobenzene and its derivatives present large third-order nonlinearity.At present,the research study the synthesis of azo dyes and the properties of azo dye solutions.Based on the research value and practicability of azo dyes,it is very important to study the preparation and analyzed the third-order nonlinearity of azo dye films and single crystals.The third-order nonlinear properties of azo dyes increase with the electron-withdrawing ability of functional groups.Three kinds of azo dyes were selected,namely:N,N-dimethyl-4-[?4-nitrophenyl?diazinyl]aniline?azo1?,4-[?4-chlorophenyl?diazinyl]-N,N-dimethylaniline?azo2?,4-?n,n-dimethyl amino?azobenzene-4'-isothiocyanate?azo3?respectively.In this work,three azo dye thin films were prepared by vacuum vapor deposition method on Al₂O₃ single crystal substrate,we successfully grown4-chloro-4-dimethylaminoazobenzene?azo2?single crystals by slow solution evaporation.The optical properties of azo dye films and single crystals were analyzed by UV-visible spectroscopy and Z-scan test techniques,respectively.The main results are as follows:1)The study found that the planarity of the azo3 film is better,and The deposition rate of the film will suddenly increase;the ultraviolet-visible spectrum of the azo1 film is hypsochromic shift by 61 nm from the azo1 solution;The azo1,azo2 and azo3 films values of fundamental energy gap(E_g^opt)are 2.67 eV,2.83 eV,and 3.01 eV,respectively;The Z-scan test results show that the azo1,azo2,and azo3 films exhibited saturated absorption and self-focusing effects,respectively.The calculation results also suggested that the third-order nonlinear polarizability?^?3?of the three films azo1,azo2,and azo3 are 7.95*10^-8?esu?,7.65*10^-8?esu?and 6.52*10^-8?esu?,respectively.The results also suggested that D-?-A?electron donors,D and electron acceptor,A?molecules with the stronger electron-accepting?nitro?substituent present better nonlinearity,which is the same as expected.2)Single crystal of 4-chloro-4-dimethylaminoazobenzene were grown with dimensions up to25*12.5*12 mm³ from methylene chloride solvent by slow evaporation method.The structure of the single crystal was measured by the four-crystal single crystal diffractometer,X-ray diffraction and infrared Raman spectroscopy,respectively.The results indicate that the single crystal belongs to the orthorhombic system,and the space group is Pn21a.The optical band gap(E_g^opt)of 4-chloro-4-dimethylaminoazobenzene?azo2?single crystal is about 2.17eV;the third-order susceptibility(?^?3?)of azo2 reached the order of 10^-7?esu?,the results suggested that the single crystal?azo2?present excellent third-order nonlinearity.Three azo dye films and azo2 single crystals have better third-order nonlinearity;and the preparation of thin films and crystals is simple,low cost,and easy to process,it can be applied to all-optical switch applications.