| Double-cyanoethyl azo dyes are an important class of disperse dyes. Their molecular structures have the characteristic of amino of coupling ring with two cyanoethyls,-N=N- between the two aromatic rings, and having the conjugatedπelectron system. With the difference of substituted groups of aromatic ring, the electronic energy levels of conjugated system will have a certain differences, and then it will affect its spectral properties.In this paper, we have synthesized twelve double-cyanoethyl azo dyes by cyanoethyl reaction and diazo coupling reaction. Furthermore, we have calculated their electronic structures and absorption spectras by density functional theory (DFT) and time-dependent density functional theory (TD-DFT). The relationship between their electronic structures and their maximum absorption wavelength (λmax) was analyzed by combining experimental results and theoretical calculations.First, three double-cyanoethyl aromatic amines were synthesized by the addition reaction of aniline, m-toluidine and m-chloroaniline with acrylonitrile in the present of anhydrous AlCl3, they were N,N-2-cyanoethyl aniline, N,N-bis (2-cyanoe-thyl)-m-toluidine and N,N-bis (2-cyanoethyl)-m-chloroaniline. Subsequently, twelve double- cyanoethyl azo dyes were synthesized by diazo coupling reaction of coupling component with diazo components, which obtained by diazotizing p-nitroaniline, p-nitro-o-chloroaniline,2,4-dinitro-6-chloroaniline and 2,4-dinitro-6- bromoaniline. Their synthetic technology was explored, at the same time their structures were characterized by 1H NMR, IR, MS, elementary analysis and UV-Vis spectrum.Secondly, The geometry of three double-cyanoethyl aromatic amine coupling component and twelve double-cyanoethyl azo dyes were fully optimized by Gaussian 03, meanwhile, their frequencies were analysed. Then we gained the quantum chemical parameters, bond length, dihedral angle, the natural charge population, frontier molecular orbital energy and composition, the molecular absorption spectras were gained by the method of TD-DFT/PCM. The results showed that:1), For three double-cyanoethyl aromatic amine coupling component, C(6) of benzene ring was predicted the best site in diazo coupling reaction. Frontier orbital energy was decreased with the introduction of CH3 and Cl, the energy gap also becomes small.2), For twelve double-cyanoethyl azo dyes, the substituted groups conjugated with the benzene ring were increased with increasing of the number of substituted groups, however, the plane of molecular skeleton were lower because the space baffle effect between substituted groups, furthermore, the conjugated ofπelectron cloud of molecular skeleton were reducing. So, the molecular electronic energy levels have increases and decreases because of the conjugate effect and the space baffle effect of substituted groups. we can predict the absorption spectra red shift or blue shift.3), Frontier orbital energy was decreased with the introduction of electron withdrawing substituted groups, it was increased with the introduction of electron donor substituted groups. Frontier orbital energy gap was decreased with the introduction of electron withdrawing substituted groups on diazo ring, it was increased with the introduction of CH3 and Cl on coupling ring. The HOMO electron cloud of twelve double-cyanoethyl azo dyes was concentrated in the coupling part of the molecule, the LUMO electron cloud was concentrated in the molecular diazo part, the electron cloud moved from the coupling ring to the diazo ring when the molecular was absorbing spectrum.-N=N- played the role of a bridge.Finally, The experimental results and calculation results were deeply analyzed. The impact of different substituted groups of double-cyanoethyl azo dyes on molecular electronic structure and absorption spectras was summarized. The results showed that theλmax of experimental data and calculated data of twelve double-cyanoethyl azo dyes have a good consistency. On the diazo ring, theλmax of dye molecules turn red shift with the increase of substituted groups, on the coupling ring, theλmax of dye molecules turn blue shift with the introduction of CH3 and Cl. The correlation coefficient ofλmax was R2=0.9177 between experimental data and the frontier orbital energy gap, the correlation coefficient ofλmax was R2=0.9531 between experimental data and calculated data under the gaseous condition, the correlation coefficient ofλmax was R2=0.8187 between experimental data and calculated data under acetone. This shows that the theoretical calculation has a good guiding significance for the design of dye molecular and forecast of absorption spectrum.
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