Study On The Relationship Between Dye Conformation And Properties

Based on Hyperchem and Gaussian program, the important properties of some kinds of dyes, such as maximum visible absorption wavelength, half band-width and reactivity are studied by quantum chemical methods.In the study of maximum absorption wavelength, with the optimized geometry obtained by B3LYP/6-311G*, the visible absorption wavelength of azobenzene compounds, pyridone azo compounds, amino pyrimidine compounds and thiazole heterocyclic azo compounds are calculated by TD-DFT method and ZINDO/S method. By setting OWF_π-π(π-π Overlap Weighting Factor) at an appropriate value, better results could be obtained by ZINDO/S method in much shorter time than TD-DFT method. In the calculation of maximum absorption wavelength by ZINDO/S method, it is found that, for azobenzene compounds, there is an excellent linear relationship between OWF_π-πand BL_N-N(the length of azo bond);for pyridone azo compounds, there is an excellent linear relationship between OWF_π-π and Z_O(the average net charge on oxygen of the two carbonyl-groups in pyridine);for amino pyrimidine derivatives, there is also a good linear relationship between OWF_π-π and α(the include angle between azo ring and pyrimidine ring);and for thiazole heterocyclic azo derivatives, there is a good linear relationship between OWF_π-π and Z_S(the net charge on sulfur in thiazole heterocycle). Further study indicates that the relationships obtained above could be extended to the prediction of visible absorption wavelength of other compounds in the same series.The research on molecular orbitals indicates that the maximum absorption wavelength of azobenzene compounds, pyridone azo compounds, amino pyrimidine derivatives and thiazole heterocyclic azo derivatives are all in accordance with the electron transiton from HOMO (the Highest Occupied Molecular Orbital) to LUMO (the Lowest Unoccupied Molecular Orbital). In view of the component of the orbitals, the transition is from regions around electron donators to those around electron acceptors.In the research of absorption half band-width, for azobenzene compounds, pyridone azo compounds, and amino pyrimidine compounds, based on the ground state geometry optimized by B3LYP/6-311G* method and the excited state geometry optimized by CIS/6-311G* method, the maximum absorption wavelength (X max) and emission wavelengths (A. *max) are calculated by TD-DFT method respectively. It is found that a good linear relationship between S (the difference between A. *max and ^ max) value and A X 1/2 (the observed absorption half band-width). Further study indicates that the relationships obtained above could be extended to the prediction of absorption half band-width of other compounds in the same series.In the research on the reactivity of reactive dyes, it is found that the dyeing reactivity could be approached through the study of the hydrolytic reactivity because of their similarity in reaction mechanism.Based on the geometry optimized by B3LYP/6-311G*, the configuration parameters and orbital parameters of a series of vinyl sulfone reactive dyes and triazine reactive dyes are obtained. Then these parameters are screened by Stepwise Regression method regarding Ink (the natural logarithm of hydrolysis rate constant) as the objective function, and the Partial Least Squares method is used to construct the QSPR equation. Using the equations obtained above to predict the hydrolysis reactivity of other compound in the same series, results agreement with the experiment data could be obtained. These equations could also be used to predict the hydrolysis reactivity of the dyes with two or more active groups and mixed dyes and to design of new type dyes.The accurate prediction of maximum visible absorption wavelength and absorption half band-width could, on one hand, reveals the relationship between molecular structure and absorption spectroscopy, and on the other hand, offers a theoretical basis for the design of dye molecules, and gives assistance in the analysis of dye samples. To further study the dyeing performace of reactive dyes and to exploit more new excellent reactive dyes, the QSPR study of the reactivity is of great significance.