Abstract: Based on B3LYP method of DFT, the geometry of pyridone azo compounds was optimized at the level of 6-311G* basis, and analyzed by NBO (nature bond orbital) method. Their visible absorption maxima were calculated with TDDFT method and ZINDO/S method, the results agreed with the observed values excellently. It was shown that the visible absorption maxima can be calculated more precisely in much shorter time with ZINDO/S method by adjusting that the value of π-π overlap weighting factor (OWF_π-π) than TDDFT method. In the process of calculation with ZINDO/S, in virtue of the method of regression it was found that the linear relationship between OWF_π-π and Z_O(the average net charge on oxygen of the two carbonyl-groups in pyridone) was excellent, OWF_π-π＝0.11425－1.04718Z_O, that is, with the drop of Z_O, OWF_π-π increased. The relationship not only could be explained in terms of quantum theory, but also could be used to predict the visible absorption maxima of other pyridone azo compounds in the same series. What′s more, the study on molecular orbital implied that the electron transition from the electron donators to electron acceptors of conjugate system resulted in their visible absorption maxima.

Key words: Pyridone azo compound, NBO, TDDFT, ZINDO/S