Study On The Relationship Between Dye Conformation And Absorption Spectroscopy

In order to improve the prediction accuracy of the absorption spectroscopy of dyes by ZINDO/S method, a new idea was introduced in this thesis, that is, OWF?(the simplification of π-π overlap weighting factor', one of the adjustable parameters in ZINDO/S method) was considered as a measurement of the conjugation extent of a molecule, rather than a certain fixed value applicable to all molecules. For compounds of the same kind, firstly, the value of OWFπ-π was so determined that the calculated absorption maximum could coincide with observed ones well, then, the method of regression was used to reveal the relationship between OWFπ-π and molecular conformation parameters.The results of this study showed that the primary conformation parameter affecting OWFπ-πwas different for different kinds of molecules. According to this study, OWFπ-πwas affected by the following conformation parameters. (1) The angle between diazo component and coupling component affected OWFπ-πgreatly for some azobenzene derivatives, aminopyrimidine derivatives and some reactive dyes, in this instance, OWFπ-π decreased linearly with the increase of the angle. (2) The charges on the substituents affected OWFπ-π greatly for some azobenzene derivatives, pyridone derivatives, nitrodiphenylamine derivatives, some reactive dyes and 1, 4-diamino anthraquinone derivatives, in this instance, OWFπ-π changed linearly with the change of the charges. (3) The length of certain bond(s) and the number of conjugate double-bond affected OWFπ-π greatly, OWFπ-π changed linearly with the change of bond length (for planar azobenzene derivatives and cyanine derivatives) and the change of conjugate double-bond number (for conjugate alkene, p-carotene and lycopene). (4) The type and position of substituents affected OWFπ-π greatly for naphthoquinone and anthraquinone derivatives. (5) The charges on coordinated bonded nitrogens and the electronegativity of central atom affected OWFπ-π greatly for phthalocyanine compounds, OWFπ-π increased linearly with the increase of the charges and the electronegativity. All the above phenomena could be explained in terms of quantum chemistry. In this study, it was also shown that the absorption half-bandwidth could be predicted roughly according to the relationship between OWFπ-π and molecular conformation parameters.In conclusion: (1) It is appropriate to consider OWFπ-π as a measurement of the conjugation extent of amolecule and it is feasible to predict the absorption half-bandwidth and absorption maximum of complex dyes according to the relationship between OWFπ-π and molecular conformation parameters obtained from simple molecules of the same kind. Consequently, a new thought to improve the prediction accuracy of the absorption spectroscopy is presented in this dissertation.(2) There is indeed some relationship between OWFπ-π and molecular conformation parameters. The obtained relationship not only could be explained in terms of quantum chemistry, but also could be extrapolated in the same series of molecules. Therefore, the prediction accuracy of absorption spectroscopy could be improved evidently.(3) The accurate prediction of absorption spectroscopy could on one hand, reveal the relationship between molecular conformation and absorption spectroscopy, and on the other, offer a theoretical basis for the design of dye molecules. Furthermore, it could also give assistance in the analysis of dye samples.