1) The electronic energy levels of five azacyanine dyes have been calculated by the simple LCAO MO method and it is shown that the absorption of the azacyanine dyes can be fairly satisfactorily explained by this method.
2) The relationships betweeen the lowest vacant levels and the desensitizing action of dyes are discussed according to the results obtained by the above method, and it has been found that the position of the lowest vacant level of the dyes having the strong desensitizing action is about 0.7 eV lower than that of the dyes having the weak desensitizing action.
3) It is well known experimentally that the number and the position of nitrogen atoms in the chain of azocyanine dyes have intimate relation with the desentizing action of the dyes. This relation is reresonably explained by theoretical treatment.

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