Absorption Spectra of Dyes. IX. Electronic Spectra of a 1 : 1 and a 1 : 2 Complex, and CT-Bands

Abstract

1) The absorption spectra of binary mixtures of Chrysophenine G (notation: G) and disazo dyes (P), which were the same as those used in a preceding study,1) have been measured at room temperature (ca. 20°C), and the characteristic spectra of the complexes have been determined by using the equilibrium constants, K1 and K2, previously obtained (at 20°C) for the 1 : 1 (PG) and 1 : 2 (PG2) complex formation. 2) The absorption spectra of the PG and PG2 complex have been compared with the respective corresponding additive spectra (P+G and P+2G), and the correlations among these spectra have been discussed in detail. 3) The MO pattern of the G molecule has been decided empirically by applying Platt’s theory; similarly, that of the P molecule has been decided by assuming that there is at least one symmetry species; then the spectral change caused by the complex formation could be explained in relation to the MO’s of the component molecules. 4) It has been confirmed that there exists an intermolecular charge transfer from P as an electron donor to G as an acceptor. It has also been shown that the first band of a disazo dye (P) consists of two electronic transitions; one is a π→π*(shorter wavelength) and the other an l→π* transition (longer wavelength).