Effect of the Basic Strength of Attached Groups on Light Absorption Spectra I. Light Absorption of Triphenylmethane Dyes

The electronic energy levels of typical triphenylmethane dyes, Döbner's Violet and Rosaniline, are calculated through the simple LCAO MO method. The electron densities and the bond orders in the ground states are also computed. Then, with these values of electron densities and the bond orders, the differences of the coulomb and of the resonance integrals, Δ α i and Δ β i j , respectively, as well as those between the carbon and the nitrogen atoms are taken into account and the electronic energy levels calculated above are modified by perturbation method. The differences of the coulomb integrals between the carbon and the nitrogen atoms cause profound effects to the absorption energy which amount to 23∼27 Kcal (40∼50 %), whereas those of different carbon atoms affect to the absorption only 4 Kcal (10 %). The energy levels of the various derivatives of Döbner's Violet and Rosaniline, e.g. dimethyl and diethyl derivatives of Döbner's Violet, Malachite Green, Brilliant Green, Hoffmann's Violet. Crystal Violet, Ethyl Violet etc. are also calculated by the method of perturbation. The values of the coulomb integrals of attached end groups are estimated through the basicity of the groups. The calculated absorption energies for these derivatives are compared with the observed light absorptions and it is shown that the course of the calculations is reasonable.