Valence bond theory of dye chemical constitutions is the most important theory of color constitutions. The various postulates of this theory are as follows.
Valence bond theory postulates
Chromophores are teams of atoms. The electrons which get in transferring from ground state to excited state by the absorption of radiation, manufacture the color. Auxochromesare teams tend to extend resonance by interacting the undivided combine of electrons on gas or atoms of the auxochromes with the π electrons of the aromatic ring. This increasing resonance will increase the intensity of absorption of sunshine and conjointly shifts the optical phenomenon to longer wavelength. Then there happens the deepening of the color. From this, it’s evident that increase in resonance should deepen the color and really it has been found to be therefore.