Experimental and calculated (PPP) electronic spectra of flavonoid, stilbene and coumarone structures

Electronic spectra of seven hydroxy and methoxy substituted flavones as well as nine hydroxy and methoxy substituted flavoneles have been studied experimentally and theoretically with the use of the semiempirical SCF LCI PPP method. The same method has been applied to electronic spectra of some model compounds of lignin of stilbene and coumarone type. The calculated excitation energies agree well with the observed ones. Results of our experimental and theoretical studies of electronic spectra of basic chromophoric structural units of lignin are summarized from the viewpoint of their contribution to color of lignin.