AM1 STUDIES OF PHOTOELECTRON-SPECTRA - 11 - 10-ALKYLPHENOTHIAZINES

Deep-lying pi- and sigma-orbitals of 10-alkylphenothiazines were studi ed by photoelectron spectroscopy and quantum-chemical AM1 calculations . It was demonstrated that in l0-ethylphenothiazine the lone electron pair of the S atom interacts with the pi-system of the aromatic fragme nts. The pi-MOs, whose energies are a function of the dihedral angle b etween the planes of the benzene rings of phenothiazines and are indep endent of the degree of pyramidality of the N atom, were found. The di fferences in the energy of these MOs were used for estimating equilibr ium dihedral angles of tricyclic molecules in the gaseous phase. These values differ only slightly from those observed in the solid phase. T he replacement of the hydrogen atom at position 10 by the methyl group leads to a decrease in the dihedral angle, leaving the orientation of the substituent unchanged. The orbital energies of phenothiazines, wh ich were calculated by the AM1 method, adequately reflect the order of changes in the ionization potential. However, contributions of the tw o highest occupied pi-MOs to the total charges on the N and S atoms ar e inconsistent with the experimental data.