Electronic Spectra of Phenanthrene Derivatives. Effect of Substitution

During the course of studies on the spectral regularities of linear conjugated systems bearing aromatic terminal groups (cf Tetrahedron Lett., 1964, 719; ibid., 1968, 1121; This Bulletin, 39, 2320 (1966); ibid., 40, 340 (1967)), we found that the free electron model (FEM) cannot explain the effect of substitution on the electronic spectrum of phenanthrene. In order to get further information the electronic spectra of forty-eight phenanthrene derivatives each bearing a substituent at 2-, 3-, or 9-positions have been examined, and it was found that the electronic spectra of these derivatives also cannot be explained on the basis of FEM. SCF-MO-CI calculation has been carried out on phenanthrylpoly-ynes and hydroxyphenanthrenes revealing that the discrepancy between the observation and the expectation from FEM in the behavior of La and Lb of phenanthrene derivative is attributable to a complex configuration interaction.