Polarization Spectra in Stretched Polymer Sheets. V. Excited States of Anthracene and Transition Moment Directions in Aminoanthracenes

Abstract

AbstractLinear dichroism in stretched polyethylene has been measured for anthracene and ten substituted anthracenes. The results show mixed polarization in the region of the 1La band which is best ascribed to vibronic mixing with the 1Bb band. A discussion of all available evidence for the often claimed presence of a weak 1Lb band in the region of the 1La band shows that there is no compelling reason to believe that the 1Lb state has ever been observed.A SCF‐CI PPP calculation for anthracene including systematically selected doubly excited configurations is reported and compared with presently available experimental data. Encouraging agreement is found.Orientation factors of the symmetrical molecules are simply related to molecular shape in agreement with the previously proposed orientation model. This permits an estimate of orientation factors for the unsymmetrical members of the series. This can be done in a nicely self‐consistent manner. It is found that methyl and fluoro substitution barely affects the polarization directions, while amino substitution has a large effect.Moment directions for the individual electronic transitions in the three aminoanthracenes obtained from the measurements are compared with SCF‐CI PPP calculations. The latter are used to examine systematically the effect of an electron‐donating mesomeric substituent on the anthracene spectrum as a function of its electronegativity.