Electronic Spectra of Biphenyl and Fluorene

The ultraviolet absorption spectrum of diprotonated-2,7-diaminofluorene has been divided into two components polarized along the long and the short axes of the molecule by using the results of the dichroic spectra in the stretched PVA sheet. By a comparison of the experimental results with those calculated by means of a semiempirical LCAO-ASMO-SCF-CI approximation including a variable β method the assignment of the absorption bands has been made. It has been found that the compound has five absorption bands above 210 mμ. The existence of the additional 300 mμ band of fluorene has been explained theoretically by increasing the ionization potentials of the 9- and 10-carbon atoms by 3 eV from the usual value (11.42 eV).