We present polarized ultraviolet (UV) absorption spectra of oriented poly (
9-hexyl-9-(2'-ethyl-hexyl) -fluorene-2, 7-diyl). Samples oriented by gel pr
ocessing in polyethylene show polarized photoluminescence and dichroism in
the near and deep UV. The spectra consist of four distinct absorption bands
with characteristic polarizations. The lowest energy band, polarized paral
lel to the draw axis, peaks at 3.3 eV. The second transition is at 5.3 eV a
nd polarized primarily perpendicular to the draw axis. There are two strong
absorption bands in the deep UV, one at 5.7 eV with polarization parallel
to the chains and the other at 6.2 eV with off-axis polarization. Electroni
c-structure calculations based on dimers of the poly(para-phenylene) repeat
unit with parameters estimated from the biphenyl spectra and supplemented
by inclusion of the Coulomb attraction between electrons and holes successf
ully predict the energies and polarizations of these spectral features. Qua
ntitative agreement of parameters that are extracted from the data indicate
s that the one-electron band structure is an appropriate starting point for
calculating the electronic structure of phenylene-based polymers. [S0163-1
829(99)08235-1].