  We show that chemical modification of the trans-polyacetylene structure that
involves substitution of the backbone hydrogen atoms with conjugated side
groups, leads to reduction of the backbone bond alternation as well as
screening of the effective Coulomb interaction. Consequently the optical gap of
the substituted material is smaller than the parent polyene with the same
backbone length, and the excited state ordering is conducive to efficient
photoluminescence. The design of organic polymeric infrared lasers, in the
ideal long chain limit, thereby becomes possible.
