Designing emissive conjugated polymers with small optical gaps: A step towards organic polymeric infrared lasers

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