Density matrix renormalization group study of conjugated polymers with   transverse pi-conjugation
  We report accurate numerical studies of excited state orderings in long hypothetical pi-conjugated oligomers in which the hydrogen atoms of trans-polyacetylene are replaced with conjugated sidegroups, within modified Hubbard models. There exists a range of the bare Coulomb repulsion for which the excited state ordering is conducive to photoluminescence in the substituted systems, even as this ordering is opposite in the unsubstituted polyenes of the same lengths. Our work provides motivation to study real pi-conjugated polymers with transverse conjugation and small optical gaps. 
Y. Yan, S. Mazumdar