DMRG study of pi-conjugated polymers with additional pi-conjugation in the transverse direction

The excited state ordering in trans-polyacetylene is not conducive to light emission: the 2A$_g$ occurs below theoptical 1B$_u$ in this system, and the excited 1B$_u$ rapidly decays to the 2A$_g$, radiative transition from which to the ground state is forbidden. It has been suggested that systems which have the same backbone pi-conjugation as linear polyenes, but which also have transverse pi-conjugation with finite extent, will simultaneously have small optical gap and excited state ordering that allows light emission. To verify this prediction, we have carried out DMRG calculations within a Hubbard Hamiltonian for a hypothetical simplified polymeric structure. The critical Hubbard U at which the 2Ag occurs below the 1Bu is larger in the subtituted polymer than in the unsubstituted linear polyene of the same length. Our results introduce the possibility of synthesizing conjugated polymers that will emit in the IR.