Theoretical studies on the optical absorption in MEH-DSB oligomer

We report theoretical studies on the optical absorption in 2-methoxy-5-(2′-ethyl-hexyloxy)-distyrl benzene (MEH-DSB). We first produce the major absorption features existing in experimental results, in particular a weak band at 5.1 eV, which has not been observed in poly(p-phenylene vinylene) (PPV). We find that this band can appear only when the strength of intersite Coulomb interactions becomes smaller, in comparison with that in five-ring PPV oligomer with no substituents. Detailed analysis of wavefunctions related to the corresponding absorption bands will give correct assignments.