Modeling the dynamics of chromophores in conjugated polymers: the case of poly(2-methoxy-5-(2'-ethylhexyl)oxy 1,4-phenylene vinylene) (MEH-PPV).

By combining force-field approaches to quantum-chemical techniques, we have explored the influence of conformational changes on the nature of the lowest electronic excitations in model chains of poly(2-methoxy-5-(2'-ethylhexyl)oxy 1,4-phenylene vinylene) (MEH-PPV). The presence of conformational kinks yields a multichromophoric picture for the electronic excitations, where conjugated segments with an average length of approximately 8 repeat units are delineated by defects. This description applies to both isolated chains and to the bulk material, though very different dynamics are at play. Calculations on interacting polymer chains show that local fluctuations in the density give rise to chains that are on average more planar and thus appear as red sites. These results are discussed in light of recent single molecule spectroscopy data.