Engineering of sidegroups to enhance luminescence efficiency of conjugated polymers

In the poly-phenylenevinylene (PPV) class of electroluminescent polymers, a significant loss of luminescence quantum efficiency is attributed to interchain excitations that are only weakly emissive at room temperature. We report evidence from photoluminescence studies of an alkoxy-substituted PPV derivative. MEH-PPV, of a high formation quantum yield of excimers that are nearly non-emissive at ambient temperature. The proximity of the x-conjugated polymer backbones in MEH-PPV thin films presumably facilitates excimer formation. A popular and synthetically feasible way to increase the interchain distance is through the addition of bulky sidegroups to the backbone. This methodology has been tried in the past, but without much success because the backbones need three-dimensional separation. To this end, polymers with a PPV backbone and large, dendritic sidegroups were synthesized. The addition of these bulky substituents to the backbone hinders interchain coupling and consequent intermolecular photoexcitations, such as excimers. This is evidenced by three times higher luminescence quantum yield relative to the polymer substituted with the second generation of the dendron relative to substitution of the first generation.