Nanoscale Conjugated Ladder Polymers

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We will synthesize, characterize and investigate the properties of nanoscale conjugated ladder polymers with rungs based on polycyclic heteroaromatics and two or three strands (termed “side rails” or “legs”) based on arylene-ethynylene-butadiynylenes, and their respective defined linear oligomers. The compounds will be equipped with flexible side chains to guarantee their solution processability. The ladder structures are expected to be rather rigid and should exhibit interesting optical properties. They will be made by homo-polymerization of bisacetylenes (Glaser-coupling) that contain additionally two protected terminal acetylenes. After formation and end-capping of the first strand, deprotection of the remaining acetylenes allows an intramolecular zipping reaction to form the ladder structure, which is then finalized with a second end-capping reaction. The polycyclic heteroaromatic “rungs” of the ladder guarantee on the one hand the stiffness of the polymer and on the other hand, the rungs are readily accessible by a reliable amine-ketone condensation. We will investigate two different polycyclic heteroaromatic rungs that lead to distances between the ladder strands of 12 Å (using diquinoxal pyrene) and 7 Å (using phenanthrazine), respectively. The polymers are end-capped so that they do not contain free acetylenic groups. The endcap can be varied widely. We will also investigate new ladder-type endcaps that allow an intramolecular second end-capping. This will overcome the need for sensitive optimization of the zipping reaction which was necessary so far to obtain structures as free of defects as possible. We will prepare ladders with two strands and also with three strands, which are expected to be even stiffer. For all series of compounds, we will synthesize, characterize (NMR, MS, UV/Vis) and investigate (fluorescence, STM in collaboration with Dr. S.-S. Jester (UNiv. Bonn)) the polymers as well as defined oligomers. We will carry out detailed spectroscopic experiments (on the bulk and single-molecule level) as well as molecular dynamic simulations in collaboration with Prof. Grimme (Univ. Bonn) and Prof. Horinek (Univ. Regensburg) which will allow us to obtain a clear picture of the structure-property relationships with respect to the molecules’ structural, conformational and optical properties.