KIP-Veröffentlichungen

The synthesis of unsubstituted oligo- para -phenylenes ( OPP ) exceeding para -hexaphenylene – in the literature often referred to as p -sexiphenyl – has long remained elusive due to their insolubility. We report the first preparation of unsubstituted para -nonaphenylenes ( 9PP s) by extending our precursor route to poly- para -phenylenes ( PPP ) to a discrete oligomer. Two geometric isomers of methoxylated syn - and anti -cyclohexadienylenes were synthesized, from which 9PP was obtained via thermal aromatization in thin films. 9PP was characterized via optical and infrared spectroscopy as well as atomic force microscopy and compared to polymeric analogues. Due to the lack of substitution, para -nonaphenylene, irrespective of the precursor isomer employed, displays pronounced aggregation in the solid state. Intermolecular electronic coupling leads to formation of H-type aggregates, red-shifting emission of the films to greenish. 9PP allows to study the structure-property relationship of para -phenylene oligomers and polymers, especially since the optical properties of PPP depend on the molecular shape of the precursor. [1-3] .