Conjugated polymers in an arene sandwich.

A series of poly(p-arylene butadiynylene)s containing zero, one, and two co-facial pi-pi interactions per repeat unit were synthesized and characterized. A surprisingly selective and high-yielding Diels-Alder cycloaddition of anthracene and nonsymmetric, sterically hindered anhydrides proved essential to generating the cofacial arene-containing monomers. Single-crystal X-ray structures display nearly parallel cofacial arenes that are within the van der Waals contact distances. The precursor molecules with cofacial arenes undergo reversible one- and two-electron oxidations to the radical cation and dication in CH2Cl2. The anhydrides were converted to N-alkyl imides to increase the solubility. High-molecular weight poly(p-arylene butadiynylene)s were prepared via Pd/Cu(I)/benzoquinone oxidative coupling of the diacetylene monomers. The resulting polymers are highly emissive in solution and thin films. The ionization potentials were measured using ultraviolet photoelectron spectroscopy with thin films. Last, fluorescence measurements of polymer thin films during continuous irradiation indicate that the most hindered polymer is more resistant to photobleaching.