Alternating Arene−Perfluoroarene Poly(phenylene ethynylenes)

Abstract

We report the synthesis of two poly(phenylene ethynylene)s (PPEs) with alternating dialkylbenzene−perfluorobenzene repeating units. The combination of low volume fraction of solubilizing side chains and enhanced intermolecular π−π stacking renders these materials insoluble. A soluble polymer analogue was realized by using a 1,2,4,5-tetralkoxy benzene in the place of dialkyl benzenes, and its properties are compared to a nonfluorinated analogue. The effects of fluorination and side-chain identity on supramolecular and thermal behavior were investigated by wide-angle X-ray diffraction, differential scanning calorimetry, and polarized optical microscopy. Single-crystal X-ray diffraction from small-molecule model compounds provided further insight, including indication that PPE's composed of alternating 1,2,4,5-tetralkoxy- and 1,2,4,5-tetrafluorobenzenes can assemble to close face-to-face π-stacks. Initial efforts to prepare these same polymers and small-molecule model compounds by alternate pathways are also described.