Homo- and Copolycyclotrimerization of Aromatic Internal Diynes Catalyzed with Co2 (CO)8 : A Facile Route to Microporous Photoluminescent Polyphenylenes with Hyperbranched or Crosslinked Architecture

Abstract

This study reports the first Co₂ (CO)₈ -catalyzed [2+2+2] polycyclotrimerization by the transformation of internal ethynyl groups of aromatic diyne monomers. The reaction yields polycyclotrimers of polyphenylene-type with either hyperbranched or partly crosslinked architecture. The homopolycyclotrimerization of the monomers with two ethynyl groups per one molecule, namely 1,4-bis(phenylethynyl)benzene, 4,4'-bis(phenylethynyl)biphenyl, and 4-(phenylethynyl)phenylacetylene, gives partly crosslinked, insoluble polyphenylenes. The soluble, hyperbranched polyphenylenes are generated via copolycyclotrimerization of 1,4-bis(phenylethynyl)benzene with 1,2-diphenylacetylene (average number of ethynyl groups per monomer molecule < 2). This one-step polycyclotrimerization path to hyperbranched or partly crosslinked polyphenylenes is an alternative to the synthesis of these polymers by Diels-Alder transformation of substituted cyclopentadienones. All polyphenylenes prepared exhibit photoluminescence with emission maxima ranging from 381 to 495 nm. Polyphenylenes with a less compact packing of segments are microporous (specific surface area up to 159 m² g^-1 ), which is particularly important in the case of soluble polyphenylenes because they can be potentially used to prepare microporous layers.

Keywords: internal diynes; microporous polymers; photoluminescence; polycyclotrimerization; polyphenylenes.