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

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. The Co2(CO)8‐catalyzed [2+2+2] polycyclotrimerization proceeding through transformation of internal ethynyl groups of aromatic diyne monomers is reported for the first time. The reaction yields polyphenylene‐type polycyclotrimers with tunable hyperbranched or partly crosslinked architecture. The microporosity and photoluminescence of the polyphenylenes prepared are governed by the compactness of their structure.