Anthryl-based poly(phenylene ethynylene)s: Tuning optical properties with Diels-Alder reactions

Soluble anthryl-based conjugated poly( phenylene ethynylene)s (PPEs) have been synthesized using palladium-catalyzed Sonogashira-Hagihara cross-coupling polymerization reactions. Molecular weights up to 3.5x10(4) g center dot mol(-1) were obtained, making them suitable for spectroscopic solution characterizations and thin film processing. The selective reactivity of these polymers as multidienes has been successfully demonstrated with strong dienophiles. Diels-Alder reactions proceed cleanly to completion with unhindered dienophiles such as N-alkylated maleimide derivatives. TGA analysis revealed thermal retro-Diels-Alder reactions at modest temperatures around 210 degrees C. Compared with their parent polymers, the cycloadduct polymers exhibited dramatic hypsochromic shifts of their emission and absorption maxima up to 80nm along with a considerable quantum yield enhancement. These original anthryl-based polymers appear attractive as reactive conjugated materials whose optical properties can easily be tuned with quantitative Diels-Alder reactions.