Intermolecular hydroarylation of alkynes under Brønsted acid catalysis: enabling metal-free access to arylidene-vinylidene polymers

Semi-conducting π-conjugated polymers are key organic materials for the development of low-cost optoelectronic devices and for renewable energy production. Such polymers are obtained through metal-based catalyzed crosscoupling routes and usually rely on complex protocols by resorting to costly and hardly removable catalysts. In addition, residual metal traces can affect optoelectronic performances, hence numerous and often tedious purification steps are required. It is thus highly desirable to develop versatile, alternative synthetic approaches to semi-conducting polymers. The aim of this work is to develop new synthetic methodologies to arylidenevinylidene polymers using metal-free organocatalysis. We focused on the synthesis of regio-/stereo-regular PPV-like polymers obtained via Brønsted acid catalyzed intermolecular hydroarylation reaction and the optimization of the reaction conditions to obtain polymers with controlled structure and suitable optoelectronic properties for the aimed applications. Original polymers with arylidene-vinylidene repeating units are targeted with the possibility to tune their optoelectronic properties, by playing on the planarity of the chain, the nature of the substituents, the regio- and stereo-selectivity to use them as active materials in organic electronics. DFT calculations on one of the most promising polymers showed excellent agreement with experimental findings and revealed the p-type character for the material, with conformationally-limited conjugation explaining the convergent optical properties even at a short chain length.