Development of a transition metal-free polymerization route to functional conjugated polydiynes from a haloalkyne-based organic reaction

The development of an efficient transition metal-free polymerization route has been an active research topic in polymer science owing to its low synthetic cost and decreased metal residue and hence elevated material performance in the products. In this work, we report a new such method for constructing conjugated polydiynes based on the organic reaction of 1-haloalkyne. In the presence of potassium iodide, the polymerizations of 1,2-bis[4-(iodoethynyl)phenyl]-1,2-diphenylethene (1), 1,4-bis(2-iodoethynyl)benzene (2) and 4,4′-bis(2-iodoethynyl)-1,1′-biphenyl (3) proceed smoothly in N,N-dimethylformamide at 120 °C under nitrogen, producing P1-3 consisting of alternate aromatic and 1,3-diyne moieties in moderate to satisfactory yields. While P1 possesses good solubility in common organic solvents, P2 and P3 are insoluble due to their rigid structures. All the polymers are thermally stable, losing 5% of their weight at a high temperature of up to 352 °C. A homogeneous film of P1 can be readily obtained by spin-coating its solution, which shows high and UV-tunable refractive index (n = 2.1125-1.7747) in a wide wavelength range (400-900 nm). A well-defined fluorescent photopattern can be generated by UV irradiation of the polymer film through a copper mask. This work thus opens a new avenue for constructing conjugated polymers with advanced functionalities.