Silole-Containing Polyacetylenes. Synthesis, Thermal Stability, Light Emission, Nanodimensional Aggregation, and Restricted Intramolecular Rotation

Abstract

We synthesized three substituted polyacetylenes carrying 1,2,3,4,5-pentaphenylsilolyl (PS) pendants, i.e., −[HCC(PS)]n− (1), −{HCC[(CH2)9OPS]}n− (2) and −{(C6H5)CC[(CH2)9OPS]}n− (3), and succeeded in turning polymers 2 and 3 from weak luminophors into strong emitters by external stimuli of aggregation and cooling. The silolylacetylene monomers HC⋮CPS (10), HC⋮C(CH2)9OPS (11), and C6H5C⋮C(CH2)9OPS (12) were polymerized by NbCl5− and WCl6−Ph4Sn catalysts, which gave high molecular weight polymers in high yields (Mw up to ∼70 × 103 Da and yield up to ∼80%). The structures and properties of the polymers were characterized and evaluated by IR, UV, NMR, DSC, TGA, PL, EL, and nanoparticle size analyses. The polymers were thermally stable and lost little weights when heated to ∼350 °C. Whereas all the polymers were practically nonluminescent when molecularly dissolved, polymers 2 and 3 became emissive when aggregated in poor solvents or when cooled to low temperatures. Restricted intramolecular rotation or twisting of the silole chromophores in the solid nanoaggregates or at the low temperatures may be responsible for the aggregation- or cooling-induced emission. A multilayer electroluminescence device using 3 as an active layer emitted a blue light of 496 nm with maximum brightness, current efficiency, and external quantum yield of 1118 cd/m2, 1.45 cd/A, and 0.55%, respectively.