Silole-containing linear and hyperbranched polymers: synthesis,thermal stability,light emission,nano-dimensional aggregation,and optical power limiting

Linear polyacetylenes and hyperbranched polyphenylenes carrying 1,2,3,4,5-pentaphenylsilolyl (PS) pendants are designed and synthesized. Homo-polymerization of HC≡CPS, HC≡C(CH₂)₉OPS, and C₆H₅C≡C(CH₂)₉OPS and (co)polycyclotrimerization of (HC≡C)₂PS with 1-octyne are effected by NbCl₅-, WCl₆-, MoCl₅-, and TaCl₅-based catalysts. High molecular weight linear ( 1-3 ) and hyperbranched polymers (6) are obtained in high yields (M_w up to ∼70 × 10³ and yield up to 85%). All the polymers are thermally stable, losing little weight when heated to 350°C. Whereas all the polymers emit faint light when molecularly dissolved, polymers 2 , 3 , and 6 become emissive when aggregated in poor solvents or when cooled to low temperatures. Restricted intramolecular rotations of the phenyl rings upon the axes of the single bonds linked to the silole cores may be responsible for the aggregation- or cooling-induced emission. A multilayer electroluminescent device using 3 as an active layer emits 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. Polymers 6 are non-linear optically active and strongly attenuate the optical power of intense laser pulses, whose optical limiting performances are superior to that of C₆₀, a best-known optical limiter.