Light-Emitting Polyacetylenes:  Synthesis and Electrooptical Properties of Poly(1-phenyl-1-alkyne)s Bearing Naphthyl Pendants

Disubstituted polyacetylenes bearing naphthalene pendants with varying spacer lengths {−[(C6H5)CC(CH2)mONap]n−; P1(m) (m = 3, 4, 9), Nap = 1-naphthyl} are synthesized, and the effects of structural variations on the optical properties of the polymers are studied. The monomers are prepared by simple etherification and coupling reactions of ω-chloro-1-alkynes. Polymerizations of the monomers are effected by NbCl5− and WCl6−Ph4Sn catalysts, with the latter affording high molecular weight polymers in high yields (Mw up to 1.3 × 105 and isolation yield up to 91%). The structures and properties of the polymers are characterized and evaluated by IR, NMR, TGA, UV, PL, and EL analyses. All the polymers enjoy high thermal stability. While they start to lose weights at temperatures of ∼430 °C under nitrogen, almost no decrease in molecular weight is observed when they are annealed in air for 2 h at 200 °C. Photoexcitation of their solutions induces strong blue light emissions at 460 nm, whose quantum efficiencies are comparable to that of poly(1-phenyl-1-octyne), a well-known highly emissive disubstituted polyacetylene. No significant shifts in the emission maxima are observed when the polymers are fabricated into thin films, suggesting that aggregate formation exerts little effect on the photophysical processes of the polymers. Multilayer electroluminescence devices with a configuration of ITO/P1(m):PVK/BCP/Alq3/LiF/Al are fabricated, which emit a blue light of 464 nm with a maximum luminance of 1019 cd/m2. The device performance varies with the spacer length, with P1(4) giving the highest value of external quantum efficiency of 0.61%.