Synthesis and light-emitting properties of disubstituted polyacetylenes carrying chromophoric naphthylethynylphenyl pendants

Poly(1-phenyl-l-alkyne)s bearing chromophoric pendants and containing alkyl spacers (-{(C₆H₅)C= C[(CH₂) _mOCOC₆H₄C≡CN_p]}_n, - [P1(m) (m = 3, 4, 9); Np = 1-naphthyl]) were synthesized, and the effects of structural variations on the optical properties, especially electroluminescence, of the polymers were investigated. The monomers were prepared in high yields by esterification and coupling reactions of n-phenyl-(n - 1)-alkyn-1-ols. Selective polymerizations of the 1-phenyl-1-alkyne unit of the monomers were effected by WCl₆-Ph₄Sn catalyst, affording polymers with high molecular weights (M_w up to 63 000) in high yields (up to 83%). Structures and properties of the polymers were characterized and evaluated by IR, NMR, TGA, UV, PL, and EL analyses. All the polymers are thermally very stable, losing almost no weight when heated up to 400°C. Photoexcitation of the polymer solutions induces strong blue light emission at 460 nm, with quantum yields up to 98%. No aggregation quenching was observed when the polymers were fabricated into solid films. Multilayer EL devices with the configuration of ITO/P1(m):PVK/BCP/Alq₃/LiF/Al were fabricated, which emitted blue light with luminance up to 498 cd/m². The device performance varied with the spacer length (m), with P1(4) giving the highest external quantum efficiency of 0.47%. The value was further enhanced to 0.86% by optimizing the layer thickness and inserting a hole-injection layer.