Green-Emitting Poly[(2-alkoxy-5-methyl-1,3-phenylenevinylene)-alt-(1,4-phenylenevinylene)s: Effect of Substitution Patterns on the Optical Properties

Green-emitting poly[(2-alkoxy-5-methyl-1,3-phenylenevinylene)- alt -(1,4-phenylenevinylene)]s ( 2 ) were synthesized via the Wittig−Horner reaction. The polymers were yellow resins with the molecular weights as high as 54 600. On the basis of FT-IR and 1 H NMR spectra, the olefins in the polymers were confirmed to be predominantly in the trans configuration. UV−vis absorption of 2 (λ max ≈ 374 − 377 nm) was about 20 nm blue-shifted from that of poly[(1,3-phenylenevinylene)- alt -(2,5-dialkoxy-1,4-phenylenevinylene)]s ( 1 ), although the chromophores in the former had the same number of alkoxy substituents as in the latter. Comparison of 2 with the model compound 7 showed that the shorter conjugation length observed from 2 (relative to 1 ) was the intrinsic property of the chromophore. Polymer 2 also exhibited a higher photoluminescence (PL) than 1 in both solution and film states, indicating the effect of the substitution pattern on the optical properties of the polymers. The vibronic structures were assigned with the aids of the low-temperature UV−vis and fluorescence spectroscopy. LED devices using 2 gave green EL output (emission λ max at 496 and 520 nm) with the external quantum efficiency of 0.082%.