Synthesis and LED device properties of carbazole and naphthalene contained conjugated polymers

Abstract

Two new fully conjugated alternating copolymers containing both carbazole and naphthalene units were prepared through the Wittig condensation polymerization (carbazole units were linked with napthalene units by 1,4- and 2,6-linkages). The maximum photoluminescence wavelengths of 2,6-PNCPV and 1,4-PNCPV were found at 498 and 545 nm, which correspond to the greenish-blue and the yellow emission region, respectively, depending on the napthalene linkage. The turn-on voltages of 2,6-PNCPV and 1,4-PNCPV were 10.4 and 9.6 V, respectively, when the single-layer light-emitting diodes of Al/2,6-PNCPV or 1,4-PNCPV/ITO glass were fabricated. The electroluminescence spectrum of 1,4-PNCPV exhibited EL emissive band at 553 nm (yellow emission). Interestingly, the EL spectrum of 2,6-PNCPV was tailed to the longer wavelength region from the EL maximum point of 496 nm, which may be caused by formation of the intermolecular excimers. The emission color of 2,6-PNCPV was almost white to the naked eyes due to the tailing of 2,6-PNCPV emission and the weak interchain excimer peak at 750 nm. (C) 2002 Elsevier Science B.V. All rights reserved.