Synthesis and Optical Properties of Copolymers Containing Electron Transporting 1,3,4-Oxadiazole Pendant Groups

Abstract

Well-defined copolymer, P(3,6-EHCZ-alt-MPAOXD), containing a triarylamine and N-alkylcarbazole groups (as hole transport moieties with blue emission) in the main chain and a 1,3,4-oxadiazole pendant group (as an electron transporting moiety) was synthesized by Pd-catalyzed polycondensation of N-(2-ethylhexyl)-3,6-dibromo carbazole with 2-methylphenyl-5-(4-aminophenyl)-1,3,4-oxadiazole. For comparison, P(3,6-EHCZ-alt-AL) containing a triarylamine and a carbazole groups in the main chain was also prepared. P(3,6-EHCZ-alt-AL) exhibited λ_max,UV at 309 nm and λ_max,PL in the range of blue emission at 452 nm. However, P(3,6-EHCZ-alt-MPAOXD) exhibited λ_max,UV at 283 nm with a new peak at 359 nm, and red-shifted PL emission at 506 nm, possibly attributed to the extended conjugation by 1,3,4-oxadiazole pendant group. The electrochemical results revealed that incorporation of 1,3,4-oxadiazole group in the polymer side chain provided a closely matched HOMO energy levels with hole-injecting PEDOT layer, and reduced the band gap energy level.

Keywords:

• hole transport
• N-alkylcarbazole
• 1,3,4-oxadiazole
• triarylamine

Acknowledgments

This research was supported by the Daegu University Grant, 2006.

Notes

^a Temperature measured at 5% weight loss based on initial weight.

^a Calculated from the crosspoint of UV-Vis and PL spectrum.

^b Measured by a RIKEN Keiki AC-2.

^c Estimated from the HOMO and band gap.