Synthesis and Light-Emitting Properties of New Polyfluorene Copolymers Containing 2,3-Diphenylfumaronitrile

Abstract

A series of polyfluorene copolymers composed of 9,9-dioctylfluorene (DOF) and 2,3-diphenylfumaronitrile (DPFN), poly(DOF-co-DPFN)s, have been synthesized through a palladium (0)-catalyzed Suzuki coupling reaction, and their light-emitting properties have been investigated. The synthesized copolymers were soluble in common organic solvents such as chloroform, toluene, etc and formed a uniform thin film after spin coating. As the contents of 2,3-diphenylfumaronitrile in the copolymers increases, the optical band gaps of the copolymers decreased and HOMO energy levels were also slightly lowered. The absorption and PL emission spectra of the copolymers containing DPFN units shifted to longer wavelength region than those of poly(9,9-dioctylfluorene). Light-emitting devices were fabricated using these polymers as the emissive layers in an ITO/PEDOT:PSS/Polymer/Balq/LiF/Al configuration.

Keywords:

• 2, 3-Diphenylfumaronitrile
• electroluminescence
• light-emitting diode
• polyfluorene copolymer

Acknowledgments

This research was financially supported by New University for Regional Innovation (NURI) program, and the National Research Foundation of Korea (NRF) grant funded by the Korean government (MEST) (No. R01-2007-000-20508-0).

Notes

^a Mn and PDI of the polymers were determined by gel permeation chromatography using polystyrene standards.

^b Temperature resulting in 5% weight loss based on initial weight.

^c Calculated by elemental analysis through calculation of the amount of nitrogen contained in copolymers.

^d The number represents feed mole ratio of each monomers.

^a Measured in chloroform solution.

^b Measured as thin films on fused quartz plates.

^c Determined from the onset voltage of the first oxidation potential with reference to ferrocene at 4.8 eV.