Polyfluorene-based light-emitting rod-coil block copolymers

Abstract

A series of novel well-defined polyfluorene-based rod-coil copolymers have been synthesized for application in light-emitting diodes (LEDs). These polymers were prepared by using polyfluorene macroinitiators to initiate the atom transfer radical polymerization of 2-(9-carbazolyl)ethyl methacrylate (CzEMA). The incorporation of CzEMA block successfully created energy transfer, and the findings showed that intramolecular energy transfer dominates in solution while intermolecular energy transfer plays a more important role in solid state. It was also demonstrated that energy transfer is more efficient for the block copolymers with respect to the corresponding polymer blends. Better spectral stability has been demonstrated with these copolymers in comparison to PF homopolymer through annealing studies. Interesting self-assembled nanostructures were observed for these polymers, which is dependent on the polymer composition. Electrochemical characterization indicated that the presence of the carbazole effectively raises the HOMO level with respect to the polyfluorene homopolymer, suggesting better hole injection properties. Preliminary LED experiments with these polymers indicated enhanced device performance compared to polyfluorene (PF) homopolymer. The results implied that rod-coil block copolymers with optoelectronic functionality are promising candidates for blue LED applications in terms of the suppression of green emission. © 2005 American Chemical Society.