Thermally stable poly(fluorene) copolymers for blue-light emission

Abstract

A variety of fluorene containing homo and copolymers have been prepared by the nickel-mediated polymerization of various dibromoarylenes. The conjugation length in a poly(fluorene) homopolymer was estimated to be approximately 12 fluorene units by absorption measurements. The electronic properties of the copolymers may be tuned somewhat by the choice of comonomer structure and composition. The formation of long wavelength excimer emission upon thermal annealing is ubiquitous among poly(fluorene) materials. This situation is exacerbated in electroluminescence studies. The incorporation of as little as 15% of anthracene attached through the 9,10-positions into the high molecular weight polymer completely suppresses the excimer formation in photoluminescence and electroluminescence. Di-n-hexylfluorene/anthracene copolymers (DHF/ANT) containing either electron donating or electron attracting substituents incorporated into the backbone show spectral shifts (red for donors and blue for acceptors) and a colorfast EL emission. The combination of both a donor and an acceptor randomly incorporated into the DHF/ANT main chain showed stable EL emission and an efficiency which exceeds that of the DHF/ANT copolymers alone.