Amorphous poly-2,7-fluorene networks

Abstract

We have developed a novel strategy for the synthesis of emitters, based on amorphous poly-2,7-fluorene (2,7-PF) networks which exhibit high glass transition temperatures and good photoluminescence properties and are suitable for incorporation into multilayer lightemitting diodes (LEDs). The materials design includes nickel(0)-mediated copolymerization of 2,7-dibromo-9,9-dihexylfluorene with a tetrafunctional spiro-compound, 2,2′,7,7′-tetra-bromo-9,9-spirobifluorene, and 4-bromostyrene as end-capping reagent. The introduction of the spiro-bifluorene leads to a 90° branch of the growing 2,7-PF chain, the number of which can be controlled via the feed ratio of monomers used. The termination of the growing network with 4-phenylethenyl end groups limits the molecular weight, hence keeps the material soluble and processable. The oligomer solution can be cast into thin films and thermally cross-linked leading to new amorphous 2,7-PF networks. The amorphous 2,7-PF networks were incorporated in bilayer and trilayer LED devices which emitted colorfast blue light.