New well-defined poly(2,7-fluorene) derivatives: Photoluminescence and base doping

Well-defined poly(2,7-fluorene) derivatives have been prepared through palladium-catalyzed couplings between various 9,9-disubstituted or 9-monosubstiiuted 2,7-dibromofluorenes and 2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-dioctylfluorene. Using this versatile synthetic method, processable polyfluorenes have been obtained in good yields. In solution, all these neutral yellow polymers exhibit blue emission (maximum of emission around 410 nm) with high quantum yields (up to 0.87). Moreover, novel acidic polyfluorene derivatives have been synthesized (i.e., poly[2,7'-(alkyl 9,9-dioctyl-7,2'-bifluorene-9'-carboxylate)]s) which show, upon base doping, electrical conductivities of 10(-6)-10(-5) S/cm. This new doping method for conjugated polymers could open the way to the preparation of air-stable electron-injecting electrodes. Both photophysical and electrical properties of these polymers are quite promising for the fabrication of efficient blue-light-emitting devices.