Well-defined poly(2,7-fluorene) derivatives have been prepared through palladium-catalyzed couplings between various 9,9-disubstituted or 9-monosubstituted 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.

We report the synthesis of novel fluorene-based π-conjugated polymers and the investigation of their electroluminescent properties in organic light-emitting devices. We also report on the photo- and electroluminescence of materials of the same class whose synthesis was recently published. The alternated incorporation of phenylene or thiophene moieties in fluorene-based π-conjugated polymers leads to the tunability of the electroluminescent properties. The spectral emission varies from blue to green or yellow, depending on the composition of the copolymers. To enhance the luminous efficiency of the devices, the hole injection and hole transport into the polymer were improved by insertion of an insulating buffer layer and the incorporation of efficient hole transport material in the polymer. The insertion of a charge injection layer such as LiF and a hole transport layer such as N,N‘-diphenyl-N,N‘-bis(3-methylphenyl)-1,1-biphenyl-4,4‘-diamine significantly improves the electroluminescence efficiency of the diode from 4.5 to 125 cd/m2.

Novel amphiphilic star-shaped polymers showing pH-sensitivity were synthesized by atom transfer radical polymerization. These new polymers present a core-shell structure similar to polymeric micelles, but are inherently stable to dilution and are referred to as unimolecular polymeric micelles. A four-armed multifunctional initiator was used for the sequential polymerization of hydrophobic ethyl methacrylate and tert-butyl methacrylate and hydrophilic poly(ethylene glycol)methacrylate. Polymers of molecular weight ranging from 9000 to 20,000 were obtained. Results of dynamic light scattering showed micelle size ranging from 11 to 40 nm. Unimolecular micelles were also analyzed by static light scattering in aqueous environment. Star-shaped polymers which presented the highest molar ratio of hydrophobic monomers tended to form high molecular weight aggregates in water. Hydrolysis of the tert-butyl methacrylate units permitted the introduction of ionizable methacrylic acid functions. Size distributions were bimodal at both acidic and basic pH. Since, the polymers were designed as potential delivery systems for the oral administration of hydrophobic drugs, they were titrated to evaluate the degree of ionization as a function of pH. In the stomach, the carboxylic functions are expected to be fully protonated. However, in the intestine, the micelles will be more than 40% ionized. Fluorescence studies were conducted in order to evaluate the polarity of the micellar core. Results showed an increase in polarity with pH due to the ionization of the acid functions present along the polymer chains. The pH rise was associated with an increase in the in vitro release rate of progesterone, which was used as hydrophobic drug model.

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A series of new well-defined acidic poly(2,7-fluorene) derivatives have been synthesized by palladium-catalyzed Suzuki couplings. Upon deprotonation (i.e., base doping), these conjugated polymers generate stable polymeric anions counterbalanced by alkali metal cations. The resulting polymeric salts exhibit interesting conducting properties. For instance, base-doped poly[2,7-(9,9-dioctylfluorene)-alt-2,7-((4-hexylphenyl)fluorene-9-carbonyl)] exhibits an electrical conductivity of 10-2−10-3 S/cm in air, at room temperature. In all these polymeric systems, a strong polarization of the electrical conduction is observed which seems to indicate a significant ionic transport. These electrical properties confirm the good potential of these novel acidic fluorene-based π-conjugated polymers for the development of various electrical and electrochemical solid-state devices.