Introduction. The use of fluorene and its derivatives as laser-generating 1 or photoactive fluorescent materials is well-known. 2 In particular, recent interest in the synthesis of π-conjugated fluorene polymer materials with fluoren-2,7-diyl units synthesized by either palladium-3 or nickel-catalyzed 4 coupling of 2,7-dibromofluorenes has found applications in the fabrication of blue polymer light-emitting diode (PLED) devices. 5 Suzuki coupling between 2,7-dibromofluorene and 2,7dioxaborolanyl fluorene derivatives, 6 chemical oxidation of fluorenes with FeCl 3 , 7 or electrochemical oxidation of fluorenes has also been reported. 8 Intractability and insolubility are a common problem with stiff conjugated polymers with increasing conjugation efficiencies. For the polymers derived from fluorenyl units, substitution at the 9-fluorenyl positions enhances the solubility and processability of the resulting polymers. 9 The two acidic hydrogens on the 9-position are available for lithiation, and 9,9-dilithiofluorenes have been found to react readily with monobromoalkanes resulting in carboncarbon bond formation. [4][5][6] In an effort to prepare polymer materials with tethered fluorene units, we have prepared a series of polymers containing fluorene units directly attached to the polymer main chain and separated by a series of alkylene spacer units. 10 The goal is to utilize this "precursor polymer" 11 toward the synthesis of conjugated polyfluorene network species via a cross-linking reaction. 12 This poly(fluoren-9,9-diyl-alt-alkan-R,ω-diyl) polymers as we describe in this paper were obtained from a modified nucleophilic substitution reaction derived from a stoichiometric 1:1 combination of 9,9dilithiofluorene and R,ω-dibromoalkane. 10,13 Crosslinking at the 2,7-positions produced a network conjugated polymer (or oligomer) derivative achieved by chemical oxidation. The procedure involved the use of the FeCl 3 system as reported by Yoshino and coworkers. 7 To our knowledge this is the first reported systematic procedure for the synthesis of π-conjugated poly(fluorene) derivative via cross-linking of a homologous series of precursor fluorene-containing polymers. 14 Experimental Section. a. Polymerization and Characterization. 10,15,16 A typical procedure is described as follows: The initial step involves activation of the fluorene ring by lithiation. 9,9-Dilithiofluorene was prepared by the dropwise addition of n-butyllithium (9.8 mL of a 2.5 M solution, 24 mmol) to a solution of fluorene (2 g, 12 mmol) in ether (50 mL) at 0 °C, followed by stirring for 45 min. Polymerization was carried out
Electropolymerization of π-conjugated polymers is considered as an alternative method for depositing and patterning charge injection, transport, and luminescent layers in organic electronic devices. In this study, a series of novel poly(fluoren-9,9-diyl-alt-alkan-R,ω-diyl) polymers with increasing alkyl spacer lengths were synthesized and used as precursors for the deposition of conjugated polymers formed by the oxidative coupling of the fluorene units. The precursor polymers and their conjugated polymer network were characterized in solution and in film form, and their charge-transport characteristics were investigated by fabricating electroluminescent polymer light emitting diode (PLED) devices. Interesting charge carrier transport properties based on thickness and co-deposition with another precursor polymer gives the potential for optimized solid-state device performance and film processing conditions. Finally, a "two-pixel" prototype PLED was demonstrated using a sequential electrochemical co-deposition method with poly-(vinylcarbazole) (PVK).
Monolayers of oligothiophene-substituted alkylsilanes, chlorodimethyl(11-(3-(2,2‘bithienyl))undecyl)silane and chlorodimethyl(11-(3‘-(2,2‘:5‘,2‘ ‘-terthienyl))undecyl)silane, are subject to electrochemical oxidation within the monolayer to afford more highly conjugated oligomers with lower redox potentials. The electrochemical polymerization of 3-methylthiophene is promoted by monolayers of the oligothiophene-substituted silanes on the electrode surface to form smooth, highly adherent films of poly(3-methylthiophene). The effect of monolayers of an electroactive monomer on the rate of deposition of poly(3-methylthiophene) is compared to the effect of low concentrations of oligomers in solution. Chemical polymerization of 3-octylthiophene on substrates modified with the redox-active silanes gives films of poly(3-octylthiophene) which display reversible solvatochromism without dissolving the polymer. These thin films are sensitive to low concentrations of chloroform in the vapor phase or in aqueous solution.
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