Towards spectrally stable polyfluorene-based materials.

摘要

An attempt at inhibiting green-emission through structural modification of polyfluorene-based (PF-based) polymers is presented. The application of well known nucleophilic and electrophilic-aromatic-substitution (S NAr and EAS, respectively) synthetic methodologies toward the preparation of unique fluorene monomers allowed for the introduction of covalently linked aromatic ether (AE) moieties to the C9 position of fluorene. In addition, the EAS methodology afforded a "one-pot" synthesis of a novel AE-containing spirofluorenexanthene (SFX) monomer. Subsequent microwave-assisted Yamamoto polymerization of AE-containing monomers resulted in thermally, oxidatively, and spectrally-stable blue photoluminescent PF-based polymers. Electroluminescence (EL) from select AE-containing PF-based polymers exhibited blue emission.Two unique fluorene-based monomers containing covalently linked AE moieties were synthesized via a CpFe+ activated SNAr methodology and subsequently polymerized to generate PF-based homopolymers via microwave-assisted Yamamoto coupling reactions. The monomers and polymers demonstrated thermal stabilities, as determined by TGA, much higher than PFO (i.e., greater than 100°C), and most importantly, the spectral emission remained stable after annealing in ambient and inert atmospheres. Polymers were annealed in an argon atmosphere at 200°C for 72 h and at 150°C in ambient atmosphere for 1 h showing no evidence of green emission. The incorporation of one polymer into PLEDs exhibited good turn-on voltages and blue electroluminescence.The results show that PFs possessing SX or AE moieties at the C9 position exhibit enhanced blue-emission stability.A unique SFX monomer, containing a covalently linked AE moiety (AESFX), and six substituted AE-containing fluorene monomers, were synthesized using an EAS methodology. Subsequent polymerization resulted in thermally, oxidatively, and spectrally-stable blue photoluminescent PF-based polymers. Their spectral emission displayed increased stability over poly(9,9'-dioctylfluorene) (PFO) after annealing in ambient and inert atmospheres. The morphological and oxidative stability of polymers were probed through annealing experiments in argon (200 to 300°C) and ambient atmospheres (150 to 300°C), respectively, for predetermined periods of time. The new polymers displayed improved blue-emission stability. The incorporation of a polymer based on AESFX into polymer light-emitting diodes (PLEDs) exhibited good turn-on voltages and blue electroluminescence.