Stable Blue Emission from a Polyfluorene/Layered-Compound Guest/Host Nanocomposite

• Published in: Advanced functional materials 2006-05, Vol.16 (7), p.980-986
• Main Authors: Aharon, E., Albo, A., Kalina, M., Frey, G. L.
• Format: Article
• Language: English
• Subjects: Blue-light emission; Conjugated polymers; Light-emitting materials; Nanocomposites; Polyfluorenes; Polymer nanocomposites
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.200500458

In this study a blue‐light‐emitting conjugated polymer, poly(9,9‐dioctylfluorene), is confined to the interlayer space of inorganic, layered metal dichalcogenide materials, metallic MoS2, and semiconducting SnS2. The nanocomposites are prepared through Li intercalation into the inorganic compound, exfoliation, and restacking in the presence of the polymer. X‐ray diffraction and optical absorption measurements indicate that a single conjugated polymer monolayer, with an overall extended planar morphology conformation, is isolated between the inorganic sheets, so that polymer aggregation or π–π interchain interactions are significantly reduced. Photoluminescence (PL) measurements show that the appearance of the undesirable green emission observed in pristine polymer films is suppressed by incorporating the polymer into the inorganic matrix. The blue emission of the intercalated polymer is stable for extended periods of time, over two years, under ambient conditions. Furthermore, the green emission is absent in the PL spectra of nanocomposite films heated at 100 °C for 7 h in air with direct excitation of the keto defect. Finally, no green emission was observed in the electroluminescence spectrum of light‐emitting devices fabricated with a polymer‐intercalated SnS2 nanocomposite film. These results support the proposed hypothesis that fluorenone defects alone are insufficient to generate the green emission and that interchain interactions are also required. Intercalation of a conjugated polymer, poly(9,9‐dioctylfluorene), into the galleries of layered MoS2 and SnS2 (see figure) stabilizes its blue photoluminescence and electroluminescence by inhibiting π–π stacking while preserving the planar conformation of the conjugated polymer. Results show that the appearance of undesirable green emission, as observed in pristine polymer films, is suppressed by incorporating the polymer into the inorganic matrix.