Copolymers of 3,4-Ethylenedioxythiophene and of Pyridine Alternated with Fluorene or Phenylene Units:  Synthesis, Optical Properties, and Devices

• Published in: Macromolecules Vol. 37; no. 11; pp. 4087 - 4098
• Main Authors: Aubert, Pierre-Henri, Knipper, Martin, Groenendaal, Lambertus, Lutsen, Laurence, Manca, Jean, Vanderzande, Dirk
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.06.2004
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Polymers with particular properties; Preparation, kinetics, thermodynamics, mechanism and catalysts; Phenylene derivative copolymer; Solution polycondensation; Photoluminescence; Pyridine copolymer; Electrochromism; Electroluminescence; Experimental study; Thermal stability; Electrochemical properties; Conjugated copolymer; Optical properties; Preparation; Alternating copolymer; Phenylene copolymer; Thiophene derivative copolymer; Fluorene derivative copolymer; Optical absorption
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma030540r

We report the synthesis of four conjugated copolymers based on alkylated fluorene or phenylene units which band gap is tuned by the regular insertion of an electron-donating or electron-withdrawing unit, (3,4-ethylenedioxy)thiophene and pyridine, respectively. The (AB) n regular sequence is achieved by Suzuki polycondensation reactions. The characterization of the copolymers by size exclusion chromatography reveals chains lengths of about 20−30 repeat units (40−60 rings), leading to a good processability for potential optical applications. The 1:1 ratio between the two units improves the solubility of the material in common organic solvents, allowing for physicochemical characterizations. Raman and FT-IR experiments indicate that the electronic structure of the backbone is rather benzenic in the neutral (undoped) state, as opposed to a quinoic oxidized structure. All copolymers exhibit interesting electrochromic properties as attested by cyclic voltammetry and UV−vis experiments. They reversibly switch among the entire visible spectra, which is of particular importance for display applications. Moreover, the EDOT-based copolymers strongly absorb in the NIR window (1200 nm up to 3000 nm) with some potential electrochromic applications related to this spectral window. Light-emitting diodes were fabricated using these copolymers as active layer. To improve hole and electron injection, the active layer was sandwiched between a ITO/PEDOT:PSSA/copolymer/Ba/Al. The emitting properties were studied on the base of photoluminescence (PL) and electroluminescence (EL) experiments. The spectral emission varies from blue-green to yellow, depending on the composition of the copolymers.