New light emitting materials: Alternating copolymers with hole transport and emitting chromophores

✍ Scribed by Min Zheng; Fenglian Bai; Daoben Zhu

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 189 KB
• Volume: 74
• Category: Article
• ISSN: 0021-8995
• DOI: 10.1002/(sici)1097-4628(19991227)74:14<3351::aid-app8>3.0.co;2-t

✦ Synopsis

A new type of novel high-efficiency light-emitting nitrogen-containing poly-(phenylene vinylene) (PPV)-related copolymers, which have hole-transfer moieties such as triphenylamine (TPA) and conjugated aromatic units such as 4,4Ј-biphenylene, 1,4-phenylene, 2,5-dimethyl-1,4-phenylene, 1,4-or 1,5-naphthylene, and 9,10-anthrylene, was designed and synthesized by the well-known Wittig-Hornor reaction. The resulting alternating copolymers were highly soluble in common organic solvents. They can spin-cast onto various substrates to give highly transparent homogeneous thin films without heat treatment. The introduction of TPA units in the PPV backbone improved processibility and limited the -conjugation length. Furthermore, the additional -electron delocalization between the lone-paired electron in the nitrogen atom and -electrons in the conjugated units contributed to the improvement of the fluorescence quantum yields of these copolymers. All these alternating copolymers except TPA-PAV have high-efficiency photoluminescence and they are very promising for light-emitting diodes (LEDs). It is very promising that TPA-PAV will emit white light when used in LED device due to the broad emission spectra. The origin of the broad spectrum is contributed by the charge-transfer complex formation, which can be proved by the absorption and emission spectra of TPA-PAV solutions. When the aromatic units were 1,4-phenylene, 1,4-or 1,5-naphthylene, 4,4Ј-biphenylene, and 9,10-anthrylene, respectively, with increase of the capability to accept electrons in aromatic units, the charge transfer from TPA to aromatic units occurred; consequently, the fluorescence quantum yield decreased. The introduction of the alkoxy-substitute group on the aromatic units in the polymer backbone caused the red shift of the absorption and emission spectra of the copolymers due to the stronger delocalization of the -conjugated system.