Kim et al. have introduced silicon atoms in PPV block copolymers to confine the conjugation length and achieve blue EL materials. Copolymers 206–208 [228] and 209 [229] have been synthesized via Wittig–Horner and Knoevenagel condensation, respectively. The emission band in this series can be tuned between 410 and 520 nm, and ITO/polymer/Al PLEDs with turn-on voltages ~7 V have been reported (Chart 2.43).
Monodisperse analogs of such π-electron systems, PPV oligomers (molecular glasses), were studied by Robinson and coworkers [230]. The films prepared from 210 by solution casting showed a completely amorphous structure due to a tetrahedral structure of the molecule and OLEDs ITO/PVK/210/Al-emitted green light with an efficiency up to 0.22 cd/A ...
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