Conjugated PPVs block copolymers

Kim et al. have introduced silicon atoms in PPV block copolymers to confine the conjugation length and achieve blue EL materials. Copolymers 188-190 [215] and 191 [216] have been synthesized by 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 2.41). 

PPV derivatives and block copolymers have probably drawn more attention than any other class of r-conjugated polymers. Several surveys of PPVs have been published recently see, e.g., the recent reiew by Friend et al.34 or the chapter by Greenham and Friend in this volume.52 The most commonly used PPV is the unsubstituted, which is typically deposited by spincoating a precursor polymer, followed by thermal conversion of the precursor to PPV, and various derivatives such as 2,5-dioctoxy PPV (DOO-PPV) or MEH-PPV. Similar to Alq3, PPVs have also been used as hosts for lower-gap emitters. 

Well-defined poly(diethylhexyl-p-phenylenevinylene-b-styrene) (PPV- -PS) semiconducting block copolymers were prepared as potentially efficient organic photovoltaic devices. The original conjugated macroinitiators were synthesized from PPV and then used for chain extension with... 

For copolymers of structure I, for both types of side-chains, there is a striking similarity with the optical properties of the corresponding models the absorption and photoluminescence maxima of the polymers arc only 0.08-0.09 eV red-shifted relative to those of the models, as shown in Figure 16-9 (left) for the octyloxy-substituted compounds. The small shift can be readily explained by the fact that in the copolymers the chromophorcs are actually substituted by silylene units, which have a weakly electron-donating character. The shifts between absorption and luminescence maxima are exactly the same for polymers and models and the width of the emission bands is almost identical. The quantum yields are only slightly reduced in the polymers. These results confirm that the active chro-mophores are the PPV-type blocks and that the silylene unit is an efficient re-conjugation interrupter. 

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