Miscellaneous Classes of Light-Emitting Polymers

In the previous sections, we described three main classes of LEP PPV, PF, and PTs, although many other conjugated and nonconjugated polymers have also been used as EL materials for LEDs. Without making an attempt to cover all types of polymers ever used as EL materials, we describe below the most important classes and the most prominent examples of EL polymers, not covered in the previous sections. Some more examples of such systems can be found in recent reviews on blue LEPs [227], polycarbazoles [571], and the general topic of organic EL materials [6,10,20]. 

Steric hindrance due to alkyl substituents increases the torsion angle between phenylene units, which results in an additional (unwanted) increase of the band gap. The emission band shifts into the violet region of the spectrum (APL 400 nm) [583]. The hypsochromic shift 

R = C7H15 474d, R = OCH3 474e, R = OCgH, 

The band gap in substituted PPPs can be tuned to some extent by diluting the substituted phenylene rings with unsubstituted phenylenes. A bathochromic shift in absorption was observed for copolymer 473 (Eg = 2.95 eV) compared to the all-substituted homopolymer 472k (Eg = 3.1 eV) [581]. Sandwiching this polymer between ITO and Ca electrodes afforded a 

A very different route to soluble PPP derivatives was demonstrated by Yoshino and coworkers [586], who introduced perfluorinated alkyl substituents into PPP 471 by reaction with perfluorobutanoyl peroxide. The resulting modified polymer 475 was soluble in common organic solvents and a solution-fabricated PLED ITO/475/Mg In emitted blue to green light (depending on voltage) with band half-width of over 200 nm. 

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