The influence of tetrakis-ethylhexyloxy groups substituted in PPV derivative for PLEDs

New electroluminescent polymer with tetrakis-alkoxy group, poly[2,3,5,6-tetrakis(2-ethylhexyloxy)-1,4-phenylenevinylene] (TEH-PPV), has been synthesized by the Gilch polymerization. In solid film state, the TEH-PPV exhibits absorption spectra with maximum peaks at 451 nm, and PL spectrum at 505-545 nm. As compared to MEH-PPV, TEH-PPV with tetrakis-ethylhexyloxy groups in phenylene unit can get shorter conjugation length, and had more blue shifted absorption and emission peaks due to steric hindrance, in spite of increasing the number of alkoxy substituents which may increase the effective conjugation length caused by the electron-donating effect. The polymer LEDs (ITO/PEDOT/polymer/Al) of TEH-PPV showed emission with maximum peaks at around 505-590 nm. Tetrakis-ethylhexyloxy groups induced very typical vibronically structured band in solid film state, since the conjugated backbone is twisted by steric hindrance. And they can enhance the internal efficiency of the conjugated polymer as emissive layer in PLED because of the restraint of inter-chain interaction by the avoidance of close packing to give decent device performance.