Effect of the side chain length on the optical and electrical properties of soluble PPV derivatives

2-Alkoxy-5-methoxy poly(1,4-phenylenevinylene) derivatives with different lengths of the alkoxy side chain have been synthesized via a modified Gilch polymerization. Their number-average molecular weights are in the range of 10,000-14,000. 1H NMR, 13C NMR, FT-IR spectroscopies have shown that the polymer structures are the expected ones and were free from defects. The polymers are amorphous and show good thermal stability up to 300 °C. The optical absorption band of MB-PPV, MH-PPV, MO-PPV and MDD-PPV thin films are at 496 nm, 496 nm, 494 nm and 507 nm, respectively. Photoluminescence emission maxima of the above polymers appear at 624 nm, 582 nm, 629 nm and 578 nm, respectively. A composite photoluminescence response is observed at the exception of MO-PPV showing a single PL maximum. Light-emitting diodes (LEDs) based on these polymers were fabricated and characterized by current-voltage measurements. The comparison of the optical and electrical properties of these different polymers showed a small influence of the length of the side alkoxy chain and/or to the length of the main polymeric chain.