Luminescence properties of PPV-based copolymers with crown ether substituents

We present the optical properties of four poly(p-phenylenevinylene) (PPV)-based statistical copolymers, which combine monomers of highly luminescent polymers and monomers carrying crown ether side groups. The photoluminescence efficiency for films on spectrosil ranges from 28% to 52%, whereas the electroluminescence (EL) efficiency of single-layer diodes with Al cathodes reaches 0.6 cd/A (internal quantum efficiency of 1.4%). Surprisingly, the efficiency for Ca cathodes diodes is lower than for Al ones. Slight variation of the EL spectra from pixel to pixel affects all the copolymers of the family, and we consider that it is indicative of chain aggregation induced by the crown ether moieties. Studies of light-emitting electrochemical cells, LECs, based on one of these polymers show that the ion mobility induced by the presence of the crown ethers is relatively small. Typical LEC behaviour was observed upon addition of poly(ethylene oxide), with EL internal quantum efficiency reaching 2.3%.