Electroluminescence in conjugated polymers: Excited states in cyano-derivatives of poly(p-phenylenevinylene)

Processible conjugated polymers can be used to fabricate a range of thin-him diodes which can be designed to show good characteristics both as electroluminescent diodes and as photoconductive diodes. We highlight the improvement to the electroluminescence efficiency that can be produced by the use of two polymer layers selected so that the heterojunction between the two layers is able to confine charge and, thus, bring about electron-hole capture to generate excitons at this interface. We present results on the photophysical properties of the cyano-substituted poly(phenylenevinylene)s which provide electron transport layers in these heterostructure devices; we find evidence for strong interchain interactions (excimer formation) for the neutral excited states in these polymers, with strong red shifts of the luminescence, though preserving high photoluminescence efficiencies.