Iridium and platinum complexes for OLEDs

The excited states generated in an organic light-emitting diode (OLED) by recombination of opposite charges may be singlet or triplet states, the latter being formed in ratios as high as 3 : 1 over the singlets. Such triplet states are normally non-emissive in a purely organic device, due to the spin selection rule. This chapter describes how phosphorescent complexes of heavy metal ions, particularly iridium(III) and platinum(II), can be used as dopants to induce emission from the triplet states, exploiting the high spin-orbit coupling constants of these elements. Design strategies for preparing highly luminescent metal complexes are discussed, together with methods for tuning the emission colour through rational structural modification. Examples of some representative blue, red and white-emitting systems are presented.