Luminescent Ionic Transition-Metal Complexes for Light-Emitting Electrochemical Cells

Higher efficiency in the end-use of energy requires substantial
progress in lighting concepts. All the technologies under development
are based on solid-state electroluminescent materials and belong to the
general area of solid-state lighting (SSL). The two main technologies
being developed in SSL are light-emitting diodes (LEDs) and organic
light-emitting diodes (OLEDs), but in recent years, light-emitting
electrochemical cells (LECs) have emerged as an alternative option.
The luminescent materials in LECs are either luminescent polymers
together with ionic salts or ionic species, such as ionic transition-metal
complexes (iTMCs). Cyclometalated complexes of IrIII are by far the
most utilized class of iTMCs in LECs. Herein, we show how these
complexes can be prepared and discuss their unique electronic,
photophysical, and photochemical properties. Finally, the progress in
the performance of iTMCs based LECs, in terms of turn-on time,
stability, efficiency, and color is presented.