Applying Ionic Transition Metal Complexes to Light-Emitting Electrochemical Cells

Since the first report on a Ru(II)-based LEC by Maness et al. in 1996, ionic transition metal complexes (iTMCs) have attracted huge interest as candidates for electroluminescent devices. In particular, after the advent of Ru-iTMCs and Os-iTMCs, Ir-iTMCs have been dominating the scene of iTMCs-based LECs, achieving high luminance and efficiency performances in concert with encouraging stabilities. Recently, the search on iTMCs based on more abundant and low-cost metals like Cu(I) or Ag(I) has attracted the interest of various research groups. Regardless of the type of iTMCs, LECs have experienced a continuous improvement in terms of efficiency, stability, turn-on time, and color by simple chemical design of iTMCs. However, there are still open challenges in the field, such as the achievement of stable and pure blue and white device. This chapter will cover selected advances regarding iTMCs with a Ru(II), Os(II), Ir(III), Cu(I), or Ag(I) ionic metal cores and their implementation in LECs divided by device color.