Complexes of cobalt, rhodium and iridium

This chapter provides an overview of the luminescence properties of Group 9 (Co, Rh, Ir) complexes. The synthesis and photophysical properties of Co(II/III), Rh(I/III), and Ir(III) complexes have been discussed with various judiciously designed ligands that fine-tune the luminescent features of the complexes with different natures of origin of luminescence, e.g., 3MLCT, 3LMCT, 3ILCT, and 3LC. The priority is given to the complexes showing the potentials for applications in sensing of metal ions, photoredox catalysis, and solid-state lighting devices (organic light-emitting diodes, OLEDs and light-emitting electrochemical cells, LECs). While Ir(III) complexes show magnificent photophysical properties due to their high spin-orbit coupling constant (3909 cm−1) and often finds applications in all these categories, intense research is yet to be performed to induce bright luminescence (ΦPL > 50%) in 3 and 4d T-metal Co(II/III) and Rh(I/III) complexes and find their practical applications.