Luminescent third-row transition metal Os(Ⅱ), Ir(Ⅲ) and Pt(Ⅱ) based complexes, particularly those with cyelometalating chelates and equivalents, play a key role in the recent development of optoelectronic technologies such as organic light emitting diode (OLED), light emitting electrochemical cells, and solid-state organic lighting applications.The attraction of these complexes comes from their higher chemical stability due to the strong metal-ligand bonding interaction, as well as the longer excitation lifetimes and higher emission quantum yields.