Addressing the development of the organic light emitting diode (OLED) based on rare-earth and transition-metal complexes--Europium, Terbium, Ruthenium, and Rhenium--this unique perspective explains how these materials can be used to build organic-LEDs, from chemistry synthesis to device operation and the related charge transfer and confinement. Examining how organic materials can be used to build organic-LEDs, the relationship between the chemistry molecule "design," and state-of-the-art and expected pathways, this intelligent report provides intensive experimental results for scientists and engineers working in this new OLED framework, while maintaining a didactic utility for graduation students and teachers studying optoelectronics.