Abstract
The aim of this chapter is to give an in-depth analysis of transition metal complexes that areuseful in conversion of solar energy into electricity, and in organic light emitting diodes. In thefirst part we discuss the historical background of sensitization phenomenon, operating principlesof dye-sensitized solar cells, tuning of photophysical and electrochemical properties of sensitizers,evolution of photovoltaic performance, present status and future prospects for dye-sensitized solarcells. In the second part, we elucidate the modulation of phosphorescent color and quantum yieldsin neutral, cationic, and anionic iridium complexes and their application in light emitting devices.