This review summarizes investigations carried out at the Laboratory of Photochemistry and Energy Conversion (LFCE) in the University of São Paulo dealing with design and characterization of ruthenium(II), rhenium(I) and iridium(III) polypyridine complexes with desired photochemical and photophysical properties in light of the development of optoelectronics and photoinduced energy conversion systems. First, the breakthroughs on molecular engineering of emissive Re I , Ru II and Ir III complexes for the development of highly efficient light-emitting devices, such as organic light-emitting diodes (OLEDs) and light-emitting electrochemical cells (LECs), are presented. Then, the photochemical and photophysical properties of fac-[Re(CO) 3 (NN)(trans-L)] + complexes (NN = bidentate polypyridyl ligands and trans-L = stilbene-like ligand), which find use in molecular machines and photosensors, are discussed. Finally, dye-sensitized energy conversion devices based on Ru II complexes and natural dyes, such as dye-sensitized solar cells (DSCs) and dye-sensitized photoelectrosynthesis cells (DSPECs), are reviewed, highlighting some strategies for photoanode engineering aiming at improved device efficiencies.