Abstract

In the search for new luminescent semiconductors to be applied in energy conversion devices, we report via DFT/ TD-DFT calculations the structure, UV-Vis absorption, and phosphorescent properties of Re(I) complexes denoted as [ReCl(CO)3(Ln)] and [ReTMP(CO)3(Ln)]+, where TMP is 2,4,6-trimethylpyridine and Ln is a bidentate ligand that corresponds to phenylimidazo(4,5-f)1,10-phenanthroline. This last ligand was analyzed for their electron-donating and -withdrawing characters with different substituents on the peripheral phenyl ring (Ln = -H, -CH3, o -F). Regarding the absorptions, at lower energy in the [ReCl(CO)3(Ln)], it was possible to identify a mixture of metal-to-ligand and ligand-to-ligand charge-transfer excitations, while the [ReTMP (CO)3(Ln)]+ series showed ligand centered transitions as responsible for absorption maximum. The phosphorescence of [ReCl(CO)3(Ln)] complexes exhibits an emission wavelength of 609-623 nm, whose deactivation path comes from pi* orbital located at Ln ligands, towards the metal and ligands orbitals. By contrast, the emission process of the [ReTMP(CO)3(Ln)]+ complexes are mainly due to ligand-centered electron promotion (70%) in line with absorption features, showing emission wavelengths in the range of 521-527 nm. The change of the substituent Cl for TMP significantly influences the absorption and emission energies, unlike substitution on the Ln ligand. However, this last substitution pattern becomes relevant when considering injection/transport of holes-electrons where the reorganization energy (lambda) for [ReCl(CO)3(L3)] neutral complexes improves due to the more balance charge transfer ability required for organic light-emitting diodes (OLED), while [ReTMP (CO)3(L2)]+ is the best choice for a light-emitting electrochemical cell (LEEC). Then, rhenium complexes can be considered as promising luminophores for device applications.