Towards an understanding of the absorption and emission spectra of rhenium(I) tricarbonyl polypyridine complexes containing NO2 group: A density functional theory study

Using the density functional theory approach, we assessed the ground state geometries, absorption, and emission properties of three transition metal complexes: (1) [Re(5-NO2-phen)(CO)3(Cl)], (2) [Re(4,4′-NO2-bpy)(CO)3(Cl)], and (3) [Re(4,4′-NO2-bpy)(CO)3(Etpy)][PF6] (phen = 1,10-phenanthroline; bpy = 2,2′-bipyridine, Etpy = 4-ethylpyridine). The UV–vis absorption spectrum agrees well with the time-dependent density functional theory. The emissive lowest-lying triplet state is an 3MLCT state for complexes 1–3. The presence of a 3d–d state was considered to be the main factor for the lack of emission in all d6 metal complexes of nitro-polypyridyl ligands.