An amine linker group modulates luminescent properties in a Rhenium(I) tricarbonyl complex. How can it be applied for ratiometric oxygen sensing?

The UV–Vis absorption spectrum of the rhenium(I) tricarbonyl complex [(NH₂-phen)Re(CO)₃Br] (ReNN-NH₂Br, a deep-orange solid) in solution shows three bands located at 300, 370 and 445 nm. TD-DFT calculations and spectroscopic data indicate that the higher energy band corresponds to a ligand centered transition (LC), while the two lower energy bands have been ascribed to have major ILCT and MLCT character. Excitation at 370 nm leads to two emission bands centered at around 490 nm and 590 nm, which have different nature, ¹ILCT and ³MLCT, respectively. Both show a low luminescent quantum yield, especially the lowest energy band. The emission quantum yields in argon-saturated solutions are largely increased, specially for the band at 590 nm. Our results demonstrate that adding the amino group has a non-innocent effect over the luminescent properties of the complex when is compared with those of [(phen)Re(CO)₃Br] (ReNNBr). The capacity of these complexes to act as singlet oxygen sensitizers and their application as oxygen sensors were explored. Both complexes, ReNNBr and ReNN-NH₂Br, were incorporated in silsesquioxane matrices and tested as ratiometric oxygen sensors using the intrinsic emission of the matrix as an emission internal reference signal. The SSO1-ReNN-NH₂Br films was the most sensitive material for this application.