Synthesis, characterization and photophysical properties of rhenium(I) tricarbonyl complexes with thiacrown ethers

Crown ethers and their derivatives are known to coordinate metal cations and organic molecules. They have an adaptable ring-opening diameter, which makes their complexations very selective. In this work, a series of rhenium (I) tricarbonyl complexes (C1-C3) based on oxathiacrown ethers conjugated with 1,10-phenanthroline (L1-L3) were designed and prepared. They were characterized by elemental analysis, spectral and electrochemical methods. They displayed microanalytical, NMR and mass spectral data consistent with their formulations. Electronic absorptions associated with 1MLCT transitions were observed at ca. 400 nm in the complexes. Their emission spectra displayed a low intensity peak at ca. 451-467 nm and a high intensity peak at ca. 605-608 nm. The low intensity peak appearing at high energy may be assigned to 3LC while the high intensity peak appearing at low energy may be assigned to 3MLCT transition. The complexes exhibited quantum yields between 0.0072 and 0.0088, lifetime measurements of 41-48 ns and large Stokes shifts at ca. 8500 cm-1. The CV of the complexes displayed one reversible ligand-centered reduction wave at ca. -1.6 V and an irreversible metal-centered oxidation wave at ca. 1.1 V (vs Ag/AgNO3). No remarkable changes were observed in the photophysical and electrochemical properties of the complexes upon increasing the macrocyclic cavity. The promising photophysical properties make them suitable candidates for application in chemosensing.