Carbon monoxide (CO) has recently been identified as being very active in the treatment of cardiovascular diseases and to prevent organ transplant rejection. However, CO is also a noxious gas, particularly difficult to handle in hospitals. This is the reason why there is a huge interest in compounds that can release CO molecules in a controlled way when excited by light. Tricarbonylrhenium(I) complexes are promising photochemical CO-releasing molecules (photoCORMs). In most cases, they are stable, biocompatible and easily incorporated by living cells. In the past few years, various complexes having the structure [Re(CO3)(L)(X)]+, where (L) is an original organic ligand, have been synthesized by our team. One of them has excellent spectroscopic properties, and we hypothesized that changing the ancillary ligand (X = Chlorine (Cl-), Acetonitrile (AN), and Triphenylphosphine (PPh3)), would influence the photochemical reactivity. The aim of this project was thus to investigate these complexes in order to estimate their potential value as phototherapy agents. First, the absorption and luminescence properties of the compounds were measured. The compounds absorb in the UV and emit phosphorescence in the visible. Compared with the Cl- ligand, the AN and PPh3 ligand induced a strong blue shift in the absorption and emission spectra. Indeed, PPh3 in these complexes draws more electron density from the metal center and stabilizes the highest occupied orbitals. Such stabilization increases the energy of the MLCT transitions. Then, organic solutions of the compounds were irradiated with UV light (300 nm and 350 nm). No changes were detected for the complexes containing Cl-and AN. In contrast, a very fast photochemical reaction was observed for the PPh3 complex. The photochemical reaction was monitored by different spectroscopic techniques. The main photoproduct was isolated and unambiguously identified as the complex in which one carbonyl group has been replaced by one solvent molecule: [Re(CO2)(L)(PPh3)(solv)]+. This work showed that the introduction of a PPh3 ligand improved the photoreactivity of our complexes. The release of CO could be monitored through the evolution of the phosphorescence emission, which is of great value for bio-imaging. Therefore, the PPh3 complex could be an attractive photo-CORM. However, irradiation needs high energy, not compatible with living cells, so that biphotonic excitation should be envisaged for further developments.

Study of new Rhenium(I) complexes in view of the controlled release of carbon monoxide

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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