Photoswitchable alkoxy-bridged binuclear rhenium(i) complexes – a potential probe for biomolecules and optical cell imaging

We describe the solvothermal synthesis, structural characterization, photophysics and potential applications as probes of two alkoxy-bridged binuclear Re(i) complexes, [{Re(CO) sub(3)(1,4-NVP)} sub(2)( mu sub(2)-OR) sub(2)] (1, R = C sub(4)H sub(9); 2, R = C sub(10)H sub(21); 1,4-NVP = 4-(1-naphthylvinyl)pyridine). Irradiation of 1 and 2 at 365 nm leads to an interesting trans-cisphotoisomerization process, which was examined by super(1)H NMR, UV-vis, emission and time-resolved techniques. Compounds 1 and 2 exhibit photoswitchable luminescence enhancement arising from photoinduced intramolecular energy transfer from the super(3)MLCT state of the Re(i) chromophore to the triplet excited state of the ligand 1,4-NVP. In addition, these Re(i) complexes serve as excellent probes for the ultrasensitive detection of biological molecules, including bovine serum albumin (BSA) and a platelet derived growth factor (PDGF) binding aptamer. Our results also suggest that, since these Re(i) complexes have low cytotoxicity and fluorescence properties under physiological conditions, they could be a useful probe for optical imaging of cancer cells by confocal laser scanning microscopy.