Utilizing a series of fac-Re(CO) < inf > 3 < /inf > core based quinonoid containing complexes for photophysical and cell imaging studies

Abstract

A series of NnO bis-chelating bridging quinone ligands (H2L1, H2L2 and H2L3) have been utilized to synthesize four dinuclear fac-Re(CO)3 based neutral complexes (1-4) by their reaction with Re(CO)5(OTf), where the N-donors 4-dimethylaminopyridine (for 1), 3,5-dibromopyridine (for 2) and acetonitrile (for 3 and 4) act as ancillary ligands. The complexes were characterized by FTIR, 1H NMR, ESI-MS and elemental analysis. The structures of complexes 1-3 were analysed by X-ray diffraction methods. Photophysical investigations revealed that all the complexes display strong visible-light absorption with absorption maxima at around 500 nm (ε = 40 000-50 000 M-1 cm-1), whereas in the solid state the complexes display high intensity broad bands in the entire UV-Vis-NIR region. Complexes 1-4 were found to be luminescent in fluid solutions at room temperature. Favorable photophysical properties allowed their utilization as luminescent probes for live-cell imaging using HeLa cells, where complexes 2 and 4 were found to display good cellular uptake with co-localization in lysosomal compartments, which was observed as yellow fluorescence. Complexes 2 and 4 displayed very low cytotoxicity, as suggested by LDH production experiments. The photophysical properties, uptake pathway, localization properties and cytotoxicity of the complexes are discussed in detail.