Luminescent rhenium(I)-chromone bioconjugate: Synthesis, photophysical properties, and confocal luminescence microscopy investigation

Luminescent Re(I) complexes represent important materials for bioimaging applications. Herewith a new Re-complex Re(CO)(3)(phen)L1, where phen = 1,10-phenanthroline and L1 = 3-CCCH2NHCOCH2CH2-6-bromo-chromone, is reported. The new conjugate displays moderately intense orange-red luminescence stemming from a (MLCT)-M-3 excited state associated with the organometallic Re(CO)(3)(phen) fragment. At ambient temperature, the emission quantum yield amounts to 0.2-0.9 % in aerated organic solvents and 7% in poly(methyl methacrylate). The emission decay times are in the order of several tens of nanoseconds to a few microseconds depending on the polarity and viscosity of the medium. Re(CO)(3)(phen)L1 penetrates into the mouse C2C12 cancer cells where it accumulates in cytoplasm, mitochondria, and endoplasmic reticulum, as it was determined by means of confocal fluorescence microscopy. Furthermore, the complex shows high photostability in live cells. No photobleaching was observed under prolonged intense irradiation (A = 405 nm, I = 0.8 W/cm(2), t = 30 min), whereas at similar conditions significant photobleaching of commonly used fluorescent stains, e.g. DAPI, occurs. (C) 2015 Elsevier B.V. All rights reserved.