Harvesting greenish blue luminescence in gold(i) complexes and their application as promising bioactive molecules and cellular bioimaging agents

Three novel highly photoluminescent mononuclear Au-I compounds (1, 2, and 3) based on mixed phosphine/thiocarbamoyl-pyrazoline materials were synthesized at good yields using a sonochemical method and then structurally characterized. X-ray diffraction studies revealed the compounds to be mononuclear cationic complexes of the [Ph3PAu(L)]PF6 type with linear coordination geometry around Au-I atoms. Investigation of photophysical properties showed an intense greenish blue emission when the complexes were excited at 305 nm in solution. The emission was attributed to mixed MLCT + IL and LLCT electronic transitions taking place after ligand complexation, as shown by DFT calculations. Full characterization of the compounds also comprised H-1 and C-13 NMR experiments, elemental analyses, infrared spectroscopy, and absorption-emission studies. Additionally, compounds 1, 2, and 3 and respective ligands were investigated as antibacterial agents against five Streptococcus aureus strains (Gram-positive) and one Escherichia coli strain (Gram-negative) with distinct antibiotic-resistance profiles. Cytotoxic activity was assessed using the MTT method against B16F10 melanoma, 4T1 mammary carcinoma, and normal BHK-21 baby hamster kidney cell lines. The synthesized Au-I compounds proved more active than the respective precursors and free ligands. Tested as probes for cellular bioimaging, the complexes showed good biodistribution in the cytoplasm of MCF-7 and MDA-MB-231 (human breast adenocarcinoma cell lines).