A curcumin-anchored luminescent and photocytotoxic ruthenium complex for theragnostic applications

A new heteroleptic luminescent and photocytotoxic ruthenium(II) polypyridyl complex, [Ru^II(bphen)₂(cur)]⁺ (bphen = bathophenanthroline, cur = curcumin), has been thoroughly investigated for its photophysical properties with potential as a luminescent probe for bioimaging and a photocytotoxic agent. The optimized lead complex was obtained via coordinating curcumin to the Ru(II) center pre-coordinated with two bathophenanthroline ligands, producing a stable cationic structure with extended π-conjugation. The incorporation of curcumin to {Ru(bphen)₂} moiety improves emissive characteristics and also enhances the biological compatibility, owing to its natural origin and functional groups that interact with biomolecular environments. The complex exhibits good photostability and strong emission under physiological conditions, enabling its application as a luminescent stain for fluorescence-based cellular imaging. Furthermore, in vitro photocytotoxicity studies in the human breast cancer cell line MCF-7 reveal a significant photocytotoxicity index (PI ∼ 19.5), indicating low dark toxicity but an enhanced cytotoxic response upon visible-light irradiation. These findings highlight the dual functionality of the [Ru^II(bphen)₂(cur)]⁺ as a theragnostic agent, serving as a luminescent bioimaging probe and a potential photosensitizing agent for light-activated therapeutic applications.