Reusable singlet oxygen-generating RupNDIp dyads for luminescent membrane imaging and antimicrobial photodynamic therapy in PBS

This study reports the photosensitizing properties of the dyad [Ru(phen)₂(pNDIp)]²⁺ (RupNDIp; phen = 1,10-phenanthroline; pNDIp = naphthalene-functionalized phenanthroline ligand) for photodynamic therapy (PDT) applications in phosphate-buffered saline (PBS). RuPNDIp displays broad and intense absorption in the UV-Vis region, along with strong emission at 600 nm from its 3 MLCT state, minimizing reabsorption and spectral overlap with endogenous biomolecules. The dyad efficiently generates singlet oxygen ( 1 O 2 ) in PBS and retains its activity through at least three consecutive 30 minutes irradiation cycles (200 mW·cm -2 ) without photobleaching. In model membranes (POPC:DOPG), RupNDIp functions as a bright luminescent probe and, under continuous 450 nm irradiation, induces membrane disruption, demonstrating its integrated imaging and therapeutic capabilities. Because membrane damage strongly enhances PDT outcomes, the ability to obtain luminescent images revealing the localization of the dyad in membranes is particularly important. The antimicrobial activity of RuPNDIp was evaluated against Escherichia coli (ATCC 25922). RupNDIp showed modest dark cytotoxicity at 25 μM, likely arising from electrostatic interactions and partial membrane uptake; however, upon 450 nm LED irradiation (7 J·cm⁻ 2 ), it induced a pronounced photocytotoxic effect, reducing E. coli viability by 4.99 log 10 , highlighting its potential as a membrane-targeted photosensitizer for antimicrobial photodynamic therapy.