Self-assembled heterometallic complexes showing enhanced two-photon absorption and their distribution in living cells

Heterometallic binuclear Ru–Pt and trinuclear Zn–Pt complexes were prepared via self-assembly by attaching PtII-tpy (tpy = 2,2′:6′,2′′-terpyridine) onto the RuII-tpy and ZnII-bis(tpy) moiety. The visible absorption bands for Ru–Pt complexes are primarily due to RuII → tpy MLCT transitions with some overlap from PtII → tpy MLCT, while no MLCT transition is observed for the Zn–Pt complex. The emission intensity of the Ru–Pt complexes was improved relative to the mononuclear RuII precursor; however, the emission of Zn–Pt was decreased when compared with strongly emissive ZnII-bis(tpy). Z-scan results revealed relatively high two-photon absorption (TPA) cross sections σ2, with maximal values of 962 GM for Ru–Pt and 200 GM for Zn–Pt. All the heterometallic complexes were proved to localize preferably into lysosomes by confocal fluorescence imaging results, which also showed improved cell-free 1O2 quantum yield compared to their mononuclear precursor.