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

Abstract

Heterometallic binuclear Ru–Pt and trinuclear Zn–Pt complexes were prepared via self-assembly by attaching Pt^II-tpy (tpy = 2,2′:6′,2′′-terpyridine) onto the Ru^II-tpy and Zn^II-bis(tpy) moiety. The visible absorption bands for Ru–Pt complexes are primarily due to Ru^II → tpy MLCT transitions with some overlap from Pt^II → 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 Ru^II precursor; however, the emission of Zn–Pt was decreased when compared with strongly emissive Zn^II-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.