Uniting Ruthenium(II) and Platinum(II) Polypyridine Centers in Heteropolymetallic Complexes Giving Strong Two-Photon Absorption

Abstract

New trinuclear RuPt₂ and heptanuclear RuPt₆ complex salts are prepared by attaching Pt^II 2,2′:6′,2″-terpyridine (tpy) moieties to Ru^II 4,4′:2′,2″:4″,4‴-quaterpyridine (qpy) complexes. Characterization includes single crystal X-ray structures for both polymetallic species. The visible absorption bands are primarily due to Ru^II → qpy metal-to-ligand charge-transfer (MLCT) transitions, according to time-dependent density functional theory (TD-DFT) calculations. These spectra change only slightly on Pt coordination, while the orange-red emission from the complexes shows corresponding small red-shifts, accompanied by decreases in intensity. Cubic molecular nonlinear optical behavior has been assessed by using Z-scan measurements. These reveal relatively high two-photon absorption (2PA) cross sections σ₂, with maximal values of 301 GM at 834 nm (RuPt₂) and 523 GM at 850 nm (RuPt₆) when dissolved in methanol or acetone, respectively. Attaching Pt^II(tpy) moieties triples or quadruples the 2PA activities when compared with the Ru^II-based cores