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

New
trinuclear RuPt2 and heptanuclear RuPt6 complex
salts are prepared by attaching PtII 2,2′:6′,2″-terpyridine
(tpy) moieties to RuII 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 RuII → 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 PtII(tpy) moieties triples or quadruples the
2PA activities when compared with the RuII-based cores.