Mono-, di- and tetra-nuclear ruthenium(II) complexes containing 2,2′-p-phenylenebis(imidazo[4,5-f]phenanthroline): Synthesis, characterization and third-order non-linear optical properties

Mono-, di- and tetra-nuclear ruthenium(II) complexes containing 2,2′-p-phenylenebis(imidazo[4,5-f]phenanthroline) (H₂bpib) have been synthesized and characterized. Electrochemical and UV/Vis data show that the first redox process in these complexes is bipyridine based and the metal-metal interaction in di- and tetra-nuclear complexes is very weak. Resonance Raman spectra provide direct evidence for a low-energy bipyridine to H₂bpib charge-transfer transition. Furthermore, the non-linear optical properties of the ruthenium(II) complexes were investigated by Z-scan techniques with 12 ns laser pulses at 540 nm, and all of them exhibit both NLO absorption and self-defocusing effect. The corresponding effective NLO susceptibilities |X³| of the complexes are 5.76 × 10^-12-21.06 × 10^-12 esu.