Linear and Third-Order Nonlinear Optical Properties of Fe(η5-C5Me5)(κ2-dppe)- and trans-Ru(κ2-dppe)2-Alkynyl Complexes Containing 2-Fluorenyl End Groups

The synthesis and characterization of a set of redox-active iron and ruthenium alkynyl complexes of general formula [[M]­Cl(1–p){C≡CC6H5–m(C≡CFlu)m}(1+p)]­[PF6]n are reported (n = 0–1; m = 1–2; [M] = [Fe­(η5-C5Me5)­(κ2-dppe)] and p = 1 or [M] = [trans-Ru­(κ2-dppe)2] and p = 0–1). The linear and third-order nonlinear optical properties of these new organometallic complexes featuring phenylalkynyl ligands functionalized by 2-fluorenyl (Flu) groups were studied in their stable redox states. Their first electronic transitions are assigned with the help of DFT calculations. We show here that these compounds possess significant third-order NLO responses in the near-IR range for molecules of their size. In particular, the remarkably large 2PA activities of the new Ru­(II) compounds in the 600–800nm range (Z-scan) make them attractive nonlinear chromophores. Structure–property studies emphasize the importance of para- versus meta-connection of the 2-fluorenylethynyl units on the phenylalkynyl core and reveal that upon progressing from mono- to bis-alkynyl complexes a further increase of the 2PA cross section can be obtained while maintaining linear transparency in the visible range.