Length-Dependent Convergence and Saturation Behavior of Electrochemical, Linear Optical, Quadratic Nonlinear Optical, and Cubic Nonlinear Optical Properties of Dipolar Alkynylruthenium Complexes with Oligo(phenyleneethynylene) Bridges

Abstract

The syntheses of trans-[Ru{4,4'-C[triple bond]CC(6)H(2)[2,5-(OEt)(2)]C[triple bond]CC(6)H(4)NO(2)}Cl(dppm)(2)] (19), trans-[Ru{4,4',4''-C[triple bond]CC(6)H(4)C[triple bond]CC(6)H(2)[2,5-(OEt)(2)]C[triple bond]CC(6)H(4)NO(2)}Cl(dppm)(2)] (20), trans-[Ru{4,4',4'',4'''-C[triple bond]CC(6)H(4)C[triple bond]CC(6)H(2)[2,5-(OEt)(2)]C[triple bond]CC(6)H(2)[2,5-(OEt)(2)]C[triple bond]CC(6)H(4)NO(2)}Cl(dppe)(2)] (21), trans-[Ru{4,4',4'',4'''-C[triple bond]CC(6)H(4)C[triple bond]CC(6)H(2)[2,5-(OEt)(2)]C[triple bond]CC(6)H(2)[2,5-(OEt)(2)]C[triple bond]CC(6)H(4)NO(2)}Cl(dppm)(2)] (22), trans-[Ru{4,4',4'',4'''-C[triple bond]CC(6)H(4)C[triple bond]CC(6)H(4)C[triple bond]CC(6)H(2)[2,5-(OEt)(2)]C[triple bond]CC(6)H(4)NO(2)}Cl(dppm)(2)] (23), and trans-[Ru{4,4',4'',4''',4''''-C[triple bond]CC(6)H(4)C[triple bond]CC(6)H(4)C[triple bond]CC(6)H(2)[2,5-(OEt)(2)]C[triple bond]CC(6)H(2)[2,5-(OEt)(2)]C[triple bond]CC(6)H(4)NO(2)}Cl(dppm)(2)] (24) are reported, together with those of precursor alkynes, complexes with the donor-pi-bridge-acceptor formulation that affords efficient quadratic and cubic NLO compounds; the identity of 19 was confirmed by a structural study. The electrochemical properties of 19-24 and related complexes with shorter pi-bridge ligands were assessed by cyclic voltammetry, and the linear optical, quadratic nonlinear optical, and cubic nonlinear optical properties were assayed by UV-vis-NIR spectroscopy, hyper-Rayleigh scattering studies at 1064 and 1300 nm, and broad spectral range femtosecond Z-scan studies, respectively. The Ru(II/III) oxidation potentials and wavelengths of the optical absorption maxima decrease on pi-bridge lengthening, until the tri(phenyleneethynylene) complex is reached, further chain lengthening leaving these parameters invariant; theoretical studies employing time-dependent density functional theory have shed light on this behavior. The quadratic nonlinearity beta(1064) and two-photon absorption cross-section reach maximal values at this same pi-bridge length, a similar saturation behavior that may reflect a common importance of ruthenium-to-alkynyl ligand charge transfer in electronic and optical behavior in these molecules.

Synthesis, Optical, Electrochemical, and Theoretical Studies of Dipolar Ruthenium Alkynyl Complexes with Oligo(phenylenevinylene) Bridges

“…The results from cyclic voltammetric studies on Ru4 , Ru6 , and Ru8 (Figure S81) reveal a fully reversible oxidation process for each complex at about 0.5 V, a potential similar to those for previously reported trans ‐[Ru(C≡CR)Cl(L 2 ) 2 ] complexes lacking acceptor groups (see, for example, Refs. ), together with an irreversible nitro‐centred reduction at about −1 V (Table ). Ruthenium complexes with 4‐nitrophenylethynyl ligands show oxidation potentials of about 0.7 V (see Ru1 , Table ), reducing on π‐system lengthening (see Ru2 and Ru3 , Table ).…”

“…The data are consistent with the longer π‐bridges in the present complexes further attenuating the electron‐withdrawing effect of the nitro on the ease of oxidation at the metal centre. The differences in oxidation potentials across the complexes are consistent with previous reports showing that increasing the length of the π‐bridge in dipolar ruthenium alkynyl complexes with OPE bridges modifies the oxidation potential on π‐system lengthening up to a tri(phenyleneethynylene) unit, the potential remaining invariant on further bridge‐lengthening …”

trans Bis-N-heterocyclic carbene bis-acetylide palladium(II) complexes

“…1 and 2, respectively. In both complexes, the palladium atoms showed the expected square planar coordination geometry with slight distortion, with the C acetylene ePdeC carbene bond angles in the range of 87.04(8) e 92.96 (10) . It is conceivable that a slight distortion from an ideal square planar arrangement could relieve steric interactions between bulky ligands.…”

Heptametallic, Octupolar Nonlinear Optical Chromophores with Six Ferrocenyl Substituents

“…[34] The results obtained were calibrated against closed-aperture (CA) Z-scan measurements performed on a fused silica plate (4.66 mm thick), [35] and compared with measurements on an identical glass cell filled with the solvent only. These wavelengths were chosen because they correspond to about twice those of the 1PA maxima, giving optimum enhancement of the NLO responses while avoiding excessive 1PA.…”

“…The total dipolar b 0 values determined for 3 and 6 ( % 10 À27 esu) are especially large for 3D chromophores and notably similar to those that we have determined previously for the related but distinct species 9 and 10 ( Figure 7), in which the NLO responses derive from MLCT and ILCT transitions that are directed away from the central metal. [11i] Cubic NLO studies: The new complex salts 1-6 were investigated by using the Z-scan technique, [34][35][36][37] affording the real and imaginary parts of g, together with the values of s 2 . [1] Efforts to assess the sensitivity of b to other factors (and to probe fundamental quantum limits) with purely organic dipoles have included electron-normalised off-resonant values b EN , [1f, 50] derived by scaling against the total number of effective p-bonding electrons (N eff ).…”