Search

Oligo(p-phenyleneethynylene)s (OPEs) end-capped with (alkynyl)bis(diphosphine)ruthenium and thiol/thiolate groups stabilize ca. 2 nm diameter gold nanoparticles (AuNPs). The morphology, elemental composition and stability of the resultant organometallic OPE/AuNP hybrid materials have been defined using a combination of molecular- and nano-material chacterization techniques. The hybrids display long-term stability in solution (more than a month), good solubility in organic solvents, reversible ruthenium-centered oxidation, and transparency beyond 800 nm, and possess very strong nonlinear absorption activity at the first biological window, and unprecedented two-photon absorption activity in the second biological window (σ2 up to 38,000 GM at 1,050 nm).

Steric control of the extent of reaction has been developed to rapidly synthesize ligated metal-containing dendrons that have been employed in arylalkynyl complex dendrimer synthesis. Reaction of 1...

The complexes trans-[Pt(C CC6H4-4-C CPh)Cl(PMe2Ph)2] (1), 1,3,5-C6H3{C CC6H4-4-C C-trans-[PtCl(PMe2Ph)2]}3 (2) and 1,3,5-C6H3(C CC6H4-4-C C-trans-[Pt(PMe2Ph)2]C C-4-C6H4C C-3,5-C6H3-{C C-trans-[Ru(C CPh)(dppe)2]}2)3 (3) have been synthesized and the identity of 1 confirmed by a single-crystal X-ray diffraction study. The optical limiting merit of 1 and 2 has been assessed at 523 nm employing 40 ns pulses; the effective absorption cross-section for 1 is low, while that of 2 is larger, but the complex is susceptible to photo-damage. The third-order nonlinearity of the Ru6Pt3 dendrimer 3 has been examined at 800 nm using 150 fs pulses; it is larger than that of a related Ru6 dendrimer, but smaller than that of a Ru9 dendrimer under the same conditions, suggesting that increasing metal content and electron richness is correlated to increased nonlinearity in these complexes.

A combination of cyclic voltammetry (CV), UV−vis−NIR spectroscopy and spectroelectrochemistry, hyper-Rayleigh scattering (HRS) [including depolarization studies], Z-scan and degenerate four-wave mixing (DFWM) [including studies employing an optically transparent thin-layer electrochemical (OTTLE) cell to effect electrochemical switching of nonlinearity], pump−probe, and electroabsorption (EA) measurements have been used to comprehensively investigate the electronic, linear optical, and nonlinear optical (NLO) properties of nanoscopic π-delocalizable electron-rich alkynylruthenium dendrimers, their precursor dendrons, and their linear analogues. CV, UV−vis−NIR spectroscopy, and UV−vis−NIR spectroelectrochemistry reveal that the reversible metal-centered oxidation processes in these complexes are accompanied by strong linear optical changes, “switching on” low-energy absorption bands, the frequency of which is tunable by ligand replacement. HRS studies at 1064 nm employing nanosecond pulses reveal large non...

The complexes trans-[Ru(C C-4-C6H4F)X(dppe)2] [X = Cl (1), C CPh (2), C C-4-C6H4NO2 (3)], trans-[Ru{C C-4-C6H4-(E)-CH CH-4-C6H4NO2}X(dppe)2] [X = C CPh (4), C C-4-C6H4C CPh (5)], and [C6H3-1,3-{C C-trans-[RuCl(dppe)2]}2-5-(C C-4-C6H4F)] (6) have been synthesized and the identity of 1 confirmed by a single-crystal X-ray diffraction study. Cyclic voltammetry reveals a metal-centered oxidation, the potential of which is largely invariant on alkynyl ligand replacement across the series 1–5; the diruthenium complex 6 shows two oxidation processes, consistent with weakly interacting metal centers. Hyper-Rayleigh scattering (HRS) studies at 1064 nm using ns pulses suggest quadratic nonlinearities for 3–5 that are amongst the largest thus far for organometallic complexes, a trend maintained with the two-level-corrected data. HRS studies at 800 nm using fs pulses and amplitude modulation to remove multi-photon fluorescence contributions reveal significant fluorescence-free nonlinearities for 3–5; the frequency-independent nonlinearities calculated from the 800 nm results are suggestive of fluorescence contributions to the 1064 nm data. Z-scan studies at 820 nm reveal cubic nonlinearities that increase with the size of the π-system, although error margins are significant.

The syntheses of [1,3,5-{(η2-dppe)(η5-C5Me5)FeC⋮C-4-C6H4C⋮C}3C6H3] (1) and [(η2-dppe)(η5-C5Me5)Fe(C⋮C-1,4-C6H4C⋮CPh)] (2) are reported, together with an X-ray diffraction study of 2. The linear optical spectra of these compounds reveal characteristic low-energy transitions at 430 and 436 nm, respectively, significantly red shifted in comparison to those recorded for [1,3,5-{(η2-dppe)(η5-C5Me5)FeC⋮C}3C6H3] (3) and [(η2-dppe)(η5-C5Me5)FeC⋮CPh] (4), respectively. Cubic nonlinear optical response data for 1, 2, and 4 are reported. Cubic molecular nonlinearities by Z-scan at 695 nm reveal an increase in nonlinearities upon introduction of the ligated metal unit and progression from linear monometallic complex to octupolar trimetallic complex. Oxidation of 1 to 13+ results in a change of sign and magnitude of the imaginary (absorptive) part of the third-order nonlinearity; that is, the molecule can be electrochemically cycled between two-photon absorber and saturable absorber states.

The complexes trans -[Os(CCPh)Cl(dppe) 2 ] ( 1 ), trans -[Os(4-CCC 6 H 4 CCPh)Cl(dppe) 2 ] ( 2 ), and 1,3,5-{ trans -[OsCl(dppe) 2 (4-CCC 6 H 4 CC)]} 3 C 6 H 3 ( 3 ) have been prepared. Cyclic voltammetric studies reveal a quasi-reversible oxidation process for each complex at 0.36–0.39 V (with respect to the ferrocene/ferrocenium couple at 0.56 V), assigned to the Os II/III couple. In situ oxidation of 1 – 3 using an optically transparent thin-layer electrochemical (OTTLE) cell affords the UV–Vis–NIR spectra of the corresponding cationic complexes 1 + – 3 + ; a low-energy band is observed in the near-IR region (11 000–14 000 cm −1 ) in each case, in contrast to the neutral complexes 1 – 3 which are optically transparent below 20 000 cm −1 . Density functional theory calculations on the model compounds trans -[Os(CCPh)Cl(PH 3 ) 4 ] and trans -[Os(4-CCC 6 H 4 CCPh)Cl(PH 3 ) 4 ] have been used to rationalize the observed optical spectra and suggest that the low-energy bands in the spectra of the cationic complexes can be assigned to transitions involving orbitals delocalized over the metal, chloro and alkynyl ligands. These intense bands have potential utility in switching nonlinear optical response, of interest in optical technology.

The “first-generation” alkynylruthenium dendrimers 1,3,5-C6H3(4-C⋮CC6H4C⋮C-trans-[Ru(dppe)2]C⋮C-3,5-C6H3{4-C⋮CC6H4C⋮C-trans-[Ru(4-C⋮CC6H4R)(dppe)2]}2)3 [R = H (19), NO2 (20)], containing nine dialkynylruthenium centers, have been prepared by convergent synthesis. Reaction of 3 equiv of 1-iodo-4-trimethylsilylethynylbenzene with triethynylbenzene, under Sonogashira coupling conditions, followed by deprotection with tetra-n-butylammonium fluoride affords 1,3,5-C6H3(4-C⋮CC6H4C⋮CH)3 (2), which is reacted with cis-[RuCl2(L)2] (L = dppe, dppm) to afford the octopolar, triruthenium dendritic cores 1,3,5-C6H3{4-C⋮CC6H4C⋮C-trans-[RuCl(L)2]}3 [L = dppe (5), L = dppm (6)] via the vinylidene intermediates [1,3,5-C6H3{4-C⋮CC6H4CHC-trans-[RuCl(L)2]}3](PF6)3 [L = dppe (3), L = dppm (4)]. Reaction of 5 with terminal alkynes 4-HC⋮CC6H4R (R = H, NO2, NEt2) affords a series of related dialkynylruthenium zero-generation dendrimers 1,3,5-C6H3{4-C⋮CC6H4C⋮C-trans-[Ru(4-C⋮CC6H4R)(dppe)2]}3 [R = H (7), NO2 (8), NEt2 (9)]. Reactio...

The syntheses of trans-[Ru(CCHR)Cl(pp)2]PF6 (pp = dppm, R = 4-C6H4C⋮CPh, 4-C6H4CHO, 4,4‘-C6H4C⋮CC6H4NO2, (E)-4,4‘-C6H4CHCHC6H4NO2, 4,4‘,4‘ ‘-C⋮CC6H4C⋮CC6H4C⋮CC6H4NO2; pp = dppe, R = 4-C6H4CHO, (E)-4,4‘-C6H4CHCHC6H4NO2) and trans-[Ru(C⋮CR)Cl(pp)2] (pp = dppm, R = 4-C6H4C⋮CPh, 4-C6H4CHO, 4,4‘-C6H4C⋮CC6H4NO2, (E)-4,4‘-C6H4CHCHC6H4NO2, 4,4‘,4‘ ‘-C⋮CC6H4C⋮CC6H4C⋮CC6H4NO2; pp = dppe, R = 4-C6H4CHO, (E)-4,4‘-C6H4CHCHC6H4NO2) are reported, together with X-ray structural studies of trans-[Ru(C⋮CR)Cl(pp)2] (pp = dppm, R = 4-C6H4C⋮CPh; pp = dppe, R = 4-C6H4CHO, (E)-4,4‘-C6H4CHCHC6H4NO2). Cyclic voltammetric, linear optical, and quadratic and cubic nonlinear optical response data for these new complexes, together with the corresponding data for the previously reported trans-[Ru(CCHR)Cl(pp)2]PF6 (pp = dppm, R = Ph, 4-C6H4NO2; pp = dppe, R = Ph, 4-C6H4NO2) and trans-[Ru(C⋮CR)Cl(pp)2] (pp = dppm, R = Ph, 4-C6H4NO2, (E)-4,4‘-C6H4CHCHC6H4NO2; pp = dppe, R = Ph, 4-C6H4NO2), are reported. Oxidation potentials for the RuII/I...

The molecular inorganic compound 1,3,5-{trans-[RuCl(dppe)2]C≡C-4-C 6 H 4 C≡C} 3 C 6 H 3 (1) is reversibly oxidized in solution using an optically transparent thin-layer electrochemical (OTTLE) cell, the oxidation to 1 3 + resulting in the appearance of a strong absorption band at 11 200 cm - 1 in contrast to 1, which is optically transparent at frequencies below 20 000 cm - 1 . This linear electrochromic behavior is accompanied by third-order nonlinear optical electrochromic behavior, which has been probed by a combination of femtosecond degenerate four-wave mixing (DFWM) and pump-probe experiments at 12 500 cm - 1 . DFWM studies of 1 and 1 3 + reveal an order of magnitude increase in the hyperpolarizability, ‖γ‖, upon oxidation with ‖γ‖ values of 2000 × 10 - 3 6 esu and 20 000 x 10 - 3 6 esu, respectively; the DFWM signal of the latter is dominated by a delayed response (relaxation time ca. 1 ps). The transient absorption (TA) data for 1 reveal efficient two-photon absorption (σ 2 10 3 GM), whereas the TA data for 1 3 + reveal saturable absorption (decay time ca. 1 ps). The switching of third-order nonlinearity in the 1/1 3 + pair represents the first demonstration of femtosecond time-scale processes being responsible for nonlinear electrochromism.

The syntheses of trans-[Os(C≡C-4-C(6)H(4)X)Cl(dppe)(2)] [X = Br (3), I (4)], trans-[Os(C≡C-4-C(6)H(4)X)(NH(3))(dppe)(2)](PF(6)) [X = H (5(PF(6))), I (6(PF(6)))], and trans-[Os(C≡C-4-C(6)H(4)X)(C≡C-4-C(6)H(4)Y)(dppe)(2)] [X = Y = H (7), X = I, Y = C≡CSiPr(i)(3) (8)] are reported, together with improved syntheses of cis-[OsCl(2)(dppe)(2)] (cis-1), trans-[Os(C≡CPh)Cl(dppe)(2)] (2), and trans-[Ru(C≡C-4-C(6)H(4)I)(NH(3))(dppe)(2)](PF(6)) (9(PF(6))) (the last-mentioned direct from trans-[Ru(C≡C-4-C(6)H(4)I)Cl(dppe)(2)]), and single-crystal X-ray structural studies of 2-4, 5(PF(6)), 6(PF(6)), and 7. Ammine complexes 5(PF(6))/6(PF(6)) are shown to afford a facile route to both symmetrical (7) and unsymmetrical (8) osmium bis(alkynyl) complexes. A combination of cyclic voltammetry, UV-vis-NIR spectroelectrochemistry, and time-dependent density functional theory (TD-DFT) has permitted identification and assignment of the intense transitions in both the resting state and the oxidized forms of these complexes. Cyclic voltammetric data show fully reversible oxidation processes at 0.32-0.42 V (3, 4, 7, 8) (with respect to ferrocene/ferrocenium 0.56 V), assigned to the (formal) Os(II/III) couple. The osmium(III) complex (di)cations 5(2+) and 7(+) were obtained by in situ oxidation of 5(+) and 7 using an optically transparent thin-layer electrochemical (OTTLE) cell. The UV-vis-NIR optical spectra of 5(2+) and 7(+) reveal low-energy bands in the near IR region, in contrast to 5(+) and 7 which are optically transparent at frequencies below 22,000 cm(-1). TD-DFT calculations on trans-1, 2, 5(+), and 7 and their oxidized forms suggest that the lowest-energy transitions are chloro-to-metal charge transfer (trans-1), chloro-to-phenylethynyl charge transfer (2), and metal-to-phenylethynyl charge transfer (5(+), 7) in the resting state and chloro-to-metal charge transfer (trans-1(+)), phosphorus-to-metal charge transfer (5(2+)), alkynyl-to-metal charge transfer (7(+)), or phenylalkynyl-centered π → π* (2(+)) following oxidation. The presence of intense CT bands in the resting states and oxidized states and their significantly different nature across the two states, coupled to their strong charge displacement suggest that these species have considerable potential as electrochemically switchable nonlinear optical materials, while the facile unsymmetrical bis(alkynyl)osmium(II) construction suggests potential in construction of multistate heterometallic modular assemblies.

Publisher Summary This chapter describes the structure and nonlinear optical (NLO) property relationships for organometallic systems. Both quadratic and cubic molecular nonlinearities obtained for specific complexes are extremely large, suggesting that the potential for application of organometallics still remains. The most popular complexes subjected to NLO study are ferrocenyl and alkynyl complexes—reassuring that these are the most stable of organometallics, thereby satisfying an important materials requirement for putative applications. NLO behavior arises from the interaction of electromagnetic fields with matter. The consequent generation of new field components (differing in amplitude, phase, frequency, path, polarization, etc.) is of enormous technological importance for optical devices, with potential applications in data storage, communication, switching, image processing, and computing. These applications have generated a need for materials with exceptional NLO properties and satisfactory materials properties (processing, stability, etc.). Two unit systems are commonly employed in describing NLO properties: the SI (MKS) and the Gaussian (cgs) systems. This chapter describes a number of popular techniques used for the measurement of second- and third-order NLO properties of organometallic molecules.

The linear (absorption and emission) and nonlinear optical (NLO) properties of a series of D(3) [(Fe(II), Ru(II), Ni(II), Cu(II), Zn(II)] octupolar metal complexes featuring the 4,4'-bis[(dibutylamino)styryl]-2,2'-bipyridine ligand are reported. Zinc(II), nickel(II), and copper(II) complexes exhibit similar absorption spectra in the visible region (lambda(ILCT) = 474-476 nm) which are assigned to intraligand charge-transfer (ILCT) bands. The quadratic and cubic NLO properties are strongly influenced by the nature of the metallic center. Harmonic light scattering studies at lambda = 1.91 microm reveal that these chromophores display large first hyperpolarizabilities beta(1.91) in the range of (211-340) x 10(-30) esu; replacing the Zn(II) metal ion by Ni(II) or Cu(II) results in a decrease of the static beta(0) coefficient by a factor of 1.5-1.6. Z-scan measurements at 765 and 965 nm reveal relatively large two-photon absorption cross-sections [650sigma(2)2200 GM], showing that both beta and sigma(2) values can be tuned by simple modification of the metal ion.

Publisher Summary This chapter describes the structure and nonlinear optical (NLO) property relationships for organometallic systems. Both quadratic and cubic molecular nonlinearities obtained for specific complexes are extremely large, suggesting that the potential for application of organometallics still remains. The most popular complexes subjected to NLO study are ferrocenyl and alkynyl complexes—reassuring that these are the most stable of organometallics, thereby satisfying an important materials requirement for putative applications. NLO behavior arises from the interaction of electromagnetic fields with matter. The consequent generation of new field components (differing in amplitude, phase, frequency, path, polarization, etc.) is of enormous technological importance for optical devices, with potential applications in data storage, communication, switching, image processing, and computing. These applications have generated a need for materials with exceptional NLO properties and satisfactory materials properties (processing, stability, etc.). Two unit systems are commonly employed in describing NLO properties: the SI (MKS) and the Gaussian (cgs) systems. This chapter describes a number of popular techniques used for the measurement of second- and third-order NLO properties of organometallic molecules.

A combination of cyclic voltammetry (CV), UV-vis-NIR spectroscopy and spectroelectrochemistry, hyper-Rayleigh scattering (HRS) [including depolarization studies], Z-scan and degenerate four-wave mixing (DFWM) [including studies employing an optically transparent thin-layer electrochemical (OTTLE) cell to effect electrochemical switching of nonlinearity], pump-probe, and electroabsorption (EA) measurements have been used to comprehensively investigate the electronic, linear optical, and nonlinear optical (NLO) properties of nanoscopic pi-delocalizable electron-rich alkynylruthenium dendrimers, their precursor dendrons, and their linear analogues. CV, UV-vis-NIR spectroscopy, and UV-vis-NIR spectroelectrochemistry reveal that the reversible metal-centered oxidation processes in these complexes are accompanied by strong linear optical changes, "switching on" low-energy absorption bands, the frequency of which is tunable by ligand replacement. HRS studies at 1064 nm employing nanosecond pulses reveal large nonlinearities for these formally octupolar dendrimers; depolarization measurements are consistent with lack of coplanarity upon pi-framework extension through the metal. EA studies at 350-800 nm in a poly(methyl methacrylate) matrix are consistent with the important transitions having a charge-transfer exciton character that increases markedly on introduction of peripheral polarizing substituent. Time-resolved pump-probe studies employing 55 ps, 527 nm pulses reveal absorption saturation, the longest excited-state lifetime being observed for the dendrimer. Z-scan studies at 800 nm employing femtosecond pulses reveal strong two-photon absorption that increases significantly on progression from linear complex to zero- and then first-generation dendrimer with no loss of optical transparency. Both refractive and absorptive nonlinearity for selected alkynylruthenium dendrimers have been reversibly "switched" by employing the Z-scan technique at 800 and 1180 nm and 100-150 fs pulses, together with a specially modified OTTLE cell, complementary femtosecond time-resolved DFWM and transient absorption studies at 800 nm suggesting that the NLO effects originate in picosecond time scale processes.

The NLO properties of iron, ruthenium, osmium, nickel, and gold alkynyl complexes and some related compounds prepared in the authors’ laboratories are reviewed. Structure-property relationships for both quadratic and cubic NLO merit for these complexes have been developed from hyper-Rayleigh scattering studies at 1.064μm and Z-scan studies at 0.800μ m, respectively

Compounds of the form Ru(X2bipy)(PPh3)2(-C triple bond CC6H4NO2-p)2(X2bipy = 4,4'-X(2)-2,2'-bipyridine, X = Me 3a, Br 3b, I 3c) have been synthesised from the mono-alkynyl precursors Ru(X2bipy)(PPh3)2(-C triple bond CC6H4NO2-p)Cl (X = Me 2a, Br 2b, I 2c); the former are the first ruthenium bis-alkynyl compounds that also contain a bipyridyl ligand. Spectroelectrochemical investigation of 3a shows that the metal is readily oxidised to form the ruthenium(III) compound 3a+, and will also undergo a single-electron reduction at each nitro group to form 3a2-. ESR and UV/visible spectra of these redox congeners are presented. We also report the synthesis of [Ru(Me2bipy)(PPh3)2(-C triple bond CBut)(N triple bond N)][PF6] during the attempted synthesis of Ru(Me2bipy)(PPh3)2(-C triple bond CBut)2, and report its X-ray crystal structure and IR spectrum. X-Ray crystal structures of 3b and 3c(as two different solvates) are presented, and the nature of the intermolecular interactions seen therein is discussed. Z-Scan measurements on Ru(Me2bipy)(PPh3)2(-C triple bond CR)Cl (R = C6H4NO2-p2a, But, Ph, C6H4Me) are also reported, and show that Ru(Me2bipy)(PPh3)2(-C triple bond CR)Cl (R = C6H4NO2-p2a, Ph) exhibit moderate third-order non-linearities.

We have been studying third-order NLO properties of ruthenium-containing organometallic dendrimers. These molecules offer large hyperpolarizabilities and the possibility to control both the refractive and absorptive parts of the nonlinear response by electrochemical switching of the oxidation state of the ruthenium centres. Time-resolved studies indicate that it is possible to switch the molecules between the form in which they are two-photon absorbers and the state where they are fast (~ 1 picosecond time scale) saturable absorbers. Measurements of the dispersion of third-order nonlinearity have been made by the Z-scan technique on a nitro decorated dendrimer. They indicate that competition between two-photon absorption and absorption saturation is present in some wavelength ranges. The dispersion of both the real and imaginary parts of the cubic polarizability could be modelled by considering leading terms of the dispersion relation.

The dispersion of cubic nonlinearity in the organometallic dendrimer 1,3,5-(3,5-{trans-[(dppe)2(4-O2NC6H4CC)RuCC]}2C6H3CCC6H4-4-CC)3C6H3 can be understood in terms of an interplay of two-photon absorption and absorption saturation. Simple dispersion relations reproduce the behavior of both the real and imaginary components of the hyperpolarizability.

A combination of cyclic voltammetry, UV-vis-NIR spectroelectrochemistry, time-dependent density functional theory (TD-DFT), and Z-scan measurements employing a modified optically transparent thin-layer electrochemical (OTTLE) cell has been used to identify and assign intense transitions of metal alkynyl complexes at technologically important wavelengths in the oxidized state and to utilize these transitions to demonstrate a facile electrochromic switching of optical nonlinearity. Cyclic voltammetric data for the ruthenium(II) complexes trans-[RuXY(dppe)(2)] [dppe = 1,2-bis(diphenylphosphino)ethane, X = Cl, Y = Cl (1), Ctbd1;CPh (2), 4-Ctbd1;CC(6)H(4)Ctbd1;CPh (3); X = Ctbd1;CPh, Y = Ctbd1;CPh (4), 4-Ctbd1;CC(6)H(4)Ctbd1;CPh (5)] show a quasi-reversible oxidation at 0.50-0.60 V (with respect to ferrocene/ferrocenium 0.56 V), which is assigned to the Ru(II/III) couple. The ruthenium(III) complex cations trans-[RuXY(dppe)(2)](+) were obtained by the in situ oxidation of complexes 1-5 using an OTTLE cell. The UV-vis-NIR optical spectra of 1(+)-5(+) contain a low-energy band in the near-IR region ( approximately 8000-16 000 cm(-)(1)), in contrast to 1-5, which are optically transparent at wavelengths22 000 cm(-)(1). TD-DFT calculations have been applied to model systems trans-[RuXY(PH(3))(4)] [X = Cl, Y = Cl, Ctbd1;CPh, or 4-Ctbd1;CC(6)H(4)Ctbd1;CPh; X = Ctbd1;CPh, Y = Ctbd1;CPh or 4-Ctbd1;CC(6)H(4)Ctbd1;CPh] to rationalize the optical spectra of 1-5 and 1(+)-5(+). The important low-energy bands in the electronic spectra of 1(+)-5(+) are assigned to the promotion of an electron from either a chloride p orbital or an ethynyl p orbital to the partially occupied HOMO. These absorption bands have been utilized to demonstrate a facile switching of cubic nonlinear optical (NLO) properties at 12 500 cm(-)(1) (corresponding to the wavelength of maximum transmission in biological materials such as tissue) using the OTTLE cell, the first electrochromic switching of molecular nonlinear refraction and absorption, and the first switching of optical nonlinearity using an electrochemical cell.

The dispersion of cubic nonlinearity in the organometallic dendrimer 1,3,5-(3,5-{trans-[(dppe)2(4-O2NC6H4CC)RuCC]}2C6H3CCC6H4-4-CC)3C6H3 can be understood in terms of an interplay of two-photon absorption and absorption saturation. Simple dispersion relations reproduce the behavior of both the real and imaginary components of the hyperpolarizability.

The title compound, [RuCl(C25H22P2)2(H2O)]PF6·1.73CH4O, contains a pseudo-octahedral ruthenium complex cation with two bidentate diphosphine ligands and cis-disposed chloro and aqua ligands, together with a disordered hexa­fluoro­phosphate anion and disordered methanol solvent mol­ecules. Identification as an aqua­ruthenium(II) complex rather than a hydroxo­ruthenium(III) complex was confirmed by cyclic voltammetry.