Joseph P. Morrall

Organotransition Metal Complexes for Nonlinear Optics

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.

Organometallic complexes for nonlinear optics. Part 31. Cubic hyperpolarizabilities of ferrocenyl-linked gold and ruthenium complexes

Abstract The complexes [Fe{η-C5H4(E)CHCH4-C6H4CCX}2] [X=SiMe3 (1), H (2), Au(PCy3) (3), Au(PPh3) (4), Au(PMe3) (5), RuCl(dppm)2 (7), RuCl(dppe)2 (8)] and [Fe{η-C5H4(E)CHCH4-C6H4CHCRuCl(dppm)2}2](PF6)2 (6) have been prepared and the identities of 1 and 7 confirmed by single-crystal X-ray structural studies. Complexes 1–8 exhibit reversible oxidation waves in their cyclic voltammograms attributed to the FeII/III couple of the ferrocenyl groups, 6–8 also showing reversible (7, 8) or non-reversible (6) processes attributed to Ru-centered oxidation. Cubic nonlinearities at 800 nm by the Z-scan method are low for 1–5; in contrast, complexes 6 and 7 exhibit large negative γreal and large γimag values. A factor of 4 difference in ∣γ∣ and two-photon absorption cross-section σ2 values for 6 and 7 suggest that they have potential as protically switchable NLO materials.

Organometallic complexes for nonlinear optics. Part 32: Synthesis, optical spectroscopy and theoretical studies of some osmium alkynyl complexes

Abstract 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.

Syntheses and spectroscopic, structural, electrochemical, spectroelectrochemical, and theoretical studies of osmium(II) mono- and bis-alkynyl complexes

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.

NLO Properties of Metal Alkynyl and Related Complexes

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

Two-photon absorption, absorption saturation, and dispersion of the real and imaginary parts of the third-order optical nonlinearity in organometallic dendrimers

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.