Gulliver T. Dalton

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.

Cubic Nonlinear Optical Properties of Platinum-Terminated Polyynediyl Chains

The wavelength dependence of the cubic nonlinearity of ligated platinum-terminated polyynes trans, trans-{(p-MeC6H4)3P}2(p-MeC6H4)Pt(C[triple bond]C)n Pt(p-C6H4Me){P(p-C6H4Me)3}2 (n = 3-6, 8, 10, 12) has been examined by femtosecond Z-scan studies in the wavelength range 520-1500 nm and the results rationalized by density functional theory calculations on the model complexes trans, trans-(H3P)2(C6H5)Pt(C[triple bond]C)n Pt(C6H5)(PH3)2 (n = 2-8, 10, 12). Although the final states for one- and two-photon transitions are not the same in these centrosymmetric molecules, the Z-scan studies reveal coincidences in one-photon absorption with features in the frequency dependencies of both real and imaginary parts of the cubic hyperpolarizability, as well as inflections in the frequency dependencies of the real part of gamma that correspond to resonances in the imaginary part of gamma. The theoretical studies suggest that the linear absorption spectra are dominated by X(1)A g --> n(1)B(3u) transitions, with the first state of B(3u) symmetry playing a steadily diminishing role upon oligoyne chain lengthening. The theoretical studies also predict a red-shift of two-photon absorption (TPA) profile with increasing conjugation length, and a significant enhancement on proceeding from the shortest to the longest chromophore, trends that are observed experimentally. The experimental low-energy TPA maxima for these complexes can be approximated by a simple Gaussian profile. The sp-carbon chain-length dependence of linear and nonlinear absorption maxima enable an estimate (neglecting saturation) of 660 and 1000 nm for the infinite carbon chain, carbyne.

Organometallic complexes for nonlinear optics. 42. Syntheses, linear, and nonlinear optical properties of ligated metal-functionalized oligo(p-phenyleneethynylene)s.

A combination of UV-vis-NIR spectroscopy, femtosecond Z-scan measurements, and time-dependent density functional theory (TD-DFT) calculations have been used to comprehensively investigate the linear optical and nonlinear optical (NLO) properties of pi-delocalizable metal-functionalized oligo(phenyleneethynylene)s. A range of unsymmetrically or symmetrically end-functionalized mono-, di-, tri-, penta-, hepta-, and nona(phenyleneethynylene)s were synthesized, with larger examples bearing varying numbers of 2,5-di(hexyloxy)phenyl groups to ensure sufficient solubility of the metal complex derivatives. The effect of incorporating varying numbers of solubilizing substituents in the OPE bridge, peripheral group modification, OPE lengthening, coligand variation, and metal location in the OPE on the linear optical properties has been established, with the first three molecular modifications resulting in significant changes in the optical absorption maxima. TD-DFT calculations reveal that the most intense transition in the linear optical spectra is localized on the OPE bridge and involves excitation from acetylenic to cumulenic molecular orbitals that are not greatly spatially separated from one another. The nonlinear optical properties are dominated by two-photon absorption, which for all but 1,4-{trans-[RuCl(dppm)(2)]C[triple bond]C}(2)C(6)H(4) appears as a band around 11,400 cm(-1) and a sharp increase of nonlinear absorption at frequencies >17,000 cm(-1). Surprisingly, there is relatively little influence of the length of the OPE bridge on the magnitude of the two-photon absorption cross sections, which are in the range 300-1000 GM.

Structural and Nonlinear Optical Properties of Aligned Heterotrinuclear [RuII‐(Spacer)‐MII‐(Spacer)‐RuII] Complexes (M=Pd, Pt; spacer=4‐ethynylpyridine)

Lewis addition between the metalloligand [RuCp(C[triple bond]Cpy-4)(dppf)] (1) (dppf = (C(5)H(4)PPh(2))(2)Fe) and MCl(2)(CH(3)CN)(2) gives [RuCp(C[triple bond]Cpy-4)(dppf)](2)[MCl(2)] (M = Pd (2) and Pt (3)), all of which have been spectroscopically and crystallographically characterized. The mixed-metal adducts show the d(6)-d(8)-d(6) metal alignment maintained by the trans disposition of the directionally rigid 4-ethynylpyridine at the centrosymmetric square-planar metal center. Electrochemical studies of these and the related known complexes trans-[RuCl(C[triple bond]Cpy-4)(dppm)(2)] (4) and [trans-RuCl(C[triple bond]Cpy-4)(dppm)(2)](2)[MCl(2)] (dppm = Ph(2)PCH(2)PPh(2)) (M = Pd (5) and Pt (6)) suggest that the spacer-linked heterotrinuclear network is able to stabilize the oxidized Ru(III) better than the metalloligand precursor. Cubic nonlinear optical responses are also generally higher for the heterometallic complexes. The gamma(real) value of the PdRu(2) dppm complex 5 is among the largest for linear organometallic complexes.

Organometallic complexes for nonlinear optics, 47 - synthesis and cubic optical nonlinearity of a stilbenylethynylruthenium dendrimer.

The synthesis of the 1st generation dendrimer 1,3,5-{trans-[Ru(C≡C-3,5-(trans-[Ru(C≡CPh)(dppe)(2) (C≡CC(6) H(4) -4-(E)-CHCH)])(2) C(6) H(3) )(dppe)(2) (C≡CC(6) H(4) -4-(E)-CHCH)]}(3) C(6) H(3) proceeds by a novel route that features Emmons-Horner-Wadsworth coupling of 1,3,5-C(6) H(3) (CH(2) PO(OEt)(2) )(3) with trans-[Ru(C≡CC(6) H(4) -4-CHO)Cl(dppe)(2) ] and 1-I-C(6) H(3) -3,5-(CH(2) PO(OEt)(2) )(2) with trans-[Ru(C≡CPh)(C≡CC(6) H(4) -4-CHO)(dppe)(2) ] as key steps. The stilbenylethynylruthenium dendrimer is much more soluble than its ethynylated analog 1,3,5-{trans-[Ru(C≡C-3,5-(trans-[Ru(C≡CPh)(dppe)(2) (C≡CC(6) H(4) -4-C≡C)])(2) C(6) H(3) )(dppe)(2) (C≡CC(6) H(4) -4-C≡C)]}(3) C(6) H(3) and, in contrast to the ethynylated analog, is a two-photon absorber at telecommunications wavelengths.

Dispersion of the complex cubic nonlinearity in two-photon absorbing organic and organometallic chromophores

There is much interest in nonlinear absorbing chromophores for applications in photonics, nanophotonics and biophotonics. We have performed studies of dispersion of the nonlinear absorption cross sections and the refractive nonlinearities of organic and organometallic nonlinear chromophores using the technique of Z-scan, with a tunable amplified femtosecond laser system. Z-scan is less sensitive than the popular technique of two-photon induced fluorescence but has advantages of being suitable for non-fluorescent substances and providing information on both absorptive and refractive nonlinearities. We have analysed the experimental results in terms of simple models and using the Kramers-Kronig transformation as shown in this paper for Coumarine 307 and an organometallic dendrimer. The dispersion curves are often dominated by two-photon resonances but inclusion of other nonlinear mechanisms seems to be necessary for better understanding of their features.

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