Adam Barlow

Record Multiphoton Absorption Cross-Sections by Dendrimer Organometalation

Large increases in molecular two-photon absorption, the onset of measurable molecular three-photon absorption, and record molecular four-photon absorption in organic π-delocalizable frameworks are achieved by incorporation of bis(diphosphine)ruthenium units with alkynyl linkages. The resultant ruthenium alkynyl-containing dendrimers exhibit strong multiphoton absorption activity through the biological and telecommunications windows in the near-infrared region. The ligated ruthenium units significantly enhance solubility and introduce fully reversible redox switchability to the optical properties. Increasing the ruthenium content leads to substantial increases in multiphoton absorption properties without any loss of optical transparency. This significant improvement in multiphoton absorption performance by incorporation of the organometallic units into the organic π-framework is maintained when the relevant parameters are scaled by molecular weights or number of delocalizable π-electrons. The four-photon absorption cross-section of the most metal-rich dendrimer is an order of magnitude greater than the previous record value.

Syntheses, Spectroscopic, Electrochemical, and Third-Order Nonlinear Optical Studies of a Hybrid Tris{ruthenium(alkynyl)/(2-phenylpyridine)}iridium Complex.

The synthesis of fac-[Ir{N,C1′-(2,2′-NC5H4C6H3-5′-C≡C-1-C6H2-3,5-Et2-4-C≡CC6H4-4-C≡CH)}3] (10), which bears pendant ethynyl groups, and its reaction with [RuCl(dppe)2]PF6 to afford the heterobimetallic complex fac-[Ir{N,C1′-(2,2′-NC5H4C6H3-5′-C≡C-1-C6H2-3,5-Et2-4-C≡CC6H4-4-C≡C-trans-[RuCl(dppe)2])}3] (11) is described. Complex 10 is available from the two-step formation of iodo-functionalized fac-tris[2-(4-iodophenyl)pyridine]iridium(III) (6), followed by ligand-centered palladium-catalyzed coupling and desilylation reactions. Structural studies of tetrakis[2-(4-iodophenyl)pyridine-N,C1′](μ-dichloro)diiridium 5, 6, fac-[Ir{N,C1′-(2,2′-NC5H4C6H3-5′-C≡C-1-C6H2-3,5-Et2-4-C≡CH)}3] (8), and 10 confirm ligand-centered derivatization of the tris(2-phenylpyridine)iridium unit. Electrochemical studies reveal two (5) or one (6–10) Ir-centered oxidations for which the potential is sensitive to functionalization at the phenylpyridine groups but relatively insensitive to more remote derivatization. Compound 11 undergoes sequential Ru-centered and Ir-centered oxidation, with the potential of the latter significantly more positive than that of Ir(N,C′-NC5H4-2-C6H4-2)3. Ligand-centered π–π* transitions characteristic of the Ir(N,C′-NC5H4-2-C6H4-2)3 unit red-shift and gain in intensity following the iodo and alkynyl incorporation. Spectroelectrochemical studies of 6, 7, 9, and 11 reveal the appearance in each case of new low-energy LMCT bands following formal IrIII/IV oxidation preceded, in the case of 11, by the appearance of a low-energy LMCT band associated with the formal RuII/III oxidation process. Emission maxima of 6–10 reveal a red-shift upon alkynyl group introduction and arylalkynyl π-system lengthening; this process is quenched upon incorporation of the ligated ruthenium moiety on proceeding to 11. Third-order nonlinear optical studies of 11 were undertaken at the benchmark wavelengths of 800 nm (fs pulses) and 532 nm (ns pulses), the results from the former suggesting a dominant contribution from two-photon absorption, and results from the latter being consistent with primarily excited-state absorption.

Organometallic Complexes for Non-Linear Optics. 51. Second- and Third-Order Non-Linear Optical Properties of Alkynylgold Complexes*

The alkynes HC≡CC6H2-2,6-Et2-4-C≡CC6H4-4-NO2 (4) and HC≡CC6H4-4-C≡CC6H2-2,6-Et2-4-C≡CC6H4-4-NO2 (6) and gold alkynyl complexes Au{C≡CC6H2-2,5-(OEt)2-4-C≡CC6H4-4-NO2}(PPh3) (7), Au(C≡CC6H2-2,6-Et2-4-C≡CC6H4-4-NO2)(PPh3) (8), and Au(C≡CC6H4-4-C≡CC6H2-2,6-Et2-4-C≡CC6H4-4-NO2)(PPh3) (9) have been synthesized. The linear optical properties and quadratic optical non-linearities of 7–9 have been measured, the latter by hyper-Rayleigh scattering at 1064 nm, and compared with data for the previously reported complexes Au(C≡CC6H4-4-NO2)(PPh3) (10) and Au(C≡CC6H4-4-C≡CC6H4-4-NO2)(PPh3) (11). The optical absorption maximum red-shifts and the first hyperpolarizabilities increase on π-system lengthening and on introduction of electron-releasing substituents on the π-bridge ring adjacent to the metal centre. The cubic non-linear optical properties of 1,4-{(PCy3)Au(C≡C)}2C6H4 (12) and {(PCy3)Au(C≡C-4-C6H4C≡C)}6C6 (13) have been assessed by wide spectroscopic range femtosecond Z-scan studies; the maximal values of the imaginary component and the effective two-photon absorption cross-section increase markedly on proceeding from linear complex 12 to 6-fold-symmetric complex 13, an increase that is maintained when data are scaled by relative molecular weight.

Crystal structure of ({4-[(4-bromophen-yl)ethynyl]-3,5-diethylphenyl}ethynyl)-triisopropylsilane

The title compound, C29H37BrSi, was synthesized by the Sonogashira coupling of [(3,5-diethyl-4-ethynylphenyl)ethynyl]triisopropylsilane with 4-bromo-1-iodobenzene. In the structure, the two phenyl rings are nearly parallel to each other with a dihedral angle of 4.27 (4)°. In the crystal, π–π interactions between the terminal and central phenyl rings of adjacent molecules link them in the a-axis direction [perpendicular distance = 3.5135 (14); centroid–centroid distance = 3.7393 (11) Å]. In addition, there are weak C—H⋯π interactions between the isopropyl H atoms and the phenyl rings of adjacent molecules.

Dynamic Permutational Isomerism in a closo‐Cluster

Permutational isomers of trigonal bipyramidal [W2RhIr2(CO)9(η(5)-C5H5)2(η(5)-C5HMe4)] result from competitive capping of either a W2Ir or a WIr2 face of the tetrahedral cluster [W2Ir2(CO)10(η(5)-C5 H5)2] from its reaction with [Rh(CO)2(η(5)-C5HMe4)]. The permutational isomers slowly interconvert in solution by a cluster metal vertex exchange that is proposed to proceed by Rh-Ir and Rh-W bond cleavage and reformation, and via the intermediacy of an edge-bridged tetrahedral transition state. The permutational isomers display differing chemical and physical properties: replacement of CO by PPh3 occurs at one permutational isomer only, while the isomers display distinct optical power limiting behavior.

Crystal structure of ({4-[(4-bromo-phen-yl)ethyn-yl]-3,5-di-ethyl-phen-yl}ethyn-yl)triiso-propyl-silane.

The title compound, C29H37BrSi, was synthesized by the Sonogashira coupling of [(3,5-diethyl-4-ethynylphenyl)ethynyl]triisopropylsilane with 4-bromo-1-iodobenzene. In the structure, the two phenyl rings are nearly parallel to each other with a dihedral angle of 4.27 (4)°. In the crystal, π–π interactions between the terminal and central phenyl rings of adjacent molecules link them in the a-axis direction [perpendicular distance = 3.5135 (14); centroid–centroid distance = 3.7393 (11) Å]. In addition, there are weak C—H⋯π interactions between the isopropyl H atoms and the phenyl rings of adjacent molecules.

Crystal structure of ({4-[(4-bromophenyl)ethynyl]-3,5-diethylphenyl}ethynyl)triisopropylsilane

The title compound, C29H37BrSi, was synthesized by the Sonogashira coupling of [(3,5-diethyl-4-ethynylphenyl)ethynyl]triisopropylsilane with 4-bromo-1-iodobenzene. In the structure, the two phenyl rings are nearly parallel to each other with a dihedral angle of 4.27 (4)°. In the crystal, π–π interactions between the terminal and central phenyl rings of adjacent molecules link them in the a-axis direction [perpendicular distance = 3.5135 (14); centroid–centroid distance = 3.7393 (11) Å]. In addition, there are weak C—H⋯π interactions between the isopropyl H atoms and the phenyl rings of adjacent molecules.