Long-Range Corrected DFT Calculations of First Hyperpolarizabilities and Excitation Energies of Metal Alkynyl Complexes

The performance of the CAM‐B3LYP, ωB97X and LC‐BLYP long‐range corrected density functional theory methods in the calculation of molecular first hyperpolarizabilities (β) and low‐lying charge transfer (CT) excitation energies of the metal alkynyl complexes M(C≡C‐4‐C6H4‐1‐NO2)(κ2‐dppe)(η5‐C5H5) [M=Fe (1), Ru (2), Os (3)] and trans‐[Ru{C≡C‐(1,4‐C6H4C≡C)n‐4‐C6H4‐1‐NO2}Cl(κ2‐dppm)2] [n=0 (4), 1 (5), 2 (6)] was assessed. The BLYP, B3LYP and PBE0 standard exchange‐correlation functionals and the Hartree‐Fock method were also examined. The BLYP functional was shown to perform poorly in the calculation of β and low‐energy CT transitions. The hybrid functionals (B3LYP and PBE0) showed significant improvement over the pure functional BLYP, but overestimated the hyperpolarizability ratios and the wavelengths of the lowest energy metal‐to‐ligand CT transitions for 5 and 6. The effect of long‐range corrections is noteworthy, particularly for the larger complexes, improving the calculation of β ratios for 4–6. However, CAM‐B3LYP, ωB97X, and LC‐BLYP considerably overestimated the low‐lying CT energies. PBE0 was found to give the best transition energy match for 4. The influence of the phenylene ring orientation in the alkynyl ligand on the calculated properties is substantial, particularly for the larger complexes. For these types of calculations, a basis set with diffuse functions (at least 6‐31+G(d)) for the heavy elements is recommended.The authors gratefully acknowledge the Australian Research Council (ARC) for financial support and also access to the Australian National University supercomputer facilities of the National Computational Infrastructure

Syntheses and Optical Properties of Azo-Functionalized Ruthenium Alkynyl Complexes

We thank the Australian Research Council (ARC), the National Natural Science Foundation of China (51432006), and the Chinese Government Ministry of Education and State Administration of Foreign Experts Affairs (111 Project: B13025) for financial support. M.P.C. thanks the ARC for an Australian Research Fellowship

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

We thank the Australian Research Council (ARC), the National Natural Science Foundation of China (51432006), the Chinese Government Ministry of Education, and the Chinese Government State Administration of Foreign Experts Affairs (111 Project: B13025). M.P.C. thanks the ARC for an Australian Research Fellowship and C.Q. thanks CONICYT (Chile) for a Chile PhD Scholarship Abroad

Linear Optical, Quadratic and Cubic Nonlinear Optical, Electrochemical, and Theoretical Studies of "Rigid-Rod" Bis-Alkynyl Ruthenium Complexes

The syntheses of oligo(p‐phenylene ethynylene)s (OPEs) end‐functionalized by a nitro acceptor group and with a ligated ruthenium unit at varying locations in the OPE chain, namely, trans‐[Ru{(C≡C‐1,4‐C6H4)nNO2}(C≡CR)(dppe)2] (dppe=1,2‐bis(diphenylphosphino)ethane; n=1, R=1,4‐C6H4C≡C‐1,4‐C6H4C≡CPh, 1,4‐C6H4NEt2; n=2, R=Ph, 1,4‐C6H4C≡CPh, 1,4‐C6H4C≡C‐1,4‐C6H4C≡CPh, 1,4‐C6H4NO2, 1,4‐C6H4NEt2; n=3, R=Ph, 1,4‐C6H4C≡CPh), are reported. Their electrochemical properties were assessed by cyclic voltammetry, their linear optical properties and quadratic and cubic nonlinear optical properties were assayed by UV/Vis/NIR spectroscopy, hyper‐Rayleigh scattering studies employing nanosecond pulses at 1064 nm, and broad spectral range Z‐scan studies employing femtosecond pulses, respectively, and their linear optical properties and vibrational spectroscopic behavior in the formally RuIII state was examined by UV/Vis/NIR and IR spectroelectrochemistry, respectively. The potentials of the metal‐localized oxidation processes are sensitive to alkynyl‐ligand modification, but this effect is attenuated on π‐bridge lengthening. Computational studies employing time‐dependent density functional theory were undertaken on model complexes, with a 2D scan revealing a soft potential‐energy surface for intra‐alkynyl‐ligand aryl‐ring rotation; this is consistent with the experimentally observed blueshift in optical absorption maxima. Quadratic optical nonlinearities are significant and cubic NLO coefficients for these small complexes are small. The optimum length of the alkynyl ligands and the ideal metal location in the OPE to maximize the key coefficients have been defined.We thank the Australian Research Council, the Fund for Scientific Research–Flanders (FWO-Vlaanderen; FWO G.0312.08), and the Katholieke Universiteit Leuven (GOA/2006/03) for financial support, and Yuwen Wu (ANU) for providing a crystal of 14 suitable for the X-ray diffraction study

Organometallic complexes for nonlinear optics.66. Synthesis and quadratic nonlinear optical studies of trans-[Ru{C=C{2,5-C4H2S-( E )-CH=CH}n-2,5-C4H2S(NO2 )}Cl(dppe)2](n1/40-2)

Oligo(2,5-thienylenevinylene)s (OTVs) end-functionalized with a ligated ruthenium alkynyl unit as adonor and a nitro as acceptor, namelytrans-[Ru{C^C-2,5-C4H2S(NO2)}Cl(dppe)2](Ru1T),trans-[Ru{C^C-2,5-C4H2S-(E)-CH]CH-2,5-C4H2S(NO2)}Cl(dppe)2](Ru2T), andtrans-[Ru{C^C-2,5-C4H2S-(E)-CH]CH-2,5-C4H2S-(E)-CH]CH-2,5-C4H2S(NO2)}Cl(dppe)2](Ru3T), have been synthesized, their elec-trochemical properties have been assessed by cyclic voltammetry (CV), their linear optical and quadratic nonlinear optical (NLO) properties have been assayed by UVeviseNIR spectroscopy and hyper-Rayleighscattering studies at 1300 nm, respectively, and their linear optical properties in the formally RuIII state have been examined by UVeviseNIR spectroelectrochemistry. The data for Ru1T-Ru3Thave beencompared to those of the oligo(p-phenylenevinylene) (OPV) analoguestrans-[Ru(C^C-1,4-C6H4NO2)Cl(dppe)2](Ru1P),trans-[Ru{C^C-1,4-C6H4-(E)-CH]CH-1,4-C6H4NO2}Cl(dppe)2](Ru2P), andtrans-[Ru{C^C-1,4-C6H4-(E)-CH]CH-1,4-C6H4-(E)-CH]CH-1,4-C6H4NO2}Cl(dppe)2](Ru3P). The RuII/IIIoxidationpotentials decrease on proceeding fromRu1TtoRu3T, while the wavelength of the UVevislmaxbandincreases on proceeding fromRu1TtoRu2T, but thereafter decreases on further progression toRu3T, similar trends to those seen proceeding fromRu1PtoRu3P. The quadratic nonlinearityb1300 increases on OTV lengthening from Ru1TthroughRu2TtoRu3T; the data are significantly larger than those of the Ru1PeRu3Panalogues which peak atRu2P. The formally RuIIIcomplexes exhibit low-energy bands thatred-shift significantly on proceeding fromRu1TtoRu3T. Computational studies employing time-dependent density functional theory were undertaken on model complexes to rationalize the optical observations and explore the impact of further OTV bridge lengthening. Computational studies on modelcomplexesRu1T′-Ru6T′are consistent with decreasing contributions of the electron donor (ligated Ru) and acceptor (NO2) groups to the HOMO and LUMO, respectively, up n-bridge lengthening.btotvalues increase on progression fromRu1T′toRu3T′, but thereafter further bridge lengthening affords little further increase in b-tot, consistent with a saturation in quadratic NLO response.We thank the Australian Research Council (ARC: DP170100408),the National Natural Science Foundation of China (51432006), theChinese Government Ministry of Education, and the Chinese Gov-ernment State Administration of Foreign Experts Affairs (111 Proj-ect: B13025). J. D. thanks the China Scholarship Council and theAustralian National University for a CSC-ANU PhD Scholarship

Computational Study of Structural and Optical Properties of Metal Alkynyl Complexes

The interaction of light with a nonlinear optical (NLO) material gives rise to new optical fields with altered properties (e.g. phase, frequency, amplitude, polarization, path, etc.), which are of utmost importance for photonic applications. The search for new efficient NLO materials for applications has thus been accelerated. In particular, interest in the NLO properties of organometallic systems has undergone enormous growth in the past decade. This thesis consists of a compilation of several papers relating to the experimental and density functional theory (DFT) studies of the nonlinear optical properties of metal alkynyl complexes. Paper 1 includes a brief introduction to nonlinear optical phenomena, in particular to the second-order NLO effects, and the popular experimental and quantum chemical methods for the determination of molecular first hyperpolarizability. It also includes a comprehensive review of previous semi empirical and DFT NLO calculations relating to organometallic complexes. Paper 2 deals with the benchmarking of DFT methods for first hyperpolarizabilities and excitation energies of metal alkynyls against the relevant experimental data. Papers 3-9 are combined experimental and computational (DFT) studies of dipolar (paper 3-8) and octupolar (paper 9) metal alkynyl complexes. The contribution from the calculations to each paper is as follows. In paper 3, linear optical and quadratic nonlinear optical properties of alkynyl complexes with different ligated metal centres (Ru, Ni, and Au) and with different bridges (phenylene, naphthalenylene, and anthracenylene) are calculated with DFT and time dependent DFT (TD-DFT). In paper 4, the linear optical and quadratic nonlinear optical properties of ruthenium alkynyl complexes with oligo(phenylenevinylene) bridges were calculated using DFT and the results compared with the experimental data. In paper 5, the experimentally determined linear optical properties and first hyperpolarizabilities of some ruthenium alkynyl complexes with yne/ene/azo inter-ring linkers are rationalized by DFT/TD-DFT calculations. In paper 6, the structural, linear optical, and nonlinear optical properties of ruthenium alkynyl complexes with P–P (= dppf, dppb, and dppe) and N–N (4,4’-di-tert-butyl-2,2’-bipyridine) donor co-ligands were rationalized from DFT calculations. Paper 7 consists of TD-DFT calculations undertaken on a series of bis(alkynyl) Ru complexes to rationalize the experimental linear optical data. In paper 8, the mechanism of two-dimensional NLO character in Y-shaped ruthenium alkynyl complexes is studied with the use of DFT/TD-DFT calculations. In paper 9, computational studies were undertaken to assign the key optical transitions for some octupolar compounds bearing (N-heterocyclic carbene) gold or diphenylamino substituents at the periphery

Computational studies of the nonlinear optical properties of organometallic complexes

Computational methods for calculating the molecular nonlinear optical (NLO) properties of molecules are reviewed, with an emphasis on clarifying the strengths and weaknesses of the various approaches. A brief introduction to the theory of NLO effects is provided, and a summary of the key experimental techniques for the determination of molecular first hyperpolarizabilities is included, with discussion of their advantages and disadvantages. Applications of semi-empirical methods and density functional theory in developing structure-quadratic NLO property relationships for organometallic complexes (and particularly metal alkynyl complexes) are reviewed.We thank the Australian Research Council (ARC) for financial support and Dr E. Kulasekera for helpful discussion

Organometallic Complexes for Non-Linear Optics. 59. Syntheses and Optical Properties of Some Octupolar (N-Heterocyclic Carbene)gold Complexes

The syntheses of octupolar alkynes 1,3,5-{4-(4-HC≡CC6H4-1-C≡C)-3,5-Et2C6H2-1-C≡C}3C6H3 (4) and 1,3,5-{4-(4-HC≡CC6H4-1-C≡C-4-C6H4-1-C≡C)-3,5-Et2C6H2-1-C≡C}3C6H3 (6), diphenylamino-substituted 1,3,5-(4-Ph2NC6H4-1-C≡C)3C6H3 (7), 1,3,5-(4-Ph2NC6H4-1-C≡C-4-C6H4-1-C≡C)3C6H3 (8), 1,3,5-{4-(4-Ph2NC6H4-1-C≡C-4-C6H4-1-C≡C)-3,5-Et2C6H2-1-C≡C}3C6H3 (9), and 1,3,5-{4-(4-Ph2NC6H4-1-C≡C-4-C6H4-1-C≡C-4-C6H4-1-C≡C)-3,5-Et2C6H2-1-C≡C}3C6H3 (10), and (N-heterocyclic carbene)gold-appended 1,3,5-{[(NHC-iPr)Au]C≡C}3C6H3 (11), 1,3,5-{[(NHC-iPr)Au]C≡C-4-C6H4-1-C≡C}3C6H3 (12), 1,3,5-{4-([(NHC-iPr)Au]C≡C-4-C6H4-1-C≡C)-3,5-Et2C6H2-1-C≡C}3C6H3 (13), and 1,3,5-{4-([(NHC-iPr)Au]C≡C-4-C6H4-1-C≡C-4-C6H4-1-C≡C)-3,5-Et2C6H2-1-C≡C}3C6H3 (14) [NHC-iPr≤C-cyclo-CN(2,6-C6H3iPr2)CH≤CHN(2,6-C6H3iPr2)] are reported. The low-energy bands in the linear optical absorption spectra of all three sets of compounds are red-shifted and increase in intensity upon π-delocalizable 'arm' lengthening. The diphenylamino- and (NHC-iPr)gold-terminated compounds do not exhibit measurable second-harmonic generation as assessed by hyper-Rayleigh scattering at 1064nm using nanosecond pulses. Computational studies have been employed to rationalize the optical properties of the new compounds. Calculations on 7-10 reveal that the lowest-energy transitions with large oscillator strengths are predominantly [Ph2NC6H4] (π) → [arms+core] (π∗) in character, whereas calculations on 11-14 suggest that the low-energy transitions relate to the transfer of electron density from the Au-alkynyl core group to the terminal NHC group

Organometallic complexes for nonlinear optics. 66. Synthesis and quadratic nonlinear optical studies of trans -[Ru{C=C{2,5-C4H2S-(E)- CH=CH}(n)-2,5-C4H2S(NO2)}Cl(dppe)(2)] (n=0-2)

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Quadratic and cubic hyperpolarizabilities of nitro-phenyl/-naphthalenyl/-anthracenyl alkynyl complexes

1-Nitronaphthalenyl-4-alkynyl and 9-nitroanthracenyl-10-alkynyl complexes [M](C≡C-4-C10H6-1-NO2) ([M] = trans-[RuCl(dppe)2] (6b), trans-[RuCl(dppm)2] (7b), Ru(PPh3)2(η5-C5H5) (8b), Ni(PPh3)(η5-C5H5) (9b), Au(PPh3) (10b)) and [M](C&8801;C-10-C14H8-9-NO2) ([M] = trans-[RuCl(dppe)2] (6c), trans-[RuCl(dppm)2] (7c), Ru(PPh3)2(η5-C5H5) (8c), Ni(PPh3)(η5-C5H5) (9c), Au(PPh3) (10c)) were synthesized and their identities were confirmed by single-crystal X-ray diffraction studies. Electrochemical studies and a comparison to the 1-nitrophenyl-4-alkynyl analogues [M](C&8801;C-4-C6H4-1-NO2) ([M] = trans-[RuCl(dppe)2] (6a), trans-[RuCl(dppm)2] (7a), Ru(PPh3)2(η5-C5H5) (8a), Ni(PPh3)(η5-C5H5) (9a), Au(PPh3) (10a)) reveal a decrease in oxidation potential for ruthenium and nickel complexes on proceeding from the phenyl- to naphthalenyl- and then anthracenyl-containing bridge. HOMO → LUMO transitions characteristic of MC&8801;C-1-C6H4 to 4-C6H4-1-NO2 charge transfer red-shift and gain in intensity on proceeding to the ruthenium complexes; the low-energy transitions have increasing ILCT character on proceeding from the phenyl- to naphthalenyl- and then anthracenyl-containing bridge. Spectroelectrochemical studies of the Ru-containing complexes reveal the appearance of low-energy bands corresponding to chloro-to-Ru^III charge transfer that red-shift on proceeding from the phenyl- to naphthalenyl- and then anthracenyl-containing bridge. Second-order nonlinear optical (NLO) studies at 1064 nm employing ns pulses and the hyper-Rayleigh scattering technique reveal an increase in quadratic optical nonlinearity upon introduction of metal to the precursor alkyne to afford alkynyl complexes and on proceeding from ligated-gold to -nickel and then to -ruthenium for a fixed alkynyl ligand. Quadratic NLO data of the gold complexes optically transparent at the second-harmonic wavelength reveal an increase in βHRS on proceeding from the phenyl- to the naphthalenyl-containing complex. Broad spectral range third-order nonlinear optical studies employing fs pulses and the Z-scan technique reveal an increase in two-photon absorption cross-section on replacing ligated-gold by -nickel and then -ruthenium for a fixed alkynyl ligand. Computational studies undertaken using time-dependent density functional theory have been employed to assign the nature of the key optical transitions and suggest that the significant optical nonlinearities observed for the ruthenium-containing complexes correlate with the low-energy formally Ru → NO2 band which possesses strong MLCT character, while the more moderate nonlinearities of the gold complexes correlate with a band higher in energy that is primarily ILCT in character.We thank the Australian Research Council (ARC), the National Natural Science Foundation of China (51432006), and the Chinese Government Ministry of Education and State Administration of Foreign Experts Affairs (111 Project: B13025) for financial support