Transition metals induce control of enhanced NLO properties of functionalized organometallic complexes under laser modulations

The molecular engineering of organometallic complexes has recently attracted renewed interest on account of their potential technological applications for optoelectronics in general and optical data storage. The transition metal which induces control of enhanced nonlinear optical properties of functionalized organometallic complexes versus not only the intensity but also the polarization of the incident laser beam is original and important for all optical switching. This makes organometallic complexes valuable and suitable candidates for nonlinear optical applications. In the present work, we report the synthesis and full characterization of four organometallic complexes consisting of N, N-dibutylamine and azobenzene fragments but differ by auxiliary alkynyl ligands or metal cations. Thus, a ferrocenyl derivative 1 and three ruthenium complexes 2-4 have been prepared. The nonlinear optical properties of the four new azo-based ruthenium and iron organometallic complexes in the solid state, using polymethylmethacrylate as matrix, have been thoroughly studied. This concept is extended to computing the HOMO and LUMO energy levels of the considered complexes, dipole moment, first and second order hyperpolarizabilities using the 6-31 + G(d,p) + LANL2DZ mixed basis set. The second and third nonlinear optical properties of the resulting polymer composites were obtained by measuring SHG and THG response by means of the Maker fringe technique using a laser generating at 1,064 nm with a 30 ps pulse duration. The values of the second and third order NLO susceptibilities of the four organometallic complexes were found to be higher than the common references used. Theoretical calculation shows that the large first and second order hyperpolarizablities are caused by strong intramolecular charge transfer between the transition metal parts and the ligands though a conjugated transmitter. These results indicate that the present organometallic complexes are valuable candidates for optoelectronic and photonic applications.

Dinuclear acetylide-bridged ruthenium(ii) complexes with rigid non-aromatic spacers

Rigid dinuclear ruthenium complexes containing non-aromatic caged and polycyclic spacer groups were synthesised and characterised. The complexes, [trans,trans-{Ru(dmpe)2(C[triple bond, length as m-dash]CtBu)}2(μ-C[triple bond, length as m-dash]C-X-C[triple bond, length as m-dash]C)], where X = 1,4-bicyclo[2.2.2]octane (C8H12) or 1,12-p-carborane (p-C2B10H10), were formed via the metathesis of terminal organic bisacetylenes with the methylruthenium complex, [trans-Ru(dmpe)2(CH3)(C[triple bond, length as m-dash]CtBu)], under mild conditions. Electrochemical studies demonstrated electronic interactions across the non-aromatic caged and polycyclic spacers was less than in the analogous complex with an aromatic spacer group, [trans,trans-{Ru(dmpe)2(C[triple bond, length as m-dash]CtBu)}2(μ-C[triple bond, length as m-dash]C-p-C6H4-C[triple bond, length as m-dash]C)]. Mononuclear complexes, [trans-Ru(dmpe)2(C[triple bond, length as m-dash]CtBu)(C[triple bond, length as m-dash]C-X-C[triple bond, length as m-dash]CH)], were also synthesised. [trans-Ru(dmpe)2(C[triple bond, length as m-dash]CtBu)(C[triple bond, length as m-dash]C-C8H12-C[triple bond, length as m-dash]CH)] and [trans,trans-{Ru(dmpe)2(C[triple bond, length as m-dash]CtBu)}2(μ-C[triple bond, length as m-dash]C-p-C2B10H10-C[triple bond, length as m-dash]C)] were structurally characterised by X-ray crystallography.

NLO-active Y-shaped ferrocene conjugated imidazole chromophores as precursors for SHG polymeric films

New Y-shaped ferrocene conjugated imidazole chromophores were prepared and fully characterized. The Y-shaped structure was confirmed by the single crystal X-ray diffraction technique. The chromophores show interesting second-order nonlinear optical (NLO) properties in solution, as determined by the Electric-Field Induced Second Harmonic generation (EFISH) technique. Remarkably, the trifluoro substituted compound 3 is characterized by a high μβEFISH value and has good potential as a molecular building block for composite films with Second Harmonic Generation (SHG) properties. For all compounds, the dipole moments and frontier orbital energies were calculated by the Density Functional Theoretical method.

Impact of the Subunit Arrangement on the Nonlinear Absorption Properties of Organometallic Complexes with Ruthenium(II) σ-Acetylide and Benzothiadiazole as Building Units §

In this paper, the nonlinear absorption properties of two complexes consisting of Ru(C≡CPh)(C≡C)(dppe)2 (dppe = Ph2PCH2CH2PPh2) as electron donor (D) and 4,7-di(2-thienyl)benzo[c][1,2,5]thiadiazole as electron acceptor (A) units in two different arrangement, i.e., A–D–A and D–A–D, are presented. They were measured in solution by the femtosecond open-aperture Z-scan method. The complexes show moderate two-photon absorption cross-sections σ(2) of several hundred to one thousand GM (here 1 GM = 10−50 cm4 s molecule−1 photon−1). Although they are formed by the same building units, it was found that the two-photon absorption values of the D–A–D arrangement are six times higher than that of the A–D–A one. This difference can be explained by the number of metal cores (one or two ruthenium centers), the geometrical configurations of the complexes (more or less planar), and the resonance enhancement by lowering the intermediate state.

An investigation on the second-order nonlinear optical response of cationic bipyridine or phenanthroline iridium(iii) complexes bearing cyclometallated 2-phenylpyridines with a triphenylamine substituent

The synthesis and characterisation of six new cationic iridium(iii) complexes bearing either 4,4'-di-tert-butyl-2,2'-bipyridine (dtBubpy) or 5-NO2-1,10-phenanthroline along with two cyclometallated 2-phenylpyridine derivative ligands, decorated with triphenylamine groups either meta or para to the Ir-CC^N bond or para to the Ir-NC^N bond, are reported. The second-order nonlinear optical (NLO) properties of all the compounds have been determined by the electric field induced second harmonic generation technique and show that the μβEFISH value can be tuned by the nature of the iridium coordination sphere. The dipole moment, μ, necessary to evaluate the quadratic hyperpolarizability βEFISH, was theoretically determined. The linear optical properties of the complexes are also presented and rationalised by quantum-chemical calculations. One of the prepared iridium compounds was incorporated into a polystyrene film, affording the first example of a second-order NLO active polymeric film based on a cationic organometallic complex.

Push-pull D-π-Ru-π-A chromophores: synthesis and electrochemical, photophysical and second-order nonlinear optical properties

The present work describes the one-pot synthesis and electrochemical, photophysical and second-order nonlinear optical (NLO) properties of a series of dipolar π-delocalized Ru(ii) dialkynyl complexes. The eight new asymmetrical D-π-Ru-π-A push-pull chromophores incorporate pyranylidene ligands as pro-aromatic donor groups (D) and formaldehyde, indane-1,3-dione, pyrimidine or pyrimidinium as electron-attracting groups (A) separated by ruthenium bis-acetylide fragments and π-conjugated linkers. The second-order nonlinear optical (NLO) properties of all eight complexes were determined by the Electric-Field-Induced Second Harmonic generation (EFISH) technique (operating at 1907 nm), and were compared to those of their purely organic analogs. All investigated compounds (organic and organometallic) exhibited positive μβ values, which dramatically increased for the complexes due to the presence of ruthenium in the π-conjugated core. The second-order NLO response could also be easily modulated by changing the nature of alkynyl substituents. The most promising ruthenium complexes 7 and 8 of the series with the pyrimidinium fragment displayed μβ values of 14 000 × 10^-48 esu. The effect of structural modifications on the redox and spectroscopic properties of the complexes was also studied. The intramolecular charge transfer (ICT) occurring through the ruthenium center of the push-pull σ-dialkynyl complexes was investigated by combining experimental and theoretical data.

Incorporation of a platinum center in the pi-conjugated core of push-pull chromophores for nonlinear optics (NLO)

In this article, we describe the synthesis, redox characteristics, and linear and nonlinear optical (NLO) properties of seven new unsymmetrical push-pull diacetylide platinum-based complexes. These D-π-Pt-π-A complexes incorporate pyranylidene ligands as pro-aromatic donor groups (D), diazine rings as electron-withdrawing groups (A), and various aromatic fragments (styryl or thienylvinyl) as π-linkers separating the platinum diacetylide unit from the donor and the acceptor groups. This is one of the first examples of push-pull chromophores incorporating a platinum center in the π-conjugated core. The NLO properties of these complexes were compared with those of their purely organic analogues. All compounds (organic and organometallic) exhibited positive μβ values, which dramatically increased upon methylation of the pyrimidine fragment. However, this increase was even more significant in the complexes due to the presence of platinum in the π-conjugated core. The effects of the linker on the redox and spectroscopic properties of the complexes are also discussed. In addition, DFT calculations were performed in order to gain further insight into the intramolecular charge transfer (ICT) occurring through the platinum center.

On the contribution of f electrons to the quadratic hyperpolarizability: the case of lanthanide terpyridyl complexes

4f-Electrons have no direct effect on first-order hyperpolarizabilities of lanthanide complexes.

Dipolar NLO Chromophores Bearing Diazine Rings as π-Conjugated Linkers

The synthesis of a series of push-pull derivatives bearing triphenylamine electron-donating group, cyclopenta[c]thiophen-4,6-dione electron acceptor and various π-linkers including (hetero)aromatic fragments is reported. All target chromophores with systematically varied π-linker structure were further investigated by electrochemistry, absorption measurements, and EFISH experiments in conjunction with DFT calculations. Based on electrochemical and photophysical measurements, when a polarizable 2,5-thienylene moiety is embedded into the chromophore π-backbone the highest intramolecular charge transfer (ICT) is observed. Benzene, pyrimidine, and pyridazine derivatives exhibit lower polarizability and extent of the ICT across these π-linkers. The elongation of the π-conjugated system via additional ethenylene linker results in a significant reduction of the HOMO-LUMO gap and an enhancement of the NLO response. Whereas it does not significantly influence electrochemical and linear optical properties, the orientation of the pyrimidine ring seems to be a key parameter on the μβ value due to significant variation of the dipolar moment (μ) value. In 2a and 2c, pyrimidine is oriented to behave as an acceptor and thus generate dipolar molecule with μ above 5 D, whereas in 2b and 2d ground state dipole moment is significantly reduced. This study seems to indicate a high aromaticity of pyrimidine and pyridazine derivatives, close to the benzene analogues and significantly higher than thiophene analogues.