Large Third-order Nonlinear Optical Properties Research Articles

Introducing a novel C50N10 azafullerene with chained nitrogen atoms on a buckyball pole: structure, stability, vibration, and electronic properties.

Fullerenes are of high significance due to their unique chemical properties and various applications in technology, particularly materials science, drug delivery, electronics, and nanoelectronics. In the recent years, many attempts have been focused to introduce new heteroatom-doped fullerenes having advanced chemical properties and tunable electronic traits, which make them a potential candidate for application in many branches of sciences. In this study, a novel C50N10 azafullerene with a fascinating structure of chained nitrogen atoms on a buckyball pole, with different electronic and optical properties compared to its other analogs, is introduced and trace of N-N substructures on the surface of C60 fullerene cage is investigated. For this molecule, four structural isomers including 3 structures with chain N atoms on a fullerene buckyball pole (NP isomers) and one isomer with separated N atoms (SN isomer) have been studied. All isomers have been studied with and without symmetry constraints, and the symmetry influence on the structure and stability of each isomer has been investigated. Although the studied NP structures have lower stability than the SN isomer, some reasons (such as their more all-carbon hexagonal rings, breaking some of their N-N bonds for partial opening of the cage and creating bigger rings in order to get rid of the unfavorable strain, as well as decreasing the N-N lone pair repulsions) lead to the acceptable stability of these structures with the bonded N atoms. The results of atomization energy and vibrational frequency calculations indicate that isomers with the bonded N atoms have acceptable stabilities and do not decompose into their constituent components. Investigation on the structural parameters demonstrates important roles of the number of all-carbon hexagonal rings, the number of N-N junction, and the molecule symmetry in the stability of the structures with the bonded N atoms. Study on the electronic and optical properties indicates that the target structures exhibit high electronic polarizability, relatively small HOMO/LUMO gap, high first- and second-order hyperpolarizability, and also large third-order nonlinear optical properties. All calculations have been performed using Gaussian G09 software using density functional theory (DFT) approach. Three-parameter Beck hybrid exchange functional (B3) hybridized with nonlocal correlation functional of Lee, Yang, and Parr (LYP) has been employed as the level of DFT calculations. All optimizations have been performed at double-zeta polarized (DZP) split valence 6-31G(d,p) and also at split valence TZP 6-311G(d,p) basis sets. The global minimum structures have been confirmed by frequency calculations at the same level of optimizations. The natural bond orbital (NBO) analyses, frontier orbital surfaces imaging, atomic charges, and charge transfer analyses have been achieved by GenNBO program package.

New quinacridone derivatives: Structure-function relationship exploration to enhance third-order nonlinear optical responses

Exploiting synergistic cooperation between multiple sources of optical nonlinearity, we report the design, synthesis, and the third-order nonlinear optical (NLO) properties of a series of quinacridone-based materials with condensed π-systems, and sterically regulated inter-aryl twist angles. By introducing dicyanoethylene groups not only successfully modified the structures and photoelectric properties of the chromophores but also led to the superior third-order NLO properties. The relationships between molecular structure and mechanisms of the enhanced nonlinear refractive index were illuminated by spectroscopic, electrochemical, and Z-scan measurements. Combined with quantum chemical calculations, the test data and theory calculations were verified. The maximum nonlinear absorptive coefficients (χ(3)) in these materials based on chromophore QA-B2 is 15.456 × 10−13 esu, which is more than 5 times higher than that of mono-modified QA. Our results clearly suggest that quinacridone-based materials have good photo-thermal stability and large third-order NLO properties, are very promising for integrated NLO devices.

Preparation and nonlinear optical properties of two acrylate polymers bearing different long conjugated pendants

Two new acrylate monomers containing different long π-election conjugation bridge structure, 4′-[(N,N-diethylacrylate) amino], 4-(pyridine-4-vinyl) stilbene (DAS) and 4′-[(N,N-diethylacrylate) amino], 4-(pyridine-4-vinyl) azobenzene (DAA), were synthesized and their copolymers with methyl methacrylate (MMA) were prepared by free radical polymerization method. Their structures and properties of these copolymers were characterized and evaluated by FTIR, 1H-NMR, UV spectra, GPC and Z-scan technique with 8 ns pulses at 532 nm wavelength. The relationship between their structures and properties was investigated. The results show that the structure of these resultant copolymers can be effectively tuned by simply varying the feed ratio and these copolymers exhibit good solubility and large third-order nonlinear optical properties. The large third-order nonlinear optical properties are mainly attributed to the substituted NLO-chromophore with long D-π-A conjugated structure. Simultaneously, it is found that poly (DAA-co-MMA) with N=N double bond as conjugation bridge has larger third-order nonlinear optical susceptibility than poly (DAS-co-MMA) with C=C double bond as conjugation bridge owing to more effective π electron conjugation effect.

Space-selective precipitation of Ge crystalline patterns in glasses by femtosecond laser irradiation

Crystalline Ge was induced space selectively inside a borosilicate glass by 800 nm, 250 kHz femtosecond laser irradiation. Micro-Raman spectra and x-ray diffraction analysis confirmed that the laser-induced crystals were cubic Ge. A periodic structure consisting of Ge crystalline lines was inscribed in the glass sample by continuously moving the focal point of the laser beam. Large third-order nonlinear optical properties and ultrafast response time were observed from the crystallization region owing to highly optical nonlinearity of Ge crystals. These results may find some applications in fabrication of functional optical and photonic devices, such as optical circuits.

Large Third-Order Optical Nonlinear Effects of Gold Nanoparticles with Unusual Fluorescence Enhancement

The third-order nonlinear optical properties of two solutions of gold nanoparticles protected by carbazolyldiacetylene derivatives were investigated using the Z-scan technique. Both gold nanoparticle colloid solutions in toluene show unusual fluorescent enhancement and large third-order nonlinear optical properties including nonlinear absorption and refractive effects. When extending the pi-conjugated length of the ligands, the third-order nonlinear properties of composite materials based on gold nanoparticles were enhanced accordingly.

Theoretical Study on the Electronic Spectrum and the Origin of Remarkably Large Third-Order Nonlinear Optical Properties of Organoimide Derivatives of Hexamolybdates

Electronic spectrum of organoimide derivatives of hexamolybdates have first been calculated within the time-dependent density-functional theory in conjunction with Van Leeuwen-Baerends (LB94) exchange correlation potential, statistical average of orbital potentials (SAOP), and gradient-regulated connection potential (GRAC), respectively. The GRAC yields much better agreement with experiments for the excitation energies comparing with both LB94 and SAOP. The analysis of transition nature indicates that there is a significant difference between the diagonal and the orthogonal substituted derivatives. The static and dynamic third-order polarizabilities are calculated using time-dependent density-functional theory combined with the sum-over-states method. The results show that these derivatives possess remarkable large molecular third-order polarizabilities, especially for system 8 with -17882.6 x 10(-36) esu. This value is about 250 times that for the C(60) molecule. Adding the organoimide segment to the [Mo(6)O(19)](2-) can substantially increase the nu value. This variation can be traced to the different electronic transition characteristics between the derivatives of [Mo(6)O(19)](2-) and [Mo(6)O(19)](2-). For our studied systems, increasing the conjugation length and diagonal substituted are efficient ways to enhance the third-order polarizability. Thus, the organoimide derivatives of hexamolybdates may comprise a new promising class of nonlinear optical materials from the standpoint of large values, small dispersion behavior, and high transparency.

Ultrafast and Large Third-Order Nonlinear Optical Properties of CdS Nanocrystals in Polymeric Film

We report the ultrafast and large third-order nonlinear optical properties of CdS nanocrystals (NCs) embedded in a polymeric film. The CdS NCs of 2 nm radius are synthesized by an ion-exchange method and highly concentrated in the two layers near the surfaces of the polymeric film. The two-photon absorption coefficient and the optical Kerr coefficient are measured with laser pulses of 250 fs duration at 800 nm wavelength. The one-photon and two-photon figures of merit are determined to be 3.1 and 1.3, respectively, at irradiance of 2 GW/cm(2). The observed nonlinearities have a recovery time of approximately 1 ps. The two-photon-generated free carrier effects have also been observed and discussed. These results demonstrate that CdS NCs embedded in polymeric film are a promising candidate for optical switching applications.

Large Third-Order Nonlinear Optical Properties of Cadmium Oxide Thin Films

This study represents the first investigation on CdO films by the z-scan technique. Deposition experiments in a low-pressure horizontal hot-wall reactor on SiO2 substrates result in CdO thin films that show large third-order nonlinear optical properties. Optical properties of CdO were tuned by varying the deposition conditions. AFM images suggest that MOCVD under more oxidizing condition results in smaller crystal sizes. The decrease of the particle dimension causes larger optical nonlinearity. Monotonic increase of the χ(3) values with the increase of the laser pulse duration is observed by comparing our results with similar literature data for metal oxides.

Third-order nonlinear optical properties and two-photon absorption in branched oligothienylenevinylenes

We report measurements of the third-order susceptibilities and two-photon absorption in branched oligothienylenevinylenes derivatives C 42H 62S 2, C 114H 174S 6, C 252H 366N 3O 6P 3S 12, using degenerate four wave mixing (DFWM) technique at λ=532 nm in picosecond regime. All the studied compounds show large third-order nonlinear optical properties with comparison with known materials such as, polydiacetylene, octupolar molecules and their dipolar subunits. We show the influence of the number of branches on the benzene cycle. We demonstrate that the values of third-order susceptibilities χ 〈3〉 and two-photon absorption coefficients β increase as the number of branches increase. As consequence the studied complexes can be very interesting for optical limiting applications.

Synthesis, crystal structure and large third-order nonlinear optical properties of two novel nest-shaped clusters [MOS3Cu3(SCN)(Py)5] (M=Mo, W)

Two new candidates for nonlinear optical (NLO) materials, [MoOS3Cu3(SCN)(Py)5] (1) and [WOS3Cu3(SCN)(Py)5] (2), were synthesized. They show nest-shaped skeletal structure. The crystal structure of compound (1) was characterized by X-ray diffraction. The NLO properties of 1 and 2 were determined through the Z-scan technique. [MoOS3Cu3(SCN)(Py)5] exhibits both very strong NLO absorption and a self-defocusing effect, α2=4.8×10-10 m W-1 and n2=-6.8×10-17 W-1 in a 2.0×10-5 mol dm-3 acetonitrile solution. NLO properties of compound [WOS3Cu3(SCN)(Py)5] are similar to those of [MoOS3Cu3(SCN)(Py)5], strong NLO absorption and self-defocusing effect, α2=6×10-11 m W-1 and n2=-1.2×10-17 W-1, when measured in a 1.9×10-5 mol dm-3 DMF solution. Their hyperpolarizability γ values were calculated to be 5.8×10-27 esu for cluster 1 and 2.2×10-27 esu for cluster 2, respectively. The large γ value should define clusters 1 and 2 as very promising candidates for NLO materials.

A pump-probe method for the determination of Im of Ni(dmg)

Various types of metal complexes have received attention because of their large third-order nonlinear optical properties. Thin films of transition metal complexes with dionedioxime have been shown to form stacks perpendicular to the molecular plane, the central metal ions forming a quasi-one-dimensional chain of delocalized electrons. We have measured the imaginary part of the third-order nonlinear optical susceptibility, , of one such material, , by using the pump-probe method. We give a detailed derivation of the analysis of from the differential transmission data and present results near the lowest energy resonance of this material. Maximum values of the continuous wave susceptibility reached esu at resonance, with a relatively slow relaxation time of the order of 1 ns. The differential transmission crossed over from negative (saturation) to positive already on the low-energy side of the absorption band.

Large third-order nonlinear optical properties of C70 fullerene in the infrared regime

The nonlinear third-order optical susceptibility of C70 in a toluene solution is measured for the first time by the method of degenerate four-wave mixing using 10 ns laser pulses at 1.06 μm. The third-order susceptibility X in (3) is 5.6×10−12 esu for a C70 toluene solution at a concentration of 0.476 g/l. The correspondent magnitude of the hyperpolarizability γ1111 of the C70 molecule is 1.2×10−30 esu which is in a good agreement with the prediction given by the model of a free electron in a spherical box.

ポリジアセチレン系非線形光学材料の合成

In order to obtain the materials with large third-order nonlinear optical properties, polydiacetylenes (PDAs) having π-conjugation between polymer backbone and substituents were synthesized by proper crystal engineering. For the monomers for PDAs aromatic rings directly bound to main chain, one of two substituents bonding to the diacetylene (DA) moiety was selected from those of non-polymerizable symmetrical DA monomers. The highest χ (3) and the expected smallest dihedral angle between the polymer backbone and aromatic rings was already realized in one of the derivatives. PDAs with acetylenic and diacetylenic groups directly bound to the main chain were synthesized by polymerization of triyne and tetrayne compounds, respectively. The diacetylenic substituents of the polymers from the latter ones could be polymerized to give di (polydiacetylene) s, where two PDA polymer backbones were conjugated.