High Nonlinear Optical Response Research Articles

Capturing a Synergistic Effect of a Conical Push and an Inward Pull in Fluoro Derivatives of Li@B10H14 Basket: Toward a Higher Vertical Ionization Potential and Nonlinear Optical Response

We present the design of fluoro derivatives of B(10)H(14) and Li@B(10)H(14) baskets. A synergistic effect of conical push and inward pull (reported independently in previous lithium nonlinear optical (NLO) complexes) has been explored in these derivatives to achieve a robustly large NLO response and a higher vertical ionization potential. Li@1,3,6,9-F(4)B(10)H(10), Li@6,9-F(2)B(10)H(12), and Li@2,4,6,9-F(4)B(10)H(10) exhibit first hyperpolarizability (β(0)) values as large as 181 624, 133 199, and 32 314 au; their vertical ionization potentials are 6.45, 6.30, and 6.78 eV, respectively. These values are significantly higher than those previously reported in Li-doped fluorocarbon chains at the same MP2/6-31+G* level of theory (Xu, H. L.; Li, Z. R.; Wu, D.; Wang, B. Q.; Li, Y.; Gu, F. L.; Aoki, Y. J. Am. Chem. Soc. 2007, 129, 2967). They also exceed those from our earlier designed Li@B(10)H(14) basket (Muhammad, S.; Xu, H. L.; Liao, Y.; Kan, Y. H.; Su , Z. M. J. Am. Chem. Soc. 2009, 131, 2967). In addition, new quantum chemical calculations of enthalpies of reaction (Δ(r)H°) at 298 K for B(10)H(14) and its lithium/fluoro derivatives highlight the changes in their thermodynamical aspects. The calculated enthalpies of lithiation reactions are -10.04, -11.29, and -13.18 kcal/mol for B(10)H(14), 6,9-F(2)B(10)H(12), and 2,4-F(2)B(10)H(12), respectively, demonstrating a higher probability of fluoro decaboranes for reaction with lithium. The obtained results not only explain the effect of position and number dependence of substituted fluoro atom(s) in B(10)H(14) and Li@B(10)H(14) but also elucidate a synergistic behavior to polarize a lithium excess electron for high NLO responses and vertical ionization potentials.

High second-order NLO responses of dehydrogenated hydrogen cyanide borane(1) oligomers

Second-order non-linear optical (NLO) properties of dehydrogenated hydrogen cyanide borane(1) oligomers (up to dodecamers) are investigated by the Hartree–Fock, hybrid DFT (including long-range corrected functionals) and MP2 approaches. Due to one-dimensional extension of the systems the longitudinal component of the properties is addressed with focus on the electronic contributions. Direct and indirect electron correlation effects are evaluated at the MP2 level paying particular attention to the basis set effects. Unit-cell asymmetry and delocalization effects in the NLO responses are discussed in terms of the evolution of the bond-length alternation parameter, dipole moment and polarizability (reduced per unit cell) with the increasing chain length. It was found that suitable combination of the unit-cell asymmetry and electron delocalization leads to extremely large NLO response (MP2/6-311++G(d,p) value for the dodecamer is 43.7 × 10 3 a.u. per unit cell) what makes the conjugated BCN oligomers (if one takes into account their thermodynamic stability) a promising material for NLO applications.

High nonlinear optical response in 4-chlorothiazole-based azo dyes

Four azo dyes showing high nonlinear optical properties were prepared, based on a 4-chlorothiazole azo moiety functionalized with strong acceptor groups and/or further donor/acceptor groups along the conjugated backbone. The effects of the acceptors as well as the lateral donor/acceptor groups upon absorption properties, thermal stability and second order nonlinear optical activity were evaluated.

Thick optical waveguides in lithium niobate induced by swift heavy ions (~10 MeV/amu) at ultralow fluences

Heavy mass ions, Kr and Xe, having energies in the approximately 10 MeV/amu range have been used to produce thick planar optical waveguides at the surface of lithium niobate (LiNbO3). The waveguides have a thickness of 40-50 micrometers, depending on ion energy and fluence, smooth profiles and refractive index jumps up to 0.04 (lambda = 633 nm). They propagate ordinary and extraordinary modes with low losses keeping a high nonlinear optical response (SHG) that makes them useful for many applications. Complementary RBS/C data provide consistent values for the partial amorphization and refractive index change at the surface. The proposed method is based on ion-induced damage caused by electronic excitation and essentially differs from the usual implantation technique using light ions (H and He) of MeV energies. It implies the generation of a buried low-index layer (acting as optical barrier), made up of amorphous nanotracks embedded into the crystalline lithium niobate crystal. An effective dielectric medium approach is developed to describe the index profiles of the waveguides. This first test demonstration could be extended to other crystalline materials and could be of great usefulness for mid-infrared applications.

Geometry and bond-length alternation in nonlinear optical materials. III. Structural parameters of two chromophores containing aromatizable donors

The planar component of 2-{3-cyano-4-[3-(1-decyl-1,4-dihydroquinolin-4-ylidene)prop-1-enyl]-5,5-dimethyl-2,5-dihydrofuran-2-ylidene}malononitrile, C(32)H(46)N(4)O, (I), forms into layers parallel to the (\overline{1}01) plane. The larger of the two spaces between layers is filled by the alkyl chains, giving a ;sandwich stack' appearance. The packing of 2-{3-cyano-4-[5-(1-decyl-1,4-dihydroquinolin-4-ylidene)penta-1,3-dienyl]-5,5-dimethyl-2,5-dihydrofuran-2-ylidene}malononitrile, C(34)H(38)N(4)O, (II), which has partial disorder in the 1-decyl group, utilizes weak C-H...N, C-H...O and C-N...pi interactions in a three-dimensional ;herring-bone' array with molecular segments parallel to the (111) and (\overline{1}1\overline{1}) planes. Different rotational isomers with respect to the polyene chain and the 5,5-dimethyl-2,5-dihydrofuran-2-ylidene link are observed in the two structures. The significance of the study lies in the delocalization of charge along the polyene chain and the supramolecular aggregation present, which highlight the difficulty in obtaining the noncentrosymmetric alignment required for high nonlinear optical (NLO) responses in zwitterionic chromophores.

Hybrid Nonlinear Optical Materials Containing Imidazole Chromophore through the Sol-Gel Process

A new sol-gel hybrid film based on heterocyclic chromophore, namely 2-[4′-(N-ethyl-N-hydroxyethyl)amino phenyl azo]-4,5-dicyanoimidazole (IZ), has been synthesized and characterized. The hybrid system possesses a high chromophore loading density up to 65 wt.-% without observing a phase separation. The initial decomposition temperatures of the chromophore and hybrid material were determined to be 260 and 272 °C, respectively. Poled films show a fairly high and stable nonlinear optical (NLO) response, even at an elevated temperature.

Very High Third-Order Nonlinear Optical Activities of Intrazeolite PbS Quantum Dots

Zeolite-intercalated semiconductor quantum dots (QDs) have long been proposed to give very high third-order nonlinear optical (3NLO) responses. However, measurements of their 3NLO responses have not been possible due to the lack of methods to prepare optically transparent QD-incorporating zeolite films supported on optically transparent substrates and to confine QDs only within zeolite interiors. We found that the zeolite-Y films grown on indium-tin-oxide-coated glass plates (Ygs) remain firmly bonded to the substrates during ion exchange with Pb2+ ions, drying, and formation of PbS QDs by treating Pb2+ ions with H2S. A series of Ygs encapsulating different numbers (n = 0, 8, 14, 23, and 33) of PbS in a unit cell [(PbS)n-Yg] were prepared. The PbS QDs were expelled by adsorbed moisture to the external surfaces, and the expelled QDs formed large QDs. Coating of the (PbS)n-Ygs with octadecyltrimethoxysilane results in effective confinement of the QDs within the internal pores. The zeolite-encapsulated PbS QDs showed remarkably high 3NLO activities at 532 and 1064 nm which are unparalleled by other PbS QDs dispersed in other matrixes.

Second order nonlinear optical properties of zinc oxide films deposited by low temperature dual ion beam sputtering

We investigated second order optical nonlinearity of zinc oxide thin films, grown on glass substrates by the dual ion beam sputtering technique under different deposition conditions. Linear optical characterization of the films was carried out by spectrophotometric optical transmittance and reflectance measurements, giving the complex refractive index dispersion. Resistivity of the films was determined using the four-point probe sheet resistance method. Second harmonic generation measurements were performed by means of the Maker fringes technique where the fundamental beam was originated by nanosecond laser at λ=1064nm. We found a relatively high nonlinear optical response, and evidence of a dependence of the nonlinear coefficient on the deposition parameters for each sample. Moreover, the crystalline properties of the films were investigated by x-ray diffraction measurements and correlation with second order nonlinearity were analyzed. Finally, we investigated the influence of the oxygen flow rate during the deposition process on both the second order nonlinearity and the structural properties of the samples.

Origin of high second- and third-order nonlinear optical response in ammonio/borato diphenylpolyene zwitterions: the remarkable role of polarized aromatic groups.

We present a quantum-chemical analysis of the molecular structure and second- and third-order polarizabilities in a series of promising nonlinear optical (NLO) chromophores, the zwitterionic ammonio/borato diphenylpolyenes, R3N+Ph(C=C)nPhB-R3, whose synthesis has been reported recently. The molecular geometries are obtained via MP2/6-31G optimization, while the NLO properties are calculated with the INDO Hamiltonian using the sum-over-states and finite-field real-space methods. The real-space approach allows the direct evaluation of the NLO-active segments of the molecules, while the sum-over-states results illustrate the virtual excitations and charge-transfer pathways that are essential in the NLO response. Both methods highlight the remarkable and unexpected result that it is the strongly polarized phenylene groups that play the key role in generating a high NLO response.

Novel Chromophore‐Functionalized Poly[2‐(trifluoromethyl) adamantyl acrylate‐methyl vinyl urethane]s with High Poling Stabilities of the Nonlinear Optical Effect

AbstractNonlinear optical vinyl polymers with high glass transition temperature (Tg) were prepared by the functionalization of a fluorinated acrylate‐methyl vinyl isocyanate copolymer. A modified pathway to obtain a thiophene bridged chromophore was worked out. Poled films of the polymers show a fairly high and stable nonlinear optical response, even at elevated temperatures.The thiophene‐bridged chromophore, based on a substituted dicyanomethylene‐dihydrofuran acceptor, synthesized here.magnified imageThe thiophene‐bridged chromophore, based on a substituted dicyanomethylene‐dihydrofuran acceptor, synthesized here.

Nonlinear optical properties of open-shell polychlorotriphenylmethyl radicals

The second-order nonlinear optical (SONLO) response of a series of the highly chemically and thermally stable polychlorotriphenylmethyl monoradicals 1–8 has been studied by Hyper-Rayleigh Scattering. These radicals exhibit relatively high nonlinear optical (NLO) responses with β values ranging from 118×10−30 to 755×10−30 esu, which may result from an enhancement of the SONLO activities according to their open-shell electronic state. Hyperpolarizability data for radicals 1–8 have also been correlated with their redox potentials, correlation that has turned out to be linearly proportional either with the oxidation or the reduction potentials. These data have been justified in terms of molecular orbital energies. Finally we have successfully explored the capacity of radicals 1–8 to participate in a molecular switching array involving two main steps, an acid/base reaction and a redox process. The presence of open-shell character for this family of compounds makes them attractive candidates to design new multifunctional materials that would simultaneously possess magnetism and NLO.

Novel diacetylene‐containing polymers for second order NLO applications: effect of main chains and structure property relationships

AbstractIn order to obtain polymers having high second order nonlinear optical (NLO) response, various novel polymers that contain polar dye molecules in side chains and diacetylenic groups in the main chains were synthesized, and their second order NLO properties were studied. Some of these polymers consisting of para‐benzoate and para‐cinnamate main chains, showed extremely high NLO coefficients, d33 of 200 ‐ 350 pm/V, and the corresponding meta polymers showed much inferior NLO coefficients. The polymers having aliphatic main chains had very little NLO response probably because of their low glass transition temperatures and flexibility of main chains. The high SHG responses of these polymers are attributed to their facile orientation of both chromophores and main chains. In the case of para‐polymers, the main chain orientation of alkoxybenzoate and cinnamate along the chromophore is thought to be a reason for their high NLO coefficients.

Hyper-Rayleigh scattering of trans-tetraammineruthenium(II) complexes

A novel series of tetraammineruthenium complex salts trans-[Ru II (NH 3) 4(L D)(L A)][PF 6] 3 has been investigated by using the hyper-Rayleigh scattering technique. These complexes exhibit very large and tunable static first hyper-polarizabilities in the range 10×10 −30 to 410×10 −30 esu. These high second-order non-linear optical responses are associated with intense, visible metal-to-ligand charge-transfer excitations. Further, changing the structure of the acceptor-substituted ligand going from a 4,4′-bipyridinium to a [ trans-2-(4-pyridyl)ethenyl]pyridinium conjugated bridge leads to the notable conclusion that the extension of the conjugated bridge in these complexes neither significantly alters the metal-to-ligand charge-transfer energies nor leads to an increase in the static first hyperpolarizabilities. The non-linear optical responses of these dipolar complexes show a great sensitivity towards the oxidation state of the metal. It is proven that chemical oxidation of the ruthenium is an excellent tool to reversibly switch the molecular first hyper-polarizabilities.

Polyhedral-based nonlinear optical materials. 2. Theoretical investigation of some new high nonlinear optical response compounds involving polyhedral bridges with charged aromatic donors and acceptors.

A theoretical study of several new classes of polyhedral-based molecules has shown that these species display large calculated nonlinear optical responses. These new classes of molecules are based on charged aromatic subunits connected through polyhedral cluster bridges, such as closo-[1-(C(7)H(6))-12-(C(5)Me(4))C(2)B(10)H(10)]. These compounds show calculated first hyperpolarizabilities (beta) ranging from 6.5 to 8413.9 x 10(-30) cm(5) esu(-1). A basis for understanding the origin of these large responses is proposed based on the two-state model and consideration of the orbital and electronic features of the molecules. In general, the highest occupied molecular orbitals for these species are localized on the aromatic donor rings, such as the cyclopentadienyl system, while the lowest unoccupied molecular orbitals are largely on the aromatic acceptor rings, such as the tropylium system. The electronic properties of these polyhedral-based systems appear to be significantly different from the analogous organic [5.6.7]quinarene system (tropyliumcyclopentadienylbenzene). The organic quinarene appears to behave as a completely electron-delocalized system over all three rings while the polyhedral-based compounds can best be described as consisting of two relatively independent, highly polarized regions.

Nonlinear optics. A semiempirical study of organic chromophores

Many donor–acceptor substituted organic compounds show internal charge separation upon excitation. Within this class, the following compounds are studied as suitable candidates for molecules with high second-order nonlinear optical (NLO) response: 4- N, N-dimethylamino-benzonitrile (DMABN), 6-propanoyl-2-(dimethylamino)-naphthalene (PRODAN), and various 4-(4- N, N-dimethylamino-phenyl)-1,3-diphenyl-pyrazolo[3,4-b]quinolines (DMA-DPPQ). The configuration interaction method with single and double excitations (CISD) is used in combination with the sum over states (SOS) approach within the semiempirical AM1 parametrization to calculate the vector component of the hyperpolarizability along the dipole axis β μ . The influence of changing molecular geometry on the second-order nonlinear properties is calculated for various intramolecular relaxation coordinates. Solvent effects are explicitly studied for DMABN by a self-consistent reaction field (SCRF) model revealing an increasing NLO-effect with increasing solvent polarity. The hyperpolarizability is discussed in relationship to the charge transfer properties of the excited state. The calculated values are in good agreement with experimental data for both DMABN and PRODAN. DMA-DPPQ is found to be a good NLO chromophore only when increasing either the donor or acceptor strength. Its nonlinear response can be drastically increased by an additional strong electron acceptor group, e.g. a NO 2-group, at the primary acceptor moiety.

Polyhedral-based nonlinear optical materials.: Part 1. Theoretical investigation of some new high nonlinear optical response compounds involving carboranes and charged aromatic donors and acceptors

A calculational investigation using semiempirical methods of the molecular and electronic structures, along with the nonlinear optical responses, of a series of compounds in which icosahedral carborane polyhedra bridge charged aromatic donor and acceptor moieties, specifically tropyl (C 7H 7 +) and cyclopentadienyl (C 5H 5 −) groups, found that these molecules show exceptionally large calculated second-order responses. These compounds were found to give calculated first hyperpolarizabilities ( β) ranging from 8.6 to 1226.0×10 −30 cm 5 esu −1 at 0.5 eV excitation energy. These nonlinear optical responses are understood within the framework of the two-state model using molecular orbital and electronic structure considerations.

Molecular beam deposition of thin films of organic semiconductors

The ultra-high vacuum technique of organic molecular beam deposition (OMBD) has been recently proved to provide a very good method for growing highly controlled thin films of organic semiconductors. The approximate ordering of a crystalline layer to a substrate, also called quasi-epitaxy, can be achieved with a proper choice of substrate and deposition conditions. Poly- and oligo-thiophenes are among the most interesting and widely studied organic semiconductors for applications in electronic and photonic devices, thanks to their high carrier mobility and large nonlinear optical response, combined with an exceptionally high flexibility of molecular engineering. Here, the deposition and the main properties of films of substituted sexithiophene molecules (6T) obtained by OMBD are discussed on the basis of X-ray diffraction and optical absorption measurements.

High order nonlinear optical response of fullerene solutions in the nanosecond regime

High order optical nonlinearities of C 60- and C 70-toluene solutions are studied in the nanosecond time regime, employing the transient degenerate wave mixing technique. The intensity dependence of the high order signals of the solutions is investigated. The ratios |χ eff (2n + 3) |χ eff (2n + 1)| are determined to be of the order of 10 −6 and 10 −5 for C 60 and C 70 respectively.

Optical properties of potassium acid phthalate

Potassium acid phthalate (KAP) crystals are promising as substrates for the growth of highly oriented films of conjugated polymers with exceedingly high and fast nonlinear optical response. We report the KAP optical properties (real and imaginary parts of the refractive index ñ = n + ik) in the near infrared and visible range deduced by ellipsometric measurements and direct inversion of transmittance and near-normal incidence absolute reflectance measurements. In the infrared region n was also deduced by the interference fringes.

Polarization Effects in Push−Pull Buckminsterfullerenes: A Semiempirical Study

We predict that push-pull Buckminsterfullerenes have a high nonlinear optical response that makes pursuing their synthesis worthwhile. Three different semiempirical quantum chemical models concur to show that some isomers of push-pull C{sub 60} have a static first-order hyperpolarizability, {beta}, comparable to or larger than that of all-trans 4-(dimethylamino)-4`-nitrodiphenyloctatetraene. Because of the geometrical structure of push-pull Buckminsterfullerenes, standard models that explain the high response in planar conjugated systems cannot be used. Rather, it is found that conjugation and inductive effects contribute at the same time to {beta} and the separation between the nitrogen-containing groups cannot fully simulate the results of the calculations. A simple perturbation approach based on icosahedral C{sub 60} further confirms the results obtained by the correlations and warrants the search of a topological model able to account for the response. In is found that a linear relation exists between {beta} and the shortest resonant paths between the grafting groups. Two types of resonant structures contribute. They are described in terms of single-double bond alternation. The first resonant structure starts and finishes with hexagon-hexagon alternation (i.e., double bonds) and contributes positively, the second starts and finishes with pentagon-hexagon (i.e., double bonds) and contributes negatively. The ratio of their contributionsmore » is roughly two to one. 19 refs., 2 figs., 3 tabs.« less