Quadratic Hyperpolarizability Research Articles

Synthesis, crystal structures, and molecular hyperpolarizabilities of a new Schiff base ligand, and its copper(II), nickel(II), and cobalt(II) metal complexes

A new ligand (HL) obtained from the Schiff base condensation of 4-(diethylamino)salicylaldehyde with 4-nitroaniline is reported, with its nickel(II), copper(II), and cobalt(II) complexes. The crystal structures are reported for the four derivatives. While, NiIIL2 and CuIIL2 are centrosymmetric molecules, CoIIL2 exhibits a pseudo-tetrahedral molecular structure. The quadratic hyperpolarizabilities (β) of HL and CoIIL2, measured by electric field induced second harmonic (EFISH) technique, are equal to 66 and 110×10−30 cm5esu−1, respectively. Beside a geometric effect (pseudo-Td symmetry), the coordination of the metal center provides an intrinsic enhancement of the NLO response. In addition, an enhancement of the thermal stability of about 60° is found upon metal complexation.

Relaxational diffusion in guest–host polyphosphazene thin films: Temperature dependence

The relaxation of poled guest–host polyphosphazene (PPZ) films containing the 4-[(4′-nitrophenyl)azo]phenoxy (NPAP) azo-dye chromophore (Tg=144 °C) has been investigated by measuring the time decay of the nonlinear optical susceptibility tensor in the 80–120 °C temperature range. The kinetic data have been analyzed on the basis of the Legendre polynomial decomposition of the orientational distribution function. In the measuring time range, two components (fast and slow) of the decay have been found together with a constant component that disappears at temperatures close to Tg. This component accounts for the nonreorientable fraction of the molecules at each temperature. The temperature dependence of the two lifetimes has been determined and fitted to an Adam–Gibbs law. At a high temperature, (120 °C) the ratio of lifetimes closely follows the predictions of the orientational diffusion equation. This allows one to determine the two nonlinear components βzzz=−88.10−30 esu and βzxx=71.10−30 esu of the quadratic hyperpolarizability tensor in our rodlike (C∞v symmetry) molecules, showing the non-negligible contribution of the nondiagonal components.

Effect of the Coordination to the “Os3(CO)11” Cluster Core on the Quadratic Hyperpolarizability oftrans-4-(4‘-X-styryl)pyridines (X = NMe2,t-Bu, CF3) andtrans,trans-4-(4‘-NMe2-phenyl-1,3-butadienyl)pyridine

Coordination to the “Os3(CO)11” cluster core of substituted styrylpyridines such as trans-4-(4‘-NMe2-styryl)pyridine (L1), trans-4-(4‘-t-Bu-styryl)pyridine (L2), trans-4-(4‘-CF3-styryl)pyridine (L3), or trans,trans-4-(4‘-NMe2-phenyl-1,3-butadienyl)pyridine (L4) produces an enhancement of their quadratic hyperpolarizability, βEFISH, measured by the solution-phase dc electric-field-induced second harmonic (EFISH) generation method. This effect is due either to a red-shift of the intraligand charge-transfer (ILCT) transition upon coordination (when the substituent in para position is a strong electron donor) or to a metal-to-ligand charge-transfer (MLCT) transition (when the substituent is a strong electron acceptor). In the latter case the quadratic hyperpolarizability has a negative sign, due to the negative value of Δμeg. Therefore the “Os3(CO)11” cluster core displays an ambivalent acceptor or donor role. Some of the complexes investigated in this study show significant values (between 500 × 10-48 and 900 × 10-48 esu) of the product μβ0.

Computational design of benzothiazole-derived push–pull dyes with high molecular quadratic hyperpolarizabilities

Semi-empirical ZINDO SOS and ab initio quadratic response function (DDRPA) calculations on a series of donor–acceptor substituted π-conjugated chromophores based on styryl benzothiazoles are used to aid in the design of dyes with high non-linear optical properties. Structural modifications studied include nature and position of the donor and/or acceptor group as well as the length of the connecting π-bridge. The most worthwhile target for synthesis are 2-tricyanovinyl-6-p-donor-styryl benzothiazoles and heteroaryl derivatives thereof.

Novel Push−Pull Phthalocyanines as Targets for Second-Order Nonlinear Applications

The second harmonic generation (SHG) hyperpolarizabilities of a family of peripherally substituted push−pull phthalocyanines 1, 2, and 3, having an ethynediyl subunit in the linking bridge between the acceptor and donor moieties, have been measured. Electric field induced second harmonic (EFISH) generation experiments at 1.064 and 1.900 μm and hyper-Rayleigh scattering (HRS) experiments at 1.064 μm have been carried out. The quadratic hyperpolarizabilities values derived from these experiments are quite significant and superior to those found for similar push−pull compounds lacking of a triple C-bond in the donor−acceptor path. The main electronic parameters of the three compounds (electric dipole moments, orbital electronic distributions, and optical transition moments) have been calculated using the ZINDO/S method for molecular geometries that have been optimized through the PM3 method. Excellent agreement with spectroscopic data has been achieved. The SHG results have been analyzed through a 3-level model associated to the ground level and two split levels responsible for the Q-band, assuming either strict (for compound 2) or approximate (for compounds 1 and 3) C2v planar symmetry. The parameters used in the model were those obtained from the electronic calculations. For molecule 2, both the theoretical diagonal and off-diagonal elements of the beta tensor, as well as βEFISH and βHRS, have been determined. Good agreement with the experimental HRS values is obtained, whereas EFISH values considerably differ from those obtained from the simple expression for γEFISH ignoring the electronic contributions.

Large, concentration-dependent enhancement of the quadratic hyperpolarizability of [Zn(CH3CO2)2(L)2] in CHCl3 on substitution of acetate by triflate.

Large, concentration-dependent enhancement of the quadratic hyperpolarizability of [Zn(CH3CO2)2(L)2] in CHCl3 on substitution of acetate by triflate.

Subphthalocyanines and Subnaphthalocyanines: Nonlinear Quasi-Planar Octupolar Systems with Permanent Polarity

The second-harmonic generation (SHG) response of unsubstituted subnaphthalocyanines (SubNcs) has been measured for the first time by electric field-induced second-harmonic generation (EFISH) (1.064 and 1.90 μm) and hyper-Rayleigh scattering (HRS) (1.064 μm) experiments. The quadratic hyperpolarizability derived from the experiments is significant (βHRS(0) = 34.7 × 10-30 esu) and similar to that also measured under the same conditions for the related unsubstituted subphthalocyanine (SubPc) molecule (βHRS(0) = 38.3 × 10-30 esu). To meaningfully discuss the nonlinear optical (NLO) data, semiempirical INDO/S calculations of the permanent dipole moments of the ground and excited states (Q band) have been performed. Moreover, the dipolar transition moments connecting the ground and degenerate excited states and the two excited states have been also determined. The calculations suggest that for those low-energy excited states responsible for the Q optical absorption band, the two molecules (SubPc and SubNc) beha...

Three-dimensional nonlinear optical chromophores based on through-space delocalization.

Six permutations of 4-fold donor and/or acceptor substitution of paracyclophane at the 4, 7, 12, and 15 positions were synthesized to probe the phenomenon of three-dimensional delocalization on the nonlinear optical properties of organic materials. The interplay between through-bond intramolecular charge transfer (ICT) as well as three-dimensional, or through-space, ICT processes gives rise to large quadratic hyperpolarizability values. The determination of dipolar (beta(J)(=1)) and octupolar (beta(J)(=3)) irreducible tensor contributions to the overall beta tensor value is made possible by the polarized harmonic light scattering technique at 1.32 microm. The electric field-induced second-harmonic generation technique was also used at 1.91 microm for comparison. Significant experimental beta values for members of the series made of two centrosymmetric benzene-like units are a clear signature of a purely through-space ICT between two aryl subunits. The two configurational isomers that pair two dipolar donor-acceptor chromophores also exhibit octupolar character. Analysis of these two with an additive model for beta(J)(=1) and beta(J)(=3) reveals a strong three-dimensional inter-ring charge transfer.

Nonlinear optical properties of polychlorotriphenylmethyl radicals: towards the design of `super-octupolar' molecules

Molecular quadratic hyperpolarizability ( β c) of substituted polychlorinated triphenylmethyl radicals, 1– 8, has been determined by using the harmonic light scattering (HLS) technique. Results showed that this opens-shell family known to possess a good chemical stability also exhibited a very large SONLO response. The presence of a permanent dipole moment in the ground state for some of these octupolar compounds makes them attractive candidates for further orientation by the poling technique. Data of compounds 1– 8 have been discussed on the basis of a model describing the evolution of the β c response for D 3h and C 2v symmetry groups.

Quadratic Hyperpolarizability of Carbomeric Structures

The ZINDO-computed quadratic hyperpolarizability (β) of p-nitroaniline (PNA) is compared with that of its carbomer in its molecular mechanics (MM) optimized geometry. Complete carbomerization of PNA leads to a new molecule with a static β0 value of 941.3 × 10-30 cm5 esu-1 which is 2 orders of magnitude better than that of PNA. Within the model of push−pull molecular topography, an empirical five-parameter formula is proposed in order to estimate the β value of 32 partial carbomer structures of p-nitroaniline. A compromise between high β values and a priori synthetic feasability is achieved for structures with three carbomerized domains only: the carbon skeleton of the p-phenylene ring, the nitro group, and the phenylene−nitro bond. The results are discussed within the framework of the two-level model on the basis of an orbital analysis. A relevant measure of the molecular NLO response is proposed to be the “specific quadratic hyperpolarizability”: [β] = β/N, where N is the number of non-hydrogen atoms i...

A critical evaluation of EFISH and THG non-linear optical responses of asymmetrically substituted meso-tetraphenyl porphyrins and their metal complexes

The experimental second and third order non-linear optical (NLO) responses γ EFISH and γ THG, measured working with a non-resonant incident wavelength of 1.907 μm, of some push–pull meso-tetraphenyl porphyrins and their metal complexes, substituted in the para position of one phenyl ring with a nitro group and with hydrogen or methyl or methoxy groups in the para position of the other three phenyl rings, are critically discussed, also with the support of semiempirical MNDO–TDHF calculations. Care must be taken in evaluating the quadratic hyperpolarizabilities β vec from γ EFISH being the contribution of the cubic term γ 0(−2 ω; ω, ω, 0) to γ EFISH not negligible at least when the second order NLO response is relatively low, as in porphyrins and their metal complexes investigated in this work. In addition experimental evidence has been produced that the value of γ EFISH of the porphyrins and their metal complexes is increased by resonance enhancement when working with an incident wavelength of 1.34 μm, due to the presence of very strong absorption bands in the region 0.400–0.650 μm and that the γ EFISH response is not significantly affected by 3d n ( n=7–10) metal coordination. On the contrary γ THG decreases by metal coordination due to the high resonance enhancement of γ THG of free porphyrins. In fact the third harmonic 3 ω (0.636 μm) in free porphyrins is quite close to some strong Q absorption bands above 0.615 μm, which are lacking in the absorption spectra of their 3d n metal complexes. A vibrational method for the evaluation of the order of magnitude of the static cubic γ 0 third order NLO response was successfully applied for the first time to a push–pull porphyrinic system.

Terpyridine Zn (II), Ru (III) and Ir (III) complexex as new asymmetric chromophores for nonlinear optics: first evidence for a shift from positive to negative value of the quadratic hyperpolarizability of a ligand carrying an electron donor substituent upon coordination to different metal centres.

The synthesis of 4'-(C6H4-p-NBU2)-2,2':6',2" -terpyridine and the strongly enhanced second-order NLO response of its Zn(II), Ru(III) and Ir(III)complexes are reported, evidencing for the first time a shift from positive to negative value of the ligand quadratic hyperpolarizability by varying the nature of the metal centre. .

Multipolar engineering of molecules and materials for quadratic nonlinear optics

The first generation of molecular engineering studies whereby a one-dimensional bipolar donor–acceptor conjugated system had served, since the early 1970s, as a quasi-exclusive template, had failed to take into account the tensorial dimension attached to the β quadratic hyperpolarizability tensor. We review here the outgoing second generation of molecular design studies based on three-dimensional multipolar charge transfer which reflects on enhanced values for all β ijk coefficients, then opening-up the possibility of polarization-independent nonlinear interactions. This can be ensured by more isotropic crystalline lattices or statistical polymer-based orientational distribution out of reach for the cruder one-dimensional systems. A particular challenge which has in fact triggered this domain in the early 1990s to this day has been set by octupolar systems whereby the symmetry-imposed cancellation of the dipole moment precludes the utilization of an electric field coupling scheme to orient molecules into a noncentrosymmetric order. We will review this new domain, encompassing both physical and chemical considerations, all the way from new molecular engineering techniques, with associated quantum modeling, to advanced characterization methods and macroscopic ordering schemes jointly aiming at promoting and exploiting the so far largely ignored tensorial dimension of nonlinear light–matter coupling schemes in molecules. To cite this article: I. Ledoux, J. Zyss, C. R. Physique 3 (2002) 407–427.

Organometallic complexes for nonlinear optics: Part 25. Quadratic and cubic hyperpolarizabilities of some dipolar and quadrupolar gold and ruthenium complexes

The complexes [Au(4-CCC 6H 4NO 2)(L)] [L=PCy 3 ( 1), PMe 3 ( 2)], [(L)Au(μ-4-CCRCC)Au(L)] [R=C 6H 4, L=PCy 3 ( 4), PPh 3 ( 5); R=C 6H 4-4-C 6H 4, L=PCy 3 ( 7), PPh 3 ( 8)], trans,trans-[RuCl(dppm) 2(μ-4,4′-CCC 6H 4C 6H 4CC)RuCl(dppm) 2] ( 11), trans-[Ru(X)(Y)(dppe) 2] [X=Cl, Y=4-CCC 6H 4I ( 12), 4-CCC 6H 4CCSiMe 3 ( 13); X=CCPh, 4-CCC 6H 4CCH ( 14)] and { trans-[Ru(CCPh)(dppe) 2]} 2(μ-4,4′-CCC 6H 4CCCCC 6H 4CC) ( 15) have been prepared and their electrochemical (Ru complexes) and nonlinear optical properties assessed. Electronic communication between the metal centers in 10, 11 and 15 diminishes as the π-delocalizable bridge is lengthened. Quadratic nonlinear optical (NLO) merit increases on replacing triarylphosphine by trialkylphosphine, the relative β values Au(4-CCC 6H 4NO 2)(PPh 3)< 1< 3 being observed. Cubic NLO values are small for the gold complexes and much larger for the ruthenium examples. Complex 15 has the largest σ 2/MWt (two-photon absorption cross-section/molecular weight) value observed thus far for an organometallic complex.

Effect of the Coordination to M(II) Metal Centers (M = Zn, Cd, Pt) on the Quadratic Hyperpolarizability of Various Substituted 5-X-1,10-phenanthrolines (X = Donor Group) and of trans-4-(Dimethylamino)-4‘-stilbazole

Coordination to a Zn(II) center of chelating π-delocalized nitrogen donor ligands such as 5-X-1,10-phenanthrolines (X = OMe, NMe2, trans-CHCHC6H4-4‘-NMe2, trans,trans-(CHCH)2C6H4-4‘-NMe2) produces ...

Design and synthesis of push-pull chromophores for second-order nonlinear optics derived from rigidified thiophene-based pi-conjugating spacers.

Two series of push-pull chromophores built around thiophene-based pi-conjugating spacers rigidified either by covalent bonds or by noncovalent intramolecular interactions have been synthesized and characterized by UV-vis spectroscopy, electric field induced second harmonic generation (EFISH) and differential scanning calorimetry. Comparison of the linear and second-order nonlinear optical properties of chromophores based on a covalently bridged dithienylethylene (DTE) spacer with those of their analogues based on open chain DTE shows that the rigidification of the spacer produces a considerable bathochromic shift of the absorption maximum together with a dramatic enhancement of the molecular quadratic hyperpolarizability (mu beta) which reaches values among the highest reported so far. A second series of NLO-phores has been derived from a 2,2'-bi(3,4-ethylenedioxythiophene) (BEDOT) pi-conjugating spacer. As indicated by X-ray and UV-vis data, rigidification of the spacer originates in that case, from noncovalent intramolecular interactions between sulfur and oxygen atoms. Again, comparison with the parent compounds based on an unsubstituted bithiophene spacer reveals a marked red shift of the absorption maximum and a large enhancement of mu beta. In an attempt to distinguish the contribution of the electronic and geometrical effects of the ethylenedioxy group, a third series of NLO-phores based on 3,4-ethylenedioxythiophene (EDOT) and 3,4-dihexyloxythiophene spacers has been synthesized. Comparison with compounds based on unsubstituted thiophene shows that, despite a red shift of lambda(max), introduction of alkoxy groups leads to a decrease of mu beta. Theoretical calculations indicate that this effect results from a decrease of the dipole moment (mu) caused by the auxiliary electron-donor alkoxy groups on the thiophene ring. In contrast, replacement of BT by BEDOT produces an increase of mu, which associated with the noncovalent rigidification of the BT system accounts for the observed enhancement of mu beta.

Theoretical estimation of nonlinear optical properties of Langmuir–Blodgett films

The quadratic hyperpolarizability of molecules of the push–pull type entering some Lengmuir–Blodgett films with the expressed nonlinear optical properties are calculated in the framework of the time-dependent Hartree–Fock semi-empirical approximation. The list of molecules includes neutral as well as charged chromophores. The Madelung interaction in a film is taken into account exactly in both cases that allows comparing the hyperpolarizability of these types of compounds.

Organometallic complexes for nonlinear optics: Part 23. Quadratic and cubic hyperpolarizabilities of acetylide and vinylidene complexes derived from protected and free formylphenylacetylenes

The acetylenes 4-HCCC 6H 4R [R=CH{OC(O)Me} 2 ( 1), CHO(CH 2) 3O ( 2)], ruthenium complexes [Ru(4-CCC 6H 4R)(PPh 3) 2(η-C 5H 5)] [R=CH{OC(O)Me} 2 ( 3), CHO ( 4)], [Ru( n-CCHC 6H 4R)Cl(dppm) 2]PF 6 [ n=4, R= CHO(CH 2) 3O ( 7); R=CHO, n=3 ( 11), 2 ( 15)], and [Ru( n-CCC 6H 4R)Cl(dppm) 2] [ n=4, R= CHO(CH 2) 3O ( 8); n=3, R=CHO ( 12)], and gold complexes [Au( n-CCC 6H 4R)(L)] [ n=4, R=CHO, L=PPh 3 ( 5), PMe 3 ( 6); n=4, R= CHO(CH 2) 3O , L=PPh 3 ( 9), PMe 3 ( 10); n=3, R=CHO, L=PPh 3 ( 13), PMe 3 ( 14)] have been prepared, and 9 characterized by a single crystal X-ray diffraction study. Electrochemical data for the ruthenium complexes reveal reversible or quasi-reversible (alkynyl complexes) or irreversible (vinylidene complexes) processes assigned to the Ru II/III couple; the effect on E 1/2 values of the various structural modifications across 3, 4, 7, 8, 11, 12 and 15 are discussed. The molecular quadratic and cubic optical nonlinearities of 1– 15 have been determined by the hyper-Rayleigh scattering technique at 1064 nm and the Z-scan technique at 800 nm, respectively; β values increase on increasing the acceptor strength, proceeding from 3-acceptor-substituted to 4-acceptor-substituted arylalkynyl ligand, and an increasing phosphine donor strength, whereas γ values increase on increasing the number of phosphine aryl groups (i.e. increasing delocalization) proceeding from PMe 3 to PPh 3-containing complex.

Enhanced second harmonic generation on passing from a mono- to a dicopper(II) bis(salicylaldiminato) schiff base complex.

A new ligand (H2LOH) obtained from the Schiff base condensation of 4-(diethylamino)salicylaldehyde with 1,3-diamino-2-propanol is reported, which yields two different copper(II) complexes: CuLOH and Cu2LO(AcO). Crystal data are as follows. CuLOH*EtOH: monoclinic, P2(1)/n, a = 17.810(2) A, b = 8.515(1) A, c = 18.912(2) A, beta = 112.72(1) degrees, Z = 4. Cu2LO(AcO)*1/2H2O: monoclinic, P2(1)/c, a = 21.407(4) A, b = 15.308(2) A, c = 20.156(3) A, beta = 116.83(2) degrees, Z = 4. Cu2LO(AcO)*1/2H2O is antiferromagnetically coupled with J = -207.7 cm(-1) (J being the parameter of the exchange Hamiltonian H = -J S(A).S(B)). CuLOH and Cu2LO(AcO) exhibit good transparencies in the visible frequency range with absorption maxima at 353 and 372 nm, respectively. An enhancement of 83% of the quadratic hyperpolarizability (beta) is observed by the electric field induced second harmonic (EFISH) technique on passing from the mono- to the dinuclear species. Qualitative ZINDO/SCI quantum-chemical predictions give a satisfactory account for this enhancement. The spin dependence of the NLO response of Cu2LO(AcO)*1/2H2O is found to be negligible within the framework of the DFT theory.

Determination of the quadratic hyperpolarizability of trans-4-[4-(dimethylamino)styryl]pyridine and 5-dimethylamino-1,10-phenanthroline from solvatochromism of absorption and fluorescence spectra: a comparison with the electric-field-induced second-harmonic generation technique

For fluorescent compounds, the combined use of absorption and emission solvatochromic data allows to estimate indirectly the cavity radius of the molecule in solution, a very critical parameter in the application of the solvatochromic method for the determination of the quadratic hyperpolarizability β of dipolar molecules. For two test compounds, trans-4-[4-(dimethylamino)styryl]pyridine (DASP) and 5-dimethylamino-1,10-phenanthroline (DAPHEN), the β values so obtained are compared with those obtained by the EFISH (Electric Field Induced Second-Harmonic generation) technique. For DAPHEN, the versatility of the method described in this work in the presence of more than one electronic transition contributing to the non-linear optical response is demonstrated.