Second-order Nonlinear Optical Properties Research Articles

Influence of noise-binding energy interplay on the second and third-order nonlinear optical properties of impurity doped quantum dots

We inspect the role of binding energy (BE) on second-order and third-order nonlinear optical (NLO) properties of doped GaAs quantum dot (QD). In the study ample stress is given on understanding the role of noise on the manifestations of these NLO properties. The profiles of these NLO properties are analyzed mainly on the basis of variation of two important criteria viz. peak-shift and peak-height as a function of BE. Both these features depend on the presence of noise, its pathway (mode) of introduction and sometimes on the identity of the NLO properties. The findings of the study deem significance in realizing the binding energy-dependence of the said NLO properties of low-dimensional semiconductor materials when noise contribution becomes noticeable.

Density Functional Theory Predictions of the Nonlinear Optical (NLO) Properties in Triphenylamine based α-Cyanocinnamic Acid Compounds: Effect of Fluorine on NLO Response

In this study, the energy gaps, second-order nonlinear optical (NLO) properties and dipole polarizabilities of triphenylamine based α-cyanocinnamic acid acetylene derivatives have been investigated via using time-dependent density functional response theory. These compounds were designed theoretically by fluorine (F) atom substitution at different positions of phenyl ring end of the α-cyanocinnamic acid segment. The results have indicated that the systems substituted by fluorine show remarkable NLO second-order response, especially D4 system with computed static second-order polarizability (βtot) of 70537.95 (a.u). Hence, these materials have the likelihood to be an excellent second-order nonlinear optical (NLO) materials. The βtot value suggests that along the x-axis the charge transfer (CT) from triphenylamine to α-cyanocinnamic acid (D-A) plays a key role in NLO response; whereas α-cyanocinnamic acid acts as an acceptor (A) and triphenylamine acts as a donor (D) in all the studied systems. Incorporation of an electron acceptor (F) at the phenyl ring end of the α-cyanocinnamic acid segment increases the computed βtot values. The present investigation therefore provides an important insight into the remarkably greater NLO properties of α-cyanocinnamic acid and triphenylamine attached via acetylene.

Theoretical exploration of second-order nonlinear optical properties of mono- and bimetallic Pt(II) dithienylcyclopentene complexes: Ligands and photoisomerization effect

On the basis of great diverse applications of nonlinear optical (NLO) materials, organometallic complexes have attracted considerable attention. In this paper, we present a detailed investigation on a series of Pt(II) dithienylcyclopentene(DTE)-based complexes via density functional theory method with the aim of evaluating their structures, electronic absorption spectra and first hyperpolarizabilities. The calculations demonstrate that the first hyperpolarizabilities can be enhanced by the introduction of quinolone into the complexes because of the enlarged spatial separation of electron density. However, Pt(II) complexes containing perfluorocyclopentene ring exhibit decreasing NLO response attributed to lower amount of charge transferred and short effective CT distance. The static first hyperpolarizabilities (βtot) of monometallic Pt(II) complexes are larger than those of bimetallic Pt(II) complexes due to correlative mixed charge-transfer patterns. More importantly, the closed-ring (1c) complex comprising DTE unit exhibits the largest βtot value approaching 144 × 10−30 esu, with the contrast over five times compared to corresponding open-ring due to the better π-conjugated delocalization and smaller HOMO and LUMO energy gap. In general, we envision our work will be beneficial for further rational design of DTE-containing Pt(II) complexes as high performance NLO materials.

DFT Studies on Second-order Nonlinear Optical Response of Ir(C^N)2(pic) Complexes

Density functional theory(DFT) was employed to calculate the geometrical structures, UV-Vis absorption spectra and second-order nonlinear optical(NLO) properties of a family of iridium(III) complexes, which possess of different cyclometallated ligands(C^N) and ancillary ligands[pyridine-2-carboxylate(pic)]. It was found that the modification of the LUMO energy levels was achieved by changing pic ligands and the energy gaps between the HOMO and LUMO were notably increased or decreased. In addition, the degree of conjugation was significantly changed with the substituent groups varied, which led to that the first hyperpolarizability β could be effectively modulated. Through the analysis of time-dependent DFT(TD-DFT) results, we predicted that these studied complexes with π→π* charge transfer was beneficial to the large second-order NLO properties. Therefore, we hope that these studied iridium( III) complexes can be considered as versatile second-order NLO materials.

Tuning the Linear and Nonlinear Optical Properties of Pyrene-Pyridine Chromophores by Protonation and Complexation to d10 Metal Centers †

The linear and second-order nonlinear optical (NLO) properties of two pyrene-pyridine chromophores, namely, 4-(pyren-1-yl)pyridine (L1) and 4-(2-(pyren-1-yl)ethyl)pyridine (L2), were investigated and modulated by performing protonation/deprotonation cycles or by complexation to d10 metal centers such as Zn(II) and Cu(I) to form the monomeric [Zn(CH3CO2)2(L1)2] complex and the [CuI(L2)]n coordination polymer, respectively. The structures of L1, L2, [Zn(CH3CO2)2(L1)2] and [CuI(L2)]n were determined by means of single-crystal X-ray diffraction studies. The NLO response, measured by the electric-field-induced second harmonic generation (EFISH) technique, was positive for both chromophores and showed an inversion of the sign after exposure to HCl vapors. This process was completely reversible and the original values were restored by simple exposure to NH3 vapors. Coordination of L1 to Zn(II) also resulted in a negative NLO response, although smaller in magnitude compared to the protonated form, due to the weak Lewis acidity of the “Zn(CH3CO2)2” fragment. The results were also interpreted on the basis of DFT/TDDFT calculations.

Second-order NLO properties of bis-cyclometalated iridium(Ⅲ) complexes: Substituent effect and redox switch

The iridium(III) complexes could be excellent second-order nonlinear optical (NLO) switch materials due to various advantages including abundant valence states, the diversity of coordination forms and rich electrochemical properties. In this work, the substituent effect and the multi-state switchable response of a series of novel Ir(CˆN)2ADC complexes (CˆN = cyclometalated ligands and ADC = diaminocarbene), induced by electrochemical behavior, have been calculated by density functional theory. The results show that the introducing strong electron-withdrawing groups on ADC ligands significantly enhanced the static first hyperpolarizabilities (βtot). Moreover, a distinct improvement of the βtot values can be found from the neutral complexes to the corresponding redox states. By this way, the remarkable multi-state NLO switch can be achieved. Remarkably, the βtot values of the one-electron-oxidized complex 1+ and the one-electron-reduced complex 1- are ∼5.4 and ∼12.7 times larger than the corresponding neutral complex 1, respectively. The larger βtot values are attributed to the lower transition energy and remarkable bathochromic shift of maximal absorption wavelength, which can be further illustrated by the separate distribution of β density. We envision that these studied iridium complexes can be seen as versatile and novel second-order NLO switching materials.

Effect of (super)alkali doping on the electronic and second-order nonlinear optical properties of graphitic C3N4

A systematic analysis of electronic and nonlinear optical properties of a novel class of (super)alkali-doped complexes M/M3O@g-C3N4 (MLi, Na, K) is presented. These compounds exhibit considerable stability with large interaction energies, and M3O@g-C3N4 has higher stability than the corresponding M@g-C3N4. It is found that doping the (super)alkali can significantly narrow the wide energy gap of the pure g-C3N4 in the range of 2.04–2.84 eV, and these doped g-C3N4 show enhanced visible-light absorption. Due to the large charge transfer from (super)alkali to g-C3N4 moiety, these doped compounds exhibited significantly large first hyperpolarizabilities up to 2165–63761 au. The ratio between the vibrational and electronic contribution on hyperpolarizability indicates that the vibrational contributions play an important role in determining the static hyperpolarizabilities of certain systems. Therefore, (super)alkali-doped g-C3N4 are expected to be potential candidates for visible-light catalysis and high-performance nonlinear optical materials. We expect this work could provide a new idea for designing functional materials using superalkali clusters.

Rational design of the nonlinear optical materials dinaphtho[2,3-b:2′,3′-d]thiophene-5,7,12,13-tetraone (DNTTRA) and its phenyldiazenyl derivatives using first-principles calculations

Using density functional theory (DFT) at the M06-2X level with the 6-311++g(d,p) basis set, the structure, frontier orbitals, and second-order nonlinear optical (NLO) properties of dinaphtho[2,3-b:2′,3′-d]thiophene-5,7,12,13-tetraone (DNTTRA) and 18 of its phenyldiazenyl derivatives are calculated. The electronic absorption spectra are calculated by time-dependent density functional theory (TD-DFT) using the TD-M06-2X method. The results show that the strongest absorption peak of the 19 molecules lies in the range of 258.8–416.1 nm. When the 2, 10 sites of the DNTTRA molecule are substituted by phenyldiazenyl groups, the maximum absorption peak is red-shifted significantly compared with substitutions at the 3, 9 and 2, 9 sites. In addition, the second-order NLO properties (β0, βµ) are increased by 22 and 2 times more compared with the substitutions at the 3, 9 and 2, 9 positions, indicating that substitution of phenyldiazenyl groups at the 2, 10 sites is superior to substitution at the 3, 9 and 2, 9 sites for the DNTTRA molecule. Moreover, substitution of strong electron-donor groups [such as –NHCH3 or –N(CH3)2] at the opposite end of the phenyldiazenyl rings is found to be beneficial to improve the second-order NLO properties of the system, resulting in second-order NLO materials with excellent performance.

Prediction of Second-Order Nonlinear Optical Properties of D–π–A Compounds Containing Novel Fluorene Derivatives: A Promising Route to Giant Hyperpolarizabilities

Herein, first attempt has been made to utilize fluorene-based dye-sensitized solar cell (DSSCs) dye JK-201 as potential nonlinear optical (NLO) material and for the theoretical designing of novel NLO chromophores JK-D1–JK-D12. DFT/TDDFT calculations were performed to compute the effect of π-linkers and acceptors-steered modulation on electronic, photophysical and NLO properties of JK-201 and JK-D1–JK-D12. Results illustrate that computed λmax (484.74 nm) and experimentally calculated λmax (481 nm) of JK-201 was found in good agreement. Maximum red shifted absorption spectrum was observed in JK-D12 with 599.38 nm. JK-D1–JK-D12 showed narrow energy gap and broader absorption spectrum as compared to JK-201. NBO analysis confirmed the formation of charge separation state due to robust range of electrons/charge transfer from donor to acceptor via π-bridge. Giant NLO response was observed in all compounds. Particularly, JK-D12 displayed surprisingly large 〈α〉 and βtot computed 1376.74 (a.u.) and 405,731.84 (a.u.) respectively. Although literature is flooded with D–π–A compounds investigated for their DSSCs properties, but research reports on their NLO properties and utilization as NLO materials are completely deserted. Our research will open new horizons to explore DSSCs materials for NLO applications. This theoretical framework also exposed that fluorene-substituted chromophores are excellent NLO candidates for modern hi-tech applications.

One-Drop Self-Assembly and Size Control of Organic Nonlinear Optical Crystal DSNS Nanowires

In this study, we demonstrate a one-drop self-assembly method for fabricating nanowires (NWs) of organic second-order nonlinear optical (NLO) material, 4-N,N-dimethylamino-4′-N′-methyl-stilbazolium 2-naphthalenesulfonate (DSNS). By controlling the parameters of the self-assembly process, we successfully controlled the length of DSNS from a few micrometers to millimeters. The obtained NWs have very high surface quality with surface roughness < 150 pm, which is highly beneficial for fabricating integrated optical devices. DSNS NW has the same triclinic crystal structure as that of bulk crystal and exhibits excellent second-order NLO and fluorescent properties, which could provide wide opportunities for on-chip optoelectronic devices and integrated photonic systems. Furthermore, the one-drop self-assembly method only requires reagents in microgram quantities, and thus this method is extremely environmentally friendly.

Redox-switching of ternary Ni(ii) and Cu(ii) complexes: synthesis, experimental and theoretical studies along with second-order nonlinear optical properties

The redox-switching behavior of the title compounds has been probed for the Ni(ii) derivatives using time-resolved spectroelectrochemistry under thin-layer conditions.

Second-order nonlinear optical properties of eight-membered centrosymmetric cyclic borasiloxanes

SHG efficiencies of eight-membered centrosymmetric cyclic borasiloxanes arise form distorted silicon atom, strong electron withdrawing group and non-covalent interactions in crystal packing.

Theoretical study on the electronic structure and second-order nonlinear optical properties of benzannulated or selenophene-annulated expanded helicenes.

Currently, discovering new materials with superior second-order nonlinear optical (NLO) performance has become a very hot research topic in the fields of chemistry and materials science. Now, density functional theory (DFT) has become a powerful tool to predict the performance of novel materials. In this paper, based on benzannulated and selenophene-annulated expanded helicenes, twenty-six helicenes are designed by introduction donor/acceptor moieties and their combinations at different substituent positions. The geometrical/electronic structures, electronic transition, and second-order NLO properties of these helicenes are full investigated by DFT/TDDFT theory. The investigations show that these helicenes have large first hyperpolarizability values (βHRS). For instance, the βHRS value (29.95 × 10−30 esu) of helicene H24 is about 7 times larger than that of the highly π-delocalized phenyliminomethyl ferrocene complex. In addition, the introduction of acceptor NO2 unit at R7 and R8 positions for helicenes H1 and H15 can obtain the largest βHRS value, which is attributed to the enhancement of electron acceptor ability. In view of large NLO response and intrinsic asymmetric structures, the studied helicenes have the possibility to be excellent second-order NLO materials.

Second-order nonlinear optical properties of [60]fullerene-fused dihydrocarboline derivates: a theoretical study on switch effect

The theoretical calculations show that [60]fullerene-fused dihydrocarboline derivatives exhibit significant first hyperpolarizability contrasts induced by their electrochemical feature.

Tailoring the Linear and Second-Order Nonlinear Optical Responses of the Titanium-MIL-125 Metal–Organic Framework through Ligand Functionalization: A First Principles Study

Density functional theory calculations have been performed to investigate the linear and second-order nonlinear optical (NLO) properties of titanium-based MIL-125 metal–organic frameworks in crystalline form, in which the 1,4-benzenedicarboxylate (BDC) linkers are modified by introducing different functional groups or by extending the BDC ligand to contain two (MIL-126) and three (MIL-127) benzene rings. Our results reveal that the functionalization of the BDC linker tends to increase the dielectric constants and the magnitude of birefringence of MIL-125, especially for the aminated derivatives. Correspondingly, the incorporation of a substituent group will improve the phase matching performance of MIL-125. As for the second-harmonic generation (SHG) susceptibility, the SHG activity of the pristine MIL-125 is comparable to KDP, which can be attributed mostly to the contributions of TiO5(OH) octahedra. It is noted that after introducing the substituent group into the BDC linker, the organic part will have a remarkable influence on the SHG intensity. However, the specific effect on the NLO response is dependent on the type of functional group incorporated into the BDC ligand, and only the inclusion of the amine group that is strongly electron-donating can obviously enhance the SHG activity of MIL-125. In addition, MIL-126 and MIL-127 with longer aromatic linking units are not suitable to act as NLO materials due to their poor phase matching abilities, but they are promising candidates for the low dielectric constant materials. The present study can provide theoretical insights to design new second-order NLO materials based on MIL-125.

State of the Art of Boron and Tin Complexes in Second- and Third-Order Nonlinear Optics §

Boron and tin complexes have been a versatile and very interesting scaffold for the design of nonlinear optical (NLO) chromophores. In this paper we present a wide range of reports since the 1990s to date, which include second-order (e.g., second harmonic generation) and third-order (e.g., two-photon absorption) NLO properties. After a short introduction on the origin of the NLO response in molecules, the different features associated with the introduction of these inorganic motifs in the organic-based NLO materials are discussed: Their effect on the accepting/donating capabilities of the substituents, on the efficiency of the π-conjugated linkage, and on the topology of the chromophores which can be tuned from the first generation of “push-pull” chromophores to more sophisticated two- or three-dimensional architectures.

Molecular Origins of the Nonlinear Optical Responses of a Series of α-(X-2-Pyridylamino)-o-cresol Chromophores from Concerted X-ray Diffraction, Hyper-Rayleigh Scattering, and Ab Initio Calculations

Faster transmission rates are desperately needed in the telecommunications industry, given that global demand for signal transmission already outstrips supply. New organic nonlinear optical (NLO) materials offer a prospective solution for the telecommunications industry given that they exhibit shorter optical response times compared to their inorganic counterparts. α-(X-2-Pyridylamino)-o-cresol-type motifs with their donor−π–acceptor (D−π–A) architecture and high level of π-conjugation are expected to afford high levels of intramolecular charge transfer (ICT). Such ICT phenomena will contribute to these types of molecules having faster optical response times and large (hyper)polarizabilities. The linear and second-order NLO properties of three new α-(X-2-pyridylamino)-o-cresol motifs (X = 4-CH3 (1); 5-Cl (2); 3,5-Cl (3)) were hence evaluated. NLO structure–function relationships were established in terms of their ICT characteristics and molecular hyperpolarizabilities (β). Given the typically large errors...

Synthesis of Pyridazine Derivatives by Suzuki-Miyaura Cross-Coupling Reaction and Evaluation of Their Optical and Electronic Properties through Experimental and Theoretical Studies.

A series of π-conjugated molecules, based on pyridazine and thiophene heterocycles 3a–e, were synthesized using commercially, or readily available, coupling components, through a palladium catalyzed Suzuki-Miyaura cross-coupling reaction. The electron-deficient pyridazine heterocycle was functionalized by a thiophene electron-rich heterocycle at position six, and different (hetero)aromatic moieties (phenyl, thienyl, furanyl) were functionalized with electron acceptor groups at position three. Density Functional Theory (DFT) calculations were carried out to obtain information on the conformation, electronic structure, electron distribution, dipolar moment, and molecular nonlinear response of the synthesized push-pull pyridazine derivatives. Hyper-Rayleigh scattering in 1,4-dioxane solutions, using a fundamental wavelength of 1064 nm, was used to evaluate their second-order nonlinear optical properties. The thienylpyridazine functionalized with the cyano-phenyl moiety exhibited the largest first hyperpolarizability (β = 175 × 10−30 esu, using the T convention) indicating its potential as a second harmonic generation (SHG) chromophore.

Second-order nonlinear optical properties of CuGaxIn1-xSe2 (x = 0.54): Experimental and theoretical investigations

CuGaxIn1-xSe2 (x = 0.54, CGISe) has been obtained by a high temperature solid-state method. It crystallizes in the typical chalcopyrite structure. CGISe exhibits a second-harmonic generation intensity about 0.5 times that of AgGaS2 in the particle size range 75–100 μm. It's band structure, density of state, and optical properties are studied by theoretical calculations. The nonlinear optical properties of CGISe and several related chalcopyrite-type chalcogenides are discussed based on optical property and dipole moment calculations.

Theoretical study of the second-order nonlinear optical properties of ionic liquids

The second-order nonlinear optical properties of ionic liquids formed by [EMIM]+, [BMIM]+, [MePyrr]+, and [BuPy]+ cations in conjunction with four anions, [BF4]−, [NO3]−, [CF3COO]−, and [PF6]−, were carried out at the framework of the Density Functional Theory. First, we determine the first hyperpolarizability for all ions and later, we study the local interactions between the ions to find the key factor that determines their nonlinear optical properties of ionic liquids. The results show that [BuPy]+[CF3COO]−, [BuPy]+[NO3]−, [BuPy]+[BF4]−, and [BMIM]+[NO3]− systems have large first hyperpolarizabilities and can be treated as a good candidate for nonlinear optical devices.