Molecular Second-order Polarizability Research Articles

Determination of the structural, electronic, optoelectronic and thermodynamic properties of the methylxanthine molecules theophylline and theobromine.

RHF and DFT (wB97XD and B3LYP) methods with the 6-31++G** basis set have been used to study structural, optoelectronic and thermodynamic properties of Theophylline and Theobromine. Dipole moment, average polarizability, anisotropy, first-order molecular hyperpolarizability, second-order molecular polarizability, HOMO and LOMO energy gap, molar refractivity, chemical hardness, chemical softness, electronic chemical potential, electronegativity, electrophilicity index, dielectric constant, electric susceptibility, refractive index and their thermodynamic properties have equally been calculated. To understand the vibrational analysis of our system, IR and RAMAN frequencies were calculated and described. Results reveal that molecules can have applications in linear and nonlinear optical devices, photonic devices and in molecular electronics. Equally, from dipole moment, average polarizability, anisotropy, first-order molecular hyperpolarizability, second-order molecular polarizability, HOMO and LOMO energy gap, molar refractivity, chemical hardness, chemical softness, electronic chemical potential, electronegativity, electrophilicity index and literature we suggest that Theophylline and Theobromine be consider as candidates for the treatment of COVID-19 and other respiratory diseases.Electronic supplementary materialThe online version of this article (10.1007/s11082-020-02617-w) contains supplementary material, which is available to authorized users.

3,4-Dinitrothiophene as a central unit of quadrupolar push-pull-push systems

3,4-Dinitrothiophene has been utilized as a central acceptor unit in quadrupolar D-π-A-π-D push-pull-push chromophores. Employing cross-coupling and Knoevenagel reactions, nine novel chromophores bearing terminal methoxythiophene donor and systematically extended/varied π-linker were synthesized. Optical properties were studied by electronic absorption spectra. Fundamental optoelectronic properties were investigated by semiempirical PM7 calculations. It was shown that by varying the π-conjugated system the longest-wavelength absorption maxima can be shifted from 341 to 489 nm. The calculated HOMO–LUMO gaps were found within the range of 6.69–7.29 eV, while the second-order molecular polarizabilities can be tuned from 0.038 to 1.578 × 10 –27 esu.

Second-Order Polarizability and Temporal Stability of Epoxy Polymers Doped with Chromophore and with Chromophore Moieties in the Main Chain

Second-order nonlinear optical (NLO) properties and temporary stability of epoxy polymers based on diglycidyl ether of bisphenol A (DGEBA) both doped with p-nitroaniline (p-NA) and functionalized linear polymer DGEBA with p-NA moieties (attached to the bearing main chain) in the main chain (DGEBA-p-NA) have been investigated. Second-order polarizabilities of both p-NA and functionalized linear polymer DGEBA-p-NA were determined by a solvatochromic method. It was shown that this method could be successfully applied to determine the molecular second-order polarizabilities of both low-molecular mass chromophores and polymers with chromophore moieties attached to the chains. The relaxation behaviour of the doped and functionalized poled epoxy polymers has been studied. The crosslinked functionalized polymer DGEBA-p-NA exhibits the highest second-order NLO properties and temporal stability.

Synthesis of novel H-shaped chromophores

A series of H-shaped chromophores with two parallel and non-conjugated D-π-A units have been synthesized, in which a 9,10-dihydroanthracene was employed as molecular backbone. The synthesis of these H-shaped chromophores 9a–11a was accomplished via an eight-step reaction, including double Claisen rearrangement, hydroboration–oxidation, Rieche formylation reaction, Knoevenagel condensation and Corey–Fuchs reaction, with a total yield about 12.5%. The corresponding mono-D-π-A unit compounds 9b–11b were also prepared in a similar procedure for the purpose of comparison. Crystal structures of three intermediates 5a, 7a and 8a were measured, which demonstrate that the two D-π-A units in a single H-shaped chromophore molecule are nearly arranged at the same direction. The studies of UV–vis spectra and the solvatochromic method indicate that the molecular second-order polarizabilities values (μβ) of H-shaped chromophores are remarkably increased compared with the corresponding mono-D-π-A unit reference compounds, without causing a large shift of the absorption band to longer wavelength.

Electronic spectra and (hyper)polarizabilities of non-centrosymmetric D–A–D chromophores. An experimentally based three-state model and a theoretical TDDFT study of ketocyanines

The electronic structure, spectra and linear and second-order polarizabilities of two symmetric ketocyanines, which are prototypic examples of D-A-D chromophores, have been investigated with two different toolsets: (i) the so-called 'essential-state model', here comprising three states, the ground and two lowest excited (1)ππ* states, has been adapted for these non-centrosymmetric, yet symmetric compounds to determine their permanent electric dipole moments, polarizabilities and first hyperpolarizabilities making use of experimental transition energies and moments; (ii) extensive TDDFT calculations have provided ground-state conformational results consistent with NMR-derived structural information, energies and dipole moments of up to 20 lowest-lying electronic states as well as, within the sum-over-states (SOS) scheme, the most relevant components of the polarizabilities and first hyperpolarizabilities. The two levels of description form consistent pictures of the ketocyanine excited states that provide the most relevant contributions to hyperpolarizabilities: extension of the SOS set beyond the three states of the basic model left unchanged (within ∼10%) the calculated vector component of the second-order polarizability tensor along the direction of the ground-state dipole moment (β(y)). Both approaches indicate that these D-A-D compounds, in spite of their quasi-linear structure, reminiscent of that of centrosymmetric quadrupolar chromophores, feature significant second-order molecular polarizabilities. These rapidly increase with the length of the polyenic bridges in the chromophores. About half of the total value of β(y) is predicted to come from the three-level-term part, β(y,3), most of which derives from the contribution involving the three electronic states of the essential-state model.

ChemInform Abstract: Electronic Structure and Nonlinear Optical Properties of Push-Pull Polyenes: Theoretical Investigation of Benzodithia Polyenals and Dithiolene Polyenals.

We report the results of ab initio Hartree-Fock calculations on the geometric and electronic structure and first-order (α) and second-order (β) molecular polarizabilities of a series of push-pull polyene molecules. The acceptor is in all cases an aldehyde group while the donor is either a benzodithia, a dithiolene, or a dithiolane group. The benzodithia polyenal compounds have recently been shown to present among the largest μ-β values ever measured. Theoretical results are found to be in excellent agreement with experimental data

Nonlinear optical properties of fullerene-porphyrin complexes

The nonlinear optical properties, optical limitation, and second- and third-order nonlinearity in a new class of noncovalently bonded fullerene-porphyrin complexes are investigated. Quantum-chemical calculations of the optimal geometry, binding energy, electronic structure, and nonlinear optical properties of donor-acceptor fullerene-prophyrin complexes are performed. As a result of the formation of a complex, the second-order molecular polarizability is higher than in porphyrins by two to three orders of magnitude, depending on the orientation of the molecule, and the third-order molecular susceptibility two orders of magnitude higher. The nonlinear absorption in thin films and solutions of the complexes is measured. In picosecond regimes, absorption saturation at 560nm wavelength is observed for pulse energy density above 0.01J∕cm2. A model is proposed for the increase of the optical nonlinearity in complexes as compared with the molecular components.

Theoretical study on the second-order nonlinear optical properties of gold (III) alkyl complexes

The equilibrium geometries of gold (III) alkyl complexes are optimized by DFT/B3LYP method. On the basis of the optimized structures, the electronic structures and second-order nonlinear optical properties are calculated by using time-dependent density-functional theory (TDDFT) combined with the sum-over-states (SOS) method. The results show that these complexes possess remarkably larger molecular second-order polarizabilities compared with the typical organometallic and organic complexes. The analysis suggests that charge transfer from the z-axis directions plays a key role in the second-order nonlinear optical response. Moreover, different ancillary ligands can substantially adjust the second-order nonlinear optical response. Thus, it can be concluded that these complexes will be hopeful candidates for the second-order nonlinear optical materials from the standpoint of high transparency, relatively large β values and small dispersion behaviors.

Theoretical study on the two-dimensional second-order nonlinear optical properties: a series of charge-transfer covalently bonded organoimido derived hexamolybdate complexes

To probe the cooperativity of charge transfer between organoimido and hexamolybdate, and enhance the second-order nonlinear optical (NLO) response of organoimido derivatives of hexamolybdates, electronic structures and second-order NLO properties of a series of charge-transfer covalently bonded organoimido derived hexamolybdate complexes with donor-(π conjugated bridge)-acceptor-(π conjugated bridge)-donor or acceptor-(π conjugated bridge)-donor-(π conjugated bridge)-acceptor structures were studied by density functional theory. Studies show that different combinations of the donor, acceptor, heterocycle, –C≡C– and –N=N– moieties, and orientation of heterocycle remarkably affect the second-order NLO responses. The complexes containing electronic acceptor matched with the direction of charge transfer possess remarkable large molecular second-order polarizabilities. Electronic transitions to crucial excited states show that x-polarized transition, contributed to the off-diagonal second-order polarizabiliy tensor (βzxx), possesses lower excited energy compared with z-polarized transition which accounted for the diagonal second-order polarizabiliy tensor (βzzz) and thus led to the large in-plane nonlinear anisotropy (u = βzxx/βzzz) value, as well as good two-dimensional (2-D) second-order NLO properties. These complexes can be used as excellent 2-D second-order NLO materials from the standpoint of both large β and u values.

Theoretical investigation of structures, electronic spectra and nonlinear optical properties of gold-pentacene (Au2C22H14) complexes

Abstract Eight systems formed by adding two gold atoms to a pentacene (Au 2 C 22 H 14 ) were investigated by density functional theory. The structures, electronic spectra and second-order nonlinear optical properties of these eight systems were calculated and were compared with AuC 22 H 14 . The covalent bonds were observed in these eight systems (Au 2 C 22 H 14 ) studied, and the Au–C bond can be strengthened by increasing the number of Au atoms. Moreover, introduction of the second Au atoms further increases the possible transitions and obvious red shift, except for system 4. This indicates that the properties of electronic transition can be tuned through changing the number of Au atoms. Systems 1, 1′, 2 and 2′ possess moderate molecular second-order polarizabilities, and β vec of System 1 is about six times larger than that of (AuC 22 H 14 ). Thus, the position of Au atoms has also great influence on the second-order NLO response.

First- and Second-Order Polarizabilities of Simple Merocyanines. An Experimental and Theoretical Reassessment of the Two-Level Model

Taking four merocyanines [(CH3)2N-(CHCH)n-C(CH 3)O; n = 1-4] (Mc1-4) as test D-A systems, we performed a close experimental and theoretical examination of the two level model with reference to its ability to provide correct predictions of both absolute values and dependence on the conjugation path length of first- and second-order molecular polarizabilities. By (1)H NMR spectroscopy merocyanines Mc1-4 were found to be approximately 1:1 mixtures of two planar conformers with cis and trans arrangements of the C(CH 3)O electron-acceptor group and all trans structure of the polyene like fragment. The degree of bond length alternancy (BLA) in the -(CHCH)n- fragment, was quantified by extensive full geometry optimizations at both semiempirical and ab initio level. DFT (6-31G**/B3LYP) optimized geometries were considered to be most reliable and were used for calculations of the excited-state properties. The applicability of the two level model, reducing the general sum-over-states (SOS) expansion to only one term involving the ground state (g) and the lowest-lying (1)(pipi*) CT state (e), was checked by analysis of fluorescence and near UV absorption spectra. Measurements of the basic two-level model quantities ( Ege, microge and Deltamicro(eg)), by which the dominant components of alpha and beta tensors are expressed (alpha XX , beta XXX , X identical with long molecular axis), were designed to give approximate free-molecule values. It is proposed, in particular, an adjustment of the solvatochromic method for the determination of Deltamicro(eg), based on accurate measurements of absorption spectral shifts in n-hexane/diethyl ether mixtures with small diethyl ether volume fractions. Such an approach led to Mc1-4 beta XXX 's matching well in both value and n-dependence with EFISH data reported in the literature for similar merocyanines. For the fluorescent Mc4, the results were qualitatively well reproduced by an approach, which combines absorption and fluorescence solvent shifts. All the measured quantities were calculated for both trans and cis Mc1-4 by three semiempirical INDO-based approaches aiming at evaluating the performances of different integral parametrizations and CI extensions: ZINDO/S, CS INDO SCI, CS INDO SDCI. In all cases, alpha XX and beta XXX were found to rise proportionally to about n (1.3) and n (2), respectively, in qualitatively good agreement with the experimental values. As to the absolute values, however, experimental alpha XX 's and beta XXX 's were best reproduced by CS INDO SDCI combining Ohno-Klopman parametrization and CI including both single and double excitations. The validity of the two-level model was checked by comparison with converged SOS calculations for the longest chain merocyanine (Mc4) and finite field calculations of linear polarizabilities for all of the four dyes (Mc1-4).

Quantum Chemical Study of Structures, Electronic Spectrum, and Nonlinear Optical Properties of Gold−Pentacene Complexes

Four isomers formed by a gold atom attached to a pentacene molecule were investigated by density functional theory due to their potential applications in molecular electronics. The aim of our study is to shed light on the bonding nature and interaction between gold and carbon, to estimate the influence of gold atoms on the electronic spectrum of the pentacene, and to predict second-order nonlinear optical (NLO) properties. The results show that the gold and carbon atom of systems 1 and 2 can form a covalent bond, which has σ single-bond character. However, there are strong donor−acceptor interactions between gold and carbon of systems 3 and 4. The influence of the number of benzene rings on the bonding nature or interactions is also discussed. Adding a gold atom to the pentacene obviously changes the transition nature of pentacene and results in an increase in possible transition, especially for systems 3 and 4. These systems possess moderate molecular second-order polarizabilities compared with the organ...

Theoretical Study on the Second-Order Nonlinear Optical Properties of Asymmetric Spirosilabifluorene Derivatives

The equilibrium geometries of four asymmetric spirosilabifluorene derivatives are optimized by means of the DFT/B3LYP method with the 6-31G* basis sets in this paper. On the basis of the optimized structures, the electronic structure and second-order nonlinear optical properties are calculated by using time-dependent density-functional theory (TDDFT) based on the 6-31G* level combined with the sum-over-states (SOS) method. The results show that these compounds possess remarkably larger molecular second-order polarizabilities than typical organometallic and organic compounds, and replacement of a carbon atom with nitrogen within the conjugated substituent has a great influence on the second-order nonlinear optical properties. Analysis of the main contributions to the second-order polarizability suggests that charge transfer from the z-axis directions plays a key role in the nonlinear optical response. These compounds have a possibility to be excellent second-order nonlinear optical (NLO) materials from the standpoint of large beta values, small dipole moment, high transparency, and small dispersion behaviors.

Quantum-chemical investigation of second-order nonlinear optical chromophores: Comparison of strong nitrile-based acceptor end groups and role of auxiliary donors and acceptors

We report a detailed quantum-chemical investigation of donor-acceptor substituted dipolar nonlinear optical chromophores incorporating the 4-(dimethylamino)phenyl donor end group and a variety of strong heterocyclic acceptor end groups, including tricyanofurans and tricyanopyrroles. In particular, we study the variation of the molecular second-order polarizability (beta) with the acceptor end group and when inserting auxiliary donors (thiophene) and acceptors (thiazole) into the pi bridge. Both finite-field calculations (in the context of local contributions) and sum-over-states calculations were carried out in order to probe the relationship between beta and the chemical structure of the various chromophores. The trends obtained with these two methods are fully consistent. The large beta values (up to 700 x 10(-30) esu) as well as the observed tunability of the optical absorption maximum (lambda(max)) make the chromophores investigated here interesting candidates for use in electro-optic applications at telecommunications wavelengths.

Predication of second-order optical nonlinearity of [(Bu2tIm)AuX] (X=halogen) using time-dependent density-functional theory combined with sum-over-states method

The dipole polarizability and second-order polarizability of recently synthesized (1,3-di-ter-butylimidazol-2-ylidine) gold complexes [(Bu2t Im)AuX] (X=halogen) were investigated by using time-dependent density-functional theory combined with sum-over-states method. We have discovered that these complexes possess remarkably larger molecular second-order polarizability compared with the organometallic and organic complexes. The value of the second-order polarizability increases in the order of F<Cl<Br<I. The analysis of the molecular orbital suggests that the charge transfer from halogen atom to the carbene ligand plays the key role in nonlinear optical response of gold complexes. The gold of these complexes is a bridge of charge transfer, unlike other organometallic complexes, the metal center may be a strong donor or acceptor. These complexes have a possibility to be excellent second-order nonlinear optical materials from the standpoint of transparency, relatively large beta values and relatively small dispersion behaviors.

Design Strategies versus Limiting Theory for Engineering Large Second-Order Nonlinear Optical Polarizabilities in Charged Organic Molecules

The combination of two design strategies for engineering large second-order nonlinear optical polarizabilities is critically analyzed and contrasted with a recent limiting theory for nonlinear molecular polarizabilities. Elongation of the conjugation path length and N-arylation in stilbazolium chromophores both are established engineering guidelines to enhance molecular optical nonlinearities. These two strategies have now been combined, resulting in extended and N-aryl substituted “stilbazolium” chromophores. The second-order nonlinear molecular polarizabilities, or first hyperpolarizabilities β, of these ionic compounds were measured by hyper-Rayleigh scattering with suppression of the multiphoton fluorescence contributions. Static first hyperpolarizabilities β0 were estimated by using the two-level model. The resulting large β0 values are compared with theoretical limiting values obtained from recently derived generally applicable sum-rules and with experimental values for neutral dipolar chromophores. It is concluded that the two design strategies are independently valid, and that their combination will therefore provide the maximum attainable β0 in an ionic compound. Crystals containing optimized ionic chromophores can hence be expected to possess electrooptic coefficients far greater than those obtained so far from either ionic crystals of stilbazolium dyes or from neutral dipolar guest chromophores in polymer matrixes.

Redox-Switchable Second-Order Molecular Polarizabilities with Electron-Rich Iron σ-Aryl Acetylides

μ·β products were experimentally derived by EFISH for several Fe(II) and Fe(III) σ-aryl acetylides of formula [(η2-dppe)(η5-C5Me5)Fe(C⋮C−Ar)]n+, n(PF6) - (dppe = 1,2-bis(diphenylphosphino)ethane; n = 0, 1), where Ar = p-Py, m-Py, o-Py (1a−c/1a+); Ar = p-C5H4-N(CH3)+, o-C5H4-N(CH3)+ (2a,b+); Ar = p-C6H4X with X = NO2, CN, CF3, H, OMe, NH2 (3a−f/3a−f +). For comparison purposes, EFISH data were also gathered on the Ru(II) analogues (4a,b) of 3a,b. Significant figures for μ·β were determined, with the Fe(II) complexes 2a+ and 3a,b possessing the most electron-deficient aryl rings opposed to the metal center, indicating good second-order molecular polarizabilities. For most representatives among 3a−f/3a−f+ and 4a,b, β and β0 values could be derived using DFT-computed dipole moments. The substituent influence on β and β0 is especially marked in the neutral complexes and follows the electron-accepting properties of X: NO2 > CN > H > OMe ≈ NH2. The comparison between 4a,b and 3a,b indicates that the Fe(II) center is more efficient than Ru(II) as an organometallic donor group when opposed to strong acceptors. In addition, we also show with (3a−f/3a−f+) that the NLO response can be fine-tuned by variation of the X substituent in each redox state. Thus, given the facile and reversible oxidation to the corresponding Fe(III) parents, Fe(II) acetylides might conveniently be used for switching purposes in molecular devices for NLO.

STUDY ON THE SECOND-ORDER NONLINEAR OPTICAL PROPERTIES OF 4-HYDROXY-3-METHOXY CINNAMYLIC ACID

Analyzed the molecular structure of 4-Hydroxy-3-Methoxy Cinnamylic Acid (HMCA), and studied the second-order nonlinear optical properties. The results reveal that it has fairly strong SHG effect and good transparency. The cut-off wavelength λcut-off=420nm.Calculated its molecular second-order polarizability β, and a comparative study on its pertinent derivatives is carried out.

Second-order nonlinear optical susceptibility in chalcone-group crystalline molecular compounds

A study is reported of the second-order nonlinear optical susceptibility in polycrystalline molecular materials of the chalcone group made by second-harmonic generation at a wavelength of 1.06 µm. Some of the compounds studied exhibit a high nonlinear activity and are transparent in the blue region of the spectrum. The measured macroscopic nonlinear polarizability χ 2 was compared with the calculated values of β, the second-order molecular polarizability tensor. The high nonlinear optical polarizability observed in some chalcone compounds is shown to be related to crystal symmetry type.

Improved optical nonlinearity of poled stilbene doped polymer films

The optical properties of corona poled 4′-N,N-dimethylamino-nitrostilbene (DANS) and a newly synthesized α′-cyano-4′-nitro-4-N,N-dimethylaminostilbene (CNDS) doped poly(methyl methacrylate) (PMMA) film were investigated with in situ second-harmonic generation (SHG) measurement and absorption measurement. Optimum corona poling temperatures of these polymer films were found to be lower than glass transition temperatures of the materials, most probably due to the dramatic increased conductivity of the films and phase separation. Under the optimum corona poling condition, the alignment ordering of CNDS was lower than that of DANS from the absorbance before and after corona poling. But the second-order nonlinear susceptibility χ (2) of CNDS/PMMA is improved compared with that of DANS/PMMA. The molecular second-order polarizability β of the CNDS/PMMA was estimated to be about 140 × 10 −30 esu from the measured absorbance and χ (2). The relaxation of SHG intensity of CNDS/PMMA was slower than that of DANS/PMMA. This showed that CNDS is a kind of better dopant than DANS as second-order nonlinear-optical material.