Hyperpolarizability Coefficient Research Articles

Impact of doping with organic dopants and mixed doping with alkali metals and organic dopants on the absorption, electronic, optoelectronic, thermodynamic and nonlinear optical properties of dibenzo[b,def]chrysene in gaseous media: DFT and TD-DFT studies.

In this study, we evaluate the geometrical, absorption, optoelectronic, electronic, nonlinear optical (NLO) and thermodynamic properties of dibenzo[b,def]chrysene molecule derivatives by means of DFT and TD-DFT simulations. In view of the aim of producing new high-performance materials for non-linear optics (NLO) by doping test, two types of doping were used. We obtained six derivatives by doping with organic dopants (Nitro, amide and ticyanoethenyl) and mixed alkali metal (potassium) and organic dopants. Doping with organic dopants produced molecules A, B and C, respectively when substituting one hydrogen with nitro (NO2), amide (CONH2) and tricyanoethenyl (C5N3) groups, while mixed doping involved considering A, B and C and then substituting two hydrogens with two potassiums to obtain compounds D, E and F respectively. The negative values of the various interaction energies calculated for all the doped molecules show that they are all stable, but also that molecules C and F are the most stable in the case of both dopings. The gap energies calculated at the B3LYP level of theory are all below 3eV, which means that all the molecules obtained are semiconductors. Better still, compounds C and F, with gap energies of 1.852eV and 1.204eV, respectively, corresponding to decreases of 35.67% and 58.18% in gap energy compared with the pristine molecule, are more reactive than the other doped molecules. Mixed doping is therefore a highly effective way of narrowing the energy gap and boosting the semiconducting character and reactivity of organic materials. Optoelectronic properties have also been improved, with refractive index values higher than those of the reference material, glass. This shows that our compounds could be used under very high electric field conditions of the order of 4.164 109V.m-1 for C and 7.410 109V.m-1 for F the highest values at the B3LYP level of theory. The maximum first-order hyperpolarizability values for both types of doping are obtained at the CAM-B3LYP level of theory by C: 10-30esu and by F: 10-30esu, and second-order values are also given by these same compounds. These values are higher than the reference value, which is urea, making our compounds potential candidates for high-performance NLO applications. In dynamic mode and at a frequency of 1064nm, at the CAM-B3LYP level of theory, the highest dynamic hyperpolarizability coefficients were obtained by C and F. Hyper-Rayleigh scattering , coefficients of the electro-optical Pockel effect (EOPE), EFISHG, third-order NLO-response degree four-wave mixing , quadratic nonlinear refractive index n2 were also calculated. The maximum values of n2 are obtained by C (6.13 10-20 m2/W) and F (6.60 10-20 m2/W), these values are 2.24 times higher than that of fused silica which is the reference for degenerate four-wave mixing so our molecules could also have applications in optoelectronics as wavelength converters, optical pulse modulators and optical switches. Using the DFT method, we were able to determine the optimized and stable electronic structures of doped dibenzo[b,def]chrysene derivatives in the gas phase. We limited ourselves to using the proven B3LYP and CAMB3LYP levels of theory for calculating electronic properties, and non-linear optics with the 6-311G + + (d,p) basis set, which is a large basis set frequently used for these types of compound. Gaussian 09 software was used to run our calculations, and Gauss View 6.0.16 was used to visualize the output files. TD-DFT was also used to determine absorption properties at the B3LYP level of theory, using the same basis set.

Unraveling the role of superalkalis in modulating the static and dynamic hyperpolarizabilities of emerging calix[4]arenes.

Calixarenes, as novel organic materials, can play a pivotal role in the development of high-performance nonlinear optical materials due to the ease of design and fabrication. In this study, DFT simulations were employed to investigate the geometric, electronic, and NLO responses of calix[4]arene doped with Li3O, Na3O, and K3O superalkalis. The computed values of the vertical ionization energies and interaction energies indicate the chemical and thermodynamic stabilities of the targeted M3O@calix[4]arene complexes. The corresponding energy gaps (2.01 to 3.49 eV) are notably reduced, indicating the semiconductor nature of the materials. Surprisingly, the M3O@calix[4]arene complexes exhibit transparency in the UV/visible range as the absorption peaks are shifted in the near infrared (NIR) region. The highest values of 5.9 × 105 a.u. and 2.3 × 108 a.u. for the respective first and second hyperpolarizabilities are observed for Na3O@calix[4]arene. Furthermore, the Na3O@calix[4]arene complex exhibits maximum values of 2.3 × 105 a.u. for second harmonic generation (SHG) and (K3O@calix[4]arene) 2.3 × 106 a.u. for the electro-optical Pockels effect (EOPE) at 1064 nm. Similarly, approximations are made for the dynamic second hyperpolarizability coefficients (EOKE and EFISHG) at different wavelengths. Notably, the Na3O@calix[4]arene complex demonstrates the highest quadratic nonlinear refractive index (n2) of 9.5 × 10-15 cm2 W-1 at 1064 nm. This research paves the way for the development of stable calix[4]arenes doped with superalkalis, leading to an improved nonlinear optical (NLO) response.

Diamondoid as potential nonlinear optical material by superalkali doping: A first principles study

Adamantane (C10H16), the smallest diamondoid molecule, has sparked considerable scientific interest due to its symmetric, single cage-shaped structure. In the current work, the geometric, electronic, and nonlinear optical responses of Li3O, Na3O and K3O clusters doped adamantanes have been investigated via DFT simulations. The calculated values of interaction energies (−5.50 to −6.91 kcal/mol) and vertical ionization energies (3.01–3.56 eV) reflected that the designed M3O-Ada complexes are thermodynamically and chemically stable. Charge transfer is probed through natural population analysis and the highest charge transfer (0.038 |e|) is observed for K3O-Ada complex. The electride nature of M3O-Ada complexes is confirmed through their electron density distribution and their energy gaps (2.19–3.06 eV) are reduced significantly. Interestingly, the absorption maxima (1387–1629 nm) of M3O-Ada electrides fall in the near infrared region. The highest first and second hyperpolarizability values of 5.9 × 105 au and 2.6 × 108 au are observed for K3O-Ada electride. The maximum hyper-Rayleigh scattering and second harmonic generation values of 1.3 × 107 au and 6.5 × 106 au are obtained at 1907 nm whereas the electro-optical Pockel's effect (6.5 × 106 au) is maximum at 1064 nm. Moreover, the dynamic second hyperpolarizability co-efficients (EOKE, EFISHG) are also computed at varying wavelengths. The M3O-Ada electrides exhibit the maximum nonlinear refractive index n2 of 1.9 × 10−7 cm2 W−1 at 1064 nm. This study will pave the way to the designing of stable superalkali doped diamondoids with enhanced NLO response.

Tuning the Photophysics of Two-Arm Bis[(dimethylamino)styryl]benzene Derivatives by Heterocyclic Substitution.

The identification of novel molecular systems with high fluorescence and significant non-linear optical (NLO) properties is a hot topic in the continuous search for new emissive probes. Here, the photobehavior of three two-arm bis[(dimethylamino)styryl]benzene derivatives, where the central benzene was replaced by pyridine, furan, or thiophene, was studied by stationary and time-resolved spectroscopic techniques with ns and fs resolution. The three molecules under investigation all showed positive fluorosolvatochromism, due to intramolecular charge-transfer (ICT) dynamics from the electron-donor dimethylamino groups, and significant fluorescence quantum yields, because of the population of a planar and emissive ICT state stabilized by intramolecular hydrogen-bond-like interactions. The NLO properties (hyperpolarizability coefficient and TPA cross-section) were also measured. The obtained results allowed the role of the central heteroaromatic ring to be disclosed. In particular, the introduction of the thiophene ring guarantees high fluorescent quantum yields irrespective of the polarity of the medium, and the largest hyperpolarizability coefficient because of the increased conjugation. An important and structure-dependent involvement of the triplet state was also highlighted, with the intersystem crossing being competitive with fluorescence, especially in the thiophene derivative, where the triplet was found to significantly sensitize molecular oxygen even in polar environment, leading to possible applications in photodynamic therapy.

Growth, Quantum Chemical Computations, NLO and Spectroscopic Studies of 2-Amino 5-Chloro Pyridine Single Crystal in Comparison with Certain Aminopyridine Derivatives.

Single crystals of an organic 2-amino 5-chloropyridine (2A5CP) have been grown by slow evaporation and confirmed by XRD. DFT calculations, spectroscopic studies, Photoluminescence, and thermal analysis were performed to characterize the crystal. The third-order nonlinearity was measured using the open and closed aperture Z-scan techniques. The most stable molecular structure is optimized by DFT/CAM-B3LYP method with 6-311++G(d,p) basis set in the Gaussian 09 program package. Optimized geometry, AIM analysis, MEP, and Mulliken Population analysis prove the presence of intermolecular N-H…N hydrogen bonds in the dimer. Natural Bond Orbital analysis predicts that the chlorine and NH2 substitutions induce hyperconjugation with σ bonds in the C-C double bond and strong π conjugation in the pyridine ring. The π*→ π* conjugative intramolecular charge-transfer interactions in 2A5CP have stabilization energy ∼ 984 kJ/mol which leads to enhancing optical properties. Experimental NMR, FTIR and FT-Raman spectra of 2A5CP have been recorded and compared with theoretical spectra. The vibrational wavenumbers are simulated (scaled) and assigned based on potential energy distribution. Hirshfeld surface analysis represented in a 2D fingerprint plot displays the percentage contribution of interactions between atoms. The optical bandgap of the grown crystal has been calculated as 3.54 eV. In the present investigation, the percentage contribution of interactions, intermolecular hydrogen-bonded interactions, charge on N and H atoms, HOMO-LUMO energy gap, electronic transitions, first-order hyperpolarizability, and two-photon absorption coefficient (β) of 2A5CP were compared with those of certain aminopyridine derivatives. The results of our investigation predict that the 2A5CP is a stable complex below 147 °C with third-order nonlinearity that can be used as a new green-light emitting organic material with potential application as an efficient optical limiter in optoelectronics.

Lanthanum doped corannulenes with enhanced static and dynamic nonlinear optical properties: A first principle study

In this work, lanthanum doping on corannulene (C20H10) buckybowls has been explored for their geometrical, electronic and nonlinear optical (NLO) properties via DFT simulations. The interaction energies of −21.75 to −40.01 kcal/mol reflect that A-D complexes are thermodynamically stable. The HOMO-LUMO energy gaps of designed complexes are decreased significantly up to 48.92%. A maximum charge transfer of 1.452 |e| is observed for complex A as revealed by natural bond orbital analysis. Non-covalent interaction (NCI) and quantum theory of atoms in molecules (QTAIM) analyses have confirmed the presence of various interactions in the complexes. The complexes are transparent in UV–Visible region and absorption maxima fall near infrared region (1123–2032 nm). The highest nonlinear optical response in terms of first hyperpolarizability value of 5.08 × 104 au is observed for complex C. The hyper-Rayleigh scattering (βHRS) and frequency dependent hyperpolarizability coefficients including electro-optical Pockel's effect and second harmonic generation are also computed theoretically.

Static, dynamic nonlinear optical (NLO) response and electride characteristics of superalkalis doped star like C6S6Li6

In search of excellent nonlinear optical (NLO) materials, new type of M3O@C6S6Li6 (M = K, Na, Li) electrides are set forth herein. The geometric, electronic and nonlinear optical properties of these electrides are evaluated by using density functional theory calculations. All the considered complexes have interaction energies in the range of -42.86 to -45.56 kcal/mol that validate their thermodynamically stability. The NBO charge analysis is performed to confirm the charge transfer between M3O and C6S6Li6. The highest amount of electronic charge transfer (0.92 |e|) is seen in K3O@C6S6Li6 electride. The frontier molecular orbitals (FMOs) and density of states (DoS) analyses are implemented to further rationalize the electronic properties. The remarkable polarizability (αo) and static first hyperpolarizability (βo) observed for these complexes validate their excellent nonlinear optical response. The highest βo (2.98×105 au) is obtained for Li3O@C6S6Li6 electride. The frequency-dependent first and second hyperpolarizability coefficients along with dipole dependent hyperpolarizability are also analyzed to get insight of NLO response under variational frequencies. Furthermore, the Hyper-Rayleigh Scattering coefficient (βHRS) of these complexes is investigated to provide information required for experimental point of view of NLO response. This study will contribute towards the development of more stable superalkalis doped electrides having pronounced NLO response.

Superalkali (Li2F, Li3F) doped Al12N12 electrides with enhanced static, dynamic nonlinear optical responses and refractive indices

In the present work, superalkalis (Li2F and Li3F) doped Al12N12 nanocages have been designed and investigated theoretically to elucidate the correlations between geometric, electronic and nonlinear optical properties. All complexes (A-E) are stable inorganic electrides as indicated by their interaction energies (−52.97 to −87.58 kcal/mol). The decrease in HOMO-LUMO energy gaps (5.44–5.87 eV) has caused a remarkable increase in the nonlinear optical response of A-E complexes. The maximum values of first hyperpolarizability (1.20 × 104 a.u.) and second hyperpolarizability (1.65 × 107 a.u.) have been achieved for complex A. The highest dynamic hyperpolarizability coefficients including second harmonic generation (9.08 × 105 a.u.) and electro-optic Pockel's effect (9.56 × 105 a.u.) are obtained for complex A at 532 nm. The electric field-induced second harmonic generation (up to 3.52 × 108 a.u.) and dc-Kerr effect (up to 8.13 ×108 a.u.) along with a large quadratic nonlinear refractive index (up to 5.41 × 10−11 a.u.) of the designed electrides reflected their large NLO response.

Nonlinear optical properties of a new panchromatic series of water-soluble bicationic push-pull fluorophores

Six water-soluble bications, characterized by a symmetric A+-π-D-π-A+ structure, were synthesized and comprehensively studied for their absorption and fluorescence properties, and their nonlinear optical response. Generally, the photobehavior exhibited by the six systems was found to be dependent on the molecular dimensionality and conjugation, unveiling the role of different electron-donor (dimethoxy-phenylene vs bithiophene) and electron-acceptor (methyl-pyridinium, methyl-quinolinum, and pyrimidin-pyridinium) substituents bound in different positions (ortho/para). Steady-state measurements revealed this series as a panchromatic family of dyes with noticeable absorption and emission abilities, covering the entire visible spectrum - from the near-ultraviolet to the near-infrared spectral region. Femtosecond-resolved spectroscopy disclosed the presence of ultrafast intramolecular charge transfer processes, as also predicted by TD-DFT calculations, from the central electron-rich moiety of the molecule towards the two lateral positively charged units. Further and for the first time, a solvatochromic method was successfully applied to this kind of quadrupolar double-charged compounds in order to estimate their static and dynamic second-order hyperpolarizability coefficients. Thanks to their appreciable fluorescence capability, significant Two-Photon Absorption cross-sections were also measured for all six dyes by means of the Two-Photon Excited Fluorescence technique. These findings, together with their good water solubility, designate these eye-catching fluorophores as potential candidates for bioimaging applications.

Structural, spectroscopic and nonlinear optical properties of sulfonamide derivatives; experimental and theoretical study

Abstract Nonlinear optical (NLO) materials have broad range applications in the field of optoelectronic devices. Nowadays great interest has been developed for synthesizing the compounds having high NLO response. Herein we are reporting the structural, spectroscopic and NLO properties of two, structurally simple sulfonamide derivatives. Both compounds are synthesized in respectable yields, characterized by using NMR (1H and 13C), FT-IR and UV–vis spectroscopic techniques. X-ray diffraction analysis confirmed the final structures. Density functional theory (DFT) at B3LYP/6-31G(d,p) method are performed for validation of experimental data (X-ray as well as spectroscopic data). Absorption studies of both compounds are performed by using TD-DFT method. Coefficients of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of both compounds reflect the high stability. First hyperpolarizability (βo), polarizability (αo) and dipole moment (μ) analyses calculated at LC-BLYP method revealed that both derivatives have reasonable nonlinear optical (NLO) response. The static, dc-Kerr effect and electric field-induced second harmonic generation (ESHG) hyperpolarizability co-efficient are also studied for refractive index (n2) calculation of both sulfonamides, to further observe their NLO response.

Single crystal, spectral and electronic transition studies on (E)-N-(3-methoxy-4-hydroxybenzylidene)-4-nitrobenzohydrazide monohydrate

The single crystal of (E)-N-(3-Methoxy-4-hydroxybenzylidene)-4-nitrobenzohydrazide monohydrate (MHBNB) was grown by a slow evaporation method. The crystal structure was determined by single crystal X-ray diffraction method. The electron density, Hirshfeld surface and fingerprint analysis reveals that the crystal packing is governed by several weak OH⋯C, OH⋯O and OH⋯N intermolecular interactions. The analysis of bond critical points (BCP) and topology of the crystalline form of MHBNB were done. The intrusion of H2O molecule does not affect the aromaticity of the pheyl rings but marginally disturbs the aromaticity of hydrazide link. The FT-IR (4000-400 cm−1) and FT-Raman (3500-50 cm−1) spectra were recorded to study the vibrational behavior of MHBNB molecule. To explore the electronic transition of MHBNB, the UV absorbance spectrum was recorded in the range of 200–800 nm. Furthermore, the Density functional theory (DFT) and Time-dependent DFT (TD-DFT) calculations were performed to investigate the molecular geometry, vibrational behavior, electronic excitation and inter-intramolecular charge transfers within the molecule. The singlet (S) and Triplet (T) electronic excited states (n state = 6) of MHBNB were examined, in which, the electron spin density (s), excitation energy (ΔE1-6), oscillator strength (f) and electric dipole moment (μ) were examined. The frontier molecular orbitals (FMOs) were studied to find the band gap of FMOs. The natural atomic orbitals (NAO) and natural localized molecular orbitals (NLMO) of MHBNB were analyzed. The density of states (DOS) and Total density of states (TDOS) of functional groups in MHBNB molecule were also evaluated. This compound has very good first order hyperpolarizability (β0) coefficient.

Photoinduced Intramolecular Charge Transfer and Hyperpolarizability Coefficient in Push-Pull Pyridinium Salts with Increasing Strength of the Acceptor Group.

The synthesis of three push-pull cationic dyes is reported here together with a photophysical study carried out by stationary and ultrafast spectroscopies. The hyperpolarizability (β) values of the three molecules have been estimated through a simple solvatochromic method based on conventional, low-cost equipment, which had been tested previously with success in our laboratory. The investigated pyridinium salts showing strong negative solvatochromism bear the same piperidine ring as a strong electron-donor group and the same thiophenes as electron-rich π-linkers, but differ in terms of the N-substituent on the electron-acceptor pyridinium unit, namely N-methyl in compound A, N-pyrimidin-2yl in B and N-2,4-dinitrophenyl in C. The derived β values were found to increase (in the order A<B<C) along with the increasing electron-acceptor strength of the pyridinium substituent, with the highest polarizability being estimated for the derivative bearing the strongest electron-withdrawing substituent dinitrobenzene. State-of-the-art femtosecond transient absorption measurements evidenced fast kinetics and dynamics in the singlet excited state in agreement with charge transfer (CT) processes promoted by excitation, with a proper ICT state observed in the case of C. This finding confirms the efficiency of photoinduced intramolecular CT as a significant factor that affects the NLO response.

Uncertainty Evaluation of an 171Yb Optical Lattice Clock at NMIJ.

We report an uncertainty evaluation of an 171Yb optical lattice clock with a total fractional uncertainty of 3.6×10-16 , which is mainly limited by the lattice-induced light shift and the blackbody radiation shift. Our evaluation of the lattice-induced light shift, the density shift, and the second-order Zeeman shift is based on an interleaved measurement where we measure the frequency shift using the alternating stabilization of a clock laser to the 6s2 1S0-6s6p 3P0 clock transition with two different experimental parameters. In the present evaluation, the uncertainties of two sensitivity coefficients for the lattice-induced hyperpolarizability shift d incorporated in a widely used light shift model by RIKEN and the second-order Zeeman shift aZ are improved compared with the uncertainties of previous coefficients. The hyperpolarizability coefficient d is determined by investigating the trap potential depth and the light shifts at the lattice frequencies near the two-photon transitions 6s6p3P0-6s8p3P0, 6s8p3P2, and 6s5f3F2. The obtained values are d=-1.1(4) μ Hz and aZ=-6.6(3) Hz/mT2. These improved coefficients should reduce the total systematic uncertainties of Yb lattice clocks at other institutes.

New Styryl Phenanthroline Derivatives as Model D-π-A-π-D Materials for Non-Linear Optics.

Four novel push-pull systems combining a central phenanthroline acceptor moiety and two substituted benzene rings, as a part of the conjugated π-system between the donor and the acceptor moieties, have been synthetized through a straightforward and efficient one-step procedure. The chromophores display high fluorescence and a peculiar fluorosolvatochromic behaviour. Ultrafast investigation by means of state-of-the-art femtosecond-resolved transient absorption and fluorescence up-conversion spectroscopies allowed the role of intramolecular charge transfer (ICT) states to be evidenced, also revealing the crucial role played by both, the polarity and proticity of the medium on the excited state dynamics of the chromophores. The ICT processes, responsible for the solvatochromism, also lead to interesting non-linear optical (NLO) properties: namely great two photon absorption cross-sections (hundreds of GM), investigated by the Two Photon Excited Fluorescence (TPEF) technique, and large second order hyperpolarizability coefficients, estimated through a convenient solvatochromic method.

Influence of number and position of nitro groups in tuning the thermodynamic and nonlinear optical properties of ethylenediaminium nitrophenolates

Estimation of thermodynamic and third-order nonlinear optical properties of a series of organic liquids based on ethylenediaminium divalent cation, [C2H10N2]X2 (where X=2-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol and 2,4,6-trinitrophenol respectively) was made. Increase in nitro groups of ethylenediaminium nitrophenolates has predominantly increased the point of decomposition (145–243°C). Various thermodynamic properties as a function of temperature were estimated theoretically from the DSC curves. Thermal conductivity and specific heat capacity was increasing while thermal diffusivity was decreasing with rise in temperature. Ethylenediaminium trinitrophenolate (EDA246TNP) showed maximum thermal conductivity (30.3Wm−1K−1) and specific heat capacity (2684Jkg−1K−1), while thermal diffusivity (9.6×10−6m2S−1) was higher for ethylenediaminium 2-nitrophenolate (EDA2NP). Z-scan experiment showed that all samples exhibit saturable absorption and self-defocusing behaviour under CW laser (532nm, 50mW) excitation. The observed nonlinearity was found to be thermal in origin with order of nonlinearity as ED246TNP>EDA24DNP>EDA4NP>EDA2NP. EDA246TNP possess maximum nonlinear absorption coefficient (8.37×10−3cm/W), nonlinear refractive index (8.41×10−8cm2/W), third-order nonlinear optical susceptibility (5.21×10−6esu), second-order hyperpolarizability (9.81×10−25esu) and thermo-optic coefficient (−0.21×10−6K−1) than other phenol-ammonium salts. All samples exhibit optical limiting action with optical limiting onset values of 35–38mW having limiting amplitude of 6.7–9.3mW. The influence of number and position of nitro groups in tuning the thermodynamic and nonlinearity of ethylenediaminium nitrophenolate was discussed in detail.

Theoretical study of second-order hyperpolarizability for nitrogen radical cation

We report calculations of the static and dynamic hyperpolarizabilities of the nitrogen radical cation in doublet state. The electronic contributions were computed analytically using density functional theory and multi-configurational self-consistent field method with extended basis sets for non-resonant excitation. The open-shell electronic system of nitrogen radical cation provides negative second-order optical nonlinearity, suggesting that the hyperpolarizability coefficient, in the non-resonant regime is mainly composed of combinations of virtual one-photon transitions rather than two-photon transitions. The second-order optical properties of nitrogen radical cation have been calculated as a function of bond length starting with the neutral molecular geometry (S0 minimum) and stretching the N–N triple bond, reaching the ionic D0 relaxed geometry all the way toward dissociation limit, to investigate the effect of internuclear bond distance on second-order hyperpolarizability.

Higher-order nonlinearity of refractive index: the case of argon.

The nonlinear coefficients, n4, of the time-dependent refractive index for argon are calculated in the non-resonant optical regime. Second-order polynomial fitting of DC-Kerr, γ((2))(-ω; ω, 0, 0), electric field induced second harmonic generation (ESHG), γ((2))(-2ω; ω, ω, 0), and static second-order hyperpolarizability, γ((2))(0; 0, 0, 0), is performed using an auxiliary electric field approach to obtain the corresponding fourth-order optical properties. A number of basis sets are investigated for the fourth-order hyperpolarizability processes at 800 nm at coupled cluster singles and doubles level of theory, starting with the t-aug-cc-pV5Z basis set and expanding that basis set by adding diffuse functions and polarization functions. Comparison shows that the results obtained with the t-aug-cc-pV5Z basis are in very good agreement with the results obtained using the q-aug-cc-pV5Z, t-aug-cc-pV6Z, and q-aug-cc-pV6Z basis sets. To calculate the nonlinear refractive index n4, an approximate formula is suggested which expresses the related degenerate six-wave mixing coefficient, γ((4))(-ω; ω, -ω, ω, -ω, ω), in terms of the DC-Kerr, γ((4))(-ω; ω, 0, 0, 0, 0), ESHG, γ((4))(-2ω; ω, ω, 0, 0, 0), and the static fourth-order hyperpolarizability coefficients. The higher-order nonlinear refractive index n4 is found to be positive over the wavelengths 300 nm-2000 nm. In the infrared spectral range, the obtained values of n4 are in qualitative agreement with the results of Kramers-Kronig-based calculations.

Molecular Origins of the High-Performance Nonlinear Optical Susceptibility in a Phenolic Polyene Chromophore: Electron Density Distributions, Hydrogen Bonding, and ab Initio Calculations

The molecular and supramolecular origins of the superior nonlinear optical (NLO) properties observed in the organic phenolic triene material, OH1 (2-(3-(4-hydroxystyryl)-5,5-dimethylcyclohex-2-enylidene)malononitrile), are presented. The molecular charge-transfer distribution is topographically mapped, demonstrating that a uniformly delocalized passive electronic medium facilitates the charge-transfer between the phenolic electron donor and the cyano electron acceptors which lie at opposite ends of the molecule. Its ability to act as a “push–pull” π-conjugated molecule is quantified, relative to similar materials, by supporting empirical calculations; these include bond-length alternation and harmonic-oscillator stabilization energy (HOSE) tests. Such tests, together with frontier molecular orbital considerations, reveal that OH1 can exist readily in its aromatic (neutral) or quinoidal (charge-separated) state, thereby overcoming the “nonlinearity-thermal stability trade-off”. The HOSE calculation also reveals a correlation between the quinoidal resonance contribution to the overall structure of OH1 and the UV–vis absorption peak wavelength in the wider family of configurationally locked polyene framework materials. Solid-state tensorial coefficients of the molecular dipole, polarizability, and the first hyperpolarizability for OH1 are derived from the first-, second-, and third-order electronic moments of the experimental charge-density distribution. The overall solid-state molecular dipole moment is compared with those from gas-phase calculations, revealing that crystal field effects are very significant in OH1. The solid-state hyperpolarizability derived from this charge-density study affords good agreement with gas-phase calculations as well as optical measurements based on hyper-Rayleigh scattering (HRS) and electric-field-induced second harmonic (EFISH) generation. This lends support to the further use of charge-density studies to calculate solid-state hyperpolarizability coefficients in other organic NLO materials. Finally, this charge-density study is also employed to provide an advanced classification of hydrogen bonds in OH1, which requires more stringent criteria than those from conventional structure analysis. As a result, only the strongest OH···NC interaction is so classified as a true hydrogen bond. Indeed, it is this electrostatic interaction that influences the molecular charge transfer: the other four, weaker, nonbonded contacts nonetheless affect the crystal packing. Overall, the establishment of these structure–property relationships lays a blueprint for designing further, more NLO efficient, materials in this industrially leading organic family of compounds.

Synthesis and characterization of a novel nonlinear optical hyperbranched polymer containing a highly performing chromophore

We report herein the peripheral functionalization of a high glass transition temperature hyperbranched polyimide with a new and highly performing electro‐optic chromophore for the elaboration of a second‐order nonlinear optical material. In this study, the CPO1 chromophore was selected for its very high quadratic hyperpolarizability coefficient (μβ = 31,000 ⋅ 10−48 esu at 1990 nm) and its ease of synthesis in multigram scale. As a result, the new electro‐optic polymer was characterized by an r33 coefficient around 40 pm/V at 1.5 µm, although the poling conditions were not optimized. For sake of comparison, the electro‐optic r33 coefficient of our previously reported similar polymer functionalized with the well‐known Disperse Red One chromophore was also measured using the technique and gave a much lower r33 coefficient. This study underscores that hyperbranched polymers are particularly promising matrices to host highly efficient chromophore to achieve more efficient and more stable electro‐optic devices than classical linear polymers. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Enhancement of electro-optic activity by introduction of a benzyloxy group to conventional donor-π-acceptor molecules

In this work, we investigated the enhancement of the electro-optic response by introducing benzyloxy group as an additional donor part on conventional donor-π-acceptor molecules. This new type donor exhibited a strong solvatochromic effect, indicating an extra donation to the π-conjugated bridge, which shifted the charge-transfer absorption of the chromophores to the lower energy region. Furthermore, the simple modification on the donor moiety resulted in about 2-fold improvement in the first hyperpolarizability and macroscopic electro-optic coefficient (r 33) over the benchmark 2-dicyanomethylen-3-cyano-4-{2-[E-(4-N,N-di(2-acetoxyethyl)-amino)-phenylene-(3,4-dibutyl)thien-5]-E-vinyl}-5,5-dimethyl-2,5-dihydrofuran (FTC) counterparts. An r 33 above 100 pm/V is ultimately achieved in conventional guest–host system.