A dual approach to study the electro-optical properties of a noncentrosymmetric L-asparagine monohydrate

Single-Crystal Investigation, Hirshfeld Surface Analysis, and DFT Study of Third-Order NLO Properties of Unsymmetrical Acyl Thiourea Derivatives

In the current research work, unsymmetrical acyl thiourea derivatives, 4-((3-benzoylthioureido)methyl)cyclohexane-1-carboxylic acid (BTCC) and methyl 2-(3-benzoylthioureido)benzoate (MBTB), have been synthesized efficiently. The structures of these crystalline thioureas were unambiguously confirmed by single-crystal diffractional analysis. The crystallographic investigation showed that the molecular configuration of both compounds is stabilized by intramolecular N-H···O bonding. The crystal packing of BTCC is stabilized by strong N-H···O bonding and comparatively weak O-H···S, C-H···O, C-H···π, and C-O···π interactions, whereas strong N-H···O bonding and comparatively weak C-H···O, C-H···S, and C-H···π interactions are responsible for the crystal packing of MBTB. The noncovalent interactions that are responsible for the crystal packing are explored by the Hirshfeld surface analysis for both compounds. The void analysis is performed to find the quantitative strength of crystal packing in both compounds. Additionally, state-of-the-art applied quantum chemical techniques are used to further explore the structure-property relationship in the above-entitled molecules. The optimization of molecular geometries showed a reasonably good correlation with their respective experimental structures. Third-order nonlinear optical (NLO) polarizability calculations were performed to see the advanced functional application of entitled compounds as efficient NLO materials. The average static γ amplitudes are found to be 27.30 × 10^-36 and 102.91 × 10^-36 esu for the compounds BTCC and MBTB, respectively. The γ amplitude of MBTB is calculated to be 3.77 times larger, which is probably due to better charge-transfer characteristics in MBTB. The quantum chemical analysis in the form of 3-D plots was also performed for their frontier molecular orbitals and molecular electrostatic potentials for understanding charge-transfer characteristics. We believe that the current investigation will not only report the new BTCC and MBTB compounds but also evoke the interest of the materials science community in their potential use in NLO applications.

Chemically Modified Quinoidal Oligothiophenes for Enhanced Linear and Third-Order Nonlinear Optical Properties

In the present investigation, quantum chemical calculations have been performed in a systematic way to explore the optoelectronic, charge transfer, and nonlinear optical (NLO) properties of different bis(dicyanomethylene) end-functionalized quinoidal oligothiophenes. The effect of different conformations (linking modes of thiophene rings) on conformational, optoelectronic, and NLO properties are studied from the best-performed dimer to octamer. The optical and NLO properties of all the selected systems (1-7) are calculated by means of density functional theory (DFT) methods. Among all the designed compounds, the largest linear isotropic (αiso) polarizability value of 603.1 × 10-24 esu is shown by compound 7 which is ∼12, ∼16, ∼9, ∼11, ∼10, and ∼4 times larger as compared to compounds 1-6, respectively. A relative investigation is performed considering the expansion in third-order NLO polarizability as a function of size and conformational modes. Among all the investigated systems, system 7 shows the highest value of static second hyperpolarizability ⟨γ⟩ with an amplitude of 7607 × 10-36 esu at the M06/6-311G** level of theory, which is ∼521, ∼505, ∼38, ∼884, ∼185, and ∼15 times more than that of compounds 1-6, respectively. The extensively larger ⟨γ⟩ amplitude of compound 7 with higher oscillator strength and lower transition energy indicates that NLO properties are remarkably dependent upon linking modes of thiophene rings and its chain length. Furthermore, to trace the origin of higher nonlinearities, TD-DFT calculations are also performed at the same TD-M06/6-311G** level of theory. Additionally, a comprehensive understanding of the effect of structure/property relationship on the NLO polarizabilities of these investigated quinoidal oligothiophenes is obtained through the inspection of Frontier molecular orbitals, the density of states (TDOS and PDOS), and molecular electrostatic potential diagrams including the transition density matrix. Hence, the current examination will not just feature the NLO capability of entitled compounds yet additionally incite the interest of experimentalists to adequately modify the structure of these oligothiophenes for efficient optical and NLO applications.

Effect of phenol red dye on monocrystal growth, crystalline perfection, and optical and dielectric properties of zinc (tris) thiourea sulfate

In this work, the growth of large size (∼25 × 29 × 5 mm and ∼25 × 24 × 6 mm) colorful single crystals of zinc (tris) thiourea sulfate (ZTS) in the presence of 0.05–2 wt% phenol red (PR) dye was achieved using a simple and low-cost technique. Powder X-ray diffraction patterns confirm the presence of PR dye, which is indicated by an enhancement of the Raman peak intensities, a shift in their position and the appearance of a few extra peaks. The quality of the grown crystals was assessed by high-resolution X-ray diffraction, which shows that the crystalline perfection of 1 wt% PR-dyed ZTS crystals is better than that of 2 wt% PR-dyed crystals. The measured UV–vis absorbance spectra show two additional, strong absorption bands at ∼430 and 558 nm in the dyed crystals, due to the presence of PR dye, along with a band at ∼276 nm which is present for all crystals but is slightly shifted for the dyed crystals. Photoluminescence spectra were recorded at two excitation wavelengths (λexc= 310 and 385 nm). The luminescence intensity is found to be enriched in dyed crystals, with some extra emission bands. An enhancement in the value of the dielectric constant and a.c. electrical conductivity was also observed in the dyed ZTS crystals.

An experimental and theoretical study on a novel donor-π-acceptor bridge type 2, 4, 5-trimethoxy-4'-chlorochalcone for optoelectronic applications: A dual approach

In this article the authors aim is to investigate and analyze the various key parameters of an organic D-π-A type novel nonlinear optical material 2, 4, 5-trimethoxy-4'-chlorochalcone (2,4,5TMCC) through experimental and quantum chemical studies. The Claisen-Schmidt condensation reaction mechanism was applied to synthesize the 2,4,5TMCC compound and its single crystal was grown by a slow evaporation solution growth (low cost) technique. The crystal structure was confirmed by powder X-ray diffraction analysis. The robust vibrational study has been done using FT-IR and FT-Raman spectra and its NLO activity was discussed. The factor group analysis was also performed. The optical absorption spectrum was recorded and the band gap was calculated to be 2.8eV. In photoluminescence spectrum, an intense emission band at ~540nm has been observed which shows that the grown crystals can be used in green organic light emitting diodes and laser applications. To achieve the stable ground state molecular geometry of 2,4,5TMCC, the computational techniques were applied at different levels of theory using 6-31G* basis set. The calculated geometrical parameters and vibrational spectra are found to be in good agreement with the experimental results. To probe the optical properties of the title compound the time dependent density functional theory was applied. The excitation wavelength was observed at ~398.63nm calculated at B3LYP/6-31G* level of theory and found close to experimental value (i.e. 396nm). The static first hyperpolarizability value is found to be 136 times higher than prototype urea molecule. Additionally, the molecular level approach was attained as HOMO-LUMO gap and electrostatic potential maps. The DSC study reveals that the titled material is stable up to 149°C. The photophysical and nonlinear optical properties suggest that the titled material could be a better choice for the fabrication of optoelectronic devices.

First-principles study of nitrogen-doped nanographene as an efficient charge transport and nonlinear optical material

The prospective of nitrogen doped graphene (NDG) as useful nonlinear optical (NLO) and charge transport materials is explored using first principles methods.

Role of a singlet diradical character in carbon nanomaterials: a novel hot spot for efficient nonlinear optical materials

Carbon atoms have the potential to produce a variety of fascinating all-carbon structures with amazing electronic and mechanical properties. Over the last few decades, several efforts have been made using experimental and computational techniques to functionalize graphene, carbon nanotubes and fullerenes for potential use in modern hi-tech electronic, medicinal, optical and nonlinear optical (NLO) applications. Since photons replaced electrons as a carrier of information, the field of NLO material design has drawn immense interest in contemporary materials science. There have been several reports of bridging the gap between the exciting fields of carbon nanomaterials and NLO materials by functionalizing carbon nanomaterials for potential NLO applications. In contrast to previous reports of the design of third-order NLO materials using conventional closed-shell materials, a novel strategy using open-shell diradical molecular systems has recently been proposed. Quantum chemically, diradical character is explained in terms of the instability of the chemical bonds in open-shell molecular systems. Interestingly, several carbon nanomaterials, which naturally possess open-shell singlet configurations, have recently gained momentum in the design of these classes of open-shell NLO materials with excellent NLO properties, stability and diversity. The present review establishes a systematic sequence of different studies (spanning over two decades of intense research efforts), starting from the simplest theoretical two-site diradical model, continuing to its experimental and theoretical realization in actual chemical systems, and finally applying the abovementioned model/rule to novel carbon nanomaterials to tune their NLO properties, particularly their second hyperpolarizability (γ). In the present report, we highlight several recent efforts to functionalize carbon nanomaterials by exploiting their open-shell diradical character to achieve efficient third-order NLO properties. Several issues and opportunities are discussed, including the inherited disadvantages of both experimental (the high reactivity and short life of diradical compounds) and quantum (need for multi-reference methodology) techniques when dealing with carbon nanomaterials. A comparative analysis of several quantum chemical investigations, along with contemporary experimental results, will be performed to emphasize the core issues and opportunities related to carbon nanomaterials with singlet open-shell diradical character. Thus, the present review will highlight carbon nanomaterials with diradical/biradical character for their prospective applications in the NLO field.

Molecular structure, spectroscopic (IR, Raman, Ultra Violet-Visible) and nonlinear optical investigation on DCBLPZ: A novel semiorganic NLO material

Dichlorobis(L-proline) zinc(II) (DCBLPZ) is an excellent nonlinear optical (NLO) material because of its ability to exhibit high second harmonic generation and having significant optical transparency. In this work, electro-optical properties of the titled material has been thoroughly investigated by Hartree–Fock (HF) and Density functional theory using different basis sets in C1 symmetry. The calculated geometrical parametres and vibrational frequencies were found to be in good agreement with reported experimental results. Highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) studies were carried out to understand the intramolecular charge transfer within the molecule. Total dipole moment ([Formula: see text]), polarizability ([Formula: see text]), anisotropy of polarizability ([Formula: see text] and first hyperpolarizability ([Formula: see text]) values were calculated. The static first hyperpolarizability value is found to be six times higher than urea. Ultra violet-visible spectrum of DCBLPZ molecule was calculated by time-dependent density functional theory (TD-DFT) in gas phase using different functionals. The calculated value of absorption wavelength was found at 234[Formula: see text]nm using TD-B3LYP/[Formula: see text]* level of theory and was in good agreement with experimental value (230[Formula: see text]nm) than other applied methods. Our results give us flexibilty to predict about possible intramolecular charge transfer from both the chlorine atoms toward both the proline units through zinc atom in the studied metallic complex. The other important parametres such as frontier molecular orbital’s (FMO), global reactivity descriptors and molecular electrostatic potential have also been calculated and discussed.

First principal studies of spectroscopic (IR and Raman, UV-visible), molecular structure, linear and nonlinear optical properties of L-arginine p-nitrobenzoate monohydrate (LANB): A new non-centrosymmetric material

In current work, the authors have been applied the density functional theory (DFT) using B3LYP and CAM-B3LYP exchange-correlation functional with 6-31G(∗) basis set on l-arginine p-nitrobenzoate monohydrate (LANB) molecule for the first time to optimize its geometry and study the spectroscopic, electronic structure, nonlinear optical properties. Vibrational modes were found in good agreement with experimental reports. The calculated UV spectra by B3LYP/6-31G(∗) and CAM-B3LYP/6-31G(∗) level of theory shows an electronic transition at ∼268 nm (4.63 eV) and 264 nm (4.70 eV) respectively. To explain the charge interaction taking place within the molecule highest occupied molecular orbital and lowest unoccupied molecular orbital were analyzed and their calculated energy gap was found to be 4.3eV with an oscillatory strength 0.3796 at B3LYP/6-31G(∗) level of theory. The dipole moment (μtot), average and anisotropy of polarizability (αtot, Δα) and static and total first hyperpolarizability (β0, βtot) values were calculated. The value of μtot and βtot are found to be 4.124D and 1.630 × 10(-30) esu and 4.127D and 1.133 × 10(-30) esu using B3LYP/6-31G(∗) and CAM-B3LYP/6-31G(∗) functional respectively. The value of βtot is >4 and >3 times higher than prototype urea molecule calculated at both level of theory, respectively. The molecular electrostatic potential (MEP), frontier molecular orbital's (FMOs), global reactivity descriptors and thermodynamic properties are also calculated and discussed. The properties of LANB calculated at B3LYP are in good correlation with experimental than the CAM-B3LYP level of theory. The obtained results show that LANB molecule can be treated as a good candidate for nonlinear optical devices.

Effect of donor strength of extended alkyl auxiliary groups on optoelectronic and charge transport properties of novel naphtha[2,1-b:6,5-b']difuran derivatives: simple yet effective strategy

The present study spotlights the designing of new derivatives of 2,7-bis (4-octylphenyl) naphtho [2,1-b:6,5-b'] difuran (C8-DPNDF) by substituting the alkyl groups (methyl, ethyl, propyl, butyl, pentyl, hexyl, and heptyl groups) at para position. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods are employed to optimize the molecular structures in ground and first excited states, respectively. Several electro-optical properties including hole/electron reorganization energies (λh/λe), electron affinities (EAs), ionization potentials (IPs), molecular electrostatic potentials (MEP), and frontier molecular orbitals (FMOs) have been evaluated. Furthermore their transfer integrals and intrinsic mobilities values have also been calculated. From this study, it is found that hole mobility of octyl containing derivative is raised to 4.69 cm(2) V(-1) s(-1). Moreover with attaching octyl group, hole transfer integral values have also been enhanced in newly designed derivatives. The balanced hole and electron reorganization energies, and improved transfer integrals lead to enhanced mobility in derivatives with octyl group, highlighting them as an efficient hole transfer material. Unlike the other electro-optical properties, the intrinsic hole mobility has increased because of transfer integral values of octyl containing derivative C8-DPNDF due to the dense and close crystal packing of C8-DPNDF. However, photostability of furan-based materials has not changed by increasing length of extended alkyl chain. Thus our present investigation highlights the importance of alkyl auxiliary groups that are often neglected/replaced with simple methyl group to save computation costs. Graphical Abstract The hole and electron reorganization energies of naphtho[2,1-b:6,5-b']difuran derivatives.

Experimental and density functional theory (DFT): a dual approach to study the various important properties of monohydrated l-proline cadmium chloride for nonlinear optical applications

In the current work we have applied the experimental and quantum chemical techniques to study the electro-optical and nonlinear optical properties of l-proline cadmium chloride monohydrate (LPCCM). Synthesis and good quality single crystals of LPCCM were grown (size=20mm×12mm×10mm). Crystal structure was confirmed by powder X-ray diffraction study. The calculated FT-IR and FT-Raman frequencies were analyzed. Detailed optical studies were carried out and various optical parameters are calculated. Using density functional theory, molecular geometry of LPCCM was optimized within framework of B3LYP/6-31G(∗). The calculated HOMO-LUMO energy gap of 5.484eV and transition energy of 5.565eV has been found in semi-quantitative agreement with experimental results. The value of dipole moment and first hyperpolarizability of LPCCM are found to be 2 and 6 times respectively, higher than that of urea. The obtained results reveal that the titled compound is a good candidate for nonlinear applications having an excellent transparency trade-off value.

Second-order nonlinear optical properties of dithienophenazine and TTF derivatives: A butterfly effect of dimalononitrile substitutions

Using density functional theory (DFT) methods, the nonlinear optical (NLO) properties have been calculated with strong donor-π-conjugation-acceptor configurations. The static first hyperpolarizability (β0) and dynamic (frequency dependent) electric field induced second harmonic generation (EFISHG) first hyperpolarizability (μβ) are calculated for all designed systems. Our DFT calculations show dithienophenazine merged TTF (2) holds larger β0 amplitudes (β0=21.04×10(3)a.u.) as compared to its corresponding compounds of TTF merged-difurophenazine (1), dicyclopentaphenazine (3) and dipyrrolophenazine (4) derivatives having β0 amplitudes of 16.25×10(3), 12.69×10(3), and 18.38×10(3)a.u., respectively. Furthermore, substitution of dimalononitrile [C(CN)2]2 groups at acceptor end of these compounds results in new derivatives 1a-4a, respectively. Interestingly, a butterfly effect on first hyperpolarizability of all systems 1a-4a has been spotted, which not only results in their robustly larger β0 amplitudes but also changes the increasing order of β0 amplitudes from systems 3<1<4<2 to 1a<2a<3a<4a at both PBE0/6-31G* and CAM-B3LYP/6-31+G* levels of theory. For example, the increase in β0 amplitudes of systems 1a, 2a, 3a and 4a are 3, 3, 5, and 19 times as compared with their corresponding non dimalononitrile derivatives at PBE0/6-31G* level of theory, respectively. Remarkably, unlike the static first hyperpolarizability, the dynamic EFISHG hyperpolarizability (μβω) has the largest value for system 4a with its amplitudes of 1378.59×10(-46) and 1349.40×10(-46)esu, at PBE0/6-31G* and CAM-B3LYP/6-31+G* levels of theory, respectively. TD-DFT calculations have been performed to trace the origin of first hyperpolarizability. It has been found that the lower transition energy and higher oscillator strengths cause robustly large amplitudes especially in systems 3a and 4a, which consequently stems in strong donor-π-conjugation-acceptor configuration of these systems. Thus the present results intrigue the butterfly effect of a two-step substitution on NLO properties of TTF merged dithienophenazine compounds that can be used as an efficient NLO material.

An investigation on the key features of a D–π–A type novel chalcone derivative for opto-electronic applications

The calculated UV-visible optical spectra at different levels of theory.

Combined experimental and computational insights into the key features of l-alanine l-alaninium picrate monohydrate: growth, structural, electronic and nonlinear optical properties

Comprising experimental and theoretical techniques we have highlighted the key features of LALAPM for electro-optical applications

How does the increment of hetero-cyclic conjugated moieties affect electro-optical and charge transport properties of novel naphtha-difuran derivatives? A computational approach

We have investigated computationally the effects of π-conjugation extension on naphtha[2,1-b:6,5-b'] difuran (DPNDF); where we increase the number of fused NDF (central core) and furan rings in the parent molecule. The molecular structures of all analogues have been optimized at the ground (S0) and first excited (S1) states using density functional theory (DFT) and time-dependent density functional theory (TD-DFT), respectively. Then highest occupied molecular orbitals (HOMOs), the lowest unoccupied molecular orbitals (LUMOs), photophysical properties, adiabatic/vertical electron affinities (EAa)/(EAv), adiabatic/vertical ionization potentials (IPa)/(IPv), and hole/electron reorganization energies λh/λe have been investigated. The effect of NDF and furan rings on structural and electro-optical properties has also been studied. Our calculated reorganization energies of 1a, 1b, and 2c reveal them, materials with balanced hole/electron charge transport, whereas 2a and 2b are good hole-transport materials. By increasing the number of furan rings; the photostability was augmented in 2a, 2b, and 2c.