Vibrational spectroscopic investigation and DFT computation of nonlinear optical crystal L-Glutaminium 4-methylbenzenesulfonate

Journal Pre-proof Vibrational spectroscopic investigation and DFT computation of nonlinear optical crystal L-Glutaminium 4-methylbenzenesulfonate P.V. Sreelaja, C. Ravikumar PII:

S0022-2860(19)31569-8

DOI:

https://doi.org/10.1016/j.molstruc.2019.127460

Reference:

MOLSTR 127460

To appear in:

Journal of Molecular Structure

Received Date: 5 September 2019 Revised Date:

11 November 2019

Accepted Date: 20 November 2019

Please cite this article as: P.V. Sreelaja, C. Ravikumar, Vibrational spectroscopic investigation and DFT computation of nonlinear optical crystal L-Glutaminium 4-methylbenzenesulfonate, Journal of Molecular Structure (2019), doi: https://doi.org/10.1016/j.molstruc.2019.127460. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier B.V.

CRediT author statement P. V. Sreelaja: Conceptualization, methodology, software, investigation, data curation, writingoriginal draft, visualization, C. Ravikumar: Validation, formal analysis, software, resources, writing-review and editing, supervision.

Graphical abstract

Vibrational spectroscopic investigation and DFT computation of nonlinear optical crystal L-Glutaminium 4-methylbenzenesulfonate P. V. Sreelaja, C. Ravikumar* Nanotechnology and Advanced Materials Research Centre, Department of Physics, CMS College, Kottayam - 686 001, Kerala, India.

Abstract A nonlinear organic crystal, L-Glutaminium 4-methylbenzenesulfonate was synthesized by slow evaporation crystal growth technique. Theoretical as well as experimental FT-IR, FT-Raman and UV-vis spectra were analyzed and the formation of crystal was confirmed using powder X-ray diffraction study. The existence of intramolecular donor-acceptor interactions through N-H…O hydrogen bonds were confirmed with vibrational spectroscopic and natural bond orbital methods. The photoluminescence spectrum was recorded and analyzed. Kurtz and Perry powder technique was employed to detect the second harmonic generation of the grown crystal. Moreover, molecular electrostatic potential and Mullikan charge distribution were studied for identifying the most reactive sites of the compound. Keywords: Density Functional Theory; SHG; Natural Bond Orbital; Raman; MEP.

*Corresponding Author: Dr. C. Ravikumar, Nanotechnology and Advanced Materials Research Centre, Department of Physics, CMS College, Kottayam – 686 001, Kerala, India. Telephone Number: +91 481 2566002 Fax Number: +91 481 2565002, E-mail: [email protected]. 1

1. Introduction Quantum chemical computations are reliable tools for unveiling the intrinsic properties of organic compounds in gas phase without the influence of environmental perturbation. Even though amino acids have zwitterionic dipolar structure, they exist neutral in gas phase and in solution. Glutamic acid is a non-essential α-amino acid utilized by living beings in the biosynthesis of protein as well as it works as a neurotransmitter [1]. L-Glutamic acid being a phase match able nonlinear optical (NLO) material having high transparency in the ultraviolet (UV) region [2] draws importance in device fabrication and applied research. Several semiorganic crystals developed out of L-glutamic acid and halogen compounds are identified as efficient second harmonic generators [2-7]. Organic NLO materials are preferred over inorganic materials, because their optical properties can be improved by fine-tuning its chemical synthesis process [8]. Organic crystals of high optical nonlinearity and synthetic flexibility obtained from modified molecular engineering can be utilized for device fabrication [9-11]. The assortment of organic counterparts for L-glutamic acid, to produce crystals with high nonlinear susceptibility and improved mechanical stability is of much importance. 4-Methylbenzenesulfonic acid has an electron donating methyl group and an electron withdrawing sulfonate group to enhance charge transfer interaction thereby making it a prime choice for producing NLO active crystalline materials. p-Toluene sulfonic acid forms strong hydrogen bonding complexes with bases like amines [12]. New nonlinear optical crystals of noncentrosymmetric structures formed on hydrogen bond interactions are reported [13-16]. In the present study, the structural correlation with NLO activity is explained by charge transfer interaction through intramolecular hydrogen bond formation. Density functional 2

theoretical (DFT) calculation included in Gaussian’ 09 [17] is used to elucidate the molecular structure, charge transfer interaction and intramolecular hydrogen bonding. This investigation had been complemented by natural bond orbital (NBO) [18] analysis for predicting charge transfer due to asymmetric electron distribution responsible for NLO activity through intramolecular contacts. Spectroscopic investigation using FT-IR and Raman spectra are utilized for finding correlation between molecular architecture and nonlinear optical response. The linear optical behavior of the crystal is studied by UV-Visible and photoluminescent spectral analysis. The global reactivity descriptors, highest occupied molecular orbital (HOMO) – lowest unoccupied molecular orbital (LUMO) energy gap and molecular electrostatic potential (MEP) surface of the molecule has been obtained to gain in-depth information about the relationships between molecular structure, nonlinear optical response and hyperpolarizability. 2. Materials and Methods 2.1 Sample preparation L-Glutaminium 4-methylbenzenesulfonate (LGM) crystals were synthesized in slow evaporation solution growth technique as described by Thayanithi et.al. [1]. L-Glutamic acid and p-toluene sulfonic acid monohydrate were taken in 1:1 ratio and dissolved in double distilled aqueous solvent by stirring the solution for about 4 hours. Colourless crystals of LGM were obtained within a month and the sample was repeatedly recrystallized before experimental analysis for obtaining clear crystals. 2.2 Spectroscopic measurements The experimental Fourier transform-infrared (FT-IR) spectrum of the title compound LGM was obtained in the range 4000 - 400 cm-1, with a spectral resolution of 1.0 cm-1 using compact

3

Spectrum One model spectrometer by Perkin Elmer. BRUKER RFS 27: Stand alone FT-Raman instrument was utilized for obtaining experimental spectrum in the range 4000 – 50 cm-1. Its instrumentation includes an Nd:YAG laser source of wavelength 1064 nm with 100 mW power and a Ge-diode as detector. The resolution of the experimental spectra is 2.0 cm-1. The UVvisible spectrum was recorded in the range 200 - 500 cm-1, using thermo scientific evolution 201 model UV-visible spectrophotometer, with double beam optics and dual silicon photodiode detector. Resolution of the spectrum is 1 nm. Photoluminescence spectral investigation was carried out using Horiba scientific fluoromax 4 spectrofluorometer which uses 150 W Xenon ozone free lamp for illuminating the sample with 0.5 nm accuracy. It consists of a calibrated photodiode reference detector and an R928P red sensitive photomultiplier tube detector. The former is used for modifying intensity and temporal fluctuations of the input and the latter is used to count the photons coming out from the sample. 2.3 Powder X-ray diffraction analysis The powdered sample of the grown crystal LGM was analyzed with Bruker D8 Advance powder X-ray diffractometer to record the diffraction pattern in the 2 theta range 4 - 70°. The analysis was done in continuous step mode with step size 0.0302° and scan time 7 minutes 28 seconds. The diffractometer was connected to a 40kV, 30 mA high voltage supply to generate Xray radiation. The instrumentation involves a Cu-Kα X-ray source containing 2.2 kW copper anode kept in a fine focus ceramic X-ray tube releasing X-rays of wavelength 1.5406 nm and LYNXEYE compound silicon strip detector for high speed data collection. The PXRD pattern recorded for LGM crystal is shown in Fig. 1. Crystalline nature of LGM is confirmed by well defined Bragg’s diffraction peaks. The unit cell parameters obtained from PXRD data are as

4

follows. a=5.35 Å, b=8.61 Å, c=28.11 Å, α=90.00°, β=94.67°, γ=90.00°. Cell volume V=1291.83 Å3. It also suggests that the compound crystallizes in monoclinic system with space group P21. All these parameter magnitudes are comparable with the data produced by Thayanithi et.al. from single crystal X-ray diffraction [1]. •

Position for Figure 1

2.3 Second harmonic generation analysis The second harmonic generation (SHG) of LGM was measured for the first time with Quanta Ray model Q switched high energy Nd:YAG laser by powder reflection technique [19]. The experimentally grown crystal was graded with a standard sieve to reduce the particle size (r) to 150
program package [17]. 3N-6 normal mode theoretical frequencies were assigned using vibrational energy distribution analysis program (VEDA 4), [20] to quantify the percentage contribution of different modes of vibration to each simulated frequency. After repeated optimization of the title compound during the potential energy distribution (PED), the group contributions greater than or equal to 10 % are taken for analysis. The simulated Raman spectra is plotted with computed Raman activities (Si) converted to relative Raman intensities (Ii) by means of equation (1) obtained from the basic theory of Raman scattering [21, 22]. The terms ν0 and νi in equation (1) represent the exciting frequency and vibrational wavenumber of ith mode respectively. A common scaling factor selected for all the peak intensities was included using the term f. Other terms in equation (1) such as k, h and c denote the universal constants.

f (ν o − ν i ) 4 S i Ii =   − hcν i ν i 1 − exp  kT 

  

(1)

The structural optimization is achieved by iteratively solving the self-consistent field equation. This optimized molecular geometry produced 3N-6 positive frequencies thus ensuring a minimum on the potential energy surface. The systematic errors of calculated vibrational wavenumbers produced by incomplete basis set, ignoring anharmonicity and electron correlation were corrected by a scaling factor 0.9613 [23-25]. The components of the hyperpolarizability tensor are given in Table S1 (Supporting information), which are calculated on the basis of finite field approach using B3LYP/6-31 G* method by assuming center of mass of the compound as origin of the Cartesian coordinate [26]. The components and magnitude of first hyperpolarizability are obtained from Eqs. (2) and (3)

6

respectively as

explained

by Thanthiriwatte and

Silva [27]. The calculated

first

hyperpolarizability of LGM is 9.83×10-29 esu which is 1.73 times that of KDP. βi= βiii + 1/3 Σ (βijj + βjij + βjji) , (i≠j)

(2)

β = [(βxxx + βxyy+ βxzz) 2 + (βyyy + βyzz+ βyxx) 2 + (βzzz + βzxx+ βzyy) 2] 1/2

(3)

4. Results and discussion 4.1 Optimized geometry Geometrical optimization of LGM structure was completed by DFT method with 6-31G* basis set. The optimized molecular structure of LGM labelled with atom numbering adopted for computation is shown in Fig. 2. The optimized structural parameters in the ground state and the single crystal XRD data [1] are given in Table 1. •

Position for Figure 2

•

Position for Table 1 The dihedral angles C6-C5-C4-C7=-178.64°, C2-C3-C4-C7=178.74° made by CH3 group

with the phenyl ring as well as that of SO3 group C3-C2-C1-S15=-177.96° and C5-C6-C1S15=178.03° are slightly distorted from its planarity about the phenyl ring due to the substituent effect. The increase in bond lengths of N20-H21, N20-H19, N20-H22, C25-O26, S15-O17, and S15-O18 is an indication for the existence of N-H…O hydrogen bonding. The truncated distance between O17…H22, O26…H21, O18…H19 also supports the formation of N-H…O bond. 4.2 NBO and NHO bond bending analysis The natural bond orbital (NBO) analysis is an effective tool for understanding the electron density transfer and hyperconjugative interaction between filled and unfilled molecular orbitals. 7

The present molecule has been analyzed with density functional theory in B3LYP level to explore the various second-order interactions between the electron donors in one subsystem to electron acceptors of another subsystem [18]. Generally, zwitterionic form of amino acids includes the NH3+ group which is a good donor and the carboxylate group, an excellent acceptor. The stabilization energy evaluated using equation (4) deduced from second order perturbation theory is a measure of donor-acceptor interaction. The parameters εj, εi denote diagonal elements and F (i, j) represents the off-diagonal Kohn-Sham matrix element. The term qi denotes occupancy of the donor orbital [28]. E(2) = ∆Eij = qi × [(F(i, j)2] ⁄ [εj-εi]

(4)

NBO analysis evidently describes the formation of hydrogen bonding interaction between lone pair electron of O18 atom LP(O18) and antibonding orbital σ∗(N20-H19) from unit one to unit two. The stabilization energy E(2) related to hyperconjugative interactions of LP1(O18) and LP3(O18) with σ∗(N20-H19) are obtained as 3.02, 15.88 kJ/mol respectively (Table 2). This is owing to the growth of electron density (ED) in the N20-H19 bond gathered not only from LP(O18) but also from the total molecule, leading to the elongation of bond length (Table 1) from its experimental value. These charge transfer interactions are responsible for the nonlinear optical activity of the compound [29, 30]. The strong hyperconjugative interaction energy between bonding and antibonding π orbitals of the phenyl ring is a clear suggestion for charge delocalization, resulting in the stabilization of the phenyl ring system.

The quantitative

contribution of s and p-character, occupancy of natural bonds and lone pairs, are calculated and are given in Table 3. •

Position for Table 2

•

Position for Table 3 8

The conjugation of lone pair electrons of n1(O18) with σ∗(N20-H19) resulting in a significant decrease in the ED of non-Lewis orbital, is a quantitative evidence for the existence of N20H19…O18 bond. The elongation of N20-H19 bond length is due to the increased p-character of σ∗(N20-H19) ie. 2.79. The E(2) values of donor acceptor interaction among LP(O26) with σ∗(C25O27) enumerated in Table 2 the strength of intramolecular hydrogen bonding. NHO directionality and bond bending display the angular deviations (DEV) between the bonding hybrids and the direct line-of-centre of nuclei. Sigma-bonded NHOs will have the DEV values are ∼0° while perpendicular pi-bond normally exhibits DEV = ∼90° [31]. Most significant bond bending represented in Table S2 (Supporting information), shows all ring NHOs exhibit pure pi-character with DEV 89.9° - 90.0°. DEV values of sigma bonded S-O atoms enumerate the degree of deviation of O atoms from the nuclear centres. Among the NHOs of oxygen atoms in SO3 group O17 exhibits least deviation because of lying in the strong charge transfer path developed by N-H…O hydrogen bond formation. The NHOs of hydrogen in σ(N-H) are more aligned and found within the threshold printing limit of 1.0° which supports the probable H-bond formation. 4.3 Vibrational spectral analysis The fundamental modes of vibrations for various functional groups were identified and analyzed with the aid of experimental FT-IR and FT-Raman spectra. The experimental peaks observed in IR and Raman spectra, their relative intensities and corresponding calculated wavenumbers are tabulated in Table 4. Experimental spectra of both FT-IR and FT-Raman obtained in the solid phase along with simulated spectra in gas phase are presented in Fig. 3 and 4 separately for visual comparison. 9

CH3 group vibrations CH3 group exhibits strong absorption peaks for stretching vibrations in IR and Raman spectra. Antisymmetric and symmetric stretching give rise to bands near 2972 cm-1 and 2882 cm-1 respectively [32]. The strong peak at 2980 cm-1 and the shoulder at 2873 cm-1 in the Raman spectra is due to the asymmetric and symmetric stretching vibrations respectively. CH3 asymmetric deformation mode is found in the region 1470 - 1430 cm-1 however symmetric deformation modes are expected near 1380 cm-1 [32]. The medium intensity peaks identified in IR at 1443 and 1377 cm-1 are attributed to asymmetric and symmetric bending of CH3 group. Raman equivalent of symmetric bending is identified at 1376 cm-1 as a medium peak. Benzene ring vibrations The benzene ring vibrations are represented according to Wilson’s numbering system [33] in Table 4. C-H stretching vibration of para-substituted benzene falls in the region, 3080 3010 cm-1 [33]. The strong absorption bands at 3072 cm-1 (mode 20a) and 3007 cm-1 (mode 20b) in IR spectra is due to C-H ring stretching. The Raman peaks are observed as a very strong peak at 3063 (mode 2) and a shoulder band identified at 3027 cm-1 (mode 7b). The C-C ring stretching modes are 8a, 8b, 14, 19a and 19b. IR band at 1622 cm-1 is attributed to 8a while weak band in Raman at 1575 cm-1 corresponds to 8b. Mode 14 is active in both IR and Raman spectra at 1298 and 1306 cm-1 which is an indication of charge transfer interaction taking place within the molecule which in turn results in a large nonlinear optical activity [34, 35]. The CH inplane bending modes 3, 9a, 18a, 18b are denoted in Table 4. Out of plane CH ring bending vibrations 10a, 10b, 11 and 17a are identified well within its normal range of 800 980 cm-1 [33]. Mode 10a is found strongly active only in Raman spectrum at 801 cm-1 whereas 10

10b is found at 903 cm-1 in IR spectra. Mode 11 is simultaneously active at 815 cm-1 in both spectra while mode 17a is identified at 921 cm-1 in IR and 926 cm-1 in Raman spectra. Enlarged portion of the spectrum containing these peaks in IR and Raman spectra are shown in Figure S2, S3 (Supporting information) respectively. The out of plane skeletal vibrations (4, 16a, 16b) and radial skeletal vibrations (1, 6a, 6b, 12) of the substituted benzene ring is denoted in Table 4. The simultaneous activation of ring normal modes 14, 11 and 17a fulfills the requirement of attaining large first order hyperpolarizability through charge transfer interaction between donor and acceptor group. SO3- group vibrations Bands due to asymmetric stretching and symmetric stretching of sulphonic acid salts absorb in the 1250 - 1140 cm-1 and 1070 - 1030 cm-1 respectively [36]. The medium bands at 1187 cm-1 and 1080 cm-1 in Raman spectra is due to the contribution of SO3 asymmetric stretching as well as symmetric stretching respectively. SO3 symmetric deformation is identified at 449 cm-1 in Raman spectrum. The shoulder band in IR at 501 cm-1 and very weak band in Raman at 496 cm-1 corresponds to SO3 rocking vibration. SO3 wagging mode at 368 cm-1 in Raman is coupled with ring stretching vibration. The C-S stretching mode expected in the region 750-500 cm-1 [36] is identified at 630 cm-1 in IR and at 633 cm-1 in the Raman spectra which is coupled with asymmetric ring deformation vibration. NH3+ group vibrations The position of stretching wavenumbers of NH3+ group is sensitive to the degree of hydrogen bonding. Due to protonation, a broad peak between 3300 - 3100 cm-1 is expected for asymmetric stretching, whereas symmetric stretching is anticipated between 3100 - 2800 cm-1 11

[36, 37]. The very strong broad peak identified at 3206 cm-1 in IR has been assigned for asymmetric stretching while absorption peaks at 3042 cm-1 and 3045 cm-1 corresponds to symmetric stretching in IR and Raman respectively. A weak band at 1696 cm-1 and a medium intensity peak at 1601 cm-1 in Raman spectra denotes blueshifted asymmetric and symmetric NH3+ deformation modes for which the normal range is 1625 - 1580 cm-1 and 1550 - 1500 cm-1 respectively [32]. Blue shifting of bending mode supports the participation of H19 and H20 atoms in N20-H19…O18 and N20-H22…O17 hydrogen bonds. The improved first order polarizability and efficient second harmonic generation of LGM is due to the π-electron cloud movement from donor to acceptor through these bonds [38]. Simultaneous activation of symmetric stretching in IR and Raman spectra supports CT interaction. The bands at 1126 cm-1 in IR and 1129 cm-1 in Raman is due to the rocking vibration of NH3+ group. Carboxylic acid group vibrations The prominent bands associated with the carboxylic group are stretching of OH, C=O, CO as well as COH bending vibrations. Among these, OH stretching of free carboxylic acid is expected in the range 3550 - 3500 cm-1 [36]. The strong broad band at 3422 cm-1 in IR spectrum is attributed to O-H stretching vibration. The very strong band in IR at 1726 cm-1 and a weak band in Raman at 1746 cm-1 is assigned for C=O stretching vibrations, for which the normal range is between 1740-1700 cm-1 [36]. The in plane bending vibration of COH comes within 1440-1200 cm-1 [32]. The peak at 1169 and 1165 cm-1 respectively in IR as well as Raman spectra ascribed for COH in plane bending vibration. An enlarged image of this spectral region in the FT-IR and FT-Raman spectra are represented in Fig. S4, S3 (Supporting information) respectively. The down shifting of stretching and bending vibration points the possible inter molecular hydrogen bond formation that result in increased stabilization which is reflected in the 12

lengthening of C25-O26, C25-O27 as well as O27-H28 [32, 39]. The shoulder peak at 790 cm-1 in IR and weak peaks seen at 675 cm-1 as well as 482 cm-1 in Raman corresponds to deformation modes of carboxylic acid group. CH2 group vibrations The characteristic range of asymmetric, symmetric and scissoring vibrations of acyclic CH2 group are 2936 - 2916, 2863 - 2843, 1420 - 1412 cm-1 respectively [32, 40]. The strong peak at 2943 cm-1 in both IR and Raman is attributed to CH2 asymmetric stretching while a shoulder band observed at 2885 cm-1 in Raman spectrum corresponds to CH2 symmetric stretching. The scissoring vibrations are assigned to the medium intensity peak at 1419 cm-1 in the IR spectrum and weak peak at 1422 cm-1 in the Raman spectrum. The rocking, wagging and twisting modes of this group arising within the range 1422 - 719 cm-1 [32] are tabulated in Table 4. The very strong band at 2922 cm-1 in the Raman spectra of LGM is due to the stretching vibration of C23H24. C-C stretching found to be active in Raman at 859 cm-1, and C-N stretching identified at 844 cm-1 in IR are enlarged and given out in Fig. S3, S2 (Supporting information). Hydrogen bonding A hydrogen bond is formed by the attraction of hydrogen atom towards a proton acceptor (Y) in the form X-H…Y. As the electronegativity of X and Y increases, the attraction also increases [41]. Hydrogen bonds not only create and stabilize crystal structures but also contribute considerably for the improvement of second-order susceptibility of crystals. The extent of charge transfer interaction confirmed by the simultaneous activation of some of the ring normal modes and symmetric stretching of NH3+ is anticipated to provide stronger hydrogen bonding interaction between the donor acceptor moieties. In LGM crystal, the glutaminium moiety is 13

connected with the sulfonate oxygen through N20-H22…O17 and N20-H19…O18. A schematic representation of hydrogen bonding is presented in Fig. S5 (Supporting information). The distance between H22…O17 and H19…O18 are 1.84 and 1.97 Å. The bond lengths of S15-O17, S15O18 involved in hydrogen bonding are elongated compared to its corresponding XRD data as well as the free S15-O16 bond. •

Position for Table 4

•

Position for Figure 3

•

Position for Figure 4

4.4 Absorption spectra and solvent effects The theoretical investigation of ultraviolet visible spectra of the title compound was carried out using density functional theory utilizing the basis set 6-311G(d,p). The experimental UV-vis spectrum in aqueous solvent and simulated spectra in gas phase as well as in water solvent is depicted in Fig. 5. •

Position for Table 5

•

Position for Figure 5

The experimental spectrum exhibits a strong absorption at a wavelength of 221 nm due to the π → π* transition in the substituted benzene ring. The frontier molecular orbitals which take part in this transition are the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) portrayed in Fig. 6a and 6b respectively. The HOMO is localized over sulphonate group while LUMO is spread over the glutamic acid moiety. So, the presence of an electron donating group and an electron accepting group favors the possibility of charge 14

transfer interaction within the molecule. The energy difference between the HOMO and LUMO calculated in the gas phase is 4.25 eV. Additionally, the energy values of frontier molecular orbitals are utilized to calculate the global chemical reactivity descriptors which quantitatively represent structure - activity, structure - toxicity as well as structure - property relationships. According to Koopman’s theorem HOMO and LUMO energies are directly related to ionization potential (I) and electron affinity (H) respectively through the following equations (5) and (6) [42]. I = -EHOMO

(5)

H = -ELUMO

(6)

Global reactivity descriptors such as hardness (η), electronegativity (χ), chemical potential (µ), electrophilicity index (ω) and softness (S) calculated in gas phase at B3LYP/6-311 G(d,p) level are tabulated in Table 6 using the following equations [43-46]. η = (I - H) / 2

(7)

χ = (I + H) / 2

(8)

µ = - (I + H) / 2

(9)

ω = µ 2/2η

(10)

S = 1/(η)

(11)

The magnitude of η value describes the stability of the molecule and it denotes the resistance to polarization owing to external perturbation on the molecular system. Chemical potential is the negative value of χ, which indicates the power to attract electrons. Electron affinity replicates the

15

ability of accepting only one electron from the surrounding, whereas ω measures the energy drop of a ligand due to maximum electron flow from donor to acceptor [43]. •

Position for Figure 6

•

Position for Table 6

4.5 Photoluminescence spectra The photoluminescence (PL) spectrum of powdered LGM taken at room temperature with an excitation wavelength of 221 nm is depicted in Fig. 7. The peaks observed at 292 nm and 378 nm reveals that the grown crystal exhibits strong UV emission. These peaks arise due to the direct recombination of charge carriers. •

Position for Figure 7

4.6 Mulliken atomic charge and molecular electrostatic potential (MEP) Analysis Dipole moment, polarizability and electronic structure are influenced by the atomic charge distribution which in turn affects the vibrational spectra of a molecular system [47-49]. The Mulliken atomic charges obtained at B3LYP/6-31 G* level using Gaussian ’09 is depicted in Fig. 8. Out of all the hydrogen atoms present in LGM, H19 and H22, which are involved in hydrogen bonding interaction, possess the highest positive atomic charges 0.410 e and 0.420 e respectively. High positive electrostatic potential makes these sites suitable for electrophilic attraction. S15 and N20 atoms attached to the electron withdrawing O and electron donating H atoms exhibits the highest positive charge and negative charge respectively in order to pull out the partial charges from the compound. Additionally, O17, O18, O26 hold high negative charges making them favorable sites for nucleophilic activity. So extensive charge delocalization is suggested between O22…H17 as well as O21…H26 16

•

Position for Figure 8 MEP mapping allows a three-dimensional visualization of charge distribution through

color grading. It is an important tool to analyze the connection between structure and activity of molecules [50-52]. Electrostatic potentials of each atom in a molecular system are categorized by red, orange, green, blue in the descending order of negative potential. MEP surface analysis allows recognizing the reactive sites for electrophilic as well as nucleophilic attack in hydrogen bonded interactions. Highest negatively charged region from where the proton experiences strongest attraction is denoted by red color indicating a preferred location for electrophilic attack [53]. The MEP surface plotted by mapping the electrostatic potential onto the isosurface range of -0.176 to +0.002 a. u. showing the relative polarity of LGM molecule obtained at B3LYP/6-31 G* level is given in Fig. 9(a). The MEP map suggests electron density is mainly concentrated over lone pair of electronegative oxygen atoms making it the most preferable site for electrophilic attack indicated in red color. Fig. 9(b) represents the contour map, which gives qualitative depiction of polarity of LGM molecule. The spatial distribution of contour lines of LGM suggests that yellow lines sandwiched inside the substituted benzene ring and near the C-C skeleton of glutamic acid moiety are dispersed away compared to the red lines demonstrating strong electrostatic field around oxygen atom since high density of MEP contour lines represent stronger electrostatic fields than the regions with fewer MEP contour lines [54]. Fig. 9(a) and 9(b) differentiates negative and positive regions of the molecule thus giving a pictorial representation of regions from where the compound can have intra molecular interactions and confirms the existence of N-H…O bond formation. •

Position for Figure 9

17

Conclusion A comprehensive vibrational spectral assignment has been detailed based on the experimental and simulated FT-IR and FT-Raman spectroscopic techniques. Red shifting of OH stretching and COH bending vibrational frequency suggests the formation of inter molecular hydrogen bonding. Blue shifting of NH3+ bending vibration supports the participation of H19 and H20 atoms in N20-H19…O18 and N20-H22…O17 intramolecular hydrogen bonds. The simultaneous appearance of modes 14, 11 and 17a are an indication of charge transfer interaction. The electronic structure properties of LGM including the energy contribution to electron delocalization were quantitatively assessed and the intramolecular charge transfer interactions through N-H…O hydrogen bonds capable of inducing enhanced nonlinear response for the molecule have been explored using NBO method. Global reactivity indices were calculated using HOMO and LUMO energy values. MEP surface analysis and contour mapping methods were utilized for picturizing the most electrophilic and nucleophilic sites within the molecule from where intramolecular bond forms. High transparency to the visible region exhibited in the electronic spectra supports the utilization of the title compound for NLO applications.

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[16] V.

Thayanithi,

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Praveen

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Mater.

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(2019),

https://doi.org/10.1088/2053-1591/aafd43. [17] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T .Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J. A. Montgomery Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, O. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski, D. J. Fox; Gaussian 09, Revision A.02; Gaussian, Inc. Wallingford CT, (2009). [18] E. D. Glendening, A. E. Reed, J. E. Carpenter, F. Weinhold; NBO Version 3.1, TCI, University of Wisconsin, Madison, (1998). [19] S. K. Kurtz, T. T. Perry; J. Appl. Phys.; 39 (1968) 3798-3813. [20] M. H. Jamroz; Vibrational energy distribution analysis VEDA 4, Warsaw, (2004). [21] G. Keresztury, S. Holly, J. Varga, G. Besenyei, A.Y. Wang, J.R. Durig; Spectrochim. Acta A: Mol. and Biomol. Spect.; 49 (1993) 2007-2026. [22] G. Keresztury, J. M. Chalmers, P. R. Griffith; Raman Spectroscopy: Theory in Handbook of Vibrational Spectroscopy; vol.1, John Wiley & Sons Ltd., New York, (2002).

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[23] P. Pulay, G. Fogarasi, G. Pongor, J. E. Boggs, A. Vargha; J. Am. Chem. Soc.; 105 (1983) 7037-2560. [24] G. Rauhut, P. Pulay; J. Phys. Chem.; 99 (1995) 3093-3100. [25] J. B. Foresman, A. Frisch; Exploring Chemistry with Electronic Structure Methods; second ed., Gaussian, Inc., Pittsburgh, PA, (1996). [26] M. Adant, M. Dupuis, J. L. Bredas; Int. J. Quan. Chem.; 56 (1995) 497-507. [27] K. S. Thanthiriwatte, K.M. Nalin de Silva; J. Mol. Struct.; 617 (2002) 169-175. [28] A. E. Reed, L. A. Curtiss, F. Weinhold; Chem. Rev.; 88 (1988) 899-926. [29] C. Ravikumar, I. H. Joe, D. Sajan; Chem. Phys.; 369 (2010) 1-7. [30] C. Ravikumar, I. H. Joe; Phys. Chem. Chem. Phys.; 12 (2010) 9452-9460. [31] F. Weinhold, E. D. Glendening; NBO 6.0 Program Manual Natural Bond Orbital Analysis Programs; (2013). [32] D. Lin-Vein, N. B. Colthup, W. G. Fateley, J. G. Grasselli; The handbook of Infrared and Raman Characteristic frequencies of Organic molecules; Academic Press, New York, (1991). [33] G. Varsanyi; Vibrational Spectra of Benzene Derivatives; Academic Press, New York, (1969). [34] P. V. Sreelaja, C. Ravikumar; Optics and Spect.; 125 (2018) 609-618. [35] C. Ravikumar, I. H. Joe, V. S. Jayakumar; Chem. Phys. Lett.; 460 (2008) 552-558. [36] G. Socrates; Infrared Characteristic Group Frequencies; John Wiley and Sons, (1980). [37] L. J. Bellamy; The Infrared Spectra of Complex Molecules; Chapman and Hall, London, (1980).

21

[38] H. Ratajczak, S. Debrus, M. May, J. Barycki, Baran; J. Bull. Pol. Acad. Sci.; 48 (2000) 189193. [39] C. James, C. Ravikumar, T. Sundius, V. Krishnakumar, R. Kesavamoorthy, V. S. Jayakumar, I. H. Joe; Vib. Spectr.; 47 (2008) 10-20. [40] M. Amalanathan, I. H. Joe, S. S. Prabhu; J. Phys. Chem. A; 114 (2010) 13055-13064. [41] C. Sandorfy; Topics in current chem.; 120 (1984) 41-84. [42] T. Koopmans; Physica; 1 (1934) 104-113. [43] R. G. Parr, R. A. Donnelly, M. Levy, W. E. Palke; J. Chem. Phys.; 68 (1978) 3801-3807. [44] R. G. Parr, L. Szentpaly, S. Liu; J. Am. Chem. Soc.; 121 (1999) 1922-1924. [45] R. G. Pearson; J. Am. Chem. Soc.; 85 (1963) 3533-3539. [46] R. G. Parr, R. G. Pearson; J. Am. Chem. Soc.; 105 (1983) 7512-7516. [47] K. Jug, Z. B. Maksic; The Meaning and Distribution of Atomic Charges in Molecules, Theoretical Model of Chemical Bonding; Springer, Berlin, Heidelberg (1991) 235-288. [48] S. Fliszar; Charge distributions and chemical effects; Springer-Verlag, New York, 1983. [49] P. E. Smith, B. M. Pettitt; J. Am. Chem Soc.; 113 (1991) 6029-6037. [50] J. S. Murray, K. Sen; Molecular Electrostatic Potentials; Elsevier, Amsterdam, (1996). [51] E. Scrocco, J. Tomasi, P. Lowdin (Ed.), Advances in Quantum Chemistry; Academic Press, New York, (1978). [52] J. Sponer, P. Hobza; Int. J. Quantum Chem.; 57 (1996) 959-970. [53] P. V. Sreelaja, C. Ravikumar; J. Mol. Struct.; 1186 (2019) 91-101. [54] M. F. Khan, R. B. Rashid, M. Al-Faruk, M. A. Rashid; World J. pharmacy and pharmaceutical Sci.; 4 (2015) 1895-1911.

22

List of Tables Table 1. Optimized geometrical parameters of LGM by B3LYP/6-31G* in comparison with XRD data. Table 2. Second-order perturbation theory analysis of Fock matrix in NBO basis Table 3. Natural bond orbital output showing the formation of Lewis and non-Lewis orbitals by the valence hybrids corresponding to the intramolecular N-H…O hydrogen bonds of LGM. Table 4. Vibrational assignment of LGM by normal mode analysis based on scaled quantum mechanical force field calculations Table 5. Calculated absorptions, energy and oscillator strength of LGM using DFT method at B3LYP/6-311G(d,p) level Table 6. Calculated HOMO-LUMO energy and global reactivity coefficients of LGM crystal

23

Figure captions Fig. 1 Powder X-ray diffraction pattern of LGM Fig. 2 Optimized structure of LGM calculated at B3LYP/6-31G*

Fig. 3 (a). The FT-IR spectrum of LGM molecule in the wavenumber range 4000-400 cm-1 (b). The simulated infrared spectrum of LGM molecule computed at B3LYP/6-31G* basis set. Fig. 4 (a). The FT-Raman spectrum of LGM molecule in the wavenumber range 4000-50 cm-1. (b). The simulated Raman spectrum of LGM molecule computed at B3LYP/6-31G* basis set. Fig. 5 (a) Experimental UV-Vis spectrum of LGM molecule in water solvent (b) Simulated UV-vis spectrum in water for LGM molecule calculated with the Polarizable Continuum method using TD CAM B3LYP/6-311G(d,p) functional. (c) Simulated UV-vis spectrum of LGM molecule in the gas phase. Fig. 6 (a). HOMO plot of LGM at B3LYP/6-31G* (b). LUMO plot of LGM at B3LYP/6-31G* Fig. 7 Photoluminescence spectrum of LGM molecule. Fig. 8 Mulliken charge distribution chart of LGM molecule Fig. 9 (a). Molecular electrostatic potential map of LGM molecule calculated at B3LYP/6-31G* (b). MEP contour plot of LGM molecule.

24

Table 1. Optimized geometrical parameters of LGM by B3LYP/6-31G* in comparison with XRD data Bond length [Å] Parameter Cal Expa C1-C2 1.40 1.38 C2-C3 1.39 1.39 C3-C4 1.40 1.37 C4-C5 1.40 1.38 C5-C6 1.40 1.40 C4-C7 1.51 1.51 C7-H8 1.10 0.96 C7-H9 1.10 0.96 C7-H10 1.10 0.96 C2-H11 1.09 0.93 C3-H12 1.09 0.93 C5-H13 1.09 0.93 C6-H14 1.09 0.93 C1-S15 1.81 1.77 S15-O16 1.48 1.44 S15-O17 1.50 1.45 S15-O18 1.50 1.46

Bond angle [°] Parameter Cal C1-C2-C3 119.92 C2-C3-C4 121.12 C3-C4-C5 118.14 C4-C5-C6 121.14 C5-C4-C7 121.07 C4-C7-H8 111.57 C4-C7-H9 111.5 C4-C7-H10 111.45 C1-C2-H11 119.08 C2-C3-H12 119.51 C4-C5-H13 119.38 C1-C6-H14 119.02 C2-C1-S15 119.62 C1-S15-O16 105.31 C1-S15-O17 104.62 C1-S15-O18 104.69 … O18 H19-N20 136.98

Exp 119.72 121.46 118.25 121.73 121.90 109.45 109.41 109.54 120.14 119.30 119.10 120.74 119.43 106.28 106.18 106.29 149.64

O18…H19

1.97

2.12

H19-N20-H21

111.11

100.03

H19-N20

1.03

0.86

H19-N20-H22

101.75

113.99

N20-H21 1.05 0.86 N20-H22 1.04 0.86 N20-C23 1.52 1.49 C23-H24 1.09 0.98 C23-C25 1.54 1.52 C25-O26 1.29 1.20 C25-O27 1.44 1.31 O27-H28 0.97 0.82 C23-C29 1.53 1.53 C29-H30 1.10 0.97 C29-H31 1.10 0.97 C29-C32 1.53 1.52 C32-H33 1.11 0.97 C32-H34 1.10 0.97 C32-C35 1.50 1.50 C35-O36 1.21 1.22 C35-O37 1.37 1.29 O37-H38 0.98 0.82 … O17 H22 1.84 2.00 … O26 H21 1.82 2.50 a Taken from Ref [1]

H19-N20-C23 C29-C32-C35 N20-C23-H24 N20-C23-C25 C23-C25-O26 C23-C25-O27 C25-O27-H28 N20-C23-C29 C23-C29-H30 C23-C29-H31 C23-C29-C32 C29-C32-H33 C29-C32-H34 C32-C35-O36 C32-C35-O37 C35-O37-H38 S15-O18…H19 O27-C25-O26 O17-S15-O18 H22-N20-H19

113.73 111.46 114.09 113.67 108.2 109.80 104.63 107.01 114.74 121.02 110.39 113.87 101.43 109.43 108.00 110.57 110.63 109.40 108.54 109.29 110.05 112.45 106.45 108.81 112.21 108.87 127.22 123.68 111.81 113.61 104.66 109.47 110.77 130.35 117.17 125.09 111.68 113.12 101.75 113.99

a

Dihedral angle [°] Parameter Cal C1-C2-C3-C4 -0.08 C2-C3-C4-C5 -0.55 C3-C4-C5-C6 0.64 C6-C5-C4-C7 -178.64 C3-C4-C7-H8 39.18 C5-C4-C7-H9 98.89 C3-C4-C7-H10 159.84 C6-C1-C2-H11 -178.12 C1-C2-C3-H12 -179.63 C3-C4-C5-H13 -179.02 H13-C5-C6-H14 0.84 H11-C2-C1-S15 3.31 C6-C1-S15-O16 145.61 C2-C1-S15-O 17 84.68 C2-C1-S15-O18 -157.73 C1-S15-O18…H19 -125.68 S15-O18…H19-N20 10.58 … O18 H19-N20120.63 H21 O18…H19-N20-1.27 H22 O18…H19-N20-C23 -127.43 H21-N20-C23-H24 144.01 H22-N20-C23-C25 147.79 N20-C23-C25-O26 -30.68 H24-C23-C25-O27 -12.71 C23-C25-O27-H28 -145.3 H19-N20-C23-C29 146.07 N20-C23-C29-H30 -58.23 N20-C23-C29-H31 59.80 N20-C23-C29-C32 178.66 C23-C29-C32-H33 -49.93 C23-C29-C32-H34 65.67 C23-C29-C32-C35 -169.69 C29-C32-C35-O36 22.60 C29-C32-C35-O37 -159.64 C32-C35-O37-H38 -177.20 C5-C6-C1-S15 178.03 C2-C3-C4-C7 178.74 C3-C2-C1-S15 -177.96

Expa 0.29 -0.92 1.53 -178.14 -2.62 -122.61 117.40 -179.72 -1.26 1.88 -1.56 0.81 -161.71 137.96 -41.79 134.57 77.58 -113.39 140.20 9.34 164.79 161.48 -47.38 15.00 -179.33 172.90 68.26 -49.80 58.59 -68.24 48.90 170.31 11.75 -169.53 -171.14 179.76 178.77 -179.19

Table 2. Second-order perturbation theory analysis of Fock matrix in NBO basis Donor (i) π(C1–C2)

ED(j) [e] 0.16771 0.15358

E(2)a [kJ/mol] 34.48 44.14

E(j) − E(i)b [arb. units] 0.31 0.29

F(I, j)c [arb. units] 0.064 0.070

π∗(C1–C2) π∗(C5–C6) π∗(C1–C2) π∗(C3–C4) σ∗(S15-O17) σ∗(S15-O18)

0.16818 0.18828

41.92 41.33

0.30 0.29

0.070 0.068

0.16818 0.16771 0.09335 0.09481

36.75 47.84 32.17 33.73

0.30 0.29 0.57 0.57

0.065 0.075 0.084 0.086

ED(i) [e]

Acceptor (j)

0.84311

π∗(C3–C4) π∗(C5–C6)

π(C3-C4)

0.83910

π(C5–C6)

0.84613

n2(O16)

0.91799

From unit 1 to unit 2 n1(O18)

0.98927

σ∗(N20-H19)

0.02402

3.02

1.17

0.037

n3(O18)

0.90540

σ∗(N20-H19)

0.02402

15.88

0.70

0.068

σ∗(S15-O18)

0.09481

σ∗(H19-N20)

0.02402

3.07

0.11

0.032

σ∗(S15-O18) σ∗(C1-S15)

0.09481 0.11558

0.21 0.25

1.08 0.95

0.010 0.010

σ∗(N20–H21) σ∗(C25–O27) σ∗(C23–C25)

0.00933 0.03784 0.03587

1.09 54.39 41.03

0.61 0.68 0.57

0.016 0.120 0.096

From unit 2 to unit 1 σ(H19-N20)

0.99506

Within unit 2 n2(O26)

0.92467

Table 3. NBO results showing the formation of Lewis and Non-Lewis orbitals by the valence hybrids corresponding to the intramolecular N-H…O hydrogen bonds of LGM BOND (AB)

ED [e]

Energy [kJ/mol]

EDA [%]

EDB [%]

σ∗(S15-O16)

0.08985

1227.564

67.63

32.37

σ∗(S15-O17)

0.09335

1225.640

68.04

31.96

σ∗(S15-O18)

0.09481

1222.182

68.16

31.84

LP1(O18) LP1(O26)

0.98927 0.98871

-

-

σ∗(H19-N20)

0.02402

-1537.224 -1352.312 1498.12

76.21

23.79

σ∗(N20-H21)

0.00933

1360.788

26.99

73.01

σ∗(N20-H22)

0.00508

1343.914

27.75

72.25

NBO

S [%]

P [%]

0.8224(sp2.79)S -0.5690 (sp2.78)O 0.8249 (sp2.83)S -0.5653(sp2.75)O 0.8256(sp2.84)S -0.5589(sp2.49)O sp0.38 sp0.65 0.8730(s)H -0.4878(sp2.79)N 0.5195(sp3.40)N -0.854(s)H 0.5268 (sp3.52)N -0.8500(s)H

25.91 26.36 25.63 26.55 25.54 26.13 72.23 60.45 100 26.35 22.72 100 22.12 100

72.34 73.23 72.54 73.04 72.59 73.47 27.74 39.52 73.60 77.23 77.82 -

Table 4. Vibrational assignment of LGM by normal mode analysis based on scaled quantum mechanical force field calculations νcal [cm-1]

νIR [cm-1]

νRaman [cm-1]

IR inta

Raman intb

3545 3542 3222 3098 3095 3093 3044 3041 2995 2992 2980 2966 2963 2934 2911 2860 2842 1751 1639

3422 vs 3206 vs 3072 s 3042 s 3007 s 2943 s 1726 vs -

3063 vs 3045 m 3027 sh 2980 s 2943 s 2922 vs 2885 sh 2873 sh 2737 w 1746 w 1696 w

5.75 39.53 441.99 15.06 5.86 776.99 32.1 39.48 30.88 21.68 4.48 9.87 31.26 24.5 55.84 242.52 344.59 322.26 360.11

1.54 0.19 2.37 0.87 0.70 3.27 0.78 0.82 0.3 0.52 0.34 0.83 0.83 0.63 2.06 1.68 27.86 60.44 1.92

Force constant s 8.5281 8.5179 7.1283 6.6798 6.6671 6.588 6.4311 6.4169 6.2532 6.288 6.1957 6.1093 6.1384 5.8222 5.6315 5.5681 5.5131 17.2318 1.8069

1596

1622 m

-

0.86

2.58

9.1006

1590

-

1601 m

29.5

0.18

1.6893

1567

-

1575 w

1.68

0.19

9.3567

1492

-

-

126.26 3.38

2.3063

1485 1465 1464 1459 1431

1507 m 1443 sh 1419 m

1494 w 1455 m 1422 w

26.6 8.53 16.79 4.26 21.14

3.2989 1.4936 1.521 1.4229 1.428

1397

-

-

1387 1384

1377 m

1376 m

1372

-

-

1336 1319

-

1297

1298 sh

1347 w 1326 w 1306 vw

0.15 0.74 0.14 1.03 5.8

201.29 25.55 5.67 1.59

2.4065

0.05 2.12

3.2247 1.5293

179.94 27.2

2.2927

53.84 8.59

0.13 9.58

1.6026 1.5961

3.06

0.97

3.8025

Assignments with PED [%]c νO27-H28 (99) νO37-H38 (99) νasNH3+ (99) 20a νRCH (95) 2 νRCH (94) νssNH3+ (93) 7b νRCH (93) 20b νRCH (93) νasCH2II (86) νasCH3 (91) νasCH2I (86) νC23H24 (87) νCH3 (92) νssCH2I (86) νssCH3ss (94) νNH3+ (86) νC32-H33 (80) νC35=O36 (82) NH3+opb (76) 8a νRCC (58), δRCH (18), δRCC (10) NH3+ipb (65), τN20H22…O17 (24) 8b νRCC (72), δRCH (11) τN20H22…O17 (33), νC25=O26 (22), NH3+ipb (12) δRCH (54), δRCC (15) δCH3 (67), τRCH (19) CH2Isci (73), τCCH2I (10) δCH3 (69), τCH3 (20) CH2IIsci (78) νC25=O26 (34), τN20H22…O17 (23) 19b νRCC (36), δRCH (36) δCH3 (93) τH34C32C35O37 (21), CH2IIrok (11) τC35C32C29H (49) δC29CH (40) 14

νRCC (45)

τH31C29C32C35 (21), δC35OH (15), νRCC (12) 3 δRCH (77) CH2Itwi (35), δC35OH (15), τH34C32C35O37 (14) τH33C32C35O37 (16), τH31C29C32C35 (15), δC35OH (15)

1298

-

-

0.28

2.15

1.9209

1282

-

-

0.36

0.03

1.4479

1263

1228 s

-

13.71

0.92

1.3099

1232

-

-

107.55 31.47

1.382

1190

1202 vs

1209 m

67.79

3.1297

νC4C7 (40), δRCH (15)

1189

-

205.08 0.8

5.8787

νasSO3 (71)

1172

1169 s

1187 m 1165 vw

65.14

49.73

1.5534

δC25OH (45), νC25=O26 (14)

1166

-

-

107.46 25.59

1.448

1163

-

1143 w

1140

-

-

1121

1126 m

1103

-

1092

-

1083 1077 1041 1033 1002

2.77

0.62

CH2IItwi (26), τH30C29C32C35 (13) 9a δRCH (70), νRCC (23) CH2IItwi (27), νC35O37 (16), δC35OH (11) NH3rok (19), δC25OH (19), νssSO3 (11) νssSO3 (39), 18bδRCH (13)

0.32

1.0361

108.03 4.95

1.5299

1129 s

79.25

2.23

1.1331

183.68 1.29

2.0981

83.29

1.69

1.1481

18a

1037 m 1009 m

1080 m 1064 vw 1038 m 1013 w

171.87 127.67 27.92 10.24 5.56

9.56 28.77 0.51 0.15 0.08

2.6181 1.5765 2.0942 1.0247 2.0514

990

-

-

218.7

81.44

1.2351

976

974 sh

-

3.71

0.3

0.8574

959

-

-

198.08 7.55

1.3869

943

-

-

314.69 4.06

6.5224

934

-

-

3.4

2.98

0.9812

933 929 895 834 824 800

921 sh 903 w 844 w 815 m -

926 m 859 vw 815 sh 801 s

6.48 1.94 24.6 19.82 0.46 22.73

0.86 0.12 25.34 16.16 0.52 0.33

0.7867 0.705 1.626 1.8028 0.5401 0.5666

794

790 sh

-

38.33

13.04

0.6939

783 698

733 w -

-

3.87 7.51

3.02 60.48

1.9718 0.8494

νRCC (66), δRCH (12) νC35O37 (19), νssSO3(19) νC32C29 (53) CH3rok (63), δCH3 (19) 1 δRCC (71) τC32C35 (21), δHCC (12), νC32C29 (11) τCH3 (56), δCH3 (17) νC25O27 (33), νC25C23 (16), δHCC (11) νssSO3(78) νC29C23 (26), δCarH (12), δH22N20C23 (11) 17a δCarH (53), τRCC (12) 10b δCarH (72) νC32C35(49) νN20C23(69) 11 δCarH (97) 10a δCarH (83) τCOH (30), τCCH (10), νC25C23 (10) 4 Rpuck (35), νC4C7 (12) νC25C23 (45), νO27C25 (16)

δRCH (44), νRCC (26)

691 679 660 644 627 610

686 m 630 w -

689 w 675 w 633 m 579 w

3.32 61.21 79.09 143.13 0.06 29.62

0.14 100.01 2.24 0.62 0.96 4.51

1.1904 1.7718 0.4486 2.2302 1.7481 0.7295

549

567 m

565 vw

53.25

2.13

1.1164

546

-

547 vw

28.28

4.54

0.7938

535

-

537 vw

39.1

0.21

0.902

523

-

-

17.37

17.86

0.3484

518

501 sh

496 vw

20.54

1.51

2.2927

486

-

482 vw

30.41

0.31

0.3839

465

-

449 vw

5.12

0.36

0.6607

421

-

-

8.99

6.14

0.367

402

-

-

23.41

6.94

0.1327

401

422 w

413 vw

6.9

1.77

0.2295

382

-

368 vw

111.71 25.65

0.3961

361 341 331 308

-

331 vw -

184.14 2.02 30.28 22.97

54.35 0.48 27.81 4.92

0.2877 0.3574 0.2558 0.1312

302

-

300 m

16.16

19.08

0.1142

269

-

-

10.15

1.55

0.3309

265 222

-

234 w -

4.15 0.05

1.69 0.95

0.2202 0.1493

210

-

-

1.29

0.9

0.128

178

-

-

7.06

0.51

0.1159

154

-

-

6.29

0.18

0.0885

134

-

-

18.78

52.27

0.0294

125 101 80 70

-

121sh 105 s 65 m

5.94 1.63 0.34 7.65

1.13 2.3 2.9 3.61

0.0648 0.0335 0.0236 0.0149

12

Rtrigd (60), τRCH (10) τC25OOH(57) τC35OOH(76) 6b Rasymd (54), νC1S15 (14) 6a Rsmd (76), νRCC (10) δO36CO (47), νO37C35 (10) 16b Rsymt (23), τO18C1O16S15(12) δO26CO (14), νO27C (12), δC25C23C29 (12) τO18C1O16S15(34), 16bτRCC (17) τO37C35(45), δO37C35C32 (13) δSO3rok (36), τO16C1O17S15(36) δOCC32 (35), τO37C35 (22), δC29CN (10) δsySO3 (43), τRC1C6C2S15 (31) δO26CO (42), δO27CC (15) 16a Rasymt (29), τC29C23N20H22 (19) 16a Rasymt (50), τC29C23N20H22 (10) δSO3wag (26), δRCC (19), δSCC (11) Rsmd (13), τC25C29N20 (24) Rsmd (33), δSO3twi (26) δC29CN (26), τC25C29N20 (22) δRCC (24), τC25O27H28 (33) τC25O27H28 (40), δRCC (17), δSO3wag(11) νC1S15 (41), δRCC (14), δO27CC (10) δO27CC (44) δC25C (28) δC25C (14), τRC1C6 C2S15 (15), τRCC (13) δSOH (28), δC1C6S15 (20) δC1C6S15 (39), δSOH (10), τO16C1O17S15 (14) τC32C29C23N20 (56), τC32C35C29C23 (11) νO17-H22 (47) δC23C29C32 (33), τRCC (14) Rsmt (50) τC35C (50)

56

-

-

1.17

4.05

0.0152

45

-

-

3.54

9.5

0.0088

33

-

-

1.59

10.93

0.0077

26

-

-

0.36

4.62

0.0007

24

-

-

0.84

10.05

0.0008

15 14 12

-

-

0.28 1.37 1.79

46.12 24.23 21.89

0.0006 0.0009 0.0006

τO27C25 (38), δC23C29C32 (18) τO27C25 (24), τSOH (16), τO37C35 (14), τN20H (10) τO37C35 (58), τC32C29C23N20 (10) τRCH (61) τRCH (36), τSOH (15), τN20HOS (11), τN20H (14) τC2C1S15O17 (69) τN22HOS (44), τSOH (20) τH22O17S15C1 (63)

vs, very strong; s, strong; m, medium; sh, shoulder; w, weak; vw, very weak; R, ring; ν, stretching; νss, symmetric stretching; νas, asymmetric stretching; δ, bending; δsy, symmetric bending; ipb, in plane bending; opb, out of plane bending; smd, symmetric deformation; asymd, asymmetric deformation; τ, torsion; sci, scissoring; rok, rocking; wag, wagging; twi, twisting; symt, symmetric torsion; asymt, asymmetric torsion; puck, puckering; trigd, triggering deformation. a

Calculated IR intensities. Relative Raman intensities normalized to 100 cf. eqn. (1). c Only PED values greater than or equal to 10% are given. b

Table 5. Calculated absorptions, energy and oscillator strength of LGM using DFT method at B3LYP/6-311G(d,p) level Gas phase

Water

Wavelength Energy Oscillator Excitation Excitation [nm] [kJ/mol] strength 84 → 85 84 → 86

75 → 85 75 → 87

84 → 85 84 → 86 84 → 87

259.86

233.39

231.00

460.35

512.57

517.87

Wavelength [nm] Cal. Exp.

Energy Oscillator [kJ/mol] strength

0.0001

77 → 85

230.59 262.00 518.79

0.0008

82 → 86 82 → 87 83 → 86 83 → 87 84 → 86 84 → 87

224.58

0.0002

82 → 86 82 → 87 83 → 86 83 → 87 84 → 86 84 → 87

204.29 221.00

-

0.0010

532.67

0.0004

585.58

0.0807

Table 6. Calculated HOMO-LUMO energy and global reactivity coefficients of LGM crystal

Parameter

Values (eV)

HOMO

-8.96

LUMO

-4.71

HOMO-LUMO Energy gap

4.25

Chemical hardness (η)

2.13

Electronegativity (χ)

6.84

Chemical potential (µ)

-6.84

Electrophilicity index (ω)

10.98

Chemical softness (S)

0.47

Highlights • • • •

FT-Raman, FT-IR and UV-Vis spectra were used to investigate L-Glutaminium 4-methylbenzenesulfonate crystal. The vibrational spectral analysis explicates the NLO activity and various electronic effects of the molecule supported by using density functional theory (DFT) calculations. The solvent effect was calculated using PCM TD B3LYP/6-311G(d,p) method. HOMO, LUMO and MEP diagrams were depicted to estimate the reactive sites.

Declaration of interests ☒The authors declare that they have no known competing financialinterestsor personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

Declarations of interest: none