Vibrational, electronic absorption, thermal and mechanical analyses of organic nonlinear optical material guanidinium phthalate

Accepted Manuscript Vibrational, electronic absorption, thermal and mechanical analyses of organic nonlinear optical material guanidinium phthalate T. Uma Devi, A. Josephine Prabha, R. Meenakshi, G. Kalpana, C. Surendra Dilip PII:

S0022-2860(16)31128-0

DOI:

10.1016/j.molstruc.2016.10.071

Reference:

MOLSTR 23072

To appear in:

Journal of Molecular Structure

Received Date: 6 July 2016 Revised Date:

21 October 2016

Accepted Date: 21 October 2016

Please cite this article as: T.U. Devi, A.J. Prabha, R. Meenakshi, G. Kalpana, C.S. Dilip, Vibrational, electronic absorption, thermal and mechanical analyses of organic nonlinear optical material guanidinium phthalate, Journal of Molecular Structure (2016), doi: 10.1016/j.molstruc.2016.10.071. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. 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.

Vibrational , Electronic ACCEPTED Absorption,MANUSCRIPT Thermal and Mechanical Analyses of Organic Nonlinear Optical Material Guanidinium Phthalate T. Uma Devia , A. Josephine Prabhab, R.Meenakshic*G.Kalpanaa, , C. Surendra Dilipe Department of Physics, Government Arts College for Women, Pudukkottai 622 001, India

b

Department of Physics, Bishop Heber College , Tiruchirappalli 620 017, India

c

Department of Physics, Cauvery College for Women , Tiruchirappalli 620 018, India

d

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a

Department of Chemistry, BIT Campus, Anna University, Tiruchirappalli 620 024, India

Abstract

The FTIR and UV spectroscopic analysis have been carried out on guanidinium phthalate

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(GUP) crystal, an organic nonlinear optical material. The spectra are interpreted with the aid

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of normal coordinate analysis following structure optimizations and force field calculations based on density functional theory (DFT). The thermogravimetric (TG) and differential thermal analysis (DTA) ensures the thermal stability of the compound. Vickers microhardness values reveals the mechanical strength of the crystal.

Corresponding Author: Dr. R. Meenakshi, [email protected]

Introduction

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1.

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*

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Key words: FT-IR; NLO; DFT; TG; DTA

The Non-linear optical (NLO) materials are of great demand due to their wide

applications in the recent technologies like lasers, optoelectronics, optical communication and data storage systems [1-5]. To design and fabricate the NLO materials much effort is being devoted to understand the origin of non-linearity in large systems and to relate NLO responses to electronic structure and molecular geometry. The phthalate crystals are widely known for optical, piezoelectric, NLO and elastic applications [6-9]. Sodium acid phthalate, rubidium acid phthalate, caesium acid phthalate, thalium acid phthalate and ammonium acid

phthalate [10-14] are the famous reported phthalate crystals. In this series, the guanidinium

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phthalate. [CN3H6]2C8H404 a representative of acid salts crystallizes in the orthorhombic system having four molecules per unit cell with a centrosymmetric space group Pbcn,as reported by Krumbe et al. [15]. The solid-state complexation of guanidine with different organic and inorganic acids has an interesting aspect concerning the formation of hydrogen

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bonds and comprises most frequently weak hydrogen bonds of N-H…O and O-H…O types [16]. The present work aims to predict the structural, electronic and spectroscopic properties of grown guanidinium phthalate (GP) crystals by experimental (FT-IR and UV–Vis

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spectroscopy) and theoretical (DFT-B3LYP level of theory with the use of standard 6311+G(d,p) basis set) method. Also the natural bond orbital (NBO) analysis is carried out to

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interpret intramolecular charge transfer (ICT). The calculated value of HOMO (highest occupied molecular orbital) - LUMO (lowest unoccupied molecular orbital) energy gap is used to interpret the NLO activity of the molecule. 2.

Experimental and Computational Details

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2.1 Preparation

In order to synthesize GUP, stoichiometric amounts (2:1) of the reactants, guanidinium carbonate and an aqueous solution of phthalic acid are used. The solution is

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stirred using magnetic stirrer at 35ºC for 2 hours. The solution is filtered, kept undisturbed and covered to avoid contamination, which yields the product in the course of time. The

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synthesized product is recrystallized several times using distilled water and is used for subsequent growth. The prepared solution is housed in the constant temperature bath maintained at 35ºC, which is the desired temperature for the growth of the title compound. After a span of 10 days, transparent single nucleation is formed. The nucleated crystal is allowed to grow into a larger size and then harvested after 10 more days. The grown single crystal is shown in Fig.1. 2.2 Characterization

Single crystal X - ray diffraction data are collected for a transparent well shaped

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single crystal of GUP using Enraf Nonius –CAD4 single crystal X–ray diffractometer . FT-IR spectrum of the synthesized material is recorded by KBr pellet technique (Thermo Nicolet AVATAR 370 DTGS FT-IR spectrophotometer) in the range 400–4000 cm−1. The spectral resolution is 1 cm-1 and 300 scans are accumulated for the acquisition. The UV–Vis

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absorption spectrum is recorded using a Shimadzu UV–Vis spectrophotometer in the spectral region of 190–1100 nm. Thermal analysis of GUP is carried out using a Perkin Elmer simultaneous thermogravimetric and differential thermal (TGA & DTA) analyzers. The

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sample is scanned in the temperature range 20-400ºC at a rate of 10ºC/min in a inert nitrogen atmosphere.

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2.3 Computation

All DFT calculations are performed with the Gaussian 09 program [17]. The geometries are fully optimized in the gas phase at DFT levels by B3LYP functions, which combine Becke’s three-parameter exchange function (B3) with the correlation function of

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Lee, Yang and Parr (LYP). The frequency calculation using the same method provides nonimaginary frequencies, which confirms the presence of real minima on the potential energy

3.1

Results and Discussion

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3

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surface of the optimized structure.

Optimized geometry The grown GUP crystals are highly transparent and non-hygroscopic. The

morphology establishes that there are well-developed faces. Single crystal X-ray diffraction study shows that GUP crystallizes in the orthorhombic crystal system and the corresponding data are listed in Table 1a. The chemical and optimized structures of GUP are shown in Fig. 2a and Fig. 2b. The optimized geometrical parameters are summarized in Table 1b. As expected there are two guanidinium and one phthalate groups which are ionized. For

guanidinium, X-ray data of C–N bond lengths lie in the range 1.333 to 1.358 A˚ [15]

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whereas the theoretical calculation yields the C–N distances in the range 1.293–1.298 A˚ .The C-C distances of phthalate

varies from 1.367 – 1.413 A˚ (Table 1b) and has almost

equivalent C-C-C angles. The benzene ring is slightly distorted from a regular hexagon whose average C-C distance is 1.39 Å and the C-C-C angle is 120.00. DFT calculation

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indicates slight increase or decrease in the angles which is associated with the charge transfer interaction. 3.2 Vibrational spectral analysis

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The FT-IR spectrum obtained for GUP is shown in Fig. 3. The vibrational spectral

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analysis is carried out based on recorded FTIR and scaled quantum mechanical (SQM) force field methodology. The corresponding observed and calculated frequencies are reported in Table 2 and interpreted as follows.

The frequency observed at 3373 cm-1 in FT-IR spectrum is assigned to the –NH2

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asymmetric stretching mode. In di-substituted benzenes, there are four C-H stretching vibrations whose wavenumbers fall in the region 3120-3010 cm-1 [18-20]. The C-H stretching modes are found to be weak which is due to the charge transfer between the hydrogen atoms

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and carbon atoms [21, 22]. The IR band at 3107 cm-1 is attributed to C-H stretching. The C-H in plane bending appears at 1565, 1436, and 1151 cm-1. The C-H out of plane bending

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vibrations are reported in the region 960-780 cm-1 [18-20] and in the present study the corresponding modes are observed at 887, 852, 790 and 719 cm-1. The carboxylate group has two strongly coupled C-O bonds with bond strengths intermediate between C-O and C=O. This deprotonated carboxylate group COO- absorbs strongly near 1600-1570 cm-1 for asymmetric stretching and weakly near 1400-1315 cm-1 for symmetric stretching [21-25]. In the present study the IR band at 1663 cm-1 and at 1380 cm-1 are assigned to COOasymmetric and symmetric stretching, respectively.

3.3 Analysis of HOMO-LUMO and Global Reactivity Descriptors

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The interaction of the molecule with other molecules can be determined from the Highest Occupied Molecular Orbitals (HOMO) and the Lowest Unoccupied Molecular Orbitals (LUMO). The difference in the energies of these levels yields the energy gap, from which the

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chemical reactivity and the kinetics of the reactions can be studied. HOMO and LUMO plots of GUP and the energies of these orbitals in the gas are shown in Fig. 4.

= -2.0408 eV

LUMO Energy

= -1.6917 eV

HOMO-LUMO Energy gap, ∆E

= 0. 3491 eV

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3.3.1 Global Reactivity Descriptors

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HOMO Energy

The estimation of the reactivity of chemical species is one of the main purposes of theoretical chemistry and a lot of work has been carried out in the same line. Density functional theory has been successful in giving theoretical background of accepted qualitative

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chemical concepts. In this framework, several reactivity descriptors have been projected and used to analyze chemical reactivity and site selectivity. Hardness, global softness, electro negativity and polarizability are the global reactivity descriptors widely used to understand

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the global nature of molecules in terms of their stability and it is possible to gain knowledge

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about the reactivity of molecules.

From Koopman’s theorem, the ionization potential (IP) and the electron affinity

(EA) are the eigen values of HOMO and LUMO with change of sign [26]. IP ≈ -EHOMO and EA ≈ -ELUMO

(1)

Several global chemical reactivity descriptors of molecules such as hardness (η), chemical potential (µ), softness (s), electronegativity (χ) and electrophilicity index (ω) are calculated based on the density functional theory (DFT). The global hardness (η) and

chemical potential (µ) are defined as the second and first derivatives respectively, of the ACCEPTED MANUSCRIPT energy (E) with respect to the number of electrons (N) at constant external potential ,V η=

and µ =

In equation (2), E and V

.

(2)

are electronic energy and external potential of an N-

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electron system respectively. Softness is a property of molecules which measures the extent of chemical reactivity. It is the reciprocal of hardness. The electronegativity is defined as the

and χ = -

=-µ

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S=

(3)

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negative of the electronic chemical potential.

Using Koopman’s theorem for closed shell molecules η, µ and χ can be redefined as; (IP-EA) ≈ (ELUMO - EHOMO)

µ≈

(IP+EA) ≈

(5)

(6)

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χ=

(EHOMO + ELUMO)

(4)

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η≈

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Electrophilicity is a useful structural depictor of reactivity and is frequently used in the

analysis of the chemical reactivity of molecules. ω=

(7)

The maximum electronic charge transfer ∆Nmax in the direction of the electrophile is predicted as follows [28],

∆Nmax

=-

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(8)

The concept of electrophilicity viewed as a reactivity index was introduced by Parr et al [27]. It is based on a second order expansion of the electronic energy with respect to the

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charge transfer ∆N at fixed geometry. This index measures the stabilization in energy when the system acquires an additional electronic charge ∆N from the environment and it is defined as above by a simple and more familiar form [28] in terms of the electronic chemical

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potential (µ) and the chemical hardness (η). Thus, while the quantity defined by equation (8)

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describes the tendency of the molecule to acquire additional electronic charge from the environment, the quantity defined in equation (7) describes the charge capacity of the molecule. All the calculated DFT reactivity descriptors are summarized in Table 3. 3.4 Electrostatic Potential analysis

In order to evaluate the molecular interactions, the molecular electrostatic potential

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(MEP) is used. The molecular electrostatic potential is the potential that a unit positive charge would experience at any point surrounding the molecule due to the electron density distribution in the molecule. The electrostatic potential is considered predictive of chemical

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reactivity because regions of negative potential are expected to be sites of protonation and

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nucleophilic attack, while regions of positive potential may indicate electrophilic sites. Fig. 5 shows the theoretical map of the electrostatic potential distribution, obtained by B3LYP level of theory at 6-311++G. As clearly seen in Fig. 5, the investigated molecule has several possible electrophilic

(more electro negative sites and are represented as red color) and nucleophilic sites (more electro positive sites and are represented as blue color). The electrostatic potential map indicates that, the oxygen atoms are the most electronegative sites in GUP. From fig. 5, it is also evident that the charges that accumulate on hydrogen atoms of the guanidine groups are

more positive, while that over ring hydrogen atoms are less positive. It is also seen that less

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electro positive region (yellow color) envelops the pi-system of benzene ring, which prevent the ring hydrogen atom from being more electrophilic. 3.5 NBO analysis To understand the nature and magnitude of the intermolecular interactions, natural

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bond orbital (NBO) analysis is conducted on the optimized geometries in the Gaussian program. In NBO analysis, the stabilization energy E(2) associated is explicitly estimated by

F(i,j)2 ε j -ε i

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E(2) = ∆Eij = q i

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the following equation,

(9)

where qi is the ith donor orbital occupancy, εi and εj are the diagonal elements (orbital energies) and F(i, j) is the off diagonal element associated with the NBO Fock matrix. In

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addition, Mulliken population analysis is also performed on the optimized structures. Natural bond orbital analysis provides an efficient method for studying intra- and inter-molecular bonding and interaction among bonds, and also provides a convenient basis

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for investigating charge transfer or conjugative interaction in molecular systems. Some electron donor orbital, acceptor orbital and the interacting stabilization energy resulting from

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the second-order micro-disturbance theory are reported [29]. The larger the E

(2)

value, the

more intensive is the interaction between electron donors and electron acceptors, i.e. the more donating tendency from electron donors to electron acceptors and the greater is the extent of conjugation of the whole system. Delocalization of electron density between occupied Lewistype (bond or lone pair) NBO orbitals and formally unoccupied (antibond or Rydgberg) nonLewis NBO orbitals correspond to a stabilizing donor–acceptor interaction. NBO analysis has been performed on the molecule at the DFT/B3LYP/6-311++G level in order to elucidate the intra-molecular, rehybridization and delocalization of electron density within the molecule.

The NBO interactions of GUP are listed in Table 4. The intra-molecular interaction is

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formed by the orbital overlap between π (C1 - C2) and π *(C5 - C6) bond orbital which results in intra-molecular charge transfer (ICT) causing stabilization of the system with the energy of 21.12 kcal/mol. Again this energy of π*(C5-C6) is redistributed to π*(C1 - C2) with the higher interaction energy of 171.15kcal/mol.The most important interaction energy

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in this molecule is arising due to electron donation from n2 (O14) to π *(C11 - O13) resulting in stabilization of GUP with the energy of 78.14 kcal/mol.

3.6 NMR spectral analysis

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The isotropic chemical shifts are frequently used as an aid in identification of reactive ionic species. It is recognized that accurate predictions of molecular geometries are essential

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for reliable calculations of magnetic properties. The isotropic shielding values are used to calculate the isotropic chemical shifts δ with respect to tetramethylsilane (TMS)

. The values of

respectively. The

13

are 182.46 and 31.88 ppm for

13

C and 1H NMR spectra,

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-

=

C and 1H theoretical and experimental chemical shifts, isotropic shielding

tensors and the assignments of GUP are summarized in Table 5. The experimental 13C and 1H

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NMR spectra are shown in Figs. 6a and 6b. 1H atom is mostly localized on the periphery of

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the molecules and their chemical shifts would be more susceptible to intermolecular interactions in the aqueous solutions as compared to other heavier atoms. Aromatic carbons give signals in overlapped areas of the spectrum with chemical shift values from 100 to 150 ppm. In our present investigation, the experimental chemical shift peaks appeared in the range 127.14–177.59 ppm are assigned to aromatic carbons. Similarly, the corresponding proton chemical shifts are in the range 7.27–7.39 ppm. The theoretical chemical shifts of GUP are in good agreement with the experimental values as shown in Table 5.

3.7 UV-Vis spectral analysis

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The UV-Vis spectrum of GUP is shown in Fig.7. It is evident from the spectrum that there is no significant absorption in the entire visible region and NIR region. The lower cut off wavelength occurs at 241 nm with 32 % absorbance. The crystal has a wide transparency

potential candidate for various optical applications.

3.8 Thermal Studies

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window from 241 nm to 1100 nm. This wide transparency window enables GUP to be a

Thermal analysis of a material gives useful information regarding the thermal stability

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of that material. Thermal behaviour of the GUP was characterized by TGA and DTA, which

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reflects the thermal stability of the sample. The thermo analytical curves of studied compound are shown in Fig. 8. The DTA curve implies that the material undergoes an irreversible endothermic transition, where melting begins. The crystal starts melting at 275°C and terminates at 345°C, having the peak corresponding to 286°C. The peak temperature corresponds to the melting point of the sample. Also it is clear that there is no phase transition

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before melting. The sharpness of the peak shows good degree of crystallinity and purity of the sample. The TG curve of this sample indicates that the sample is stable upto 275°C. The

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endothermic peak of the DTA at 286°C corresponds to the major phase of the weight loss in the

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TG curve, indicating the decomposition of the sample.

3.9 Micro hardness measurements The structure and molecular composition of the crystals greatly influence their

mechanical properties. In order to study the mechanical stability, the GUP single crystal is subjected to Vickers microhardness test. The indentations are carefully made on as grown crystal surface with a dwell time of 5 s. The plot between hardness number (Hv) and load (P) is shown in the Fig. 9a. It is observed that hardness number increases as load increases. This can be described on the pattern of depth of penetration of the indenter. When load increases, a

few surface layers are initially penetrated and then the inner surface layers are also penetrated

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by the indenter. The measured hardness is a characteristic of these layers and the increase in hardness number is due to the overall effect on the surface and inner layers of the sample [30]. Beyond 100g, significant cracks occurred around the indentation mark, which is due to the release of internal stress generated locally by the indentation. By plotting log P versus log

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d, the value of the work hardening coefficient ‘n’ is found and it is shown in Fig. 9(b). According to Onitsch, the value of n is below 1.6 for hard materials and n > 1.6 for soft materials [31]. The work hardening coefficient value of GUP is 2.4 and hence, it is evident

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that the grown GUP crystal belongs to soft material category.

4. Conclusions

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The experimental and theoretical spectroscopic analyses on GUP have been performed. UV- Vis spectrum shows that the GUP crystal is optically transparent in the visible region. FTIR spectrum has also been recorded and analyzed. The molecular geometry, vibrational wavenumbers and HOMO - LUMO energy gap of GUP in the ground state has

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been calculated using density functional theory. The lowering of the HOMO-LUMO energy gap value has substantial influence on the intramolecular charge transfer and nonlinearity of the molecule. The NBO analysis confirms the intramolecular charge transfer.

The TG

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analysis shows GUP is thermally stable up to 275°C and the Vicker’s microhardness analysis suggests that the crystal is a soft material.

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Acknowledgement

T.U. (T. Uma Devi) thanks the University Grants Commission (UGC) for the fund

provided for the minor research project MRP 5164/14 (SERO /UGC).

References:

[1] P.N. Prasad, D.J. Williams, Introduction to Nonlinear Optical Effects in molecules

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and Polymers, John Wiley & sons, New York, 1991. [2] H.S. Nalwa, S. Miyata (Ed.), Nonlinear Optics of Organic Molecules and Polymers, CRC Press: Boca Raton, FL, 1997. [3] S.R. Marder, B. Kippelen, A.K.-Y. Jen, N. Peyghambarian, Nature. 388 (1997) 845-851.

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[11] R. A. Smith, Acta Cryst. B31 (1975) 2347.

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[13] G.Tietang, J. Cryst. Growth. 142 (1994) 327-331. [14] Y. Okaya , R. Pepinsky, Acta Cryst. 10 (1957) 324.

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[15] W.Krumbe, Z. Haussühl, Kristallogr. 179(1987) 267-279. [16] Y. Okaya, Acta Cryst. 19 (1965) 879. [17] M.J.Frisch, G.W. Trucks, H.B. Schlegal. et al., (2009).GAUSSIAN 09W. Revision A.02, Gaussian, Inc., Wallingford CT. [18] S. George, Infrared and Raman Characteristic Group Wavenumbers, Tables and Charts, 3rd ed, Wiley, Chichester, U.K, 2001.

[19] D. Lin-Vien, N.B. Colthup, W.G. Fateley, J.G. Graselli, The Hand Book of Infrared and

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Raman Characteristic Frequencies of Organic Molecules, Academic Press, New York, 1991. [20] G. Socrates, Infrared Characteristic Group Frequencies, Wiley Interscience Publication, New York, 1980.

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[2] C. Ravikumar, I. Hubert Joe, D. Sajan, Chem. Phys. 369 (2010) 1.

[22] C. Ravikumar, I. Hubert Joe, V.S. Jayakumar, Chem. Phys. Lett. 460 (2008) 552-558. [23] N.P.G. Roeges, A Guide to the Complete Interpretation of Infrared Spectra of

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Organic Structure, Wiley, New York, 1999.

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[25] L. Bellamy, The Infrared Spectra of Complex Molecules, Chapmann and Hall, London, 1975.

[26] R.G.Pearson , Proc. Natl. Acad. Sci. (USA). 83 (1986) 8440. [27] C.Lee ,W. Yang , G.R Parr , Phys. Rev. B. 37 (1988) 785.

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[28] R.G.Parr, L.V.Szentpa´ly, S. Liu. J. Am. Chem. Soc. 121 (1999) 1922. [29] Jun-na Liu, Zhi-rang Chen, Shen-fang Yuan, J. Zhejiang, Univ. Sci. 6B (2005) 584.

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[30] K. Li, X. Wang , D. Xue, A Simple method for Hardness prediction of Transition Metal Compound, Materials focus. 1 (2012) 142-148.

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[31] K. Sangwal, On the Reverse Indentation Size Effect and microhardness measurement of solids, Mater. Chem. Phys. 63 (2000) 145-152.

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Table 1a Comparison of unit cell parameters of GUP.

a ( Å)

b (Å)

c (Å)

References

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S.No.

14.845

9.259

10.124

Present Work

2.

14.856

9.269

10.138

[15]

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1.

Table 1b

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Experimental and theoretical geometric data for GUP at B3LYP/6-311++G. level.

Bond angles (º)

Bond length (Å) Atoms

1.413 1.379 1.413 1.375 1.367 1.375

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C1-C2 C2-C3 C3-C4 C4-C5 C5-C6 C6-C1

C27-N35 C27-N33 C27-N34 C17-N23 C17-N24 C17-N25

1.358 1.35 1.333 1.358 1.35 1.333

Atoms

Theoretical

Phthalate ion 1.401 C1-C2-C3 1.385 C2-C3-C4 1.401 C3-C4-C5 1.392 C4-C5-C6 1.378 C5-C6-C1 1.367 C6-C1-C2 Guanidinium ion 1.298 N33-C27-N35 1.293 N34-C27-N33 1.2936 N33-C27-N34 1.298 N24-C17-N23 1.293 N25-C17-N24 1.2936 N23-C17-N25

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XRD [15]

XRD [15]

Theoretical

119.3 120.2 120.5 119.3 120.2 120.5

120.09 121.5 120.9 120.12 120.22 120.45

119.4 120.2 120.5 119.4 120.2 120.5

118.9 119.9 119.9 118.8 121.1 121.1

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Assignments

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NH2 asymmetric stretch C-H stretching vibrations COO- asymmetric stretch C-H in plane bending vibration C-H in plane bending vibration COO- symmetric stretch C-H in plane bending vibration C-H out of plane bending vibration C-H out of plane bending vibration C-H out of plane bending vibration

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Wavenumbers (cm-1) FT-IR Calculated 3373 3467 3107 3221 1663 1773 1565 1666 1436 1499 1380 1388 1151 1123 832 828 760 799 696 712

TABLE 3

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The theoretical reactivity descriptors of GUOM by B3LYP/6-311++ G method.

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PARAMETERS HOMO energy (EHOMO) LUMO energy (ELUMO) Energy gap (Eg) Ionization potential (IP) Electron affinity (EA) Hardness (ɳ) Softness (s) Chemical potential (µ) Electronegativity (χ) Electrophilicity index (ω) Charge Transfer (∆Nmax)

VALUES (eV) - 2.0408 - 1.6917 0. 3491 2.0408 1.6917 0.1746 0.0349 -1.866 1.866 9.9712 10.6872

Table 4 ACCEPTED MANUSCRIPT NBO analysis of Second order perturbation theory of Fock matrix of GUP at /6311++G level.

E(2) E(j)-E(i) Kcal/mol a.u Intramolecular Interactions in Phthalate moiety σ (C 1 - C2) σ *( C 1 - C 6) 4.36 1.26 σ (C1 - C2) σ *( C 2 - C 3) 4.22 1.26 π(C1 - C2) π *( C 3 - C 4) 19.86 0.28 π(C 1 - C2) π *( C 5 - C 6) 21.12 0.27 π(C1 - C2) π *( C 11 - O 13) 18.07 0.25 π (C1 - C2) π *( C 12 - O 16) 13.77 0.30 σ(C1 - C6) σ *( C 1 - C 2) 4.83 1.27 π(C3 - C4) π *( C 1 - C 2) 20.10 0.29 π(C3 - C4) π *( C 5 - C 6) 20.64 0.27 σ(C3 - H7) σ *( C 1 - C 2) 4.79 1.08 σ(C3 - H7) σ *( C 4 - C 5) 4.06 1.06 σ(C6 - H10) σ *( C 4 - C 5) 4.16 1.07 π(C11 - O13) π *( C 1 - C 2) 4.58 0.35 σ(O 14 - O15) σ *(C 11 - O 13) 6.11 0.99 σ(O 14 - O15) σ *(C 12 - O 16) 5.97 0.95 n2 (O13) σ *( C 1 - C 11) 12.00 0.59 n2 (O13) σ *( C 11 - O 14) 21.66 0.65 n2 (O14) σ *( C 1 - C 11) 5.94 1.00 n2 (O14) π *( C 11 - O 13) 78.14 0.27 n1 (O15) σ *( C 2 - C 12) 5.96 1.00 n2 (O15) π *( C 12 - O 16) 63.55 0.31 n2 (O16) σ *( C 2 - C 12) 11.96 0.59 n2 (O16) σ *( C 12 - O 15) 21.78 0.65 π *( C1 - C2) π *(C 12 - O 16) 178.49 0.01 π *( C3 - C4) π *( C 1 - C 2) 273.35 0.01 π *( C5 - C6) π *( C 1 - C 2) 171.15 0.02 π *( C 11 - O13) π *( C 1 - C 2) 67.57 0.03 Intramolecular Interactions in Guanidinium moiety σ(H 32 - N 33 ) σ *( C 27 - N 35 ) 5.52 1.20 σ(N 35 - H 36 ) σ *( C 27 - N 33 ) 5.54 1.20 σ(H 31 - N 33) σ *( C 27 - N 34) 5.84 1.13 σ(H 18 - N 24) σ *( C 17 - N 23 ) 4.72 1.19 σ(H 19 - N 24) σ *( C 17 - N 25 ) 4.75 1.20 σ(H 20 - N 25) σ *( C 17 - N 24 ) 5.69 1.15 σ(H 21 - N 23 ) σ *( C 17 - N 24) 5.60 1.15 σ(H 22 - N 23) σ *( C 17 - N 25) 5.39 1.21 Acceptor (j)

F(i,j) a.u 0.066 0.065 0.067 0.068 0.061 0.058 0.070 0.068 0.067 0.064 0.059 0.059 0.040 0.069 0.068 0.076 0.108 0.070 0.130 0.070 0.125 0.076 0.109 0.065 0.082 0.083 0.068

AC C

EP

TE D

M AN U

SC

RI PT

Donor (i)

0.073 0.073 0.073 0.067 0.068 0.073 0.072 0.072

Table 5 ACCEPTED MANUSCRIPT Experimental and theoretical chemical shifts( δ in ppm ) of 13C and 1H of GUP at B3LYP/6-311++G level.

Exp.

Theor.

Atoms

Exp.

Theor.

Atoms

C C C C C

177.59 157.95 137.55 128.83 127.14

186.147 146.844 135.389 128.137 124.101

H H H H H H H H H

7.27 7.27 7.28 7.29 7.29 7.30 7.31 7.35 7.39

7.22 7.22 7.34 7.34 7.34 7.22 7.22 7.34 7.41

H H H H H H H H

SC

M AN U TE D EP AC C

Exp. 7.35 7.35 7.36 7.36 7.37 7.37 7.38 7.39

Theor. 7.34 7.34 7.32 7.22 7.35 7.35 7.36 7.41

RI PT

Atoms

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

Fig. 1. As grown GUP single crystal

Fig. 2a. Chemical Structure of GUP

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

TE D

Fig.2b. Optimized Structure of GUP

110 100 90

60

EP

70

AC C

%T

80

50 40 30

4400

4000

3600

3200

2800

2400

2000

1600 -1

Wavenumber (cm )

Fig. 3. FT-IR spectrum of GUP

1200

800

400

ACCEPTED MANUSCRIPT

EH = - 2.0408 eV

AC C

EP

TE D

M AN U

Eg = 0.3491 eV

SC

RI PT

EL = - 1.6917 eV

Fig. 4. HOMO and LUMO molecular orbitals of GUP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

Fig. 5. MESP surfaces of GUP

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

Fig. 6a. 1H NMR Spectrum of GUP along with theoretical spectrum.

Fig. 6b. 13C NMR Spectrum of GUP along with theoretical spectrum.

ACCEPTED MANUSCRIPT 3.5 3.0

2.0

RI PT

Absorbance

2.5

1.5 1.0

SC

0.5

200

400

M AN U

0.0

600

800

Wavelength (nm)

AC C

EP

TE D

Fig. 7. UV–Vis spectrum of GUP

1000

1200

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

Fig. 8. TG and DTA of GUP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

2

Hardness number Hv (kg/mm )

50

EP

40

30

AC C

20

10

0 0

20

40

60

80

Load P (g)

Fig. 9a. Microhardness of GUP

100

RI PT

ACCEPTED MANUSCRIPT

SC

2.2 2.0

M AN U

1.8

log P

1.6 1.4 1.2

0.8 0.6

1.4

EP

1.3

TE D

1.0

1.5

1.6

log d

AC C

Fig. 9b. log d Vs log P of GUP

1.7

1.8

ACCEPTED MANUSCRIPT HIGHLIGHTS

RI PT

SC M AN U TE D EP

• •

UV- Vis spectrum shows that the GUP crystal is optically transparent. FTIR spectrum has also been recorded and analyzed. The lowering of the HOMO-LUMO energy gap value has substantial influence on the intramolecular charge transfer and nonlinearity of the molecule. The NBO analysis confirms the intramolecular charge transfer. The TG analysis shows GUP is thermally stable up to 275°C.

AC C

• • •