A Theoretical and Experimental Approach U.Reeta Felscia

Subscriber access provided by READING UNIV

Article

Electronic and Nonlinear Optical Properties of L-Histidine on Silver: A Theoretical and Experimental Approach U.Reeta Felscia, Beulah J.M. Rajkumar, Monickaraj Nidya, and Pranitha Sankar J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.7b07493 • Publication Date (Web): 10 Jan 2018 Downloaded from http://pubs.acs.org on January 11, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

The Journal of Physical Chemistry A is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

Electronic and Nonlinear Optical Properties of L-Histidine on Silver: A Theoretical and Experimental Approach U.Reeta Felsciaa, Beulah J.M. Rajkumara,*, Monickaraj Nidyaa, and Pranitha Sankarb a PG & Research Department of Physics, Lady Doak College, Madurai 625002, India b Light and Matter Physics Group, Raman Research Institute, Bangalore, Karnataka, India

*Corresponding author Email: [email protected] Phone: +91 9944952925 Abstract Investigation on the electrostatic interactions between histidine and silver have been analysed using Density Functional Theory (DFT). Variations in the structural parameters were identified to be significant at those atoms of histidine near the silver cluster. Shifting of frontier molecular orbitals, reduction in bandgap, molecular electrostatic potential(MEP) and the overlap of Natural Bond Orbitals(NBO) between silver and histidine have been theoretically calculated. The results confirm the redistribution of charges consequent to the process of adsorption. Based on the Time-Dependent Density Functional Theory (TDDFT), two peaks were generated at 301 nm and 409 nm in the simulated UV-Vis spectrum. Theoretical vibrational Raman analysis of the investigated molecules strongly confirms the process of adsorption. Nonlinear optical (NLO) properties are predicted by theoretical studies and confirmed experimentally (Open aperture ZScan). The adsorption of histidine on silver enhances the NLO parameters, indicating that it is a promising candidate for NLO devices.

1 ACS Paragon Plus Environment

The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1. Introduction Over the past few decades, materials that exhibit strong nonlinear optical (NLO) behavior have received considerable interest due to their applications in the field of optical switching, data storage and image transmission.1 The polarizability of the material can be enhanced in π electron systems by linking donor and acceptor moieties at either side and this is the strategy used for designing efficient materials.2 Optical limiting is an essential NLO property where the material is opaque to higher and transparent to lower energy laser pulses. This property can be exploited to protect the human eye as well as sensitive sensors from powerful laser beams.3 Measurements of NLO parameters of different materials have been carried out using several experimental techniques. Of these, the Z-scan is an extensively used technique as it is both simple and sensitive.1 Although the optical limiting behavior of organic, inorganic, organometallic and semiconductor systems have been investigated in the past,

4-6

it is only in the recent past that nanomaterials as

optical power limiters have attracted significant attention.7 Of the two metal nanoparticles (NPs), Ag and Au, the higher enhancement in the plasmon excitation is two orders of magnitude greater in the former as compared to the latter.8 Currently, there is a growing interest in the production of ligand capped metal NPs to enhance the surface to volume ratio and hence improve their utility as analytical tools9 including NLO applications.10 Studies report that the stabilization of metal NPs by ligands renders it photostable even at intense laser irradiation resulting in the enhancement in the optical nonlinearity of the systems. In general, adsorption of ligand on metals is also known to result in higher thermal stability than their metal counterparts.11 Amino acids exhibit molecular chirality, zwitterionic nature and do not have strongly conjugated bonds.12 L-histidine is one such amino acid, exhibits a vital role in biochemical reactions. A few 2 ACS Paragon Plus Environment

Page 2 of 25

Page 3 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


investigators have studied the interactions between different forms of amino acids adsorbed on gold and silver NPs.13,14 Several investigators have analyzed the interaction between amino acids and silver clusters. These studies report that these molecular systems can be used in bioanalytical applications, fabrication of bioelectronic devices and sensors.15-18 More recently, Sanader et.al have carried out the optical studies of histidine (anionic and cationic) complexes with Ag and Ag3. They have established that, silver labelling is a potential tool for the detection of histidine or histidine-tagged proteins.19 Over the past two decades, extensive studies have been undertaken on the NLO properties of novel materials. These studies indicate that there are important influencing factors that can lead to dramatic increase in the first hyperpolarizability of these materials.20 Density functional theory (DFT) is the most standard computational method, because of its reasonable cost and good accuracy in predicting the adsorption behavior of the molecular systems. This method has proved to be one of the most accurate methods for the computation of the electronic structure.21-24 As compared to the other ab initio methods, the DFT computations include electron correlation via functionals.25 Recent investigations by Inoue et.al reported that the nucleation stages of Ag NPs originated from Ag3 clusters. Over the past 3 decades, a large number of theoretical studies of Ag3 clusters have provided meaningful results which have complemented experimental studies.26,27 In the current work, experimental investigations on the nonlinearity of histidine capped silver NPs (His-Ag) using the short-pulse excitation regime are reported. The NLO property is investigated using the open aperture Z-scan technique (Laser wavelength:532 nm, Laser Pulse Duration:5 ns and Laser pulse energy: 50 µJ). Theoretical investigations on the structural parameters, electronic and NLO properties are derived using the modified hybrid density



functional CAM-B3LYP which takes into account the long-range interactions.28 This study also includes the comparison of theoretical and experimental13 UV-Vis and Raman vibrational spectra. 2. Methods 2.1 Computational Methods The molecular geometry optimizations were investigated for histidine and interactions between histidine and silver cluster (His-Ag3) using the DFT/CAM-B3LYP implemented through the Gaussian 09 software.29 The basis set 6-31++G(d,p) was used for histidine which involves polarization and diffuse functions in all the computations.30,31 For Ag3 clusters, on the other hand, Stuttgart/Dresden ECP (SDD) was applied, which is a well-known typical basis set for metal atoms.32 After the geometry optimization for each molecule, it was confirmed that no imaginary vibrational frequencies were present indicating a true local minimum on the potential energy surface. Investigations on the structural properties, frontier molecular orbitals (FMOs) and Natural Bond Orbitals (NBO) give an insight into the adsorption process. In order to gain a better understanding on the interactions between ligand and the metal cluster, the MEP surface is plotted over the optimized geometry of the studied molecules and the charges on each atom is calculated. Further, theoretical and experimental NLO properties of the system were investigated. The simulated Raman spectra of both histidine and His-Ag3 are compared with the available experimental observations.13 2.2. Experimental 2.2.1 Materials Silver nitrate (AgNO3) of 99.8% purity (NICE) was used as a precursor, L-histidine (C6H9N3O2 99.0% – HIMEDIA) and sodium borohydride (NaBH4 95% – MERCK) was used as the capping and reducing agent respectively. In order to adjust the pH in water nitric acid (HNO3) and 4 ACS Paragon Plus Environment

Page 4 of 25

Page 5 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


sodium hydroxide (NaOH) was used. Without further purification, all chemicals of analytical grade were used directly. Millipore water was used throughout the experiments.

2.2.2 Sample preparation 8 mL of L-histidine (1 mM) was added drop by drop to 20 mL of AgNO3 (1 mM), and stirred in the magnetic stirrer. With the continuous vigorous stirring, the as-prepared L-histidine-mixed AgNO3 solution was added drop by drop to 60 mL of NaBH4 (1 mM) solution. There was a noticeable change in the color from yellow to greenish gray and the identified pH value was 8.1. The L-histidine-capped silver NPs solution was stable for more than a month. 2.2.3 Characterization Films of His-Ag were drop-casted on glass substrates and the X-ray diffraction (XRD) measurements carried out on a Model X’Pert, PRO, PW 3050/60 using Cu Kα radiation (λ = 1.5406 Å). Measurement of the nonlinear absorption coefficient was taken using the Z-scan technique established by Sheik-Bahae et.al.33 Herein, a focused beam is used to excite the sample and the direction of beam propagation is taken as the Z-axis and the position Z=0 as a focal point. Higher energy density has been observed at the focus, with the energy profile being symmetrically reducing on either side Z=0 position. In the experiment, the sample is scanned along the Z-axis in small steps toward the focus and beyond, and at each step, the corresponding transmission is measured. The Z-scan curve is drawn by plotting the normalized transmittance of the sample Tnorm against the sample position Z, from where the nonlinear absorption coefficient is calculated.7 The second harmonic output of a Q-switched Nd:YAG laser (MiniLite, Continuum) was used for exciting His-Ag NPs in aqueous solution. The laser pulses were plane polarized, 5 ACS Paragon Plus Environment


had a Gaussian spatial profile, and an FWHM temporal width of 5 ns (5 x 10-9 s). The sample had a linear transmission of 85%.

3. Results and Discussion 3.1 Structural Studies Optimized molecular geometries of histidine and His-Ag3 are calculated based on DFT (Fig.1). In order to find the potential adsorption site, His-Ag3 was optimized at two different sites of adsorption on Ag3 – namely, through the oxygen in the carboxylate group and through the nitrogen of the imidazole ring. The lower minimum energy of the latter indicates that adsorption via the nitrogen of the imidazole ring gives a more stable structure. The local minimum energies of the optimized structures are calculated as -1.49 x 104 eV and -2.69 x 104 eV for histidine and His-Ag3 respectively. After adsorption on silver, there is considerable reduction in the minimum energy confirming the enhanced stability of the molecule. The optimized structural parameters of the molecules are presented in Table 1.

Fig.1 Optimized Geometries of histidine and His-Ag3 at the DFT/CAM-B3LYP level of theory.


Page 6 of 25

Page 7 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


After adsorption on silver, the various bond lengths of imidazole ring and carboxylate moiety of histidine are significantly increased. An intramolecular hydrogen bond is identified between the amine and carboxylate group of the histidine molecule which is in keeping with the experimental results obtained by experimentalists.13 The N---H hydrogen bond gets stronger in the presence of the Ag3 cluster as is evident by the shortening of the N---H bond length subsequent to adsorption. Thus, nitrogen in the imidazole ring is the most likely site of adsorption to the silver cluster. Further, after adsorption, variations in the bond angles of histidine are also identified with the changes being more pronounced at the amine group and the imidazole ring of histidine. Almost all the dihedral angles of histidine are significantly altered after the adsorption process. The computed shortest distance between the histidine and Ag3 cluster is 2.176 Å. Changes in structural parameters can be associated with the electrostatic interactions between the silver cluster and histidine, mainly noticed at the imidazole moiety. Table 1 Structural Parameters of histidine and His-Ag3 Histidine His-Ag3 Bond Length (Å) C6-O18 1.336 1.358 C6=O20 1.207 1.234 C9-N10 1.380 1.404 N10-C12 1.310 1.333 C11-N13 1.375 1.391 O18-H19 0.984 1.004 Bond Angle ( ̊ ) H2-N1-C3 111.5 114.1 H2-N1-H17 107.7 110.8 C3-N1-H17 111.6 113.2 C3-C6-O18 113.7 112.3 N10-C9-C11 109.9 108.4 C9-N10-C12 105.9 107.3 N10-C12-N13 111.3 109.8 N13-C12-H15 122.7 124.3



3.2 XRD Analysis XRD measurements of His-Ag NPs were compared with the diffraction peak characteristics of metallic silver (JCPDS file no. 04-0783). Fig.2 shows that there are three prominent diffraction peaks are identified at 43.28, 68.11 and 73.34, which correspond respectively to the 111,200, 220 and 311 planes of fcc crystalline structure of metallic silver. The average crystallite size of NPs is calculated using Debye–Scherrer formula,

0.9/ cos

Where, λ is the wavelength of X-ray radiation (1.5406 Å), β and θ are the full width half maximum of the peak and Bragg angle respectively. The average crystallite size of the His-Ag NPs was found to be 63 nm.

Fig.2. XRD pattern of His-Ag NPs. 8 ACS Paragon Plus Environment

Page 8 of 25

Page 9 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


3.3 Molecular Electrostatic Potential The MEP is an important tool to understand the reactive behavior of several molecular systems interms of color gradient. In according to convention, the negative (electrophilic site) and positive (nucleophilic site) regions are indicated in red and blue respectively.22 For the investigated molecules, the reactive sites are predicted by the MEP drawn over the geometries with an isovalue of 0.004 a.u (Fig.3).

Fig.3 MEP plot of histidine and His-Ag3 with an isovalue of 0.004 a.u at DFT/CAM-B3LYP level of theory. It is evident from Fig.3, that the investigated molecule has possible electrophilic sites at N10 in the imidazole ring and oxygen atoms of the carboxylate moiety. The higher electrostatic positive region is identified around the amine group and N13-H16 of the imidazole ring. In order to analyze the interaction between histidine and silver, an Ag3 cluster was placed at each of the electrophilic and nucleophilic sites and optimized. The optimized structure revealed that the adsorption process takes place via the N10 of imidazole ring. This is in keeping with the experimental observations from the SERS.13 The MEP plot reveals that adsorption on silver induces a charge transfer from histidine to the metal cluster, which results in regions of negative 9 ACS Paragon Plus Environment


Page 10 of 25

potential around the cluster enhancing the polarization. The redistribution of the electron density and the enhancement in the polarization can be attributed by the ligand-metal interaction. The calculated MEP charges (Table 2) indicate that the hydrogen atoms of histidine are positively charged while higher negative charges are identified in the oxygen, nitrogen and carbon (5C,11C) atoms. In the case of His-Ag3, adsorption causes a redistribution of charges in histidine resulting in higher negative charges on the silver atoms and a higher positive charge on the nitrogen (N10) in the imidazole ring, confirming charge transfer from histidine to silver. Significant variations in the charge values correlate well with the changes in electron density distributions in the MEP plot. Table 2 MEP Charges of histidine and His-Ag3 Atoms N1 H2 C3 H4 C5 C6 H7 H8 C9 N10 C11

His -0.923 0.341 0.491 -0.038 -0.281 0.644 0.064 0.054 0.459 -0.629 -0.362

His-Ag3 -0.750 0.288 0.503 -0.091 -0.116 0.749 -0.036 -0.031 -0.026 0.042 -0.224

Atoms C12 N13 H14 H15 H16 H17 O18 H19 O20 Ag21 Ag22 Ag23

His 0.266 -0.250 0.229 0.066 0.302 0.350 -0.536 0.334 -0.577

His-Ag3 -0.050 -0.142 0.216 0.123 0.302 0.164 -0.691 0.381 -0.627 -0.107 -0.036 -0.073

3.4 NBO Analysis NBO provides a better understanding of the intra and inter molecular interactions and the charge transfers from the filled (bonding or lone pair) to the virtual orbital spaces (antibonding and Rydberg).34 The procedure uses mainly the information pertaining to the atomic orbital overlap and the density matrices. The orthogonalization of the atomic orbitals forms the natural atomic


Page 11 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


orbitals (NAOs) transformation, which is followed by a bond orbital transformation to obtain the NBOs.35

3.4.1 Second Order Perturbation Analysis In NBO analysis, second order perturbation theory helps to identify the role of intermolecular interactions. The occupied and unoccupied NBOs undergo a delocalization of electron density corresponding to a stabilizing donor–acceptor interaction, which can be estimated in terms of the second order perturbation interaction energy, E(2).34 Higher E(2) values correspond to intense interaction between the electron donors and acceptors within the entire system, which can be calculated as,36

, 2 ∆ −

Where qi is the orbital occupancy of the ith donor, Ej and Ei are the diagonal elements (orbital energies) and F(i,j) is the off diagonal NBO Fock matrix element. In the present work, NBO analysis on histidine and the His-Ag3 system identifies the most interacting orbitals and establishes the occurrence of strong intra- and inter molecular interactions (Table 3) Table 3 NBOs with the highest stabilization energy of histidine and His-Ag3. Histidine

His-Ag3

Donor

Acceptor

n N13 n O18 n N13 n O20 π N10 - C12 n O20 π C9 - C11

π* N10 - C12 π* C6 - O20 π*C9 - C11 σ* C6 - O18 π*C9 - C11 σ*C3 - C6 π* N10 - C12

E(2) Kcal/mol 65.96 54.05 41.84 39.20 28.34 23.26 23.06

Donor

Acceptor

n O20 n N13

π* C6 - O18 π* N10 - C12 π* C9 - C11 n* Ag 21 σ* C6 - O20 σ* C6 - O18 π*C9 - C11

n N10 n O20 π N10 - C12


E(2) Kcal/mol 35.32 39.91 19.31 16.57 13.87 12.57 12.55


n N1 n N10

σ*O18 - H19 σ*C12 - N13

15.99 9.69

n O20 n N1

Page 12 of 25

σ* C3 – C6 σ* O18 - H19

10.18 9.71

In the case of histidine, the highest value for E(2) originates from the lone pair electrons of the donor atom nitrogen (N13) which shares its stabilization energy with the antibonding orbitals of the atoms in the imidazole ring. In a similar way, the lone pair electrons on oxygen (O18), with a high E(2), shares its stabilization energy with the antibonding orbitals of the atoms in the carboxylate moiety. However, in the case of His-Ag3, in addition to these interactions, overlap of orbitals between silver and histidine are also identified. This correlate well with the MEP charges and the redistribution of electron density in the plot of MEP. 3.5 Optical Properties Based on finite field approach,37 the linear and nonlinear optical parameters (dipole moment, polarizability and first hyperpolarizability) of histidine and His-Ag3 molecules were calculated. When an external electric field (E) is applied, the energy of the system varies as a function of the electric field. First hyperpolarizability is a third rank tensor that can be described by a 3x3x3 matrix with 27 components. This can be reduced to 10 components because of Kleinman symmetry.38 The 3x3x3 matrix subsequently can be written in the lower tetrahedral format. The energy of an uncharged molecule under a weak, general electric field can be expressed by a Buckingham type expansion,

− − 1⁄2 − 1⁄6 − ⋯

where, E is the energy of the molecule under the electric field F, E0 is the energy of the unperturbed free molecule, Fi is the vector component of the electric field in the ith direction, µi, αij, βijk are the dipole moment, polarizability and the first hyperpolarizability respectively, with i,j and k denoting the indices of the Cartesian axes. The total static dipole moment µ, the mean


Page 13 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


polarizability α0 and the mean first hyperpolarizability βtot using the x,y,z components are defined as,34 " + $ + % &⁄

"" + $$ + %% 3

()( " + $ + % &⁄ and,

" """ + "$$ + "%%

$ $$$ + ""$ + $%% % %%% + ""% + $

%$Dipole moment and polarizability are important parameters that play a vital role in interpreting molecular interactions. A higher dipole moment indicates a more reactive system.34 Comparing the calculated dipole moment of histidine (1.032 Debye) with that of His-Ag3 (2.116 Debye), His-Ag3 is identified to have larger dipole moment indicating increased interactions between the molecules.

Interestingly, the calculated optical parameters of histidine are

significantly higher after adsorption on the silver cluster (Table 4).

Results show that the

hyperpolarizability of His-Ag3 is nearly 101 times that of urea (0.4125 X 10-30 esu), suggesting this material as a potential candidate for NLO devices.34

After incorporating Ag3 to histidine,

there is a reduction in the HOMO–LUMO energy gap leading to an enhancement of the first hyperpolarizability making His-Ag3 a potential system for NLO devices. Table 4 Calculated Optical properties of histidine and His-Ag3 at the CAM-B3LYP level of theory. Dipole Moment (Debye) & Polarizability

Histidine

His-Ag3

Hyperpolarizability Parameters Histidine (a.u)


His-Ag3


Page 14 of 25

Parameters (a.u) µx µy µz µtot αxx αxy αyy αxz αyz αzz α0 (x 10-23esu)

0.060 1.028 -0.058

0.134 2.102 -0.204

1.032 107.618 6.838 100.858 -14.858 -3.078 74.819

2.116

310.362 -33.985 271.720 -0.214 -33.464 155.850

1.399

3.645

βxxx βxxy βxyy βyyy βxxz βxyz βyyz βxzz βyzz βzzz

-20.856 26.912 41.842 56.150 31.389 -12.882 -17.942 -17.714 23.525 28.521

-4301.947 1425.067 -139.018 -1274.229 -83.663 -188.676 124.557 -349.995 -271.975 223.800

βtot (x 10-30esu)

0.990

41.467

3.5.1 Z-Scan Studies The open aperture Z-scan data and the nonlinear transmission curve extracted from the Z-scan data are shown in Fig.4. The measured data (open circles) fits well to the nonlinear transmission equation for two-photon absorption with weak absorption saturation. The result obtained is similar to that obtained for compounds like Ninhydrin

39

and Rhodamine B.40 The presence of

saturable absorption (SA) and two-photon absorption (TPA) modifies, the intensity dependent effective nonlinear absorption coefficient α(I) to, ∝ +=

∝,

&-

. ./

+ 011 +

where, α0 is the unsaturated linear absorption coefficient at the excitation wavelength, I is the laser intensity, Is is the saturation intensity and βeff is the effective TPA coefficient. The best-fit values of Is and βeff can be found by a numerical fit of the data to the corresponding propagation equation given by, 41 2+ − 45 6 7 + 011 +8 + 23 1+ 6/


Page 15 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Where, x indicates the propagation distance within the sample. The calculated values of TPA coefficient and saturation intensity are 6x10-12 m/W and 2x1013 W/m2 respectively. Prominent absorption saturation is known to occur in pristine noble metal colloidal solutions when excited near the surface plasmon resonance.42,43 It is interesting to note that in the present case, the saturation is quite subdued due to the adsorption of histidine on silver, which results in a corresponding decrement in the plasmon intensity13 resulting in an enhancement of the optical limiting effect. In comparison to the typical excited state lifetimes, the 5 ns laser pulses are relatively longer. The excited state contribution to the observed nonlinear absorption is therefore considerable. A consequence of this is that the absorption is not a genuine TPA.8 The sample recovers its linear transmission property once the intense laser

beam is withdrawn as

indicated by the symmetrical nature of the Z scan. This confirms the photostability of the His-Ag NPs.11 The Z-Scan measurements, substantiated by theoretical calculations of a high first hyperpolarizability indicate that His-Ag can find application in efficient optical limiting devices protecting sensitive optical instruments and the human eye from intense light beams.



Fig.4 Open aperture Z-scan curves of His-Ag NPs 3.6 UV-Vis Spectra In order to understand the electronic transitions of the His-Ag3, time-dependent density functional (TDDFT) calculations on gas phase were performed. The computed absorption wavelength for Histidine is obtained at 201 nm. The experimental value of this peak which we obtained from the UV data of the recorded spectrum of histidine is 269 nm which compares well with literature.44 The discrepancy between the theoretical and experimental values can be attributed to the fact that the theoretical analysis is for a single molecule in the gas phase. The calculated absorption wavelengths (λ), oscillator strengths (f) and the major transition contributions are tabulated in Table 5. As can be identified from the theoretically simulated spectra and its corresponding transition (Fig.5), the most intense electronic transitions are at 301 nm and 409 nm for His-Ag3. Further, the theoretical spectrum derived using His-Ag3 has matched with the experimental absorption spectrum of histidine adsorbed on silver, where the 16 ACS Paragon Plus Environment

Page 16 of 25

Page 17 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


peak was identified at 392 nm by our group.13 This theoretical peak corresponds to the transition associated with the greater oscillator strength (probability of transition).

Fig.5.UV-Vis absorption spectrum of His-Ag3 and its corresponding FMO transitions. Table 5. Absorption wavelength λ (nm), oscillator strengths (f) and major transitions of His-Ag3

301

Oscillator Strength (f) 0.127

HOMO-2 to LUMO

409

0.360

HOMO to LUMO

Wavelength(nm)

Major Transitions

Based on the difference between frontier orbital energies, the chemical reactivity and optical polarizability of the molecule can be analyzed – the lower energy gap, the greater reactivity of the system.45 As seen from Fig.5, In the His-Ag3, HOMO is chiefly located around silver atoms. The LUMO of His-Ag3 is extended to imidazole ring of the histidine molecule. Interestingly, the HOMO-LUMO gap of His-Ag3 (3.924 eV) is much lower as compared to that of histidine (5.796 eV). Reduction in HOMO-LUMO gap enhances the photoconductivity suggesting its potential applications in optoelectronic materials.46 17 ACS Paragon Plus Environment


3.7 Raman Spectral Analysis In order to identify the nature of interaction between histidine and silver cluster, comparison between the theoretical and experimental Raman vibrational modes are analyzed (Fig.6). Theoretically derived frequencies of histidine and His-Ag3 are in quite good agreement with the frequencies reported in nRS and SERS by our group.13 The variations noticed in the theoretically calculated and the experimentally observed frequencies can be attributed to the differences due to the isolated molecule considered in gas phase for the theoretical calculation. An intense peak noticed at 240 cm-1 in the theoretical spectrum of His-Ag3 which is absent in the spectrum of histidine, pertain to the Ag-N stretching vibration is suggestive of a strong interaction between histidine and silver through the nitrogen atom in the imidazole ring. This correlates well with the peak noticed at 236 cm-1 in experimental SERS13 which is absent in the case of normal Raman spectra of histidine and is attributed to the attachment of the Ag nanoparticle with histidine through the imidazole group. Another noteworthy aspect is the downshifting of C-N stretching vibrational mode from a weak peak at 1004 cm-1 (His) to a strong peak at 960 cm-1 (His-Ag3). In the experimental SERS, a peak at 1004 cm-1 is not noticeable but a well enhanced C-N stretching vibration is identified at 953 cm-1. The large red shift of this vibration indicates that the nitrogen atom in the imidazole ring is attached to the surface of silver and can be correlated to the transfer of electron density from histidine to silver. This correlates well with the molecular orbitals, NBO and MEP plot.


Page 18 of 25

Page 19 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Fig.6 Theoretical Raman Spectra of histidine and His-Ag3 Conclusions Electronic and nonlinear optical properties of the interactions between histidine and silver are carried out using DFT and TDDFT methods and open aperture Z-scan technique. From the plot of MEP surface, MEP charges, NBO analysis and the reduction in the bandgap, it is established that there is a process of charge redistribution between silver and histidine. Vibrational Raman analysis revealed a downshifting of C-N stretching confirming the process of adsorption between the nitrogen atom of imidazole ring and valance orbitals of silver. This correlates very well with the shifting of molecular orbitals, MEP Plot, MEP charges and the NBO analysis. The simulated UV- Vis spectrum correlates well with the experimental result. Theoretical NLO studies reveal that His-Ag3 has a larger first hyperpolarizability value as compared to that of urea and the Zscan studies predicts the enhanced optical limiting behavior of His-Ag, confirming it to be well suited in the design and development of NLO materials. 19 ACS Paragon Plus Environment


Acknowledgements The authors thank Dr. Reji Philip, Light and Matter Physics Group, Raman Research Institute, Bangalore, India for the use of the Z-scan facilities in his lab. The authors also thank Mr.Alcides Pinto Simão, AMRSC, University of Coimbra, Portugal for several meaningful discussions and for help in the theoretical calculations. The present work has been carried out without the support of any funding agency.

References (1)

Raneesh,B.; Rejeena,I.; Rehana,P.U.; Radhakrishnan,P.; Saha,A.; Kalarikkal,N Nonlinear Optical Absorption Studies of Sol–Gel Derived Yttrium Iron Garnet (Y3Fe5O12) Nanoparticles by Z-Scan Technique. Ceram. Int. 2012, 38, 1823–1826.

(2)

Sajan, D.; Chaitanya, K.; Safakath,K.; Philip, R.; Suthan, T.; Rajesh,N.P. ThreePhoton Absorption and Vibrational Spectroscopic Study of 2-Methylamino-5Chlorobenzophenone. Spectrochim. Acta Part A. 2013, 106, 253–261.

(3)

Woldu, T.; Raneesh, B.; Sreekanth, P.; Reddy, M.V.R.; Philip, R.; Kalarikkal, N. Size Dependent Nonlinear Optical Absorption in BaTiO3 Nanoparticles. Chem. Phys. Lett. 2015, 625, 58–63.

(4)

Reshak, A.H.; Kamarudin, H.; Kityk, I. V.; Auluck, S., Dispersion of Linear, Nonlinear Optical Susceptibilities and Hyperpolarizability of C11H8N2O (o Methoxydicyanovinylbenzene) Crystals. J. Phys. Chem. B, 2012, 116, 13338−13343.

(5)

Reshak, A. H.; Kamarudin, H.; Auluck S., Acentric Nonlinear Optical 2,4Dihydroxyl Hydrazone Isomorphic Crystals with Large Linear, Nonlinear Optical Susceptibilities and Hyperpolarizability, J. Phys. Chem. B, 2012, 116, 4677−4683.

(6)

Reshak, A.H.; Chen, X.; Auluck, S.; Kamarudin, H.; Chyský, J.; Wojciechowski, A.; Kityk, I.V., Linear and Nonlinear Optical Susceptibilities and the Hyperpolarizability of Borate LiBaB9O15 Single-Crystal: Theory and Experiment, J. Phys. Chem. B, 2013, 117, 14141−14150.


Page 20 of 25

Page 21 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(7)

Thomas, J.J.; Krishnan, S.; Sridharan, K.; Philip, R.; Kalarikkal, N.; A Comparative Study on the Optical Limiting Properties of Different Nano Spinel Ferrites with ZScan Technique, Mater. Res. Bull. 2012, 47,1855–1860.

(8)

Nidya, M.; Umadevi, M.; Sankar, P.; Philip, R.; Rajkumar, B.J.M. L-Phenylalanine Functionalized

Silver

Nanoparticles:

Photocatalytic

and

Nonlinear

Optical

Applications. Opt. Mater. 2015, 42, 152–159. (9)

Hussain, J.I.; Kumar, S.; Hashmi, A.A; Khan, Z. Silver Nanoparticles: Preparation, Characterization, and Kinetics. Adv. Mater. Lett. 2011, 2,188–194.

(10)

Huang, T.; Hao, Z.; Gong, H.; Liu, Z.; Xiaob, S.; Li, S.; Zhai, Y.; You, S.; Wang, Q.; Qin, J. Third-order Nonlinear Optical Properties of a New Copper Coordination Compound: A Promising Candidate for All-optical Switching. Chem. Phys. Lett. 2008, 451, 213–217.

(11)

Philip, R.; Kumar, G.R.; Sandhyarani, N.; Pradeep, T.

Picosecond Optical

Nonlinearity

Gold-Silver

in

Monolayer-protected

Gold,

Silver

and

Alloy

Nanoclusters. Phys. Rev. B 2000, 62,13160–13166. (12)

Caroline, M.L.; Sankar, R.; Indirani, R.M.; Vasudevan, S. Growth, Optical, Thermal and Dielectric Studies of an Amino Acid Organic Nonlinear Optical Material: LAlanine. Mater. Chem. Phys. 2009,114,490–494.

(13)

Nidya, M.; Umadevi, M.; Rajkumar, B.J.M. Optical and Morphological Studies of LHistidine Functionalised Silver Nanoparticles Synthesised by Two Different Methods. J. Exp. Nanosci. 2015,10,167–180.

(14)

Pakiari, A.H.; Jamshidi, Z.

Interaction of Amino Acids with Gold and Silver

Clusters, J. Phys. Chem. A 2007,111,4391-4396. (15)

Compagnon,I.; Tabarin T.; , Antoine, R.; Broyer, M.; Dugourd, P.; Mitrić, R.; Petersen, J.; Koutecký,V.B., Spectroscopy of Isolated, Mass-Selected TryptophanAg3 Complexes: A Model for Photo Absorption Enhancement in NanoparticleBiomolecule Hybrid Systems, J. Chem. Phys. 2006, 125, 164326.

(16)

Koutecky, V.B.; Kulesza, A.; Gell, L.; Mitric, R.; Antonine, R.; Bertorelle, F.; Hamouda, R.; Rayane, D.; Broyer, M.; Tabarin, T.; Dugourd, P. Silver ClusterBiomolecule Hybrids: From Basic Towards Sensors.



(17)

Page 22 of 25

Mitrić, R.; Petersen, J.; Kulesza, A.; Koutecký, V.B.; Tabarin, T.; Compagnon, I.; Antoine, R.; Broyer, M.; Dugourd, P. Photoabsorption and Photofragmentation of Isolated Cationic Silver Cluster–Tryptophan Hybrid Systems, J. Chem. Phys. 2007, 127, 134301.

(18)

Liu, Z.; Xing, Z.; Zu, Y.; Tan, S.; Zhao, L.; Zhou, Z.; Sun, T., Synthesis and Characterization of L-Histidine Capped Silver Nanoparticles, Mater.Sci.C. 2012, 32,811–816.

(19)

Sanader, Z.; Mitrić, R.; Koutecký, V.B.; Bellina, B.; Antoine, R.; Dugourd, P. The Nature of Electronic Excitations at the Metal–Bioorganic Interface Illustrated on Histidine–Silver Hybrids. Phys. Chem. Chem. Phys. 2014, 16,1257-1261.

(20)

Siddiqui, S.A.; Rasheed, T.; Faisal, M.; Pandey, A.K.; Khan, S.B.

Electronic

Structure, Nonlinear Optical Properties, and Vibrational Analysis of Gemifloxacin by Density Functional Theory. Spectrosc. Int. J. 2012, 27,185–206. (21)

Hohenberg, H.P. ; Kohn, W., Inhomogeneous Electron Gas, Phys. Rev. B. 1964,136, 864-871.

(22)

Fleming, G.D.; Golsio, I.; Aracena, A.; Celis, F.; Vera, L.; Koch, R.; Vallette, M.C., Theoretical Surface-Enhanced Raman Spectra Study of Substituted Benzenes I. Density Functional Theoretical SERS Modelling of Benzene and Benzonitrile, Spectrochimica Acta Part A, 2008, 71,1049–1055.

(23)

Reshak, A.H.; Stys, D.; Auluck, S.; Kityk, I.V., Dispersion of Linear and Nonlinear Optical Susceptibilities and the Hyperpolarizability of 3-methyl-4-phenyl-5-(2pyridyl)-1,2,4-triazole, Phys. Chem. Chem. Phys., 2011,13,2945–2952.

(24)

Reshak, A. H., Ab Initio Study of TaON, an Active Photocatalyst Under Visible Light Irradiation, Phys. Chem. Chem. Phys. 2014, 16,10558-10565.

(25)

Liu, W.L.; Wang, Z.G.; Zheng, Z.R.; Li, A.H.; Su, W.H. Effect of β-Ring Rotation on the Structures and Vibrational Spectra of β-Carotene: Density Functional Theory Analysis. J. Phys. Chem. A. 2008, 112, 10580–10585.

(26)

Felscia, U.R.; Rajkumar, B.J.M.; Sankar, P.; Philip, R.; Mary, M.B.; Optical Nonlinearity and Charge Transfer Analysis of Pyrene Adsorbed on Silver: Computational and Experimental Investigations. Spectrochim. Acta. Part A. 2017,184,286-293. 22 ACS Paragon Plus Environment

Page 23 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(27)

Huang, M.J.; Watts, J.D. Theoretical Study of Triatomic Silver (Ag3) and its Ions with Coupled-Cluster Methods and Correlation-Consistent Basis Sets. Phys. Chem. Chem. Phys. 2012,14,6849–6855.

(28)

Cai,Z.L.;,Crossley,M.J.;Reimers,J.R.;Kobayashi,R.;Amos,R.D., Density Functional Theory for Charge Transfer: The Nature of the N-Bands of Porphyrins and Chlorophylls Revealed Through CAM-B3LYP, CASPT2, and SAC-CI Calculations, J. Phys. Chem. B. 2006,110,15624-15632.

(29)

Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A. et al, Gaussian 09, Revision D.01. Wallingford CT, 2010.

(30)

Clark, T.; Chandrasekhar, J.; Spitznagel, G.W.; Schleyer, P.V.R. Efficient Diffuse Function‐Augmented Basis Sets for Anion Calculations. III. The 3‐21+ G Basis Set for First‐row Elements, Li–F, J. Comput. Chem. 1983, 4,294-301.

(31)

Frisch, M.J.; Pople, J.A.; Binkley, J.S. Self Consistent Molecular Orbital Methods 25. Supplementary Functions for Gaussian Basis Sets. J. Chem. Phys. 1984, 80, 32653269.

(32)

Buhl, M.; Reimann,C.; Pantazis, D.A.; Bredow, T.; Nees, F. Geometries of ThirdRow Transition-Metal Complexes from Density Functional Theory, J.Chem.Theory Comput. 2008, 4, 1449–1459.

(33)

Shiek-Bahae, M.; Said, A.A.; Wei, T.H.; Hagan, D. J.; Stryland, E.W.V. Sensitive Measurement of Optical Nonlinearities Using a Single Beam. IEEE J. Quantum Electron. 1990, 26,760-769.

(34)

Esme, A.; Sagdinc, S.G. The Vibrational Studies and Theoretical Investigation of Structure, Electronic and Non-linear Optical Properties of Sudan III [1-{[4(phenylazo) phenyl] azo}-2-naphthalenol], J. Mol. Struct. 2013,1048,185-195.

(35)

Reed, A.E.; Weinhold, F.; Curtiss, L.A.; Pochatko, D.J.

Natural Bond Orbital

Analysis of Molecular Interactions: Theoretical Studies of Binary Complexes of HF, H2O, NH3, N2, O2, F2, CO, and CO2 with HF, H2O, and NH3, J. Chem. Phys. 1986, 84, 5687–5705. (36)

Choudhary, N.; Agarwal, P.; Gupta, A.; Tandon, P. Quantum Chemical Calculations of Conformation, Vibrational Spectroscopic, Electronic, NBO and Thermodynamic 23 ACS Paragon Plus Environment


Properties of 2, 2-dichloro-N-(2, 3-dichlorophenyl) acetamide and 2, 2-dichloro-N(2, 3-dichlorophenyl) acetamide. Comp. Theor. Chem. 2014, 1032, 27-41. (37)

Cohen, H.D.; Roothaan, C. C. J.; Electric Dipole Polarizability of Atoms by the Hartree—Fock Method. I. Theory for Closed Shell Systems, J.Chem.Phys. 1965, 43, 34-39.

(38)

Kleinman, D.A. Nonlinear Dielectric Polarization in Optical Media. Phys Rev. 1962, 126, 1977–1979.

(39)

Sajan, D.; Devi, T.U.; Safakath, K.; Philip, R.; Nemec, I.; Karabacak, M. Ultrafast Optical Nonlinearity, Electronic Absorption, Vibrational Spectra and Solvent Effect Studies of Ninhydrin. Spectrochim. Acta. Part A 2013,109,331–343.

(40)

Srinivas, N.K.M.N; Rao, S.V.; Rao, D.N.; Saturable and Reverse Saturable Absorption of Rhodamine B in Methanol and Water. J. Opt. Soc. Am. B 2003, 20, 2470-2479.

(41)

Sutherland, R.L. Handbook of Nonlinear Optics. Marcel Dekker, New York, 1996.

(42)

Philip, R.; Chantharasupawong,P.; Qian, H.; Jin, R.; Thomas, J. Evolution of Nonlinear Optical Properties: From Gold Atomic Clusters to Plasmonic Nanocrystals. Nano. Lett. 2012, 12, 4661-4667.

(43)

Karthikeyan, B.; Anija, M.; Philip, R. In situ Synthesis and Nonlinear Optical Properties of Au:Ag Nanocomposite Polymer Films. Appl. Phys. Lett. 2006, 88, 053104.

(44)

Fasman, G. D., Handbook of Biochemistry and Molecular Biology, 3rd Edition, Proteins, Volume I, pp. 183-203, CRC Press, Cleveland, Ohio,1976.

(45)

Sheela, N.R.; Muthu, S.; Sampathkrishnan, S.; Molecular Orbital Studies (Hardness, Chemical Potential and Electrophilicity), Vibrational Investigation and Theoretical NBO Analysis of 4-40-(1H-1,2,4-triazol-1-yl methylene) Dibenzonitrile Based on Abinitio and DFT Methods. Spectrochim. Acta. Part A, 2014, 120, 237–251.

(46)

Toyoda, K.; Hamada, I.; Lee, K.; Yanagisawa, S.; Morikawa, Y. Density Functional Theoretical Study of Pentacene Noble Metal Interfaces with Van Der Waals Corrections: Vacuum Level Shifts and Electronic Structures. J. Chem. Phys. 2010, 132, 134703.


Page 24 of 25

Page 25 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TOC Graphic

ACS Paragon Plus Environment

A Theoretical and Experimental Approach U.Reeta Felscia

Recommend Documents