First principles study of the n-channel thiophene based heterocyclic chalcones

Accepted Manuscript Title: First principles study of the n-channel thiophene based heterocyclic chalcones Authors: Irfan Ahmad, Abdullah G. Al-Sehemi, Aijaz Rasool Chaudhry, Shabbir Muhammad PII: DOI: Reference:

S0030-4026(17)30336-4 http://dx.doi.org/doi:10.1016/j.ijleo.2017.03.070 IJLEO 58993

To appear in: Received date: Accepted date:

16-12-2016 17-3-2017

Please cite this article as: {http://dx.doi.org/ 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.

First principles study of the n-channel thiophene based heterocyclic chalcones

Ahmad Irfana,b, Abdullah G. Al-Sehemia,b, Aijaz Rasool Chaudhryb,c, Shabbir Muhammad b,c

a

Department of Chemistry, Faculty of Science, King Khalid University, Abha 61413,

P.O. Box 9004, Saudi Arabia b

Research Center for Advanced Materials Science, King Khalid University, Abha 61413,

P.O. Box 9004, Saudi Arabia c

Department of Physics, Faculty of Science, King Khalid University, Abha 61413, P.O.

Box 9004, Saudi Arabia



Corresponding author: Ahmad Irfan E-mail: [email protected] Tel.:0096672418632 Fax:0096672418426

1

GRAPHICAL ABSTRACT

Abstract In present investigation, we limelight the key electro-optical properties including electronic structure, optical, charge transport and nonlinear optical properties of two novel chalcone derivatives ((E)-1-(2,5-Dimethyl-3-thienyl)-3-(2-hydroxyphenyl)prop-2en-1-one

(chalc1)

and

(2E)-3-[4-(Dimethylamino)phenyl]-1-(2,5-dimethyl-3-

thienyl)prop-2-en-1-one (chalc2). The ground (S0) and excited state (S1) geometries are optimized using B3LYP/6-31G** and TD-B3LYP/6-31G**

levels

of theory,

respectively, which show reasonably good agreement to the available experimental data of respective crystal structures. A comprehensive electronic structure-property relationship is elucidated through the prism of frontier molecular orbitals (FMOs), orbital energy gap (Eg) analysis, density of states (DOS), as well as molecular electrostatic potential (MEP) plots. The effect of electron donating groups (-OH and -N(CH3)2) is investigated on the absorption and emission wavelengths, ionization potentials (IP),

2

electron affinities (EA), reorganization energies. Finally, the n-channel charge transport nature of these compounds is considered on the bases of our calculated transfer integrals and intrinsic mobilities.

Keywords: Semiconductors; Ab initio calculations; Electronic properties; Transport properties; Nonlinear optical properties

1. Introduction The chalcones possess divers electro-optical properties which make them suitable for biological active compounds [1], sensors [2] and semiconducting devices such as organic light emitting diodes (OLEDs), display materials, thin film field effect transistors (TF-FET) [3], solar cells [4] and photo-reaction agents (absorb energy in the form of light to initiate the reaction) [5]. Moreover, thiophene based materials are auspicious because of the semiconducting nature [6], nonlinear optical behavior [7] and efficient electron transport properties [8]. Previously, thiophene based heterocyclic chalcones showed improved properties [9]. In the present study, we selected two chalcone derivatives with the aim to investigate their structural, electronic, optical (absorption (λabs) and fluorescence (λfl) spectra), charge transport (ionization potentials (IPs), electron affinities (EAs), hole/electron reorganization energies (λh/λe.), hole/electron transfer integrals (th/te), hole/electron intrinsic mobilities (μh/μe) and nonlinear optical (NLO) properties. To the best of our knowledge, there is no such investigation for these recently synthesized chalcone derivatives. The structural, electro-optical, charge transport and NLO of these chalcone derivatives, including (E)-1-(2,5-Dimethyl-3-thienyl)-3-(2-hydroxyphenyl)prop2-en-1-one (hereafter refer as chalc1) [10], and (2E)-3-[4-(Dimethylamino)phenyl]-1(2,5-dimethyl-3-thienyl)prop-2-en-1-one (hereafter refer as chalc2), will be studied (see 3

Fig. 1) [11]. The paper is organized as follow: after introduction in section 1, the section 2 presents a brief detail of the Density Functional Theory (DFT) and Time Dependent Density Functional Theory (TDDFT) methods, including the rationale for choosing the hybrid functional and the basis set. Section 3 contains the frontier molecular orbital (FMO) plots, electronic, optical, NLO and charge transport properties; while the section 4 provides the major conclusions of the present investigation.

2. Computational details In several previous studies, it has been seen that among the standard DFT [12-18] functionals, the B3LYP provides the good results for geometry optimizations of medium and large size molecules [19-23]. Over the time, the B3LYP was used many times to predict and to calculate the properties of interests, which were found in good agreement with experimental data [24]. The B3LYP hybrid functional along with the 6-31G** basis set was used by Preat et al. to optimize the geometries at the ground state (S0) and they concluded that this level of theory [25, 26] is suitable for small organic molecules. Earlier, Huong et al. testified that the B3LYP/6-31G** level of theory is good to reproduce the experimental crystal structure data [27]. Moreover, this level is rational to shed some light on the electronic and charge transport properties [27]. The maximum absorption wavelengths of numerous organic dyes were computed with an average deviation close to 0.20 eV with TD-B3LYP functional [28]. In the present study, B3LYP/6-31G** level of theory was adopted to optimize the S0 geometries, whereas the excited state (S1) geometries were optimized at TD-DFT [29] using the TD/B3LYP/631G** level. Then the same TD-DFT level was applied to evaluate the absorption and emission spectra which already verified to be a proficient method [30]. The charge transfer proficiency has a vital character within the organic layers. The organic-organic interfaces can be used to refine the charge transfer, while in the bulk, the recombination 4

processes are favored by the high charge mobilities [31]. The Marcus theory eq. 1 described the charge transfer rate [32]. W=t2/h(π/λkB)1/2 exp(- λ/4kBT)

(1)

The self-exchange electron transfer rates and charge mobility can be determined by the two major parameters; i) the transfer integrals t among contiguous molecules, that ought be maximized; and ii) the reorganization energy (λ), it should be small for substantial charge transfer [33]. The computational details about the IP, EA, λ, transfer integral and intrinsic mobility calculations can be found in supporting information. All these quantum chemical calculations were performed by using Gaussian09 package [34]. The total/partial density of states (TDOS/PDOS) were computed by GGA (generalized gradient approximation) at pw91 functional [35] and DNP basis set [36] via DMol3 code [37] employed through the Accelrys Materials Studio package [38]. 3. Results and discussion 3.1. Ground and excited state geometries The important geometrical parameters, i.e., bond lengths (Å) and bond angles (degrees, 0) of two chalcone derivatives Chalc1 and Chalc2 at the S0 at B3LYP/6-31G** and S1 at TD-B3LYP/6-31G** level of theory have been tabulated in Table 1 (see numbering scheme Fig. 1). Here, the calculated bond lengths and bond angles at the S0 have been compared with the experimental crystal structure data. We observed that the B3LYP/6-31G** level is sound to reproduce the crystal structure geometrical parameters except the S1-C12 (S1-C14) bond lengths which are being overestimated 0.029 (0.029), 0.042 (0.038) Å in Chalc1 and Chalc2, respectively and C9-O2 underestimated 0.029 Å in 2, [10, 11]. These over- and under-estimations in the bond lengths are because of the geometrical parameters calculated in the present study are in gas phase while the crystal structural parameters are in the solid phase. In Chalc1, maximum lengthening from the S0 to S1 has been observed for C9-O2 bond length, i.e., 0.080 Å. In Chalc2, maximum 5

lengthening from the S0 to S1 has been observed for S1-C12 and C9-O2 bond lengths, i.e., 0.026 and 0.053 Å. The C10-C9-O2 bond angle decrease 5.170 from the S0 to S1 in Chalc1. The C10-C9-C8 bond angle increases 5.290 and 9.140 from the S0 to S1 in Chalc1 and Chalc2, respectively. Usually, the S0 geometrical parameters of both chalcone derivatives are alike while the variation has been discerned at the S1. 3.2. Electro-optical properties In Figs. 2 and 3, charge density distribution pattern of the major frontier molecular orbitals for the S0 and S1 involved in the absorption and emission spectral wavelengths have been illustrated. The major transitions in the absorption spectra of Chalc1 (Chalc2) are H → L and H-1 → L (H → L and H-3 → L). At S0, HOMO-1 and HOMO of Chalc1 are delocalized on the entire structure of molecule. The oxygen of keto group is taking part in the formation of HOMO-1 while no charge is localized on oxygen of keto group in HOMO. Mainly LUMO is localized at 3-(2-hydroxyphenyl)prop-2-en-1one moiety. Comprehensive intra-molecular charge transport (ICT) has been observed from thiophene of the HOMO-1/HOMO to the 3-(2-hydroxyphenyl)prop-2-en-1-one unit. The HOMO-3 of Chalc2 is distributed on the thiophene and oxygen of keto group. The HOMO and LUMO is distributed on the phenyl]-prop-2-en-1-one moiety and nitrogen of amino group. A significant ICT was observed from thiophene (HOMO-3) to the rest of the ring (LUMO). The major transitions in the emission spectra of Chalc1 (Chalc2) are L → H and L → H-1 (L → H-2 and L → H-1). At S1, the HOMO-1 and HOMO of Chalc1 are distributed on the entire system but HOMO charge density on phenyl group is less than the HOMO-1. The charge distribution style of S1 is almost similar to that of S0. In Chalc2, HOMO-2 is distributed on 2,5-dimethyl-3-thienyl moiety and oxygen of keto group, HOMO-1 at keto group, HOMO and LUMO at (amino)phenyl]-prop-2-en-1-one moiety.

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The calculated S0 and S1 HOMO energies (EHOMO), LUMO energies (ELUMO) and HOMO-LUMO energy gaps (Eg) of chalcone compounds at B3LYP/6-31G** and TDB3LYP/6-31G** levels of theory, respectively are presented in Table 2. The tendency in the energy level of the EHOMO and ELUMO is as follow: Chalc2 > Chalc1 for the S0. The trend in the energy level of the EHOMO and ELUMO is as Chalc2 > Chalc1 and Chalc1 > Chalc2 for the S1, respectively leading to the Eg Chalc2 < Chalc1. The smaller energy gap of Chalc2 at S0 would ultimately promote the red shift in the absorption and emission spectra in Chalc2 as compared to the Chalc1. In the present work, the electron injection energy of Chalc1 and Chalc2 has been calculated and compared with each other. The electron injection energy can be evaluated as (=−ELUMO − (−work function of metal)). Here, the work function of aluminum, i.e., −4.08 eV has been taken. The electron injection energy has been found 2.30 eV (=−1.78 − (−4.08)), and 2.52 eV (=−1.56 − (−4.08)) from the Chalc1 and Chalc2 to aluminum electrode, respectively. It can be found from above results that lower energy, i.e., 2.30 eV is needed for Chalc1 to overcome the injection barrier as compared to the Chalc2, i.e., 2.52. Thus it is expected that Chalc1 might be better electron charge transport material than its other counterpart. Previous studies showed that if the ELUMO would be smaller then injected electron might be thermodynamically more stable. In the present case, the ELUMO of Chalc1 is low-lying than Chalc2 revealing that it would be thermodynamically more stable and charge transport can’t be quenched by losing the electron. Furthermore, hole injection energy of Chalc1 and Chalc2 has also been anticipated, i.e., 1.81 eV (=−4.08 − (−5.89)) and 1.04 eV (=−4.08 − (−5.12)) from Chalc1 and Chalc2 to the aluminum electrode, respectively.

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The oscillator strengths (f), absorption wavelengths (λa), emission wavelengths (λe) and major transitions elaborated in the λa and λe at TD-B3LYP/6-31G** level of theory have been tabulated in Table 3. The maximum λa of Chalc1 was perceived at 321 nm with major transition H-1 → L and second peak at 342 nm (f=0.181) with major transition H → L. The maximum λa of Chalc2 was noticed at 371 nm with major transition H → L and second peak at 272 nm (f=0.188) with major transition H-3 → L. It can be understood that substitution of –N(CH3)2 at para position (Chalc2) would lead the red shift in λa, i.e., 50 nm compared to the Chalc1 (containing –OH at ortho position). The maximum λe of Chalc1 was detected at 344 nm with major transition L → H-1 and second peak at 390 nm (f=0.111) with major transition L → H. The maximum λa of Chalc2 was remarked at 370 nm with major transition L → H-1 and second peak at 453 nm (f=0.010) with major transition L → H-2. It can be realized that substitution of – N(CH3)2 at para position (Chalc2) would lead the red shift in λa and λe i.e., 50 and 26 nm, respectively compared to the Chalc1 (containing –OH at ortho position). It is found that – N(CH3)2 at para position would tune the photophysical properties towards red shift.

3.3. Charge transport parameters 3.3.1. Ionization potential, electron affinity and reorganization energies The IP and EA are two important chemical descriptors to apprehend the charge transport nature of the organic semiconductor material which play noteworthy role to understand the charge injection. The smaller IP and bigger EA values ultimately reduce the hole and electron injection barrier of the materials which would lead to the effective hole and electron injection ability, respectively. The IPa, IPv EAa and EAv of Chalc1 and Chalc2 have been presented in Table 4. The IPa/IPv of Chalc2 decreases 0.73/0.75 eV than the Chalc1. The λh and λe of studied chalcone derivatives Chalc1 and Chalc2 were presented in Table 4. The λh of Chalc1 and Chalc2 are smaller than the λe. The λ values 8

are illuminating that both of the compounds might be hole transport candidates but as this is not the only one parameter to properly understand the charge transport nature. Thus, to shed light on the p- or n-channel ability of the studied compounds, most significant parameter, i.e., transfer integrals have been calculated. Additionally, in the present study, μh and μe has been calculated in section 3.3.2. 3.3.2. Transfer integrals and intrinsic mobility We defined four distinct neighboring hopping pathways to study the charge transport performance of Chalc1 and Chalc2 in detail. Table 5 displays the th and te determined by the scheme expressed in Eq. 6 of computational details (see, supporting information). The values of th and te for Chalc1 are -0.54, 0.3, -2.3 and 4.3 meV/-52.1, 58.8, -14.6 and 0.3 meV for first, second, third and fourth pathways, respectively. Similarly, the first, second, third and fourth pathways of Chalc2 display the th and te as 3.5, 2.9, -0.3 and -0.7 meV/95.1, 9.8, 3.2 and -8.1meV, respectively. All the dimers with their packing have been shown in Figs. 4 and S1 for further clear understanding of the hopping pathways for Chalc1 and Chalc2. The highest values of te as compared to the th revealed that the Chalc1 and Chalc2 would be good electron transport materials. The μh and μe of Chalc1 and Chalc2 have been evaluated as stated in eq. 8 of computational details (see, supporting information) for four pathways and presented in Table 5. The second pathway of Chalc1 and first pathway of Chalc2 shows the highest value for μe as 0.19 and 0.11cm2V-1s-1, respectively, which is because of the stack packing of these dimers. The pathways with negligible small values of μh and μe are not discussed in the text. The Fig. 4 illustrates the dimers with their packing for more clear demonstration of the hopping pathways for Chalc1 and Chalc2. The high value of μe as compared to the μh illuminates that the Chalc1 and Chalc2 would be better as electron transport material.

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3.4. Nonlinear optical property (NLO) Over the past several years, NLO materials have got significant importance [39-43] due their several potential applications in laser frequency doubling, telecommunications and digital data writing etc. [44]. Organic materials especially chalcones are considered as front running contenders due to their ease of fabrication, diverse variety of new synthetic routes. Over the past some years, chalcones are extensively investigated for their potential NLO properties [45]. We have also presented some reports highlighting different strategies to tune the NLO response in some chalcones [46, 47]. These strategies include the impact of number and position of methoxy groups [46] and tuning the push-pull configuration etc. [47]. As in present investigation, the Chalc1 and Chalc2 possess donor-acceptor type configurations, which specify their possible potential for efficient NLO response. To check the possibility of Chalc1 and Chalc2 for their potential applications as NLO materials, we have calculated their molecular electronic static first hyperpolarizability (βtot), which is fundamental requirement for a molecule to possess NLO response. The first hyperpolarizability and its components for Chalc1 and Chalc2 were calculated using finite field (FF) approach at B3LYP/6-31G** level of theory (Methodology details; see supporting information). The first hyperpolarizability (βtot) of Chalc1 and Chalc2, which have non-zero amplitudes of 9.36×10−30 and 67.41×10−30 esu, respectively. The non-zero value of βtot shows that the titled molecules possess microscopic first static hyperpolarizability. The first hyperpolarizability value of Chalc1 and Chalc2 are about 25 and 180 times larger than that of urea (a prototype NLO molecule) as calculated in present investigation at the same B3LYP/6-31G* level of theory, which shows that Chalc1 and Chalc2 can also be considered as a potential candidate for NLO applications. Similarly, the βtot amplitudes of Chalc2 is also ~ 6 times larger than that of para-nitroaniline (PNA = 1330 a. u. at

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B3LYP/6-31G* levels of theory as calculated in present investigation), which is usually used as standard reference NLO molecule to calculate experimental NLO response. From Table 6, it can be seen that hyperpolarizability value of Chalc2 is larger than that of Chalc1 as calculated at B3LYP/6-31G* level of theory. How does changing donor-acceptor configuration enhance the β value of Chalc2 molecule? The trend of first hyperpolarizabilities can be understand in terms of simple two-level expression [48]. For the static first hyperpolarizability, a simple two-level expression [48] is usually used in literature to roughly estimate the β0 values (see supporting information). From Table 3, it can be seen that Chalc2 has lower energy transition ΔE of 3.341 eV with significantly larger oscillator strengths (fo) of 0.921 resulting in its significantly larger β amplitude as compared to that of Chalc1. Additionally, the analysis of these transitions indicates an ICT nature as explained in preceding section of FMOs. 3.5. Density of States The total and partial DOS were calculated by applying CASTEP module available in Materials Studio software program within the framework of DFT at GGA/PW91/DNP level of theory to understand the electronic structure of Chalc1 and Chalc2 comprehensively. The PDOS and TDOS with contributions from s, p-orbital are shown in Fig. S2 for Chalc1 and Chalc2. For Chalc1, the peaks in the lower valence band at energy regime -0.9 to -0.3 Ha is defined mostly by the s-orbitals; the peaks in higher valance bands between –0.4 to 0 Ha are contribution from p-orbitals, In lower conduction bands, the peaks from 0.05 to 0.1 Ha have major contribution from s-orbitals, while from 0 to 0.1 Ha the p-orbitals showing the major contribution (see Fig. S2). The peaks in the lower valence band for Chalc1 at energy regime -0.9 to -0.2 Ha are mostly contributed by the s-orbitals; the peaks between -0.5 to -0.1Ha at upper valance bands are contribution from p-orbitals, the p-orbitals have the major contribution in lower conduction bands from 0 to 0.1 Ha (see Fig. S2). Our analysis of the DOS profiles and electronic properties 11

shows that Chalc1 and Chalc2 with good electronic properties would be potential candidates for organic electro-optical device applications including OLEDs, OPVDs and OFETs.

3.6. Molecular electrostatic potential (MEP) The reactivity of the molecule can be explored by a very important feature termed as molecular electrostatic potential (MEP) surfaces. The areas with major positive potential are specified by blue color and these regions are preferred sites for nucleophilic attack, whereas the maximum negative potential sections have been presented in red color, which are favored site for electrophilic attack as shown in Fig. 5. The different colors are indicating the distinct intensities of MEP surfaces and increases in the order red < orange < yellow < green < blue. In MEP profile the blue and red colors demonstrate the strongest attraction and repulsion, respectively. The lone pair of electronegative atoms is mainly associated to the negative potential regions. The negative potential regions are on the O atom for Chalc1, while for Chalc2 the negative potential regions are on the S atoms. The O atom in the Chalc1 and S atom for Chalc2 are representing the red color and will perform as electrophile regions. Similarly, the blue color indicates the nucleophile regions and illustrates the regions with electron insufficiency, which also represents the nucleonic energy of the LUMO orbitals. These outcomes reveal that the maximum repulsion will be shown by O atom of Chalc1 and S atom for Chalc2. 3.7. Fukui indices The highly stable compounds are the demand of era. Fukui function is usually used to understand the reactive sites of the compounds. It is also expected that Fukui indices can shed some light on the stability of the compounds, i.e., less reactive sites might lead to more stability. The chemical species can adjust its density by Fukui function which leads the preferred regions. It also displays the electronic density affinity after the donation or 12

acceptance of electron to distort at a specific position [49]. If the electrons are reformed in a molecule then the local reactivity descriptor e.g. The Fukui function directs the favorite regions where a chemical species will adjust its density. It also shows the affinity of the electronic density to distort at a specific position after electron withdrawing or donating [49]. On the jth atom site the condensed or atomic Fukui functions can be defined as:

(2) (3) (4) where

,

and

are nucleophilic, electrophilic and free radical on the reference

molecule, respectively. In these equations, qj is the atomic charge at the jth atomic site is the neutral (N), anionic (N + 1) or cationic (N - 1) chemical species. Previously Morell et al. [50] anticipated a dual descriptor (Δƒ(r)), that is the alteration among the electrophilic and nucleophilic Fukui function which can be represented according to the following eq. Δƒ(r) =

–

(5)

If the Δƒ(r) > 0, then the site might be ideal for a nucleophilic attack, however if Δƒ(r) < 0, then the site is favorite for an electrophilic attack. The values of calculated Fukui functions (

,

and

) and Δƒ(r) have been given in Table 7. Here the Δƒ(r) delivers

a clear difference between nucleophilic and electrophilic attack at a specific position with their sign. The positive value disposed to nucleophilic attack while negative value is suitable for electrophilic attack. It is expected that S (1) and O (40) positions in Chalc2 might favor the electrophilic attack (i.e., Δƒ < 0). It is also anticipated that there would be no favorable site for the nucleophilic attack in both the compounds. From the Δƒ values of Table 7, it is anticipated that Chalc1 would be more stable than the other counterpart as prior compound has almost no attractive site for the electrophile or nucleophile attack. 13

Position of reactive electrophilic sites and nucleophilic sites are accordance with the total electron density surface and chemical behavior.

4. Conclusions Thus, the present investigation highlights the importance of above entitled chalcone derivatives as efficient optical and nonlinear optical materials. Nevertheless, following sub-conclusions can be derived as follow: 1. A clear intra-molecular charge transfer has been observed from occupied to unoccupied molecular orbitals leading to a unique donor-acceptor configuration. 2. The smaller energy gap of Chalc2 is eventually promoting the red shift in the absorption and emission spectra than the Chalc1 indicating that the former possesses a good donor-acceptor configuration. 3. The present investigation predicts that the superior donor strength of -N(CH3)2 group in Chalc2 would likely to influence not only its hole transport properties but also finely tune its absorption/emission properties towards red shift as compared to Chalc1. 4. The larger transfer integrals values as well as reasonably high value of electron intrinsic mobilities as compared to the hole one illuminates that the Chalc1 and Chalc2 would be better as electron transport materials. 5. The first hyperpolarizability value of Chalc1 and Chalc2 are about 25 and 180 times larger than that of urea (a prototype NLO molecule). The βtot amplitudes of Chalc2 is also ~ 6 times larger than that of para-nitroaniline indicating their significant potential as efficient NLO-phores 6. Our analysis shows that Chalc1 and Chalc2 with good electronic and charge transport properties would be potential candidates for organic electro-optical device applications including OLEDs, OPVDs and OFETs. 14

Acknowledgements Authors would like to acknowledge the support of the King Khalid University for this research through a grant RCAMS/KKU/001-16 under the (Research Center for Advanced Materials Science) at King Khalid University, Kingdom of Saudi Arabia. A. Irfan also acknowledges the Zhang Jingping to provide technical support about MS calculations.

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[35] J.P. Perdew, J.A. Chevary, S.H. Vosko, K.A. Jackson, M.R. Pederson, D.J. Singh, C. Fiolhais, Atoms, molecules, solids, and surfaces: Applications of the generalized gradient approximation for exchange and correlation, Phys. Rev. B 46 (1992) 6671-6687. [36] A.B. Nadykto, A. Al Natsheh, F. Yu, K.V. Mikkelsen, J. Herb, Chapter 21 Computational Quantum Chemistry: A New Approach to Atmospheric Nucleation, in: E.G. Michael, S.J. Matthew (Eds.) Adv. Quantum Chem., Academic Press, 2008, pp. 449-478. [37] B. Delley, From molecules to solids with the DMol3 approach, J. Chem. Phys. 113 (2000) 7756-7764. [38] R.A.I. Materials Studio Modeling, San Diego,, Materials Studio Modeling, Release 3.0.1. (2004) Accelrys Inc., San Diego,, in, 2004. [39] B.F. Levine, C.G. Bethea, Second and third order hyperpolarizabilities of organic molecules, J. Chem. Phys. 63 (1975) 2666-2682. [40] N. Zaitseva, L. Carman, Rapid growth of KDP-type crystals, Progress in Crystal Growth and Characterization of Materials 43 (2001) 1-118. [41] J. Badan, R. Hierle, A. Perigaud, J. Zyss, D. Williams, NLO properties of organic molecules and polymeric materials, in: American Chemical Society Symposium Series, American Chemical Society Washington, DC, 1993. [42] S. Muhammad, A. Irfan, M. Shkir, A.R. Chaudhry, A. Kalam, S. AlFaify, A.G. Al‐Sehemi, A. Al‐Salami, I. Yahia, H.L. Xu, How does hybrid bridging core modification enhance the nonlinear optical properties in donor‐π‐acceptor configuration? A case study of dinitrophenol derivatives, J. Comput. Chem. 36 (2015) 118-128. [43] S. Muhammad, H.-L. Xu, R.-L. Zhong, Z.-M. Su, A.G. Al-Sehemi, A. Irfan, Quantum chemical design of nonlinear optical materials by sp2-hybridized carbon nanomaterials: issues and opportunities, J. Mater. Chem. C 1 (2013) 5439-5449. [44] M.G. Papadopoulos, A.J. Sadlej, J. Leszczynski, Non-linear optical properties of matter, Springer, 2006. [45] L.M.G. Abegão, F.A. Santos, M. Alencar, J.J. Rodrigues Jr, R.D. Fonseca, E.C. Barbano, C.R. Mendonça, L. Misogut, L. De Boni, NONLINEAR OPTICAL PROPERTIES OF CHALCONES, in: The European Conference on Lasers and Electro-Optics, Optical Society of America, 2015, pp. CE_9_5. [46] S. Muhammad, A.G. Al-Sehemi, A. Irfan, A.R. Chaudhry, H. Gharni, S. AlFaify, M. Shkir, A.M. Asiri, The impact of position and number of methoxy group (s) to tune the nonlinear optical properties of chalcone derivatives: a dual substitution strategy, J. Mol. Model. 22 (2016) 1-9. [47] S. Muhammad, A.G. Al-Sehemi, Z. Su, H. Xu, A. Irfan, A.R. Chaudhry, First Principles Study for the Key Electronic, Optical and Nonlinear Optical Properties of Novel Donor-Acceptor Chalcones, J. Mol. Graphics Modell. [48] J.L. Oudar, D.S. Chemla, Hyperpolarizabilities of the nitroanilines and their relations to the excited state dipole moment, J. Chem. Phys. 66 (1977) 2664-2668. [49] P.W. Ayers, R.G. Parr, Variational Principles for Describing Chemical Reactions:  The Fukui Function and Chemical Hardness Revisited, J. Am. Chem. Soc. 122 (2000) 2010-2018. [50] C. Morell, A. Grand, A. Toro-Labbé, New Dual Descriptor for Chemical Reactivity, J. Phys. Chem. A 109 (2005) 205-212.

17

2

15

O

H3C

15 H3C 14

14 10

1

9

1 S

S

12 H3C13

11

HO

12

2 O 10 9 11

H 3C 13

CH3 N CH3

Fig. 1. The thiophene based chalcone derivatives Chalc1 (left) and Chalc2 (right) along with numbering scheme investigated in the presented study.

18

Chalc2 HOMO3

HOMO

LUMO

Chalc1 HOMO1

HOMO

LUMO

Fig. 2. Distribution patterns of the HOMOs and LUMOs of chalcone derivatives at the ground states

19

HOMO-2

Chalc2 HOMO-1

HOMO

LUMO

Chalc1 HOMO-1

HOMO

LUMO

Fig. 3. Distribution patterns of the HOMOs and LUMOs of chalcone derivatives at the first excited states.

20

Fig. 4. The dimers of Chalc1 studied in current investigation to calculate the transfer integrals and intrinsic mobilities.

21

Fig. 5. The molecular electrostatic potential (MEP) of the thiophene based chalcone derivatives Chalc1 (left) and Chalc2 (right).

22

Table 1 Selected optimized bond lengths in Angstrom (Å) and bond angles (degree) of ground and first excited states for chalcone derivatives at the B3LYP/6-31G** and TDB3LYP/6-31G** levels of theory, respectively. Parameters

States

Chalc1a

Chalc2b

Parameters

States

Chalc1a

Chalc2b

S1-C12

S0

1.752

1.751

C12-S1-C14

S0

93.00

92.97

(1.723)

(1.709)

(93.47)

(93.32)

S1

1.754

1.777

S1

92.79

92.16

S0

1.739

1.740

S0

120.74

120.49

(1.710)

(1.702)

(121.58)

(121.53)

S1

1.741

1.724

S1

115.57

99.66

S0

1.235

1.236

S0

118.14

118.41

(1.230)

(1.265)

(118.20)

(118.61)

1.315

1.289

123.43

127.55

S1-C14

C9-O2

S1 a

C10-C9-O2

C10-C9-C8

S1

exp = Experimental data of from references [10, 11]

23

Table 2 The HOMO energies (EHOMO), LUMO energies (ELUMO), and HOMO-LUMO energy gaps (Eg) in eV for ground and first excited states computed at the B3LYP/6-31G** and TD-B3LYP/6-31G** levels of theory, respectively. Complexes

Ground states

Chalc1 Chalc2

First excited states

EHOMO

ELUMO

Eg

EHOMO ELUMO Eg

-5.89

-1.78

4.11

-5.81

-2.16

3.65

-5.12

-1.56

3.56

-4.62

-2.24

2.38

Table 3 Calculated absorption (λa) and emission wavelengths (λe) in (nm) of chalcone derivatives at the TD-B3LYP/6-31G** level of theory. Complexes Chalc1

Chalc2

f

λa

Transition

f

λe

Transition

0.181

342

H→L

0.111

390

L→H

0.367

321

H-1 → L

0.558

344

L → H-1

0.921

371

H→L

0.010

453

L → H-2

0.188

272

H-3 → L

1.096

370

L → H-1

f = Oscillator Strength

24

Table 4 The vertical and adiabatic ionization potentials (IPv/IPa), vertical and adiabatic electronic affinities (EAv/EAa), hole reorganization energies (λh)and electron reorganization energies λe of chalcone derivatives (in eV) at the B3LYP/6-31G** level of theory. Complexes Chalc1 Chalc2

IPa

EAa

IPv

EAv

λh

λe

7.22

0.43

7.33

0.27

0.219

0.318

6.49

0.35

6.58

0.13

0.200

0.439

Table 5 Calculated hole/electron transfer integrals (th/te), mass centers and hole/electron intrinsic mobilities (μh/μe) of Chalc1 and Chalc2 for the five pathways computed with DFT. Molecules

Pathways

Transfer

Integrals Mass

(meV)

Chalc1

Chalc2

Intrinsic

Centers

(cm2/V.s)

Mobility

th

te

(Å)

μh

μe

i

-0.54

-52.1

3.88

6.6×10-7

9.2×10-2

ii

3.0

-58.8

4.33

7.7×10-4

0.19

iii

-2.3

-14.6

6.46

5.9×10-4

1.5×10-3

iv

4.3

0.3

7.80

1.0×10-2

2.5×10-10

i

3.5

95.1

2.88

1.2×10-3

0.11

ii

2.9

9.8

4.92

1.6×10-3

3.4×10-5

iii

-0.3

3.2

6.20

3.8×10-7

6.1×10-7

iv

-0.7

-8.1

7.66

1.2×10-5

3.8×10-5

25

Table 6 The calculated values of polarizability (α), hyperpolarizability (β) and dipole moment (μ) along their individual tensor components for Chalc1 and Chalc2 Chalc1 Chalc2 −30 Component a. u. esu (×10 ) Component a. u. βxxx -631 -5.45 βxxx -7710 βxxy -923 -7.98 βxxy -2031 βxyy 31 0.27 βxyy 133 βyyy 48 0.41 βyyy 100 βxxz 2 0.02 βxxz 25 βxyz 0 0.00 βxyz -1 βyyz -1 -0.01 βyyz 10 βxzz -39 -0.34 βxzz 17 βyzz 1 0.01 βyzz 8 βzzz -1 -0.01 βzzz 11 βtot 1083 9.36 βtot 7800 βtot (urea) a 43 0.37 βtot (urea) a 43 a a βtot (PNA) 1330 11.49 βtot (PNA) 1330 −30 a For β, 1 a. u. = 0.008629×10 esu, Calculated in present study at the 31G* level of theory

esu (×10−30) -66.62 -17.55 1.15 0.86 0.22 -0.01 0.09 0.15 0.07 0.10 67.41 0.37 11.49 same B3LYP/6-

26

Table 7 The calculated Fukui indices Fukui(-), Fukui(+) and Fukui(0) of thiophene based heterocyclic chalcones. Comp.

Atom No.

Fukui(-)

Fukui(+)

Fukui(0)

Δƒ(r)

Chalc1

S (1)

0.045

0.044

0.044

-0.001

O (2)

0.017

0.017

0.017

0.000

O (3)

0.009

0.009

0.009

0.000

S (1)

0.065

0.063

0.064

-0.002

O (2)

0.031

0.031

0.031

0.000

N (3)

0.012

0.012

0.012

0.000

O (40)

0.032

0.028

0.030

-0.004

Chalc2

27