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Exploring the functional properties of Trimethoxy-Phenylpyridine as efficient optical and nonlinear optical material: A quantum chemical approach
Journal of Molecular Structure 1185 (2019) 268e275
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Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc
Exploring the functional properties of Trimethoxy-Phenylpyridine as efficient optical and nonlinear optical material: A quantum chemical approach Aijaz Rasool Chaudhry a, *, Shabbir Muhammad b, Bakhtiar Ul Haq b, Santosh Kumar c, Abdullah G. Al-Sehemi d, Ahmad Irfan d, A. Laref e, Arshad Hussain f, g a
Deanship of Scientific Research, University of Bisha, Bisha, 61922, P.O. Box 551, Saudi Arabia Department of Physics, College of Science, King Khalid University, Abha, 61413, P.O. Box 9004, Saudi Arabia Division of Chemical Engineering, Konkuk University, Seoul, 143701, South Korea d Department of Chemistry, College of Science, King Khalid University, Abha, 61413, P.O. Box 9004, Saudi Arabia e Department of Physics and Astronomy, College of Science, King Saud University, Riyadh, 11451, Saudi Arabia f Shenzhen Key Laboratory of Advanced Thin Films and Applications, College of Physics and Energy, Shenzhen University, Shenzhen, 518060, PR China g Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen, 518060, China b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 January 2019 Received in revised form 18 February 2019 Accepted 25 February 2019 Available online 28 February 2019
In the current study, the 2,6-diphenyl-4-(3,4,5-trimethoxyphenyl)pyridine (compound 1) has been investigated as proficient material for optoelectronic and nonlinear optical (NLO) applications. In order to highlight the potential at both solid-state (bulk) and molecular levels, different electronic and optical parameters were investigated. The optical and electronic parameters such as refractive index, reflectivity, dielectric function, extinction coefficient, conductivity, electronic band structure, density of states (DOS) of newly reported trimethoxy-phenylpyridine at bulk (solid-state) level have been studied. The band gap is found to be 2.817 eV, which revealed the photon absorption competency has been improved in compound 1 due to narrow band gap and has the capability of containing the absorbed energy. Other calculated optoelectronic properties also revealed that the compound 1 might be better for semiconductor applications. Additionally, the geometric parameters, polarizability (isotropic and anisotropic) and third-order NLO polarizability have been computed at molecular level. For compound 1, its isotropic and anisotropic values are found to be 63.41 1024 esu and 46.22 1024 esu, respectively. The calculated g amplitude for studied material has been computed as 187.53 1036 esu that is about 25 times bigger than that of the g amplitude for pNA (a prototype NLO molecule). The third order NLO response for compound 1 has been further tuned through the designing of its further derivatives in the form of compounds 1a, 1b and 1c. Thus, the present study highlights the important optoelectronic and NLO properties of compound 1 and its derivatives. © 2019 Elsevier B.V. All rights reserved.
Keywords: Electro-optical properties NLO material Semiconductor Photovoltaic application Reflectivity
1. Introduction Organic semiconductor materials (OSMs) have been fascinating the experimental as well as theoretical scientists owing to the flexibility, cheaper cost of procedures, great performance, less weight and easiness of fabrication on bendy surfaces [1e9]. As firstly stated in 1986 [10], OSMs have been widely investigated for
* Corresponding author. E-mail address: [email protected] (A.R. Chaudhry). https://doi.org/10.1016/j.molstruc.2019.02.102 0022-2860/© 2019 Elsevier B.V. All rights reserved.
their applications in optoelectronic and micro-electronics, like organic light emitting diodes (OLEDs) [11,12] and organic photovoltaic devices (OPVs) [12,13]. An interesting synthetic strategy is one-pot multicomponent coupling reactions to synthesize the pyridine containing complexes. In this technique, numerous organic moieties can be joined in a single phase, for carbon-carbon as well as carbon-heteroatom bond foundation to synthesize smallmolecules with various degrees of structural diversities [14]. Using this strategy, recently two multiaryl substituted pyridine compounds were modeled and synthesized with high HOMO and LUMO energies and have been reported as good electron
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transporters [15]. The hugely switched pyridine compounds, such as 2-amino-4-aryl-3,5-dicyano-6-sulfanylpyridines have substantial and various medical uses [16,17]. A new terpyridine ligand and the well-known calix[4]resorcinarene have been synthesized, which allows access to a new type of supramolecular pyridine compound and reduces the overall waste [18]. A series of metalloporphyrin comprising cyclical hosts was synthesized. The synthetic scheme of these compounds permits easy approach to a vast variety of asymmetrical cyclic hosts and analyze the binding between cavities [19]. Recently, the trimethoxy-phenylpyridine has been synthesis under solvent-free condition. A moderate and environmentally friendly technique was established to synthesize this compound by cyclo compression of aromatic ketones aldehydes and ammonium carbonate catalyst [20]. Although different properties of trimethoxy-phenylpyridine have been studied, a comprehensive study of electronic, optical and nonlinear optical (NLO) properties is still necessary. According to the recent literature review, no study with electronic, optical and NLO properties was found. In the present study, we used trimethoxy-phenylpyridine [20] (in text denoted by compound 1; see Fig. 1) to study its electro-optical and NLO properties. The key intention of present investigation is to explore the electro-optical properties including electronic band structure, total and partial density of states (TDOS/PDOS) along with the optical properties such as conductivity, extinction coefficient, reflectivity, dielectric function and refractive index for trimethoxyphenylpyridine at the solid-state (bulk) level. Furthermore, at molecular level the structural and NLO properties were also studied for this fascinating compound.
269
2.2. Single molecular methodology In the present investigation, we have performed quantum computational analysis at two levels, which includes single molecular calculations that were performed using Gaussian 09 [27]. For single molecular analysis, all geometries were fully optimized to their respective energy minimum before doing any further functional property calculations. The PBE0 functional is used among density functional theory (DFT) methods to optimization and other single molecular property calculations. The PBE0 is usually considered as a reliable choice for the calculations of different optoelectronic properties as evident from several previous contemporary studies. The choice of 6-311G** basis set is satisfactory which is triple-zeta basis set with double polarizations. The optimized geometry of compound 1 is compared with experimental values and there is a reasonable agreement among these bonding parameters. To calculate the polarizability and third-order NLO polarizability, we used finite field (FF) method within Tconvention as given in different literature. The following expressions were used to calculate the average isotropic polarizability (aiso ) as under:
aiso ¼
1 axx þ ayy þ azz 3
(1)
While for anisotropy of polarizability (Da),
1
aaniso ¼ pffiffiffi
2
rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi h i axx ayy 2 þ ayy azz 2 þ ðazz axx Þ2 þ 6a2xz (2)
Similarly, for average g third-order polarizability: 2. Computational details 2.1. Solid-state methodology The experimental molecular crystal of compound 1 was imported into Materials Studio [21] for geometry optimization. The experimental lattice parameters were used to optimize the crystal structure of compound 1 (a ¼ 19.554, b ¼ 14.7990, c ¼ 7.5795, a ¼ g ¼ 90, b ¼ 101.157) with Cc space group and monoclinic lattice type [20]. The CASTEP module [22] as offered with Material studio [21] has been applied to evaluate the optoelectronic properties. The Perdew, Burke, and Ernzerhof parameterized GGA/PBE [23] within DFT framework is applied to estimate exchange and correlation energy/potential. The particulars of Brillouin Zone (BZ) have been described in supporting information and in references [24e26].
g ¼
1 X giijj þ gijij þ gijji 15
(3)
ij¼x;y;z
Under Kleinmann symmetry, the static second hyperpolarizability components are limited to only six components which were calculated using PBE0/6-311G** level of theory.
g ¼
1 gxxxx þ gyyyy þ gzzzz þ 2 gxxyy þ gxxzz þ gyyzz 5
(4)
3. Results and discussion 3.1. Solid-state optical and electronic properties The optical and electronic properties for OSMs are very critical to distinguish prospective utilization of these compounds into semiconductors, OFETs, OLEDs and photovoltaic device applications. The optical and electronic properties are also mandatory to evaluate the competence of organic materials.
Fig. 1. The representation of chemical structure for compound 1 [2,6-diphenyl-4(3,4,5-trimethoxyphenyl)pyridine].
3.1.1. Electronic band structure The electronic band structure exploration is very vital to unveil the potential of a material for optical applications. The compound 1 electronic band structure has been computed using GGA/PBE level of theory in the Brillouin Zone (BZ) at symmetrical points as demonstrated in Fig. 2. The total density of states (TDOS) as well as partial DOS (PDOS) have been displayed in Figs. 3 and 4 for all probable energy states arrangement that take a vital part in the electronic and optical properties of a OSMs. The optoelectronic parameters of compound 1 are generally formed by the bands confined adjoining Fermi level, hereafter enlarged band structure
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Fig. 2. The electronic band structure along with density of states (top) and zoomed spectra (bottom) for molecular crystal of compound 1 are schematically shown.
of compound 1 contiguous to Fermi level are presented in Fig. 2 to illuminate the bandgap more precisely. Fig. 2 presents the valence band maximum (VBM) of compound 1 has been created at G-point in BZ, whereas the conduction band minima (CBM) also has been originated at G-point, illuminating the fact that the compound 1 exhibits direct band gap as 2.817 eV on symmetrical G-point.
3.1.2. Density of states The density of states describes by the distribution of electron in energy spectrum of a material. The TDOS and PDOS have been calculated at GGA/PBE level of DFT for in-depth exploration of electronic properties of compound 1. Figs. 3 and 4 displayed the impact of s- and p- orbitals as well as the contribution of C, O and N atoms in the formation of TDOS and PDOS, respectively in the
energy ranging from 4 to 4 eV. It is clear from Fig. 3 that the energy peaks in the deep valance band (VB) are defined by s-orbitals, yet the participation from s-orbitals at the higher VB and in conduction band (CB) is negligibly small, clarifying a minor contribution from s-orbitals into the electronic properties. The peaks among the energy of 4 to 4 eV have been subjugated by the p-orbitals in VB as well as in CB. The exploration of electronic structure sketch establishes that compound 1 having remarkable optoelectronic characteristics would be a subsequent contestant for photovoltaic device applications.
3.1.3. Dielectric function To estimate the efficiency of OSMs, the optical properties of these organic materials are very essential to investigate. The real
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271
peaks between energy range of 1e5 eV and quickly fall down to zero, while after 6 eV presenting the identical spectra with zero intensity for all directions. The unchanging spectra unveiled the ultimate stability for compound 1 which eventually originating a large ability for transmitting electron inside the crystal, enlightening a greater intra- and inter-molecular charge transportation in the studied compound 1.
Fig. 3. Total density of states (TDOS) for compound 1 molecular crystals for s, p orbitals.
(ε1) and imaginary (ε2) parts for the dielectric function of compound 1 molecular crystal have been displayed in Fig. 5. The ε1 displays strong peaks in the smaller energy range between 2 and 3 eV with (100) and (010) directions (2.74 and 3.19, respectively) for compound 1. The static dielectric function ε(0) is evaluated as 1.90 and 2.10, respectively for (100) and (010) directions. The ε(0) with good values at 0 eV exposed the substantial ability to carry the electron within compound 1. Oxygen atoms in compound 1 may be responsible for the superior value of ε(0). The ε2 is primarily dominated in (100) as well as (010) directions for compound 1. The peaks of ε2 illuminate transfer of an electron from occupied valance band to unoccupied conduction band. It displayed that compound 1 would be good compound for charge transport. 3.1.4. Conductivity The conductivity function's real and imaginary parts (s1/s2) are displayed in Fig. 5. The s1 is dominated by the (100) and (010) directions (1.06 and 1.23, respectively) for compound 1 crystal structure. The s1 spectrum for compound 1 demonstrated high
3.1.5. Reflective index and extinction coefficient To shed light on the electro-optical characteristics of a material, it is very crucial to calculate the refractive index (n) and extinction coefficient (k). The evaluated maximum n is 1.434 in the polarization vector (010) direction for compound 1 at 0 eV as shown in Fig. 6. The evaluated n revealing that compound 1 would be better to refract a photon at lesser energy level. The compound 1 shows good values of n at lowermost energy between 0 and 4 eV, however after 4 eV the peaks start falling and established persistent and unchanged indices of 0.9 intensity after 10 eV. Fig. 6 reveals that the studied compound might be capable to yield decent outputs at lower energy inputs of 4 eV. 3.1.6. Reflectivity and loss function The reflectivity and energy loss function for compound 1 have been calculated and presented in Fig. 7 to understand the studied material. The compound 1 displayed good values at smaller energy in reflectivity peaks, then begins to reach a uniform value consequently after 8 eV as could be found in Fig. 7. The compound 1 revealed the higher reflectivity as 0.275 along (010) direction, that arises in the energy ranges from 4 to 6 eV. The reflectivity for a material is inversely proportional to transparency, thus inferior reflectivity unveils that the studied compound 1 might be capable materials for OPV application at lower energy. The loss function is an essential parameter demonstrating energy loss for a quickly moving electron passing within the molecular crystal structure [28e30]. The loss function for compound 1 was computed and presented graphically through Fig. 7. The highest peaks in loss function occur around 6 eV for compound 1 with a value of 3.49 in the (010) direction. The maximum peak in the calculated loss function spectrum corresponds to the quick decline of reflectivity (see Fig. 7).
Fig. 4. Partial density of states (PDOS) for compound 1 crystals from C (left), O (middle) and N (right).
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Fig. 5. Computed dielectric and conductivity for real (ε1/s1) along with imaginary part (ε 2/s2) for compound 1.
Fig. 6. Graphical representation of refractive index (n) and extinction coefficient (k) for compound 1.
Fig. 7. The computed reflectivity and energy loss function of compound 1.
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3.2. Single molecular electro-optical properties of compound 1 3.2.1. Single molecular geometry The single molecular geometry was completely optimized without any symmetry constrains. The initial geometries of compound 1 are extracted from its experimental crystallographic structure and later it has been optimized to its energy minima. A generally accepted PBE0/6-311** level was utilized to optimize the molecular geometry because PBE0 has been reported as a good approach to reproduce the molecular geometries as reported in previous studies [31e33]. The comparison of experimental crystallographic and optimized geometrical structures of compound 1 has been illustrated in Fig. 8. It is seen that the quantum chemical calculations reproduced the experimental geometry reasonably good. The experimental and calculated NeC bond distances of pyridine rings are 1.339 Å and 1.334 Å, respectively. The CeC bond distance between pyridine ring and phenyl rings are found to be 1.491 Å (experimental) and 1.482 Å (calculated). Similarly, the experimental and calculated central CeC bonds between trimethoxy phenyl and diphenyl pyridine moieties are found to be 1.485 Å (experimental) and 1.477 Å (calculated). The experimental and calculated CeNeC bond angles of pyridine rings are found to be 118.2 and 119.2 , respectively. Somewhat similar agreement is also seen between bond angles of trimethoxy -phenyl ring, which shows an overall agreement among the optimized and experimental structures (see Fig. 8). 3.2.2. Polarizability and third-order NLO polarizability For compound 1, its isotropic and anisotropic polarizabilities amplitudes (aiso and aaniso) have been collected in Table 1. Among the individual components, the axx amplitude is found to be the largest mounting to 76.82 1024 esu, which is due to its orientation along the central charge transfer axis as showed in Fig. 8. For compound 1, its isotropic and anisotropic values are found to be 63.41 1024 esu and 46.22 1024 esu, respectively, (see Table 1). The difference in isotropic and anisotropic values are 17.19 1024 esu. Furthermore, the third-order nonlinear polarizabilities (g) of compound 1 were also calculated to see its potential as third-order NLO material. Usually, the third-order NLO polarizability is assumed as origin of its microscopic nonlinear susceptibility, which can lead to different NLO phenomena like thirdharmonic generation (THG), two photon absorption (TPA), and optical Kerr effect etc. For instance, in THG, three photons of intense laser light are destroyed to generate a single light photon having a tripled frequency and/or one-third the wavelength, which has many modern technological applications. For compound 1, its calculated g amplitude is shown in Table 1 accompanied by its
273
Table 1 The polarizability (a, 1024 esu) and third-order polarizability (g 1036 esu) along with their individual components for compound 1 at PBE0/6-311G** level of theory.
a
a
1024 esu
g
1036 esu
axx axy ayy axz ayz azz aiso aaniso
76.82 5.11 60.38 5.66 22.48 53.03 63.41 46.22
gxxxx gyyyy gzzzz gxxyy gxxzz gyyzz pNA
258.26 106.70 123.81 80.393 62.859 81.178 187.53 7.489
For a, 1 a. u. z 1.148176 1024 cm3.
individual components. For compound 1, it can be seen that like the polarizability component axx, the gxxxx component of g amplitude is the largest mounting to 258.26 1036 esu. The average g amplitude of compound 1 is computed as 187.53 1036 esu, which is reasonably larger for its practical application. To seek its real-time applications, the g amplitude of para-nitroaniline (pNA) has been also calculated in present investigation, which is often used as standard organic molecule for relative NLO response calculations in experiments. The molecular geometry and calculation of NLO properties were performed at the same level of theory for pNA, which makes the comparative analysis more reliable. The calculated average g amplitude of pNA is found to be 7.489 1036 esu as shown in Table 1. A comparison of calculated average g amplitude of compound 1 and pNA shows that the compound 1 possesses the average g amplitude which is about 25 times greater than that of the g amplitude of pNA.
3.2.3. Derivatives and Structure-NLO property relationship To comprehend the details about the structure-NLO property relationship, we have designed further derivatives for compound 1. The main idea in designing the new derivatives based on enhancing the push-pull configuration so that to move around the electron density for enhancing the efficient NLO compounds. The H atoms of terminal phenyl groups were replaced by NO2, C2PhNO2 and C2(CN)3 groups, which were all expected to act as good electron pulling groups (see Scheme 1). The third-order NLO polarizabilities for all the derivatives (1a, 1b and 1c) were calculated at the same PBE0/6-311G** level of theory and collected in Table 2 along with compound 1. As it can be seen in Table 2 that all the derivatives show significant enhancements in their g amplitudes. For example, the average g amplitudes of 1a, 1b and 1c are found to be 412.71 1036, 3153.9 1036 and 1804 1036 esu, respectively.
Fig. 8. The experimental (Exp.) and calculated (Cal.) geometries for compound 1 at PBE0/6-311** level of DFT.
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A.R. Chaudhry et al. / Journal of Molecular Structure 1185 (2019) 268e275 Table 3 The transition energies (DE), oscillator strength (fo), transition moment (mng), and % configuration interaction (C.I.) for all the compounds at TD-PBE0/6-311G** level of theory. Comp.
Electronic Excitation
DE (eV)
fo
mng
Transition
C.I.
1
S0/S1 S0/S2 S0/S1 S0/S5 S0/S1 S0/S2 S0/S1 S0/S5
4.145 4.207 3.315 3.775 3.127 3.226 2.339 2.789
0.149 0.435 0.001 0.628 1.780 0.803 0.004 0.816
1.183 2.055 0.048 2.591 4.819 3.187 0.227 3.412
103 105 127 125 179 179 155 153
0.563 0.694 0.670 0.693 0.465 0.482 0.631 0.692
1a 1b 1c
Scheme 1. The schematic representation for the derivatives of Compound 1 [2,6diphenyl-4-(3,4,5-trimethoxyphenyl)pyridine].
Table 2 The third-order polarizability (g 1036 esu) and its individual components as for compounds 1-1d at PBE0/6-311G** level.
g
1
1a
1b
1c
pNA
gxxxx gyyyy gzzzz gxxyy gxxzz gyyzz
258.26 106.70 123.81 80.393 62.859 81.178 187.53
776.77 15.49 622.19 8.011 303.53 10.40 412.71
7532.8 17.010 2034.9 33.43 3035.2 25.836 3153.9
4531.7 31.291 1221.9 63.646 1513.7 43.5782 1804.9
35.387 2.436 2.4964 0.1895 0.5767 1.012 7.489
These g amplitudes of 1a, 1b and 1c are about 2, 16 and 10 times higher than the average g amplitudes for parent compound 1. Interestingly, a comparison of average g amplitudes of systems 1a, 1b and 1c with that of pNA also shows remarkably larger NLO response properties of systems 1a, 1b and 1c. To see the real-time importance of designed derivatives, we have also compared the average g amplitudes of designed compounds to several recently designed compounds and found that our derivatives possess thirdorder NLO polarizability amplitudes, which is larger than these compounds. For example, derivatives of bromocoumarin [34] and aminoquinoline (6AQ) [35] illustrated g amplitudes of 22.34 1036 and 39.30 1036 esu at CAM-B3LYP/6-311G** and B3LYP/6-311G** levels of theory, respectively. Among several complexes, the importantly investigated berylliumehydrocarbon complex has shown g amplitudes of 139.30 1036 esu at PBE0/ 6-311þþG** level [36] and conjugated TTF-quinones showed 4.13 1036 and 4.66 1036 esu at TDHF/6-311 þ G** level [37]. It is essential to discuss that the effect of methodology may influence the average g amplitudes among different studies as above reported. Nonetheless, we believe that our designed derivatives are potential candidates for their use as efficient NLO materials.
3.2.4. The substitutional effect on NLO properties As seen in the above discussion that there is significant substitutional effect on the g amplitudes of parent compound 1. For instance, the g amplitudes of 1a, 1b and 1c are ~2 times, 16 times and 10 times larger than the parent system 1. In order to understand and compare the substitutional effects on the g amplitudes of systems 1a, 1b and 1c, we have calculated the TD-DFT calculations for all the systems as shown in Table 3. The substitutional effect on the third-order NLO response in compounds 1, 1a, 1b and 1c, we may consider the simple threestates approximations based on perturbative formula for static longitudinal gL (gzzzz) values as under [38]:
2
->106 ->106 ->128 ->129 -> 181 -> 180 ->156 ->156
3
X m2ng m2mn m2 Dm2 m4 5 gL ¼ 244 ng 3 ng ng3 þ DEng DEng mðmsnÞ E2ng DEmg
(5)
where mng ; DE and Dm are transition moment, transition energy and change in dipole moment related with transition from ground (jg) to crucial excited (jn) state. This so called three-state approximation is widely applied in theory and experiments to explain the changes in hyperpolarizabilities (b and g) using spectroscopic parameters of several donor-acceptor types of molecules. For further details of above approximations, we refer the reader to the works of Bredas [39], Nakano [40] and similar other researchers [41,42]. It can be perceived from above equation (5) that an optimal longitudinal component (in present case gzzzz) for a chemical compound can be achieved with lower DE and larger mng values. For present investigation, the spectroscopic parameters are calculated with TD-PBE0/6-311G** level of theory. The calculated values of fo ; DE and mng for two lowest transitions are collected in Table 3. A careful analysis of Table 3 shows that the compounds 1b and 1c possess larger transition moments/oscillator strengths and lower transition energies, which perhaps lead to their significantly larger g amplitudes. For instance, unlike systems 1 and 1a, the S0 to S1 transitions for systems 1b and 1c possess the lower transition energies of 3.127 and 2.339 eV, respectively. Additionally, the transition moment/oscillator strength of systems 1b is the largest that is perhaps the reason for its largest NLO response. Thus, the substitutions on compound 1 causes an enhanced push-pull effect for better intramolecular charge transfer process, which results in lower energy strong transitions in derivatives especially in compounds 1b and 1c. 4. Conclusions The present investigation highlights various insights into structure-property relationship of trimethoxy-phenylpyridine compound 1. The computed value of band gap is 2.817 eV for compound 1 that indicates the high photon absorption competency at lower energy level. This narrow band gap will enhance the smooth transfer of electron from valance to conduction bands. The optical and electronic properties like refractive index, reflectivity, dielectric function, conductivity, extinction coefficient, electronic band structure, density of states (DOS) of newly reported trimethoxy-phenylpyridine at bulk (solid-state) revealed the potential of compound 1 as good optoelectronic applications. The average g amplitude for compound 1 has been computed as 187.53 1036 esu with PBE0 method which are reasonably larger than similar prototype molecules. Furthermore, we have designed push-pull type derivatives of compound 1 as 1a, 1b and 1c. Interestingly, the average g amplitudes of 1a, 1b and 1c are found to be
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412.71 1036, 3153.9 1036 and 1804 1036 esu, respectively. A further comparison showed that the g amplitudes of 1a, 1b and 1c are about 2, 16 and 10 times larger than the average g amplitudes of parent compound 1. The origin of larger g amplitudes are traced using three-state approximation through TD-DFT calculations. Thus, the present investigation highlights that our studied compounds are prospective competitors to be used in electro-optical and NLO device applications. Acknowledgement Authors are thankful to Deanship of Scientific Research at King Khalid University for funding this work through Research Group Project under grant number (R. G. P. 2/17/40). S. Kumar is also thankful to research support of KU brain pool Konkuk University 2019. The author A. Laref acknowledges the support from the “Research Center of the Female Scientific and Medical Colleges”, Deanship of Scientific Research, King Saud University. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.molstruc.2019.02.102. References [1] S. Azam, J. Bila, H. Kamarudin, A. Reshak, Electronic structure, electronic charge density and optical properties of 3-methyl-1, 4-dioxo-1, 4dohydronaphthalen-2-yl-sulfanyl (C13H10O4S), Int. J. Electrochem. Sci. 9 (2014) 445e459. [2] S. Azam, A. Reshak, Electronic structure of 1, 3-dicarbomethoxy4, 6benzenedicarboxylic acid: density functional approach, Int. J. Electrochem. Sci. 8 (2013) 10359e10375. [3] A.H. Reshak, H. Kamarudin, S. Auluck, Acentric nonlinear optical 2,4dihydroxyl hydrazone isomorphic crystals with large linear, nonlinear optical susceptibilities and hyperpolarizability, J. Phys. Chem. B 116 (2012) 4677e4683. [4] A.H. Reshak, H. Kamarudin, S. Auluck, Electronic structure, density of electronic states, and the chemical bonding properties of 2,4-dihydroxyl hydrazone crystals (C13H11N3O4), J. Mater. Sci. 48 (2013) 3805e3811. [5] A.H. Reshak, H. Kamarudin, I. Kityk, S. Auluck, Dispersion of linear, nonlinear optical susceptibilities and hyperpolarizability of C11H8N2O (o-Methoxydicyanovinylbenzene) crystals, J. Phys. Chem. B 116 (2012) 13338e13343. [6] A.H. Reshak, H. Kamarudin, I.V. Kityk, S. Auluck, Electronic structure, charge density, and chemical bonding properties of C11H8N2O o-methoxydicyanovinylbenzene (DIVA) single crystal, J. Mater. Sci. 48 (2013) 5157e5162. ski, [7] I. Fuks-Janczarek, A.H. Reshak, W. Ku znik, I.V. Kityk, R. Gaban M. Łapkowski, et al., UVevis absorption spectra of 1,4-dialkoxy-2,5-bis[2(thien-2-yl)ethenyl]benzenes, Spectrochim. Acta A: Mol. Biomol. Spectrosc. 72 (2009) 394e398. [8] A. Wojciechowski, K. Ozga, A.H. Reshak, R. Miedzinski, I.V. Kityk, J. Berdowski, et al., Photoinduced effects in l-alanine crystals, Mater. Lett. 64 (2010) 1957e1959. [9] M. Pokladko, E. Gondek, J. Sanetra, J. Nizioł, A. Danel, I.V. Kityk, et al., Spectral emission properties of 4-aryloxy-3-methyl-1-phenyl-1H-pyrazolo[3,4-b] quinolines, Spectrochim. Acta A: Mol. Biomol. Spectrosc. 73 (2009) 281e285. [10] A. Tsumura, H. Koezuka, T. Ando, Macromolecular electronic device: fieldeffect transistor with a polythiophene thin film, Appl. Phys. Lett. 49 (1986) 1210e1212. [11] C.W. Tang, S.A. VanSlyke, Organic electroluminescent diodes, Appl. Phys. Lett. 51 (1987) 913e915. [12] P.K.H. Ho, J.-S. Kim, J.H. Burroughes, H. Becker, S.F.Y. Li, T.M. Brown, et al., Molecular-scale interface engineering for polymer light-emitting diodes, Nature 404 (2000) 481e484. [13] F. Padinger, R.S. Rittberger, N.S. Sariciftci, Effects of postproduction treatment on plastic solar cells, Adv. Funct. Mater. 13 (2003) 85e88. [14] A. Ulaczyk-Lesanko, D.G. Hall, Wanted: new multicomponent reactions for generating libraries of polycyclic natural products, Curr. Opin. Chem. Biol. 9 (2005) 266e276. [15] N. Li, P. Wang, S.L. Lai, W. Liu, C.S. Lee, S.T. Lee, et al., Synthesis of multiarylsubstituted pyridine derivatives and applications in non-doped deep-blue OLEDs as electron-transporting layer with high hole-blocking ability, Adv. Mater. 22 (2010) 527e530. [16] L.C. Chang, J.K. von Frijtag Drabbe Künzel, T. Mulder-Krieger, R.F. Spanjersberg, S.F. Roerink, G. van den Hout, et al., A series of ligands displaying a remarkable agonistic antagonistic profile at the adenosine A1
275
receptor, J. Med. Chem. 48 (2005) 2045e2053. [17] M.W. Beukers, L.C. Chang, J.K. von Frijtag Drabbe Künzel, T. Mulder-Krieger, R.F. Spanjersberg, J. Brussee, et al., New, non-adenosine, high-potency agonists for the human adenosine A2B receptor with an improved selectivity profile compared to the reference agonist N-ethylcarboxamidoadenosine, J. Med. Chem. 47 (2004) 3707e3709. [18] G.W. Cave, M.J. Hardie, B.A. Roberts, C.L. Raston, A versatile six-component molecular capsule based on benign Synthons selective confinement of a heterogeneous molecular aggregate, Eur. J. Org. Chem. 2001 (2001) 3227e3231. [19] Z. Clyde-Watson, N. Bampos, J.K. Sanders, Mixed cyclic trimers of porphyrins and dioxoporphyrins: geometry vs. electronics in ligand recognition, New J. Chem. 22 (1998) 1135e1138. [20] Y. Kanithi, Synthesis of 2, 4, 6-triaryl pyridines under solvent free condition, Int. J. Appl. Pure Sci. Agric. (IJAPSA) 02 (2016) 80e84. [21] M. Studio, Version 7.0, Accelrys Software Inc., San Diego, CA, 2013. [22] S.J. Clark, M.D. Segall, C.J. Pickard, P.J. Hasnip, M.I. Probert, K. Refson, et al., First principles methods using CASTEP, Z. Kristallogr. 220 (2005) 567e570. [23] J.P. Perdew, K. Burke, M. Ernzerhof, Generalized gradient approximation made simple, Phys. Rev. Lett. 77 (1996) 3865e3868. [24] A.R. Chaudhry, R. Ahmed, A. Irfan, M. Mohamad, S. Muhammad, B. Ul Haq, et al., Optoelectronic properties of naphtho[2, 1-b:6, 5-b0 ]difuran derivatives for photovoltaic application: a computational study, J. Mol. Model. 22 (2016) 1e13. [25] A.R. Chaudhry, A. Irfan, S. Muhammad, A.G. Al-Sehemi, R. Ahmed, Z. Jingping, Computational study of structural, optoelectronic and nonlinear optical properties of dynamic solid-state chalcone derivatives, J. Mol. Graph. Model. 75 (2017) 355e364. [26] A. Irfan, A.R. Chaudhry, S. Muhammad, A.G. Al-Sehemi, Exploring the potential of boron-doped nanographene as efficient charge transport and nonlinear optical material: a first-principles study, J. Mol. Graph. Model. 75 (2017) 209e219. [27] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, et al., Gaussian 09, Revision B.01, 2009. Wallingford CT. [28] G. Fabricius, E.P. y Blanca, C. Rodriguez, A. Ayala, P. De la Presa, A.L. García, Electronic structure of cubic SrHfO 3: ferroelectric stability and detailed comparison with SrTiO 3, Phys. Rev. B 55 (1997) 164. [29] B. Luo, X. Wang, Y. Zhang, Y. Xia, First principles study of structural, electronic and optical properties of Pb doped SrHfO3, Mater. Chem. Phys. 133 (2012) 857e862. [30] H. Liu, Z.-T. Liu, J. Ren, Q.-J. Liu, Structural, electronic, mechanical, dielectric and optical properties of TiSiO4: first-principles study, Solid State Commun. 251 (2017) 43e49. [31] S. Muhammad, M.R.S.A. Janjua, Z. Su, Investigation of dibenzoboroles having p-electrons: toward a new type of two-dimensional NLO molecular switch? J. Phys. Chem. C 113 (2009) 12551e12557. [32] 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. Graph. Model. 72 (2017) 58e69. [33] J. Andzelm, B.C. Rinderspacher, A. Rawlett, J. Dougherty, R. Baer, N. Govind, Performance of DFT methods in the calculation of optical spectra of TCFchromophores, J. Chem. Theor. Comput. 5 (2009) 2835e2846. [34] A.N. Castro, L.R. Almeida, M.M. Anjos, G.R. Oliveira, H.B. Napolitano, C. Valverde, et al., Theoretical study on the third-order nonlinear optical properties and structural characterization of 3-Acetyl-6-Bromocoumarin, Chem. Phys. Lett. 653 (2016) 122e130. [35] P.S.P. Silva, H. El Ouazzani, M. Pranaitis, M.R. Silva, C.T. Arranja, A.J.F.N. Sobral, et al., Experimental and theoretical studies of the second-and third-order NLO properties of a semi-organic compound: 6-Aminoquinolinium iodide monohydrate, Chem. Phys. 428 (2014) 67e74. [36] K. Hatua, P.K. Nandi, Theoretical study of electronic structure and third-order optical properties of berylliumehydrocarbon complexes, Theor. Comput. Model. 996 (2012) 82e90. [37] A. Karakas, A. Migalska-Zalas, Y. El Kouari, A. Gozutok, M. Karakaya, S. Touhtouh, Quantum chemical calculations and experimental studies of third-order nonlinear optical properties of conjugated TTFequinones, Opt. Mater. 36 (2013) 22e26. [38] D.L. Andrews, D.S. Bradshaw, M.M. Coles, Perturbation theory and the twolevel approximation: a corollary and critique, Chem. Phys. Lett. 503 (2011) 153e156. [39] J.L. Bredas, C. Adant, P. Tackx, A. Persoons, B.M. Pierce, Third-order nonlinear optical response in organic materials: theoretical and experimental aspects, Chem. Rev. 94 (1994) 243e278. [40] M. Nakano, M. Okumura, K. Yamaguchi, T. Fueno, CNDO/S‒CI calculations of hyperpolarizabilities. III. Regular polyenes, charged polyenes, di-substituted polyenes, polydiacetylene and related species, Mol. Cryst. Liq. Cryst. Inc. Nonlinear Optic. 182 (1990) 1e15. [41] A. Willetts, J.E. Rice, D.M. Burland, D.P. Shelton, Problems in the comparison of theoretical and experimental hyperpolarizabilities, J. Chem. Phys. 97 (1992) 7590e7599. [42] Z.-J. Li, F.-F. Wang, Z.-R. Li, H.-L. Xu, X.-R. Huang, D. Wu, et al., Large static first and second hyperpolarizabilities dominated by excess electron transition for radical ion pair salts M 2þ TCNQ(M¼ Li, Na, K), Phys. Chem. Chem. Phys. 11 (2009) 402e408.
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Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc
Exploring the functional properties of Trimethoxy-Phenylpyridine as efficient optical and nonlinear optical material: A quantum chemical approach Aijaz Rasool Chaudhry a, *, Shabbir Muhammad b, Bakhtiar Ul Haq b, Santosh Kumar c, Abdullah G. Al-Sehemi d, Ahmad Irfan d, A. Laref e, Arshad Hussain f, g a
Deanship of Scientific Research, University of Bisha, Bisha, 61922, P.O. Box 551, Saudi Arabia Department of Physics, College of Science, King Khalid University, Abha, 61413, P.O. Box 9004, Saudi Arabia Division of Chemical Engineering, Konkuk University, Seoul, 143701, South Korea d Department of Chemistry, College of Science, King Khalid University, Abha, 61413, P.O. Box 9004, Saudi Arabia e Department of Physics and Astronomy, College of Science, King Saud University, Riyadh, 11451, Saudi Arabia f Shenzhen Key Laboratory of Advanced Thin Films and Applications, College of Physics and Energy, Shenzhen University, Shenzhen, 518060, PR China g Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen, 518060, China b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 January 2019 Received in revised form 18 February 2019 Accepted 25 February 2019 Available online 28 February 2019
In the current study, the 2,6-diphenyl-4-(3,4,5-trimethoxyphenyl)pyridine (compound 1) has been investigated as proficient material for optoelectronic and nonlinear optical (NLO) applications. In order to highlight the potential at both solid-state (bulk) and molecular levels, different electronic and optical parameters were investigated. The optical and electronic parameters such as refractive index, reflectivity, dielectric function, extinction coefficient, conductivity, electronic band structure, density of states (DOS) of newly reported trimethoxy-phenylpyridine at bulk (solid-state) level have been studied. The band gap is found to be 2.817 eV, which revealed the photon absorption competency has been improved in compound 1 due to narrow band gap and has the capability of containing the absorbed energy. Other calculated optoelectronic properties also revealed that the compound 1 might be better for semiconductor applications. Additionally, the geometric parameters, polarizability (isotropic and anisotropic) and third-order NLO polarizability have been computed at molecular level. For compound 1, its isotropic and anisotropic values are found to be 63.41 1024 esu and 46.22 1024 esu, respectively. The calculated g amplitude for studied material has been computed as 187.53 1036 esu that is about 25 times bigger than that of the g amplitude for pNA (a prototype NLO molecule). The third order NLO response for compound 1 has been further tuned through the designing of its further derivatives in the form of compounds 1a, 1b and 1c. Thus, the present study highlights the important optoelectronic and NLO properties of compound 1 and its derivatives. © 2019 Elsevier B.V. All rights reserved.
Keywords: Electro-optical properties NLO material Semiconductor Photovoltaic application Reflectivity
1. Introduction Organic semiconductor materials (OSMs) have been fascinating the experimental as well as theoretical scientists owing to the flexibility, cheaper cost of procedures, great performance, less weight and easiness of fabrication on bendy surfaces [1e9]. As firstly stated in 1986 [10], OSMs have been widely investigated for
* Corresponding author. E-mail address: [email protected] (A.R. Chaudhry). https://doi.org/10.1016/j.molstruc.2019.02.102 0022-2860/© 2019 Elsevier B.V. All rights reserved.
their applications in optoelectronic and micro-electronics, like organic light emitting diodes (OLEDs) [11,12] and organic photovoltaic devices (OPVs) [12,13]. An interesting synthetic strategy is one-pot multicomponent coupling reactions to synthesize the pyridine containing complexes. In this technique, numerous organic moieties can be joined in a single phase, for carbon-carbon as well as carbon-heteroatom bond foundation to synthesize smallmolecules with various degrees of structural diversities [14]. Using this strategy, recently two multiaryl substituted pyridine compounds were modeled and synthesized with high HOMO and LUMO energies and have been reported as good electron
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transporters [15]. The hugely switched pyridine compounds, such as 2-amino-4-aryl-3,5-dicyano-6-sulfanylpyridines have substantial and various medical uses [16,17]. A new terpyridine ligand and the well-known calix[4]resorcinarene have been synthesized, which allows access to a new type of supramolecular pyridine compound and reduces the overall waste [18]. A series of metalloporphyrin comprising cyclical hosts was synthesized. The synthetic scheme of these compounds permits easy approach to a vast variety of asymmetrical cyclic hosts and analyze the binding between cavities [19]. Recently, the trimethoxy-phenylpyridine has been synthesis under solvent-free condition. A moderate and environmentally friendly technique was established to synthesize this compound by cyclo compression of aromatic ketones aldehydes and ammonium carbonate catalyst [20]. Although different properties of trimethoxy-phenylpyridine have been studied, a comprehensive study of electronic, optical and nonlinear optical (NLO) properties is still necessary. According to the recent literature review, no study with electronic, optical and NLO properties was found. In the present study, we used trimethoxy-phenylpyridine [20] (in text denoted by compound 1; see Fig. 1) to study its electro-optical and NLO properties. The key intention of present investigation is to explore the electro-optical properties including electronic band structure, total and partial density of states (TDOS/PDOS) along with the optical properties such as conductivity, extinction coefficient, reflectivity, dielectric function and refractive index for trimethoxyphenylpyridine at the solid-state (bulk) level. Furthermore, at molecular level the structural and NLO properties were also studied for this fascinating compound.
269
2.2. Single molecular methodology In the present investigation, we have performed quantum computational analysis at two levels, which includes single molecular calculations that were performed using Gaussian 09 [27]. For single molecular analysis, all geometries were fully optimized to their respective energy minimum before doing any further functional property calculations. The PBE0 functional is used among density functional theory (DFT) methods to optimization and other single molecular property calculations. The PBE0 is usually considered as a reliable choice for the calculations of different optoelectronic properties as evident from several previous contemporary studies. The choice of 6-311G** basis set is satisfactory which is triple-zeta basis set with double polarizations. The optimized geometry of compound 1 is compared with experimental values and there is a reasonable agreement among these bonding parameters. To calculate the polarizability and third-order NLO polarizability, we used finite field (FF) method within Tconvention as given in different literature. The following expressions were used to calculate the average isotropic polarizability (aiso ) as under:
aiso ¼
1 axx þ ayy þ azz 3
(1)
While for anisotropy of polarizability (Da),
1
aaniso ¼ pffiffiffi
2
rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi h i axx ayy 2 þ ayy azz 2 þ ðazz axx Þ2 þ 6a2xz (2)
Similarly, for average g third-order polarizability: 2. Computational details 2.1. Solid-state methodology The experimental molecular crystal of compound 1 was imported into Materials Studio [21] for geometry optimization. The experimental lattice parameters were used to optimize the crystal structure of compound 1 (a ¼ 19.554, b ¼ 14.7990, c ¼ 7.5795, a ¼ g ¼ 90, b ¼ 101.157) with Cc space group and monoclinic lattice type [20]. The CASTEP module [22] as offered with Material studio [21] has been applied to evaluate the optoelectronic properties. The Perdew, Burke, and Ernzerhof parameterized GGA/PBE [23] within DFT framework is applied to estimate exchange and correlation energy/potential. The particulars of Brillouin Zone (BZ) have been described in supporting information and in references [24e26].
g ¼
1 X giijj þ gijij þ gijji 15
(3)
ij¼x;y;z
Under Kleinmann symmetry, the static second hyperpolarizability components are limited to only six components which were calculated using PBE0/6-311G** level of theory.
g ¼
1 gxxxx þ gyyyy þ gzzzz þ 2 gxxyy þ gxxzz þ gyyzz 5
(4)
3. Results and discussion 3.1. Solid-state optical and electronic properties The optical and electronic properties for OSMs are very critical to distinguish prospective utilization of these compounds into semiconductors, OFETs, OLEDs and photovoltaic device applications. The optical and electronic properties are also mandatory to evaluate the competence of organic materials.
Fig. 1. The representation of chemical structure for compound 1 [2,6-diphenyl-4(3,4,5-trimethoxyphenyl)pyridine].
3.1.1. Electronic band structure The electronic band structure exploration is very vital to unveil the potential of a material for optical applications. The compound 1 electronic band structure has been computed using GGA/PBE level of theory in the Brillouin Zone (BZ) at symmetrical points as demonstrated in Fig. 2. The total density of states (TDOS) as well as partial DOS (PDOS) have been displayed in Figs. 3 and 4 for all probable energy states arrangement that take a vital part in the electronic and optical properties of a OSMs. The optoelectronic parameters of compound 1 are generally formed by the bands confined adjoining Fermi level, hereafter enlarged band structure
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Fig. 2. The electronic band structure along with density of states (top) and zoomed spectra (bottom) for molecular crystal of compound 1 are schematically shown.
of compound 1 contiguous to Fermi level are presented in Fig. 2 to illuminate the bandgap more precisely. Fig. 2 presents the valence band maximum (VBM) of compound 1 has been created at G-point in BZ, whereas the conduction band minima (CBM) also has been originated at G-point, illuminating the fact that the compound 1 exhibits direct band gap as 2.817 eV on symmetrical G-point.
3.1.2. Density of states The density of states describes by the distribution of electron in energy spectrum of a material. The TDOS and PDOS have been calculated at GGA/PBE level of DFT for in-depth exploration of electronic properties of compound 1. Figs. 3 and 4 displayed the impact of s- and p- orbitals as well as the contribution of C, O and N atoms in the formation of TDOS and PDOS, respectively in the
energy ranging from 4 to 4 eV. It is clear from Fig. 3 that the energy peaks in the deep valance band (VB) are defined by s-orbitals, yet the participation from s-orbitals at the higher VB and in conduction band (CB) is negligibly small, clarifying a minor contribution from s-orbitals into the electronic properties. The peaks among the energy of 4 to 4 eV have been subjugated by the p-orbitals in VB as well as in CB. The exploration of electronic structure sketch establishes that compound 1 having remarkable optoelectronic characteristics would be a subsequent contestant for photovoltaic device applications.
3.1.3. Dielectric function To estimate the efficiency of OSMs, the optical properties of these organic materials are very essential to investigate. The real
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271
peaks between energy range of 1e5 eV and quickly fall down to zero, while after 6 eV presenting the identical spectra with zero intensity for all directions. The unchanging spectra unveiled the ultimate stability for compound 1 which eventually originating a large ability for transmitting electron inside the crystal, enlightening a greater intra- and inter-molecular charge transportation in the studied compound 1.
Fig. 3. Total density of states (TDOS) for compound 1 molecular crystals for s, p orbitals.
(ε1) and imaginary (ε2) parts for the dielectric function of compound 1 molecular crystal have been displayed in Fig. 5. The ε1 displays strong peaks in the smaller energy range between 2 and 3 eV with (100) and (010) directions (2.74 and 3.19, respectively) for compound 1. The static dielectric function ε(0) is evaluated as 1.90 and 2.10, respectively for (100) and (010) directions. The ε(0) with good values at 0 eV exposed the substantial ability to carry the electron within compound 1. Oxygen atoms in compound 1 may be responsible for the superior value of ε(0). The ε2 is primarily dominated in (100) as well as (010) directions for compound 1. The peaks of ε2 illuminate transfer of an electron from occupied valance band to unoccupied conduction band. It displayed that compound 1 would be good compound for charge transport. 3.1.4. Conductivity The conductivity function's real and imaginary parts (s1/s2) are displayed in Fig. 5. The s1 is dominated by the (100) and (010) directions (1.06 and 1.23, respectively) for compound 1 crystal structure. The s1 spectrum for compound 1 demonstrated high
3.1.5. Reflective index and extinction coefficient To shed light on the electro-optical characteristics of a material, it is very crucial to calculate the refractive index (n) and extinction coefficient (k). The evaluated maximum n is 1.434 in the polarization vector (010) direction for compound 1 at 0 eV as shown in Fig. 6. The evaluated n revealing that compound 1 would be better to refract a photon at lesser energy level. The compound 1 shows good values of n at lowermost energy between 0 and 4 eV, however after 4 eV the peaks start falling and established persistent and unchanged indices of 0.9 intensity after 10 eV. Fig. 6 reveals that the studied compound might be capable to yield decent outputs at lower energy inputs of 4 eV. 3.1.6. Reflectivity and loss function The reflectivity and energy loss function for compound 1 have been calculated and presented in Fig. 7 to understand the studied material. The compound 1 displayed good values at smaller energy in reflectivity peaks, then begins to reach a uniform value consequently after 8 eV as could be found in Fig. 7. The compound 1 revealed the higher reflectivity as 0.275 along (010) direction, that arises in the energy ranges from 4 to 6 eV. The reflectivity for a material is inversely proportional to transparency, thus inferior reflectivity unveils that the studied compound 1 might be capable materials for OPV application at lower energy. The loss function is an essential parameter demonstrating energy loss for a quickly moving electron passing within the molecular crystal structure [28e30]. The loss function for compound 1 was computed and presented graphically through Fig. 7. The highest peaks in loss function occur around 6 eV for compound 1 with a value of 3.49 in the (010) direction. The maximum peak in the calculated loss function spectrum corresponds to the quick decline of reflectivity (see Fig. 7).
Fig. 4. Partial density of states (PDOS) for compound 1 crystals from C (left), O (middle) and N (right).
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Fig. 5. Computed dielectric and conductivity for real (ε1/s1) along with imaginary part (ε 2/s2) for compound 1.
Fig. 6. Graphical representation of refractive index (n) and extinction coefficient (k) for compound 1.
Fig. 7. The computed reflectivity and energy loss function of compound 1.
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3.2. Single molecular electro-optical properties of compound 1 3.2.1. Single molecular geometry The single molecular geometry was completely optimized without any symmetry constrains. The initial geometries of compound 1 are extracted from its experimental crystallographic structure and later it has been optimized to its energy minima. A generally accepted PBE0/6-311** level was utilized to optimize the molecular geometry because PBE0 has been reported as a good approach to reproduce the molecular geometries as reported in previous studies [31e33]. The comparison of experimental crystallographic and optimized geometrical structures of compound 1 has been illustrated in Fig. 8. It is seen that the quantum chemical calculations reproduced the experimental geometry reasonably good. The experimental and calculated NeC bond distances of pyridine rings are 1.339 Å and 1.334 Å, respectively. The CeC bond distance between pyridine ring and phenyl rings are found to be 1.491 Å (experimental) and 1.482 Å (calculated). Similarly, the experimental and calculated central CeC bonds between trimethoxy phenyl and diphenyl pyridine moieties are found to be 1.485 Å (experimental) and 1.477 Å (calculated). The experimental and calculated CeNeC bond angles of pyridine rings are found to be 118.2 and 119.2 , respectively. Somewhat similar agreement is also seen between bond angles of trimethoxy -phenyl ring, which shows an overall agreement among the optimized and experimental structures (see Fig. 8). 3.2.2. Polarizability and third-order NLO polarizability For compound 1, its isotropic and anisotropic polarizabilities amplitudes (aiso and aaniso) have been collected in Table 1. Among the individual components, the axx amplitude is found to be the largest mounting to 76.82 1024 esu, which is due to its orientation along the central charge transfer axis as showed in Fig. 8. For compound 1, its isotropic and anisotropic values are found to be 63.41 1024 esu and 46.22 1024 esu, respectively, (see Table 1). The difference in isotropic and anisotropic values are 17.19 1024 esu. Furthermore, the third-order nonlinear polarizabilities (g) of compound 1 were also calculated to see its potential as third-order NLO material. Usually, the third-order NLO polarizability is assumed as origin of its microscopic nonlinear susceptibility, which can lead to different NLO phenomena like thirdharmonic generation (THG), two photon absorption (TPA), and optical Kerr effect etc. For instance, in THG, three photons of intense laser light are destroyed to generate a single light photon having a tripled frequency and/or one-third the wavelength, which has many modern technological applications. For compound 1, its calculated g amplitude is shown in Table 1 accompanied by its
273
Table 1 The polarizability (a, 1024 esu) and third-order polarizability (g 1036 esu) along with their individual components for compound 1 at PBE0/6-311G** level of theory.
a
a
1024 esu
g
1036 esu
axx axy ayy axz ayz azz aiso aaniso
76.82 5.11 60.38 5.66 22.48 53.03 63.41 46.22
gxxxx gyyyy gzzzz gxxyy gxxzz gyyzz
258.26 106.70 123.81 80.393 62.859 81.178 187.53 7.489
For a, 1 a. u. z 1.148176 1024 cm3.
individual components. For compound 1, it can be seen that like the polarizability component axx, the gxxxx component of g amplitude is the largest mounting to 258.26 1036 esu. The average g amplitude of compound 1 is computed as 187.53 1036 esu, which is reasonably larger for its practical application. To seek its real-time applications, the g amplitude of para-nitroaniline (pNA) has been also calculated in present investigation, which is often used as standard organic molecule for relative NLO response calculations in experiments. The molecular geometry and calculation of NLO properties were performed at the same level of theory for pNA, which makes the comparative analysis more reliable. The calculated average g amplitude of pNA is found to be 7.489 1036 esu as shown in Table 1. A comparison of calculated average g amplitude of compound 1 and pNA shows that the compound 1 possesses the average g amplitude which is about 25 times greater than that of the g amplitude of pNA.
3.2.3. Derivatives and Structure-NLO property relationship To comprehend the details about the structure-NLO property relationship, we have designed further derivatives for compound 1. The main idea in designing the new derivatives based on enhancing the push-pull configuration so that to move around the electron density for enhancing the efficient NLO compounds. The H atoms of terminal phenyl groups were replaced by NO2, C2PhNO2 and C2(CN)3 groups, which were all expected to act as good electron pulling groups (see Scheme 1). The third-order NLO polarizabilities for all the derivatives (1a, 1b and 1c) were calculated at the same PBE0/6-311G** level of theory and collected in Table 2 along with compound 1. As it can be seen in Table 2 that all the derivatives show significant enhancements in their g amplitudes. For example, the average g amplitudes of 1a, 1b and 1c are found to be 412.71 1036, 3153.9 1036 and 1804 1036 esu, respectively.
Fig. 8. The experimental (Exp.) and calculated (Cal.) geometries for compound 1 at PBE0/6-311** level of DFT.
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A.R. Chaudhry et al. / Journal of Molecular Structure 1185 (2019) 268e275 Table 3 The transition energies (DE), oscillator strength (fo), transition moment (mng), and % configuration interaction (C.I.) for all the compounds at TD-PBE0/6-311G** level of theory. Comp.
Electronic Excitation
DE (eV)
fo
mng
Transition
C.I.
1
S0/S1 S0/S2 S0/S1 S0/S5 S0/S1 S0/S2 S0/S1 S0/S5
4.145 4.207 3.315 3.775 3.127 3.226 2.339 2.789
0.149 0.435 0.001 0.628 1.780 0.803 0.004 0.816
1.183 2.055 0.048 2.591 4.819 3.187 0.227 3.412
103 105 127 125 179 179 155 153
0.563 0.694 0.670 0.693 0.465 0.482 0.631 0.692
1a 1b 1c
Scheme 1. The schematic representation for the derivatives of Compound 1 [2,6diphenyl-4-(3,4,5-trimethoxyphenyl)pyridine].
Table 2 The third-order polarizability (g 1036 esu) and its individual components as for compounds 1-1d at PBE0/6-311G** level.
g
1
1a
1b
1c
pNA
gxxxx gyyyy gzzzz gxxyy gxxzz gyyzz
258.26 106.70 123.81 80.393 62.859 81.178 187.53
776.77 15.49 622.19 8.011 303.53 10.40 412.71
7532.8 17.010 2034.9 33.43 3035.2 25.836 3153.9
4531.7 31.291 1221.9 63.646 1513.7 43.5782 1804.9
35.387 2.436 2.4964 0.1895 0.5767 1.012 7.489
These g amplitudes of 1a, 1b and 1c are about 2, 16 and 10 times higher than the average g amplitudes for parent compound 1. Interestingly, a comparison of average g amplitudes of systems 1a, 1b and 1c with that of pNA also shows remarkably larger NLO response properties of systems 1a, 1b and 1c. To see the real-time importance of designed derivatives, we have also compared the average g amplitudes of designed compounds to several recently designed compounds and found that our derivatives possess thirdorder NLO polarizability amplitudes, which is larger than these compounds. For example, derivatives of bromocoumarin [34] and aminoquinoline (6AQ) [35] illustrated g amplitudes of 22.34 1036 and 39.30 1036 esu at CAM-B3LYP/6-311G** and B3LYP/6-311G** levels of theory, respectively. Among several complexes, the importantly investigated berylliumehydrocarbon complex has shown g amplitudes of 139.30 1036 esu at PBE0/ 6-311þþG** level [36] and conjugated TTF-quinones showed 4.13 1036 and 4.66 1036 esu at TDHF/6-311 þ G** level [37]. It is essential to discuss that the effect of methodology may influence the average g amplitudes among different studies as above reported. Nonetheless, we believe that our designed derivatives are potential candidates for their use as efficient NLO materials.
3.2.4. The substitutional effect on NLO properties As seen in the above discussion that there is significant substitutional effect on the g amplitudes of parent compound 1. For instance, the g amplitudes of 1a, 1b and 1c are ~2 times, 16 times and 10 times larger than the parent system 1. In order to understand and compare the substitutional effects on the g amplitudes of systems 1a, 1b and 1c, we have calculated the TD-DFT calculations for all the systems as shown in Table 3. The substitutional effect on the third-order NLO response in compounds 1, 1a, 1b and 1c, we may consider the simple threestates approximations based on perturbative formula for static longitudinal gL (gzzzz) values as under [38]:
2
->106 ->106 ->128 ->129 -> 181 -> 180 ->156 ->156
3
X m2ng m2mn m2 Dm2 m4 5 gL ¼ 244 ng 3 ng ng3 þ DEng DEng mðmsnÞ E2ng DEmg
(5)
where mng ; DE and Dm are transition moment, transition energy and change in dipole moment related with transition from ground (jg) to crucial excited (jn) state. This so called three-state approximation is widely applied in theory and experiments to explain the changes in hyperpolarizabilities (b and g) using spectroscopic parameters of several donor-acceptor types of molecules. For further details of above approximations, we refer the reader to the works of Bredas [39], Nakano [40] and similar other researchers [41,42]. It can be perceived from above equation (5) that an optimal longitudinal component (in present case gzzzz) for a chemical compound can be achieved with lower DE and larger mng values. For present investigation, the spectroscopic parameters are calculated with TD-PBE0/6-311G** level of theory. The calculated values of fo ; DE and mng for two lowest transitions are collected in Table 3. A careful analysis of Table 3 shows that the compounds 1b and 1c possess larger transition moments/oscillator strengths and lower transition energies, which perhaps lead to their significantly larger g amplitudes. For instance, unlike systems 1 and 1a, the S0 to S1 transitions for systems 1b and 1c possess the lower transition energies of 3.127 and 2.339 eV, respectively. Additionally, the transition moment/oscillator strength of systems 1b is the largest that is perhaps the reason for its largest NLO response. Thus, the substitutions on compound 1 causes an enhanced push-pull effect for better intramolecular charge transfer process, which results in lower energy strong transitions in derivatives especially in compounds 1b and 1c. 4. Conclusions The present investigation highlights various insights into structure-property relationship of trimethoxy-phenylpyridine compound 1. The computed value of band gap is 2.817 eV for compound 1 that indicates the high photon absorption competency at lower energy level. This narrow band gap will enhance the smooth transfer of electron from valance to conduction bands. The optical and electronic properties like refractive index, reflectivity, dielectric function, conductivity, extinction coefficient, electronic band structure, density of states (DOS) of newly reported trimethoxy-phenylpyridine at bulk (solid-state) revealed the potential of compound 1 as good optoelectronic applications. The average g amplitude for compound 1 has been computed as 187.53 1036 esu with PBE0 method which are reasonably larger than similar prototype molecules. Furthermore, we have designed push-pull type derivatives of compound 1 as 1a, 1b and 1c. Interestingly, the average g amplitudes of 1a, 1b and 1c are found to be
A.R. Chaudhry et al. / Journal of Molecular Structure 1185 (2019) 268e275
412.71 1036, 3153.9 1036 and 1804 1036 esu, respectively. A further comparison showed that the g amplitudes of 1a, 1b and 1c are about 2, 16 and 10 times larger than the average g amplitudes of parent compound 1. The origin of larger g amplitudes are traced using three-state approximation through TD-DFT calculations. Thus, the present investigation highlights that our studied compounds are prospective competitors to be used in electro-optical and NLO device applications. Acknowledgement Authors are thankful to Deanship of Scientific Research at King Khalid University for funding this work through Research Group Project under grant number (R. G. P. 2/17/40). S. Kumar is also thankful to research support of KU brain pool Konkuk University 2019. The author A. Laref acknowledges the support from the “Research Center of the Female Scientific and Medical Colleges”, Deanship of Scientific Research, King Saud University. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.molstruc.2019.02.102. References [1] S. Azam, J. Bila, H. Kamarudin, A. Reshak, Electronic structure, electronic charge density and optical properties of 3-methyl-1, 4-dioxo-1, 4dohydronaphthalen-2-yl-sulfanyl (C13H10O4S), Int. J. Electrochem. Sci. 9 (2014) 445e459. [2] S. Azam, A. Reshak, Electronic structure of 1, 3-dicarbomethoxy4, 6benzenedicarboxylic acid: density functional approach, Int. J. Electrochem. Sci. 8 (2013) 10359e10375. [3] A.H. Reshak, H. Kamarudin, S. Auluck, Acentric nonlinear optical 2,4dihydroxyl hydrazone isomorphic crystals with large linear, nonlinear optical susceptibilities and hyperpolarizability, J. Phys. Chem. B 116 (2012) 4677e4683. [4] A.H. Reshak, H. Kamarudin, S. Auluck, Electronic structure, density of electronic states, and the chemical bonding properties of 2,4-dihydroxyl hydrazone crystals (C13H11N3O4), J. Mater. Sci. 48 (2013) 3805e3811. [5] A.H. Reshak, H. Kamarudin, I. Kityk, S. Auluck, Dispersion of linear, nonlinear optical susceptibilities and hyperpolarizability of C11H8N2O (o-Methoxydicyanovinylbenzene) crystals, J. Phys. Chem. B 116 (2012) 13338e13343. [6] A.H. Reshak, H. Kamarudin, I.V. Kityk, S. Auluck, Electronic structure, charge density, and chemical bonding properties of C11H8N2O o-methoxydicyanovinylbenzene (DIVA) single crystal, J. Mater. Sci. 48 (2013) 5157e5162. ski, [7] I. Fuks-Janczarek, A.H. Reshak, W. Ku znik, I.V. Kityk, R. Gaban M. Łapkowski, et al., UVevis absorption spectra of 1,4-dialkoxy-2,5-bis[2(thien-2-yl)ethenyl]benzenes, Spectrochim. Acta A: Mol. Biomol. Spectrosc. 72 (2009) 394e398. [8] A. Wojciechowski, K. Ozga, A.H. Reshak, R. Miedzinski, I.V. Kityk, J. Berdowski, et al., Photoinduced effects in l-alanine crystals, Mater. Lett. 64 (2010) 1957e1959. [9] M. Pokladko, E. Gondek, J. Sanetra, J. Nizioł, A. Danel, I.V. Kityk, et al., Spectral emission properties of 4-aryloxy-3-methyl-1-phenyl-1H-pyrazolo[3,4-b] quinolines, Spectrochim. Acta A: Mol. Biomol. Spectrosc. 73 (2009) 281e285. [10] A. Tsumura, H. Koezuka, T. Ando, Macromolecular electronic device: fieldeffect transistor with a polythiophene thin film, Appl. Phys. Lett. 49 (1986) 1210e1212. [11] C.W. Tang, S.A. VanSlyke, Organic electroluminescent diodes, Appl. Phys. Lett. 51 (1987) 913e915. [12] P.K.H. Ho, J.-S. Kim, J.H. Burroughes, H. Becker, S.F.Y. Li, T.M. Brown, et al., Molecular-scale interface engineering for polymer light-emitting diodes, Nature 404 (2000) 481e484. [13] F. Padinger, R.S. Rittberger, N.S. Sariciftci, Effects of postproduction treatment on plastic solar cells, Adv. Funct. Mater. 13 (2003) 85e88. [14] A. Ulaczyk-Lesanko, D.G. Hall, Wanted: new multicomponent reactions for generating libraries of polycyclic natural products, Curr. Opin. Chem. Biol. 9 (2005) 266e276. [15] N. Li, P. Wang, S.L. Lai, W. Liu, C.S. Lee, S.T. Lee, et al., Synthesis of multiarylsubstituted pyridine derivatives and applications in non-doped deep-blue OLEDs as electron-transporting layer with high hole-blocking ability, Adv. Mater. 22 (2010) 527e530. [16] L.C. Chang, J.K. von Frijtag Drabbe Künzel, T. Mulder-Krieger, R.F. Spanjersberg, S.F. Roerink, G. van den Hout, et al., A series of ligands displaying a remarkable agonistic antagonistic profile at the adenosine A1
275
receptor, J. Med. Chem. 48 (2005) 2045e2053. [17] M.W. Beukers, L.C. Chang, J.K. von Frijtag Drabbe Künzel, T. Mulder-Krieger, R.F. Spanjersberg, J. Brussee, et al., New, non-adenosine, high-potency agonists for the human adenosine A2B receptor with an improved selectivity profile compared to the reference agonist N-ethylcarboxamidoadenosine, J. Med. Chem. 47 (2004) 3707e3709. [18] G.W. Cave, M.J. Hardie, B.A. Roberts, C.L. Raston, A versatile six-component molecular capsule based on benign Synthons selective confinement of a heterogeneous molecular aggregate, Eur. J. Org. Chem. 2001 (2001) 3227e3231. [19] Z. Clyde-Watson, N. Bampos, J.K. Sanders, Mixed cyclic trimers of porphyrins and dioxoporphyrins: geometry vs. electronics in ligand recognition, New J. Chem. 22 (1998) 1135e1138. [20] Y. Kanithi, Synthesis of 2, 4, 6-triaryl pyridines under solvent free condition, Int. J. Appl. Pure Sci. Agric. (IJAPSA) 02 (2016) 80e84. [21] M. Studio, Version 7.0, Accelrys Software Inc., San Diego, CA, 2013. [22] S.J. Clark, M.D. Segall, C.J. Pickard, P.J. Hasnip, M.I. Probert, K. Refson, et al., First principles methods using CASTEP, Z. Kristallogr. 220 (2005) 567e570. [23] J.P. Perdew, K. Burke, M. Ernzerhof, Generalized gradient approximation made simple, Phys. Rev. Lett. 77 (1996) 3865e3868. [24] A.R. Chaudhry, R. Ahmed, A. Irfan, M. Mohamad, S. Muhammad, B. Ul Haq, et al., Optoelectronic properties of naphtho[2, 1-b:6, 5-b0 ]difuran derivatives for photovoltaic application: a computational study, J. Mol. Model. 22 (2016) 1e13. [25] A.R. Chaudhry, A. Irfan, S. Muhammad, A.G. Al-Sehemi, R. Ahmed, Z. Jingping, Computational study of structural, optoelectronic and nonlinear optical properties of dynamic solid-state chalcone derivatives, J. Mol. Graph. Model. 75 (2017) 355e364. [26] A. Irfan, A.R. Chaudhry, S. Muhammad, A.G. Al-Sehemi, Exploring the potential of boron-doped nanographene as efficient charge transport and nonlinear optical material: a first-principles study, J. Mol. Graph. Model. 75 (2017) 209e219. [27] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, et al., Gaussian 09, Revision B.01, 2009. Wallingford CT. [28] G. Fabricius, E.P. y Blanca, C. Rodriguez, A. Ayala, P. De la Presa, A.L. García, Electronic structure of cubic SrHfO 3: ferroelectric stability and detailed comparison with SrTiO 3, Phys. Rev. B 55 (1997) 164. [29] B. Luo, X. Wang, Y. Zhang, Y. Xia, First principles study of structural, electronic and optical properties of Pb doped SrHfO3, Mater. Chem. Phys. 133 (2012) 857e862. [30] H. Liu, Z.-T. Liu, J. Ren, Q.-J. Liu, Structural, electronic, mechanical, dielectric and optical properties of TiSiO4: first-principles study, Solid State Commun. 251 (2017) 43e49. [31] S. Muhammad, M.R.S.A. Janjua, Z. Su, Investigation of dibenzoboroles having p-electrons: toward a new type of two-dimensional NLO molecular switch? J. Phys. Chem. C 113 (2009) 12551e12557. [32] 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. Graph. Model. 72 (2017) 58e69. [33] J. Andzelm, B.C. Rinderspacher, A. Rawlett, J. Dougherty, R. Baer, N. Govind, Performance of DFT methods in the calculation of optical spectra of TCFchromophores, J. Chem. Theor. Comput. 5 (2009) 2835e2846. [34] A.N. Castro, L.R. Almeida, M.M. Anjos, G.R. Oliveira, H.B. Napolitano, C. Valverde, et al., Theoretical study on the third-order nonlinear optical properties and structural characterization of 3-Acetyl-6-Bromocoumarin, Chem. Phys. Lett. 653 (2016) 122e130. [35] P.S.P. Silva, H. El Ouazzani, M. Pranaitis, M.R. Silva, C.T. Arranja, A.J.F.N. Sobral, et al., Experimental and theoretical studies of the second-and third-order NLO properties of a semi-organic compound: 6-Aminoquinolinium iodide monohydrate, Chem. Phys. 428 (2014) 67e74. [36] K. Hatua, P.K. Nandi, Theoretical study of electronic structure and third-order optical properties of berylliumehydrocarbon complexes, Theor. Comput. Model. 996 (2012) 82e90. [37] A. Karakas, A. Migalska-Zalas, Y. El Kouari, A. Gozutok, M. Karakaya, S. Touhtouh, Quantum chemical calculations and experimental studies of third-order nonlinear optical properties of conjugated TTFequinones, Opt. Mater. 36 (2013) 22e26. [38] D.L. Andrews, D.S. Bradshaw, M.M. Coles, Perturbation theory and the twolevel approximation: a corollary and critique, Chem. Phys. Lett. 503 (2011) 153e156. [39] J.L. Bredas, C. Adant, P. Tackx, A. Persoons, B.M. Pierce, Third-order nonlinear optical response in organic materials: theoretical and experimental aspects, Chem. Rev. 94 (1994) 243e278. [40] M. Nakano, M. Okumura, K. Yamaguchi, T. Fueno, CNDO/S‒CI calculations of hyperpolarizabilities. III. Regular polyenes, charged polyenes, di-substituted polyenes, polydiacetylene and related species, Mol. Cryst. Liq. Cryst. Inc. Nonlinear Optic. 182 (1990) 1e15. [41] A. Willetts, J.E. Rice, D.M. Burland, D.P. Shelton, Problems in the comparison of theoretical and experimental hyperpolarizabilities, J. Chem. Phys. 97 (1992) 7590e7599. [42] Z.-J. Li, F.-F. Wang, Z.-R. Li, H.-L. Xu, X.-R. Huang, D. Wu, et al., Large static first and second hyperpolarizabilities dominated by excess electron transition for radical ion pair salts M 2þ TCNQ(M¼ Li, Na, K), Phys. Chem. Chem. Phys. 11 (2009) 402e408.