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Modulating the Charge Transfer of D-SA Molecules: Structures and NLO Properties Hong-Liang Xu J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/jp5103127 • Publication Date (Web): 23 Dec 2014 Downloaded from http://pubs.acs.org on January 4, 2015

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Modulating the Charge Transfer of D-S-A Molecules: Structures and NLO Properties

Journal: Manuscript ID: Manuscript Type: Date Submitted by the Author: Complete List of Authors:

The Journal of Physical Chemistry jp-2014-103127.R1 Article 23-Dec-2014 Zhang, Xue; Northeast Normal University, Xu, Hong-Liang; Northeast Normal University, Department of Chemistry Sun, Shi-Ling; Northeast Normal University , Wu, Heng-Qing; Northeast Normal University, Department of Chemistry Su, Zhong-Min; Northeast Normal University, Faculty of Chemistry

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Modulating the Charge Transfer of D-S-A Molecules: Structures and NLO Properties Xue Zhang, Heng-Qing Wu, Hong-Liang Xu,* Shi-Ling Sun*, and Zhong-Min Su Institute of Functional Material Chemistry, Faculty of Chemistry, Northeast Normal University, Changchun 130024, Jilin, People’s Republic of China E-mail: [email protected], [email protected] Abstract Very recently, the investigation of Li atom doped effect on “through-space” electronic interaction (S) of Donor-S-Acceptor (D-S-A, 1) shows that Li-doping effect can modulate the first hyperpolarizability of 1 (Dyes and Pigments, 2014, 106, 7-13). Can we further enhance the first hyperpolarizability (βtot) of 1 by modulating the charge transfer of D-S-A molecules? The present work indicates that the βtot value can be successfully modulated by replacing sp2-hybridized CH=CH moiety connected with substituted paracyclophane (PCP). On the other hand, the NO2 contributes more than NH2 to βtot value. The results of Time-dependent density functional theory (TD-DFT) provide a good explanation for the variation in βtot value. Interestingly, the βtot value of 3 (4.09×103 au) is larger than 1.52×103 au of 4, while the difference between the dipole moments (∆µ) of the ground state and the crucial excited state value of 3 (2.93 Debye) is smaller than that of 4 (7.79 Debye). Further, the charge transfer excitation length (DCT) of 3 (1.41 Å) is smaller than that of 4 (2.89 Å). Therefore, DCT is the major factor in determining ∆µ value. Keywords: D-S-A; First Hyperpolarizability; Charge Transfer; Dipole Moment

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1 Introduction Due to potential applications in optical and electro-optical devices, nonlinear optical (NLO) materials have been extensively explored over the past three decades.1-9 Many kinds of effective strategies have been put forward by experimenters and theorists to modulate NLO response. These strategies mainly include the extension of π-electron systems,10 the enhancement of the strength of donor and acceptor,11-13 the utilization of ocupolar molecules,5, 14 the change of framework shape,15-17 the use of bond length alternation (BLA) theory,18-19 the introduction of Li-doped electride/salt complexes,20-22 and so forth. Among them, the most typical strategy is based on donor–(π–conjugate bridge)–acceptor (D–π–A) structure,5 in which the donor and/or the acceptor, or the bridge moieties are selectively replaced by different groups. As a result, the push-pull electron effect of D–π–A molecule can be successfully modulated.5 Different from D–π–A scheme, Zyss introduced a new molecular engineering strategy (D–S–A) for NLO materials.23 In D–S–A form, the “S” moiety is referred to a novel kind of noncovalent charge transfer which can be expressed as “through-space” electronic interaction, such as π–π interaction. Intramolecular charge transfer (ICT) processes of D–S–A molecules (from a donor toward an acceptor moiety) are mainly through through-space electronic interactions instead of π–conjugate bridge. As noncovalent through-space electronic interactions could full or partial eliminate the conjugated electronic path which may ensure practical applications such as favorable displacement of the nonlinearity/transparency tradeoff or a possible improvement of the thermal stability, much effort has been devoted to investigate this interesting through-space electronic interaction.24-32 In our previous work,32 the methods of Li atom doping was used to investigate the interaction with novel noncovalent through-space electronic interaction (S) for the first time. The results show that Li atom can obviously modulate the first hyperpolarizability of D-S-A molecules. Moreover, the location of Li atom can also change NLO response.

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In Zyss’s work, D–S–A compound 4–(4–dihexylaminostyryl)–16–(4-nitrostyryl)[2.2] paracyclophane (PCP) was designed and synthesized.23 In order to reduce the amount of calculation, we use donor group (NH2) instead of donor group N(Hex)2. To the best of our knowledge, two phenyl groups in a bimolecular stack of D–S–A molecule were kept by two CH2-CH2 sp3 lateral vertical linkages. Our previous work show that when lateral vertical linkages were replaced by sp2-hybridized CH=CH, the βtot value is 9.16 ×103 au which is close to 9.13 ×103 au.32 The results indicate that lateral vertical linkages have little influence on βtot value. By doping Li atom, the βtot value of D-S-A molecules can be modulated. Here an interesting question emerges: how to modulate the βtot value of D–S–A molecule instead of doping? In order to answer above question, on the basis of D–S–A molecule (1), 2, 3 and 4 were designed in theory. 2 Methods As shown in investigations by Truhlar and Zhao,33-34 the global hybrid generalized gradient approximation M06-2X functional performs well in aromatic-aromatic stacking and main group chemistry, which is suitable for noncovalent interactions in our work. Therefore, the optimized geometric structures of all molecules were performed at the M06-2X/6-31G(d) level. The values of nucleus independent chemical shifts (NICS) were obtained at the CAM-B3LYP/6-311G++(d,p) level. For the calculation of the hyperpolarizability, it is important to choose a suitable method. The previous investigations indicate that the traditional density functional theory (DFT) methods overestimate the (hyper)polarizabilities for some systems.35 The second-order Møller–Plesset perturbation (MP2) method is more reliable than DFT methods in the hyperpolarizability calculations, but it is limited to small and medium-sized systems due to the high computing cost. Fortunately, coulomb-attenuated hybrid exchange-correlation functional (CAM-B3LYP) combines the hybrid qualities of B3LYP and the long-range correction presented by Tawada et al,36 has been proposed specifically to calculate the first hyperpolarizabilities of π-conjugated systems.37-39 Moreover, in

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our previous work, the CAM-B3LYP has been proved to be a proper method in calculating the first hyperpolarizability of D–S–A molecule.32 Thus, the βtot values were all evaluated at CAM-B3LYP/6-31+G(d) level throughout this work by analytical third energy derivatives. The TD DFT method was applied to calculate the maximum absorption wavelengths. The first hyperpolarizability is noted as:

β tot = ( β x2 + β y2 + β z2 )1 / 2 Where β i = β iii + β ijj + β ikk , i , j , k = x, y , z All of the above calculations were performed with Gaussian 09 program package.40 In addition, the hyper-Rayleigh scattering (HRS) response βHRS(−2ω;ω,ω) were evaluated by NLO Calculator program.41-42 The βHRS(−2ω;ω,ω) is described as: 2

2

β HRS (-2ω; ω ,ω ) = (〈 β zzz 〉 + 〈 βzxx 〉 )1 / 2 3 Results and Discussions 3.1 Geometrical Parameters The optimized structures of four molecules (1, 2, 3 and 4) are given in Fig. 1. Different from 1, in molecule 2, the electronic bridge connected with benzene ring (II) is replaced by sp3-hybridized CH2-CH2, which indicates that charge transfer of electron-donating group (NH2) is hindered. Similarly, sp3-hybridized CH2-CH2 is used to replace sp2-hybridized CH=CH moiety connected with benzene ring (I) in molecule 3 disrupting charge transfer towards electron-withdrawing group (NO2). In molecule 4, both sp2-hybridized CH=CH moieties connected with substituted paracyclophane (PCP) are replaced by sp3-hybridized CH2-CH2 groups. From Table 1, it is clear that C-C π bond connected with PCP is about 1.343 Å. The C-C (I) of 1 and 2 are all 1.343 Å and C-C (II) of 1 and 3 are 1.344 Å and 1.343 Å. On the other hand, C-C σ bond connected with PCP of 3 and 4 (C-C (I) of 3 and 4) are all 1.523 Å. Interestingly, the C-C σ bond connected with PCP in molecule 2 (C-C (II) of 2) is 1.532 Å which is longer than that

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of 1.523 Å. It indicates that bond strength of C-C σ bond connected with PCP in molecule 2 is weaker than corresponding σ bond in 3 and 4. To get more structural information, we calculate the dihedral angles (θ) of two C-C chemical bonds connected with PCP. As listed in Table 1, the θ of four molecules change in the order: 2 (-23.9°) < 4 (0.4°) < 1 (0.8°) < 3 (25.3°). Considering the absolute values of θ, it is clear that 1 and 4 are similar as well as 2 and 3. It has been accepted that the chemical properties are dependent on its chemical structures. Thus, structure-property relationships will be discussed in the following section. 3.2 The Nucleus Independent Chemical Shifts (NICS) and Absorption Spectrum It is well known that all that aromaticity as a central concept in chemistry is a very crucial property of conjugated cyclic molecules in the determination of their stability. However, aromaticity cannot be measured directly experimentally. Luckily, some valuable papers indicate that NICS value has a strong correlation with aromaticity.43-45 For example, the unusual aromaticity of planar hetero[8]circulenes have been widely described by the NICS criterion.46 In the present work, on the basis of magnetic shielding tensor of the ghost atom, the NICS values were calculated employing gauge-independent atomic orbital (GIAO) method. For 1, 2, 3 and 4, the distances between benzene ring (I) and benzene ring (II) are almost the same, which is about 3 Å indicating that C-C chemical bonds connected with PCP have little influence on distances between benzene ring (I) and benzene ring (II). To give clear understanding of our systems, in the central position of benzene ring (I) is defined as NICS(0.00) and that of the benzene ring (II) is NICS(3.00) as shown in Fig. 2. And then, we placed a ghost atom every 0.25 Å between the centers of benzene ring (I) and benzene ring (II) and 13 ghost atoms were employed. Interestingly, as shown in Fig. 2 and Table 2, it is obvious that NICS values of the four molecules are all negative, indicating their strong aromatic and stable abilities. The two local most negative values of four molecules are observed at NICS(1.00) and NICS(2.00) and the values of NICS(1.00) and NICS(2.00) of 2, 3 and 4 are slightly smaller than those of 1. The results indicate that C-C chemical bonds connected with PCP can slightly affect

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aromaticities of two stacked aromatic rings and the electronic structures of four molecules might be different. In addition, the NICS values of 4 are all smaller than those of 1, which indicates the replacement of both sp2-hybridized CH=CH moieties connected with substituted paracyclophane (PCP) by sp3-hybridized CH2-CH2 groups results in more negative aromaticities of two stacked aromatic rings. The absorption spectra of the four molecules (1, 2, 3 and 4) are shown in Fig. 3. It can be found that all of the four molecules have obvious absorption peaks within the visible region. In addition, the maximum absorption wavelength (in Table 1) of 1, 2, 3 and 4 change in the order of 1 (λmax=330.0 nm) > 2 (λmax=329.0 nm) > 3 (λmax=310.6 nm) > 4 (λmax=251.3 nm). It suggests that the λmax shows hypochromic shift when the C-C π bond connected with PCP is replaced by C-C σ bond. This hypochromic shift λmax might lead to the effect on nonlinear optical responses. On the basis of the discussion above, we are interested in how do C-C chemical bonds connected with PCP influence on the first hyperpolarizability? 3.3 The Static First Hyperpolarizabilities (βtot) According to Table 3, it can be obviously found that the major contribution to the βtot value is βz, which is the direction of charge transfer. The βtot values change in the order: 9.13×103 (1) > 5.41×103 (2) > 4.09×103 (3) > 1.52×103 au (4). When both sp2-hybridized CH=CH moieties connected with substituted PCP are replaced by sp3-hybridized CH2-CH2 groups, the charge transfers of NO2 and NH2 are hindered resulting in the smallest βtot value. Moreover, the βtot value of 2 (5.41×103 au) is larger than that of 3 (4.09×103 au) indicating NO2 contributes larger than NH2 to βtot value. The results also show that the βtot value of D–S–A molecule (1) can be successfully modulated by sp3-hybridized CH2-CH2 group replacing sp2-hybridized CH=CH moiety connected with PCP. To provide an understanding of the origins of first hyperpolarizabilities, we focused on the relative electronic spatial extent, . As listed in Table 3, the values of four molecules are the same order of magnitude, which change in the order: 2.76×104 (1) > 2.77×104 (2) > 2.78×104 (3) > 2.82×104 au (4). To the best of our knowledge,

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the is a physical property which characterizes the electron density volume around the molecule.47 The more diffuse electron cloud may lead to larger value resulting in larger βtot value. However, in our system, 4 has smallest βtot value (1.52×103 au) associated with the largest value (2.82×104 au). Why? According to the approximate two-level expression:48-49 the βtot value is proportional to the difference between the dipole moments of the ground state and the crucial excited state (∆µ) and the oscillator strength (f0) but inversely proportional to the third power of the transition energy (∆E). It is obvious that the ∆E is the decisive factor in determining the first hyperpolarizability. In this work, the ∆µ, f0 and ∆E values of crucial excited state for four molecules were estimated by the time-dependent CAM-B3LYP/6-31+G(d) method, and the results are listed in Table 3. The crucial excited state is the lowest excited state with larger oscillator strength among all excited states calculated by TD-DFT calculations. The order of ∆E values for 1, 2, 3 and 4 is 3.73 (1) < 3.77 (2) < 3.99 (3) < 4.95 eV (4). Obviously, the order of ∆E3 values is opposite to that of the βtot values for the two-level expression. Furthermore, as shown in Fig. 4, the variation trend of ∆µf0/∆E3 is consistent with βtot value, suggesting that the trend in ∆µf0/∆E3 provides a good explanation for the variation in βtot value. It is worth noting that the βtot value of 3 (4.09×103 au) is larger than 4 (1.52×103 au), while the ∆µ value of 3 (2.93 Debye) is smaller than that of 4 (7.79 Debye). In addition, the ∆µ value of 1 and 2 are similar. Investigating further, we focused on analyzing the molecular orbitals of the crucial transition states of 1, 2, 3 and 4 to understand the origin of these properties. As shown in Fig. 5, the major transitions of 1 and 2 are similar resulting in the similar ∆µ value. On the other hand, the major transition of 3 occurs at the side of donor group because of disrupting charge transfer towards electron-withdrawing group (NO2). For 4, though both sp2-hybridized CH=CH moieties connected with substituted paracyclophane (PCP) are replaced by sp3-hybridized CH2-CH2 groups, electron cloud transfers from the benzene ring connected with NO2 to NO2 indicating that benzene ring connected with NO2 acts as a new electron-donating group.

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On the basis of above discussion, the crucial transition of four molecules can still hardly explain why ∆µ value of 3 is smaller than that of 4. Recently, a qualitative index of spatial extent (DCT, qCT and µCT) in charge-transfer excitations proposed by Ciofini may help us understand the spatial extent associated to an electronic transition from the ground state to the excited state.50-51 The computational details have been shown in supporting information. Among them, DCT is the CT excitation length as the distance between the two barycenters of density distributions (increment and depletion) upon electronic excitation, qCT is charge transfer amount and µCT is dipole moment variation. From Table 3, it is obvious that DCT value of 3 (1.41 Å) is smaller than that of 4 (2.89 Å). What’s more, the variation trend of DCT values (1.41 (3) < 2.89 (4) < 3.05 (2) < 3.35 Å (1)) is agreement with that of ∆µ values (2.93 (3) < 7.79 (4) < 9.22 (2) < 9.99 Debye (1)). Therefore, DCT value is the major factor in determining the ∆µ value. 3.4 The Static and Dynamic Hyper-Rayleigh Scattering Response With the help of NLO Calculator program, the static and dynamic hyper-Rayleigh scattering (HRS) responses βHRS(−2ω;ω,ω) were evaluated. In all the studied systems, the charge transfer axes are chosen as Z-axis. As listed in Table 4, the static βHRS(−2ω;ω,ω) values change in the order: 3.83×103 (1) > 2.30×103 (2) > 1.72×103 (3) > 6.68×102 au (4), which is in accordance with βtot values. For dynamic case, the βHRS(−2ω;ω,ω) values of four molecules increase with decreasing λ from 1907 to 1064 nm. Therefore, different from Li-doped D-S-A molecules, there is no resonances occur in 1, 2, 3 and 4. What’s more, the results show that frequency-dependent effect is not very obvious for 1, 2, 3 and 4. For example, the βHRS(−2ω;ω,ω) value (λ = 1460 nm) of 4 (9.32×102 au) is no more than 2 times than corresponding static βHRS(−2ω;ω,ω) value (6.68×102 au). 4 Conclusions In the present work, on the basis of D-S-A molecules 1, 2, 3 and 4 were designed by using sp3-hybridized CH2-CH2 group replacing sp2-hybridized CH=CH moiety connected with substituted paracyclophane (PCP). The results

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indicate that C-C chemical bonds connected with PCP can slightly affect aromaticities of two stacked aromatic rings. The absorption corresponding to the maximum wavelength of molecules shows a blue shift from 2, 3, to 4. Interestingly, by replacing sp2-hybridized CH=CH connected with substituted PCP, the first hyperpolarizability (βtot) can be successfully modulated and the βtot value change in the order: 9.13×103 (1) > 5.41×103 (2) > 4.09×103 (3) > 1.52×103 au (4). TD-DFT calculations suggest that the trend in ∆µf0/∆E3 provides a good explanation for the variation in βtot value. It is worth noting that the βtot value of 3 (4.09×103 au) is larger than 4 (1.52×103 au), while the ∆µ value of 3 (2.93 Debye) is smaller than that of 4 (7.79 Debye). Investigating further, we find the charge transfer excitation length (DCT) plays important role in determining the ∆µ value. In addition, there is no resonances occur in 1, 2, 3 and 4. Acknowledgments The authors gratefully acknowledge financial support from National Science Foundation of China (NSFC) (21003019, 21473026), the Science and Technology Development Planning of Jilin Province (201201062 and 20140101046JC), the Computing Center of Jilin Province provided essential support and H.-L.X. acknowledges support from the Hong Kong Scholars Program. And Project funded by China Postdoctoral Science Foundation 2014M560227). Supporting Information The NICS values (ppm) of the four molecules obtained by different methods and computational details of Ciofini’s scheme are shown in supporting information. This material is available free of charge via the Internet at http://pubs.acs.org.

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Hyperpolarizability/Bond-Length Alternation Parameter Relationship. Proc. Natl. Acad. Sci. U. S. A. 2010, 107, 16453-16458. (20) Chen, W.; Li, Z.-R.; Wu, D.; Li, Y.; Sun, C.-C.; Gu, F. L. The Structure and the Large Nonlinear Optical Properties of Li@Calix[4]pyrrole. J. Am. Chem. Soc. 2005, 127, 10977-10981. (21) Xu, H.-L.; Li, Z.-R.; Wu, D.; Wang, B.-Q.; Li, Y.; Gu, F. L.; Aoki, Y. Structures and Large NLO Responses of New Electrides: Li-Doped Fluorocarbon Chain. J. Am. Chem. Soc. 2007, 129, 2967-2970. (22) Muhammad, S.; Xu, H.; Liao, Y.; Kan, Y.; Su, Z. Quantum Mechanical Design and Structure of the Li@B10H14 Basket with a Remarkably Enhanced Electro-Optical Response. J. Am. Chem. Soc. 2009, 131, 11833-11840. (23) Zyss, J.; Ledoux, I.; Volkov, S.; Chernyak, V.; Mukamel, S.; Bartholomew, G. P.; Bazan, G. C. Through-Space Charge Transfer and Nonlinear Optical Properties of Substituted Paracyclophane. J. Am. Chem. Soc. 2000, 122, 11956-11962. (24) Diederich, F. Complexation of Neutral Molecules by Cyclophane Hosts. Angew. Chem. Int. Ed. Engl 1988, 27, 362-386. (25) Cozzi, F.; Cinquini, M.; Annuziata, R.; Siegel, J. S. Dominance of Polar/.pi. over Charge-transfer Effects in Stacked Pheny Interactions. J. Am. Chem. Soc. 1993, 115, 5330-5331. (26) Bazan, G. C.; Oldham, W. J.; Lachicotte, R. J.; Tretiak, S.; Chernyak, V.; Mukamel, S. Stilbenoid Dimers: Dissection of a Paracyclophane Chromophore. J. Am. Chem. Soc. 1998, 120, 9188-9204. (27) Oldham, W. J.; Miao, Y.-J.; Lachicotte, R. J.; Bazan, G. C. Stilbenoid Dimers: Effect of Conjugation Length and Relative Chromophore Orientation. J. Am. Chem. Soc. 1998, 120, 419-420. (28) Purring, C.; Zou, H.; Wang, X.; McLendon, G. Stoichiometry, Free Energy, and Kinetic Aspects of Cytochrome c: Apaf-1 Binding in Apoptosis. J. Am. Chem. Soc. 1999, 121, 7435-7436.

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(29) Bartholomew, G. P.; Ledoux, I.; Mukamel, S.; Bazan, G. C.; Zyss, J. Three-Dimensional Nonlinear Optical Chromophores Based on Through-Space Delocalization. J. Am. Chem. Soc. 2002, 124, 13480-13485. (30) Hong, J. W.; Woo, H. Y.; Liu, B.; Bazan, G. C. Solvatochromism of Distyrylbenzene Pairs Bound Together by [2.2]Paracyclophane: Evidence for a Polarizable “Through-Space” Delocalized State. J. Am. Chem. Soc. 2005, 127, 7435-7443. (31) Mukhopadhyay, S.; Jagtap, S. P.; Coropceanu, V.; Brédas, J.-L.; Collard, D. M. π-Stacked Oligo(phenylene vinylene)s Based on Pseudo-Geminal Substituted [2.2]Paracyclophanes: Impact of Interchain Geometry and Interactions on the Electronic Properties. Angew. Chem. Int. Ed. 2012, 51, 11629-11632. (32) Wu, H.-Q.; Xu, H.-L.; Sun, S.-L.; Su, Z.-M. Li Doped Effect of Through Novel Noncovalent Charge Transfer on Nonlinear Optical Properties. Dyes Pigments 2014, 106, 7-13. (33) Zhao, Y.; Truhlar, D. G. Density Functionals with Broad Applicability in Chemistry. Acc. Chem. Res. 2008, 41, 157-167. (34) Zhao, Y.; Truhlar, D. The M06 Suite of Density Functionals for Main Group Thermochemistry, Thermochemical Kinetics, Noncovalent Interactions, Excited States, and Transition Elements: Two New Functionals and Systematic Testing of Four M06-class Functionals and 12 Other Functionals. Theor. Chem. Acc. 2008, 120, 215-241. (35) Champagne, B.; Perpète, E. A.; Jacquemin, D.; van Gisbergen, S. J. A.; Baerends, E.-J.; Soubra-Ghaoui, C.; Robins, K. A.; Kirtman, B. Assessment of Conventional Density Functional Schemes for Computing the Dipole Moment and (Hyper)polarizabilities of Push−Pull π-Conjugated Systems. J. Phys. Chem. A 2000, 104, 4755-4763. (36) Tawada, Y.; Tsuneda, T.; Yanagisawa, S.; Yanai, T.; Hirao, K. A Long-Range-Corrected Time-Dependent Density Functional Theory. J. Chem. Phys. 2004, 120, 8425-8433.

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(37) Polavarapu, P. L.; Donahue, E. A.; Shanmugam, G.; Scalmani, G.; Hawkins, E. K.; Rizzo, C.; Ibnusaud, I.; Thomas, G.; Habel, D.; Sebastian, D. A Single Chiroptical Spectroscopic Method May Not Be Able To Establish the Absolute Configurations of Diastereomers: Dimethylesters of Hibiscus and Garcinia Acids. J. Phys. Chem. A 2011, 115, 5665-5673. (38) Ma, F.; Li, Z.-R.; Zhou, Z.-J.; Wu, D.; Li, Y.; Wang, Y.-F.; Li, Z.-S. Modulated Nonlinear Optical Responses and Charge Transfer Transition in Endohedral Fullerene Dimers Na@C60C60@F with n-Fold Covalent Bond (n = 1, 2, 5, and 6) and Long Range Ion Bond. J. Phys. Chem. C 2010, 114, 11242-11247. (39) Cai, Z.-L.; Crossley, M. J.; Reimers, J. R.; Kobayashi, R.; Amos, R. D. Density Functional Theory for Charge Transfer: The Nature of the N-Bands of Porphyrins and Chlorophylls Revealed through CAM-B3LYP, CASPT2, and SAC-CI Calculations. J. Phys. Chem. B 2006, 110, 15624-15632. (40) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A. et al. GAUSSIAN 09w, Revision D.01, Gaussian, Inc., Wallingford CT, 2013. (41) Dongdong Qi, NLO Calculator, Version 0.2, University of Science and Technology Beijing, Beijing 100083, China. (42) Zhang, L.; Qi, D.; Zhao, L.; Chen, C.; Bian, Y.; Li, W. Density Functional Theory Study on Subtriazaporphyrin Derivatives: Dipolar/Octupolar Contribution to the Second-Order Nonlinear Optical Activity. J. Phys. Chem. A 2012, 116, 10249-10256. (43) Chen, Z.; Wannere, C. S.; Corminboeuf, C.; Puchta, R.; Schleyer, P. v. R. Nucleus-Independent Chemical Shifts (NICS) as an Aromaticity Criterion. Chem. Rev. 2005, 105, 3842-3888. (44) Schleyer, P. v. R.; Maerker, C.; Dransfeld, A.; Jiao, H.; Hommes, N. J. R. v. E. Nucleus-Independent Chemical Shifts: A Simple and Efficient Aromaticity Probe. J. Am. Chem. Soc. 1996, 118, 6317-6318.

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(45) Xu, S.; Wang, C.; Cui, Y. Aromaticity of Ionic Structures: Investigation and Application of NICS Value and 4n + 2 rule. Int. J. Quantum. Chem. 2010, 110, 1287-1294. (46) Baryshnikov, G. V.; Valiev, R. R.; Karaush, N. N.; Minaev, B. F. Aromaticity of the Planar Hetero[8]circulenes and Their Doubly Charged Ions: NICS and GIMIC Characterization. Phys. Chem. Chem. Phys. 2014, 16, 15367-15374. (47) Scuderi, D.; Paladini, A.; Satta, M.; Catone, D.; Piccirillo, S.; Speranza, M.; Guidoni, A. G. Chiral Aggregates of Indan-1-ol with Secondary Alcohols and Water: Laser Spectroscopy in Supersonic Beams. Phys. Chem. Chem. Phys. 2002, 4, 4999-5003. (48) Oudar, J. L.; Chemla, D. S. Hyperpolarizabilities of the Nitroanilines and Their Relations to the Excited State Dipole Moment. J. Chem. Phys. 1977, 66, 2664-2668. (49) Oudar, J. L. Optical Nonlinearities of Conjugated Molecules. Stilbene Derivatives and Highly Polar Aromatic Compounds. J. Chem. Phys. 1977, 67, 446-457. (50) Le Bahers, T.; Adamo, C.; Ciofini, I. A Qualitative Index of Spatial Extent in Charge-Transfer Excitations. J. Chem. Theory Comput. 2011, 7, 2498-2506. (51) Ciofini, I.; Le Bahers, T.; Adamo, C.; Odobel, F.; Jacquemin, D. Through-Space Charge Transfer in Rod-Like Molecules: Lessons from Theory. J. Phys. Chem. C 2012, 116, 11946-11955.

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Table 1 The selected geometrical parameters of four molecules obtained at the M06-2X/6-31G(d) level and the λmax of four molecules obtained at the CAM-B3LYP/6-31+g(d) level. C-C (I) (Å) is C-C chemical bond connected with benzene ring (I) and the similar definition for C-C (II) and θ (°) is dihedral angles of two selected C-C chemical bonds

C-C (I) C-C (II) θ λmax

1

2

3

4

1.343 1.344 0.8 330.0

1.343 1.532 -23.9 329.0

1.523 1.343 25.3 310.6

1.523 1.523 0.4 251.3

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Table 2 The NICS values (ppm) of the four molecules obtained at the CAM-B3LYP/6-311G++(d, p) level

NICS (0.00)a NICS (0.25) NICS (0.50) NICS (0.75) NICS (1.00) NICS (1.25) NICS (1.50) NICS (1.75) NICS (2.00) NICS (2.25) NICS (2.50) NICS (2.75) NICS (3.00) a

1

2

3

4

-9.1 -10.9 -12.9 -14.1 -14.3 -14.2 -14.1 -14.3 -14.5 -14.0 -12.5 -10.4 -8.9

-9.0 -10.6 -12.7 -14.1 -14.6 -14.6 -14.5 -14.8 -15.0 -14.6 -13.2 -11.0 -9.3

-9.1 -10.7 -13.0 -14.6 -15.1 -14.9 -14.6 -14.6 -14.7 -14.4 -13.2 -11.1 -9.3

-9.3 -11.1 -13.2 -14.7 -15.1 -15.0 -14.9 -15.0 -15.0 -14.4 -12.8 -10.7 -9.2

Central position of benzene ring (I) is defined as NICS(0.00) and that of the benzene ring (II) is NICS(3.00) as

shown in Fig. 2. And then, a ghost atom every 0.25 Å have been placed between the centers of benzene ring (I) and benzene ring (II) and 13 ghost atoms were employed.

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Table 3 The first hyperpolarizabilities (au) of four molecules and electronic spatial extent (au) at CAM-B3LYP/6-31+G(d) level. The oscillator strength f0, the transition energy ∆E (eV), the difference between the dipole moments of the ground state and the crucial excited state (∆µ in Debye) and the index of spatial extent (DCT in Å, qCT in au and µCT in Debye) in charge-transfer excitations at the TD- CAM-B3LYP/6-31+G(d) level

βx βy βz βtota f0 ∆E µg µe ∆µ ∆µf0/∆E3 major contribution DCT qCT µCT

1

2

3

4

-6.52×102 1.08×103 -9.04×103 9.13×103 9.52×103 2.76×104 1.18 3.73 8.61 18.60 9.99 0.23 H-1→Lb (0.61c)

-4.42×102 5.91×102 -5.36×103 5.41×103 5.67×103 2.77×104 0.86 3.77 7.56 16.78 9.22 0.15 H-1→L (0.58)

-1.56×102 2.05×102 -4.08×103 4.09×103 3.97×103 2.78×104 0.92 3.99 8.07 11.00 2.93 0.04 H→L+1 (0.68)

-1.29×102 5.4×101 -1.52×103 1.52×103 1.46×103 2.82×104 0.32 4.95 7.05 14.84 7.79 0.02 H-6→L (0.48)

3.35 0.63 10.08

3.05 0.64 9.35

1.41 0.44 2.95

2.89 0.57 7.91

a

The values of βtot in the second line were calculated at BHandHLYP /6-31+G(d) level.

b

H=HOMO and L=LUMO

c

Configuration interaction

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Table 4 The static and dynamic (λ = 1907, 1460, 1340, and 1064 nm) βHRS(−2ω;ω,ω) value (au) of four molecules obtained at the CAM-B3LYP/6-31+G(d) level. λ 0.000 1907 1460 1340 1064

1

2 3

3.83×10 4.64×103 5.40×103 5.80×103 7.81×103

3 3

2.30×10 2.78×103 3.23×103 3.47×103 4.66×103

4 3

1.72×10 1.98×103 2.20×103 2.31×103 2.84×103

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6.68×102 7.35×102 7.90×102 8.17×102 9.32×102

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Fig.1 The optimized structures of four molecules (1, 2, 3 and 4).

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Fig.2 The NICS values of four molecules, in which NICS (0.00) is in the central position of benzene ring (I) and NICS (3.00) is in the central position of benzene ring (II).

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Fig.3 The computed maximal absorption spectra for four molecules (1, 2, 3 and 4).

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Fig.4 The relationship between βtot vaules and ∆µf0/∆E3 of four molecules.

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Fig.5 The crucial transitions of four molecules.

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Modulating the charge transfer of D-S-A molecules: structures and NLO properties.

Very recently, the investigation of an Li atom doped effect on the "through-space" electronic interaction (S) of a donor-S-acceptor (D-S-A, 1) shows t...
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