Davydov Collective Vibrational Modes and Infrared SpectrumFeatures in Aniline Crystal: Influence of Geometry Change Inducedby van der Waals InteractionsYuan Kong,† Dong Hou,† Hou-Dao Zhang,*,† Xiao Zheng,†,‡ and Rui-Xue Xu*,†

†Department of Chemical Physics and Hefei National Laboratory for Physical Sciences at the Microscale and Synergetic InnovationCenter of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China‡Guizhou Provincial Key Laboratory of Computational Nano-Material Science, Institute of Applied Physics, Guizhou Normal College,Guiyang, Guizhou 550018, China

*S Supporting Information

ABSTRACT: Intermolecular interactions have significant influences on molecular crystals,oligomers, and various van der Waals clusters. They are essential in determining the quantumoptics, quantum transport, and chemical properties of complex molecular systems. In this work,we investigate the infrared spectra of aniline crystal via the density functional theory. Then weidentify four intriguing collective modes that are featured by NHHN wagging vibrations andfour other collective modes that are featured by NH2 wagging vibrations. All these eightcollective modes are due to Davydov splitting. To clarify the origin of such vibrational pattern,we further simulate aniline molecule and oligomers, and thoroughly analyze the spectradifferences on some key vibrational modes, such as N−H wagging and torsional vibrations. Ourresults reveal that the chain structure of aniline crystal significantly enhances the van der Waalsforces among adjacent molecules, and the intermolecular interactions are responsible for thoseNHHN wagging collective modes. Our study provides insights in intermolecular interactions and collective motions in anilinecrystal and also establishes a standard protocol for the theoretical investigation of other van der Waals clusters.

■ INTRODUCTION

Molecular crystals and aggregates are formed by hydrogenbonds and other intermolecular interactions. Among them,collective motions due to interactions over distant moleculesare of particular interest. They are dictated by the details ofmolecules in aggregation, supported by the structurally orderedhydrogen bonds,1−4 π−π stacking,5−7 delocalized excitonicinteractions,8−12 and so on. Collective intermolecular inter-actions play important roles in quantum optics,13−17 inquantum transport,18−23 and in determining the chemical24−29

and biological30−32 properties of complex molecular systems.Recently, the scanning tunneling microscope induced lumines-cence method has made it possible to probe coherent dipole−dipole interactions at the atomic level.33−36 However, it is stilldifficult to observe collective intermolecular motions inmolecular crystals or oligomers directly in experiments. Thatis because the collective intermolecular interactions inmolecular crystals or oligomers are more delicate than thedipole−dipole interactions in the organic macromolecules. Acomprehensive interpretation of the subtle relation betweencollective motions and intermolecular interactions calls fortheoretical modeling and simulations, based on such as thedensity functional theory (DFT) calculations.In this work, we investigate the collective motions in the

aniline crystal, by studying its infrared (IR) spectra via DFTcalculations. To account for the van der Waals (vdW)interactions, we adopt the DFT-D2 method,37−42 which

comes up with a semiempirical dispersion potential correctionto the conventional DFT energy. We choose the Perdew−Burke−Ernzerhof (PBE) exchange correlation functional forelectronic structure calculations. We list out our basic findingsas follows: (1) There are eight aniline molecules per unit cell inaniline crystal. (2) The N−H wagging modes in the anilinemolecules exhibit collective vibrational behavior in the crystal.(3) The total eight modes aggregate into NHHN and NH2wagging subbands due to Davydov splitting,43,44 with eachsubband consisting of four modes. The general Davydovsplitting is known as the splitting of bands in the electronic orvibrational spectra of crystals due to the presence of more thanone interacting molecular entity in the unit cell, and thissplitting is quite common in molecular crystals.45−48 (4) Thefour vibrational modes in the XNHHN wagging subband showthat half of the adjacent hydrogen atoms in the NH2 endsquench their motions, whereas those four in the XNH2

waggingsubband show synergistically vibrational motions for all theadjacent hydrogen atoms in the NH2 ends. (5) Theoreticalstudies on the vibrational modes of similar molecular crystalssuch as acetanilide, furan, and pyridine have also been carriedout. However, none of them exhibits such intermolecularcollective behavior as the XNHHN wagging subband here. (6)

Received: March 27, 2017Revised: August 1, 2017Published: August 3, 2017

Article

pubs.acs.org/JPCC

© 2017 American Chemical Society 18867 DOI: 10.1021/acs.jpcc.7b02862J. Phys. Chem. C 2017, 121, 18867−18875

Both XNHHN and XNH2subbands are blueshifted in the crystal

infrared spectra.

■ COMPUTATIONAL DETAILSNowadays, DFT methods39−42 have been very popular forelectronic structure calculations in solid-state physics andquantum chemistry. It is very convenient to utilize thesemethods in aniline crystal or aggregates.49,50 In this work, weadopt the Vienna ab-initio simulation package (VASP) codesfor the modelization and simulation of aniline monomer,oligomers, and crystal. To consider the vdW effect, the DFT-D2 method of Grimme38,51 is used in simulating the anilinedimer, trimer and crystal IR spectroscopy in this paper. Wehave verified our relaxed structure by other DFT methods withdispersion correction, such as vdW-DF52,53 and DFT-D3.54,55

In the structural optimizations, we use the Perdew−Burke−Ernzerhof exchange-correlation functional and PAW pseudo-

potentials with an energy cutoff of 600 eV. A singlecrystallographic unit cell was used for all calculations, withthe reciprocal lattice being sampled using k points 6 × 9 × 2.To obtain the IR spectroscopy intensities, we switch on thedensity-functional perturbation theory vibrational analysis. Thisapproach enables us to calculate the Born effective chargetensors after structural optimization. Applications of thismethod can be found in some earlier researches.56−59

■ RESULTS AND DISCUSSION

Figure 1a presents the unit cell that consists of eight anilinemolecules. The crystal structure is first deduced from theexperiment.60 The lattice parameters and atom coordinates arethen relaxed to their equilibrium values, and to obtain the stablestructure for IR spectra calculations without imaginaryfrequencies. We present the relaxed structure in Figure 1b,with the geometric details being referred to the figure caption.

Figure 1. (a) Unit cell of the aniline crystal. (b) Vibrational pattern of mode X1 (588 cm−1) in the relaxed geometric structure. The eight benzenes

within one unit cell are labeled as “1” to “8”, and the dihedral angles between these benzene ring planes are 152.1(12)° , 150.2(34)° , 147.1(56)° , 150.5(78)° ,152.1(13)° , 150.3(35)° , 148.6(57)° , and 148.5(71)° , respectively. The eight vibrational vectors along with their associated hydrogen atoms are labeled as “a” to“h”, and the angles between these vectors are 88.2(ab)° , 91.1(bc)° , 87.1(cd)° , 89.2(da)° , 87.5(ef)° , 89.4(fg)° , 90.2(gh)° , and 89.3(he)° . The distances between twoneighboring hydrogen atoms are 2.48 Å(ab)(cd)(ef)(gh) and 2.24 Å(bc)(da)(fg)(he). (c) Vibrational patterns of modes X1 (588 cm−1), X2 (586 cm−1), X3(585 cm−1), and X4 (584 cm−1) in the simplified diagrams.

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In Figure 1b, we also show the vibrational pattern of mode X1.Clearly, this vibrational mode is dominated by the collectivemovement of the adjacent hydrogen atoms in the NH2 ends.These hydrogen atoms, with the same labels from “a” to “h” astheir individually associated vibrational vectors, constitute apeculiar chain in the aniline crystal. We denote these hydrogenatoms as type-1. In comparison, the rest hydrogen atoms ofNH2 ends are less active in mode X1, and attributed to type-2.In fact, the four collective modes are nearly degenerate, withalmost the same frequency (from 584 to 588 cm−1) and similarvibrational patterns, see the simplified sketches in Figure 1c.The above findings indicate that all these collective modesoriginate from the same vibrational mode in the anilinemonomer. Moreover, they constitute a single XNHHN waggingsubband in the crystal IR spectra.In analogy to XNHHN wagging subband, the four modes of

XNH2wagging subband are also nearly degenerate and share

similar vibrational patterns. In Figure 2a, we therefore onlyshow one case for illustration. Comparing the vibrationalpattern of mode X1 in Figure 1b to that in Figure 2a, we findthe movements of Type-2 hydrogen atoms are quenchedduring the crystallization, while those of Type-1 hydrogenatoms are enhanced in mode X1. However, in the vibrationalmode of Figure 2a, the synergistically vibrational motions ofeight molecules in one unit cell indicate the vibrationalstructure of mode 32 in the monomer is preserved in thecrystal. Therefore, we denote the subband that consists ofmodes X1,2,3,4 as XNHHN wagging subband, and the other as XNH2

wagging subband throughout this paper, respectively.Parts a and b of Figure 3 present the IR spectra of an isolated

aniline monomer and the aniline crystal, respectively. For theaniline crystal simulation in Figure 3b, we adopt the PBEfunctional with the DFT-D2 dispersion potential correc-tion.38,51 To investigate the vdW interaction effects, we furtherpresent in Figure 3c the IR spectra of a reference aniline crystal,where the DFT-D2 dispersion correction is not considered inboth the structure optimization and IR spectra calculation.Therefore, we denote this reference model as the pseudocrystalin the rest of this paper. It is worthy to note that the crystal and

the “pseudo”-crystal have quite different geometric structuresafter the relaxation. These structural differences further lead tosignificant frequency shifts and intensity variations of severalvibrational modes in the IR spectra. In the aniline crystal andthe “pseudo”-crystal simulations, each unit cell contains eightmolecules. Therefore, a single vibrational mode in isolatedmonomer would transform into a band of eight modes in thecrystal. In our paper, the index number of the mode refers tothat of isolated monomer or the band consisting of twosubbands in the crystal.To further investigate the IR spectra differences among the

isolated aniline monomer, the crystal and the “pseudo”-crystal,

Figure 2. (a) Vibrational pattern of one selected mode from XNH2subband in aniline crystal. (b) Vibrational pattern of one selected mode from band

35 in aniline crystal.

Figure 3. Comparison of calculated IR spectra of (a) aniline monomerin the gas phase; (b) aniline crystal with DFT-D2 correction; (c)aniline reference crystal model without DFT-D2 correction. The insetpresents the vibrational pattern of mode 32, which becomes theXNHNH and XNH2

subbands in the crystal, due to the combined effectsof the Davydov splitting and the vdW dispersion relaxation.

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we list the calculated vibrational frequencies of somerepresentative modes/subbands in Table 1. By studying Table1, we find three major differences on IR spectra between theaniline crystal and isolated monomer, see also parts a and b ofFigure 3 for comparison.First of all, the mode 32 that is located at 461 cm−1 in the

monomer IR spectra (Figure 3a) transforms into collectiveXNHHN and XNH2

subbands in the crystal IR spectra (Figure 3b).The large frequency splitting (81 cm−1) between these twosubbands is evident. The splitting is determined by the vdWintermolecular interactions in the unit cell, which is well-knownas Davydov splitting.43,44 This enormous splitting duringcrystallization of band 32 suggests the band is quite sensitiveto vdW interactions. Moreover, the blueshifts of XNH2

subband(206 cm−1) and XNHHN subband (125 cm−1) are quite large.The second remarkable difference comes from the vibrational

mode/band 35 in the aniline monomer/crystal. In thesimulated IR spectra of monomer, this mode is located at325 cm−1, and has been attributed to the N−H torsionalvibration in previous studies.61−63 Compared to the monomerresult in Figure 3a, we observe large blueshift of the band 35 inFigure 3b. Besides, band 35 also contains two subbands, withfrequency blueshifts being about 145 and 165 cm−1. However,the Davydov splitting between these two subbands is extremelysmall (20 cm−1). This observation is in consistent with the factthat the two subbands have similar vibrational patterns, quitedifferent from the case of XNHHN and XNH2

subbands in band32. In Figure 2b, we only depict the vibrational pattern of onemode from band 35. Apparently, all the hydrogen atoms inNH2 ends contribute to the vibrational band 35, similar to theXNH2

subband in band 32. The above observations also implythat the vdW interactions have a great influence on band 35.The last notable difference between IR spectra of aniline

crystal and monomer involves the antisymmetric N−H (mode1 in Figure 3) and symmetric N−H (mode 2 in Figure 3)vibrations. Each mode transforms into the corresponding bandwith two subbands in the aniline crystal, see Figure 1b. InTable. 1, the redshifts of their frequencies (61−120 cm−1 incrystal) are quite large, which indicate a weakening of the N−Hbond in aniline during crystallization. Moreover, the intensitiesof these N−H stretching vibrations in aniline crystal aredramatically enhanced. All these observations are supported bysome earlier researches.62,63 On the contrary, the splittingbetween two subbands is not very large (21−59 cm−1 in thecrystal), compared to the high frequencies of these modes inthe monomer (>3500 cm−1). Thus, the large redshifts and theenhancement of intensities of those bands indicate vdWinteractions also have non-negligible influences on bands 1and 2 during crystallization. Meanwhile, small Davydov splittingbetween two subbands reflects the influences of vdW

interactions are not as evident as band 32, and intermolecularsubband like XNHHN does not emerge. The large red shifts andsplitting of vibrational spectra of crystals in modes of type 1 and2 are listed in Table 2. We depict vibrational patterns ofantisymmetry mode 1a and mode 1b in Figure 4, parts a and b,and vibrational patterns of symmetry mode 2c and mode 2d inFigure 4, parts c and d.

At this moment, we also like to point out that the modesmixing during crystallization could be analyzed via vibrationalpatterns that account directly for the dipole−dipole interaction.We take mode 27 (736 cm−1 in monomer) as an example. Thevibrational pattern of mode 27 in monomer is illustrated inFigure S2 in the Supporting Information, which is found tohave only a small change in the crystal, due to our calculation.The blue shifts of this mode are only 13−17 cm−1 duringcrystallization; see Table S2 in the Supporting Information.That is because in mode 27, the major contribution is from thebenzene ring but not the hydrogen atoms in NH2 end whichtake little contribution to the vibrations. While in the NHHNand NH2 wagging modes, the hydrogen atoms in NH2 end takea major part in the vibrations. Thus, it is hardly the modes likemode 27 mix with NHHN or NH2 wagging modes since thedipole−dipole interaction between them would be too small totake effects.In the aniline crystal simulation, the intensities of all

demonstrated absorption spectroscopies should have includedthe dipole−dipole interaction and dispersion effects. Tointerpret the frequency shifts observed in Figure 3b, thedipole−dipole interactions are also calculated. The dipole−dipole interaction is calculated using the following textbookequation:

Table 1. Comparison of the Vibrational Frequencies of Some Representative Modes in Aniline Crystal and Monomera

crystal (“Pseudo”-crystal)

index name monomer

1 antisymmetric N−H 3615 −66 (−40) −87 (−53)2 symmetric N−H 3509 −61 (−43) −120 (−61)32 wagging N−H 461 206 (183)* 125 (129)**35 torsional N−H 325 165 (185) 145 (165)

aThe frequency shifts of the subband centers of the crystal from the monomer references are reported, and the “pseudo”-crystal results are listed inparentheses. The XNHHN and XNH2

subbands are labeled with * and **, respectively.

Table 2. Calculated Frequencies and Intensities of the N−HStretching Modes in Aniline Crystala

N−H antisymmetry modes N−H symmetry modes

frequency (cm−1) intensity frequency (cm−1) intensity

3550 0.0 3449 0.0963548a 0.921 3449 0.0093548 0.352 3448 0.0113547 0.003 3448c 0.3853529 0.0 3399 0.03528 0.229 3399 0.1553527 0.011 3398 0.03527b 1.0 3387d 1.0

aThe left two columns are N−H anti-symmetric modes and the righttwo are the symmetric modes. Intensities of same stretching modes arenormalized. Some modes marked by superscript a, b, c, and d areshown in parts a−d of Figure 3, respectively.

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∑μ μ

πθ θ θ= −

ϵ−V r

r( )

2

4(cos 3 cos cos )

ij

i j

ijij i j

03

(1)

The above summation runs over involved dipoles of theparticularly selected vibrational mode of all molecules in onecell, where ϵ0 is the permeability of space, μi and μj denote twovibrational dipoles, θij and rij are the angle and distance betweenthem, respectively, and θi and θj are the angles formed by thetwo dipoles with respect to the line connecting their centers. Inthe equation, the distance between two dipoles is vital. Thus,we consider only the dipoles contributed from adjacent andsecondary adjacent ones in our calculation. The resultsobtained for XNH2

and XNHHN wagging modes are 167 and 48cm−1, respectively. The ratio between them is 3.48. While theratio between the energy blue shifts of the two modes in the IRspectrum of Figure 3b is 1.65 (206 cm−1/125 cm−1). They areof the same magnitude. Therefore, the dipole−dipole couplingbasically explains the trends of energy shifts between crystal andmonomer.Among these differences in IR spectra between aniline crystal

and the isolated monomer, the most evident one is theemergence of intermolecular collective modes. These collectivemodes aggregate into XNHHN subband in the crystal. In therelaxed aniline crystal, the distances between two adjacent type1 hydrogen atoms are 2.24 and 2.48 Å. As we know, the vdWradius of two hydrogen atoms is 2.40 Å. Thus, the

interhydrogen interactions lead to an alternating chainstructure. This structural property indicates the weak vdWforces between adjacent molecules significantly alter the latticeparameters and atomic positions, and are therefore responsiblefor the NHHN wagging collective modes.In this work, the aniline crystal simulation incorporate the

dispersion corrections provided in the DFT-D2 method, whilethe “pseudo”-crystal simulation does not account for suchdispersion effects. This single factor leads to significantdifferences on both structural and spectra properties betweenaniline crystal and the “pseudo”-crystal. The relaxed geometricstructure of “pseudo”-crystal is quite different from that of thecrystal. For instance, the distances between two adjacent type 1hydrogen atoms in “pseudo”-crystal are 2.32 and 2.60 Å, whichare larger than those in crystal. Furthermore, these geometricdifferences further result in the deviations in the IR spectra. Bystudying the details of Table 1, we find two major differencesbetween the IR spectrum of the aniline crystal in Figure 3b andthat of the “pseudo”-crystal in Figure 3c.In Figure 3c, the IR spectrum of aniline “pseudo”-crystal also

has the collective wagging subband XNHHN and collectivewagging subband XNH2

. However, their intensities become

much smaller than those in Figure 3b. Moreover, the splittingbetween these two subbands in the “pseudo”-crystal (54 cm−1)is much smaller than that in the crystal (81 cm−1). It is becausethe decrease of vdW interactions weakens the Davydov splitting

Figure 4. (a) Details of N−H antisymmetry stretching vibration mode, marked as 3548a in Table 3. (b) Details of N−H antisymmetry stretchingvibration mode, marked as 3527b in Table 3. (c) Details of N−H symmetry stretching vibration mode marked as 3448c in Table 3. (d) Details of N−H symmetry stretching vibration mode marked as 3887d in Table 3, respectively.

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in “pseudo”-crystal. These results suggest the XNHHN and XNH2

collective subbands are vital to analyze the intermolecularinteractions.Moreover, we use the same geometry obtained from the

DFT-D2 method to calculate the infrared spectrum without theDFT-D2 method. The spectrum changes slightly compared tothe infrared spectrum with the DFT-D2 method. Sincegeometry determines the IR spectra, as known, propertreatments of van der Waals effects in simulating molecularcrystals are crucial.Thus, we find that the vdW forces affect the equilibrium

geometry of the crystal, which then affects how the vibrationalmodes couple to each other. Therefore, it is crucial to includethe vdW effects in determining the geometry and spectroscopyof crystals.Compared to the monomer results, it is clearly shown that

the IR spectra of crystal and “pseudo”-crystal is altered. Informing molecular crystal, the neighboring molecules arejointed by weak vdW interactions. These long-rangeintermolecular interactions determine the detailed long chainstructure and also alter the symmetry of the crystal field. Thus,the intermolecular interactions which are enhanced byhydrogen atoms chains are the main reasons for the largeDavydov splitting between XNH2

and XNHHN subbands, andother vibrational differences during crystallization such as largeblueshifts in band 32 and 35, redshifts in band 1 and 2, and thechanges of their intensities.To explore the principle and mechanism of the weak

interactions in aniline crystal, we also carry out calculations formolecular aniline dimer and trimer for comparison. In thedimer case, we follow previous researches64−66 and study twotypical aniline dimers: the NH−NH type and the NH−π type,see the molecular structures in the right panels of Figure 5,parts a and b. The former is featured by the intermolecularNH−NH interaction, while the latter is featured by theintermolecular interaction between hydrogen atom and thecenter of π bonds. The situation of trimer is much morecomplicated, and we only investigate the NH−NH−NH type,see Figure 5c for details. For accuracy, DFT-D2 dispersioncorrection is used for all the oligomers calculations. Afterrelaxing all the crystal structures to their equilibrium conditions,we obtain the IR spectrum of the NH−π type dimer in Figure5a, the NH−NH type dimer in Figure 5b, and the NH−NH−NH trimer in Figure 5c. In Figure 5d, we repeat the theoreticalIR spectrum of the isolated aniline monomer as a reference.Moreover, to further investigate details of IR spectra in anilineoligomers, we present some representative mode frequencies ofthe oligomers in Table 3.In Figure 5, there are two attractive features among aniline

oligomers. First, all the oligomers do not have XNHHN and XNH2

subbands. To answer that, we examine the distances betweentwo adjacent hydrogen atoms in NH2 ends. As we know, thevdW radius of two hydrogen atoms is 2.40 Å. Theinterhydrogen distances in the NH−NH type dimer are biggerthan it, while that in the trimer are smaller than it. However, inaniline crystal, the most intriguing phenomenon is that theinterhydrogen distances form an alternating chain structure incrystal, Moreover, the special hydrogen atoms chain structureenhances the vdW interactions, which leads to the largeblueshifts of mode 32 and a huge Davydov splitting betweentwo subbands during crystallization. Thus, it is the cardinalfactor for the emergence of XNHHN wagging subband.

Second, the blueshift of mode 32 in NH−π type dimer (25cm−1) is much smaller than those in NH−NH type dimer (191cm−1), the trimer (234 cm−1) and the crystal (125 and 206cm−1). This phenomenon is explained by the fact that band 32is significantly influenced by intermolecular interactions amongadjacent hydrogen atoms in oligomers and crystal. In NH−πtype dimer, the distances (>3 Å) between two hydrogen atomsin NH2 ends are much larger than other three situations (<2.48Å). It indicates the intermolecular interactions via adjacenthydrogen atoms are sharply decreased in NH−π type dimer.That is why, in NH−π type dimer, the shifts and intensitychanges of mode 32 are not as significant as others. On theother hand, the intensities of the mode 31 which are mainlycontributed by the phenyl ring vibrations are sharply enhancedin the IR spectra of the NH−π type dimer. Notably, we namethis mode Xe′, and present its vibrational pattern in the inset ofFigure 5a. This mode indicates the intermolecular interactionsbetween the hydrogen atom and π bond are greatly increased inNH−π type dimer.

Figure 5. Theoretical IR spectra and geometry structure of anilineaggregates. (a) Theoretical IR spectrum and geometry structure ofaniline NH−π type dimer, the distance between Ha and center of the πbonds is 2.26 Å. The inset presents the NH−π intermolecularvibrational mode. (b) Theoretical IR spectrum and geometry structureof aniline NH−NH type dimer, the distance between Ha···Hb is 2.56 Åand between Ha···Hc is 2.60 Å. (c) Theoretical IR spectrum andgeometry structure of NH−NH−NH aniline type trimer, the distancebetween Ha···Hb is 2.27 Å, between Hb···Hc is 2.27 Å, and betweenHa···Hc is 2.26 Å. (d) Theoretical IR spectrum and geometry structureof aniline monomer.

Table 3. Comparison of the Vibrational Frequencies of SomeRepresentative Modes in Aniline Monomer, Dimers andTrimera

index monomer dimer NH−π (NH−NH) trimer

1 3615 −20 (−42) −822 3509 −19 (−89) −22431 505 45 (−10) −432 461 25 (191) 23435 325 11 (25) 55

aThe results of the NH−NH type dimer are presented in theparentheses after those of the NH−π type dimer.

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■ CONCLUSIONIn summary, we have identified the collective wagging subbandXNHHN and collective wagging subband XNH2

in aniline crystal,which are originated from the vibrational N−H wagging modein aniline molecule. However, this kind of long-rangeintermolecular delocalized behaviors are not observed in similarmolecular crystals such as acetanilide, furan, and pyridine,according to our calculations. In aniline crystal, the hydrogenatoms chain structure significantly enhances the vdWintermolecular interactions and, therefore, is responsible forthese collective vibrational subbands. These intermolecularinteractions determine the symmetry of the crystal field andlead to other vibrational differences between the isolatedmonomer and corresponding molecular crystal such as largeDavydov splitting, frequency shifts, and the changes ofintensity. Recently, some outstanding experimental re-searches33−36 are carrying out to visualize coherent intermo-lecular dipole−dipole couplings. Then our findings explain howto directly identify the collective intermolecular modes inmolecular crystals and oligomers. Our work provides aparticular view on further studies of intermolecular interactionsin hydrogen-bonded complexes, vdW clusters, and molecularcrystals and a practical approach to reveal the physical meaningof weak interaction.

■ ASSOCIATED CONTENT*S Supporting InformationThe Supporting Information is available free of charge on theACS Publications website at DOI: 10.1021/acs.jpcc.7b02862.

Acetanilide crystal infomation and detailed IR spectra(PDF)

■ AUTHOR INFORMATIONCorresponding Authors*(H.-D.Z.) E-mail: hdz@ustc.edu.cn.*(R.-X.X.) E-mail: rxxu@ustc.edu.cn.ORCIDYuan Kong: 0000-0002-5637-2511Hou-Dao Zhang: 0000-0002-1729-1583Xiao Zheng: 0000-0002-9804-1833NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTSThe support from the Ministry of Science and Technology(Grant Nos. 2016YFA0400900 and 2016YFA0200600), theNatural Science Foundation of China (Grant Nos. 21373191,21633006, 21573202, and 21233007), the FundamentalResearch Funds for the Central Universities (Grant Nos.2030020028 and WK2060030025), the Strategic PriorityResearch Program (B) of the Chinese Academy of Sciences(XDB01020000), the Fundamental Research Funds forChinese Central Universities (Grant No. 2340000074) andthe Anhui Provincial Natural Science Foundation (Grant No.1708085QB30) is gratefully acknowledged.

■ REFERENCES(1) Bernstein, J.; Davis, R. E.; Shimoni, L.; Chang, N.-L. Patterns inhydrogen bonding: functionality and graph set analysis in crystals.Angew. Chem., Int. Ed. Engl. 1995, 34, 1555−1573.

(2) MacGillivray, L. R.; Atwood, J. L. A chiral spherical molecularassembly held together by 60 hydrogen bonds. Nature 1997, 389,469−472.(3) Kitaigorodsky, A. Molecular crystals and molecules; Elsevier: 2012;Vol. 29.(4) Mukherjee, A.; Tothadi, S.; Desiraju, G. R. Halogen bonds incrystal engineering: like hydrogen bonds yet different. Acc. Chem. Res.2014, 47, 2514−2524.(5) Wu, Y.; Li, Z.; Ma, W.; Huang, Y.; Huo, L.; Guo, X.; Zhang, M.;Ade, H.; Hou, J. PDT-S-T: a new polymer with optimized molecularconformation for controlled aggregation and π-π stacking and itsapplication in efficient photovoltaic Devices. Adv. Mater. 2013, 25,3449−3455.(6) Konarev, D. V.; Zorina, L. V.; Ishikawa, M.; Khasanov, S. S.;Otsuka, A.; Yamochi, H.; Saito, G.; Lyubovskaya, R. N. Moleculardesign of anionic phthalocyanines with π-π stacking columnararrangement. Crystal structures, optical, and magnetic properties ofsalts with the iron (I) hexadecachlorophthalocyanine anions. Cryst.Growth Des. 2013, 13, 4930−4939.(7) Suponitsky, K. Y.; Masunov, A. E. Supramolecular step in designof nonlinear optical materials: Effect of π-π stacking aggregation onhyperpolarizability. J. Chem. Phys. 2013, 139, 094310.(8) Silinsh, E. A. Organic molecular crystals: their electronic states;Springer Science & Business Media: 2012; Vol. 16.(9) Bardeen, C. J. Excitonic processes in molecular crystallinematerials. MRS Bull. 2013, 38, 65−71.(10) Bardeen, C. J. The structure and dynamics of molecularexcitons. Annu. Rev. Phys. Chem. 2014, 65, 127−148.(11) Chenu, A.; Scholes, G. D. Coherence in energy transfer andphotosynthesis. Annu. Rev. Phys. Chem. 2015, 66, 69−96.(12) Zengin, G.; Wersall, M.; Nilsson, S.; Antosiewicz, T. J.; Kall, M.;Shegai, T. Realizing strong light-matter interactions between single-nanoparticle plasmons and molecular excitons at ambient conditions.Phys. Rev. Lett. 2015, 114, 157401.(13) Coles, D. M.; Yang, Y.; Wang, Y.; Grant, R. T.; Taylor, R. A.;Saikin, S. K.; Aspuru-Guzik, A.; Lidzey, D. G.; Tang, J. K.-H.; Smith, J.M. Strong coupling between chlorosomes of photosynthetic bacteriaand a confined optical cavity mode. Nat. Commun. 2014, 5, 5561.(14) Hellmann, C.; Paquin, F.; Treat, N. D.; Bruno, A.; Reynolds, L.X.; Haque, S. A.; Stavrinou, P. N.; Silva, C.; Stingelin, N. Controllingthe interaction of light with polymer semiconductors. Adv. Mater.2013, 25, 4906−4911.(15) Wang, K.; Zhang, H.; Chen, S.; Yang, G.; Zhang, J.; Tian, W.;Su, Z.; Wang, Y. Organic polymorphs: one-compound-based crystalswith molecular-conformation-and packing-dependent luminescentproperties. Adv. Mater. 2014, 26, 6168−6173.(16) Pollard, B.; Maia, F. C. B.; Raschke, M. B.; Freitas, R. O.Infrared vibrational nano-spectroscopy by self-referenced interferom-etry. Nano Lett. 2016, 16, 55.(17) Husu, H.; Siikanen, R.; Makitalo, J.; Lehtolahti, J.; Laukkanen, J.;Kuittinen, M.; Kauranen, M. Metamaterials with tailored nonlinearoptical response. Nano Lett. 2012, 12, 673−677.(18) Li, J.; Cushing, S. K.; Meng, F.; Senty, T. R.; Bristow, A. D.; Wu,N. Plasmon-induced resonance energy transfer for solar energyconversion. Nat. Photonics 2015, 9, 601−607.(19) Guilleme, J.; Cavero, E.; Sierra, T.; Ortega, J.; Folcia, C. L.;Etxebarria, J.; Torres, T.; Gonzalez-Rodríguez, D. Polar switching in alyotropic columnar nematic liquid crystal made of bowl-shapedmolecules. Adv. Mater. 2015, 27, 4280−4284.(20) Guo, X.; Puniredd, S. R.; Baumgarten, M.; Pisula, W.; Mullen, K.Rational Design of Benzotrithiophene-Diketopyrrolopyrrole-Contain-ing Donor-Acceptor Polymers for Improved Charge Carrier Trans-port. Adv. Mater. 2013, 25, 5467−5472.(21) Li, R.; Zhang, J.; Tan, R.; Gerdes, F.; Luo, Z.; Xu, H.;Hollingsworth, J. A.; Klinke, C.; Chen, O.; Wang, Z. CompetingInteractions between Various Entropic Forces towards Assembly ofPt3Ni Octahedra into a Body-Centered-Cubic Superlattice. Nano Lett.2016, 16, 2792.

The Journal of Physical Chemistry C Article

DOI: 10.1021/acs.jpcc.7b02862J. Phys. Chem. C 2017, 121, 18867−18875

18873

(22) Kotiuga, M.; Darancet, P.; Arroyo, C. R.; Venkataraman, L.;Neaton, J. B. Adsorption-Induced Solvent-Based Electrostatic Gatingof Charge Transport through Molecular Junctions. Nano Lett. 2015,15, 4498−4503.(23) Noriega, R.; Rivnay, J.; Vandewal, K.; Koch, F. P.; Stingelin, N.;Smith, P.; Toney, M. F.; Salleo, A. A general relationship betweendisorder, aggregation and charge transport in conjugated polymers.Nat. Mater. 2013, 12, 1038−1044.(24) Yang, J.; Hu, W.; Usvyat, D.; Matthews, D.; Schutz, M.; Chan,G. K.-L. Ab initio determination of the crystalline benzene latticeenergy to sub-kilojoule/mol accuracy. Science 2014, 345, 640−643.(25) Eisele, D.; Cone, C.; Bloemsma, E.; Vlaming, S.; van der Kwaak,C.; Silbey, R. J.; Bawendi, M. G.; Knoester, J.; Rabe, J.; Vanden Bout,D. Utilizing redox-chemistry to elucidate the nature of excitontransitions in supramolecular dye nanotubes. Nat. Chem. 2012, 4,655−662.(26) Yan, Y.; Zhang, C.; Yao, J.; Zhao, Y. S. Recent advances inorganic one-dimensional composite materials: Design, construction,and photonic elements for information processing. Adv. Mater. 2013,25, 3627−3638.(27) Lupton, J. M. Single-molecule spectroscopy for plasticelectronics: materials analysis from the bottom-up. Adv. Mater. 2010,22, 1689−1721.(28) Lin, H.; Camacho, R.; Tian, Y.; Kaiser, T. E.; Wurthner, F.;Scheblykin, I. G. Collective fluorescence blinking in linear J-aggregatesassisted by long-distance exciton migration. Nano Lett. 2010, 10, 620−626.(29) Wurtz, G. A.; Evans, P. R.; Hendren, W.; Atkinson, R.; Dickson,W.; Pollard, R. J.; Zayats, A. V.; Harrison, W.; Bower, C. Molecularplasmonics with tunable exciton-plasmon coupling strength in J-aggregate hybridized Au nanorod assemblies. Nano Lett. 2007, 7,1297−1303.(30) Jeffrey, G. A.; Saenger, W. Hydrogen bonding in biologicalstructures; Springer Science & Business Media: 2012.(31) Pullman, A. Intermolecular forces; Springer Science & BusinessMedia: 2013; Vol. 14.(32) Bozoky, Z.; Krzeminski, M.; Muhandiram, R.; Birtley, J. R.; Al-Zahrani, A.; Thomas, P. J.; Frizzell, R. A.; Ford, R. C.; Forman-Kay, J.D. Regulatory R region of the CFTR chloride channel is a dynamicintegrator of phospho-dependent intra-and intermolecular interactions.Proc. Natl. Acad. Sci. U. S. A. 2013, 110, E4427−E4436.(33) Zhang, Y.; Luo, Y.; Zhang, Y.; Yu, Y.-J.; Kuang, Y.-M.; Zhang, L.;Meng, Q.-S.; Luo, Y.; Yang, J.-L.; Dong, Z.-C.; et al. Visualizingcoherent intermolecular dipole-dipole coupling in real space. Nature2016, 531, 623−627.(34) Pacchioni, G. Imaging techniques: A tale of two dipoles. Nat.Rev. Mater. 2016, 1, 16027.(35) Imada, H.; Miwa, K.; Imai-Imada, M.; Kawahara, S.; Kimura, K.;Kim, Y. Real-space investigation of energy transfer in heterogeneousmolecular dimers. Nature 2016, 538, 364−367.(36) Meng, X.; Guo, J.; Peng, J.; Chen, J.; Wang, Z.; Shi, J.-R.; Li, X.-Z.; Wang, E.-G.; Jiang, Y. Direct visualization of concerted protontunnelling in a water nanocluster. Nat. Phys. 2015, 11, 235−239.(37) (a) Kresse, G.; Furthmuller, J. Software VASP, Vienna (1999).Comput. Mater. Sci. 1996, 6, 15. (b) Kresse, G.; Furthmuller, J. Phys.Rev. B: Condens. Matter Mater. Phys. 1996, 54, 11169−11186.(38) Grimme, S. Semiempirical GGA-type density functionalconstructed with a long-range dispersion correction. J. Comput.Chem. 2006, 27, 1787−1799.(39) Fraser, G.; Pine, A. van der Waals potentials from the infraredspectra of rare gas−HF complexes. J. Chem. Phys. 1986, 85, 2502.(40) Buckingham, A.; Fowler, P. A model for the geometries of vander Waals complexes. Can. J. Chem. 1985, 63, 2018−2025.(41) Wormer, P. E.; van der Avoird, A. Intermolecular potentials,internal motions, and spectra of van der Waals and hydrogen-bondedcomplexes. Chem. Rev. 2000, 100, 4109−4144.(42) Hutson, J. M. Intermolecular forces from the spectroscopy ofvan der Waals molecules. Annu. Rev. Phys. Chem. 1990, 41, 123−154.

(43) Davydov, A. The theory of molecular excitons. Sov. Phys.Uspekhi 1964, 7, 145.(44) Wermuth, C.; Ganellin, C.; Lindberg, P.; Mitscher, L. Glossaryof terms used in medicinal chemistry (IUPAC Recommendations1998). Pure Appl. Chem. 1998, 70, 1129−1143.(45) Careri, G.; Buontempo, U.; Galluzzi, F.; Scott, A.; Gratton, E.;Shyamsunder, E. Spectroscopic evidence for Davydov-like solitons inacetanilide. Phys. Rev. B: Condens. Matter Mater. Phys. 1984, 30, 4689.(46) Zallen, R.; Slade, M.; Ward, A. Lattice vibrations and interlayerinteractions in crystalline As 2 S 3 and As 2 Se 3. Phys. Rev. B 1971, 3,4257.(47) Williams, Q.; Knittle, E. Infrared and Raman spectra of Ca 5(PO 4) 3 F 2-fluorapatite at high pressures: compression-inducedchanges in phosphate site and Davydov splittings. J. Phys. Chem. Solids1996, 57, 417−422.(48) Song, Q.; Tan, Q.; Zhang, X.; Wu, J.; Sheng, B.; Wan, Y.; Wang,X.; Dai, L.; Tan, P. Physical origin of Davydov splitting and resonantRaman spectroscopy of Davydov components in multilayer MoTe 2.Phys. Rev. B: Condens. Matter Mater. Phys. 2016, 93, 115409.(49) Neumann, M. A.; Leusen, F. J.; Kendrick, J. A major advance incrystal structure prediction. Angew. Chem., Int. Ed. 2008, 47, 2427−2430.(50) Wojciechowski, P. M.; Zierkiewicz, W.; Michalska, D.; Hobza, P.Electronic structures, vibrational spectra, and revised assignment ofaniline and its radical cation: Theoretical study. J. Chem. Phys. 2003,118, 10900.(51) Wu, X.; Vargas, M.; Nayak, S.; Lotrich, V.; Scoles, G. Towardsextending the applicability of density functional theory to weaklybound systems. J. Chem. Phys. 2001, 115, 8748.(52) Dion, M.; Rydberg, H.; Schroder, E.; Langreth, D. C.;Lundqvist, B. I. Van der Waals density functional for generalgeometries. Phys. Rev. Lett. 2004, 92, 246401.(53) Roman-Perez, G.; Soler, J. M. Efficient implementation of a vander Waals density functional: application to double-wall carbonnanotubes. Phys. Rev. Lett. 2009, 103, 096102.(54) Grimme, S.; Ehrlich, S.; Goerigk, L. Effect of the dampingfunction in dispersion corrected density functional theory. J. Comput.Chem. 2011, 32, 1456−1465.(55) Moellmann, J.; Grimme, S. DFT-D3 study of some molecularcrystals. J. Phys. Chem. C 2014, 118, 7615−7621.(56) Esfarjani, K.; Hashi, Y.; Onoe, J.; Takeuchi, K.; Kawazoe, Y.Vibrational modes and IR analysis of neutral photopolymerized C_{60} dimers. Phys. Rev. B: Condens. Matter Mater. Phys. 1998, 57, 223.(57) Baroni, S.; de Gironcoli, S.; Dal Corso, A.; Giannozzi, P.Phonons and related crystal properties from density-functionalperturbation theory. Rev. Mod. Phys. 2001, 73, 515.(58) Giannozzi, P.; Baroni, S. Vibrational and dielectric properties ofC from density-functional perturbation theory. J. Chem. Phys. 1994,100, 8537.(59) Karhanek, D.; Bucko, T.; Hafner, J. A density-functional study ofthe adsorption of methane-thiol on the (111) surfaces of the Ni-groupmetals: II. Vibrational spectroscopy. J. Phys.: Condens. Matter 2010, 22,265006.(60) Fukuyo, M.; Hirotsu, K.; Higuchi, T. The structure of aniline at252 K. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1982,38, 640−643.(61) Larsen, N. W.; Hansen, E.; Nicolaisen, F. Far infraredinvestigation of aniline and 4-fluoroaniline in the vapour phase.Inversion and torsion of the amino group. Chem. Phys. Lett. 1976, 43,584−586.(62) Niu, Z.; Dunn, K. M.; Boggs, J. E. Theoretical prediction ofvibrational spectra: III. The harmonic force field and vibrationalspectra of aniline, aniline-NHD, and aniline-ND2. Mol. Phys. 1985, 55,421−432.(63) Piest, H.; von Helden, G.; Meijer, G. Infrared spectroscopy ofjet-cooled neutral and ionized aniline−Ar. J. Chem. Phys. 1999, 110,2010.

The Journal of Physical Chemistry C Article

DOI: 10.1021/acs.jpcc.7b02862J. Phys. Chem. C 2017, 121, 18867−18875

18874

(64) Yamamoto, N.; Hino, K.; Mogi, K.; Ohashi, K.; Sakai, Y.; Sekiya,H. Hole-burning spectroscopy and ab initio calculations for the anilinedimer. Chem. Phys. Lett. 2001, 342, 417−424.(65) Ohashi, K.; Inokuchi, Y.; Izutsu, H.; Hino, K.; Yamamoto, N.;Nishi, N.; Sekiya, H. Electronic and vibrational spectra of aniline−benzene hetero-dimer and aniline homo-dimer ions. Chem. Phys. Lett.2000, 323, 43−48.(66) Wang, Z. Y.; Yang, C.; Gao, J. P.; Lin, J.; Meng, X.; Wei, Y.; Li,S. Electroactive polyimides derived from amino-terminated anilinetrimer. Macromolecules 1998, 31, 2702−2704.

The Journal of Physical Chemistry C Article

DOI: 10.1021/acs.jpcc.7b02862J. Phys. Chem. C 2017, 121, 18867−18875

18875