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Electronic structure, non-linear properties and vibrational analysis ofAcenaphthene and its carbonyl derivative Acenaphthenequinone bydensity functional theory

Leena Sinha, Onkar Prasad *, Vijay Narayan, Rajesh K. SrivastavaPhysics Department, University of Lucknow, Lucknow 226 007, India

a r t i c l e i n f o

Article history:Received 1 June 2010Received in revised form 15 July 2010Accepted 16 July 2010Available online 23 July 2010

Keywords:Frontier orbitalsNormal modesMolecular electrostatic potentialcontours/surfaces

a b s t r a c t

The non-linear optical properties of Acenaphthene (ANP) and its derivative Acenaphthenequinone(ANPQ) have been evaluated and compared using the Hartree Fock (HF) and density functional theory(DFT). According to the calculations, the b value of ANP is more than five times and ANPQ is almost fivetimes than that of urea. The molecular HOMO, LUMO composition, their respective energy gaps, MESPcontours/surfaces have also been drawn and compared to explain the activity of ANPQ over ANP. For acomplete description of molecular dynamics, vibrational wavenumber calculation along with normalmode analysis have been carried out at the DFT level.

� 2010 Elsevier B.V. All rights reserved.

1. Introduction

Acenaphthene (ANP) and its carbonyl derivative Acenaphthen-equinone (ANPQ) with their extensive p electron conjugation andcharge transfer ability, present themselves as model of great inter-est from the view point of non-linear optical (NLO) applications.Acenaphthene, an ethylene-bridged three-ring polycyclic aromatichydrocarbon (PAH) is a constituent of coal tar and mostly findsapplications as intermediaries in pharmaceutical, agricultural andchemical industries. ANPQ is a quinone derived from Acenaph-thene. It is an alpha-dicarbonyl which has two carbonyl groupsside-by-side. The dicarbonyl compounds manifest unique combi-nation of important chemical and biological properties and findversatile applications in synthesis of biomolecules, agrochemicals,dyes, pigments and pharmaceuticals including vitamins [1,2].

The present communication is aimed at to investigate themolecular structural properties, vibrational and energetic data ofANP and ANPQ, in gas phase, due to their biological and pharma-ceutical importance. The ground state properties of the title mole-cules have been calculated employing DFT/B3LYP level of theory.The first static hyperpolarizability of both the molecules have beencalculated and compared. In order to obtain a complete description

of molecular dynamics, vibrational wavenumber calculation alongwith the normal mode analysis have been carried out at the DFT le-vel. The vibrational spectroscopic analysis provides immenselyinvaluable information about the structure and conformation ofthe molecules if used in synergy with quantum chemical calcula-tions. The reported geometries, molecular properties such asequilibrium energy, dipole moment, polarizability as well as firststatic hyperpolarizability components along with the electrostaticpotential contours and surfaces have also been used to understandthe activity of the molecules.

2. Experimental: structure and spectra

The model molecular structure of ANP and its carbonyl derivativeANPQ has been given in the Fig. 1. The experimental and calculatedFTIR spectra and calculated Raman spectra have been given Fig. 2.The FTIR spectra was recorded on Brucker spectrophotometer inthe wavenumber range 4000–400 cm�1 with the spectral resolutionof 4 cm�1. The pellet in solid phase was prepared using 10 mg of thesample in the fine powder form with KBr. The calculated Ramanspectra of the two molecules agree well with the experimental spec-tral data reported by the Sigma–Aldrich chemical website [3].

3. Computational details

In the present communication, the density functional theory [4]has been employed using Becke’s three parameter hybrid exchange

0166-1280/$ - see front matter � 2010 Elsevier B.V. All rights reserved.doi:10.1016/j.theochem.2010.07.026

* Corresponding author. Address: C/o Dr. L.P. Srivastastava, M-4/67 Vinay KhandGomti-Nagar, Lucknow 226010, Uttar Pradesh, India. Tel.: +91 9415313779; fax:+91 0522 2392853.

E-mail addresses: onkarprasad1@gmail.com, prasad_onkar@lkouniv.ac.in (O.Prasad).

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functionals [5] with Lee–Yang–Parr correlation functionals [6,7] tooptimize the structure and calculate the electronic structure prop-erties of both the molecules. The Gaussian 09 program [8] wasused to calculate the dipole moment (l), polarizability (a), the firststatic hyperpolarizability (b) of both the molecules, based on thefinite field approach. The vibrational frequencies are also calcu-lated and scaled down by the appropriate factor [9,10]. The vibra-tional wavenumber assignments have been carried out bycombining the results of the Gaussview 5 program [11], symmetryconsiderations and the VEDA 4 program [12].

The Raman intensities were calculated from the Raman activi-ties (Si) obtained with the Gaussian 09 program, using the follow-ing relationship derived from the intensity theory of Ramanscattering [13,14]

Ii ¼ ½f ðm0 � miÞ4Si�=½mif1� expð�hcmi=kTÞg�

where m0 being the exciting wavenumber in cm�1, mi is the vibra-tional wave number of ith normal mode, h, c and k are the universalconstants and f is a suitably chosen common normalization factorfor all peak intensities. Raman spectra has been calculated accord-ing to the spectral database reported by the Sigma–Aldrich chemi-cal website (Nd:YAG laser source with 1064 nm as excitingwavelength) [3]. The calculated FTIR and Raman spectra have beenplotted using the pure Lorentzian band shape with a band width of10 cm�1 FWHM and are shown in Fig. 2.

Density functional theory has also been used to calculate the di-pole moment l, mean polarizability hai and first static hyperpolar-izability b. Following Buckingham’s definitions [15], the totaldipole moment and the mean polarizability in a Cartesian frameis defined by

l ¼ ðl2x þ l2

y þ l2z Þ

1=2

hai ¼ 1=3½axx þ ayy þ azz�

The total intrinsic hyperpolarizability bTOTAL [16] and a compo-nent of the first hyperpolarizability along the direction of thedipole moment represented by �b [16,17] are defined as

bTOTAL ¼ ½b2x þ b2

y þ b2z �

1=2

�b ¼ ð3=5Þðbxlx þ byly þ bzlzÞ=l

where bx = bxxx + bxyy + bxzz, by = byyy + byzz + byxx, bz = bzzz + bzxx +bzyy.

4. Results and discussion

4.1. Molecular geometry optimization and energies

The structure of ANP which is the ancestor of the ANPQ hasbeen investigated as a reference, in order to assess the effect ofintroduction of two electron withdrawing carbonyl groups at it.

The equilibrium geometry optimization for both the moleculeshas been achieved by energy minimization, using DFT at theB3LYP level, initially employing the split valence basis set6-311++G(d,p), then the higher set 6-311++G(3d,2p). The opti-mized geometry of both molecules under study are confirmed tobe located at the local true minima on potential energy surface,as the calculated vibrational spectra contains no imaginary wave-number. The X-ray diffraction data of ANP and ANPQ obtainedfrom Cambridge Crystallographic Data Center (CCDC) have beenused as the starting point for the optimization of the structures.The molecular symmetry of ANP and its derivative ANPQ, rulesout the existence of any other conformation, hence the optimizedgeometry corresponds to the most stable conformation. The opti-mized molecular structures thus obtained along with the number-ing scheme of the atoms are shown in Fig. 1. The bond lengths offive-membered ring in case of ANP/ANPQ are as follows: C(7)–C(15)/C(1)–C(2) = 1.568 Å/1.588 Å; C(1)–C(7)/C(2)–C(3) = 1.519 Å/1.485 Å and C(14)–C(15)/C(1)–C(11) = 1.519 Å/1.485 Å. The carbonatoms of ethylene/carbonyl bridge are sp3 and sp2 hybridized,respectively, in case of ANP and its derivative molecule. The substi-tution of electron withdrawing carbonyl group in place of eachmethylene group in the present case, results in a perturbation ofvalence electron distribution of the ancestor molecule resultingin the modulation in the various physiochemical properties ofthe derivative. The endocyclic angles in ANPQ (ANP) are 105.4�(104.9�) at [C(1) and C(2)] ([C(7) and C(15)]) and 108.8� (108.7�)at [C(3) and C(11)] ([C(1) and C(14)]). Both C(1)@O(13) andC(2)@O(14) bond lengths are equal to 1.204 Å, close to the stan-dard C@O bond length (1.220 Å) [18,19]. All the endocyclic andexohedral C–C–C angles of naphthalene ring are found to deviatefrom the usual value of 120.0�. The naphthalene endocyclic C–C–C angles in ANP/ANPQ are found to decrease and lie between116.3� and 118.8� at C(1)/C(3), C(14)/C(11), C(2)/C(4) and C(18)/C(10) atoms, respectively, and increases to 122.4�/122.1� at C(3),C(16)/C(5), C(9). In both ANP/ANPQ there is a sharp rise in the exo-hedral angle values i.e. 127.5�/127.6�, at C(5)/ C(7) atoms and sharpfall in the angle values i.e. 112.7�/114.1� at C(6)/C(12) atoms. In thesix-membered rings all the C–C bond distances are in the range1.375–1.422 Å, while in the five-membered rings the C–C bonddistances vary from 1.485 Å to 1.588 Å. The C–H bond lengths re-mained between 1.085 Å and 1.094 Å in both the molecules underinvestigation. The calculated bond lengths are in full agreementwith those reported in [18]. According to our calculations boththe carbonyl oxygen atoms in ANPQ carry a net negative charge(�0.2281 u). The significance of this is further discussed in termsof its activity in the next section.

4.2. Electronic properties

The frontier orbitals, HOMO and LUMO determine the way themolecule interacts with other species. The frontier orbital gaphelps characterize the chemical reactivity and kinetic stability ofthe molecule. A molecule with a small frontier orbital gap is morepolarizable and is generally associated with a high chemical reac-tivity, low kinetic stability and is also termed as soft molecule[20]. According to the present DFT calculations, the frontier orbitalgap in case of ANPQ is 0.8683 eV lower than ANP. The 3D plots ofthe frontier orbitals, HOMO and LUMO and the molecular electro-static potential (MESP) map for both molecules are shown in Fig. 3.It can be seen from Fig. 3 that, the HOMO, which primarily acts asan electron donor, is distributed uniformly in the ANP but in case ofANPQ, the HOMO is shifted mainly towards the five-memberedring and a part of naphthalene ring. LUMO, the orbital that largelyacts as the electron acceptor, is found to be spread over entire mol-ecule in both the cases. The LUMO of ANP shows more antibondingcharacter than that of ANPQ.

Fig. 1. Optimized structure of Acenaphthene and Acenaphthenequinone.

34 L. Sinha et al. / Journal of Molecular Structure: THEOCHEM 958 (2010) 33–40

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The importance of MESP lies in the fact that it simultaneouslydisplays molecular size, shape as well as positive, negative andneutral electrostatic potential regions in terms of colour grading(shown in Fig. 3) and is very useful in investigation of molecularstructure with its physiochemical property relationship [21–25].

The sliced 2D MESP contour maps of the title molecules have alsobeen plotted in Fig. 4. Such a representation provides more de-tailed information regarding electrostatic potential distribution,by showing the values in a manifold of spatial location aroundthe molecule [26,27]. The MESP surface and 2D contour maps for

Fig. 2. Experimental and theoretical IR spectra (4000–400 cm�1) and theoretical Raman (0–4000 cm�1) spectra of Acenaphthene and Acenaphthenequinone.

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ANPQ drawn in the plane 1.5 Å above the molecular plane clearlysuggests that the carbonyl oxygen atoms represent the most elec-tronegative region (electrostatic potential = �0.04 a.u.) and possessexcess negative charge. The two carbonyl carbon atoms (electro-static potential = 0.04 a.u.) and the naphthalene hydrogen atoms(electrostatic potential = 0.02 a.u.) bear the maximum brunt of po-sitive charge (blue region). The MESP surface/contour of ANP, theparent molecule reveals that the negative charge (value rangingfrom �0.001 a.u. to �0.008 a.u.) is primarily concentrated overthe naphthalene ring (mainly the reddish and the surrounding

yellowish region, Fig. 4). The values of the extreme potentials forMESP maps of both molecules have been taken same for the sakeof comparison and drawing the conclusions. The predominanceof green region in the MESP surfaces corresponds to a potentialhalfway between the two extremes red and dark blue colour. Froma closer inspection of various plots given in Figs. 3 and 4 and theelectronic properties listed in Table 1, one can easily concludehow the two carbonyl groups when attached to the ANP molecule,modify the physico-chemical properties of the ANPQ.

4.3. Electric moments

The dipole moment in a molecule is an important property thatis mainly used to study the intermolecular interactions involvingthe non bonded type dipole–dipole interactions, because higherthe dipole moment, stronger will be the intermolecular interac-tions. The calculated value of dipole moment in case of ANPQ isfound to be almost seven times higher than its parent molecule(Table 1) and is attributed to the presence of two highly electronwithdrawing carbonyl groups. The lower frontier orbital energygap and very high dipole moment for ANPQ are manifested in itshigh activity and less stability as compared to ANP.

The calculation of electric polarizability and hyperpolarizabilityis very sensitive to the quality of level of theory as well as basis setemployed. The exhaustive and seminal studies carried out by Mar-oulis [28–30] and others [31,32] show the importance of electroncorrelation and basis set, including the relative merit of differentmethods employed for the calculation of these quantities. How-ever, in absence of experimental data on polarizability and hyper-polarizability of the title molecules, the relative values ofpolarizability and hyperpolarizability calculated at the same levelof theory and the same basis in the present work, can provide asatisfactory picture of these quantities. The mean polarizabilityvalue of ANPQ calculated at HF/6-311++G(3d,2p) and B3LYP/6-311++G(3d,2p) are found to be almost 5% higher than ANPcalculated at same levels of theories (refer to Table 2). This is inaccordance with the smaller frontier orbital gap of ANPQ as com-pared to ANP. The present polarizability calculation in case ofANP agrees very well with the values reported by Hinchliffe andSoscun Machado [33]. The calculated components of a shows thatthe inclusion of electron correlation through the B3LYP increasesthe in plane polarizability components from those calculated atHF almost by 8% in ANP and about 5% in case of ANPQ, but has anegligible effect on the normal component (refer to Table 2).

The calculated values for the total intrinsic hyperpolarizabilitybTOTAL and the component of the hyperpolarizability along the

Fig. 3. 3D surfaces of Acenaphthene and Acenaphthenequinone.

Fig. 4. Electrostatic potential contour plots (values in a.u.) for Acenaphthene and Acenaphthenequinone calculated at B3LYP/6-311++G(3d,2p), 1.5 Å above the molecularplane. The blue lines are representing positive isopotential and negative isopotential lines are red. (For interpretation of the references to colour in this figure legend, thereader is referred to the web version of this article.)

36 L. Sinha et al. / Journal of Molecular Structure: THEOCHEM 958 (2010) 33–40

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direction of the dipole moment �b are given in Table 2. The bTOTAL

value is found to be lowered in case of ANPQ (115.7 a.u.) as com-pared to ANP (130.7 a.u.) (refer to Table 2). Also according to thepresent calculations, the b value of ANP is more than five timesand ANPQ is almost five times than that of urea. The largest contri-bution to the first static hyperpolarizability to come from bYYY andbXXX in case of ANP and ANPQ, respectively. The normal componentsin both cases do not seem to contribute much to the total b value (re-fer to Table 2). In addition it has been found that bTOTAL values do notseem to follow the same trend as a does, with the frontier orbital en-ergy gaps. This behavior could be explained by a poor communica-tion between the two frontier orbitals of ANPQ as the non-linearoptical response is dictated by charge transfer excitations involvingthe HOMO and LUMO frontier orbitals. The difference in the compo-sition of HOMO, LUMO orbitals of the two molecules has a directinfluence on their first static hyperpolarizability. The first statichyperpolarizability is found to be higher in ANP as compared toANPQ, due to larger spread of the electron charge density and bettercommunication between HOMO and LUMO in the former than thelatter. Reasonably good value of hyperpolarizability derived by the-oretical calculations suggests the possible use of these compoundsfor electro-optics applications.

4.4. Vibrational assignments

The experimental and computed vibrational wavenumbers,their IR and Raman intensities and the detailed description of eachnormal mode of vibration of ANP and ANPQ carried out in terms of

their contribution to the total potential energy are given in Table 3and 4. The calculated FTIR and Raman spectra (Fig. 2) of both themolecules agree well with the recorded FTIR spectra and the FT-Ra-man data reported by the Sigma–Aldrich chemical websites,respectively [3].

The DFT calculated wavenumbers, for the majority of the nor-mal modes, are typically slightly higher than that of their experi-mental counterpart and thus proper scaling factors [9,10] areemployed to have better agreement with the experimental wave-numbers. In the present study, vibrational wavenumbers calcu-lated at B3LYP/6-311++G(3d,2p) level have been scaled by 0.9679.

The 50/48 fundamental modes of vibrations of ANP/ANPQ aredistributed among the functional and the finger print region. Thefunctional group region in case of the parent molecule containsmainly the stretching vibration due to naphthalene ring as wellas the methylene group. The vibrational modes of ANPQ are almostsimilar except the additional modes due to carbonyl group.

4.4.1. Naphthalene ring vibrationsMultiple weak bands in the range 3100–3000 cm�1 are in gen-

eral observed in the case of aromatic compounds. These bands aredue to aromatic C–H stretching vibrations. In case of ANP andANPQ, both having two aromatic rings fused together show veryweak bands in this region of the FTIR spectra. The modes calculatedat 3079/3091 and 3078/3091, 3066/3080, 3065/3080, 3056/3066and 3055/3064 cm�1 are identified as symmetric and asymmetricC–H stretching modes of ANP/ANPQ and are assigned well withFTIR and Raman spectra. The C–C stretching modes are observedas mixed modes in the wavenumber range 1600 cm�1 to980 cm�1 for both the molecules and are in good agreement withgeneral appearance of C–C stretching modes. The naphthalene ringwagging starts below 960 cm�1 in case of ANP and 975 cm�1 incase of ANPQ. The calculated modes at 622 cm�1/558 cm�1 repre-sent the pure naphthalene ring breathing modes. The modesappearing below 600 cm�1 are ascribed to skeletal out of planedeformations or the torsional modes.

4.4.2. CH2 vibrationsThere are two methylene group attached to the ANP molecule.

The peaks in the wavenumber range 1455–1420 cm�1 of ANP aredue to the methylene scissoring modes with more than 80% contri-bution to the total P.E.D and are assigned very well at 1451/1447 cm�1 and 1420/1420 cm�1 in the reported Raman/recordedFTIR spectra. Methylene wagging calculated at 1267 cm�1 (35%P.E.D.) and 1207 and 1206 cm�1 (41% P.E.D.) show considerablemixing with other mode, whereas the methylene twisting modesare calculated at 1206 cm�1 and 1134 cm�1 with 97% and 81% con-tribution to P.E.D. The mode calculated at 992 cm�1 and 735 cm�1

are identified as methylene rocking with 78% and 50% contributionto the total P.E.D.

4.4.3. C@O stretchThe appearance of a strong band in IR spectra around

1700 cm�1 shows the presence of carbonyl group and is due tothe C@O stretch. As expected the modes calculated at higher wave-

Table 1Ground state optimized parameters at DFT/B3LYP level of theory for Acenaphthene and Acenaphthenequinone.

Parameters Acenaphthene AcenaphthenequinoneB3LYP/ B3LYP/

6-311++G(d,p) 6-311++G(3d,2p) 6-311++G(d,p) 6-311++G(3d,2p)

Ground state energy (in Hartree) �463.42641 �463.44377 �611.49146 �611.51388Frontier orbital energy gap (in eV) 4.61 4.61 3.74 3.73Dipole moment (in Debye) 0.97 0.98 6.77 6.67

Table 2Polarizabilitya data and hyperpolarizabilityb data for Acenaphthene and Acenaph-thenequinone calculated at HF and DFT/B3LYP level of theory.

Components Acenaphthene Acenaphthenequinone

HF B3LYP HF B3LYP

6-311++G(3d,2p) 6-311++G(3d,2p)

Polarizabilitya

aXX 170.798 183.143 173.801 184.945aYY 147.122 159.297 177.705 186.387aZZ 78.173 79.191 73.015 72.441

hai 132.031 140.544 141.507 147.924

Hyperpolarizabilityb

bXXX 0.0 0.0 153.7 260.4bXXY 33.5 21.7 0.0 0.0bXYY 0.0 0.0 �107.4 �70.2bYYY �96.3 �119.4 0.0 0.0bXXZ 0.0 0.0 �0.2 0.0bXYZ 0.0 0.0 0.0 0.0bYYZ 0.0 0.0 �0.1 0.0bXZZ 0.0 0.0 �73.7 �74.5bYZZ �43.1 �33.1 0.0 0.0bZZZ 0.0 0.0 �0.1 0.0

bTOTAL 105.9 130.7 27.4 115.7

�b �63.5 �78.5 �16.4 �69.4

a In atomic units. Conversion factor to the SI units, 1e2a20E�1

h ¼ 1:648778�10�41 C2 m2 J�1.

b In atomic units. Conversion factor to the SI units, 1e3a30E�2

h ¼ 3:206361�10�53 C3 m3 J�2.

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number (1759 cm�1) and the one at slightly lower wavenumber(1740 cm�1) have been are identified as the asymmetric and sym-metric stretching modes of two C@O groups and are assigned tothe observed peaks at 1745 cm�1 and 1725 cm�1 in Raman spectra.The electron withdrawing naphthalene ring increases the strengthof the C@O bonds causing the vibrations to occur at a relativelyhigher value.

5. Conclusions

In the present work we have calculated the geometric parame-ters, the vibrational frequencies, frontier orbitals, MESP contoursand surfaces and the non-linear optical properties of ANP and itsderivative using HF and DFT/B3LYP methods. The lower frontierorbital energy gap and the higher dipole moment value make the

Table 3Theoretical and experimentala wave numbers (in cm�1) of Acenaphthene.

Calc. unsc. waveno. in cm�1

Sc. wave no.in cm�1

Exp. FTIR waveno. in cm�1

Exp. a Ramanwave no in cm�1

IRIntensity

Ramanintensity

Assignment of dominant modes in order ofdecreasing potential energy distribution (PED)

3181 3079 – 3089 12.25 26.73 ms(C–H)Np (95)3180 3078 – 3089 36.90 1.45 mas(C–H)Np (97)3168 3066 3051 3067 24.95 7.42 mas(C–H)Np (99)3167 3065 3051 3067 6.77 3.73 mas(C–H)Np (99)3157 3056 3051 3046 2.24 2.17 mas(C–H)Np (95)3156 3055 3051 3046 0.02 3.76 mas(C–H)Np (97)3075 2976 – 2977 24.32 8.81 mas methylene (C–H) (100)3055 2957 – 2945 0.00 2.01 mas methylene (C–H) (92)3046 2948 2920 2945 44.90 24.62 ms methylene (C–H) (92)3035 2938 2920 2925 17.06 2.89 ms methylene (C–H) (91)1652 1599 1601 1602 9.74 1.08 m(C–C)Np (27) + b(C–C–C)Np (25) + b(H–C–C)Np (20)1633 1581 1601 1602 25.76 9.53 m(C–C)Np (54) + b(H–C–C)Np (25)1631 1579 – – 0.03 5.68 m(C–C)Np (53) + b(H–C–C)Np (17)1530 1481 1487 1480 4.22 0.33 m(C–C)Np (19) + b(C15–C14–C18) (18) + b(H–C–C)Np (17)

+ b(C2–C1–C7) (17)1502 1454 1447 1451 4.67 12.52 sc CH2 (93)1501 1453 1447 1451 0.59 0.22 b(H–C–C)Np (42) + m(C–C)Np (37)1476 1429 1420 1420 2.36 3.27 sc CH2 (83)1463 1416 1420 1420 0.31 34.81 m(C–C)Np (42) + b(H–C–C)Np (19)1447 1401 – 1400 2.47 12.73 b(H–C–C)Np (19) + m(C–C)Np (18) + b(C–C–C)Np (10)1392 1347 1366 1375 13.79 15.31 m(C–C)Np (31) + b(H–C–C)Np (19) + b(C–C–C)Np (16)1384 1340 – 0.40 1.61 m(C–C)Np (49) + b(H–C–C)Np (18)1309 1267 1277 1270 0.76 0.02 Methylene wag (35) + m(C1–C7) (18) + m(C5–C14) (18)

+ b(H–C–C)Np (10)1279 1238 1255 1225 1.25 2.38 b(C–C–C)Np (30) + b(H–C–C)Np (29) + methylene wag (13)1247 1207 1212 1225 1.08 4.45 Methylene wag (41) + b(H–C–C)Np (16)1246 1206 1212 1225 0.00 0.77 Methylene twisting (97)1246 1206 1212 1225 0.00 0.73 b(H–C–C)Np (32) + b(C–C–C)Np (29)1235 1195 – 1170 0.51 0.00 b(H–C–C)Np (41) + m(C–C)Np (27)1197 1159 1173 1150 2.00 0.39 b(H–C–C)Np (59) + m(C–C)Np (10)1174 1136 – 1150 0.63 1.46 b(H–C–C)Np (54) + m(C–C)Np (17)1172 1134 – 1150 0.00 0.22 Methylene twisting (81)1099 1064 – 1045 1.95 0.78 b(C–C–C)Np (33) + m(C–C)Np (13) + b(H–C–C)Np (10)1063 1029 1015 1005 0.11 13.61 b(H–C–C)Np (20) + b(C2–C1–C7) (19) + b(C15–C14–C18) (18)1033 1000 1015 1005 4.93 0.03 b(C–C–C)Np (30) + m(C–C)Np (14) + b(H–C–C)Np (12)

+ b(C2–C1–C7) (12) + b(C15–C14–C18) (11)1025 992 – 982 0.00 0.18 Methylene rocking (78)1012 980 – 982 0.64 4.05 m(C–C)P (81) + m(C–C)Np (19)989 957 938 942 1.37 0.33 C–H out of plane Np ring wag (87)981 950 938 942 0.00 0.14 C–H out of plane ring wag (82)945 915 – – 0.42 0.30 m(C7–C15) (28) + b(C2–C1–C7) (26) + b(C15–C14–C18) (25)920 890 894 891 0.11 0.01 C–H out of plane Np ring wag (81)893 864 – – 0.00 0.86 C–H out of plane Np ring wag (84)851 824 831 840 14.53 1.56 Methylene rocking (48) + C–H out of plane Np ring wag (28)

+ bout(C–C–C)Np (20)833 806 – 805 0.55 0.01 b(C–C–C)P (38) + b(C–C–C)Np (36)813 787 778 780 0.55 5.39 Np ring deformation (74)799 773 778 780 79.76 0.00 C–H out of plane Np ring wag (93)759 736 745 750 0.00 1.51 C–H out of plane Np ring wag (76)759 735 745 750 5.82 0.14 Methylene rocking (50) + C–H out of plane Np ring wag (18)666 645 – 645 3.81 0.17 (Np + P) ring deformation (81)643 622 – – 0.00 55.22 Breathing mode (82)623 603 – – 0.00 0.01 Np ring torsion (38) + P ring torsion (25)566 548 541 550 1.08 0.08 Np ring torsion (41) + P ring torsion (20)552 534 541 550 1.00 7.08 P ring Deformation (76) + b(H–C–C)Np (20)510 494 – 503 0.11 12.88 Np ring deformation473 458 462 450 0.14 0.14 (Np + P) ring Torsional mode (80)452 437 446 450 0.76 3.76 b(C2–C1–C7) (32) + b(C15–C14–C18) (30)448 434 – 450 0.0 0.15 (Np + P) Torsional mode (88)423 409 410 420 1.61 2.28 (Np + P) ring deformation (71)

Abbreviations used here have following meaning: m: stretching; ms: symmetric stretching; mas: asymmetric stretching; b: in plane bending; bout: out of plane bending; sc:scissoring, Np: naphthalene ring, P: five-membered ring.

a Experimental Raman data as reported in www.sigmaaldrich.com/united-states.html website.

38 L. Sinha et al. / Journal of Molecular Structure: THEOCHEM 958 (2010) 33–40

Author's personal copy

ANPQ the more reactive and more polar, hence lesser stable thanANP molecule. NLO behavior of both the title molecules wereinvestigated by the determination of the dipole moment, the polar-izability and the first hyperpolarizability using the HF/6311++G(3d,2p) and DFT/B3LYP/6311++G(3d,2p) methods. In general, agood agreement between experimental and calculated normalmodes of vibrations has been observed. The molecular electrostaticpotential surfaces and contours have also been drawn to explainthe activity of ANPQ over its ancestor. The present quantum chem-ical study may further play an important role in understanding ofdynamics of these molecules.

Acknowledgements

The authors (O.P. and L.S.) are grateful to University GrantsCommission for financial support. Authors wish to thank Prof.

Tracy Field for providing the crystal data of ANP as well as ANPQand Prof. M.H. Jamroz for providing his VEDA 4 software.

References

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Table 4Theoretical and Experimentala wave numbers (in cm�1) of Acenaphthenequinone.

Calc. unsc. waveno. in cm�1

Calc. sc. wave no.in cm�1)

Exp. FTIR waveno. in cm�1

Exp.a Raman waveno. in cm�1

IRIntensity

RamanIntensity

Assignment of dominant modes in order of decreasingpotential energy distribution (PED)

3194 3091 – 3086 4.19 24.75 ms(C–H)Np (94)3194 3091 – 3086 10.54 0.13 mas(C–H)Np (90)3182 3080 – 3086 11.70 5.03 mas(C–H)Np (99)3182 3080 – 3086 2.71 7.26 mas(C–H)Np (95)3168 3066 3051 3075 1.76 5.76 mas(C–H)Np (94)3166 3064 3051 3075 0.41 0.46 mas(C–H)Np (89)1817 1759 – 1745 86.94 3.87 mas(C@O) (87)1798 1740 1705 1725 517.37 36.98 ms(C@O) (87)1654 1601 1600 1603 0.01 0.56 m(C–C)Np (27) + b(C–C–C) Np (25) + b(H–C–C)Np (15)1638 1585 – 1595 47.98 11.46 m(C–C)Np (63) + b(H–C–C)Np (20)1621 1569 – – 43.60 34.71 m(C–C)Np (62) + b(H–C–C)Np (13)1524 1475 – 1490 11.64 0.35 b(H–C–C)Np (36) + b(C–C–C)Np (19) + m(C–C)Np (14)1480 1432 1447 1440 0.29 1.04 b(H–C–C)Np (43) + b(C–C–C)Np (16) + m(C–C)Np (16)1468 1421 1420 1420 7.35 24.46 b(H–C–C)Np (41) + m(C–C)Np (26)1446 1400 1420 1400 7.16 19.39 m(C–C)Np (48) + b(H–C–C)Np (29)1377 1333 – – 0.90 7.98 m(C–C)Np (39) + b(H–C–C)Np (24)1371 1327 – – 0.23 0.67 m(C–C)Np (40) + b(H–C–C)Np (27)1290 1249 1255 – 56.77 3.79 b(H–C–C)Np (40) + m(C1–C11) (11) + m(C2–C3) (11)1249 1209 – – 0.41 1.51 b(H–C–C)Np (37) + m(C–C)Np (16) + b (C–C–C)Np (14)1226 1187 1173 1185 12.52 0.51 m(C–C)Np (39) + b(H–C–C)Np (38) + m(C1–C11)

(10) + m(C2–C3) (10)1200 1161 1173 1165 6.53 0.98 b(H–C–C)Np (69) + m(C–C)Np (10)1175 1137 – – 4.33 2.18 b(H–C–C)Np (49) + m(C–C)Np (31)1117 1081 – 1070 2.99 0.38 m(C–C)Np (15) + b(H–C–C)Np (13) + m(C1–C11)

(11) + m(C2–C3) (11) + b(C–C–C)Np (10)1071 1037 1014 1022 0.66 7.66 m(C–C)Np (40) + b(H–C–C)Np (17) + m(C1–C2) (10)1030 997 – 994 3.11 0.04 m(C–C)Np (57) + b(H–C–C)Np (10)1008 976 – – 67.87 2.50 b(C–C–C)Np (34) + m(C1–C11) (16) + m(C2–C3) (16)1006 974 – – 1.07 0.32 C–H out of plane Np ring wag (86)999 967 – – 0.00 0.05 C–H out of plane Np ring wag (87)955 924 – 925 0.04 0.00 C–H out of plane Np ring wag (77)944 914 – 925 0.00 0.39 C–H out of plane Np ring wag (89)930 900 894 – 4.23 18.63 b(C–C–O) (42) + b(C–C–C)Np (22) + m(C1–C2) (11)899 870 839 – 27.83 0.09 b(C–C–O) (53) + b(C–C–C)Np (20) + m(C1–C11)

(10) + m(C2–C3) (10)842 815 839 835 37.76 0.64 C–H out of plane Np ring wag (92)839 812 – – 0.00 0.01 bout(C–C–O) (70) + C–H out of plane Np ring wag (15)809 783 784 795 0.35 5.41 b(C–C–C) Np (62) + m(C–C)Np (14)793 768 745 780 52.07 0.06 bout(C–C–C)Np (43) + C–H out of plane Np ring wag

(12) + bout(C–C–O) (12)761 737 745 – 0.00 0.69 C–H out of plane Np ring wag (70) + bout(C–C–O) (18)703 680 – – 1.40 0.21 b(C–C–O) (33) + b(C–C–C) (30)620 600 – – 0.00 0.01 (Np + P) ring torsion (80)600 581 – 583 0.03 0.20 (Np + P) ring torsion (87)587 568 – 583 0.84 0.42 (Np + P) ring deformation (79)577 558 – – 0.04 53.50 Breathing mode (80)523 506 – 520 7.98 4.65 (P + Np) ring deformation (73)474 459 446 480 2.04 0.06 (Np + P) ring torsion (87)472 457 – – 0.01 19.89 (Np + P) ring deformation (75)423 409 415 407 0.00 1.80 (Np + P) ring torsion (88)421 407 – 407 23.70 0.97 (Np + P) ring torsion (85)

Abbreviations used here have following meaning: m: stretching; ms: symmetric stretching; mas: asymmetric stretching; b: in plane bending; bout: out of plane bending; Np:naphthalene ring, P: five-membered ring.

a Experimental Raman data as reported in www.sigmaaldrich.com/united-states.html website.

L. Sinha et al. / Journal of Molecular Structure: THEOCHEM 958 (2010) 33–40 39

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