Density functional theory studies on the structures and vibrational spectroscopic characteristics of nickel, copper and zinc naphthalocyanines

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 217 (2019) 8–17

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Density functional theory studies on the structures and vibrational spectroscopic characteristics of nickel, copper and zinc naphthalocyanines Zhongqiang Liu a,⁎, Zhao-Xu Chen b, Biaobing Jin c a b c

School of Chemistry and Chemical Engineering, Qilu Normal University, Jinan 250200, PR China Institute of Theoretical and Computational Chemistry, Key Lab of Mesoscopic Chemistry of MOE, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, PR China Research Institute of Superconductor Electronics (RISE), Dept. of Electronic Science & Engineering, Nanjing University, Nanjing 210093, PR China

a r t i c l e

i n f o

Article history: Received 21 November 2018 Received in revised form 11 March 2019 Accepted 11 March 2019 Available online 12 March 2019 Keywords: Naphthalocyanine DFT method Molecular geometry Electronic structure IR spectra Raman spectra

a b s t r a c t Molecular geometries and electronic structure calculations and spectroscopic assignments for metallonaphthalocyanines NiNc, CuNc and ZnNc are performed on the optimized geometries at B3LYP/6–31G* level. The order of the bond lengths of the N\\M bonds is computed to be NiNc b CuNc b ZnNc. The Mulliken atomic charges of the central M vary in the same order as the bond lengths. The metal dependent frequencies of IR–active and Raman–active vibrational modes decrease in the order of NiNc N CuNc N ZnNc, which is in reverse sequence of the N–M bond length. The strongest Raman lines predicted at 1570 (NiNc), 1546 (CuNc) and 1525 (ZnNc) cm−1 are highly sensitive to the metal ion. Comparison of the calculated properties of MNcs and MPcs (metallphthalocyanines) compounds reveals some interesting and meaningful results due to extension of the conjugated systems. © 2019 Published by Elsevier B.V.

1. Introduction Naphthalocyanines (Ncs) are conjugated macrocyclic molecules containing an inner 16–membered ring formed by four benzoisoindole units linked by four nitrogen atoms, thus they are phthalocyanines (Pcs) derivatives with a larger heterocyclic aromatic system. Nc denotes the naphthalocyaninato anion C48 H24 N8 2− , and H2Nc stands for the metal–free form. Both Nc and Pc ligands can coordinate various metals in the central position, which are classified by the valency of the central metal. When the central metals have the oxidation state of 2+, the metal derivatives of naphthalocyanines and phthalocyanines, i.e., metallonaphthalocyanines (MNcs) and metallophthalocyanines (MPcs), are formed. MNcs (Fig. 1) are chemically modified analogues of MPcs where the macrocyclic ligand is extended with a further peripheral benzoannulation. In addition, Nc contains four additional benzene rings and possesses higher degree of π-electron delocalization in comparison with Pc. This extended π-conjugation system gives rise to a change in their optical, electrical, and electrochemical properties [1,2]. Ncs exhibit strong absorption bands in near– infrared region [3]. This spectral characteristic and their photoconductive properties make them suitable candidates for applications

⁎ Corresponding author. E-mail address: [email protected] (Z. Liu).

https://doi.org/10.1016/j.saa.2019.03.029 1386-1425/© 2019 Published by Elsevier B.V.

in optical storage media [4], solar energy conversion and laser electrophotography [5] etc. Previously density functional theory (DFT) methods have been extensively employed investigating Pcs and their derivatives [6–8]. We have also approached the geometry and electronic structure of metal free porphyrazine, phthalocyanine, and naphthalocyanine and their magnesium complexes [9] as well as the molecular and electronic structures and the vibrational spectra of a series of transition metal complexes of phthalocyanines [10,11] and aza-analogues of the phthalocyanies [12,13]. As Ncs have higher conjugation extent, better optical and electrical performances are expected for MNcs. However, unlike MPcs, less attention has been paid to MNcs both experimentally and theoretically. To the best of our knowledge, no IR spectrum of NiNc is available. Although the IR spectra of the divalent metal derivatives of Ncs such as CuNc and ZnNc have been measured [14,15], detailed assignment of the absorption bands is still unavailable because the structural complexity of naphthalocyanine molecules renders such assignment unfeasible. Computer simulation as an attractive alternative to experiment can provide valuable information. Therefore, to get more insights into the molecular structures, electronic structures, and vibrational spectra of naphthalocyanine compounds, it is worthwhile to conduct quantum chemistry calculations. In the present paper, we report theoretical calculations of molecular geometries, electronic structures and spectroscopic properties of NiNc, CuNc and ZnNc, and show how these properties vary systematically with increasing atomic number of the central

120.32

118.45

119.92

121.08

N

N

Ni

1.91072

N

119.89

N

N

Cu

1.96021

N

109.50

125.70

123.08

108.59 N

127.76

N

N

N

1.32376 1.37607

N

1.42170 1.41851

1.08736

1.44545

1.08629

120.30

118.47

119.86

120.88

N

118.55

a

121.13

b

Fig. 1. Structure of NiNc, CuNc and ZnNc.

120.08

121.12

118.57

118.66

N

Zn

120.09

c

121.11

118.58

118.82

1.08655

N

N

1.32896 1.37390

N

1.46042

1.37677

1.41862

1.42276

1.37549

1.99708

N

108.78

125.11

124.50

109.78 N

127.64

N

106.33

120.31

120.97

121.31

Cε

1.41886 Cω

118.46

106.20

Cγ

Cδ

1.44623

1.08734

121.45

Cβ

1.41551

1.08614

1.45714

1.37714

CuNc

106.06

118.47

120.08

Cα

1.38139

1.31709

Nm

Nc

N

NiNc

121.62

110.50

126.56

121.35

106.89 N

127.77

N

1.45251

1.37776

1.41748

1.41816

1.42302

1.37527

1.37497

1.42339

1.08655

1.08654

1.42662

1.41827

1.08737

1.44484

1.08640

ZnNc

Z. Liu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 217 (2019) 8–17 9

10

Z. Liu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 217 (2019) 8–17

metal atom in a given group in the periodic table. Since MNcs are derived from the extension of π–conjugation system of MPcs through the addition of four additional fused benzenes, comparisons of the MNcs and MPc properties are also carried out. Some interesting and meaningful results are obtained. 2. Computational method The initial structures for NiNc, CuNc and ZnNc are taken from the crystal structures reported [16]. Previous studies [6–10,12,13] demonstrate that the 6–31G* basis set and the density functional B3LYP [17,18] are suitable for both geometry optimization and frequency/intensity calculations for these derivatives. The default Mulliken's method was used for atomic charge calculation. The Berny algorithm using redundant internal coordinates [19] was employed in energy minimization and tight convergence criteria were adopted throughout. D4h symmetry for these derivatives in the input structures was kept in the course of optimization. With the optimized structures, normal coordinate analyses were carried out to guarantee that all the energy– minimized structures located are true local minima on potential energy surfaces (without imaginary frequencies). All calculations were performed employing Gaussian03 program [20]. The calculated vibrational frequencies were scaled by the factor 0.9613 recommended in our previous research work [10,12,13]. Detailed assignments of the N–M vibrational modes and normal mode descriptions were obtained with calculated potential energy distribution (PED) and assistance of animated pictures produced based on the normal coordinates. Because of the similarity of the three derivatives, only PED of NiNc was conducted. Detailed assignment of the calculated Raman spectrum should take account of resonance, which changes the intensities of Raman vibrations depending on the frequency of the given excitation line used in measurement. Thus the calculated Raman activities were converted to relative Raman intensities (Ii) using the following conversion formula [21,22]: Ii ¼

f ðν 0 −ν i Þ4 Si νi ½1− expð−hcνi =kT Þ

where Si is Raman activities. ν0 is the exciting frequency in reciprocal centimeters (ν0 = 1/λ0 with λ0 being the laser wavelength, 514.5 nm in this work) [14]. νi is the vibrational frequency of the ith normal mode. h, k, c and T are Planck's and Boltzmann's constants, speed of light, and temperature in Kelvin (273.2 K in this work), respectively. f is a common scaling factor chosen suitably for all band intensities. 3. Results and discussion 3.1. Molecular structures Fig. 1 and Table 1 show the structures and the corresponding geometrical parameters. As can be seen from Table 1, the X-ray crystal parameters for CuNc [16] are in very good agreement with our calculated data. The N–M distances (1.911, 1.960 and 1.997 Å) for NiNc, CuNc and ZnNc are all slightly longer than those calculated (1.905, 1.954 and 1.991 Å) for the corresponding MPcs [10]. This trend is also consistent with the ordering of the bond length determined by X-ray diffraction for these complexes [10,16]. Since conjugation in Ncs is higher than in Pcs, the longer N\\M bond in MNc implies that increasing the conjugation weakens the N\\M bonding. The sequence of N\\M distances, NiNc b CuNc b ZnNc, agrees very well with the experimental one. Both the lengths of Cα\\Nm, Cα\\Cβ and Cβ\\Cβ bonds and the angles of the ∠CαNmCα and ∠CαNcCα also follow the same ordering, whereas the lengths of Cα\\Nc and bond angles of ∠MNcCα and ∠NcCαCβ are in the reverse order, i.e., NiNc N CuNc N ZnNc. Notably, the magnitude of angle of ∠NcCαNm changes little. The other structural parameters for

Table 1 Bond length (Å) and bond angle (°) of experiment and calculation for NiNc, CuNc and ZnNc. Parameter

M–Nc Cα–Nm Cα–Nc Cα–Cβ Cβ–Cβ Cβ–Nγ Nγ–Nδ Nδ–Nδ Nδ–Cε Cε–Cω Cω–Cω M–Nc–Cα Nc–Cα–Nm Cα–Nm–Cα Cα–Nc–Cα Nc–Cα–Cβ Cα–Cβ–Cβ Cβ–Cβ–Nγ Cβ–Nγ–Nδ Nγ–Nδ–Nδ Nδ–Nδ–Cε Nδ–Cε–Cω Cε–Cω–Cω a

NiNc

CuNc

ZnNc

Exp.a

DFT

Exp.a

DFT

Exp.a

DFT

1.929

1.911 1.317 1.381 1.453 1.416 1.378 1.417 1.446 1.423 1.375 1.419 126.6 127.8 121.4 106.9 110.5 106.1 121.6 118.5 119.9 118.6 121.1 120.3

1.951 1.320 1.373 1.455 1.406 1.370 1.408 1.427 1.414 1.362 1.401 125.7 128.3 121.7 108.7 109.2 106.5 121.3 118.8 119.9 118.3 121.5 120.2

1.960 1.324 1.376 1.457 1.422 1.377 1.418 1.445 1.423 1.375 1.419 125.7 127.8 123.1 108.6 109.5 106.2 121.5 118.7 119.9 118.6 121.1 120.3

1.983

1.997 1.329 1.374 1.460 1.427 1.377 1.419 1.445 1.423 1.375 1.418 125.1 127.6 124.5 109.8 108.8 106.3 121.3 118.8 119.9 118.6 121.1 120.3

Cited from Ref. [16].

the three complexes remain almost unvaried. These structural features are similar to those calculated for the MPcs [10].

3.2. Electronic structures and atomic charges 3.2.1. Electronic structures The energies of the molecular orbitals from HOMO(highest occupied molecular orbital)–5 to LUMO(lowest unoccupied molecular orbital) + 3 of the three derivatives are comparatively shown in Table 2 and Fig. 2. CuNc is an open–shell system. The HOMO–LUMO gaps are 1.87 (α) and 1.91 (β) eV. The lower gap, 1.87 eV for α orbitals is effective and will be used for comparison with the other two compounds. The computed HOMO–LUMO gaps for NiNc and ZnNc are 1.92 and 1.88 eV, respectively. The corresponding values are 2.24 (NiPc) and 2.19 (ZnPc) eV respectively for Pc compounds. Obviously the HOMO–LUMO gaps decrease from MPcs to MNcs. This result implies that the Q band will shift to lower energy from MPcs to MNcs. Experimentally it is reported that the absorption maximum peaks of Ncs in the Q-band region are red–shifted by 80–100 nm with respect to Pcs due to the extension of πconjugation system through the addition of four additional fused

Table 2 Energy levels (in eV) and symmetry species of some occupied and unoccupied molecular orbitals for NiNc, CuNc and ZnNc. NiNc

CuNc α

ELUMO+3 ELUMO+2 ELUMO+1 ELUMO ΔE EHOMO EHOMO−1 EHOMO−2 EHOMO−3 EHOMO−4 EHOMO−5

−1.46 −1.55 −2.61 −2.61 1.92 −4.53 −5.95 −5.95 −5.97 −6.35 −6.35

B1g B2u Eg Eg A1u Eg Eg B1u Eg Eg

−1.44 −1.59 −2.64 −2.64 1.87 −4.51 −5.96 −5.99 −5.99 −6.18 −6.57

ZnNc β

A2u B2u Eg Eg A1u B1u Eg Eg B1g A1u

−1.57 −1.94 −2.62 −2.62 1.91 −4.53 −5.96 −5.99 −5.99 −6.56 −6.56

B2u B1g Eg Eg A1g B1u Eg Eg Eg Eg

−1.45 −1.55 −2.64 −2.64 1.88 −4.52 −5.96 −5.99 −5.99 −6.56 −6.58

A2u B2u Eg Eg A1u B1u Eg Eg A1u B2u

Z. Liu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 217 (2019) 8–17

-1

eV

CuNc

NiNc

ZnNc

Raman–active vibrations if doubly-degenerate Eg and Eu modes are taken into account twice). Those 19 A2g, 9 A1u, 10 B1u and 10 B2u vibrational modes are neither infrared active nor Raman-active. Vibrational modes and the intensities of the calculated frequencies are summarized in Tables 4 and 5. Both IR and Raman spectra were simulated from the calculated frequency and intensity data by adding a Lorentzian lineshape with a halfwidth at half-maximum of 6 cm−1 [11]. The simulated IR and Raman spectra based on the B3LYP/6–31G* calculated results are depicted in Fig. 3 and Fig. 4. To show the vibrational modes clearly, the key vibrational modes corresponding to the strongest IR and Raman bands for NiNc are demonstrated in Fig. 5.

-2

-3

-2.61

LUMO

1.92

-2.62

-2.64 1.87

-2.64

1.91

1.88

-4

HOMO

-4.53

-4.51

-4.53

11

-4.52

-5

3.3.1. The vibrations involving C\\H bonds All the bands between 3057 cm−1 and 3087 cm−1 are connected with the C\\H stretching vibrations (Fig. 3 and Table 4). The typical C\\H OPB (out of plane bending) vibrations are the very weak bands located at 925 cm−1 for NiNc, CuNc and ZnNc. Bands predicted at around 875 cm−1 and 740 cm−1 also deal with the C\\H OPB. Experimentally two bands at 752 and 888 cm−1 were detected for CuNc. The former is attributed to the C\\H wag [14]. Our analysis shows that the latter that corresponds to calculated 876 cm−1 is caused by the C\\H OPB. For ZnNc, the two observed intense bands at 889 and 750 cm−1 are assigned to the out-of-plane bending of the C\\H in the naphthalene rings by Yanagi et al. [15], which agrees with our assignments. These two bands correspond to our computed bands at 877 and 740 cm−1, respectively. All the vibrational modes from 1007 to 1613 cm−1 (the corresponding experimental frequencies in CuNc are from 1013 to 1632 cm−1) involve the C\\H IPB (in plane bending) vibrations. Such a broad range of the C\\H IPB vibrations is due to the fact that to bend a bond in the planar macrocyclic ring of naphthalocyanine will involve other bonds unavoidably. It is worthy to point out that previous identification of vibrational bands in this range is rather incomplete. For example, for CuNc only the vibrations from 1013 to 1262 cm−1, corresponding to the predicted region of 1008–1241 cm−1, are assigned (to the C\\H IPB) [14] while for ZnNc just 1021 cm−1 is identified (to the C\\H IPB) [15].

-6

-7 Fig. 2. Orbital energies of NiNc, CuNc and ZnNc.

benzenes [23,24], in nice agreement with our calculated HOMO– LUMO gaps. 3.2.2. Atomic charges Both MPcs and MNcs contain the basic porphyrazine (Pz) structural unit and additional π–conjugated rings. The Mulliken atomic charges for the central M [0.798 (Ni), 0.878 (Cu) and 0.948 (Zn) e] (Table 3) increase in the same order as the N–M bond lengths: NiNc b CuNc b ZnNc, and are consistent with the sequence of the radius for M atoms. The negative charges on Nc [−0.705 (NiNc), −0.716 (CuNc) and −0.723 (ZnNc) e] and Nm [−0.556 (NiNc), −0.559 (CuNc) and −0.561 (ZnNc) e] increase with the M atomic number. The larger negative charges on Nc than the ones on Nm demonstrate that the inner pyrrole Nc atoms are more basic than the meso Nm atoms. A simple calculation shows that the total atomic charges of the extended peripheral benzene ring annulated to MPc are essentially the same for NiNc, CuNc and ZnNc, indicating that the central metal ions have negligible influence on the total charges of the extended peripheral benzene ring annulated to MPc.

3.3.2. The vibrations involving N\\M bonds The central metal does not display significant influence on most of the vibrational frequencies, as evidenced by the close values of frequency for the same vibrational mode in different complexes (Table 4). However, the metal dependent absorption bands do vary with the metal atoms. According to our analyses, the bands at 849 (NiNc), 844(CuNc) and 841(ZnNc)cm−1 mainly involve the stretching of N\\M bonds, coupled with the IPB of C\\Nm\\C bridge bonds and the deformation of benzoisoindoles. For CuNc, the band at 844 cm−1 should correspond to the observed, but unassigned band at 861 cm−1 [14]. Analyses reveal that the weak intensity bands at 1532 (NiNc), 1505 (CuNc) and 1498 (ZnNc) cm−1 deal with the drastic stretching of pyrrole rings and the stretching of the C\\Nm, Cβ\\Cγ bonds and benzene rings as well as the IPB of Cγ\\H, N\\M and C\\Nm\\C bonds. The very strong bands predicted at 1365 (NiNc), 1360 (CuNc) and 1356 (ZnNc) cm−1 are mainly characterized by the stretching of the naphthalenes, C\\Nm bonds and pyrroles along with the IPB of the C\\H bonds. These bands obeys the regularity of NiNc N CuNc N ZnNc, indicating that they are metal–dependent. At variance with the experimental assignment of the band at 1340 cm−1 to pyrrole stretching in CuNc [14], we

3.3. IR spectra Each MNc possesses 8 nitrogen atoms, 48 carbon atoms, 24 hydrogen atoms and one metal atom, and therefore has 237 normal vibrational modes. Also, owning to having the same symmetry, D4h, they all have the same vibrational modes as below: ΓvibðMNcÞ ¼ 20A1g ðRÞ þ 19A2g þ 20B1g ðRÞ þ 20B2g ðRÞ þ 19Eg ðRÞ þ9A1u þ 11A2u ðIRÞ þ 10B1u þ 10B2u þ 40Eu ðIRÞ IR and R in the parentheses denote infrared active and Raman-active modes, respectively. These vibrations can be divided into two groups: one group consisting of the in-plane vibrations (A1g, A2g, B1g, B2g and Eu), the other consisting of the out-of-plane modes (A1u, A2u, B1u, B2u and Eg). A2u and Eu modes are infrared active, and Raman-active modes are A1g, B1g, B2g and Eg. Therefore, there are 51 infrared active vibrations and 79 Raman-active vibrations (or 91 infrared active and 98 Table 3 Atomic charge (in e) for NiNc, CuNc and ZnNc. Atom

Nc

Nm

Cα

Cβ

Cγ

Cδ

Cε

Cω

Hγ

Hε

Hω

M

NiNc CuNc ZnNc

−0.705 −0.716 −0.723

−0.556 −0.559 −0.561

0.482 0.484 0.483

0.092 0.088 0.086

−0.278 −0.279 −0.280

0.137 0.137 0.137

−0.185 −0.185 −0.185

−0.137 −0.137 −0.137

0.152 0.152 0.151

0.134 0.134 0.134

0.134 0.134 0.134

0.798 0.878 0.948

12

Z. Liu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 217 (2019) 8–17

Table 4 Calculated and experimental infrared active vibrational modes for NiNc, CuNc and ZnNc. NiNc

CuNc

Sym.

Fre.

Int.

3 A2u 7 Eu 8 Eu 13 A2u 21 A2u 25 Eu 26 Eu 29 Eu 30 Eu 37 A2u 39 A2u 40 Eu 41 Eu 45 A2u 51 A2u 52 Eu 53 Eu 58 Eu 59 Eu 64 Eu 65 Eu 70 Eu 71 Eu 78 A2u 79 Eu 80 Eu 87 Eu 88 Eu 92 A2u 99 Eu 100 Eu 107 Eu 108 Eu 113 A2u 119 Eu 120 Eu 125 A2u 130 Eu 131 Eu 135 Eu 136 Eu 138 Eu 139 Eu 142 Eu 143 Eu 146 Eu 147 Eu 150 Eu 151 Eu 155 Eu 156 Eu 159 Eu 160 Eu 163 Eu 164 Eu 167 Eu 168 Eu 170 Eu 171 Eu 175 Eu 176 Eu 178 Eu 179 Eu 182 Eu 183 Eu 187 Eu 188 Eu 191 Eu 192 Eu 194 Eu 195 Eu 198 Eu 199 Eu 202 Eu

23 62 62 109 199 225 225 287 287 320 344 363 363 412 470 490 490 518 518 559 559 611 611 702 705 705 736 736 738 792 792 849 849 874 901 901 925 1007 1007 1039 1039 1088 1088 1117 1117 1143 1143 1150 1150 1194 1194 1206 1206 1241 1241 1325 1325 1334 1334 1354 1354 1365 1365 1420 1420 1447 1447 1486 1486 1501 1501 1532 1532 1579

0.68 1.73 1.73 0.96 0.85 1.29 1.29 0.15 0.15 5.36 1.00 0.57 0.57 0.68 39.52 18.78 18.78 0.04 0.04 2.55 2.55 5.17 5.17 6.17 71.11 71.11 0.60 0.60 158.62 1.71 1.71 43.10 43.10 106.30 2.55 2.55 18.00 30.20 30.20 34.69 34.69 608.82 608.82 67.37 67.37 16.93 16.93 94.54 94.54 15.98 15.98 2.81 2.81 25.66 25.66 149.96 149.96 0.19 0.19 2.33 2.33 516.53 516.53 9.95 9.95 1.74 1.74 19.78 19.78 10.83 10.83 58.26 58.26 27.31

Exp.a

752

861 888

1013 1035 1094 1128 1158

1200

1262 1340

1374 1432

1470

1515 1601

ZnNc Sym.

Fre.

Int.

2 A2u 7 Eu 8 Eu 13 A2u 19 A2u 25 Eu 26 Eu 28 Eu 29 Eu 34 A2u 40 A2u 38 Eu 39 Eu 45 A2u 51 A2u 52 Eu 53 Eu 57 Eu 58 Eu 63 Eu 64 Eu 70 Eu 71 Eu 80 A2u 78 Eu 79 Eu 87 Eu 88 Eu 92 A2u 99 Eu 100 Eu 107 Eu 108 Eu 113 A2u 119 Eu 120 Eu 125 A2u 131 Eu 132 Eu 135 Eu 136 Eu 138 Eu 139 Eu 142 Eu 143 Eu 146 Eu 147 Eu 150 Eu 151 Eu 155 Eu 156 Eu 158 Eu 159 Eu 163 Eu 164 Eu 167 Eu 168 Eu 169 Eu 170 Eu 175 Eu 176 Eu 178 Eu 179 Eu 182 Eu 183 Eu 187 Eu 188 Eu 191 Eu 192 Eu 194 Eu 195 Eu 198 Eu 199 Eu 203 Eu

21 61 61 92 157 223 223 261 261 284 332 330 330 411 470 488 488 510 510 558 558 610 610 702 701 701 736 736 739 789 789 844 844 876 896 896 925 1008 1008 1025 1025 1089 1089 1116 1116 1141 1141 1149 1149 1192 1192 1204 1204 1241 1241 1320 1320 1330 1330 1354 1354 1360 1360 1415 1415 1444 1444 1466 1466 1497 1497 1505 1505 1575

0.53 1.71 1.71 2.76 2.07 1.40 1.40 0.19 0.19 1.46 5.38 1.74 1.74 0.17 40.62 18.63 18.63 0.20 0.20 2.46 2.46 5.21 5.21 8.04 78.48 78.48 0.20 0.20 164.07 0.95 0.95 46.14 46.14 102.75 1.55 1.55 18.75 33.47 33.47 61.79 61.79 551.21 551.21 108.06 108.06 45.46 45.46 69.53 69.53 16.04 16.04 2.82 2.82 23.85 23.85 110.83 110.83 30.95 30.95 15.51 15.51 592.70 592.70 3.29 3.29 0.19 0.19 0.62 0.62 3.97 3.97 52.33 52.33 24.14

Exp.b

750

889

1021

1092

Assignment (PED) of NiNc Sym.

Fre.

Int.

2 A2u 8 Eu 9 Eu 6 A2u 15 A2u 25 Eu 26 Eu 28 Eu 29 Eu 30 A2u 41 A2u 38 Eu 39 Eu 45 A2u 51 A2u 52 Eu 53 Eu 55 Eu 56 Eu 63 Eu 64 Eu 70 Eu 71 Eu 81 A2u 79 Eu 80 Eu 84 Eu 85 Eu 91 A2u 99 Eu 100 Eu 107 Eu 108 Eu 113 A2u 115 Eu 116 Eu 125 A2u 131 Eu 132 Eu 135 Eu 136 Eu 139 Eu 140 Eu 142 Eu 143 Eu 146 Eu 147 Eu 150 Eu 151 Eu 155 Eu 156 Eu 158 Eu 159 Eu 163 Eu 164 Eu 167 Eu 168 Eu 169 Eu 170 Eu 175 Eu 176 Eu 178 Eu 179 Eu 182 Eu 183 Eu 187 Eu 188 Eu 191 Eu 192 Eu 194 Eu 195 Eu 198 Eu 199 Eu 203 Eu

16 61 61 50 126 216 216 234 234 264 337 319 319 412 470 487 487 507 507 558 558 610 610 706 699 699 735 735 740 785 785 841 841 877 892 892 925 1008 1008 1016 1016 1089 1089 1116 1116 1139 1139 1150 1150 1191 1191 1203 1203 1241 1241 1312 1312 1328 1328 1353 1353 1356 1356 1411 1411 1440 1440 1456 1456 1483 1483 1498 1498 1573

0.00 1.68 1.68 8.51 1.17 3.43 3.43 0.15 0.15 1.41 5.53 2.22 2.22 0.06 40.86 20.22 20.22 0.79 0.79 2.88 2.88 4.85 4.85 6.11 84.21 84.21 0.07 0.07 170.16 0.16 0.16 49.95 49.95 100.19 1.59 1.59 19.26 39.07 39.07 85.09 85.09 469.66 469.66 144.65 144.65 58.11 58.11 53.15 53.15 15.67 15.67 3.05 3.05 22.58 22.58 77.19 77.19 66.17 66.17 53.06 53.06 598.17 598.17 0.52 0.52 2.13 2.13 2.12 2.12 14.92 14.92 28.86 28.86 21.01

80.0Ske. dom. 3.2NM 15.0Iso. str., 49.2Beniso. 3.4NM 4.6CNmC 3.4CγH IPB 3.2NM 15.0Iso. str., 49.2Beniso. 3.4NM 4.6CNmC 3.4CγH IPB 75.4Ske. 2.9NM 7.2CγH 4.8CεH 3.2CωH OPB 67.5Ske. 6.9NM 8.0CγH 4.0CεH 3.2CωH OPB 66.0Ske. boa.,7.4NM 2.4CNm str., 3.8NM 3.8CγH IPB 66.0Ske. boa.,7.4NM 2.4CNm str., 3.8NM 3.8CγH IPB 13.4NM str., 61.0Beniso. 5.2NM 2.0CγH 0.6CεH IPB 13.4NM str., 61.0Beniso. 5.2NM 2.0CγH 0.6CεH IPB 4.5NM 64.3Ske. 5.6CγH 4.0CεH 4.0CωH OPB 12.0NM 76.0Ring OPB 14.4NM str., 43.2Beniso. 11.6NM 4.2CNmC 3.2CγH IPB 14.4NM str., 43.2Beniso. 11.6NM 4.2CNmC 3.2CγH IPB 65.6Ske. 3.2NM 18.0CγH OPB 44.0Naph. 18.4CγH 14.4CεH 5.6CωH OPB 61.2Beniso. def., 3.8NM 1.2CNm str., 6.8NM 5.8CNmC 1.6CγH 1.6CεH IPB 61.2Beniso. def., 3.8NM 1.2CNm str., 6.8NM 5.8CNmC 1.6CγH 1.6CεH IPB 55.2Beniso. def., 11.0NM 3.6CNm str., 2.8NM 4.8CγH 2.8CεH 1.6CωH IPB 55.2Beniso. def., 11.0NM 3.6CNm str., 2.8NM 4.8CγH 2.8CεH 1.6CωH IPB 49.8Beniso. def., 1.0NM str., 4.4NM 2.0CγH 5.0CεH 7.0CωH 7.6CNmC IPB 49.8Beniso. def., 1.0NM str., 4.4NM 2.0CγH 5.0CεH 7.0CωH 7.6CNmC IPB 49.0Naph. def., 2.8NM str., 7.6CγH 10.4CεH 5.6CωH IPB 49.0Naph. def., 2.8NM str., 7.6CγH 10.4CεH 5.6CωH IPB 7.2NM 61.6Ske. 8.3CγH 7.2CεH 6.4CωH OPB 68.0Beniso. def., 7.0NM 3.6 CNm str., 2.8CγH 2.0CωH IPB 68.0Beniso. def., 7.0NM 3.6 CNm str., 2.8CγH 2.0CωH IPB 55.4Beniso. bre., 7.6Beniso. def., 1.6NM str., 1.6NM 2.2CNm 2.8CεH 4.8CωH IPB 55.4Beniso. bre., 7.6Beniso. def., 1.6NM str., 1.6NM 2.2CNm 2.8CεH 4.8CωH IPB 11.2CγH 27.6CεH 25.2CωH 13.6Ske. OPB 3.4NM 1.6CNm str., 10.2CNmC 3.2NM 6.0CγH 1.6CεH 3.2CωH IPB, 57.0Beniso. def. 3.4NM 1.6CNm str., 10.2CNmC 3.2NM 6.0CγH 1.6CεH 3.2CωH IPB, 57.0Beniso. def. 4.8NM 1.6 CNm str., 15.6CNmC 6.8CγH 2.4CεH 5.2CωH IPB, 51.2Beniso. def. 4.8NM 1.6 CNm str., 15.6CNmC 6.8CγH 2.4CεH 5.2CωH IPB, 51.2Beniso. def. 50.4CγH 3.2CεH 12.8CωH 14.0Naph. OPB 2.2NM str., 10.0CNmC 3.8NM IPB, 64.0Beniso. def. 2.2NM str., 10.0CNmC 3.8NM IPB, 64.0Beniso. def. 16.0CγH 40.8CεH 24.0CωH 6.4Ben. OPB 6.8CγH 20.4CεH 12.0CωH IPB, 44.0Naph. def. 6.8CγH 20.4CεH 12.0CωH IPB, 44.0Naph. def. 2.2NM 9.0CγH 5.0CωH 2.6CNmC IPB, 4.4NM 6.0CNm str., 12.6Py. 37.4Beniso. def. 2.2NM 9.0CγH 5.0CωH 2.6CNmC IPB, 4.4NM 6.0CNm str., 12.6Py. 37.4Beniso. def. 18.4CγH 5.6CεH 6.0NM IPB, 20.0Py. 26.2Beniso. def., 1.2NM 4.0CNmC str. 18.4CγH 5.6CεH 6.0NM IPB, 20.0Py. 26.2Beniso. def., 1.2NM 4.0CNmC str. 9.0CγH 9.6CεH 20.0CωH 0.6NM 2.6CNmC IPB, 32.7Beniso. def., 1.0NM 1.2CNm str. 9.0CγH 9.6CεH 20.0CωH 0.6NM 2.6CNmC IPB, 32.7Beniso. def., 1.0NM 1.2CNm str. 4.8CγH 22.0CεH 28.8CωH IPB, 23.2Beniso. def. 4.8CγH 22.0CεH 28.8CωH IPB, 23.2Beniso. def. 12.8CγH 17.8CεH 11.2CωH 3.6CNmC IPB, 42.4Beniso. def., 2.0CNm str. 12.8CγH 17.8CεH 11.2CωH 3.6CNmC IPB, 42.4Beniso. def., 2.0CNm str. 24.0CγH 10.8CεH 10.8CωH IPB, 28.0Beniso.def., 0.8NM 1.2CNm str. 24.0CγH 10.8CεH 10.8CωH IPB, 28.0Beniso.def., 0.8NM 1.2CNm str. 19.2CγH 4.8CεH 12.0CωH 2.0CNm IPB, 40.2Beniso.def., 1.4NM 1.6CNm str. 19.2CγH 4.8CεH 12.0CωH 2.0CNm IPB, 40.2Beniso.def., 1.4NM 1.6CNm str. 14.0CγH 24.0CεH IPB, 46.0Naph. def. 14.0CγH 24.0CεH IPB, 46.0Naph. def. 2.6NM 43.0Beniso. 1.6CNm str., 6.0CNmC 9.0CγH 8.5CεH 10.4CωH IPB 2.6NM 43.0Beniso. 1.6CNm str., 6.0CNmC 9.0CγH 8.5CεH 10.4CωH IPB 18.9Py. 3.2NM str., 25.4Beniso. def., 8.8CNmC 9.6CγH 11.6CεH 12.8CωH IPB 18.9Py. 3.2NM str., 25.4Beniso. def., 8.8CNmC 9.6CγH 11.6CεH 12.8CωH IPB 63.0Naph. str., 14.8CγH 2.8CεH 6.4CωH IPB 63.0Naph. str., 14.8CγH 2.8CεH 6.4CωH IPB 27.0Naph. 4.4CNm 12.0Py. str., 16.0CγH 15.0CεH 9.0CωH IPB 27.0Naph. 4.4CNm 12.0Py. str., 16.0CγH 15.0CεH 9.0CωH IPB 26.4Beniso. 4.4Py. def., 13.2CγH 20.2CεH 9.8CωH IPB, 2.4CNm str. 26.4Beniso. 4.4Py. def., 13.2CγH 20.2CεH 9.8CωH IPB, 2.4CNm str. 43.8Beniso. def., 2.0CNm str., 10.4CγH 9.4CεH 20.6CωH IPB 43.8Beniso. def., 2.0CNm str., 10.4CγH 9.4CεH 20.6CωH IPB 52.2Beniso. def., 12.4CNmC str., 8.0CγH 1.6CεH 11.6CωH IPB 52.2Beniso. def., 12.4CNmC str., 8.0CγH 1.6CεH 11.6CωH IPB 42.6Naph. 3.2CNmC str., 8.8CγH 14.4CεH 19.6CωH IPB 42.6Naph. 3.2CNmC str., 8.8CγH 14.4CεH 19.6CωH IPB 42.4Py. 14.8CNm 2.6Ben. 2.0CβCγ str., 10.4Py. def, 4.2CγH 1.6NM 1.6CNmC IPB 42.4Py. 14.8CNm 2.6Ben. 2.0CβCγ str., 10.4Py. def, 4.2CγH 1.6NM 1.6CNmC IPB 64.0Beniso. str., 7.2CγH 6.8CεH 8.0CωH IPB

Z. Liu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 217 (2019) 8–17

13

Table 4 (continued) NiNc

CuNc

Sym.

Fre.

Int.

203 Eu 207 Eu 208 Eu 210 Eu 211 Eu 215 Eu 216 Eu 219 Eu 220 Eu 223 Eu 224 Eu 227 Eu 228 Eu 231 Eu 232 Eu 235 Eu 236 Eu

1579 1607 1607 1613 1613 3058 3058 3062 3062 3075 3075 3084 3084 3085 3085 3087 3087

27.31 2.64 2.64 14.86 14.86 3.00 3.00 1.43 1.43 43.42 43.42 14.88 14.88 11.21 11.21 141.63 141.63

Exp.a

1632

3050

ZnNc Sym.

Fre.

Int.

204 Eu 207 Eu 208 Eu 211 Eu 212 Eu 215 Eu 216 Eu 219 Eu 220 Eu 223 Eu 224 Eu 227 Eu 228 Eu 231 Eu 232 Eu 234 Eu 235 Eu

1575 1607 1607 1613 1613 3058 3058 3062 3062 3074 3074 3083 3083 3084 3084 3087 3087

24.14 3.06 3.06 12.28 12.28 2.95 2.95 1.41 1.41 42.28 42.28 15.61 15.61 0.49 0.49 155.21 155.21

Exp.b

Assignment (PED) of NiNc Sym.

Fre.

Int.

204 Eu 207 Eu 208 Eu 211 Eu 212 Eu 215 Eu 216 Eu 219 Eu 220 Eu 223 Eu 224 Eu 227 Eu 228 Eu 231 Eu 232 Eu 234 Eu 235 Eu

1573 1606 1606 1613 1613 3057 3057 3062 3062 3074 3074 3081 3081 3082 3082 3087 3087

21.01 3.29 3.29 10.80 10.80 2.96 2.96 1.39 1.39 40.94 40.94 17.34 17.34 0.05 0.05 157.30 157.30

64.0Beniso. str., 7.2CγH 6.8CεH 8.0CωH IPB 50.0Beniso. str., 7.6CγH 16.0CεH 14.0CωH IPB 50.0Beniso. str., 7.6CγH 16.0CεH 14.0CωH IPB 57.2Beniso. 1.6CNm str.,15.6CγH 9.6CεH IPB 57.2Beniso. 1.6CNm str.,15.6CγH 9.6CεH IPB 2.4CγH 43.2CεH 34.8CωH str., 8.4Ben. def. 2.4CγH 43.2CεH 34.8CωH str., 8.4Ben. def. 3.2CγH 54.0CεH 22.2CωH 6.8Ben. str. 3.2CγH 54.0CεH 22.2CωH 6.8Ben. str. 6.4CγH 34.4CεH 43.6CωH 6.0CεCω str. 6.4CγH 34.4CεH 43.6CωH 6.0CεCω str. 65.6CγH 6.4CεH 4.4CωH 15.2Ben.str. 65.6CγH 6.4CεH 4.4CωH 15.2Ben.str. 49.8CγH 6.0CεH 23.6CωH str. 49.8CγH 6.0CεH 23.6CωH str. 23.6CγH 18.4CεH 41.4CωH 4.0Ben. str. 23.6CγH 18.4CεH 41.4CωH 4.0Ben. str.

Exp., experimental; Sym., symmetry; Fre., frequency (cm−1); Int., intensity; Ske., skeletal; dom., doming; boa., boating; Ring, 16–membered ring; Beniso., benzoisoindole; Ben., benzene; Naph., naphthalene; Py., pyrrole; Iso., isoindole; IPB, in−plane bending; OPB, out-of -plane bending; def., deformation; str., stretching. a Cited from Ref. [14]. b Cited from Ref. [15].

find this band (predicted at 1320 cm−1) is associated with the stretching of the N\\M, C\\Nm bonds and benzoisoindoles, entangled with the IPB of the C\\Nm–C and C\\H bonds. Note there is only one vibration at around 1325 cm−1 for NiNc and 1320 cm−1 for CuNc, while for ZnNc two bands at 1328 and 1312 cm−1 can be seen (Fig. 3). This is because the other band at 1334 cm−1 for NiNc and 1330 cm−1 CuNc is extremely weak. The bands at 1039 (NiNc), 1025 (CuNc) and 1016 (ZnNc) cm−1 decrease in the order of NiNc N CuNc N ZnNc, again showing the metal independence. These vibrational bands are characterized by the IPB of the N\\M, Cγ\\H, Cω\\H and C\\Nm\\C bonds, the stretching of the N\\M, C\\Nm along with the deformation of benzoisoindoles and pyrroles. The bands at 705 (NiNc), 701 (CuNc) and 699 (ZnNc) cm−1 are mainly caused by the deformation of benzoisoindoles, coupled with the stretching of the N\\M and C\\Nm bonds besides the IPB of the Cγ\\H and Cω\\H bonds. The vibrational modes at 490 (NiNc), 488 (CuNc) and 487 (ZnNc) cm−1 are due to the deformation of benzoisoindoles as well as the stretching of two N– M bonds and the IPB of the other two N\\M, C\\Nm\\C and Cγ\\H, Cε\\H bonds. The two group vibrational bands of 363, 330, 319 and 287, 261, 234 cm−1 show the typical metal dependence. However, owning to the low intensity, these bands are almost invisible. 3.4. Raman spectra 3.4.1. The strongest, the second strongest and the medium intensity bands According to our calculations, the strongest bands at 1570 (NiNc), 1546 (CuNc) and 1525 (ZnNc) cm−1 mainly involve the drastic stretching of the C\\Nm\\C bonds as well as the stretching of the benzoisoindoles coupled with the IPB vibrations of Cε\\H and Cω\\H bonds (see Fig. 4 and Table 5). The largest difference computed for the three compounds is 45 cm−1 (between NiNc and ZnNc), indicating that these bands are sensitive to the metal ion presented in naphthalocyanine compounds. This is because of a change in shape of the entire ring [25]. The magnitude of the frequency decreases in the order of NiNc N CuNc N ZnNc, in a reverse ordering of atomic charges on the central M and the N\\M bond lengths. The second strongest bands at 1387 cm−1 for NiNc, CuNc and ZnNc mainly involve the intense stretching of the bensoisoindoles and the IPB of the Cγ\\H and Cε\\H bonds. On the other hand, the frequency values of these bands are much larger than those (1311, 1300 and 1291 cm−1) [10] of the corresponding MPcs, with the largest difference (96 cm−1) computed between ZnNc and ZnPc, indicating that these bands are closely related

to the extension of the peripheral benzoannulation. The band at 1352 cm−1 for CuNc is in fact composed of three vibrations at 1352, 1353 and 1354 cm−1 (see Table 5). These vibrations merge into a medium intensity single band. The similar situation happens with NiNc and ZnNc. Different from the previous assignment to naphthalene stretching [14], we find the vibration at 1352 cm−1 for CuNc is the stretching of the N\\M bonds and benzoisoindoles, entangled with the IPB of the C\\Nm\\C and C\\H bonds. The shoulder at 1540 (NiNc), 1513 (CuNc) and 1490 (ZnNc) cm−1 are associated to the drastic stretching of C\\Nm\\C bonds and the isoindoles mixed with the Cγ\\H IPB. The bands computed at 1431 (NiNc), 1425 (CuNi) and 1420 (ZnNc) cm−1 mainly involve the IPB of C\\H bonds as well as the stretching of benzoisoindoles. The medium intensity bands at 1305 (NiNc), 1297 (CuNc) and 1290 (ZnNc) cm−1 originate from the stretching of the N–M bonds and benzoisoindoles along with the IPB of the Cγ\\H, Cω\\H and C\\Nm bonds. However, the experimental frequency of 1288 cm−1, corresponding to the theoretical 1297 cm−1 for CuNc, is not identified in Ref. [14]. It should be noted that all the bands mentioned above follow the order NiNc N CuNc N ZnNc, which is the reverse order of the M\\N distances. The medium intensity bands at 1177 (NiNc), 1178 (CuNc) and 1178 (ZnNc) cm−1 are resulted from the IPB of the Cγ\\H, Cε\\H, C\\Nm\\C and N\\M\\N bonds, together with the deformation of benzoisoindoles. Another group of medium intensity bands at 1116 (NiNc), 1115 (CuNc) and 1112 (ZnNc) cm−1 are due to the IPB of C\\H bonds coupled with the stretching of the N–M bands and benzoisoindoles. 3.4.2. The remaining vibrational modes On the basis of our calculation, all the bands between 3050 and 3090 cm−1 for the three molecules are from the C\\H stretching vibrations. For NiNc, the vibrational modes at 954, 925, 894, 874 and 835 cm−1 (Table 5) which are difficult to be seen in Fig. 4 because of very low intensity are typical C\\H bond OPB vibrations. CuNc and ZnNc have the similar situation. In addition, the weak bands of 823 (NiNc), 816 (CuNc) and 814 (ZnNc) cm−1 are characterized by the stretching of the N\\M bonds and benzoisoindoles mixed with the Cγ\\H IPB. The weak bands at around 742 (NiNc), 740 (CuNc) and 738(ZnNc) cm−1 are ascribed to the breathing of naphthalocyanines and the stretching of N\\M bonds. The weak bands of 728 (NiNc), 724 (CuNc) and 725 (ZnNc) cm−1 are due to the stretching of N\\M, C\\Nm\\C bonds and the breathing of benzoisoindoles besides the IPB of Cγ\\H bonds. The bands at 676

14

Z. Liu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 217 (2019) 8–17

Table 5 Calculated and experimental Raman−active vibrational modes for NiNc, CuNc and ZnNc. NiNc

CuNc

Sym.

Fre.

Int.

4 Eg 5 Eg 6 B2g 10 Eg 11 Eg 16 Eg 17 Eg 18 B1g 19 A1g 22 Eg 23 Eg 27 B2g 31 B2g 32 Eg 33 Eg 34 Eg 35 Eg 43 Eg 44 Eg 47 B1g 49 Eg 50 Eg 54 Eg 55 Eg 56 A1g 61 B2g 62 B2g 66 Eg 67 Eg 68 B1g 69 A1g 75 A1g 76 Eg 77 Eg 82 B1g 84 Eg 85 Eg 90 Eg 91 Eg 93 B1g 94 A1g 96 Eg 97 Eg 101 B1g 102 B2g 105 Eg 106 Eg 109 A1g 111 Eg 112 Eg 116 Eg 117 Eg 121 B2g 123 Eg 124 Eg 127 Eg 128 Eg 132 B1g 133 A1g 134 B2g 140 A1g 141 B1g 144 B2g 148 A1g 149 B1g 153 B2g 154 A1g 157 B2g 158 B1g 162 B2g 166 B1g 172 B2g 173 A1g 174 B1g

40 40 55 73 73 143 143 145 187 205 205 229 294 296 296 302 302 400 400 455 469 469 501 501 504 524 548 575 575 606 609 676 688 688 728 728 728 738 738 742 745 755 755 823 828 835 835 862 874 874 894 894 912 925 925 954 954 1008 1008 1019 1098 1116 1121 1143 1143 1177 1190 1203 1203 1241 1305 1335 1352 1354

0.09 0.09 8.44 3.77 3.77 0.17 0.17 0.08 2.07 0.03 0.03 1.78 0.20 0.01 0.01 0.01 0.01 0.13 0.13 0.07 0.02 0.02 0.00 0.00 0.38 1.55 1.35 0.01 0.01 0.34 2.87 8.74 0.10 0.10 7.15 0.00 0.00 0.13 0.13 8.08 4.42 0.07 0.07 4.76 1.38 0.01 0.01 0.00 0.01 0.01 0.01 0.01 0.03 0.00 0.00 0.00 0.00 1.44 0.71 0.76 4.61 17.54 0.86 0.98 0.00 18.31 4.19 2.64 0.84 0.08 19.33 1.88 23.27 11.26

Exp.a

221

474

517 555

615 680

722

756

811 842 857 873

1026 1012 1090 1127

1151 1184

1215 1288 1360

ZnNc

Assignment (PED) of NiNc

Sym.

Fre.

Int.

Sym.

Fre.

Int.

4 Eg 5 Eg 6 B2g 10 Eg 11 Eg 16 Eg 17 Eg 14 B1g 21 A1g 22 Eg 23 Eg 24 B2g 35 B2g 32 Eg 33 Eg 36 Eg 37 Eg 43 Eg 44 Eg 46 B1g 49 Eg 50 Eg 55 Eg 56 Eg 54 A1g 61 B2g 62 B2g 66 Eg 67 Eg 68 B1g 69 A1g 75 A1g 76 Eg 77 Eg 82 B1g 84 Eg 85 Eg 90 Eg 91 Eg 93 B1g 94 A1g 96 Eg 97 Eg 101 B1g 102 B2g 104 Eg 105 Eg 109 A1g 111 Eg 112 Eg 116 Eg 117 Eg 121 B2g 123 Eg 124 Eg 127 Eg 128 Eg 133 B1g 134 A1g 130 B2g 140 A1g 141 B1g 144 B2g 149 A1g 148 B1g 153 B2g 154 A1g 160 B2g 157 B1g 162 B2g 166 B1g 172 B2g 173 A1g 174 B1g

39 39 54 75 75 137 137 131 186 208 208 220 290 284 284 302 302 399 399 443 470 470 505 505 503 521 549 582 582 605 608 671 693 693 724 733 733 738 738 740 744 757 757 816 826 836 836 859 876 876 895 895 909 925 925 954 954 1008 1008 1006 1092 1115 1121 1143 1143 1178 1187 1205 1199 1240 1297 1334 1352 1353

0.02 0.02 7.16 2.75 2.75 0.18 0.18 0.43 1.43 0.01 0.01 1.23 0.31 0.01 0.01 0.00 0.00 0.11 0.11 0.02 0.01 0.01 0.00 0.00 0.29 1.39 1.10 0.01 0.01 0.44 2.51 7.65 0.08 0.08 8.85 0.00 0.00 0.10 0.10 5.14 3.31 0.06 0.06 5.05 1.10 0.01 0.01 0.00 0.01 0.01 0.00 0.00 0.01 0.00 0.00 0.00 0.00 1.24 0.60 0.35 4.71 17.13 0.55 0.68 0.09 15.98 2.91 3.39 0.54 0.08 17.28 1.60 18.99 8.99

3 Eg 4 Eg 7 B2g 11 Eg 12 Eg 16 Eg 17 Eg 14 B1g 21 A1g 22 Eg 23 Eg 24 B2g 35 B2g 32 Eg 33 Eg 36 Eg 37 Eg 43 Eg 44 Eg 46 B1g 49 Eg 50 Eg 57 Eg 58 Eg 54 A1g 60 B2g 62 B2g 66 Eg 67 Eg 68 B1g 69 A1g 74 A1g 77 Eg 78 Eg 82 B1g 86 Eg 87 Eg 92 Eg 93 Eg 89 B1g 94 A1g 96 Eg 97 Eg 101 B1g 102 B2g 103 Eg 104 Eg 109 A1g 111 Eg 112 Eg 118 Eg 119 Eg 121 B2g 123 Eg 124 Eg 127 Eg 128 Eg 133 B1g 134 A1g 130 B2g 138 A1g 141 B1g 144 B2g 149 A1g 148 B1g 153 B2g 154 A1g 161 B2g 157 B1g 162 B2g 166 B1g 172 B2g 173 A1g 174 B1g

37 37 53 76 76 131 131 119 186 210 210 216 288 275 275 306 306 399 399 435 470 470 507 507 503 518 549 587 587 604 607 665 699 699 725 736 736 740 740 738 743 759 759 814 824 836 836 859 877 877 896 896 908 925 925 954 954 1008 1008 995 1087 1112 1121 1143 1142 1178 1185 1207 1195 1240 1290 1332 1352 1353

0.00 0.00 7.18 2.47 2.47 0.21 0.21 1.01 1.21 0.00 0.00 1.08 0.37 0.01 0.01 0.00 0.00 0.11 0.11 0.12 0.01 0.01 0.00 0.00 0.27 1.38 1.05 0.00 0.00 0.52 2.68 7.65 0.07 0.07 9.37 0.01 0.01 0.09 0.09 4.28 2.96 0.06 0.06 6.46 1.01 0.01 0.01 0.00 0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.23 0.61 0.21 5.33 18.55 0.44 0.57 0.27 15.40 2.47 4.04 0.37 0.08 16.55 1.52 14.61 8.78

80.2Ske. wav. 80.2Ske. wav. 63.2Ske. 16.4NMN 3.2CγH IPB 65.6Ske. tw., 5.2NMN 6.8CγH 3.2CεH OPB 65.6Ske. tw., 5.2NMN 6.8CγH 3.2CεH OPB 58.8Ske. tw., 10.4NMN 7.6CγH 6.4CεH 2.0CωH OPB 58.8Ske. tw., 10.4NMN 7.6CγH 6.4CεH 2.0CωH OPB 61.6Ske. bre.,18.4NM str., 3.2CγH IPB 68.4Ske. bre., 10.4NM str. 33.7Beniso. 15.0NMN 19.4CNmC 6.4CγH 6.0CεH 2.0CωH OPB 33.7Beniso. 15.0NMN 19.4CNmC 6.4CγH 6.0CεH 2.0CωH OPB 45.6Beniso. 28.4NMN 7.6CNmC 2.4CγH IPB 60.8Beniso. 17.6NMN IPB 46.8Beniso. 0.7NMN 19.4CNmC 5.6CγH 4.8CεH 4.2CωH OPB 46.8Beniso. 0.7NMN 19.4CNmC 5.6CγH 4.8CεH 4.2CωH OPB 34.8Beniso.17.6NMN 17.6CNmC 3.2CγH 2.0CεH 2.0CωH OPB 34.8Beniso.17.6NMN 17.6CNmC 3.2CγH 2.0CεH 2.0CωH OPB 58.8Beniso. 2.8NMN 7.6CγH 6.4CεH 3.6CωH OPB 58.8Beniso. 2.8NMN 7.6CγH 6.4CεH 3.6CωH OPB 8.8NM 57.6Beniso. str., 8.4CNm 4.0CεH 2.4CωH IPB 46.4Beniso. 16.8CγH 15.6CεH 8.0CωH OPB 46.4Beniso. 16.8CγH 15.6CεH 8.0CωH OPB 57.2Beniso. 6.0CγH 5.2CεH 8.4CωH OPB 57.2Beniso. 6.0CγH 5.2CεH 8.4CωH OPB 63.6Ske. bre., 8.6NM str., 3.2CγH 3.2CωH IPB 4.0CNmC str., 67.2Beniso. def., 5.2NMN 9.6 CγH IPB 60.0Beniso. def., 6.4CNmC 4.0CεH 10.4CωH IPB 43.2Beniso. 23.0CNmC 4.1NMN 3.6CγH 2.4CεH 8.0CωH OPB 43.2Beniso. 23.0CNmC 4.1NMN 3.6CγH 2.4CεH 8.0CωH OPB 53.2Naph. 2.0NM str., 7.2 CωH IPB 48.4Naph. 2.8NM str., 7.2 CωH IPB 5.6CNmC str., 22.0CNmC IPB, 52.4Iso. def. 5.3NMN 7.6CγH 4.4CεH 3.2CωH 60.7Ske. OPB 5.3NMN 7.6CγH 4.4CεH 3.2CωH 60.7Ske. OPB 6.4NM 4.0CNmC str., 72.8Beniso.bre., 4.8CγH 2.4CεH 3.2CωH IPB 11.6CγH 7.2CεH 1.2CωH 63.4Ske. OPB 11.6CγH 7.2CεH 1.2CωH 63.4Ske. OPB 10.0CγH 26.0CεH 12.8CωH 23.6Ske. OPB 10.0CγH 26.0CεH 12.8CωH 23.6Ske. OPB 71.6Beniso. bre., 2.4NM 4.0CNmC str., 4.0CγH 3.2CεH 4.0CωH IPB 64.4Beniso. bre., 1.6NM str., 10CNmC 6.4CγH 4.8CεH 5.6CωH IPB 14.0CγH 10.4CεH 1.8CωH 61.3Beniso. OPB 14.0CγH 10.4CεH 1.8CωH 61.3Beniso. OPB 6.8NM 67.6Beniso. str. 6.4CγH IPB 20.8CNmC 4.0CεH 10.4CωH IPB, 51.0Beniso. def. 19.6CγH 37.4CεH 21.4CωH 14.9Naph. OPB 19.6CγH 37.4CεH 21.4CωH 14.9Naph. OPB 8.4NM 3.2CNmC 55.6Beniso. str., 5.6CNmC 11.2CγH IPB 22.2Beniso. 50.0CγH 6.2CεH 11.8CωH OPB 22.2Beniso. 50.0CγH 6.2CεH 11.8CωH OPB 27.2Beniso. 44.8CγH 7.2CεH 9.8CωH OPB 27.2Beniso. 44.8CγH 7.2CεH 9.8CωH OPB 48.8Beniso. def., 6.4CγH 6.4CεH 9.6CωH 16.0CNmC 3.2NMN IPB 11.6Naph. 16.4CγH 40.2CεH 24.2CωH OPB 11.6Naph. 16.4CγH 40.2CεH 24.2CωH OPB 3.6CγH 27.8CεH 47.4CωH 14.4Ben. OPB 3.6CγH 27.8CεH 47.4CωH 14.4Ben. OPB 8.0CγH 24.0CεH 12.8CωH IPB, 41.6Ben.bre. 6.0CγH 24.0CεH 14.4CωH IPB, 41.6Ben. bre. 20.0CNmC 12.4NMN 2.4CγH 3.2CωH IPB, 9.6CNmC str., 37.6Beniso. def. 28.8CγH 7.2CωH IPB, 4.0NM 3.2CNmC 39.2Iso. str. 31.2CγH 8.8CεH 3.2CωH IBP, 2.8NM 34.8Beniso. str. 16.0CεH 24.8CωH IPB, 4.8CNcC str., 30.6Naph. def. 6.4CγH 27.2CεH 32.0CωH IBP, 22.0Naph. str. 26.4CεH 35.2CωH IBP, 18.0Naph.str. 13.6CγH 16.0CεH 12.4CNmC 1.6NMN IPB, 42.4Beniso. def. 10.4CγH 20.0CωH 2.4CNm IPB, 29.6Beniso. 1.6NM str. 34.4CγH 10.4CεH 1.2NMN 1.6CNmC IPB, 36.0Beniso. def. 3.2NM 42.8Beniso. str., 9.6CNm 2.4CγH 3.2CεH 20.0CωH IBP 15.2CγH 25.6CεH 3.2CωH IBP, 44.0Naph. def. 4.4NM 53.6Beniso. str., 12.8CNm 10.4CγH 6.4CωH IPB 12.8CγH 18.4CεH 22.3CωH IPB, 28.8Beniso. def. 2.4NM 44.8Beniso. str., 11.6CNmC 15.2CγH 8.0CεH 6.4CωH IPB 67.2Naph. str., 14.4CγH 2.4CεH 6.4CωH IPB

Z. Liu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 217 (2019) 8–17

15

Table 5 (continued) NiNc

CuNc Exp.a

Sym.

Fre.

Int.

177 A1g 180 B1g 181 A1g 184 A1g 185 B1g 186 B2g 190 B2g 193 B1g 196 A1g 200 A1g 201 B1g 204 B1g 205 A1g 209 B2g 213 B2g 217 B2g 218 B1g 221 A1g 225 B2g 229 B2g 230 B1g 233 A1g 234 B1g 237 A1g

1355 1387 1404 1421 1431 1442 1477 1500 1501 1540 1570 1579 1582 1608 1614 3058 3062 3062 3075 3084 3085 3085 3087 3087

2.13 41.48 6.94 2.23 23.20 1.31 0.86 0.07 1.17 12.80 100 15.25 1.25 0.46 3.00 0.02 0.18 0.01 0.66 0.07 0.19 0.04 0.35 1.96

1432

1504 1527 1603

ZnNc

Assignment (PED) of NiNc

Sym.

Fre.

Int.

Sym.

Fre.

Int.

177 A1g 180 B1g 181 A1g 184 A1g 185 B1g 186 B2g 190 B2g 196 B1g 197 A1g 200 A1g 201 B1g 202 B1g 205 A1g 209 B2g 213 B2g 217 B2g 218 B1g 221 A1g 225 B2g 229 B2g 230 B1g 233 A1g 236 B1g 237 A1g

1354 1387 1399 1416 1425 1433 1461 1498 1499 1513 1546 1575 1578 1607 1614 3058 3062 3062 3074 3083 3084 3084 3087 3087

2.41 35.81 5.65 0.29 16.04 1.90 0.27 0.60 2.71 8.93 100 0.75 1.37 0.44 2.62 0.01 0.14 0.00 0.51 0.06 0.07 0.01 0.35 1.56

177 A1g 180 B1g 181 A1g 184 A1g 185 B1g 186 B2g 190 B2g 197 B1g 200 A1g 196 A1g 201 B1g 202 B1g 205 A1g 209 B2g 213 B2g 217 B2g 218 B1g 221 A1g 225 B2g 229 B2g 230 B1g 233 A1g 236 B1g 237 A1g

1353 1387 1395 1413 1420 1421 1454 1497 1499 1490 1525 1572 1576 1607 1614 3057 3062 3062 3074 3081 3082 3082 3087 3087

6.58 36.84 4.06 0.00 13.86 2.35 0.03 1.81 0.00 12.08 100 0.07 1.64 0.45 2.44 0.01 0.13 0.00 0.47 0.07 0.05 0.04 0.35 1.44

2.4NM 64.5Beniso. str.,12.8CNmC 3.2CγH 3.2CεH IPB 45.2Beniso. str., 14.4CγH 20.0CεH IPB 38.4Beniso. 4.0CNmC str., 9.6CNmC 18.4CγH 8.8CεH IBP 16.8CγH 25.6CεH 8.0CωH IBP, 20.0Beniso. str. 22.4CγH 20.0CεH 9.6CωH IBP, 28.0Beniso. str. 5.6CNmC str., 8.8CεH 21.6CωH IBP, 44.8Beniso. def. 11.2CNmC str., 4.8NMN 3.2CγH 12.8CωH IPB, 49.6Beniso. def. 39.2Beniso. str., 8.8CγH 15.2CεH 20.8CωH IBP 43.2Beniso. str., 7.2CγH 15.2CεH 21.6CωH IBP 14.4CNmC 66.8Iso. str, 10.4CγH IPB 19.2CNmC 55.6Beniso. str., 4.0CεH 3.2CωH IBP 57.0Beniso. 7.2CNmC str., 5.6CγH 4.8CεH 7.2CωH IBP 64.0Beniso. str., 6.4CγH 5.6CεH 8.8CωH IBP 47.0Beniso. str., 3.2CγH 18.4CεH 16.0CωH IBP 59.0Beniso. str., 18.0CγH 8.8CεH 2.4CωH IBP 2.4CγH 44.0CεH 35.2CωH str. 4.0CγH 53.6CεH 22.4CωH str. 4.0CγH 53.6CεH 22.4CωH str. 6.4CγH 34.4CεH 44.0CωH str. 66.0CγH 7.2CεH 4.0CωH 8.8Ben. str. 50.0CγH 6.4CεH 25.0CωH str. 48.0CγH 6.4CεH 26.0CωH str. 23.0CγH 19.0CεH 42.0CωH str. 24.0CγH 19.0CεH 41.0CωH str.

Exp., experimental; Sym., symmetry; Fre., frequency (cm−1); Int., intensity; Ske., skeletal; wav., waving; Iso., isoindole; Beniso., benzoisoindole; Ben., benzene; Naph., naphthalene; Py., pyrrole; IPB, in−plane bending; OPB, out−of −plane bending; bre., breathing; def., deformation; str., stretching; tw., twisting. Note: The intensity values are normalized to a maximum of 100. a Cited from Ref. [14].

3000

1600

1400

1200

1000

600

400

200

0

200

0

1356

1498

ZnNc

925

0.2

1150

1016

1312

3087

1089

740

1328

0.6

699

1116

0.8

877

1.0

0.4

800

841

3300 1.2

0.0 1360 1089

739

876

CuNc 701

1505

844

0.2

925

3087

1320

0.4

1149

0.6

1025 1008

1116

0.8

0.0

1.0

1088

1365

NiNc 705

738 849

925 874

1532

1007

3087

0.2

1150

0.4

1117

0.6

1039

0.8

1325

Absorbance

1.0

0.0 3300

3000

1600

1400

1200

1000

800 -1

Wavenumbers (cm ) Fig. 3. Simulated IR spectra for NiNc, CuNc and ZnNc.

600

400

16

Z. Liu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 217 (2019) 8–17

3200

3000

100

1600 1400 1200 1000

800

600

400

200

0

1525

80

4. Conclusions

ZnNc

60

We have performed density functional theory calculations on three naphthalocyanine derivatives NiNc, CuNc and ZnNc. Our calculations show that all the three complexes have D4h geometry, and the order of the N\\M bond lengths is NiNc b CuNc b ZnNc. The calculated Mulliken atomic charges of the central M vary in the identical order with the bond lengths. The HOMO–LUMO gaps for MNc decrease with respect to the ones of MPc, due to the extension of π-conjugation system upon the addition of four fused benzenes. Detailed assignments for the vibrational bands in the IR and Raman spectra for the three molecules have been made. Inconsistent with the N\\M bond length, the metal dependent frequencies decrease in the order of NiNc N CuNc N ZnNc. The strongest Raman lines predicted at 1570 (NiNc), 1546 (CuNc) and 1525 (ZnNc) cm−1 are very sensitive to the metal ion, thus they can be used as indicators to identify the complexes.

1387

40 20

607

53

608

54

Relative Raman Intensity

0 100

1546

80

CuNc

60

1387

40 20 0 100

1570

Acknowledgements

80 60

1387

40

The authors thank the National Natural Science Foundation of China (Grant Nos. 20973090, 61071009).

NiNc

References 609

20

55

0 3200

bonds. The vibrational bands at 55 (NiNc), 54 (CuNc) and 53 (ZnNc) cm−1 involve the whole naphthalocyanine skeleton IPB.

3000

1600 1400 1200 1000

800

600

400

200

0

Wavenumbers (cm-1) Fig. 4. Simulated Raman spectra for NiNc, CuNc and ZnNc.

(NiNc), 671 (CuNc) and 665 (ZnNc) cm−1 are associated with the stretching and the IPB of C\\Nm\\C bonds along with the deformation of isoindoles. The very weak bands at around 609, 608 and 607 cm−1 are characterized by the breathing of 16–membered ring, the stretching of naphthalenes and the N\\M bonds as well as the IPB of the Cω\\H

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IR 1360

Fig. 5. Calculated normal modes of CuNc corresponding to the strongest IR and Raman bands.

Raman 1546

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