Effects of central metal on electronic structure, magnetic properties, infrared and Raman spectra of double-decker phthalocyanine

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Effects of central metal on electronic structure, magnetic properties, infrared and Raman spectra of double-decker phthalocyanine Atsushi Suzuki ∗ , Takeo Oku The University of Shiga Prefecture, 2500 Hassaka, Hikone, Shiga 522-8533, Japan

a r t i c l e

i n f o

Article history: Received 10 October 2015 Received in revised form 1 February 2016 Accepted 4 February 2016 Available online xxx Keywords: Double-decker phthalocyanine NMR Chemical shift Density functional theory Electron spin resonance Infrared/Raman spectra

a b s t r a c t The effects of the central metal in double-decker metal phthalocyanine on the electronic structure, magnetic properties, and infrared and Raman spectra of the complex were investigated. Electron density distributions were delocalized on the phthalocyanine rings. The narrow energy gap and infrared peaks observed in the ultra-violet–visible–near infrared spectra of the systems were attributed to phthalocyanine ring–ring interactions the between overlapping ␲-orbitals on each ring. The chemical shift behavior of the phthalocyanine rings was separated by the deformation of their structure owing to nuclear magnetic interaction of the nuclear quadrupole interaction as determined by the electronic field gradient and asymmetric parameters. The magnetic parameters of principle g-tensors were dependent on the perturbation of the crystal field by the hybridization of the d-spin in the central metal conjugated with nitrogen ligands. In the case of the vanadyl system, the IR vibration modes were shifted by the soft vibration mode for resolving the symmetrical structure. Inactive Raman vibration modes arose from no-polarization on the phthalocyanine rings. Double-decker metal phthalocyanines have great advantages for the control of the magnetic mechanism for quantum spin entanglement in the relaxation process. © 2016 Elsevier B.V. All rights reserved.

1. Introduction The experimental realization of a nuclear magnetic resonance (NMR) quantum computer has been studied by a number of researchers. For example, nitrogen-vacancy color centers in diamond, pentafluorobutadienyl cyclopenta-dienyldicarbonyliron complexes, copper phthalocyanines, and nitrogen endohedral fullerene have been used to control quantum entanglement, quantization bits, and quantum calculations [1–3]. The magnetic behavior of magnetic interactions and the spin dynamics of organometallic transition complexes have been studied for application to spintronic devices, single molecular magnetism, and the entanglement of quantum spin in quantum calculations [4–11]. For instance, resonance frequency, spin dynamics based on the paramagnetic behavior and magnetic interaction of nuclear spin in copper phthalocyanine was independently used to control the entanglement of quantum spin in spin-lattice relaxation process [4]. The molecular design of endohedral metallofullerenes has been investigated for application to multi-quantum spin gates with decoupling pulses for quantum computers [5–11]. Experiment based on theoretical considerations of the magnetic behavior

∗ Corresponding author. E-mail address: [email protected] (A. Suzuki).

in these endohedral metallofullerene derivatives were carried out to elucidate the magnetic mechanism and spin dynamics of the spin-lattice relaxation. The magnetic mechanism and magnetic interaction were found to change upon chemical modification of the perturbation of metal-ligand crystal field, the central metal at the multi-state, the conjugation system, and electron donating and accepting groups. The chemical modification of organic transition complexes with multiplicity of quantum-spin, nuclear spin interaction, and spin-lattice relaxation is important for the control of spin gate entanglement in NMR quantum computers. Especially, the perturbation of the metal-ligand crystal field at the multi-state has been used to control the magnetic properties based on magnetic interaction at the multi-state and spin dynamics in the spin lattice relaxation process. The entanglement of nuclear spin as a quantum bit in superconducting circuits has been applied in a commercial quantum computer using superconducting flux qubits by the quantum computing company D-Wave Systems [12,13]. The performance of NMR quantum calculation using organometallic transition complexes in multi-states can be controlled by magnetic interaction involving hybridization of the d-spins and f-spins of the central metal under the ligand field. For instance, Rabi oscillations and coherent single nuclear spin manipulation have been experimentally demonstrated using an all-electrically controlled nuclear spin qubit transistor based on a single molecular magnet of double-decker terbium based

http://dx.doi.org/10.1016/j.apsusc.2016.02.026 0169-4332/© 2016 Elsevier B.V. All rights reserved.

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phthalocyanine, through the use of the hyperfine Stark effect [14]. To improve spin multiplicity, spin dynamics, and entanglement in quantum spin, experimental investigations of the electronic structures and magnetic interaction of multi-decker phthalocyanines have been performed by NMR, alternating current magnetic susceptibility measurements, isothermal hysteresis curve measurements, scanning tunneling microscopy, and density functional theory [15–17]. Recently, experimental investigations and theoretical quantum calculations of the magnetic properties of bis(phthalocyaninato) terbium(III) doubledecker phthalocyanine and quintuple-decker phthalocyanine and tris(phthalocyaninato) yttrium were performed for the development of single-molecule magnet and electron magnetic devices [18,19]. The single-molecular magnetic behavior of the terbium (III)-phthalocyaninato quintuple-decker complex was found to be strongly influenced by the magnitude of the terbium–terbium interaction with decreasing distance and quantum tunneling of the magnetization [19]. The magnetic relaxations and spin dynamics were dominated by the two-phonon Orbach mechanism. The magnetic relaxations were preferentially contributed from the direct process rather than the Raman process [20]. Experimental results and quantum chemical calculations elucidated the magnetic properties of the system based on electron delocalization and exchange repulsion of ␲-electrons in the phthalocyanine ring [21]. Experimental studies on the magnetic properties and electronic structure of multi-decker phthalocyanines using NMR, ultraviolet–visible (UV–vis), near infrared (NIR), infrared (IR), Raman, and near edge X-ray absorption fine structure spectroscopy analysis have been reported [22,23]. Especially, the electronic structure and magnetic interaction can be determined from the isotropic chemical shift observed in 13 C NMR and 1 H NMR, while the vibration modes seen in IR and Raman spectra derive from the magnetic interaction and spin dynamics in the relaxation process. The dynamic relaxation processes of quadruple-decker phthalocyanine complexes with terbium or dysprosium ions as magnetic centers have been found to depend on the magnetic interaction based on f–f interactions. The spin relaxation phenomena and nuclear spin driven quantum tunneling of magnetization of these complexes have also been discussed using experimental results and a theoretical model [24]. The magnetic relaxation phenomena based on quantum tunneling magnetizations in the quadruple-decker phthalocyanines has been measured using alternate current magnetic susceptibility data and the numerically calculated Zeeman diagram of the f-electronic centers [25]. IR spectroscopic investigations of the oxidized forms of these complexes have revealed characteristic electronic transitions and fingerprint regions. The observed bands were assigned to –* transitions in ␲-electronic systems having narrow molecular orbital energy gap [26]. The switching of the single-molecule magnetic properties and self-assembly of terbium–porphyrin double-decker complexes has been studied for application in molecular spintronics [27]. The electronic structure and magnetic behavior of doubledecker phthalocyanine complexes with unoccupied electron spin in the central metal on the phthalocyanine ring in cation, anion, and radical states have great advantages for the development of spintronic devices, single-molecule magnets, and quantum calculation. Especially, double-decker phthalocyanine complexes having a dspin transition metal ion of scandium, yttrium, or vanadyl atoms as their central metal exhibit crystal field splitting with multidegeneracies of d spin orbitals under the ligand field. In the case of d-spin in the transition metal ion, quantum chemical consideration based on perturbation theory requires investigation of the electronic structure and magnetic interaction of the nuclear quadrupole interaction, which can be determined by EFG and , and IR and Raman vibration modes. For complexes containing f-spin transition metal ions, experimental measurements must be carried out

at extremely low temperature owing to their short relaxation time, making it difficult to detect experimental results with quantitative analysis. Quantitative analysis of the magnetic mechanism must consider the incorporation of high level sections on the crystal field. The purpose of this research is to investigate the effects of the central metal in double-decker phthalocyanine on its electronic structure, magnetic and optical properties, and IR and Raman vibrations. Especially, the effects of central metals such as vanadium, scandium, and yttrium as d-spin transition metal ions on the magnetic parameters is investigated through quantum chemical calculation of the chemical shift of 13 C, 1 H, 14 N NMR spectra, UV–vis–NIR spectra, excitation processes, and IR and Raman vibration modes. The magnetic mechanism will be discussed on the basis of nuclear spin interaction, spin–local interaction, nuclear–spin interaction, nuclear quadrupole interaction based on EFG and  related to electronic and charge density distribution caused by overlapping ␲-orbitals on the deformed phthalocyanine rings. 2. Calculation method The isolated molecular structures of multi-decker metal phthalocyanines in M(Pc)2 , (M = V, Sc, Y) at neutral and doublet states were optimized by ab-initio quantum chemical calculations using unrestricted Hartree–Fock (URHF) as a unrestricted open shell self-consistent field (SCF) calculation and by density functional theory (DFT) calculation using the Gaussian 03 program with Becke’s unrestricted three-parameter hybrid functional B3LYP (UB3LYP) [28,29] method in order of STO-3G*, 3-31G*, 6-31G*, and LANL2MB as the basis set. The highest occupied molecular orbital (HOMO), HOMO-1, the lowest unoccupied molecular orbital (LUMO), LUMO+1, and the HOMO–LUMO band gap (Eg ) were calculated. Mulliken atomic charges, electron density distributions, and the electrostatic potential (ESP) on the phthalocyanine ring were estimated by Mulliken population analysis. After calculating the optimized structures and electron structures near frontier molecular orbital, the isotropic chemical shifts of 13 C, 1 H, 14 N NMR spectra, principle g-tensors, V-tensors of EFG, and  of 13 C, 14 N, 45 Sc, and 89 Y atoms in the double decker phthalocyanines were calculated by DFT using gauge-independent atomic orbitals (GIAO) [30] with a hybrid functional UB3LYP method and LANL2MB as the basis set. The IR and Raman vibration modes and frequencies of the optimized structures at the ground state were calculated by DFT with UB3LYP with LANL2MB using frequency calculations. UV–vis–NIR spectra and excited processes of the optimized structures were calculated by time dependent DFT (TDDFT) with UB3LYP with LANL2MB as the basis set [31]. The TDDFT intense excitation energies, oscillator strengths, and transition process expressed in terms of the frontier molecular orbitals were also computed. 3. Results and discussion The electronic structures of V(Pc)2 , Sc(Pc)2 and Y(Pc)2 at HOMO and LUMO were calculated by DFT with hybrid functional calculation UB3LYP using LANL2MB as the basis set. The optimized structures, electron density distributions, and energy levels at the HOMO and LUMO of V(Pc)2 , Sc(Pc)2 , and Y(Pc)2 are shown in Fig. 1 and Table 1. As shown in Fig. 1(a)–(c), the optimized structures of V(Pc)2 , Sc(Pc)2 , and Y(Pc)2 were sandwich structures with degeneration of the energy levels around the frontier orbital. The optimized structures were slightly perturbed by chemical modification as the central metal diameter varied. The deformation of the structure caused by the changes in chemical bond and angle between the central metal and nitrogen ligand influenced the energy levels near the frontier orbital and band gap. The length of the chemical bond between the metal and nitrogen and the angle of the N M N bonds

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Table 1 Atomic radius of central metal, bond length and angle between metal atom and nitrogen ligand in optimized structure of M(Pc)2 .

Fig. 1. Optimized structure and electron density distribution (isovalue 0.02 a.u.) at HOMO and LUMO of V(Pc)2 , Sc(Pc)2 , and Y(Pc)2 , calculated by DFT using hybrid functional calculation UB3LYP and LANL2BM as the basis set. Dark blue atoms are nitrogen, dark gray atoms are carbon, and white atoms are hydrogen. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

in M(Pc)2 were obtained as 2.27 A˚ and 117◦ for V(Pc)2 , 2.33 A˚ and 115◦ for Sc(Pc)2 , and 2.41 A˚ and 113◦ for Y(Pc)2 , respectively. The calculated atomic radius of the V, Sc, and Y atoms were 171 pm, 184 pm, and 212 pm, respectively, compared with reported empirically measured values of 135 pm, 160 pm, and 180 pm [32,33]. Therefore, the phthalocyanine ring distance increased with the diameter of the central metal. The intermolecular force between the phthalocyanine rings would influence the energy gap, and IR and Raman vibration modes of the complexes. The obtained asymmetrical structures would resolve the degeneracy of energy levels around the frontier orbital with a narrow band gap between the HOMO and LUMO. The electron density distribution at the HOMO

M(Pc)2

Atomic radius (pm) [32,33]

M N (Å)

Angle N M N (◦ )

V(Pc)2 Sc(Pc)2 Y(Pc)2

135 160 180

2.27 2.33 2.41

117 115 113

and LUMO was delocalized on the ␲-orbitals of the phthalocyanine rings with hybridization of the sp2 orbitals on N and C atoms. The calculated electron density distribution at the LUMO of V(Pc)2 was consistent with hybridization between d-spin orbitals in vanadium atom and nitrogen ligand and overlapping ␲-orbitals on the phthalocyanine rings. The effect of the central metal on the ESP of the complex was investigated as shown in Fig. 2. The electrostatic potentials showed a similar behavior of red and blue color contrast near the nitrogen atoms on the phthalocyanine rings. Symmetrical bridged-phase electrostatic potential mapping on the phthalocyanines ring was obtained for all three metal atoms. There was a lack of balance in the charge density distribution near the central metal nitrogen ligand under crystal field on the phthalocyanine rings. This behavior suggests polarization and electronegativity, which will cause a slight movement of 1 H NMR and 14 N NMR chemical shifts in a low magnetic field. The 13 C NMR and 14 N NMR chemical shifts of the phthalocyanine rings originate from the nuclear quadrupole interaction based on the EFG and  on the phthalocyanine ring. Next, the effect of the central metal on the energy levels in M(Pc)2 was investigated. As shown in Fig. 3, there was a twofold degeneracy of the energy level of the LUMO near the frontier orbital. The details of the energy levels, energy gap, and wavelength of V(Pc)2 , Sc(Pc)2 , and Y(Pc)2 are listed in Table 2. The energy level of the LUMO in V(Pc)2 , Sc(Pc)2 , and Y(Pc)2 was estimated to be −1.76 eV, −0.88 eV, and −0.85 eV, respectively. Energy gaps, Eg , of 0.99 eV, 2.11 eV, and 2.29 eV were obtained for V(Pc)2 , Sc(Pc)2 , and Y(Pc)2 , respectively. Thus, the energy level of the LUMO of V(Pc)2 is greatly decreased compared with those of Sc(Pc)2 and Y(Pc)2 . The energy level of the LUMO, which determines the electron donating characteristics, is influenced by the metal to ligand charge transfer, which is dependent on the deviation between the anion charge on the phthalocyanine rings with the cation charge of the central metal, as listed in Table 4. The narrow Eg of V(Pc)2 therefore results from the strong phthalocyanine ring–ring interaction caused by the overlapping of ␲-orbitals on the phthalocyanine rings with

Fig. 2. Electrostatic potential (ESP) mapping of (a) V(Pc)2 , (b) Sc(Pc)2 , and (c) Y(Pc)2 .

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Fig. 3. Energy levels near frontier orbital and energy gaps (Eg ) of V(Pc)2 , Sc(Pc)2 , and Y(Pc)2 . ˛ and ˇ correspond to upward and downward spin, respectively. Table 2 Energy levels, energy gap (Eg ), and wavelength () of V(Pc)2 , Sc(Pc)2 , and Y(Pc)2 . V(Pc)2

HOMO-1

HOMO

LUMO

LUMO+1

Eg (eV)

˛ (eV) ˇ (eV)

−3.73 −3.76

−2.76 −2.80

−1.76 −1.23

−1.76 −1.23

0.99 1.56

 (nm) 1248 794

Sc(Pc)2

HOMO-1

HOMO

LUMO

LUMO+1

Eg (eV)

 (nm)

˛ (eV) ˇ (eV)

−3.81 −4.21

−2.99 −3.41

−0.88 −2.03

−0.60 −0.80

2.11 1.38

588 897

Y(Pc)2

HOMO-1

HOMO

LUMO

LUMO+1

Eg (eV)

 (nm)

˛ (eV) ˇ (eV)

−3.72 −3.31

−3.14 −3.31

−0.85 −2.19

−0.65 −0.76

2.29 1.12

542 1110

decreasing metal radii, suggesting a long absorption spectrum wavelength of 1248 nm for the –* transition of the phthalocyanine rings. A slight perturbation of the metal ligand crystal field on the phthalocyanines ring will influence the magnetic interaction of the complex, which will affect the magnetic parameters of 13 C and 14 N NMR chemical shifts, isotropic g-tensors, V-tensors of EFG, and  at ground and excited states. UV–vis–NIR spectra and the excitation process were calculated by TDDFT using UB3LYP as the basis set. The UV–vis–NIR spectra of V(Pc)2 and Sc(Pc)2 are compared in Fig. 4 and Table 3. The excited states of V(Pc)2 appeared in the range of 500–1800 nm in its UV–vis–NIR spectrum, which were identified to be 7000

0.18 TD-DFT

6000

0.15

Sc(Pc)2

0.12

4000 0.09 3000 2000 1000

V(Pc)2

0 0

500

1000

1500

2000

Frequency

Epcilon

5000

multiple Q bands [34] including one strong absorption at 815.1 nm as the first excitation state from HOMO to LUMO+6, while the weak absorption at 815.1 nm is the second excitation state from HOMO1 to LUMO+6. In contrast, the UV–vis–NIR spectrum of Sc(Pc)2 covered the range of 400–2500 nm, which was identified as the electronic transition from the semi-occupied orbital to a degenerated LUMO [34,35] involving –* transition of from HOMO to LUMO and HOMO to LUMO+3 as first and second excited states at 593.8 nm and 1196 nm, respectively. These excited states suggest a multi-excitation process resolving the degeneracy of energy levels near the frontier orbital. The excitation energy and transition are dependent on the increasingly strong phthalocyanine ring–ring interactions between ␲-orbitals with decreasing central metal radius [22]. The altered electronic structure caused by the strong interactions between the ␲-type orbitals of the two phthalocyanine moieties gives double-decker phthalocyanine its characteristic excitations compared with those experimentally observed for the typical metal phthalocyanines [36]. The effect of the central metal in M(Pc)2 on 13 C, 1 H, and 14 N NMR chemical shifts was investigated by DFT using NMR mode with GIAO. The calculated chemical shifts are shown in Fig. 5(a)–(c). The chemical shifts of the 13 C NMR spectra of V(Pc)2 , Sc(Pc)2 , and Y(Pc)2 as relative to that of TMS appeared at 98 ppm and 60–70 ppm, which were identified to be carbon atoms on the aromatic rings and in CN bonds, respectively. In the case of V(Pc)2 , a slight shift of the signal near 98 ppm compared with those of the other metals originated from the external magnetic shielding effect on the phthalocyanine rings caused by the asymmetrical structure. The slightly different behavior also observed for the shifts around 60–70 ppm likely derived from slight polarization of the charge distribution on the CN bond. As shown in Fig. 5(b), the 1 H NMR chemical shifts of V(Pc) , Sc(Pc) , and Y(Pc) relative to 2 2 2 that of TMS appeared at around 6.8–7.8 ppm. The chemical shifts of V(Pc)2 were changed by the external magnetic shielding effect Table 3 Wavelength, excited states, and oscillator strength of V(Pc)2 and Sc(Pc)2 .

0.06

V(Pc)2 (nm)

Excited states

Oscillator strength

0.03

815.6 815.1

HOMO-1 → LUMO+6 HOMO → LUMO+6

0.003 0.041

Sc(Pc)2 (nm)

Excited states

Oscillator strength

1196.0 793.6 593.8 580.5

HOMO → LUMO HOMO → LUMO+2 HOMO → LUMO+3 HOMO-2 → LUMO+1

0.144 0.009 0.052 0.002

0.00 2500

Wavelength / nm Fig. 4. Calculated UV–vis–NIR spectra of V(Pc)2 and Sc(Pc)2 .

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Fig. 5. Calculated chemical shifts of (a) 13 C NMR, (b) 1 H NMR and (c) 14 N NMR for V(Pc)2 , Sc(Pc)2 , and Y(Pc)2 .

on the deformed phthalocyanine rings. As shown in Fig. 5(c), the NMR chemical shifts of V(Pc)2 were influenced by the slight perturbation of the deformed crystal field by the charge density distribution. Thus, the changes in the 13 C NMR, 1 H NMR, and 14 N NMR chemical shifts among the different complexes were caused by the nuclear magnetic interaction arising from nuclear spin coupling between carbon, nitrogen and proton atoms on the deformed phthalocyanine rings. Until now, a detailed analysis and experimental investigation on the NMR chemical shifts of V(Pc)2 , Sc(Pc)2 , and Y(Pc)2 has not been reported. Recently, the contributions to the chemical shift of paramagnetic trivalent ions by the phthalocyanine ligands of double-, triple- and quadruple-decker phthalocyanine complexes were reported in experimental and theoretical studies of NMR spectra [19,21,37]. Quantum chemical calculation based on perturbation theory requires understanding of the electronic structure and magnetic interaction through measurement of the nuclear quadrupole interaction based on EFG and , excitation process, and IR and Raman vibration modes. Generally, chemical shift is a sum of diamagnetic and paramagnetic terms. According to the Karplus–Pople equation, the chemical shift is mainly dominated by the paramagnetic term with spin–local interaction, 14 N

the hybridization of molecular orbital at excited state, and the nuclear quadrupole interaction based on EFG and . The magnetic parameters of chemical shift are based on spin–local interactions and the process of excitation from the ground state. The magnetic parameters, chemical shift, g-tensor, V-tensors of EFG, and  will be influenced by the deformed structure of the complex accompanied by the slight deviation of the electron and charge density distribution. The calculated atomic charge, spin density, principle g-tensors, V-tensors of EFG, and  for V(Pc)2 , Sc(Pc)2 , and Y(Pc)2 are listed in Table 4. Notably, the V(Pc)2 system had 0.21 e charge and a spin density of 0.986 for the vanadyl atom, anisotropic behavior of the g-tensors and the EFG V-tensors in the z–axis direction and , suggesting a wide separation of chemical shifts in a low magnetic field. This result arose from the nuclear quadrupole interaction of nuclear spin on the deformed phthalocyanine rings with a slight polarization of the charge distribution of the central metal conjugated with the nitrogen ligand on the phthalocyanine ring. The allowed ESR and NMR transitions can be explained by the energy level diagrams of the V, Sc, and N atoms under crystal field. The spin Hamiltonian is a sum of the Zeeman effects of electron and nuclear spin under

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Table 4 Magnetic parameters, principle g-tensors, V-tensors of EFG, and  of V(Pc)2 , Sc(Pc)2 , and Y(Pc)2 . M

M charge

Spin density

gxx

gyy

gzz

Vxx

Vyy

Vzz



V Sc Y

0.212 0.367 0.314

0.986 0.019 0.014

1.96064 2.00000 1.99944

1.96064 2.00000 1.99944

1.99548 2.00388 2.00846

−0.365 −0.016 −0.006

−0.365 −0.016 −0.006

0.729 0.032 0.012

2.74 × 10−6 0 0

magnetic field, spin-nuclear spin interaction as dipole–dipole interaction, and nuclear quadrupole interaction based on the V-tensors of EFG and . The magnetic g-tensor parameters of V(Pc)2 , Sc(Pc)2 , and Y(Pc)2 depend on the spin local interaction, electron density distribution, and energy transition from the ground state. The calculated vibration modes of the IR and Raman spectra of V(Pc)2 , Sc(Pc)2 , and Y(Pc)2 are shown in Fig. 6(a) and (b). The strong IR spectrum vibration modes at 1381 cm−1 were attributed to pyrrole C C stretching. The IR vibration modes of Sc(Pc)2 and Y(Pc)2 at 1165 cm−1 likely correspond to the hard mode of their symmetrical structures. The IR vibration mode at 1058 cm−1 was assigned to aza CN stretching as an in-plane deformation vibration on the phthalocyanine ring in all cases [38,39]. In the case of

V(Pc)2 , the IR vibration modes were separated and shifted, owing to the soft vibration mode for resolving the symmetrical structure caused by the variation of the bond length and angle between the central metal and ligand on the phthalocyanine rings. As shown in Fig. 6(c) and (d), the Raman vibration modes of Y(Pc)2 and Sc(Pc)2 appeared at 1543 cm−1 and 1058 cm−1 , respectively, and were assigned to aza CN stretching vibration as in-plane deformation vibration on the phthalocyanine rings owing to their symmetrical structure. In the case of V(Pc)2 , no vibration modes near 1058 cm−1 was present because it was an inactive mode owing to no-polarization on the phthalocyanine rings. These theoretically calculated of IR and Raman vibration modes are in approximate agreement with experimental results reported for

Fig. 6. (a) Calculated IR and (b) Raman spectra of V(Pc)2 , Sc(Pc)2 , and Y(Pc)2 . The Raman vibration modes of (c) V(Pc)2 at 1543 cm−1 and (d) Y(Pc)2 at 1058 cm−1 .

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bis(phthalocyaninato) rare earth complexes [22,38,39]; the vibration modes of the IR and Raman spectra were influenced by the deformed structure and the slight perturbation of the metal ligand crystal field. The vibration mode, including lattice vibration (phonon), of the in-plane deformation vibration on the phthalocyanine rings is expected to be direct proportional to the spin-lattice relaxation time arising from the magnetic interaction of the double decker phthalocyanines. The relaxation mechanism including the spin-lattice relaxation can be explained by the IR and Raman vibration modes of the phthalocyanine rings. The relaxation mechanism related to the magnetic interaction is an important factor for controlling the entanglement of quantum spin in quantum calculation. The magnetic behavior and spin dynamics at the multi-spin state can be controlled by molecular modification of the complex by changing the central metal, conjugated system, and functional groups. A slight perturbation of the metal ligand crystal field will affect the multi-states, the magnetic interaction, and the spin dynamics in the spin-lattice relaxation. The present double-decker metal phthalocyanines therefore have great advantages for the control of the multi-state magnetic mechanism in quantum computation.

4. Conclusion The effects of the central metal in double-decker phthalocyanine on the electronic structure, magnetic properties, and IR and Raman spectra of the complex were investigated. Electronic structures, 13 C, 14 N, and 1 H NMR chemical shifts, principle g-tensors, V-tensors of EFG, , UV–vis–NIR spectra, IR and Raman vibration modes were calculated for the complexes using density functional theory. The electron density distributions at the HOMO and LUMO of Sc(Pc)2 and Y(Pc)2 were found to be delocalized on the phthalocyanine rings. The energy level of the LUMO was influenced by metal to ligand charge transfer based on the difference between the anionic charge on the phthalocyanine ring and the cationic charge of the central metal. The narrow Eg of V(Pc)2 derived from the strong phthalocyanine ring–ring interaction between the overlapping ␲-orbitals of each phthalocyanine ring with decreasing metal radius, suggesting a long absorption spectrum wavelength of 1248 nm for the –* transition of the phthalocyanine rings. The wide wavelength range of the absorption in the visible and infrared regions of the UV–vis–NIR spectrum of Sc(Pc)2 originated from the narrower energy gap of the deformed structure with overlapping ␲-orbitals on the phthalocyanine rings. A slight perturbation of the metal ligand crystal field on the phthalocyanine rings influenced the magnetic properties, including the magnetic parameters determined by the 13 C and 14 N NMR chemical shifts, isotropic g-tensors, V-tensors of EFG, and ␩ at the ground state. A slight difference in the behavior of the 13 C, 14 N, and 1 H NMR chemical shifts of V(Pc)2 , Sc(Pc)2 , and Y(Pc)2 obeyed the perturbation of the electronic structure based on the electron density distribution and magnetic interaction of the nuclear quadrupole interaction. The magnetic parameters of principle g-tensors, V-tensors, and  were influenced by the hybridization of the d-spin in the vanadyl atom conjugated with the nitrogen ligands under crystal field of the deformed structures. The IR and Raman vibration modes of Sc(Pc)2 , V(Pc)2 , and Y(Pc)2 were identified as in-plane deformation vibration, pyrrole C C, and aza CN stretching vibrations of the metal-ligand coordination bonds on the phthalocyanine rings. The vibration modes were slightly influenced by the perturbation of the metal-ligand crystal field of the deformed structures. In the case of V(Pc)2 , a slight shift of the IR vibration mode derived from the soft mode of vibration for resolving the symmetrical structure with a change in chemical bond length and angle between the central metal and ligands

7

on the phthalocyanine rings. The Raman vibration modes of this complex disappeared owing to the no-polarization of the phthalocyanine rings. The relaxation mechanism including the spin-lattice relaxation can be explained by the IR and Raman vibration modes of the phthalocyanine rings. The magnetic behavior at the multispin state can be controlled by the modification of the central metal and conjugated system of the complex. A slight perturbation of the metal ligand crystal field influences the magnetic interaction during the spin-lattice relaxation. The present double-decker metal phthalocyanines have great advantages for the control of the magnetic mechanism at the multi-state for quantum spin entanglement in the relaxation process. Acknowledgments This work was supported by JSPS KAKENHI Grant Number 26390047. References [1] N. Mizuochi, P. Neumann, F. Rempp, J. Beck, V. Jacques, P. Siyushev, K. Nakamura, D.J. Twitchen, H. Watanabe, S. Yamasaki, F. Jelezko, J. Wrachtrup, Coherence of single spins coupled to a nuclear spin bath of varying density, Phys. Rev. B 80 (2009) 41201–41211. [2] L.M.K. Vandersypen, M. Steffen, G. Breyta, C.S. Yannoni, M.H. Sherwood1, I.L. Chuang, Experimental realization of Shor’s quantum factoring algorithm using nuclear magnetic resonance, Nature 414 (2001) 883–887. [3] J.J.L. Morton, A.M. Tyryshkin, A. Ardavan, S.C. Benjamin, K. Porfyrakis, S.A. Lyon, G.A.D. Briggs, The N@C60 nuclear spin qubit: bang–bang decoupling and ultrafast phase gates, Phys. Status Solidi B 243 (2006) 3028–3031. [4] M. Warner, S. Din, I.S. Tupitsyn, G.W. Morley, A.M. Stoneham, J.A. Gardener, Z. Wu, A.J. Fisher, S. Heutz, C.W.M. Kay, G. Aeppli, Potential for spin-based information processing in a thin-film molecular semiconductor, Nature 503 (2013) 504–508. [5] A.A. Popov, N.B. Shustova, A.L. Svitova, M.A. Mackey, C.E. Coumbe, J.P. Phillips, S. Stevenson, S.H. Strauss, O.V. Boltalina, L. Dunsch, Redox-tuning endohedral fullerene spin states: from the dication to the trianion radical of Sc3 N@C80 (CF3 )2 in five reversible single-electron steps, Chem. Eur. J. 16 (2010) 4721–4724. [6] A. Suzuki, T. Oku, Geometrical effects of (14 N@C60 )2 , 14 N@C60 and C59 N endohedral fullerenes within single-walled carbon nanotube as peapods on electronic structure and magnetic properties, Physica B 406 (2011) 3274–3278. [7] A. Suzuki, T. Oku, Electronic structure and magnetic properties of 31 P@C60 -SWCNT as peapods, J. Phys. Conf. Ser. 352 (2012) 12012–12021. [8] A. Suzuki, T. Oku, Electronic structure and magnetic properties of endohedral metallofullerenes based on mixed metal cluster within fullerene cage with trifluoromethyl groups, J. Phys. Conf. Ser. 433 (2013) 12004–12011. [9] A. Suzuki, T. Oku, Electronic structures and magnetic properties of Sc2 YN@C80 (CF3 )2 dimer, Jpn. J. Appl. Phys. 53 (2014), 05FN01. [10] A. Suzuki, T. Oku, Influence of chemical substitution in Scx Y3−x N@C80 (CF3 )n endohedral fullerenes on magnetic properties, Physica B 428 (2013) 18–26. [11] Y. Abe, A. Suzuki, T. Oku, Electronic structures and magnetic properties of Sc4 O2 @C80 (CF3 )n (n = 2 and 4), Jpn. J. Appl. Phys. 53 (2014), 05FN02. [12] A. Blais, A.M. Zagoskin, Operation of universal gates in a solid-state quantum computer based on clean Josephson junctions between d-wave superconductors, Phys. Rev. A 61 (2000), 042308-1-4. [13] S. Boixo, T.F. Rønnow, S.V. Isakov, Z. Wang, D. Wecker, D.A. Lidar, J.M. Martinis, M. Troyer, Evidence for quantum annealing with more than one hundred qubits, Nat. Phys. 10 (2014) 218–224. [14] S. Thiele, F. Balestro, R. Ballou, S. Klyatskaya, M. Ruben, W. Wernsdorfer, Electrically driven nuclear spin resonance in single-molecule magnets, Science 344 (2014) 1135–1138. [15] T. Komeda, H. Isshiki, J. Liu, Y.-F. Zhang, N. Lorente, K. Katoh, B.K. Breedlove, M. Yamashita, Observation and electric current control of a local spin in a single-molecule magnet, Nat. Commun. 2 (2011), 217-1-7. [16] H. Isshiki, J. Liu, K. Katoh, M. Yamashita, H. Miyasaka, B.K. Breedlove, S. Takaishi, T. Komeda, Scanning tunneling microscopy investigation of tris(phthalocyaninato)yttrium triple-decker molecules deposited on Au(1 1 1), J. Phys. Chem. C 114 (2010) 12202–12206. [17] K. Katoh, T. Komeda, M. Yamashita, Surface morphologies, electronic structures, and Kondo effect of lanthanide(III)-phthalocyanine molecules on Au(1 1 1) by using STM, STS and FET properties for next generation devices, Dalton Trans. 39 (2010) 4708–4723. [18] M. Urdampilleta, S. Klayatskaya, M. Ruben, W. Wernsdorfer, Magnetic interaction between a radical spin and a single-molecule magnet in a molecular spin-valve, ACS Nano 9 (2015) 4458–4464. [19] Y. Horii, K. Katoh, N. Yasuda, B.K. Breedlove, M. Yamashita, Effects of f–f interactions on the single-molecule magnet properties of

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8

[20]

[21]

[22]

[23]

[24]

[25]

[26]

[27]

[28]

terbium(III)–phthalocyaninato quintuple-decker complexes, Inorg. Chem. 54 (2015) 3297–3305. T. Fukuda, N. Shigeyoshi, T. Yamamura, N. Ishikawa, Magnetic relaxations arising from spin–phonon interactions in the nonthermally activated temperature range for a double-decker terbium phthalocyanine single molecule magnet, Inorg. Chem. 53 (2014) 9080–9086. M. Sumimoto, Y. Kawashima, K. Horia, H. Fujimoto, Theoretical study on the stability of double-decker type metal phthalocyanines, M(Pc)2 and M(Pc)2 + (M = Ti, Sn and Sc): a critical assessment on the performance of density functionals, Phys. Chem. Chem. Phys. 17 (2015) 6478–6483. Y. Zhang, X. Cai, Y. Zhou, X. Zhang, H. Xu, Z. Liu, X. Li, J. Jiang, Structures and spectroscopic properties of bis(phthalocyaninato) yttrium and lanthanum complexes: theoretical study based on density functional theory calculations, J. Phys. Chem. A 111 (2007) 392–400. I. Bidermane, J. Lüder, S. Boudet, T. Zhang, S. Ahmadi, C. Grazioli, M. Bouvet, J. Rusz, B. Sanyal, O. Eriksson, B. Brena, C. Puglia, N. Witkowski, Experimental and theoretical study of electronic structure of lutetium bi-phthalocyanine, J. Chem. Phys. 138 (2013) 234701–234711. T. Fukuda, K. Matsumura, N. Ishikawa, Influence of intramolecular f–f interactions on nuclear spin driven quantum tunneling of magnetizations in quadruple-decker phthalocyanine complexes containing two terbium or dysprosium magnetic centers, J. Phys. Chem. A 117 (2013) 10447–10454. T. Fukuda, N. Ishikawa, Quadruple-decker phthalocyanines – one additional layer for a molecule, one giant leap for phthalocyanine chemistry, J. Porphyr. Phthalocyanines 18 (2014) 615–629. T. Fukuda, K. Hata, N. Ishikawa, Observation of exceptionally low-lying –* excited states in oxidized forms of quadruple-decker phthalocyanine complexes, J. Am. Chem. Soc. 134 (2012) 14698–14701. T. Inose, D. Tanaka, H. Tanaka, O. Ivasenko, T. Nagata, Y. Ohta, S.D. Feyter, N. Ishikawa, T. Ogawa, Switching of single-molecule magnetic properties of TbIII –porphyrin double-decker complexes and observation of their supramolecular structures on a carbon surface, Chem. Eur. J. 20 (2014) 11362–11369. C. Lee, W. Yang, R.G. Parr, Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density, Phys. Rev. B: Condens. Matter 37 (1988) 785–789.

[29] A.D. Becke, A new mixing of Hartree–Fock and local density-functional theories, J. Chem. Phys. 98 (1993) 1372–1377. [30] J.R. Cheeseman, G.W. Trucks, T.A. Keith, M.J. Frisch, A comparison of models for calculating nuclear magnetic resonance shielding tensors, J. Chem. Phys. 104 (1996) 5497–5509. [31] J. Liu, W. Liang, Analytical approach for the excited-state Hessian in time-dependent density functional theory: formalism, implementation and performance, J. Chem. Phys. 135 (2011) 184111. [32] J.C. Slater, Atomic radii in crystals, J. Chem. Phys. 41 (1964) 3199. [33] E. Clementi, D.L. Raimondi, W.P. Reinhardt, Atomic screening constants from SCF functions. II. Atoms with 37 to 86 electrons, J. Chem. Phys. 47 (1967) 1300. [34] Y. Li, Y. Bian, M. Yan, P.S. Thapaliya, D. Johns, X. Yan, D. Galipeau, J. Jiang, Mixed (porphyrinato)(phthalocyaninato) rare-earth(III) double-decker complexes for broadband light harvesting organic solar cells, J. Mater. Chem. 21 (2011) 11131–11141. [35] F. Lu, X. Sun, R. Li, D. Liang, P. Zhu, C.-F. Choi, D.K.P. Ng, T. Fukuda, N. Kobayashi, M. Bai, C. Maa, J. Jiang, Synthesis, spectroscopic properties and electrochemistry of heteroleptic rare earth double-decker complexes with phthalocyaninato and meso-tetrakis (4-chlorophenyl)porphyrinato ligands, New J. Chem. 28 (2004) 1116–1122. [36] M. Sumimoto, T. Honda, Y. Kawashima, K. Horia, H. Fujimoto, Theoretical and experimental investigation on the electronic properties of the shuttlecock shaped and the double-decker structured metal phthalocyanines, MPc and M(Pc)2 (M = Sn and Pb), Dalton Trans. 41 (2012) 7141–7150. [37] N. Ishikawa, T. Iino, Y. Kaizu, Study of 1 H NMR spectra of dinuclear complexes of heavy lanthanides with phthalocyanines based on separation of the effects of two paramagnetic centers, J. Phys. Chem. A 107 (2003) 7879–7884. [38] F. Lu, Q. Yang, J. Cui, X. Yan, Infra-red and Raman spectroscopic study of tetra-substituted bis(phthalocyaninato) rare earth complexes peripherally substituted with tert-butyl derivatives, Spectrochim. Acta A: Mol. Biomol. Spectrosc. 65 (2006) 221–228. [39] W. Wang, G. Bao, Y. Mao, F. Lu, Infrared spectroscopic characteristics of mixed rare earth triple-decker complexes with phthalocyaninato and 5-(4-hydroxyphenyl)-10, 15,20-tris(4-octyloxy)porphyrinato ligands, Spectrochim. Acta A: Mol. Biomol Spectrosc. 104 (2013) 165–170.

Please cite this article in press as: A. Suzuki, T. Oku, Effects of central metal on electronic structure, magnetic properties, infrared and Raman spectra of double-decker phthalocyanine, Appl. Surf. Sci. (2016), http://dx.doi.org/10.1016/j.apsusc.2016.02.026