Computational Approach To Understand the Adsorption Behavior of

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C: Plasmonics; Optical, Magnetic, and Hybrid Materials

A Computational Approach to Understand the Adsorption Behavior of Iron (II) Phthalocyanine on Doped Graphene Surface Amrit Sarmah, and Pavel Hobza J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b11357 • Publication Date (Web): 01 Mar 2019 Downloaded from http://pubs.acs.org on March 1, 2019

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The Journal of Physical Chemistry

A Computational Approach to Understand the Adsorption Behavior of Iron (II) Phthalocyanine on Doped Graphene Surface Amrit Sarmah,*,a,b Pavel Hobzaa,b aInstitute

of Organic Chemistry and Biochemistry of the Czech Academy of Sciences,

Flemingovo nam. 2, CZ-16610 Prague 6, Czech Republic bDepartment

of Physical Chemistry, Palacky University, CZ–77146 Olomouc, Czech Republic

Abstract: We have employed dispersion corrected density functional theory (DFT-D) based calculations to elucidate the adsorption behavior of Iron (II) Phthalocyanine on the doped graphene surface, which is also experimentally tailored recently. The experimental realization of electronic modulations through non-covalent interaction is well appreciated from the electronic structure calculations. It is important to note that the spin-dependent electronic properties of the of Iron (II) Phthalocyanine can be precisely tuned depending on the nature of the graphene surface beneath. Qualitative interpretations of the forces instituted from the interaction between the disintegrated magnetic moment of the components are also realized (based on some analytical expression). Further, the compelling, magnetic perturbations accounted from the longrange interaction in the overall system are addressed through a series of systematic investigations. Current findings ingrained the manipulation of electronic and magnetic properties of the adsorbate at the molecule-substrate interface and open-up promising avenue for the spintronic device fabrication.

*Corresponding author. E-mail address: [email protected] Mobile No: +420731015016

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1. Introduction: The two-dimensional nanoallotrope of carbon, graphene has a significant impact on the contemporary scientific research. The atypical electronic, mechanical, optical, and transport properties of the material have the potential to bring phenomenal success in the nanotechnology along with the elegant sophistication in the device fabrication.1,2 Graphene has certain inherent physical characteristics, such as large values of intrinsic mobility, thermal and electric conductivity, optical transmittance, Young’s modulus, surface area, etc. which are highly promising for digital electronics.3–6 Subsequently, both pristine and chemically functionalized graphene generates intense excitement for a broad spectrum of applications, covering electronics/optoelectronics, energy generation and storage, and various medical, chemical, catalytic, and environmental processes.7,8,9 With an aim to introduce the higher degree of sophistication within a small surface area of electronic devices, thrives the endeavors to explore the electronic and magnetic properties at a molecular level. These single molecule system would potentially be the building block in a particular molecular device.10,11 Owing to their unique electronic and magnetic characteristics, organometallic complexes are the particular class of molecules. The transition metal atom present in their structural framework is mainly responsible for the unorthodox electronic behavior of the complex. The organometallic complexes are assumed to be the bridging element between the two novel disciplines of spintronics and molecular electronics.12 The inherent spin localization in such molecule institute the possibility of molecular spintronics devices consisting of one or a few magnetic molecules. Indeed, the precise understanding on the coupling of the molecular spin to the environment, especially to the surface on which the molecule is adsorbed,


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and the resulting effect of their mutual spin interaction on the overall magnetic behavior is vital to realize the existence of such devices. Metal phthalocyanines (MPcs) are the special group of complexes having a planar geometry. The central metal atom in the complex is surrounded by the π-conjugated macrocyclic ligand. Depending on the spin state of the central metal atom, it can regulate various spin configurations, account for the possibility of considering as tunable nanomagnets. It is worth noting that the Iron (II) phthalocyanine (FePc) exhibits unique electronic and magnetic properties and found to have the unusual intermediate triplet spin state S=1.13,14 Subsequently, a strong spin-orbit coupling in the FePc complex partially brakes the spin degeneracy of the triplet state introducing singlet ground state along with the doubly degenerate excited spin states. This is particular energy splitting phenomena occurred without the presence of an external magnetic field and known as the ‘zero field splitting’ (ZFS).15 Taking the analogy from the above discussion, it is clear that the spin component of the electron has a substantial impact on the electronic behavior of the FePc-Graphene (FePc-Gr) composite system. We have performed standard interaction energy calculations on the modeled systems for a better understanding of the overall thermodynamic stability. However, the standard interaction energy calculation does not account any explicit approximation to the interaction between two magnetic dipoles in a uniform magnetic field. In the present study, both FePc and doped-graphene has their individual magnetic moment and can be considered as the interaction between two magnetic dipoles separated by a finite distance. The force between two magnetic dipoles has undoubtedly some contribution towards the overall stabilization of the composite structure. The details on the equations and simplification about the analytical expression are provided in the supporting information. A great deal of research work has been carried out to


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study the interaction of magnetic dipoles. Previously the magnetic force has been proposed based on the magnetic interaction of two magnetic particles.16,17 Unfortunately, to the best of authors’ knowledge, a systematic investigation on the energetic contribution from the interaction of magnetic dipoles in a uniform magnetic field to the overall thermodynamic stability has not been addressed so far. In the present study, DFT based theoretical calculations are performed to address the structural and electronic modulations of the Iron (II) phthalocyanine adsorbed on the doped graphene surface. Very recently, in a sophisticated AFM simulation study by Torre et al. explicitly showed the spin transition in FePc adsorbed on the nitrogen-doped graphene surface accounted from the weak orbital intermixing between iron and nitrogen.18 In another important study by the Lisi et al. extensively investigated the graphene-induced magnetic anisotropy of a two-dimensional iron phthalocyanine network.19 Along the same line, we have opted DFT based computer simulation to address the adsorption behavior of Iron (II) phthalocyanine on three other doped graphene surfaces containing boron, nitrogen and sulfur impurities. In the logical scene, it is irrelevant to execute every other possibility on experimental ground. So, the computer simulation is the best solution to develop a preliminary understanding and the forefront of our current study. Additionally, some analytical expressions are also devised to approximate the strength of the magnetic dipole-dipole interaction in the composite structure. The energy requires for the spin-crossover in the FePc-N-doped graphene nanocomposite is significantly small and occurs without any external stimulation. So, it can be argued that the force due to the interaction between the individual magnetic moments of the two systems is one of the required energy components that trigger the spin-crossover process. 2. Computational Details:


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In the present study open source Quantum Espresso 5.4.0 code20 is used to perform the calculations within the framework of density functional theory using Troullier and Martins21 norm-conserving pseudopotentials integrated with the Becke-Lee-Yang-Parr (BLYP)22,23 exchange-correlation (xc). Beside BLYP method, we have tested the performance of generalized gradient approximation (GGA) with the parametrization of Perdew-Burke-Ernzerhof (PBE)24 formalism for specific cases. These systematic analyses enable us to account the performance and relative computational cost of both (BLYP and PBE) the methods for this particular study. Without considering any generalized conclusions, BLYP attains relatively faster SCF convergence with respect to the PBE method yields an improved description of our model. It is important to note that such observations are exclusively system specific and could not be extend towards a general assumption. The semi-empirical Grimme's DFT-D2 methodology25 (as implemented in Quantum Espresso) is being embedded to account the van der Waals correction in the calculations. This approach has been successfully implemented to describe the graphenebased structures.26 In the previous reports, this method performed reasonably well to describe the electronic structures of graphene nanoribbon/h-BN27-29 and graphene nanoribbon/AlN30,31 interfaces with the ambient accuracy. The cutoffs for the standard kinetic energy and the charge density are set at 40 and 160 Ry, respectively. The results of the calculations for convergence in the surface energy and interplanar distances confirmed that the above mentioned standard kinetic energy and the charge density cutoffs are quite sufficient to realize the reliable electronic structure for the model systems. The reciprocal space integrations were performed at the ‘Γ’ point. The model systems are considered inside a simple cubic supercells with the 8×8 graphene layer, provided the periodic images were separated by at least 15 Å of vacuum space along the z direction, that account the negligible interactions between the repetitive unites. The forces on


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modeled systems were minimized up to < 10-3 Ry/a.u. for all atoms to obtain a relaxed atomic geometry. Geometry optimizations were performed based on the Broyden–Fletcher–Goldfarb– Shanno (BFGS) algorithm32 as implemented in the Quantum Espresso. The interaction energies were calculated according to the standard formalisms, i.e 𝐸𝐼𝑛𝑡 = 𝐸𝐹𝑒𝑃𝑐 + 𝑔𝑟𝑎𝑝ℎ𝑒𝑛𝑒 ―(𝐸𝐹𝑒𝑃𝑐 + 𝐸𝑔𝑟𝑎𝑝ℎ𝑒𝑛𝑒)

(I)

Where, EInt is the computed total interaction energy, 𝐸𝑔𝑟𝑎𝑝ℎ𝑒𝑛𝑒 + 𝐹𝑒𝑃𝑐 is the total energy of the composite system, 𝐸𝑔𝑟𝑎𝑝ℎ𝑒𝑛𝑒 and 𝐸𝐹𝑒𝑃𝑐 are the energies of the graphene (doped or pristine) surface and the FePc molecules, respectively. Subsequently, the equation (I) implies that the more negative the interaction energy is stronger the tendency of FePc molecule binds to the surface. 3. Results and discussions: (a) Thermodynamic stability based on energy decomposition analysis: The FePc molecule has the planar geometry having the D4h symmetry. The molecular structure contained a flat ring bonded to four benzene rings with a single iron ion in the central cavity. The optimized structures of the systems considered for the present paper are represented in Figure 1. Introduction of a foreign impurity to the carbon network of graphene is an effective strategy to open the zero bandgaps and provide the possibility to tune its electronic, magnetic, and optical properties. To be precise, foreign atom substitution to the graphene network breaks the lattice symmetry of graphene resulting in the formation of the energy gap between π and π* bands. Substitution of boron to the graphitic carbon imparts p-type semi-conducting nature to the graphene. Again, the nitrogen and sulfur doping on the graphene generates n-type semiconducting situation due to the excess of electrons.


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Figure 1: The pictorial representation of the model systems considered for the present study. All structures are relaxed at BLYP-D level using Troullier and Martins norm-conserving pseudopotentials. The colored circular dots in the figure symbolically represent the different atoms in the structures. The computed interaction energy values are reported in Table 1. It is observed that the impurity doping on the graphene surface, improve the thermodynamic stability to the interacting systems up to a certain extent. As we have noted (in Table 1), the interaction energy value for the pristine graphene and FePc system is -78.40 Kcal/mol. Similarly, in case of doped graphene surface the energy values are -75.64, -96.16 and -191.40 kcal/mol for the boron, nitrogen and sulfur-doped graphene, respectively in the BLYP+D2 level of theory. Subsequently, the energy values obtained at the PBE+D2 level of theory also exhibit the similar interaction strength with


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marginally lower values of interaction energies. It is important to note that in a recent study Halder et al. performed extensive DFT analyses to understand the adsorption behavior of FePc on graphene and MoS2 substrate.33 Their reported adsorption energy value for the pristine graphene and FePc system is almost the same as that of our present study. It is seen that the nitrogen and sulfur doping on the graphene surface enhanced the thermodynamic stability of the interaction between the graphene surface and the FePc. Some recent reports also argued the similar observations.34-36 However, the presence of boron impurity in the carbon network tends to hinder the noncovalent interaction between FePc and graphene to a certain extent as evident from the relatively lower interaction energy value. Table 1: Computed interaction energy values based on the equation (I). The interaction energy components from the magnetic dipole interaction are presented as MM INT at the extreme right column. All the energy values are in kcal/mol. System

Interaction energy (BLYP+D2)

Interaction energy (BLYP)

Interaction energy (PBE+D2)

Interaction energy (PBE)

MM INT

FePc-Gr

78.40

35.28

71.20

22.41

0

FePc-BGr

75.64

49.58

69.08

37.05

-0.16x10-2

FePc-NGr

96.16

53.27

95.18

48.39

-2.36x10-2

FePc-SGr

191.40

81.40

187.66

115.3

-3.64x10-2

The long-range weak van der Waals type interaction is an important parameter to describe the electronic structure for these kinds of composite systems. The dispersion component has a significant influence on the overall stabilization process. We have also included the interaction energy values in the absence of the empirical D2 corrections in Table 1. It is worth mentioning here that there is a marked decrease in the overall interaction energy values without having the dispersion corrections. Indeed, the impurity doping on the graphene surface induces


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some critical modulations to the dispersion forces in the systems. So, at this point, we can argue that the dispersion interaction between the FePc and the substrate is a critical factor in determining the relative stability of the composite structures. In the relaxed structures, we have observed certain structural distortions in the systems containing boron and sulfur impurities. The strong electrostatic interaction is pulling out the boron and sulfur atoms present in the graphene network from its molecular plane. However, there is no distortion in the nitrogen-doped graphene surface, and its remains planner likes the pristine surface. The optimized distance between the FePc and pristine graphene layers are found to be 3.26 A0. This layered distance between FePc and graphene is slightly increased (3.31 A0) in case of the nitrogen-doped system. Again, the iron atom of the FePc molecule adsorbed on the N-doped surface is not located vertically above the N-dopant instead it is slightly shifted from the impurity center. These observations are consistent with our previous report.18 For the other two model systems (containing boron and sulfur impurities in the graphene network) the optimized distance between the central iron atom of FePc and the dopant is found to be 2.72 and 2.06 A0 for the boron and sulfur, respectively. The relatively large structural deformation in case of the sulfur-doped system leads to the Fe-S bond formation in the composite structure. It is important to note that the contribution from magnetic dipole interaction to the overall stability of the system is also included in the last column of Table 1. As we have observed, the computed energy values (based on the analytical expression discussed in the supporting information section) are very small compared to that of the other four energy components. However, the trend of relative stability for the model systems obtained from the magnetic dipolar interaction is correlated well with the overall stability of the systems. Eventually there is some minimal contribution from the magnetic dipole-dipole interaction in the systems. Indeed, the


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spin-dependent interaction part is always crucial in nano-electronics. A higher degree of sophistication is needed to provide reasonable interpretations to the spin component of the electron from the application prospect. As we have seen from our previous study, the energy requires for the spin-crossover in the N-doped Graphene- Iron-phthalocyanine composite is very low,17 and the spin transition can occur without an external stimuli. Subsequently, there is a possibility that the necessary driving force for this process could be the interaction between the individual magnetic moments of the two systems. Now, the question is how can we tune this force to implement the spin-transition? A simple approach is to introduce the impurities (doping) on the graphene surface that can effectively control the spin transition. To be precise, the overall magnetic state of the system can be tuned (strongly magnetic or non-magnetic) according to the nature of the doping element present on the graphene surface. The composite structure (FePcdoped graphene) is equivalent to an engineered device that can self regulate the electronic spin without any external (force) assistance. Hence, it is anticipated that a comprehensive overview on the interaction strength of the spin-magnetic moments will be promising for the fundamental development in nanoscale device fabrication. (b) Electronic Structure: The key to developing a precise application strategy for the nanomaterials is directly related to the better understanding of the electronic structure of the system. Perhaps, N and B are the widely used graphene dopants considering the fact that either one fewer or one additional valence electron than C and mainly make them convenient n- and p-type dopants, respectively. Moreover, the comparable size and electronic structure to C provide specific advantages for them to substitute into the sheet with minimal strain, maintaining the overall graphene structure. The incorporation of impurities in graphene sheet induces new electronic states to the original


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electronic structure resulting in n- or p-type graphene. It is important to note that, based on the number of valence electrons of each element relative to C, N, and B as substitutional dopants expected to lose and gain electron density, respectively. However, contrary to the fact, single N dopants gain electron density while B dopant structures lose electron density.37,38 The five valence electrons of the nitrogen atom in N-doped graphene are distributed among the four localized orbitals. This comprised of three sp2 σ-bonds, shares with its three C atom neighbors, along with the pz orbital located perpendicular to the graphene surface. The lone-pair electron of nitrogen occupied the pz orbital. The N’s pz orbital linearly combined with the C pz orbitals to generate the overall band structure. In this process, one of the nitrogen pz electrons is located in a valence π-band, and the other one is residing in the lowest π* conduction band. Here, we can argue that the first electron involves in graphene’s π network account the energy lowering through resonance stabilization and the second N pz electron must be contributed to an antibonding band that raises the energy of the graphene sheet. The n-type dopant behavior of N-doped graphene can be understood from the presence of nitrogen’s single pz electron into the π*-space of the band structure. Although the N atom transferred one of its pz electrons to the conduction band, due the relatively higher electronegativity of N pulls the bonding electron pair of the N−C σ-bond toward it, “accepting” electron density. On the other hand, the B atom in the doped graphene behaves oppositely to that of the N. The pz orbital of the B atom is initially empty during the formation of three B-C σ-bonds. However, some orbital intermixing between the B pz orbital and the graphene’s π- space triggers the shifting of partial electron density from graphene’s occupied π-band into the empty pz orbital of the B atom. Subsequently, B loses the electron density (due to the higher electron affinity of C than B) to neighboring C atoms through the B−C σ-bonds. The shifting of electron density in the B-C σ-


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bonds result partially positive and negative charges on the B and C atoms, respectively. Consequently, despite the acceptance of electron densities from graphene’s π-space, the B atom behaves as the electron deficient center in the system. The sulfur doping to the graphene results significant structural distortion of the hexagonal lattice. Indeed, the S-C bond length is longer than the C-C bond length. The electronegativity difference between the sulfur and carbon atoms effectively modulates the charge distribution on graphene near the doping position, which can lead to the charge transfer between the sulfur and carbon atoms. The nearest-neighbor carbon atoms of the doped sulfur atom possess negative charges, which is the result of the Coulomb electrostatic interaction. Therefore, the doping of one sulfur atom into the graphene, there is one electron transferred from the sulfur atom to the graphene, which further results in the charge redistribution of the graphene. The adsorption strength of FePc on the pristine or doped graphene surface primarily depends on two key factors namely, dispersion and charge transfer interaction. As we have considered the single atom doping on the graphene surface for our present study, the variation on dispersion forces will be minimum for different systems. So, in this situation, we can argue that the charge transfer interaction will be the deciding factor in determining the relative stability of the composite structures. The iron atom of FePc having the +2 oxidation state with d6 electronic configuration in the complex and isolated FePc is found to be in the triplet state. The dispersion interaction stabilizes the adsorption of FePc on the pristine graphene. The interfacial charge transfer is hindered due to the absence of orbital intermixing between FePc and graphene surface. While in the case of N-dopant, weak intermixing between the orbitals with z-component i.e., pz of nitrogen and dzx, dyz and dz2 of Fe atom provide additional stability to the system. The consequence of orbital intermixing causes upward energy shift to the dz2 orbital compared to dzx


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and dyz and promotes the electron pairing in the dzx and dyz level. The low-spin state of the complex (due to pairing of electrons) is reflected on the lower magnetic moment (1.01 BM) of the FePc-NGr system. Similarly, for the B-dopant the empty pz orbital does not facilitate the orbital intermixing in the system. As we have discussed earlier the shifting of electron density in the B-C σ-bond makes the boron partially positive. The metal center (Fe atom of FePc molecule) is electropositive by nature. So, the long-range electrostatic interaction between the metal center and B atom impart destabilization to the overall structure. This interaction also disturbed the degenerate electronic states of the iron d-orbitals which is evident from the higher magnetic moment (2.91 BM) value of the system. Finally, the substantial structural distortion in the FePcSGr system brings the Fe and S atoms to a favorable distance for the bond formation. The weak C-S bonds could not hold the S-dopant on the graphene plane. The strong electrostatic interaction between iron and sulfur pulls the S atom out of the graphene surface. The sharing of electrons during the process of bond formation can be attributed from the lower magnetic moment (0.04 BM) value of the system. Perhaps, the substantially high interaction energy (191.40 kcal/mol) also registered the possibility of covalent bond formation in the FePc-SGr system. The computed spin-resolved electronic projected densities of states (PDOS) for the four different systems are reported in Figure 2. The electron confinement effect is responsible for the observed unusual electronic behavior in the nanosystems. The doping induced modulations to the electronic properties of the systems are prevalent from the PDOS plots. Subsequently, FePc adsorbed on pristine graphene incorporated metallic nature to the composite system. The spin-up and spin-down DOS are symmetric, which indicates that the FePc-Gr shows non-magnetic


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ground states. The essential contributions from the d and p orbitals of iron and nitrogen atoms at the Fermi level can be realized from the compute PDOS.

Figure 2: Computed spin polarized projected density of states (PDOS) plots for the four nanocomposite systems. Here, the black (spin-up) and red (spin-down) lines represent carbon atoms p- electrons contribution. The green (spin-up) and light pink (spin-down) are the electronic contribution from the p-orbitals of nitrogen atoms. The purple and golden lines exhibit the contributions of spin up and down electrons, respectively from the d-orbital of the iron atom.

The introduction of boron impurity on the graphene surface reduced the metallic nature of the system. The system represents more or less spin-gapless semi-conducting states with a small band-gap opening for the up-spin electrons. The d-orbital contribution from the iron atom


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is also significant near the Fermi level. The FePc-NGr system is also half-metallic in nature. Here, there is a large energy gap between the CBM (conduction band minima) and VBM (valence band maxima) for the spin-up electrons while the spin-down electrons exhibit metallic nature. Substantially large contribution from the d-orbital of iron near the Fermi level is well realized from the PDOS plot. The electronic characteristics for the FePc-SGr system are distinctly different from the other three systems as evident from the PDOS plots. The system tends toward a spin-gapless semiconducting state. The symmetric nature of the spin up and down electronic states institutes a non-magnetic ground state for the composite structure.

Figure 3: The spin density distribution plots for the four different FePc-graphene systems. The red and purple color regions in the plot represent the oppositely aligned excess spin densities. The numerical value within the parenthesis represents the total magnetic moment of the system. We have observed distinct changes to the spin polarity of the systems with the addition of impurity centers on the graphene surface. The spin-density maps along with the total magnetic moment values are reported in Figure 3. As we have seen that the existing spin-polarity of the systems are mainly originated from the d-electrons of the iron atom, and the excess electron density is residing on the iron atom. The undoped graphene-FePc composite is mostly spinpolarized (total magnetic moment 2.00μB) and equivalent to triplet state. Here, the excess spindensities are primarily located on the iron atom. Introduction of boron impurity on the graphene network produced significant increment in the magnetization of the system. It is important to


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note that the excess spin densities located on the iron as well as the doped surface having the same arrangements (blue isosurface in the figure) responsible for the enhancement in the overall magnetic moment of the system. Interestingly, there is some considerable drop in the total magnetic moment value (1.01μB) for the FePc-NGr system. As we have seen those excess spin densities on the iron atom is surrounded by the oppositely aligned spin densities on the ligand Natoms of the FePc complex. Moreover, the presence of excess spin-densities around the doped nitrogen atom in the graphene surface plays the crucial role to hinder the overall magnetic moment of the system. Perhaps, the negative (or beta) spin-densities around the doped N atom effectively screened by the positive (or alpha) magnetic moment of an iron atom, resulting a substantial drop in the total magnetic moment of the system. This particular observation is similar to that of the previous reports.39 On the other hand, the presence of sulfur impurity on the graphene surface results in a non-magnetic ground state for the FePc-SGr composite. Here, the magnetic moment on the iron atom is almost entirely quenched by the opposite magnetic moment on sulfur impurity. The non-magnetic ground state of the system is also realized from the symmetric nature of the PDOS plots as we have discussed before. The discussion on the magnetic behavior of Graphene-FePc nanocomposite leads to a possibilities of tuning the magnetic properties using impurity doping as the external stimuli. The intrinsic magnetic behavior of the FePc is preserved in the undoped graphene composite. Subsequently, impurity doping on the graphene surface triggers certain non-covalent interaction mediated modulations to the spin-dependent properties of the FePc. This through-space interaction is highly effective to tune the electronic behavior of the graphene-FePc composite structure. The experimental realization of the through-space interaction induced modulations to the spin magnetic moment in the FePc-graphene complexes is already establish from our previous study.17


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Figure 4: The Highest occupied level (valence band maxima (VBM)) and corresponding Lowest unoccupied level (conduction band minimum (CBM)), represented in the lower and upper panel, respectively for the four model systems. The numerical value within the parenthesis represents the energy gap between the VBM and CBM levels of the system.

Frontier molecular orbitals (FMOs) analysis is essential for the conceptual understanding on the charge transfer and electronic excitations prospects of the model systems. Subsequently, Figure 4 represents the electronic wavefunction propagations at the valence band maxima (VBM) and conduction band minima (CBM) levels for the four different nanocomposite systems. In the pristine graphene and FePc system, the VBM part is located on the FePc and corresponding CBM is positioned on the graphene surface. A moderate energy gap between VBM and CBM institutes the possibility of charge transfer between the two interacting fragments. It is worth mentioning here that the impurity doping probed distinct changes to the position of FMOs in the composite structure. Both the VBM and CBM states are now positioned on the FePc molecule. The opening of the energy gap between the frontier states is prevalent in the boron and sulfur-doped systems.


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Consequently, there is a significant decrease in the energy gap for the nitrogen-doped structure. In FePc-BGr, the iron dz2 orbital is the solo contributor for the VBM state, while the CBM state is positioned on the phenyl rings of the FePc. The closing of the energy gap between the FMO states is the critical feature of the FePc-NGr interaction. As we can see, there is no contribution from the iron atom of FePc in the VBM state and spread across the ligands while the CBM state mainly consists of the dxz orbital of iron. In the FePc-SGr system exhibits similar characteristics to that of the boron doped system. Both CBM and VBMs are located on the FePc with some relatively higher contributions from iron d-orbitals in both the states. There is a substantially high energy gap (0.85eV) between the VBM and CBM states. As we have seen from the FMO analysis, the impurity doping on the graphene surface dramatically influences the position as well as the energy gap between CBM and VBM states in the FePc-graphene nanocomposites. 4. Conclusions: In the present article, we have assayed the adsorption behavior of iron (II) phthalocyanine on the doped graphene surface. The DFT based calculations are performed to address the relative thermodynamic stability of the adsorption along with the relevant electronic and magnetic modulations on the systems. For the very first time, the current study is rendering with a simplified analytical expression to compute the interaction energy between two magnetic dipoles placed in a homogeneous magnetic field. Although the calculated interaction energy values for the magnetic dipole-dipole interaction are small compared to the other energy components (such as electrostatic, dispersion, etc.), it is relevant to develop a precise understanding on the spindependent behavior of nanostructures. The DFT calculations are implemented to monitor the electronic and magnetic modulations in the FePc due to the close vicinity of doped graphene


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surface. Primarily, the electronic states of the model systems (i.e., FePc-doped graphene) are immaculately regulated by the presence of FePc molecule. Subsequently, the spin-dependent behavior of FePc molecules on graphene can be tuned locally through adsorption-induced noncovalent interaction. The foreign impurity doping on the graphene transmitted electronic perturbations to the selected iron d-orbitals driven by their weak through-space interactions. This institutes the mechanical realization for controlled modulation to the spin-dependent behavior of a molecular system by positioning of the molecule onto a suitably functionalized graphene substrate. We are also optimistic about the fact that the particular theoretical interpretations in the present study could be transferred to other analogous model systems in a broader family of functionalized graphene. We expect that our findings will have a considerable impact on the experimental realization of phthalocyanine-based organic photovoltaic (OPV) device fabrication.


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Associated Content Electronic Supplementary Material (ESM): Electronic supplementary material is available. An elaborate discussion on the magnetic dipole–dipole interaction with the relevant analytical expressions and their necessary simplification are included. The optimized coordinates of the relaxed systems are also available.

AUTHOR INFORMATION Corresponding Author *Email: [email protected]

Acknowledgements: This work was supported by research project RVO 61388963 of the Czech Academy of Sciences. We acknowledge the financial support of the Czech Science Foundation (AS, PH: P208/12/G016). This work was supported by the Ministry of Education, Youth and Sports from the Large Infrastructures for Research, Experimental Development and Innovations project ‘‘IT4Innovations National Supercomputing Center – LM2015070’’ as well as from project LO1305 (PH). We have also highly appreciated the help and suggestions from Prof. Oded Hod, School of Chemistry, Tel-Aviv University, during the preparation of the manuscript.


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TOC Graphic

A Computational Approach to Understand the Adsorption Behavior of Iron (II) Phthalocyanine on Doped Graphene Surface Amrit Sarmah,*ab Pavel Hobzaa,b aInstitute

of Organic Chemistry and Biochemistry of the Czech Academy of Sciences,

Flemingovo nam. 2, CZ-16610 Prague 6, Czech Republic bDepartment

of Physical Chemistry, Palacky University, CZ–77146 Olomouc, Czech Republic

TOC Graphic

*Corresponding Author: Amrit Sarmah E-mail Address: [email protected]


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Computational Approach To Understand the Adsorption Behavior of

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