Density Functional Theory Investigation on Boron Subphthalocyanine

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A: Spectroscopy, Molecular Structure, and Quantum Chemistry

Density Functional Theory Investigation on Boron-Subphthalocyanine-Ferrocene Dyads Maria Harris Rasmussen, Andreas Lynge Vishart, Freja Eilsø Storm, and Kurt V. Mikkelsen J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.8b04710 • Publication Date (Web): 29 Aug 2018 Downloaded from http://pubs.acs.org on August 30, 2018

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The Journal of Physical Chemistry

Density Functional Theory Investigation on Boron-Subphthalocyanine-Ferrocene Dyads Maria Harris Rasmussen,†,‡ Andreas Lynge Vishart,†,‡ Freja E. Storm,† and Kurt V. Mikkelsen∗,† †Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark ‡These authors contributed equally to this work E-mail: [email protected]

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Abstract 12 dyad structures were investigated using Time-Dependent Density Functional Theory (TD-DFT). The dyads are all functionalized Boron Subphthalocyanines (SubPcs), where the SubPc unit acts as an acceptor, and ferrocene was chosen as the donor. Both axial and peripheral functionalization was investigated using four different linker groups between the SubPc unit and the ferrocene unit. The calculated molecular orbitals were compared for the 12 structures and discussed in the context of possible electron transport through the system and the use in organic photovoltaics. Optical properties of the 12 structures were investigated using a TD-DFT approach with the generalized gradient approximation type exchange correlation functional, BP86 and using the Pople style basis set 6-31++G(d,p). Both changes in absorption properties by changing the linker group and changes in absorption properties when changing the position of the linker group were considered.

Introduction Photosynthesis in Nature relies on chlorophyll light-harvesters, which are macrocyclic and π-conjugated molecules based on four pyrrole units. Porphyrins and phthalocyanines are the chemist’s approach for mimicking chlorophylls as these molecules also contain four pyrrole units. They have found wide interest for their absorption and fluorescent properties in the quest for artificial photosynthesis devices or solar cells as well as molecular sensors. Much less effort has been devoted to the contracted systems, such as subphthalocyanines (SubPcs) or subporphyrazines (SubPzs),with only three pyrrole rings connected together incorporating a boron in the center. Presently, we consider boron subphthalocyanines (SubPcs) that are a class of macrocyclic compounds with interesting optical and electrochemical properties. Recently, SubPcs have attracted considerable attention as active units in artificial photosynthetic systems, 2


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sensors, light-emitting devices, field-effect transistors, supramolecular systems, and low band gap molecular solar cells. 1–7 Our intentions are to develop and understand lightharvesting and fluorescent macrocyclic chromophores where the isoindole units of SubPc are replaced by different rings and functionalized through the central boron atom. We have undertaken theoretical investigations of SubPcs. These systems consist of three isoindole units bridged by aza-linkages and we consider the compounds to be very attractive as light harvesters. This is due to the intense low-energy absorptions of the molecular systems. We investigate the thermodynamical and optical properties of the compounds using Density Functional Theory (DFT) and Time Dependent DFT (TD-DFT) Generally, SubPcs are aromatic dyes with a central unit of 14 π-electrons that due to the central sp3 -hybridized boron atom leads to a unique curvature involving the three isoindole units connected by aza-linkages. 8–11 Meller and Ossko discovered the SubPcs in 1972 12 and the work by several groups has extended the procedures for synthesis and has shown how to functionalize the SubPcs. 13–24 Several groups have shown that it is possible to design and synthesize modified SubPcs that could act as both donors and acceptors, thereby utilized in photo voltaic devices with a power-conversion efficiency of 8.4 %. 25–27 Other modifications of SubPcs where the inner pyrrole or isoindole units are replaced by other ring structures were reported. 28–31 In the present investigation we wish to investigate how to design and modify SubPcs in order to improve the efficiency of photo voltaic devices based on SubPcs. Our aim is to answer the following three questions: (i) Are the locations both in terms of energy and spatial distribution of the molecular orbitals appropriate for photo induced electron transfer? (ii) Do the proposed molecular systems absorb solar radiation with high intensities in the wave length region of large solar flux? (iii) Do the linkers between the SubPc (chromophore) and the donor change the absorption of the dyad? In order to answer these question, we have considered 12 different structures of SubPc connected through linkers to a ferrocene unit. We have focused on the molecular geome-

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tries, the molecular orbitals and the UV-Vis absorption. First we introduce the definition of the investigated structures and conditions of the molecular orbitals used to evaluate if an investigated dyad is suitable for photo induced electron transfer. Then, we provide the computational details, and then results and discussions related to computational approaches, molecular geometries, molecular orbitals and electronic absorption. In the final section we present conclusions and perspectives of the investigations.

SubPc derivatives ɑ Axial

β

O

O Fe

Fe

N N N

B N

O

1

N

2

O

O

N

Fe

Fe

O O O

3

4

Axial

ɑ

β

A1

1

H

H

A2

2

H

H

A3

3

H

H

A4

4

H

H

⍺1

Cl

1

H

⍺2

Cl

2

H

⍺3

Cl

3

H

⍺4

Cl

4

H

β1

Cl

H

1

β2

Cl

H

2

β3

Cl

H

3

β4

Cl

H

4

Figure 1: Structures of SubPc derivatives with the SubPc moiety in the left upper corner, the linker and donor at the right upper corner and the nomenclature of the 12 structures is given in the table.

The 12 derivatives of SubPc investigated are shown in Figure 1. The structures have three parts: a chromophore/acceptor part, which is a SubPc unit, a linker part and a donor 4


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part, which is ferrocene for all structures.

The linkers (1) and (3) consisting of an ether and ester group, respectively, were chosen based on previous studies of these linkers in which they showed promise in facilitating the desired donor-acceptor charge transfer. 32 Linkers (2) and (4) are extended versions of linkers (1) and (3), where a p-phenyloxy unit has been incorporated. Linker (4) has been investigated for a SubPc- ferrocene derivative linked in the axial position, which showed a long lifetime (up to 231 µs) of the desired charge-transfer state. 33 The position and type of the linker gives the name of the structure. If the linker is at the axial position the structure is called AX where X is the number of the linker. In the same way a structure with names αX or βX identify the linker as being at the orthoperi or metaperi, respectively. When the linker is in α or β position, the axial position is functionalized with a Cl atom. All peripheral positions are bound to hydrogen, when they are not bound to the linker, see the table in Figure 1. The optimized vacuum structure of α4 is shown in Figure 2. The remaining 11 full structures are shown in the supporting information, Figure S1.

Figure 2: Vacuum structure of α4 calculated at the BP86/6-31++G(d,p) level of theory

Molecular Orbitals

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The Molecular Orbitals (MOs) are a useful tool in predict-

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Acceptor-LUMO

ing chemical properties of the investigated structures, as well as aid in the prediction of the use of these materials in solar cell applications. For dyad systems like the investigated,

Donor-HOMO

the possibility of electron transfer is what makes them suitable candidates for use in dye-sensitized solar cells. One of

Acceptor-HOMO

Figure 3: Schematics of the criteria needed to be fulfilled is that the highest occupied the desired order of the MOs molecular orbital (HOMO) of the donor must be higher in energy than the HOMO of the chromophore/acceptor, and furthermore the lowest unoccupied molecular orbital (LUMO) of the chromophore should have a higher energy than the HOMO of the donor, but lower energy than the LUMO of the donor (Figure 3). 34–36 Ferrocene is a good donor, 37 since it has a high energy HOMO, which allows ferrocene to easily donate its electrons. Another advantage is that ferrocene is stable even when it has donated its electrons, increasing the likelihood that ferrocene will be reduced by the electrolyte in the dye-sensitized solar cell before decomposition of the dyad/triad, and thereby increasing the operational time of the entire cell.

Computational The 12 structures were all investigated using DFT 38,39 as incorporated in Gaussian09. 40 Each structure was optimized first in vacuum and then in a dielectric medium simulating the interaction with dichloromethane (DCM) since DCM is a solvent often used for experimental investigations. 8–11,25–27 The solvent-molecule interactions were described by the Integral Equation Formalism variant of the Polarizable Continuum Model (IEF-PCM) 41 incorporated in Gaussian09. After each geometry optimization it was confirmed that the found geometry corresponded to a minimum on the potential energy surface, by calculat-

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ing the eigenvalues of the Hessian and making sure they were all positive. Once a geometry corresponding to a minimum on the potential energy surface was found, absorption spectra were calculated using Time Dependent-DFT (TD-DFT). 42–44 These excitation energies correspond to poles in the linear response function, and returns vertical excitation energies. This method does not take the vibrational coupling between the initial and final state into account and vibrational fine structure will also not be shown in the calculated spectra, as the vibronic couplings were not calculated in these investigations. The TD-DFT calculations only return discrete excitation energies. In real absorption spectra, there will be a broadening due to both vibrational and solvent effects. In order to get calculated absorption spectra reminiscent of the experimental ones, the molar attenuation coefficient, (˜ ν ) corresponding to each absorption band is assumed to be the shape of a Gaussian function when expressed as a function of the wavenumber ν ˜. For a given absorption band the maximum of that Gaussian will be located at the wavelength corresponding to the calculated excitation energy, and the integrated Gaussian function related to the calculated oscillator strengths. The extent of broadening of the absorption band is then given through the full width half maximum of that Gaussian, σ, which was chosen to be 0.3 eV for all calculations. The total absorption spectrum was simulated by summing all of these Gaussian functions. The basis set and exchange correlation functional to use was determined from a test on SubPc in vacuum and DCM based on geometry and absorption properties described in the following section. For all calculations, the basis set and exchange correlation functional used for the geometry optimization and the following TD-DFT calculation were the same.

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Results and Discussion Investigation of basis sets & functionals Geometry In choosing a DFT functional and basis set, geometry is one parameter to investigate. The geometry is optimized for ferrocene and SubPc. The investigated exchange correlation functionals were the long-range corrected hybrid exchange correlation functional CAM-B3LYP, 45–49 the hybrid type exchange correlation functional PBE0, 50,51 the generalized gradient approximation type exchange correlation functionals, BP86 49,52 and BPV86 (including a correction to the correlation energy, VWN 53 ). The investigated basis sets were all Pople style basis sets. 54,55 The investigations show that all of the investigated functionals are suitable for the description of both SubPc and ferrocene. Since the investigated molecules all contain both a SubPc unit and a ferrocene unit, both should be described accurately by the chosen exchange correlation functional. The calculated geometry of ferrocene in vacuum can be compared to the experimental data from Gas Electron Diffraction (GED) 56,57 with mean absolute error (M AE) calculated using Eq. 1. M AE =

N 1 X

N

|yi − xi |

(1)

i=1

where yi is the calculated bond length, xi is the experimental bond length of bond i and N is the number of bonds used in the comparison. For the ferrocene structure, investigations showed that the structure is well described with BP86/BPV86 using the basis set 6-311++G(d,p) (Figures S4 and S6). In the same way the geometry of the SubPc can be compared to experimental data from X-ray crystallography 10 (Figures S5 and S7). However, it should be kept in mind, that this is a calculated vacuum structure compared with a crystal structure, which is not expected to give the same structure. In the present case there are not significant differences between

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the GED and X-ray determined structures. 57 The functional CAM-B3LYP and the basis set 6-31++G(d,p) explains the geometry of SubPc best compared to experimental data from X-Ray crystallography. Generally, CAMB3LYP and PBE0 geometries are close to the experimental results. In order to get a sense of how "sensitive" the SubPc structure is to the environment the calculated vacuum structure of SubPc is compared with the calculated structure of SubPc in acetonitrile using the basis set 6-31++G(d,p)(Figure S8). It is seen that the mean absolute differences for the bond distances in SubPc in acetonitrile compared to in vacuum (Figure S8) are of the same order of magnitude as the MAE seen for the calculated bond lengths in vacuum compared to the bond lengths from X-Ray diffraction (Figure S7). Based on this the deviation from the X-Ray diffraction geometries found with all the investigated functionals are of a reasonable size, and all functionals might therefore be a reasonable choice.

Linear Absorption Test calculations on SubPc (Figure S9) showed that the absorption spectrum was highly dependent on the class of DFT functional used, where the use of generalized gradient functionals (BP86 and BPV86) predicted absorption properties closest to the experimental value (maximum absorption at 564 nm), 32 when considering the absorption band in the visual part of the spectrum. Since the visual absorption band is of most interest for use in solar cell application since: i) this absorption determines how much solar energy can be harvested by the system, ii) the corresponding excited state is the initial state in the ET process and iii) this absorption describes rotations of high-lying occupied and low-lying unoccupied (with respect to energy) molecular orbitals, which are the orbitals important when considering ET processes. Based on calculated absorption spectra for 5 different Pople style basis sets (Figure S10), 6-31++G(d,p) and the functional BP86 showed good agreement with ex9



perimental results for the linear response.

Molecular Orbitals

3.50 3.75 4.00 Energy / [eV]

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4.25 4.50 4.75 5.00 5.25 5.50

SubPc ( *)

Fc SubPc A1 A2 A3 A4

Fc

SubPc ( )

1 2 3 Structures

Linker

4

1

2

3

4

Figure 4: Energy diagram of the MOs calculated with BP86 and 6-31++G(d,p) for ferrocene, SubPc and the 12 structures in DCM.

As outlined above, an important property of a dyad system, that should be able to undergo photo-induced ET is that the HOMO of the chosen donor should be higher in energy than the HOMO of the chosen chromophore/acceptor. Previously undertaken experimental investigations on A1 and A3 32 indicated that this is indeed the case for ferrocene as donor and SubPc as chromophore/acceptor. Only orbitals predicted by either of the two GGA functionals BP86 and BPV86 were seen to fulfill this condition. The occupied orbitals predicted based on calculations with 10


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The Journal of Physical Chemistry HOMO HOMO

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

HOMO

HOMO-1 HOMO-1

HOMO-1

HOMO-2 HOMO-2

LUMO+1 LUMO+1 HOMO-2

HOMO-3 HOMO-3

LUMO LUMO HOMO-3

HOMO-4 HOMO-4

HOMOHOMO HOMO-4

SubPcSubPc

A3

SubPc

A3

A3

HOMO-1 Figure 5: The molecular orbitals of SubPc andHOMO-1 A3 calculated with BP86/6-31++G(d,p).

CAM-B3LYP/6-31++G(d,p) and PBE0/6-31++G(d,p) show the HOMO of the combined system to be located at the SubPc unit (Figures S11 and S12). Previously, it has been obHOMO-2 served for strong charge transfer systemsHOMO-2 that range-separated hybrids are not performing

optimally 58 In combination with the geometries and linear response results, we conclude that the combination of BP86 as exchange correlation functional and 6-31++G(d,p) as basis set HOMO-3 HOMO-3

is suitable for the treatment of SubPc-ferrocene dyads. Therefore, the combined system is described by the BP86 functional and the 6-31++G(d,p) basis set. The following presented results are based on that combination. HOMO-4 HOMO-4

The difference in energy between the HOMO of isolated ferrocene and isolated SubPc

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SubPcSubPc

A3

A3


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HOMO LUMO+1

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HOMO-1 LUMO

HOMO-2 HOMO

HOMO-3 HOMO-1

HOMO-4 HOMO-2

A1

A2

A3

A4

FigureHOMO-3 6: MOs of structures A1 to A4 calculated with BP86/6-31++G(d,p). (Figure 4) is in the order of 1 eV. The LUMO and LUMO+1 for isolated ferrocene are not shown since the LUMO and LUMO+1 have a much higher energy (-1.517 eV and -1.515 HOMO-4

eV, respectively) and are thus not relevant for the discussion. For all 12 dyad structures, the MO (Figures, 5, 6, 7 and 8) most reminiscent of the A1

A2

A3

A4

HOMO of isolated SubPc is either HOMO-3 or HOMO-4 (green colored level in Figure 4), which is similar in energy to the isolated SubPc-HOMO. Likewise, the HOMO of all the dyad systems is very reminiscent of the HOMO of isolated ferrocene. However, the energy of this orbital (HOMO) is seen to vary much more for the different structures. In particular, there seems to be a tendency for the structures containing linkers 1 and 2 to have an energetically higher lying HOMO compared to structures containing linkers 3 and 4. The energy difference between the orbitals corresponding to donor and acceptor/chromophore HOMOs is seen to vary across the different dyad systems, with the

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LUMO+1

LUMO

HOMO LUMO+1

Figure 7: MOs of structures α1 to α4. HOMO-1 LUMO

HOMO-2 HOMO

HOMO-3 HOMO-1

HOMO-4 HOMO-2

β1 M1

HOMO-3

β2 M2

β3 M3

β4 M4

Figure 8: MOs of structures β1 to β4.

HOMO-4

13

M1

ACS Paragon Plus Environment M2

M3

M4


highest energy difference observed for A1 and the smallest for α4 between the HOMO and HOMO-3. The largest energy difference between HOMO localized mostly at ferrocene and HOMO localized mostly on the SubPc is α2. All 12 investigated structures are seen to fulfill the qualitative requirement of having the HOMO primarily situated at the ferrocene unit, making this orbital energetically higher than the highest occupied MO with electron density primarily located at the SubPc unit. The LUMO of all dyad systems is most similar to the LUMO of isolated SubPc and it does not show a strong dependence on neither position nor linker group. Structures A2 and α2 show an MO with electron density primarily located at the linker group (Figures 6 and 7) and with higher energy than the HOMO with electron density primarily localized on the SubPc-unit (HOMO-4 for these two systems). This allows for a different kind of mechanism for the ET through a two step ET process from ferrocene to linker to SubPc. In general the MOs predicted for the axially substituted structures (Figure 6) are more highly localized on the different sub-units of the dyads compared to the MOs predicted for the peripherally linked structures (Figures 7, 8), where especially orbitals on the SubPcunit and linker group start to mix. The varying energy differences in the HOMO located at the ferrocene unit compared to the HOMO located at the SubPc unit across the twelve structures show that even a small change in the nature of the linker (e.g. A1 to A3) can result in a big change in this energy difference. The position of the linker-donor group was seen to both affect the energetics of the orbital picture, but also (by visual inspection of the orbitals) a higher degree of mixing of the orbitals on different units for the peripherally functionalized structures.

The linker dependence The predicted position of the Q-band is almost completely unaffected by the linker-group for the axially linked structures (Figure 9), in agreement with previous studies. 36,59,60 14


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8 1e4

A2 vac λmax = 531nm A3 vac λmax = 531nm A4 vac λmax = 531nm A1 DCM λmax = 547nm A2 DCM λmax = 549nm A3 DCM λmax = 549nm A4 DCM λmax = 549nm

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ε / Lmol−1 cm−1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


5 4 3 2 1 0 300

400

500

λ / nm

600

700

800

Figure 9: TD-DFT calculations in vacuum (dashed lines) and TD-DFT PCM calculations in DCM. The spectra are all for ferrocene in the axial position, while the linker group is varied. Hence, it is expected, that the linker group can be varied quite freely without affecting the optical properties of the system, but could also suggest a low coupling through the axial position. In contrast, the β substituted species show a much greater dependence on which linker is used (Figure 10). With respect to the maximum absorption in the visual part of the spectrum, the structures β1 and β4 show a red shift compared to structure β2 and β3. A difference between the species is also seen with respect to the intensity of the maximum absorption band in the visual part of the spectrum, where the highest intensity is calculated

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β1 vac λmax = 545nm β2 vac λmax = 530nm β3 vac λmax = 539nm β4 vac λmax = 543nm β1 DCM λmax = 566nm β2 DCM λmax = 551nm β3 DCM λmax = 555nm β4 DCM λmax = 566nm

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5 4 3 2 1 0 300

400

500

λ / nm

600

700

800

Figure 10: TD-DFT calculations in vacuum (dashed lines) and TD-DFT PCM calculations in DCM. The spectra are all for ferrocene in the β position, while the linker group is varied. for β3 and the lowest intensity is calculated for β1. Multiple extra absorption bands also show compared to the axially substituted structures, especially for β1, around 450 nm, and β2, around 680 nm. In general, the optical properties for the meta substituted species are predicted to change a lot when varying the linker-group compared to the axially substituted species. This makes sense based on the above discussion of the molecular orbitals, which showed that the molecular orbitals for the peripherally substituted species were much more perturbed by the linker-group compared to the axially substituted species, and so the description of absorption in the Q-band as being entirely localized on the SubPcunit starts to break down. 16


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8 1e4

α1 vac λmax = 559nm α2 vac λmax = 544nm α3 vac λmax = 547nm α4 vac λmax = 563nm α1 DCM λmax = 584nm α2 DCM λmax = 561nm α3 DCM λmax = 564nm α4 DCM λmax = 586nm

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5 4 3 2 1 0 300

400

500

λ / nm

600

700

800

Figure 11: TD-DFT calculations in vacuum (dashed lines) and TD-DFT PCM calculations in DCM. The spectra are all for ferrocene in the α position, while the linker group is varied.

Likewise, the optical properties for the structures substituted at the α-position show dependence on the nature of the linker connecting the SubPc-unit and ferrocene-unit. The split of the position of the maximum absorption band is similar to the one seen for the structures substituted at the β-position with α1 and α4 being redshifted compared to α2 and α3. Again, the predicted intensity is highest for the structure with linker 3 (α3). Additional transitions are predicted in the visual part of the spectra (400 nm - 500 nm) for structures α1 and α4.

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The dependence of the spatial position of ferrocene Fixing instead each linker and exploring the dependence of moving the linker-donor group from axial to β to α position results in the absorption spectra presented in Figures 11 along with S19, S20, S21 and S22 in SI. There is a clear tendency for the Q-band for each linker, that a redshift of the maximum absorption is seen when going from axial position to β position to α position, a trend seen for other peripherally substituted SubPcs 61 . 62 This shows, in line with previous experiments, the greater susceptibility of structures substituted at the α-position to induce changes in the optical properties.

Conclusion We have provided answers to the three questions posed in the introduction. In order to investigate if positions of the MOs of the investigated dyads were appropriate for photo induced electron transfer, we have utilized the following requirements; HOMO of the donor is energetically located above the HOMO of the chromophore and LUMO of the chromophore is located higher than the HOMO of the donor. Based on this we have found that our 12 selected molecular systems are potential candidates for a photo voltaic device. Furthermore, we have in order to show the range of visible light absorbed by the investigated dyads performed calculations of excitation energies and intensities. We have found that among the 12 systems that the compounds α3 and β3 have the largest absorption intensities around 550nm. The third question concerned the effects of the linker on the absorption properties and we consider the position of the linker and linker type. For the linkers placed in the α and β position, we observed shifts towards longer wavelengths depending on the properties of the linker. Whereas we did not see any changes of the absorption when the linkers were placed in the axial position. A recent investigation on a related molecular system where the SubPc is connected to a linker (1,1,4,4-tetracyanobuta-1,3-diene(TCBD)) acting as acceptor which is furthermore 18


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connected to ferrocene has clearly shown that linkers have crucial effects on the optical and redox properties of the system. 63 The authors of that study showed that by changing the alkyne unit in the precursor SubPc-Fc dyad for a TCBD unit, they obtained large changes of the optical and redox properties depending on the location of the TCBD linker. In line with our present work they also showed that it is possible to tune the absorption depending on the properties and location of the linkers. Based on the presented results, all 12 structures should be able to undergo photo induced electron transport from the ferrocene unit to the SubPc unit upon a localized SubPc electronic transition. For the axially substituted entities, the linker group did not perturb the investigated properties, whereas the peripherally substituted entities showed quite strong dependencies of both absorption properties and MOs on the nature of the linker. Based on the answers to question two we find the two molecular systems α3 and β3 to be the most promising candidates for a photo voltaic device. Another important parameter when discussing efficiency of electron transport is the coupling between the initial electronic configuration (electron on donor-HOMO) and the final electronic configuration after electron transport (electron on acceptor-HOMO). For this coupling parameter, the nature of the linker is going to be very important, and future work will include finding eligible ways of estimating this coupling element.

Conflict of Interest The authors have no conflict of interest to declare

Acknowledgement The authors thank University of Copenhagen, the Danish center for Scientific Computing, and the Center for Exploitation of Solar Energy for support and computational time.

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Supporting Information Available The following data are available free of charge in the supporting information. • Figure of evaluated bond lengths • MOs for A1 and A3 calculated with CAM-B3LYP/6-31++G(d,p) and PBE0/6-31++G(d,p) • Extended energy diagram for MOs: HOMO-4 to LUMO+1 for all structures • Extended MO plots for HOMO-4 through LUMO+1 for all 12 structures • Calculated UV-Vis pr. linker in A, α and β position This material is available free of charge via the Internet at http://pubs.acs.org/.

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Density Functional Theory Investigation on Boron Subphthalocyanine

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