CorroleâFullerene Dyads: Stability, Photophysical, and Redox

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Corrole–Fullerene Dyads: Stability, Photophysical, and Redox Properties Andressa C. Bevilacqua, Mateus Henrique Köhler, and Paulo C. Piquini J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.9b04321 • Publication Date (Web): 08 Aug 2019 Downloaded from pubs.acs.org on August 12, 2019

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The Journal of Physical Chemistry

Corrole–Fullerene Dyads: Stability, Photophysical, and Redox Properties Andressa C. Bevilacqua,† Mateus H. Köhler,∗,†,‡ and Paulo C. Piquini∗,† †Departamento de F´ısica, Universidade Federal de Santa Maria, 97105-900, Santa Maria, Brazil ‡Programa de Pós-Gradua¸cão em Qu´ımica, Universidade Federal de Santa Maria, 97105-900, Santa Maria, Brazil E-mail: [email protected]; [email protected]

Abstract In this contribution, we explore the photophysics of covalently linked fullerenes C60 with corroles through density functional first principles calculations. The results show the relative stability of these structures, and the possibility of tuning their optical absorbance by changing either the number of fullerenes or the position at which the fullerene is attached to the corrole. We also found the electronic transitions highly influenced by the electronic states of the fullerene carbon atoms. Additionally, the analysis of the reduction and oxidation potentials shows that the one-fullerene β−substituted corrole covers the whole water redox gap, offering good grounds for application in the hydrogen evolution reaction through the breakdown of water.

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Introduction Studies on artificial donor-acceptor systems mimicking natural photosynthesis are at the heart of photosynthetic solar energy conversion. In recent years, molecular and supramolecular dyads have been investigated in order to produce long-lived charge-separated states through a charge migration route 1,2 or performing antenna-reaction center events. 3 Porphyrinoids have posed as natural candidates to perform as photoactive catalysts, mostly due to its resemblance to the natural photosynthetic chlorophyll pigment. 4 Additionally, porphyrin-like molecules with interesting photo- and redox properties, as chlorins 5 and corroles, 6–8 have also been successfully utilized as active components in donor-acceptor systems. In order to increase the efficiency of the electronic transitions involved in the photocatalytic reactions, electron acceptor structures have been attached to these molecules. Fullerene (C60 ) stands as a prominent candidate for electron acceptor, mostly due to its high electronegativity, three-dimensional structure, strong absorption in the UV-visible region, 9 and small reorganization energy in electron-transfer reactions. 10 Symmetric tetrapyrroles, such as porphyrin, have been extensively used in the majority of donor−fullerene linked systems for direct charge recombination reactions. 11 However, when compared with porphyrins, the corrole macrocycles exhibit lower oxidation potentials, 7 higher fluorescence quantum yields, 12 and relatively more intense absorption of red light, 13,14 all desirable characteristics in photo-induced charge recombination processes. The corrole structure possess the skeleton of corrin (macrocycle found in vitamin B12 ) with three mesocarbons between the four pyrrole rings. 15 The lower oxidation potential of corroles allows the covalently linked corrole−fullerene dyads to have a long-lived charge-separated state in nonpolar solvents, 16 a feature not evident in porphyrin−fullerene donor−acceptor systems. 17 Time-resolved absorption studies revealed efficient photoinduced electron transfer from the singlet excited corrole to the fullerene entity. 16 In this experimental study by D’Souza and colleagues, meso-pentafluorophenyl substituents were found to provide high stability to the 2


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corrole−fullerene dyad, suitably positioning the energy level of the charge-separated states to achieve long-lived radical ion-pairs. Unlike the protagonism played by porphyrin−fullerene supramolecular systems in the last decades, the physical chemistry and photophysical aspects of corrole−fullerene dyads remain as an open subject, largely unexplored and poorly understood. Investigation on these properties is crucial for the potential use of those compounds as light-harvesting molecules, 16,18 in supramolecular assembly, 19 in photodynamic therapy, 20 as well as to a deep understanding of water splitting processes for hydrogen evolution reaction (HER). 21,22 In this work, we performed first-principles calculations to study the optical and the redox properties of corrole−fullerene dyads. The following molecular structures were investigated: one fullerene connected to a β−position of the corrole (namely, β-1A and β-1B), two fullerenes connected to β−positions (β-2A and β-2B), and one fullerene connected to a meso−position of the corrole, either directly (meso-A) or through a phenyl ring (meso-B). We observed a strong influence of the fullerene position on the dyad absorption spectra, and on the spatial distribution of the molecular orbitals involved in the electronic transitions, highlighting the effect of the acceptor agent on the optical and electronic properties of corroles. The remainder of the paper is organized as follows. In the next section, Computational Details and Methods are described. In Results and Discussion, the main results on the photophysical properties are discussed. Summary and Conclusions are presented in last section.

Computational Details and Methods The Density Functional Theory (DFT) has been used to study the electronic, optical, and redox properties of β− and meso−substituted corrole−fullerene dyads. The exchange and correlation potentials were described through the long-range corrected CAM-B3LYP func-

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tional. 23 All calculations were performed within the Gaussian 09 package. 24 The molecular orbitals were represented by linear combinations of the 6-31G+(d,p) split valence atomic basis set. 25 The atomic coordinates were obtained from the crystallographic data of corrole. 26,27 The structures, fully optimized through conjugated gradient techniques, were then used to build the β and meso conjugated corrole−fullerene dyads. Six different photosensitive molecules have been investigated. They differ in the position at which the fullerene is attached, as well as in the number of C60 molecules connected to the corrole macrocycle. The structures are depicted in the insets of Figure 1. Since the stability plays an important role in the corrole family, 28 we have chosen meso-functionalized corroles with three pentafluorophenyl groups (positions 5, 10 and 15). This allows the corrole structure to achieve a higher level of stability, prerequisite for accurate calculations of the optical and redox properties. The geometries were verified to have only real infrared frequencies. The optical spectra were then calculated at the optimized geometries through time-dependent DFT (TD-DFT). The spectrum for each molecule is broadened by applying a Lorentzian fit with a half-width at half-maximum (HWHM) of 7 nm. We have also analyzed the redox properties. The experimental results for oxidation and reduction potentials depend on the solvent and the reference electrodes. Previous theoretical DFT studies 29–31 have shown to be capable to suitably treat these dependencies, leading to estimations for the oxidation and reduction potentials, at different solvents and reference electrodes, that are in good agreement with experimental findings. The polarizable continuum model (PCM) 32 was employed in order to calculate the molecular properties in polar (acetonitrile, dielectric constant = 35.7) as well as in nonpolar (toluene, = 2.3) solvents. Redox potentials were calculated through the Born-Haber (BH) thermodynamic cycle. It requires the evaluation of the molecular properties both in gas and solution phases. 33 In the BH cycle, the reduction and oxidation potentials in the solution phase can be calculated

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by: 34 red/ox

E0 = red/ox

where −∆Gsol

−∆Gsol nF

− ESHE ,

(1)

is the free energy for reduced/oxidized species, n is the number of electrons

involved in the reaction of interest (here n = 1), F is the Faraday constant (F = 23.061 kcal·mol−1 ·V−1 ), and ESHE is the potential of the reference electrode (Standard Hydrogen Electrode - SHE). 35

Results and Discussion Structural Stability Corroles and porphyrins share very similar structures, the former being one carbon shorter, the non-natural analogue of the latter. This structural difference results in distinct stability, 8 photo-physical 7 and redox properties. 36 Particularly, the analysis of structural stability is a central issue for corroles. Here, in order to analyze the energetic stability associated with the corrole−fullerene dyads, the formation energies have been calculated as: 37

EFORM = ETOT − ECORROLE − EC60 − nC µC ,

(2)

where ETOT stands for the total energy of the corrole−fullerene system, ECORROLE is the energy associated with an isolated 5,10,15-tris(pentafluorophenyl)corrole, EC60 is the energy of a C60 fullerene, nC is the number of C atoms, and µC is the corresponding chemical potential. The atomic chemical potential µC is obtained as the total energy per atom of the C2 molecule. 38 The formation energies of the six compounds in Figure 1 are shown in Table 1. As can be observed, the one-fullerene β−substituted systems (β-1A and -1B) have the lowest formation energies among all the compounds, with a slightly energetic advantage for the β-1B structure. The general trend follows the order EFORM (β-1B) < EFORM (β-1A) < EFORM (β-2B) < EFORM (meso-B) < EFORM (β-2A) < EFORM (meso-A), highlighting the energetic stability of 5



the β-1 systems. Table 1: The calculated formation energy EFORM per atom for each corrole−fullerene compound. Structure EFORM (eV/atom) β-1A β-1B β-2A β-2B meso-A meso-B

-0.772 -0.773 -0.563 -0.731 -0.500 -0.584

The higher formation energies of meso systems in comparison with the β−substituted corroles are likely related to the removal of a pentafluorophenyl ring. To circumvent the lower stability of corroles under light and air, 39 several types of functionalization have been developed. In this regard, tri-(pentafluorophenyl)-substituted corroles have been identified to be stable under oxidative degradation. 40 In fact, functionalization of the aryl ring at the meso- or para-position with pentafluorophenyl groups is the most common and relatively easy modification. 41,42 Additionally, Ooi and co-workers 43 have found destabilized frontier orbitals in free meso-corroles, while Bursa and collaborators 44 have utilized pentafluorophenyl groups to provide meso-substituted corroles with higher stability. The β-2A compound shows increased formation energy EFORM as compared with the β1A and -1B systems. Interestingly, there is a considerable energetic difference between the two-fullerene systems (β-2A and -2B). The difference can be associated with the spatial distribution of the fullerenes around the corrole macrocycle. In the β-2A (Figure 1c) the fullerenes are diagonally aligned, with a geometry that puts the fullerenes as far as possible. On the other hand, in the β-2B geometry (Figure 1d) the fullerenes are closer to each other promoting additional carbon−carbon interactions, which contributes favorably to the formation energy. This is in agreement with experimental findings on structural motifs in polymeric fullerides. 45,46 Tightly-packed C−C bridging fullerenes were found at these com-

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pounds. In the case of ionic complexes of metalloporphyrins with fullerenes, for instance, the fullerene anions form various packings and σ bonded fullerene structures: one-dimensional chains of C60 , 47 isolated dianions (C60 2− ), 48 diamagnetic and paramagnetic dimers (C60 )2 bound by one 49 and two C−C bonds, 50 respectively. Zigzag fullerene chains formed by metal−fullerene dimers were also reported. 51 These results suggest therefore an energetic cooperativity of fullerenes when placed close to each other around the tetrapyrrolic macrocycles.

Absorption Spectra and Electronic Transitions Tetrapyrrolic macrocycles have been widely used as photosensitizers in dye-sensitized solar cells. 52 The absorption features in the near-UV, visible and near-IR region of the solar spectrum are of fundamental importance for the use of these materials as efficient photocatalysts. Figure 1 shows the absorption spectra for the six corrole−fullerene structures embedded in two different solvents (acetonitrile and toluene) and in vacuum. The solvent is expected to play an important role in the prediction of the material’s optical response, as well as in the redox properties. 30,53 Particularly, the solvent polarity can influence the optical and electronic properties of corroles. 44 However, using the nonpolar toluene ( = 2.3) for all the compounds, we do not observe any differences in the absorption spectra in comparison with vacuum. On the other hand, we noticed that the polar acetonitrile ( = 35.7) solvent induces small deviations (red-shifts) in the absorption peaks: markedly a displacement is observed in the first peak (∆λ = 23 nm, or 0.15 eV) in Figure1(a) for the β-1A. For the β-2B system, the polarity of the solvent affects the intensities of the two peaks around 550 nm, turning the highest energy peak more intense in acetonitrile. We also noticed differences in the absorption intensities around 400 nm for the β-1B and the meso-A, as can be observed in Figures 1(b) and (e), with a significant increase in the peak intensity for the more polar solvent. It is interesting to note, however, that the solvents do not alter the peak positions appreciably, leading to similar results for the absorption spectra of the studied 7



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systems. Remarkably, we observed that one of the most stable systems, the β-2B (see Table 1), shows absorption peaks in the region of maximum solar incidence (500-600 nm), which makes it very promising for photocatalytic applications. A more pronounced effect in the absorption spectra is caused by the number and the relative positioning of the fullerenes. When one fullerene is bonded to the β− or to the meso−position of the macrocycle, two peaks are observed around ∼ 400 and ∼ 550 nm, as can be seen in Figures 1(a),(b),(e) and (f). Similarly, corrole-fullerene dyads synthesized by D’Souza and collaborators 16 revealed absorption bands around 410 and 560 nm. They have used donor-acceptor dyads linked together by a phenyl or a biphenyl spacer unit. The corrole containing two meso-pentafluorophenyl entities was used as a donor. The introduction of a second fullerene leads to a shift of the absorption peaks to lower energies. When the fullerenes are arranged diagonally at β−positions (β-2A), occupying opposite sides of the ring, we observe two absorption peaks close to 550 and 625 nm, Figure 1(c). On the other hand, when the two fullerenes are attached at neighboring β−sites of the corrole, the 625 nm peak is almost suppressed, with an increase of the peak around 550 nm. It shows that both the number of fullerenes and the positions they are attached to the molecule play an important role in the absorbance behavior of the corrole-fullerene dyads. In fact, the incorporation of fullerenes into photocatalytic systems (e.g., diblock and triblock copolymers, 54 in the backbone of conjugated polymers 55 and pyrrolic macrocycles 16 ) has been used to induce a broadening of the absorption spectra, especially when coupled to “push-pull” systems linked to donor conjugates (oligothiophenic chains). 56 The natural transition orbitals (NTOs) associated with the absorption peaks of β-substituted systems can be visualized in Figure 2. A careful analysis of the NTOs indicates two main kinds of electronic transitions. The first one implicates transitions only between π−orbitals inside the corrole ring, which can be observed at 545 nm for the β-1A, at 547 nm for β-2A, and at 547 nm for β-2B, Figures 2(a), (c) and (d), respectively. The second type involves transitions from the π−orbitals at the corrole ring to the orbitals distributed on the fullerene.

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These transitions can be better observed in the absorption peaks at 403 and 553 nm in the β-1B, at 629 nm for β-2A, and at 563 nm for the β-2B system, Figures 2(b)-(d), respectively. The transition observed for the 420 nm peak of the β-1A, Figure 2(a), presents a distinct characteristic, with the electron being promoted to the fullerene from the orbital associated with the corrole−fullerene covalent bond. In Figure 3 we show the NTOs associated with the absorption peaks of meso-substituted systems. Again, transitions between π−orbitals inside the ring are observed at 557 nm for meso-A, and at 563 nm for the meso-B compound, Figures 3(a) and (b), respectively. We also observe transitions to the fullerene orbitals from the π−orbitals at the ring of the mesoA system, Figure 3(a). Figure 3(b) shows a slight different transition at 405 nm for the meso-B, from the π−orbitals inside the ring to the pentafluorophenyl group attached to the corrole. Experimental and theoretical analysis of the electronic interactions between the corrole and fullerene entities have already shown the HOMO state of the dyad located mainly on the corrole π−system, with part of the HOMO also located on the phenyl spacer, while the LUMO state is placed on the fullerene. 16 The spatial distributions of HOMO and LUMO suggest the formation of corrole+ −fullerene− charge-separated states during photoinduced electron transfer. For the two-fullerene systems (β-2A and -2B), all optical transitions are restricted to the corrole ring. In other words, the addition of a second fullerene suppresses the electronic transitions that involve a charge transfer between the corrole ring and the fullerenes. The absorption properties of a material are directly related to their electronic structure. 5,57 Figure 3 shows the Density of States (DOS) and the corresponding individual atomic contribution to the DOS (PDOS) of the six corrole-fullerene dyads. For the cases in which only one fullerene is attached to the corrole macrocycle (β-1A and -1B, meso-A and meso-B) the results clearly shows a substantial influence of the fullerene carbon atoms (red curves) on the frontier electronic states, mainly in the lowest unoccupied molecular orbitals (LUMO).

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In these systems, the fullerene carbon atoms actively participate in the electronic transitions, introducing electronic states at the bottom of the conduction shell, as can be seen in Figures 3(a),(b),(e) and (f). On the other hand, when two fullerenes are attached to the corrole (β-2A and -2B) the contribution of the fullerene atoms to the frontier electronic levels is reduced, being less pronounced than those of the carbon atoms of the corrole. This also reflects the modest contribution of the fullerene to the electronic transitions in the absorption spectra of Figure 2(c) and (d). Altogether, these results show how the relative distribution of the fullerene carbon atoms have a clear influence on the electronic structure of the systems, with far reaching consequences on their optical properties.

Considering Explicit Solvents: A Qualitative Analysis with Water A detailed microscopic understanding of the factors controlling absorption of light is particularly challenging at the experimental level. First principles calculations offers an opportunity to look closely at the parameters that are sensitive to the light absorption spectra. The solvent is an important parameter, and there are different approaches to describe it computationally. So far, we have used the PCM implicit solvation model. Whether considering explicit solvents can influence the absorption spectra calculations is a current open subject that deserves further investigation. For instance, Law and Hassanali 58 have shown that the inclusion of quantum effects due to the presence of hydrogen bond groups can influence photophysical predictions of chromophores. On the other hand, the same authors showed previously for 9-methylguanine that the overall calculated absorption spectrum does not depend on microsolvation. 59 Figure 5 shows a comparison between the absorption spectra of β-1A in vacuum, with the implicit PCM parameters for water as solvent, and surrounded by explicit water molecules. As we can see, the increase in the number of explicit water molecules red-shifts the β1A spectrum. Interestingly, the same behavior is observed when Nuclear Quantum effects 10


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(NQE) are considered for chromophores in water. 58,59 We also notice the rise of a new peak around 560 nm when we introduce 10 water molecules around the corrole−fullerene dyad. Nevertheless, the NTO associated with this absorption peak shows exactly the same profile found previously: transitions between π−orbitals inside the corrole ring. It means that in this case, the electronic transitions are described in the same way either with explicit or implicit solvents. It is important to note that water is a largely polar solvent, with important hydrogen bonding properties that can affect both the absorption and the charge separation events. Further investigations are needed to fully elucidate the role of considering explicit solvents on the light absorption of these molecules. Additionally, several factors can lead to shift and broadening of spectra such as finite lifetime of excited states and the coupling of electronic and vibrational transitions leading to vibronic effects. 60–62

Redox Properties Tetrapyrrolic macrocycles, such as corroles, have been widely investigated as candidate systems for photocatalytic water splitting. 63,64 Some conditions must be fulfilled by these candidate molecules: (i) their reduction potential must be more negative than that of water; (ii) their oxidation potential must be more positive than that of water; (iii) the difference between their reduction and oxidation potentials must be larger than 1.23 V. Relatively to the standard hydrogen electrode (SHE), the water reduction and oxidation potentials are -0.47 V and +0.82 V, respectively. 65 The oxidation and reduction potentials of the corroles are susceptible to vary according to the substituents attached at the meso, and β-pyrrole positions. This variability can be used to tune their redox potentials in order to satisfy the requirements for the HER. As shown in Table 2, the oxidation and reduction potentials of the corrole−fullerene dyads present distinct behaviors. The β-1A and -1B structures show oxidation potentials slightly larger than that of water ∼ 0.9 V, which is suitable for the HER. The meso-substituted 11



Table 2: Oxidation and reduction potentials. Eox

Ered

Eox − Ered

(V vs. SHE)

β-1A β-1B β-2A β-2B meso-A meso-B

0.90 0.86 0.84 0.63 0.69 0.67

-0.65 -0.69 -0.65 -0.61 -0.66 -0.78

1.55 1.55 1.49 1.24 1.35 1.45

corroles, on the other hand, present oxidation potentials close to ∼ 0.7 V, below to that expected for the HER of the water molecule. Interestingly, the two-fullerene systems (β2A and -2B) were determined to have oxidation potentials that differ by 0.21 V. The β-2A system exhibiting an oxidation potential of Eox = 0.84 V, closest to that of water, and the β-2B an oxidation potential of 0.63 V. In other words, the relative positions at which the two fullerenes are attached to the corrole is decisive to achieve oxidation potentials in the appropriate range to the HER. Previous works have shown that donor substituents tend to lower oxidation and reduction potentials while acceptor substituents tend to increase the redox potentials. 5 The interplay of these factors lead to redox potentials for the corrole−fullerene dyads (relative to SHE) that are summarized in Figure 6. Markedly, three out of six systems show suitable redox gaps for the water splitting process required in the HER: the one-fullerene β-substituted corroles (β-1A and -1B) and the two-fullerene β-2A system. The β-2B shows either the smallest oxidation and the larger reduction potential among all the systems, leading to the 1.24 V redox gap shown in Table 2. Considering the calculated formation energies, optical absorbances, and redox potentials of the six corrole−fullerene dyads, it can be suggested that the β-1A and -1B systems are the best candidates for photocatalytic applications. Recent advances in redox band-gap engineering have revealed nanomaterials such as TiO2 , MoS2 and black phosphorus with gaps of 3.2, 66 1.75 67 and 1.5 eV, 68 respectively. As 12


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demonstrated here, the corrole−fullerene dyads could be coupled to these ultra-thin films in order to amplify both their optical absorbance and their redox potentials.

Summary and Conclusions The energetic, optical, electronic and redox properties of six corrole−fullerene dyads have been studied through TD-DFT calculations. The one-fullerene β-substituted corrole systems show the average lower formation energy. It is shown to be possible to tune absorption spectra of the dyads by changing both the number and the position of the fullerenes attached to the corrole ring. Particularly, the two-corrole systems have been found to collapse the absorption peaks at ∼ 550 nm. Further, the oxidation potentials of the β-substituted systems are seen to be substantially higher than the meso-substituted, making them suitable for the HER step of the water splitting process. Altogether, the results indicate the susceptibility of corrole−fullerene dyads to modifications in the position at which the fullerene is attached, as well as to the addition of a second fullerene. It allows for a promising tune of the optical properties of synthetical tetrapyrrole macrocycles and acceptor-donor dyads for optoelectronic and photocatalytic applications.

Acknowledgement This work was partially supported by the Coordena¸cão de Aperfei¸coamento de Pessoal de N´ıvel Superior (CAPES) - Finance Code 001, and Conselho Nacional de Desenvolvimento Cient´ıfico e Tecnológico (CNPq), Grant Number: 312388/2018-7. The authors thanks CENAPAD-SP and CPAD-UFSM for the computer time.

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Page 23 of 29

a β -1A

b β -1B

c β -2A

d β -2B

e meso-A

f meso-B

Intensity (a. u.)

Intensity (a. u.)

Acetonitrile Vacuum Toluene

Intensity (a. u.)

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


300

400

500

600

700

300 300

400

λ (nm)

500

600

700

λ (nm)

Figure 1: Absorption spectra for the six corrole−fullerene structures (illustrated in the insets).

23



a

HOMO

λ = 420 nm

LUMO

HOMO

Page 24 of 29

λ = 545 nm

LUMO

β −1A

b

λ = 403 nm

λ = 553 nm

λ = 547 nm

λ = 629 nm

λ = 547 nm

λ = 563 nm

β −1B

c β −2A

d β −2B

Figure 2: NTO associated with the absorption peaks of β-substituted corrole−fullerene systems.

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a

HOMO

λ = 407 nm

LUMO

HOMO

λ = 557 nm

LUMO

meso −A

b

λ = 405 nm

λ = 563 nm

meso −B

Figure 3: NTO associated with the absorption peaks of meso-substituted corrole−fullerene systems.

25



30

Total C60 C (corrole) H N F

(a) β -1A

15 0 30

(b) β -1B 15 0 40

Density of States

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

Page 26 of 29

(c) β -2A

20 0 40

(d) β -2B

20 0 30

(e) meso-A

15 0 30

(f) meso-B

15 0 -10

-8

-6

-4

-2

0

2

Energy (eV)

Figure 4: Total DOS (black line) and PDOS for the different chemical species present in the corrole structure as well as for the fullerene carbon atoms (red line).

26


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HOMO

LUMO

PCM - Water (ε = 78) Vacuum 1 H2O 2 H2O 3 H2O 5 H2O 10 H2O

Intensity (a. u.)

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


300

300

400

400

500

500

700

600

600

700

λ (nm)

Figure 5: Absorption spectra for β-1A with explicit water molecules as solvent. The inset shows the NTO associated with the indicated (red) absorption peak.

27


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

Potencial (V) vs SHE


-0.5

Page 28 of 29

+

H /H2

0

0.5 H2O/O2

1 β -1A

β-2B

β -1B

meso-A

β -2A

meso-B

Figure 6: Schematic representation of the reduction and oxidation potentials.

28


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TOC Graphic

Optical Absorbance

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


Wavelength

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CorroleâFullerene Dyads: Stability, Photophysical, and Redox

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