Cyclotriveratrylene-Containing Porphyrins - Inorganic Chemistry (ACS

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Cyclotriveratrylene-Containing Porphyrins Jude Deschamps,† Adam Langlois, Gael̈ Martin,‡ Léo Bucher,†,‡ Nicolas Desbois,‡ Claude P. Gros,*,‡ and Pierre D. Harvey*,† †

Département de Chimie, Université de Sherbrooke, Sherbrooke, Québec Canada, J1K 2R1 Université de Bourgogne Franche-Comté, ICMUB (UMR CNRS 6302), 9, Avenue Alain Savary, BP 47870, Dijon 21078 Cedex, France

‡

S Supporting Information *

ABSTRACT: The C3-symmetric cyclotriveratrylene (CTV) was covalently bonded via click chemistry to 1, 2, 3, and 6 zinc(II) porphyrin units to various host for C60. The binding constants, Ka, were measured from the quenching of the porphyrin fluorescence by C60. These constants vary between 400 and 4000 M−1 and are considered weak. Computer modeling demonstrated that the zinc(II) porphyrin units, [Zn], exhibit a strong tendency to occupy the CTV cavity, hence blocking the access for C60 to land on this site. Instead, the pincer of the type [Zn]----[Zn] and in one case [Zn]----CTV, were found to be the most probable geometry to promote host−guest associations in these systems.

1. INTRODUCTION The C3-symmetric cyclotriveratrylene (CTV) scaffold represents an excellent platform for the construction of functionalized molecular devices for 2D (on surfaces) or 3D self- and host−guest assemblies, including catenanes, gels, liquid crystals, polymers and dendritic systems.1 Some of the popular guest molecules are fullerenes, namely C60 and C70, because of their globular shapes and their redox-active properties.2 The structure of CTV-hosts exhibits a large variability of side arm functions, where numerous pendent groups and chain residues were covalently connected to the central CTV core, all designed to bind fullerenes.3 The measurements of the binding constants using UV−vis titration or fluorescence quenching by the guest fullerenes show that there are two categories. The host−guest assemblies with binding constants, Ka, smaller than ∼103 M−1,3c−f and larger than ∼103 M−1.3a,b These reported Ka values are ranging from 101 to 106 M−1 and indicate the presence of high variability. However, some trends are noticeable. Larger Ka values are obtained for CTV-containing cages and pincers,3a,b whereas “three-leg” devices often exhibit lower bindings constants.3c−f A recent theoretical characterization of these novel fullerene receptors suggested that some hosts are simply extremely flexible and the host−guest energy is quite modest.4 However, some exceptions exist. Indeed, when the pendent groups are 2-[9-(1,3-dithiol-2-ylidene)anthracen10(9H)-ylidene]-1,3-dithiole, carbazole, 2-carbonyl-N-methylpyrrole and 4-ureidopyrimidinone, the Ka values are larger than 103 M−1.5 The common feature for these pendent groups is that they bears either a N- or S atoms, presumably capable to provide electronic density to the guest electron acceptor fullerenes. In this respect, the electron rich metalloporphyrins are also known for their well-demonstrated ability to form host−guest assemblies with fullerenes,6 but to the best of our © XXXX American Chemical Society

knowledge, there is no CTV-metalloporphyrin constructs so far. It appeared obvious to explore the binding properties of such potential host molecular devices. We now report a series of CTV-zinc(II) porphyrins covalently linked by click chemistry (Chart 1). These assemblies can easily be studied using absorption and fluorescence spectroscopy, including fluorescence quenching by C60. Quite surprisingly, no host−guest behavior has been observed, where only 1:1 species are graphically deducted and exhibiting rather small Ka values (∼103 M−1). The amplitude of the ππ-interactions between C60 and the zinc(II) porphyrin unit are just too weak to benefit from the additivity/cooperativity due to the nature of the chain (i.e., ring stress) despite they are believed to be small.

2. RESULTS AND DISCUSSION 2.1. Synthesis. Only few examples of molecular wheels based on porphyrin units covalently linked to circular scaffolds have been reported in the literature.7 In our case, we were interested in the cyclotriveratrylene macrocycle, displaying a bowl-shaped conformation with a C3 symmetry. CTV derivatives are known to bind fullerenes and their use in the separation of mixtures of fullerenes has been demonstrated.5c They have also been used in the solubilizing and immobilizing of fullerene compounds.3a,8 The CTV central scaffold can be synthesized from a veratrole alcohol upon acid catalysis and further functionalized upon methoxy deprotection. Following the report of this synthetic route, Han et al. have recently reported the design of sugarfunctionalized water-soluble cyclotriveratrylene derivatives along with their interactions with fullerene.9 Starting from Received: May 25, 2016

A

DOI: 10.1021/acs.inorgchem.6b01261 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Chart 1. Structures of the CTV−Zinc(II) Porphyrin Derivatives and Comparison Compounds

Scheme 1. Synthesis of 1PZn, 2PZn, and 3PZna

a

(i) MeOH, HClO4; (ii) CH2Cl2, CuI, DIPEA, rt, 2 days

Scheme 2. Synthesis of 6PZna

a

(i) MeOH, HClO4; (ii) CH2Cl2, CuI, DIPEA, rt, 2 days

3PZn, the mono- and disubstituted CTV’s scaffolds 1PZn and 2PZn were also very conveniently formed and separated. In all cases, a perfect match between experimental and simulated ionic patterns from HR-MS measurements (MALDI/TOF) was observed, thus confirming the structures of 1PZn, 2PZn, 3PZn, and 6PZn (see Figure S1−S4 for the spectra). For example, the calculated mass for the 3PZn is equal to 2451.9243 Da (chemical formula C144H141N21O6Zn3), agreeing well with the experimental value found at 2451.9253 Da. The new CTV-porphyrin scaffolds were further characterized by 1H NMR spectroscopy. The spectra analysis demonstrates the C3 symmetry based on the equivalency of each of the porphyrin units attached to the central triazole rings. The multiplicities of the porphyrin proton signals are similar to those observed for the same protons for the starting azido porphyrin 3. The triazolic protons appear at 8.03−8.44 ppm,

cyclotriveratrylene (CTV), a classical demethylation using BBr3 in anhydrous methylene chloride afforded the cyclotricatechylene (CTC) and the six phenolic hydroxyl groups were further propargylated upon exposure to propagyl bromide. A Cu(I)catalyzed azide/alkyne click ligation was further used to connect either glucose or lactose units. A methodology for the click reaction of azido porphyrin (and corrole analogs) has been developed in our laboratory.10 Thus, we were interested in covalently linking the zinc(II) azidoporphyrin 3 to tri- or hexapropargylated CTV central scaffolds (Schemes 1 and 2). We elected to mono- or dipropargylated the veratrole alcohol unit first and then to cyclize it in the presence of perchloric acid. This way, we were able to easily isolate the tris- and hexakispropargyl-substituted CTV’s 2 and 5 (Schemes 1 and 2). Under classical Huisgen conditions,11 the expected 3PZn and 6PZn derivatives were prepared and isolated. During the synthesis of B


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Inorganic Chemistry

Figure 1. Absorption (black), excitation (blue), and emission spectra (fluorescence and phosphorescence; red) of 3 (PZn), 3PZn, and 6PZn in 2MeTHF at 298 and 77 K.

Table 1. Absorption and Photophysical Properties of CTV−Zinc(II) Porphyrins in 2MeTHF compound 3

1PZn

2PZn

3PZn

6PZn

ε × 104 (M−1cm−1) 5.42 (389 nm) 39.0 (410 nm) 1.81 (540 nm) 1.35 (575 nm) 2.13 (389 nm) 13.9 (410 nm) 0.741 (540 nm) 0.554 (575 nm) 8.44 (389 nm) 54.7 (410 nm) 2.80 (540 nm) 2.04 (575 nm) 15.9 (389 nm) 62.8 (410 nm) 3.53 (540 nm) 2.57 (575 nm) 16.6 (389 nm) 70.4 (410 nm) 4.42 (540 nm) 3.18 (576 nm)

τF (298 K) (ns)a

τF (77K) (ns)a

τP (77K) (ms)

ΦFb 0.031

1.79

1.97

81.0

χ2 = 1.076

χ2 = 1.024

λem = 725 nm

1.77

2.00

84.7

χ2 = 1.049

χ2 = 1.067

λem = 705 nm

1.74

2.01

83.0

χ2 = 1.028

χ2 = 1.058

λem = 705 nm

0.47 (14.2%) 1.66 (85.8%) χ2 = 1.073

0.70 (13.5%) 1.97 (86.5%) χ2 = 1.061

19.8 (13.4%) 71.3 (82.4%) λem = 725 nm

0.018

0.37 (6.7%) 1.71 (93.3%) χ2 = 1.012

0.46 (6.8%) 1.89 (93.2%) χ2 = 1.069

33.6 (27.4%) 67.1 (71.2%) λem = 715 nm

0.017

0.032

0.029

Using λexc = 378 nm and monitored at λem = 580 nm in 2MeTHF. The uncertainties are ±50 ps, the temporal detection limit. bQuantum yields were measured in reference to TPPZn (ΦF = 0.033) in 2MeTHF. a

CTV-zinc(II) porphyrins show similar profiles to that of 3 (PZn), used as a model, as well as zinc(II) porphyrin (TPPZn; Figure 1). Indeed, all compounds exhibit a strong Soret band absorption at 410 nm and two Q-bands located at 540 and

further proving the occurrence of the cyclo-addition reaction. The 1H NMR spectra are provided in the Supporting Information (SI). 2.2. Absorption and Emission Spectra and Photophysical Characterization. The absorption spectra of the C


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Inorganic Chemistry 575 nm. The absorptivity measurements of the CTV-zinc(II) porphyrins exhibit an expected general increase of the molar extinction coefficient as the number of porphyrin units on the CTV center increases (Table 1). Their emission spectra at 298 K exhibit emission bands centered at 580 and 635 nm, again typical of zinc(II) porphyrins. The emission spectra for 6PZn and 3PZn at 77 K closely resemble that of 3, which also show emission bands centered at 580 and 635 nm. At 77 K, 1PZn and 2PZn exhibit fluorescence bands at 580 and 635 nm, but also show strong phosphorescence bands at 705 and 790 nm. 3PZn and 6PZn present lower intensity phosphorescence at 690 and 725 nm for 3PZn and 687 and 715 nm for 6PZn (Table 2).

Figure 2. Evolution of the absorption spectra of 3PZn in 5% THF in xylenes (as a representative example) upon addition of C60 also in 5% THF in xylenes.

Table 2. Emission Band Maxima for CTV−Zinc(II) Porphyrins in 2MeTHF fluorescence maxima (nm) compound 3 1PZn 2PZn 3PZn 6PZn

298 K 579, 579, 581, 580, 578,

633 635 635 634 630

77 K 585, 575, 575, 585, 579,

644 632 632 644 637

phosphorescence maxima (nm) 77 K 726 705, 706, 690, 687,

788 786 725 714

Figure 3. Evolution of the fluorescence spectra of 3PZn in 5% THF in xylenes (∼1 × 10−4 M) upon additions of C60. Each line represents an addition of 0.2 mL of a C60 also in 5% THF in xylenes ([C60] = ∼1 × 10−3 M).

The excitation spectra of all compounds monitored at λem = 620 nm exhibit a good match with the absorption spectra at both 298 and 77 K. Concurrently, the excitation spectra monitored in their respective phosphorescent bands, also show a good match with the absorption spectra indicating that the phosphorescence emission bands come from the same chromophore as the fluorescence. In the absence of a quencher, the fluorescence decays for all compounds exhibit two components. The largest one exhibits a fluorescence lifetime (τF) that falls in the 1.66 to 1.79 ns time scale at 298 K and in the 1.89 to 2.01 ns time scale at 77 K, which is typical of zinc(II) porphyrin chromophore. The expected slight increase in fluorescence lifetime at 77 K compared to 298 K is due the rigidity of the glassy matrix. Some significant rapid (∼370−700 ps) minor components (6−14% for 3PZn and 6PZn) are also observed. Their relative contributions and τF values are found concentration independent. This result and the monoexponential behavior of the fluorescence decays for 3, 1PZn, and 2PZn indicate that these species arise from a conformation favoring nonradiative relaxations, presumably via close contacts. This photophysical behavior is also noted for the phosphorescence (τP). The long component ranges from 67 to 85 ms (Table 2). 2.3. Interactions between the CTV−Zinc(II) Porphyrins and C60. These interactions were monitored by UV−vis and emission spectroscopy. Typically, the CTV-zinc(II) porphyrins/C60 ratio were typically 1:5 at the end of all experiments, due to solubility issues. A representative example is shown in Figure 2, where the characteristic signal of C60 is depicted at 600 and 625 nm. Upon addition, no isosbestic is observed. Only a superposition of spectra of the zinc(II) porphyrin and C60 chromophore are recorded. To better address these interactions, fluorescence quenching experiments were performed instead. Upon additions of C60, an expected fluorescence quenching occurs generally due to an electron transfer for the zinc(II) porphyrin dye to the C60 electron acceptor. The quenching experiments were carried out on all CTV−zinc(II) porphyrin compounds. The Stern−Volmer analysis was based on a linear

relationship between the ratio of the fluorescence intensity (F0/ F), and the quencher concentration [Q], where F0 and F are the unquenched and quenched fluorescence intensities, respectively (Figure 4 and eq 1). The quenching constants, KSV, for all dyes

Figure 4. F0/F and τ0/τ for 1PZn in 5% THF in xylenes.

are similar to each other, except for 1PZn, which is larger, and all compare surprisingly well to that of TPPZn (Table 3). F0 = KSV[Q ] + 1 (1) F Moreover, the τF values are found invariable with [Q] and eq 2 does not apply (i.e., τ0/τ = 1 for all [Q]) as shown in Figure 4 for a representative example. τ0 = KSV[Q] + 1 (2) τ 12 This behavior is indicative of a static quenching here of the type dyes* + Q → (dye···Q), where dye* and (dye···Q) are respectively emissive and nonemissive. In the event of a mixed static and dynamic quenching, the Stern−Volmer relationship D


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Inorganic Chemistry

stronger association is consistent with the stronger binding constants values, Ka, reported for the CTV-containing devices where the pendent groups are 2-[9-(1,3-dithiol-2-ylidene)anthracen-10(9H)-ylidene]-1,3-dithiole, carbazole, 2-carbonylN-methylpyrrole and 4-ureidopyrimidinone.6 The second question is addressed using computer modeling using PCModel. The 1PZn compound is first examined since it exhibits the largest Ka value and exhibits the least sterically demanding structure (Figure 5). Two (families of) conformations for 1PZn are investigated: quasi-pincer and open. Upon energy minimization (vide infra), the individual total energies are collected. Then the dye and C60 are added near the cavity (not inside) and let the program minimize the structure. Then the resulting total energy is noted. By adding the individual energies and comparing these with those calculated for the assemblies, then a stabilization energy of the dye···C 60 interactions, ΔE, is obtained. These stabilization energy values are 8.73 and 10.95 kcal/mol for the open and quasi-pincer conformations, respectively. To make comparisons and validate this approach, the TPPZn and 3 dyes are also investigated in the same manner (Figure 6) and a table comparing this ΔE with Ka is made (Table 5). A clear trend is observed where Ka increases with ΔE. As the number of pendent groups increases, Ka becomes smaller (Table 4) and one wonder whether steric factors may prevent the C60 from approaching the zinc(II) porphyrin chromophore. For 2ZnP, four conformations were analyzed (Figure 7 and SI). The lowest energy conformation composed of a slipped cofacial bisporphyrin zinc(II) dimer, one of which is entered slightly in the CTV cavity via one Me group, at 325.29 kcal/mol (compared to 331.25, to 339.38, and to 349.73 kcal/mol). This unique conformation exhibits a structure that clearly precludes the C60 substrate to have access to the bowlshaped CTV host. The above results presented in Table 5 indicated that the CTV cavity has a significant effect on the host−guest stabilization energy. This particular conformation for 2ZnP is stabilized by ππ-stacking and again by host−guest interactions (as one Me group falls inside the CVT cavity). Because the energy is significantly lower (Figure 7) than the others (SI), that is, by ∼6 kcal/mol, it is assumed this conformation is dominant. In this case, only interactions resembling that for TPPZn···C60 and 3′···C60 (Figure 6) are most likely to occur. Therefore, there is no surprise to observe a Ka value that stands between that for TPPZn and 3. By applying the same methodology as above, 2110.93 (2ZnP··· C60) − 1793.12 (C60) = 317.81 kcal/mol, then ΔE = 325.29 (2ZnP) − 317.81 = 7.48 kcal/mol. The 3ZnP exhibits a different situation as a new pincer-shape host can be formed (Figure 8). Indeed, a “baseball glove” conformation may be depicted as one of the low-energy geometry capable of pinching C60. However, a completely collapsed conformation composed of the slipped cofacial bisporphyrin zinc(II) unit (similar to that of Figure 7) and a porphyrin zinc(II) unit folding onto the CTV bowl can also be formed. Although the “baseball glove” conformation provides the largest ΔE for the 3PZn···C60 assembly (11.29 kcal/mol) compared to the collapsed geometry (8.10 kcal/mol), a significant energy difference (i.e., by ∼6 kcal/mol) is noted between these two lowest energy conformations for 3PZn (collapsed < “baseball glove”). Consequently, the former geometry is not likely to be accessible. Other conformations were investigated but again, these geometries exhibited higher energies (one of them is provided in the SI for convenience).

Table 3. Stern−Volmer and Modified Stern−Volmer Data for the CTV−Zinc(II) Porphyrin Compounds KSV (103 L·M−1)

R2

compound

Stern− Volmer

modified S− Va

Stern− Volmer

modified S− Va

TPPZn 3 1PZn 2PZn 3PZn

1.39 1.06 2.86 1.12 1.11

1.61 1.12 2.73 1.18 0.99

0.978 0.993 0.995 0.996 0.995

0.942 0.966 0.998 0.988 0.988

a

Intercept of the regression curves was forced to 1.

becomes quadratic in nature, this is not the case here. The decrease of fluorescence emission intensity can also be analyzed according to what is known as a “modified Stern−Volmer” analysis (eq 3). This analysis takes into account the possibility for the fluorophore to be partly inaccessible to the quencher. The fraction of the initial fluorescence that can be quenched is therefore defined by f.13 F0 1 1 = + F0 − F fKSVQ f

(3)

This modified Stern−Volmer analysis was indeed also carried out. Because all fluorophores should be accessible to the quencher, the intercept of the regression curves of the modified Stern−Volmer plots were forced to 1. The resulting KSV values were found to be similar to the ones obtained from the Stern− Volmer plots. The first conclusion is that the ability of the hostdevice to capture C60 is similar to that for TPPZn. This observation appears, at first glance, surprising taking into account the rich host−guest chemistry reported in the literature for CTV-containing molecular devices toward fullerenes.3a−e,4−6 To confirm this conclusion, the data were then analyzed using the equation log((F0 − F)/F) = log(Ka) + (n log[Q]), where Ka is the binding constant, and n is the average number of binding sites sites that are occupied by a guest molecule.14 In this work, the binding sites are the cavity of the CTV and the porphyrin faces. Values of n ≈ 1 was obtained in all cases when plotting log((F0 − F)/F) vs log([C60]) (Table 4, the graphs are placed in the SI), clearly Table 4. Comparison of the Ka and n Data compound

Ka (M−1)

n

R2

TPPZn 3 1PZn 2PZn 3PZn 6PZn

300 1400 4000 400 2500 900

0.79 1.03 1.04 0.87 1.11 0.92

0.994 0.984 0.996 0.993 0.996 0.978

indicating weak host−guest interactions. The explanation for this unexpected outcome arises from the extracted Ka values from the intercepts. These values turned out to be rather small (102−103 M−1) falling into the first category mentioned in the Introduction. Then two new question arises. First, are the fluctuations observed in Ka significant? Second, why no logical trend is obtained going from 1PZn → 2PZn → 3PZn? The first question is answered by comparing the sterically similar TPPZn with 3. The latter macrocycle is electron richer than the former one by virtue of the cumulative inductive effect of the eight alkyl groups at the β-positions, and consequently a E


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Figure 5. Computer modeling of the 1PZn···C60 assembly in its quasi-pincer (top) and open (bottom) conformations.

Figure 6. Computer modeling of the TPPZn···C60 (left) and 3′···C60 (right) assemblies in its quasi-pincer (top) and open (bottom) conformations. The CH2N3 fragment was replaced by CH3 for simplicity and the code is then 3′.

Table 5. Comparison of the Ka and ΔE Data compound

Ka (M−1)

TPPZn 3′ 1PZn

300 1400 4000

2ZnP 3ZnP

400 2500

ΔE (kcal/mol) 2.72 4.49 8.73 10.95 7.48 8.10 11.29

(open) (quasi-pincer) (collapsed, most stable) (bb. glove)

Figure 7. Computer modeling of 2PZn (various views, a−c) and 2PZn···C60 (d) in their lowest energy conformations. See SI for the upper energy conformations.

The correlation between experimental Ka and ΔE is clear but the data 2ZnP are outside the trend as the calculated ΔE appears over evaluated. No explanation is possible at this time. 2.4. Fast Photophysics. Attempts were made to measure the fs transient absorption spectra of the species involved in the charge separated states in these assemblies with the hope to correlate the rates for electron transfers with the binding constants.15 Unfortunately, these attempts stubbornly failed. The main reason is most likely because of the weak Ka values preventing the formation of large amounts of host−guest species relative to the dissociated ones. Indeed, earlier reported host guest assemblies built upon [Zn]-containing hosts and C60, which successfully exhibited the charge separated state signatures, concurrently exhibited binding constants >105 M−1. In this work, the largest value is only 4 × 103 M−1.

capture C60. However, the flexibility of the anchoring chains between the CTV bowl and the [Zn] units prevented favorable conformation for doing so. Instead, pincer conformations were found to be responsible for the host−guest associations.

4. EXPERIMENTAL SECTION 4.1. Materials. Chemicals and Reagents. Solvents were dried and distilled under argon before use. All the analysis were performed at the Plateforme d’Analyses Chimiques et de Synthèse Moléculaire de l’Université de Bourgogne. Synthesis of compound 4 was done as previously reported.10a (3-Methoxy-4-(prop-2-yn-1-yloxy)phenyl)methanol (1) was prepared from 4-(hydroxymethyl)-2-methoxyphenol as previously described in the literature.16 Unless otherwise stated, all chemicals were of analytical reagent quality and were used as received. Dry THF was obtained by distillation over Na/benzophenone. Dry 2MeTHF was obtained by filtration over alumina followed by distillation under inert atmosphere using CaH2 as a drying agent. Dry 2-MeTHF was degassed by repeated cycles of vacuum and

3. CONCLUSION Various porphyrin−CTV scaffolds were readily accessible using the convenient click chemistry with the hope to prepare “giant” C3-symmetry host molecular devices specifically design to F


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Figure 8. Computer modeling of 3PZn and 3PZn···C60 in two different conformations. 4.1.3. CTV−(Alkyne)6 (5). (3,4-Bis(prop-2-yn-1-yloxy)phenyl)methanol 4 (0.4 g, 1.85 mmol) was introduced under nitrogen to a round-bottom flask. Methanol (5 mL) was added to help solubilization and the reaction mixture was cool with an ice-bath. After addition of HClO4 (1.19 mL), the coloration turned from yellow to brown. The reaction mixture was stirred overnight at room temperature. The coloration of the solution turned gray. Water was then added The reaction mixture was extracted three times with dichloromethane. The organic layers were combined, washed with water then dried over magnesium sulfate. After evaporation under reduced pressure, the title compound 5 was isolated as a white powder in 24% yield (259 mg, 0.43 mmol). Spectroscopic data are in accordance with the literature.9 1 H NMR (CDCl3, 300 MHz): δ (ppm) = 7.03 (s, 6 H, Haromatic), 4.74 (t, 3 H, CH2), 4.69 (m, 12 H, CH2), 3.56 (d, 3 H, J = 13.4 Hz, CH2), 2.53 (t, 6 H, J = 2.4 Hz, Halkyne). 13C NMR (CDCl3, 75 MHz) δ (ppm) = 146.6, 133.4, 117.6, 79.0, 76.1, 57.5, 36.5. 4.1.4. CTV−Porphyrins: (1PZn), (2PZn), and (3PZn). CTV− (alkyne)3(OMe)3 2 (12.5 mg, 0.025 mmol) and azido-porphyrin 3 (53 mg, 0.0825 mmol) were introduced under nitrogen to a roundbottom flask and dissolved in 10 mL of dichloromethane. Copper iodide (15 mg, 0.08 mmol) and DIPEA (20 μL) were then added. The reaction mixture was then stirred at room temperature for 2 days. The reaction mixture was washed with water then dried over magnesium sulfate. After evaporation under reduce pressure, the residue was dissolved in a small amount of dichloromethane and purified by chromatography on silica using a gradient from 9:1 dichloromethane/ ethyl acetate to neat ethyl acetate as eluent. The title compound 3PZn was isolated as a red powder in 25% yield (33 mg, 0.013 mmol). 1PZn and 2PZn were isolated as side products in 21 and 19% yield respectively (13 mg, 0.011 mmol for 1PZn and 18 mg, 0.010 mmol for 2PZn). 1PZn. 1H NMR (DMSO-d6, 300 MHz): δ (ppm) = 10.06 (s, 2H, Hmeso), 9.97 (s, 1H, Hmeso), 8.44 (s, 1H, Htriazole), 8.01 (d, 2H, Hphenyl‑porph), 7.68 (m, 2H, Hphenyl‑porph), 7.15 (s, 3H, Hphenyl−CTV), 7.06 (s, 3H, Hphenyl‑CTV), 6.00 (s, 2H, Hmethylene), 5.21 (m, 2H, Hmethylene), 4.72 (m, 4H, Hmethylene), 4.65 (m, 3H, Hmethylene,axial‑CTV), 4.02 (m, 4H, Hethyl), 3.81 (s, 3H, Hmethoxy), 3.79 (s, 3H, Hmethoxy), 3.74 (s, 3H, Hmethoxy), 3.72 (s, 2H, Halkyne), 3.59 (s, 6H, Hmethyl), 3.53 (m, 3H, Hmethylene,equatorial‑CTV), 3.46 (s, 6H, Hmethyl), 2.33 (s, 6H, Hmethyl), 1.84 (s, 6H, Hethyl). HR-MS (MALDI/TOF): m/z = 1165.4419 [M]+·,

purging with an inert gas (Ar), while submerged in a sonic bath. Once degassed the 2-MeTHF solution was stored inside a glovebox under an argon atmosphere (O2 levels less than 10 ppm). Anhydrous 1,2dichlorobenzene, purchased from Sigma-Aldrich was used without any further drying but was degassed and stored in the same manner as the 2-MeTHF. 4.1.1. CTV−(Alkyne)3(OMe)3 (2). (3-Methoxy-4-(prop-2-yn-1yloxy)phenyl)methanol 1 (0.8 g, 4.2 mmol) was introduced under nitrogen to a round-bottom flask. Methanol (5 mL) was added to help solubilization and the reaction mixture was cool with an ice-bath. After addition of HClO4 (2.7 mL), the coloration turned from yellow to brown. The reaction mixture was stirred overnight at room temperature. Water was then added and the reaction mixture was extracted three times with dichloromethane. The organic layers were combined, washed with water then dried over magnesium sulfate. After evaporation under reduced pressure, the title compound 2 was isolated as a white powder in 17% yield (368 mg, 0.7 mmol). Spectroscopic data are in accordance with the literature.16 1H NMR (CDCl3, 300 MHz): δ (ppm) = 6.93 (d, 6 H, J = 4.2 Hz, Haromatic), 4.75 (d, 3 H, J = 13.6 Hz, CH2axial), 4.70 (d, 6 H, J = 2.4 Hz, CH2), 3.83 (s, 9 H, OCH3), 3.55 (d, 3 H, J = 13.8 Hz, CH2equat.), 2.44 (t, 3 H, J = 2.4 Hz, Halkyne). IR: ν (cm−1) 3234 (weak, νC−H), 2352 (weak, νCC), 1261 (strong, sharp, νC−O ether). 4.1.2. (3,4-Bis(prop-2-yn-1-yloxy)phenyl)methanol (4). Sodium borohydride (0.17 g, 4.6 mmol) was suspended in methanol (5 mL) and introduced under nitrogen to a round-bottom flask. A solution of 3,4-bis(prop-2-yn-1-yloxy)benzaldehyde17 (0.50 g, 2.3 mmol) dissolved in dichloromethane was added dropwise at 0 °C. The reaction mixture was stirred at room temperature for 30 min at 0 °C then water was slowly added until formation of a white coloration. The reaction mixture was extracted three times with dichloromethane. The organic layers were combined, washed with water then dried over magnesium sulfate. After evaporation under reduced pressure, the title compound 4 was isolated as a yellow oil in 87% yield (432 mg, 2 mmol). 1H NMR (CDCl3, 300 MHz): δ (ppm) = 6.99 (m, 3 H, Haromatic), 4.74 (m, 4 H, CH2), 4.61 (s, 2 H, CH2OH), 2.49 (m, 2 H, Halkyne). 13C NMR (CDCl3, 75 MHz): δ (ppm) = 147.7, 147.0, 135.1, 120.6, 115.1, 113.9, 78.5, 75.8, 65.1, 57.0, 56.9. IR: ν (cm−1) 2355 (medium, broad, νO−H), 1255 (strong, sharp, νC−Oether), 1028 (strong, broad, νC−Oalcohol). MS (ESI): m/z = 238.97 [M + Na]+, 239.07 calc. for C13H12NaO3. G


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Inorganic Chemistry 1165.4439 calc. for C70H67N7O6Zn1. Analytical HPLC (CHCl3/ MeOH, 95/5): t1 = 1.70 min. 2PZn. 1H NMR (DMSO-d6, 300 MHz): δ (ppm) = 10.06 (s, 4H, Hmeso), 9.97 (s, 2H, Hmeso), 8.43 (m, 2H, Htriazole), 7.99 (m, 4H, Hphenyl‑porph), 7.66 (m, 4H, Hphenyl‑porph), 7.41 (m, 2H, Hphenyl‑CTV), 7.24 (m, 2H, Hphenyl‑CTV), 7.13 (m, 2H, Hphenyl‑CTV), 5.97 (m, 4H, Hmethylene), 5.22 (m, 4H, Hmethylene), 4.81 (m, 2H, Hmethylene), 4.76 (m, 3H, Hmethylene,axial‑CTV), 4.05 (m, 8H, Hethyl), 3.82 (m, 9H, Hmethoxy), 3.69 (s, 1H, Halkyne), 3.63 (m, 3H, Hmethylene,equatorial‑CTV), 3.58 (m, 12H, Hmethyl), 3.45 (m, 12H, Hmethyl), 2.32 (m, 12H, Hmethyl), 1.80 (m, 12H, Hethyl). HR-MS (MALDI/TOF): m/z = 1808.6841 [M]+·, 1808.6841 calc. for C107H104N14O6Zn2. Analytical HPLC (CHCl3/MeOH, 95/5): t1 = 1.63 min. 3PZn. UV−visible (CH2Cl2): λmax (nm) (ε × 10−3 M−1 cm−1) = 393 (90), 404 (110), 538 (9.5), 574 (8.4). 1H NMR (DMSO-d6, 300 MHz): δ (ppm) = 10.03 (s, 6H, Hmeso), 9.96 (s, 3H, Hmeso), 8.40 (s, 3H, Htriazole), 7.97 (d, 6H, Hphenyl‑porph), 7.64 (d, 6H, Hphenyl‑porph), 7.41 (s, 3H, Hphenyl‑CTV), 7.25 (s, 3H, Hphenyl‑CTV), 5.95 (s, 6H, Hmethylene), 5.24 (q, 6H, Hmethylene), 4.79 (d, 3H, Hmethylene,axial‑CTV), 4.04 (q, 12H, Hethyl), 3.87 (s, 9H, Hmethoxy), 3.64 (d, 3H, Hmethylene,equatorial‑CTV), 3.55 (s, 18H, Hmethyl), 3.42 (s, 18H, Hmethyl), 2.30 (s, 18H, Hmethyl), 1.80 (t, 18H, Hethyl). HR-MS (MALDI/TOF): m/z = 2451.9253 [M]+·, 2451.9243 calc. for C144H141N21O6Zn3. Analytical HPLC (CHCl3/ MeOH, 95/5): t1 = 1.61 min. 4.1.5. CTV−(Porphyrin)6 (6PZn). CTV−(alkyne)6 5 (12.5 mg, 0.021 mmol) and azido-porphyrin 3 (89.4 mg, 0.138 mmol) were introduced under nitrogen to a round-bottom flask and dissolved in 15 mL of dichloromethane. Copper iodide (26 mg) and DIPEA (35 μL) were then added. The reaction mixture was then stirred at room temperature for 2 days. The reaction mixture was washed with water then dried over magnesium sulfate. After evaporation under reduce pressure, the residue was dissolved in a small amount of dichloromethane and purified by chromatography on silica using neat dichloromethane as eluent first then 1 to 5% MeOH/dichloromethane. The title compound 6PZn was isolated as a red powder in 49% yield (46 mg, 0.01 mmol) after purification on TLC plate (using 1% MeOH/dichloromethane as eluent). UV−visible (CH2Cl2): λmax (nm) (ε × 10−3 M−1 cm−1) = 392 (203), 405 (165), 538 (18), 575 (16). 1H NMR (THF-d8, 300 MHz): δ (ppm) = 9.90 (m, 6H, Hmeso), 8.03 (s, 6H, Htriazole), 7.68 (m, 12H, Hphenyl‑porph), 7.38 (m, 18H, Hphenyl‑porph, Hphenyl‑CTV), 5.59 (m, 24H, Hmethylene), 4.81 (m, 3H, H methyl ene,axi al‑CTV ), 3.96 (m, 24H, H ethyl ), 3.65 (m, 3H, Hmethylene,equatorial‑CTV), 3.41 (m, 36H, Hmethyl), 3.22 (m, 36H, Hmethyl), 2.14 (m, 36H, Hmethyl), 1.77 (m, 36H, Hethyl). MS (MALDI/TOF): m/ z = 4465.99 [M]+·, 4465.45 calc. for C261H252N42O6Zn6. HR-MS (MALDI/TOF): m/z = 4082.2657 [M-6Zn+12H]+·, 4082.1644 calc. for C261H264N42O6 (due to this high molecular weight and despite different conditions used for the registration of the MS spectrum, the 6PZn form did not fly easily in the TOF analyzer. We have used TFA to remove the six zinc metal ions and to help ionization by MALDI mode). Analytical HPLC (CHCl3/MeOH, 95/5): t1 = 1.50 min. 4.2. Instrumentation. 1H NMR was performed on Bruker 300 and 500 Avance III or on a Bruker 600 Avance II spectrometer. Mass spectra were obtained by MALDI-TOF with a Bruker DALTONICS Ultraflex II spectrometer. High resolution mass measurements were carried out using a Bruker DALTONICS Ultraflex II spectrometer (HR-MS MALDI-TOF). The HPLC analyses were performed on Thermo Scientific Dionex Ultimate 3000 system, with a photodiode array detector using a Silica column (150 × 4.6 mm, particles size 3 μm) at a flow rate of 1 or 2 mL min−1. Absorption spectra were measured on a Varian Cary 300 Bio UV−vis spectrometer at 298 K and on a Hewlett-Packard 8452A diode array spectrometer with a 0.1 s integration time at 77K. Steady state fluorescence and excitation spectra were acquired on either a Fluorolog SPEX 1680 equipped with double monochromators for both excitation and emission arms or on an Edinburgh Instruments FLS980 phosphorimeter equipped with single monochromators. All fluorescence spectra were corrected for instrument response. Fluorescence lifetime measurements were made on the FLS908 phosphorimeter using a 378 nm picosecond pulsed diode laser (fwhm = 78 ps) as an excitation source. Data collection on

the FLS980 system is done by time correlated single photon counting (TCSPC). Phosphorescence lifetime measurements were made using an Edinburgh Instruments FLS980 Phosphorimeter using a microsecond flash lamp as an excitation source. Phosphorescence measurements were all made with a 540 nm excitation wavelength and a repetition rate of 1 Hz. 4.3. Quantum Yield Measurements. Measurements were performed in distilled and degassed 2-methyltetrahydrofuran (2MeTHF). Quartz cuvettes of 3 mL with path length of 1 cm equipped with a septum were used. A minimum of three replicate measurements (i.e., different solutions) were performed for each quantum yield. The sample concentrations were chosen to obtain an absorbance of about 0.05. The fluorescence quantum yield (ΦF) measurements were performed with the slit width of 1.0−3.0 nm for both excitation and emission monochromators. Relative quantum efficiencies were obtained by comparing the areas under the corrected emission spectra of the sample relative to a known standard, and the following equation was used to calculate quantum yield: ΦF(sample) = ΦF(standard) (I sampl e /I stan dard ) (F stan dard /F sample ) (η sample 2 /η sta ndard 2 ),where ΦF(standard) is the reported quantum yield of the standard, I is the integrated emission spectrum, F is the absorptance (F = 1−10−A, where A is the absorbance) at the excitation wavelength, and η is the refractive index of the solvents used. Tetraphenylporphyrin Zinc(II) (TPPZn) (ΦF = 0.033),18 was used as a standard for all quantum yield measurements. 4.4. Computations. Computations were performed using PCModel V 7.0 from Serena Software (St. Louis). It utilizes the MMX molecular mechanics force field. No constraint was applied and the interactions energies are for gas phase models. No solvation energies are included and the various dispersive interactions with fullerene are not taken into accounts. This study is qualitatively comparative.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b01261. HRMS ESI mass spectrum of compound 4, HRMS MALDI/TOF mass spectra of 1PZn, 2PZn, 3PZn, 6PZn, 1H NMR spectra of 4 (300 MHz, CDCl3), 5 (300 MHz, CDCl3), 1PZn (300 MHz, DMSO-d6), 2PZn (300 MHz, DMSO-d6), 3PZn (300 MHz, DMSO-d6), and 6PZn (300 MHz, THF-d8), 13C NMR spectra of 4 (75 MHz, CDCl3) and 5 (75 MHz, CDCl3), analytical HPLC of 1PZn, 2PZn, 3PZn, and 6PZn, graphs reporting log[(F0 − F)/F] vs log[C60], and computer modeling of 2PZn and corresponding 2PZn···C60 and 3PZn and corresponding 3PZn···C60 (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*Fax: +33 (0)3 8039 6112. E-mail: Claude.Gros@u-bourgogne. fr. *Fax: +819 821-8017. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC), le “Fonds Québécois de la Recherche sur la Nature et les Technologies (FQRNT)”, the “Centre d’Etudes des Matériaux Optiques et Photoniques de l’Université de Sherbrooke (CEMOPUS)”. The “Centre National de la Recherche Scientifique” (ICMUB, H


Article

Inorganic Chemistry UMR CNRS 6302) is gratefully thanked for financial support. L.B. also gratefully acknowledges the French Research Ministry for a PhD fellowship. Support was provided by the CNRS, the “Université de Bourgogne” and the “Conseil Régional de Bourgogne” through the 3MIM integrated project (“Marquage de Molécules par les Métaux pour l’Imagerie Médicale”). “Réalisé avec le soutien du Service de Coopération et d’Action Culturelle du Consulat Général de France à Québec” (Samuel de Champlain grant).

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197. (b) Makha, M.; Purich, A.; Raston, C. L.; Sobolev, A. N. Structural Diversity of Host−Guest and Intercalation Complexes of Fullerene C60. Eur. J. Inorg. Chem. 2006, 3, 507−517. (c) Boyd, P. D. W.; Reed, C. A. Fullerene-Porphyrin Constructs. Acc. Chem. Res. 2005, 38 (4), 235−242. (d) Boyd, P. D. W.; Hosseini, A.; van Paauwe, J. D.; Reed, C. A. Porphyrin-Fullerene Supramolecular Chemistry In Handbook of Carbon Nano Materials; D’Souza, F., Kadish, K. M., Eds. World Scientific: Singapore, 2011; Vol. 1, pp 375−390. (7) (a) Takase, M.; Ismael, R.; Murakami, R.; Ikeda, M.; Kim, D.; Shinmori, H.; Furuta, H.; Osuka, A. Efficient Synthesis of BenzeneCentered Cyclic Porphyrin Hexamers. Tetrahedron Lett. 2002, 43, 5157−5159. (b) Lensen, M. C.; van Dingenen, S. J. T.; Elemans, J. A. A. W.; Dijkstra, H. P.; van Klink, G. P. M.; van Koten, G.; Gerritsen, J. W.; Speller, S.; Nolte, R. J. M.; Rowan, A. E. Synthesis and SelfAssembly of Giant Porphyrin Discs. Chem. Commun. 2004, 762−763. (c) Lensen, M. C.; Takazawa, K.; Elemans, J. A. A. W.; Jeukens, C. R. L. P. N.; Christianen, P. C. M.; Maan, J. C.; Rowan, A. E.; Nolte, R. J. M. Aided Self-Assembly of Porphyrin Nanoaggregates into RingShaped Architectures. Chem. - Eur. J. 2004, 10, 831−839. (d) Cho, H. S.; Rhee, H.; Song, J. K.; Min, C.-K.; Takase, M.; Aratani, N.; Cho, S.; Osuka, A.; Joo, T.; Kim, D. Excitation Energy Transport Processes of Porphyrin Monomer, Dimer, Cyclic Trimer, and Hexamer Probed by Ultrafast Fluorescence Anisotropy Decay. J. Am. Chem. Soc. 2003, 125, 5849−5860. (e) Biemans, H. A. M.; Rowan, A. E.; Verhoeven, A.; Vanoppen, P.; Latterini, L.; Foekema, J.; Schenning, A. P. H. J.; Meijer, E. W.; De Schryver, F. C.; Nolte, R. J. M. Hexakis Porphyrinato Benzenes. A New Class of Porphyrin Arrays. J. Am. Chem. Soc. 1998, 120, 11054−11060. (f) Aratani, N.; Osuka, A. Synthetic Strategies Toward Multiporphyrinic Architectures. In Handbook of Porphyrin Science; Kadish, K. M., Smith, K. M., Guilard, R., Eds.; World Scientific: Singapore, 2010; Vol. 1, pp 1−132. (8) Atwood, J. L.; Bond, A. M.; Miao, W. J.; Raston, C. L.; Ness, T. J.; Barnes, M. J. Electrochemical and Structural Studies on Microcrystals of the (C60)x(CTV) Inclusion Complexes (x = 1, 1.5; CTV = cyclotriveratrylene). J. Phys. Chem. B 2001, 105 (9), 1687−1695. (9) Yang, F.; Chen, Q.; Cheng, Q.-Y.; Yan, C.-G.; Han, B.-H. SugarFunctionalized Water-Soluble Cyclotriveratrylene Derivatives: Preparation and Interaction with Fullerene. J. Org. Chem. 2012, 77 (2), 971−976. (10) (a) Takai, A.; Chkounda, M.; Eggenspiller, A.; Gros, C. P.; Lachkar, M.; Barbe, J.-M.; Fukuzumi, S. Efficient Photoinduced Electron Transfer in a Porphyrin Tripod−Fullerene Supramolecular Complex via π−π Interactions in Nonpolar Media. J. Am. Chem. Soc. 2010, 132, 4477−4489. (b) Desbois, N.; Pacquelet, S.; Dubois, A.; Michelin, C.; Gros, C. P. Easy Access to Heterobimetallic Complexes for Medical Imaging Applications via Microwave-Enhanced Cycloaddition. Beilstein J. Org. Chem. 2015, 11, 2202−2208. (c) Brizet, B.; Desbois, N.; Bonnot, A.; Langlois, A.; Dubois, A.; Barbe, J.-M.; Gros, C. P.; Goze, C.; Denat, F.; Harvey, P. D. Slow and fast singlet energy transfers in BODIPY-gallium(III)corrole dyads linked by flexible chains. Inorg. Chem. 2014, 53 (7), 3392−3403. (11) Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Click Chemistry: Diverse Chemical Function from a Few Good Reactions. Angew. Chem., Int. Ed. 2001, 40, 2004−2021. (12) Sugunan, S. K.; Robotham, B.; Sloan, R. P.; Szmytkowski, J.; Ghiggino, K. P.; Paige, M. F.; Steer, R. P. Photophysics of Untethered ZnTPP−Fullerene Complexes in Solution. J. Phys. Chem. A 2011, 115, 12217−12227. (13) Lakowicz, J. R. Principles of Fluorescence Spectroscopy; Springer: Berlin, 2006. (14) Makarska-Bialokoz, M. Fluorescence Quenching Effect of Guanine Interacting with Water-Soluble Cationic Porphyrin. J. Lumin. 2014, 147, 27−33. (15) (a) Kuramochi, Y.; Satake, A.; Sandanayaka, A. S. D.; Araki, Y.; Ito, O.; Kobuke, Y. Fullerene- and Pyromellitdiimide-Appended Tripodal Ligands Embedded in Light-Harvesting Porphyrin Macrorings. Inorg. Chem. 2011, 50, 10249−10258. (b) Kamimura, T.; Ohkubo, K.; Kawashima, Y.; Ozako, S.; Sakaguchi, K.-I.; Fukuzumi, S.; Tani, F. Long-Lived Photoinduced Charge Separation in Inclusion

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Cyclotriveratrylene-Containing Porphyrins - Inorganic Chemistry (ACS

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