Ultrafast Singlet Energy Transfer in Porphyrin Dyads - ACS Publications

Oct 6, 2016 - Jean-François Longevial , Sébastien Clément , Jennifer A. Wytko , Romain Ruppert , Jean Weiss , Sébastien Richeter. Chemistry - A Eu...
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Ultrafast Singlet Energy Transfer in Porphyrin Dyads Hervé Dekkiche,† Antoine Buisson,‡ Adam Langlois,‡ Paul-Ludovic Karsenti,‡ Laurent Ruhlmann,† Pierre D. Harvey,*,‡ and Romain Ruppert*,† †

Institut de Chimie, UMR 7177 du CNRS, Université de Strasbourg, 4 rue Blaise Pascal, 67000 Strasbourg, France Département de Chimie, Université de Sherbrooke, Sherbrooke, Quebec J1K2R1, Canada

‡

S Supporting Information *

ABSTRACT: A weakly fluorescent Pt-bridged dyad composed of zinc(II) porphyrin (Zn; donor) and free base (Fb; acceptor) has been designed and exhibits an ultrafast singlet energy transfer between porphyrins. The use of larger atoms within the central linker significantly increases the MO coupling between the two chromophores and inherently the electronic communication.

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INTRODUCTION Chlorophylls and bacteriochlorophylls are considered the pigments of life. They exhibit multiple key photophysical roles within the photosynthetic membrane, including excitation energy migration and energy and electron transfers. Nature spent ∼3.5 billion years (since the appearance of the first photosynthetic bacteria)1 to optimize rates and efficiencies. The time scales generally range from several hundred fs to 50 ps.2 Laboratories around the world designed models to mimic such photophysical events, and only a handful of rates and time scales have been reported that approach, and sometimes even slightly exceed, those observed in these membranes.3 Two years ago, our groups reported a dyad composed of zinc and free base porphyrin motifs rigidly held together by a palladium(II) ion coordinated by two enaminoketone chelates conjugated to the aromatic core of the porphyrins. This dyad exhibited an ultrafast energy transfer rate (Figure 1, PdO-ZnFb, 660 fs).4 We subsequently reported another dyad, this time replacing the

linking palladium(II) by platinum(II), and the rate was drastically increased (Figure 1, PtO-ZnFb, 105 fs),5 similar to to the fastest one seen in nature (in photosystem II, P680* ↔ C670* equilibrium; time scale 100 ± 50 fs).6 To explain this drastic improvement by simply changing one atom, a significant increase in MO coupling was demonstrated using electronic spectroscopy, electrochemical findings, and DFT computations. We now report a further improvement by using a transplatinum(II) with two enaminothioketone ligands as a linker. As for the other homodimers and dyads studied before, results from electronic spectroscopy, electrochemical studies, and DFT calculations were used to explain the even faster energy transfer measured in this new system (Figure 1, PtS-ZnFb).

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RESULTS AND DISCUSSION All of the compounds studied are shown in Figure 1. The nickel(II) porphyrin monomers bearing an enaminoketone or an enaminothioketone external coordination site were previously described.7 All new porphyrin homodimers and dyads were obtained by classical methods in reasonable yields. The two homodimers PtS-NiNi and PtS-ZnZn, obtained by refluxing the respective nickel or zinc porphyrin in dichlorobenzene in the presence of Pt(acac)2, were isolated in 90% and 75% yield, respectively. Removal of the zinc(II) from the dimer PtS-ZnZn in acidic conditions gave the free base dimer PtS-FbFb, which was then remetalated with less than 1 equiv of Zn(OAc)2. After purification by column chromatography, the dyad PtS-ZnFb was isolated and fully characterized. The 1H NMR clearly Received: July 4, 2016

Figure 1. Molecular structures of the compounds studied. © XXXX American Chemical Society

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DOI: 10.1021/acs.inorgchem.6b01594 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry showed that the signals of dyad PtS-ZnFb were almost the sum of the signals of the two corresponding homodimers PtS-ZnZn and PtS-FbFb (Figure 2).

Figure 4. Electrostatic potential map of PtS-ZnFb (red and blue for electron rich and poor areas).

Figure 2. 1H NMR of two homodimers and of dyad PtS-ZnFb (pyrrolic area in CDCl3).

In the absence of X-ray structures, the geometries of the dimers and dyad were optimized by DFT calculations (dyad in Figure 3, dimers in ESI with Cartesian coordinates). In all cases,

Figure 5. Electronic spectra: sum of the spectra of the two homodimers (PtS-ZnZn + PtS-FbFb) in red and spectrum of the dyad PtS-ZnFb in blue.

exhibits bands covering the UV and visible range all the way to ∼850 nm in the near-IR region (see Experimental Section for peak position and absorptivity data), and bears a clear resemblance to those for the homodimer models PtS-ZnZn and PtS-FbFb (Figure 5). The sum of the individual spectra of the dimer units matches almost perfectly that for PtS-ZnFb. These findings were confirmed by the electrochemical data (a summary is provided in Table 1 and additional data in the Supporting Information). As expected, the electrochemical band gap decreases continuously going from PdO-NiNi to PtSNiNi. The splitting of the first oxidation waves in these homodimers also increases going from PdO-NiNi to PtS-NiNi. The splitting value of 280−290 mV measured for this last system is now comparable to the one found in highly

Figure 3. Side (a) and top (b) views of the optimized geometry of the dyad PtS-ZnFb.

the structures exhibit an obvious distortion due to the presence of the small nickel(II) ion and a fused phenyl in the porphyrin. The calculated electronic density map (Figure 4) indicates a higher concentration of density within the bis-enaminothioketone-Pt(II)-bridge consistent with the electron rich S, NH−, and Pt residues. The conjugated π-system also exhibits significant electronic density as expected. In a comparison of the electronic spectra of the nickel(II) porphyrin monomer and dimer PtS-NiNi, the electron delocalization is obvious. The Soret band is split in the dimer, and the lowest energy band is shifted bathochromically by almost 100 to 780 nm. The same observation could be made for the zinc and free base homodimers and for the zinc−free base dyad (Figure 5). The absorption spectrum of PtS-ZnFb

Table 1. Selected Electrochemical Data for the Nickel Porphyrin Homodimers compd PdO-NiNib PdS-NiNi PtO-NiNic PtS-NiNi

λmax in nm (in eV) lowest-energy band 696 732 727 780

(1.78) (1.69) (1.70) (1.58)

e-chem band gap (V)

E°ox2 − E°ox1 (in mV)

1.77 1.65 1.70 1.60

160 190 220 280−290

a

All data in volts. Experimental conditions: 0.1 M NBu4PF6 in dichloromethane, scan rate = 0.1 V s−1. E° = (Epc + Epa)/2 in volts vs Fc/Fc+. bFrom ref 7b. cFrom ref 5. B

DOI: 10.1021/acs.inorgchem.6b01594 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry conjugated, covalently linked porphyrin dimers reported earlier by the groups of Therien, Osuka, and Anderson.8 The role of the energy donor and acceptor is normally assigned on the basis of the position of the lowest energy absorption bands as well as the 0−0 peak of the fluorescence. As no fluorescence is detected at 298 K and a noisy signal is recorded at 77 K, only absorption data for PtS-ZnZn (804.2 (298 K), 800 nm (77 K)) and PtS-FbFb (805.5 (298 K), 802 nm (77 K)) in 2MeTHF are used (Supporting Information), which assign the donor to the [Zn] unit ([Zn] = zinccontaining chromophore). This assignment is fully expected for dyads composed of the [Zn] and [Fb] fragments,9 but interestingly the energy difference between the 0−0 peak positions is very small (∼20 ± 5 cm−1) compared to the other related dyad systems (590 ± 60 cm−1 (PdO-ZnZn vs PdOFbFb)4 and 370 ± 65 cm−1 (PtO-ZnZn vs PtO-FbFb)).5 Because the energy difference is small, heavy MO mixing is anticipated. This hypothesis was readily corroborated from a computational study. The DFT and TDDFT (B3LYP) computations provide an interpretation for these spectra. The frontier MO representations using the optimized geometries of the dimers and dyad indicate the presence of the anticipated π-system (i.e., the nature of the excited states are ππ*), which extends well over both units, notably in the HOMO and LUMO (Figure 6). The

Table 2. Relative Atomic Contributions (in %) of the Various Fragments in the Dyads PtS-ZnFb, PtO-ZnFb, and PdO-ZnFb H−1 [Zn] [Fb] Pt Aryls

7.5 77.7 1 13.8

[Zn] [Fb] Pt Aryls

8.5 77.0 0.6 13.9

[Zn] [Fb] Pd Aryls

2.0 97.1 0.2 0.7

H PtS-ZnFb 48.5 35.9 13.5 2.2 PtO-ZnFb 52.8 33.6 11.2 2.4 PdO-ZnFb 65.1 30.0 4.6 0.3

L

L+1

35.3 58.3 0.2 6.2

55.4 33.8 3.3 7.4

24.9 67.9 0.2 7.0

65.4 24.6 2.1 8.0

14.4 85.0 0.2 0.4

83.7 14.7 1.0 0.5

a H = HOMO; L = LUMO (see SI for dimers and other MOs). Substantial contributions are listed in bold.

more prone to electronic communication between the two chromophores in this MO. These trends also parallel that of the energy differences between the 0−0 peak positions in the homodimers as stated above. Essentially, as the size of the atom in the bridge increases (PdO → PtO → PtS), the MO coupling increases as well. No fluorescence band was observed in the vicinity of 800 nm using a conventional spectrometer. However, using a laser source and a Streak camera, very weak signals were indeed confidently detected at 77 K (SI), but again not at 298 K. The emission decays, τF’s, are less than the IRF profile in these cases (i.e., 14 ps). These values are shorter than those measured for PdO-ZnZn, PdO-FbFb, and PdO-ZnFb under the same conditions (respectively 77.2 ± 0.1, 93.1 ± 0.2, and 91.1 ± 0.2 ps), which indicate an accentuated heavy atom effect by the bis-enaminothioketone-Pt-bridge compared to that for the bisenaminoketone-Pd-bridge. Because these species are not fluorescent at 298 K, femtosecond transient absorption spectroscopy was used. Evidence for an accentuated MO coupling can also be obtained by comparing the rates of singlet energy transfer, kET(S1). Evidence for energy transfer was obtained from the comparison of the transient spectra of the dyad with those of the various individual units comprised within the dyad (i.e., model compounds). This is well-exemplified with the signal decaying on the nanosecond time scale (i.e., triplet state, Figure 7) and on the short picosecond time scale (i.e., singlet state; 0.18 ps (PtS-ZnZn), 0.60 ps (PtS-FbFb), and 0.50 ps (PtSZnFb), SI) for the dyad, which is almost identical to that for the PtS-FbFb dimer but not to that of PtS-ZnZn. These results are clearly indicative of an energy transfer 1[Zn]* → 1,3[Fb]*. The large decreases between τF’s at 77 K (Streak camera) and the singlet lifetimes measured by transient absorption spectroscopy at 298 K are certainly related to medium rigidity effect. The rate for energy transfer, kET(S1), is extracted from the rise time of the final product (i.e., acceptor), which should correspond to the decay of the donor. These were detected for PdO-ZnFb (650 fs)4 and PtO-ZnFb (105 fs).5 Attempts to detect the rise time of the transient species for PtS-ZnFb failed, as all species were formed within the excitation pulse (fwhm =

Figure 6. Representations of the frontier MOs for dyad PtS-ZnFb (energy in au, see Supporting Information for other MOs and those for the two homodimers).

reason why these two MOs are specifically monitored stems from TDDFT computations (below), which indicate that the lowest energy transitions are composed of almost exclusively HOMO → LUMO (95%). The computational results on the extended atomic contribution over both chromophores indicate the presence of MO coupling, a property that was also observed for the two previously reported dyads (PdO-ZnFb and PtOZnFb)4,5 and corresponding dimers. The atomic contributions for the frontier MOs for PtS-ZnZn are compared to those for PdO-ZnFb and PtO-ZnFb (Table 2).4,5 The MO mixing can be probed from the relative atomic contributions, which can range from 100/0−0/100% (uncoupled) to 50/50% (fully coupled). The atomic contribution ratios [Zn]/[Fb] for the HOMO vary from 65.1/30.0 → 52.8/33.6 → 48.5/35.9 and 14.4/85.0 → 24.9/67.9 → 35.3/58.3 for the LUMO going from PdO-ZnFb to PtO-ZnFb to PtS-ZnZn, respectively, indicating an increasing trend in the mixing. Moreover, the contribution of the bridging metal atom to the HOMO varies from 4.6% → 11.2% → 13.5% in this same order, indicating that the latter is C

DOI: 10.1021/acs.inorgchem.6b01594 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

chromophores (Table 2), it is now apparent that the Dexter mechanism is significantly accentuated in the PtS-ZnFb dyad. With consideration of the obvious contribution of the heavy atom effect [for example, τS1 values for PdO-FbFb, PtO-FbFb, and PtS-FbFb are, respectively, 59.7, 2.1, and 0.59 ps at 298 K (Table 3)], then the S1 manifold of the donor in the dyads is depleted by two main mechanisms: intersystem crossing and energy transfer, as illustrated in Figure 8. To approximate the

Figure 7. Top: Comparison of the triplet state transient absorption spectra (i.e., the major product after the probe experiment) of the PtSFbFb and PtS-ZnZn dimers and the PtS-ZnFb dyad in MeTHF at 298 K (λmax = 795 nm; pulse width = 49 fs). Bottom: Normalized kinetic traces of the same compounds monitored at the maximum of the nanosecond-lived transient bands at ∼550 nm. The short component in the PtS-FbFb decay is due to a minor component perceptible at this monitoring wavelength associated with the relaxation of the S1 state (i.e., ∼588 fs).

Figure 8. Scheme showing the two possible main nonradiative pathways depleting the S1 state in the dyads.

rates for intersystem crossing, kisc, the fluorescence lifetime of the Zn-monomer without any heavy atom (τF = 0.85 ns for the enaminoketone monomer4) is compared to that for the bridgeZnZn dimers (Table 3). Using kisc ∼ [1/τS1(bridge-ZnZn)] − [1/τS1(Zn-monomer)], the expected trend is observed (Table 4; kisc varies as PdO < PtO < PtS). The efficiency of the energy transfer, η, given by η = [(1/τ(S1)) − (1/τ°(S1))]/(1/τ(S1)),9 indicates a decrease going from bridge = PdO → PtO → PtS. Assuming that the energy transfer and intersystem crossing are the two dominant processes deactivating the S1 level of the donor, here Zn-chromophore, then the term 100% − η should be the portion of the S1 species undergoing the intersystem crossing. In this cases, these estimated values are found increasing from bridge = PdO → PtO → PtS, as well. By calculating the ratios kET /(kET + kisc) for the three dyads and comparing them with η we obtain a very good correspondence (Table 4).

49 fs). A clear demonstration is provided in Figure 6 (bottom) where, for all three investigated compounds, the transient signals were generated within the laser pulse. In conclusion, the energy transfer process in PtS-ZnFb occurred faster than 49 fs. The kET(S1) value is given by (1/τ(S1)) − (1/τ°(S1)), where τ(S1) and τ°(S1) are the singlet lifetimes of the donor chromophore (here [Zn]) in the presence (15 × 10 8.3 × 1012 1.5 × 1012

12

eff (η) %

kisc (s−1)a

100% − η

kET + kisc (s−1)b

kET/(kET + kisc)

73 87 98

5.6 × 10 1.3 × 1012 2.3 × 1010

27 13 2

>20.6 × 1012 9.6 × 1012 1.523 × 1012

∼0.73 ∼0.86 ∼0.98

12

τS1(Zn-monomer) is taken as 0.85 ns for all three cases. bFor convenience, the significant figures as well as the “>” uncertainty limit are not taken into account to permit comparison. a

dual CCD camera of 64 × 1024 pixels sensitive between 200 and 1100 nm (S7030, Spectronic Devices). The delay line permitted probing up to 4 ns with an accuracy of ∼4 fs. The results were analyzed with the program Glotaran (http://glotaran.org) permitting extraction of a sum of independent exponentials (I(λ, t) = C1(λ)exp(−t/τ1) + C2(λ)exp(−t/τ2) + ...) that fits the whole 3D transient map. Computations. All density functional theory (DFT) and time dependent density functional theory (TD-DFT) calculations were performed with Gaussian 0912 at the Université de Sherbrooke with the Mammouth supercomputer supported by Le Réseau Québécois De Calculs Hautes Performances. The DFT geometry optimizations as well as TD-DFT calculations13−22 were carried out using the B3LYP method. A 6-31g* basis set was used for the central chromophores, and a 3-21g* basis set was used for solubilizing (3,5-ditertbutylphenyl) groups.23−28 VDZ (valence double ζ) with SBKJC effective core potential was used for the platinum atoms.23−28 A THF solvent field was applied to all calculations. The calculated absorption spectra were obtained from GaussSum 2.1.29 Synthesis. All the Ni(II) porphyrins were synthesized with both 4-tbutylphenyl and 3,5-di-tbutylphenyl. Compounds substituted with 4-tbutylphenyl groups were used for spectrophotometric and electrochemical measurements (less electrode passivation). Photochemical measurements were performed with the compounds substituted with di-tbutylphenyl groups. The monomeric porphyrins S−Ni and S−Zn (Ar = 3,5-di-tbutylphenyl) were prepared as previously described.7 The preparation of S−Ni (Ar = 4-tbutylphenyl) can be found in the SI. Synthesis of PdS-NiNi (Ar = 4-tbutylphenyl). A solution of the nickel(II) porphyrin S−Ni (50 mg, 55.8 μmol) in toluene (30 mL) was refluxed in the presence of Pd(OAc)2 (6.2 mg, 27.9 μmol, 0.5 equiv) under argon for 2 h. The solvent was removed under vacuum, and the products were purified by column chromatography (silica gel, toluene/cyclohexane, 1/1). Two isomers (cis and trans coordination geometry around Pd(II)) were obtained. The cis-complex was transformed into the trans-complex by refluxing it in 1,2-dichloroethane for 30 min. The trans isomer of PdS-NiNi (aryl =4-tbutylphenyl) was isolated as a brown powder after recrystallization from dichloromethane/methanol (50.4 mg, 26.5 μmol, 95%). 1H NMR (400 MHz, CDCl3, 25 °C): δ = 12.25 (S, 1H; NH), 9.13−9.10 (m, 2H; Hpyrr + HcyclPh), 8.71 (d, 3J = 4.9 Hz, 1H; Hpyrr), 8.45 (d, 3J = 4.9 Hz, 1H; Hpyrr), 8.39 (d, 3J = 4.8 Hz, 1H; Hpyrr), 8.30 (d, 3J = 4.8 Hz, 1H; Hpyrr), 8.27 (d, 3J = 4.9 Hz, 1H; Hpyrr), 8.10 (d, 3J = 7.6 Hz, 1H; HcyclPh), 7.86−7.79 (m, 6H; Hortho), 7.74−7.63 (m, 7H; 6Hmeta + 1HcyclPh), 7.54−7.50 (br ddd; HcyclPh), 6.16 (s, 1H; NH), 1.55 (s, 9H; HtBu), 1.54 (s, 9H; HtBu), 1.52 ppm (s, 9H; HtBu). 13C NMR (125 MHz, CDCl3, 25 °C): δ = 193.5, 164.2, 152.6, 151.0, 150.9, 144.2, 143.9, 142.9, 141.5, 141.1, 140.3, 138.9, 136.8, 136.7, 135.1 (CH), 134.7 (CH), 134.2, 133.2 (CH), 132.9 (CH), 132.2 (CH), 131.9 (CH), 131.8 (CH), 130.9 (CH), 130.83 (CH), 130.77 (CH), 130.4 (CH), 129.8, 129.4 (CH), 126.5 (CH), 126.0 (CH), 124.3, 124.2 (CH), 124.1 (CH), 122.9, 121.1, 119.1, 103.9, 35.1, 34.89, 34.88, 31.62 (CH3), 31.59 (CH3), 31.56 ppm (CH3). UV−vis (CH2Cl2): λmax (ε) = 380 (55 800), 421 (69 500), 464 (50 600), 487 (90 100), 557 (8300), 623 (11 500), 668 nm (22 000 M−1 cm). HRMS (ESI-TOF) (m/z) Calcd for C57H52N5NiS+: 896.3291. Found for [M + H]+: 896.3352. Synthesis of PtS-NiNi (Ar = 4-tbutylphenyl). A solution of the nickel(II) porphyrin S−Ni (50 mg, 55.8 μmol) in chlorobenzene (30 mL) was refluxed in the presence of Pt(acac)2 (11.0 mg, 27.9 μmol, 0.5 equiv) under argon for 6−7 h. The solvent was removed under vacuum, and the products were purified by column chromatography

macrocycles. A platinum(II) linker and enaminothioketone external coordination sites are probably the optimum association for maximum electronic delocalization, but a heavy atom effect may decrease the efficiency.

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EXPERIMENTAL SECTION

General. 1H and 13C NMR spectra were recorded on BRUKER Avance 400 or 500 MHz (cryoprobe for 13C) using CDCl3 or C2D2Cl4 as solvents. Chemical shifts are given in ppm relative to TMS. 1H, 13C, DEPT, and COSY spectra of all new compounds are shown in the Supporting Information. ESI-TOF MS experiments were performed on a Bruker daltonics microTOF spectrometer. Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) were obtained with a BRUKER Autoflex II TOF-TOF instrument equipped with a nitrogen laser (337 nm) using dithranol as matrix. Routine UV−vis spectra were measured on a HP diode-array spectrometer, and extinction coefficients were measured on a Cary 5000 UV−vis−NIR spectrometer. Solvents used for reactions or chromatographic separations were distilled from sodium/benzophenone ketyl (THF and toluene) or calcium hydride (dichloromethane). Thin-layer chromatography and column chromatography were performed with Merck TLC silica gel 60 F254 and Kieselgel Si 60 (40−63 μm). Electrochemical Measurements. Dichloromethane was dried over molecular sieves and kept under argon. Tetrabutylammonium hexafluorophosphate was used as received (Fluka, puriss). The electrochemical experiments were carried out in dichloromethane containing 0.1 M NBu4PF6 in a three-electrode cell. The working electrode was a glassy carbon electrode (3 mm diameter). The auxiliairy and the pseudoreference electrodes were Pt wires. All potentials were referenced to the ferrocene/ferrocenium (Fc/Fc+) couple used as an internal standard. The cell was connected to a computerized electrochemical device Autolab (Eco Chemie BV, Utrecht, The Netherlands) driven by a GPES software. Instruments. 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 77 K. Steady state UV−vis emission spectra were acquired on an Edinburgh Instruments FLS980 spectrometer equipped with single monochromators, while steady state near-infrared (NIR) emissions were measured by QuantaMaster 400 phosphorimeter from Photon Technology International (PTI), excited by a xenon lamp, and recorded with a NIR PMT-7-B detector. All emission spectra were corrected for instrument response. Fast Kinetic Fluorescence Measurements. The fluorescence spectra were measured with a Streak camera. The decays were performed using the output of an OPA (OPA-800CF, SpectraPhysics) operating at λexc = 400 nm, pulse width of 100 fs, rep rate = 1 kHz, pulse energy = 2.2 μJ/pulse, spot size = ∼1 mm, and a Streak camera (Axis-TRS, Axis Photonique Inc.) with less than 6 and 8 ps time resolution, respectively, at 77 K. The results were also globally analyzed with the program Glotaran which permitted the extraction of a sum of independent exponentials (I(λ, t) = C1(λ)exp(−t/τ1) + C2(λ)exp(−t/τ2) + ...). Femtosecond Transient Absorption Measurements. The femtosecond transient spectra and decay profiles were acquired on a homemade system using the SHG of a Soltice (Spectra Physics) Tisapphire laser (λexc = 795 nm; fwhm = 49−58 fs; pulse energy = 0.3 μJ per pulse, rep rate = 500 Hz; spot size = ∼500 μm), a white light continuum generated inside a sapphire window, and a custom-made E

DOI: 10.1021/acs.inorgchem.6b01594 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry (silica gel, toluene/cyclohexane, 1/1). Two isomers (cis and trans coordination geometry around Pt(II)) were obtained. The cis-complex was isolated and transformed into the trans-complex by refluxing it in 1,2-dichloroethane for 4 h. Purification by column chromatography afforded the platinum(II) dimer PtS-NiNi after recrystallization from dichloromethane/methanol (25.4 mg, 12.8 μmol, 46%). 1H NMR (400 MHz, C2D2Cl4, 75 °C): δ = 9.28 (s, 2H; NH), 9.12 (d, 3J = 8.2 Hz, 2H; HcyclPh), 9.01 (d, 3J = 4.9 Hz, 2H; Hpyrr), 8.65 (d, 3J = 4.9 Hz, 2H; Hpyrr), 8.34−8.32 (m, 6H; 4Hpyrr + 2HcyclPh), 8.20 (d, 3J = 4.9 Hz, 2H; Hpyrr), 8.04−8.02 (m, 4H; Hortho), 7.94−7.82 (m, 16H; 8Hortho + 4Hmeta + 2Hpyrr + 2HcyclPh), 7.70−7.64 (m, 10H; 8Hmeta + 2HcyclPh), 1.70 (s, 18H; HtBu), 1.57 (s, 18H; HtBu), 1.56 ppm (s, 18H; HtBu). 13C NMR (125 MHz, C2D2Cl4, 25 °C): δ = 160.0, 152.4, 150.4, 148.5, 146.3, 142.6, 142.5, 141.1, 139.7, 138.1, 135.9, 135.7, 134.4 (CH), 133.1, 132.4 (CH), 132.2, 132.0 (CH), 131.4 (CH), 130.5 (CH), 130.1 (CH), 129.7 (CH), 128.4 (CH), 127.8 (CH), 127.0, 126.1 (CH), 125.4 (CH), 124.1, 123.7 (CH), 123.6 (CH), 122.7, 119.8, 114.2, 102.3, 98.9, 34.6, 34.21, 34.21, 31.2 (CH3), 31.04 (CH3), 31.01 ppm (CH3). UV−vis (CH2Cl2): λmax (ε) = 339 (33 100), 387 (68 100), 449 (67 400), 497 (60 200), 532 (72 700), 604 (16 200), 655 (24 200), 713 (13 400), 745 (8300), 780 nm (9800 M−1 cm). HRMS (ESI-TOF) (m/z) Calcd for C114H100N10Ni2PtS2+: 1983.5928. Found for M+: 1983.5823. Synthesis of PtS-ZnZn (Ar = 3,5-ditbutylphenyl). The nickel(II) porphyrin S-Ni (210 mg, 197 μmol) was demetalated in a TFA/ H2SO4 solution (12 mL, 5/1) for 20 min. After addition of dichloromethane (15 mL), the mixture was poured on ice. After neutralization with a concentrated sodium hydroxide aqueous solution (3 times 25 mL), the organic layer was washed with water (3 times 25 mL) and dried over sodium sulfate. The solvent was evaporated under reduced pressure in the presence of triethylamine, and the crude free base (140 mg) was redissolved in chloroform (30 mL); a solution of Zn(OAc)2·2H2O (45 mg, 210 μmol) in methanol (2 mL) was added. After 15 min of reaction, the solvents were removed, and the zinc(II) porphyrin S-Zn was obtained after recrystallization from dichloromethane/methanol (95 mg, 86 μmol, 43%). A solution of this solid (34.6 mg, 31.4 μmol) in 1,2-dichlorobenzene (10 mL) was refluxed in the presence of Pt(acac)2 (6.8 mg, 17.3 μmol, 0.55 equiv) under argon for 2 h. The solvent was removed under vacuum, and the product was purified by column chromatography (silica gel, toluene). The platinum(II) dimer PtS-ZnZn was obtained after crystallization from dichloromethane/methanol (27.3 mg, 11.8 μmol, 75%). 1H NMR (400 MHz, CDCl3, 45 °C): δ = 9.73 (s, 2H; NH), 9.58 (dd, 3J = 8.0 Hz, 4J = 1.3 Hz, 2H; HcyclPh), 9.34 (d, 3J = 4.7 Hz, 2H; Hpyrr), 8.91 (d, 3 J = 8.2 Hz, 2H; HcyclPh), 8.71 (d, 3J = 4.7 Hz, 2H; Hpyrr), 8.50 (d, 3J = 4.7 Hz, 2H; Hpyrr), 8.47−8.46 (m, 4H; 2Hpyrr + 2Hpara), 8.40 (d, 3J = 4.5 Hz, 2H; Hpyrr), 8.13−8.09 (m, 2H; HcyclPh), 8.00−7.98 (m, 8H; Hortho), 7.93−7.89 (m, 6H; 2Hpyrr + 2HcyclPh + 2Hortho), 7.79 (t, 4J = 1.8 Hz, 2H; Hpara), 7.74 (t, 4J = 1.8 Hz, 2H; Hpara), 1.67 (s, 36H; HtBu), 1.55 (s, 36H; HtBu), 1.50 ppm (s, 36H; HtBu). 13C NMR (125 MHz, CDCl3, 25 °C): δ = 160.8, 154.9, 152.1, 151.8, 150.3, 149.9, 149.4, 148.9, 148.8, 148.3, 148.0, 147.4, 142.4, 141.0, 141.0, 138.6, 137.1 (CH), 134.9, 133.5, 132.9 (CH), 132.5 (CH), 130.8 (CH), 130.5 (CH), 129.5 (CH), 129.4 (CH), 129.2 (CH), 129.0 (CH), 128.4, 128.3 (CH), 128.0 (CH), 127.6, 127.5, 125.2 (CH), 122.5 (CH), 121.2 (CH), 121.1 (CH), 116.7, 105.9, 35.5, 35.1, 35.0, 31.9 (CH3), 31.8 (CH3), 31.7 ppm (CH3). UV−vis (CH2Cl2): λmax (ε) = 402 (160 000), 476 (153 000), 507 (121 000), 543 (161 000), 705 (54 800), 724 (50 700), 794 nm (24 600 M−1cm). HRMS (ESITOF) (m/z) Calcd for C138H150N10PtS2Zn22+: 1166.9859. Found for [M + 2H]2+: 1166.9853. Synthesis of PtS-ZnFb and PtS-FbFb (Ar = 3,5-ditbutylphenyl). A solution of dichloromethane/TFA (0.6 mL, 10/1) was added to a solution of dimer PtS-ZnZn (25 mg, 10.7 μmol) in dichloromethane/ toluene (6 mL, 5/1). After 10 min, the reaction was quenched with water (10 mL). The organic fraction was separated, dried over sodium sulfate, and filtered on alumina (dichloromethane, 1% Et3N). After evaporation of the solvent the residue was dissolved in chloroform (10 mL) and stirred with Zn(OAc)2·2H2O (1 mg, 4,6 μmol) in MeOH (1 mL) for 15 min. After evaporation of the solvents, the three products

of the reaction (PtS-ZnZn, PtS-ZnFb, and PtS-FbFb) were separated by column chromatography (silica gel, cyclohexane/dichloromethane, 2/1, 1% Et3N). The dimer PtS-FbFb (12.8 mg, 5.8 μmol) and dyad PtS-ZnFb (8,3 mg, 3,6 μmol) were obtained after crystallization from dichloromethane/methanol. Data for PtS-FbFb follow. 1H NMR (400 MHz, CDCl3, 45 °C): δ = 9.82 (s, 2H; NH), 9.54 (dd, 3J = 8.0 Hz, 4J = 1.3 Hz, 2H; HcyclPh), 9.36 (d, 3J = 4.9 Hz, 2H; Hpyrr), 8.93 (d, 3J = 8.1 Hz, 2H; HcyclPh), 8.71 (d, 3J = 4.9 Hz, 2H; Hpyrr), 8.58 (d, 3J = 5.0 Hz, 2H; Hpyrr), 8.46 (t, 4J = 1.8 Hz, 2H; Hpara), 8.43 (d, 3J = 4.5 Hz, 2H; Hpyrr), 8.41 (d, 3J = 4.5 Hz, 2H; Hpyrr), 8.11 (ddd, 3J = 8.2 Hz, 3J = 7.0 Hz, 4J = 1.3 Hz, 2H; HcyclPh), 8.06 (d, 3J = 5.0 Hz, 2H; Hpyrr), 8.03 (d, 4 J = 1.8 Hz, 4H; Hortho), 8.00 (d, 4J = 1.8 Hz, 4H; Hortho), 7.96−7.92 (m, 6H; 2HcyclPh + 4Hortho), 7.80 (t, 2H, 4J = 1.8 Hz; Hpara), 7.75 (t, 2H, 4J = 1.8 Hz; Hpara), 1.67 (s, 36H; HtBu), 1.56 (s, 36H; HtBu), 1.51 (s, 36H; HtBu), −0.15 ppm (s, 4H; Hfb). 13C NMR (125 MHz, CDCl3, 25 °C): δ = 162.9, 154.1, 153.5, 152.3, 150.3, 149.8, 149.1, 148.9, 146.6, 142.2, 140.6, 140.5, 138.2, 137.9, 137.7, 137.0 (CH), 136.3, 134.7, 133.54 (CH), 133.52, 133.3 (CH), 129.49 (CH), 129.45 (CH), 129.2, 128.7 (CH), 128.6 (CH), 128.5 (CH), 128.4 (CH), 127.9 (CH), 126.2 (CH), 125.9 (CH), 125.8, 125.7 (CH), 124.3, 122.7 (CH), 121.4 (CH), 121.2 (CH), 114.7, 106.0, 35.5, 35.1, 35.0, 31.9 (CH3), 31.8 (CH3), 31.7 ppm (CH3). UV−vis (CH2Cl2): λmax (ε) = 396 (128 000), 487 (155 000), 554 (93 900), 618 (29 900), 699 (29 100), 793 nm (15 800 M−1 cm). HRMS (ESI-TOF) (m/z) Calcd for C138H154N10PtS22+: 1105.0721. Found for [M + 2H]2+: 1105.0718. Data for PtS-ZnFb follow. 1H NMR (400 MHz, CDCl3, 45 °C): δ = 9.82 (s, 1H; NH), 9.74 (s, 1H; NH), 9.58−9.54 (m, 2H; HcyclPh), 9.36 (d, 3J = 4.9 Hz, 1H; Hpyrr), 9.34 (d, 3J = 4.9 Hz, 1H; Hpyrr), 8.94−8.90 (m, 2H; HcyclPh), 8.71−8.70 (m, 2H; Hpyrr), 8.58 (d, 3J = 4.9 Hz, 1H; Hpyrr), 8.50 (d, 3J = 4.6 Hz, 1H; Hpyrr), 8.47−8.46 (m, 3H; 2Hpara + Hpyrr), 8.42−8.40 (m, 3H; Hpyrr), 8.13−8.09 (m, 2H; HcyclPh), 8.05 (d, 3 J = 5.0 Hz, 1H; Hpyrr), 8.03 (d, 4J = 1.8 Hz, 2H; Hortho), 8.00−7.98 (m, 6H, Hortho), 7.96−7.89 (m, 6H; 2HcyclPh + 4Hortho), 7.80−7.79 (m, 2H; Hpara), 7.76−7.74 (m, 2H; Hpara), 1.67 (br s, 36H; HtBu), 1.56 (br s, 36H; HtBu), 1.504 (s, 18H; HtBu), 1.500 (s, 18H; HtBu), −0.15 ppm (s, 2H; Hfb). 13C NMR (125 MHz, CDCl3, 25 °C): δ = 162.9, 160.8, 154.9, 154.1, 153.5, 152.3, 152.1, 151.8, 150.4, 150.3, 149.9, 149.8, 149.4, 149.1, 148.93, 148.90, 148.8, 148.3, 148.0, 147.4, 146.6, 142.4, 141.04, 140.99, 140.6, 140.5, 138.6, 137.9, 137.7, 137.1 (CH), 137.0 (CH), 136.3, 134.9, 134.7, 133.6, 133.5 (CH), 133.4, 133.3 (CH), 132.9 (CH), 132.5 (CH), 130.8 (CH), 130.5 (CH), 129.53 (CH), 129.49 (CH), 129.45 (CH), 129.4 (CH), 129.24, 129.15 (CH), 129.04, 129.01 (CH), 128.7 (CH), 128.54 (CH), 128.53 (CH), 128.39 (CH), 128.36, 128.3 (CH), 128.2, 127.97 (CH), 128.0 (CH), 127.6, 127.5, 126.2 (CH), 125.9 (CH), 125.73, 125.70 (CH), 125.2 (CH), 124.3, 122.7 (CH), 122.5 (CH), 121.4 (CH), 121.2 (CH), 121.1 (CH), 116.7, 114.7, 106.0, 105.9, 35.5, 35.1, 35.02, 35.01, 31.91 (CH3), 31.90 (CH3), 31.78 (CH3), 31.76 (CH3), 31.7 ppm (CH3). UV−vis (CH2Cl2): λmax (ε) = 399 (119 000), 485 (129 000), 548 (89 900), 620 (22 500), 701 (32 500), 793 nm (15 400 M−1 cm). HRMS (ESI-TOF) (m/z) Calcd for C138H150N10PtS2Zn+: 2270.0426. Found for M+: 2270.0420. To ensure that none of the three dimers (PtS-ZnZn, PtS-ZnFb, and PtS-FbFb) was polluted by small amounts of another dimer (indistinguishable by NMR or elemental analyses, but clearly separated on column or on thin layer chromatography), we passed each individual dimer again through a silica gel column and recrystallized again the compounds before running the photophysical experiments.

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DOI: 10.1021/acs.inorgchem.6b01594 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Continuous financial support from the Université de Strasbourg and the CNRS are acknowledged. This project was also partly financed by the Labex CSC (ANR-10-LABX-0026_CSC). H.D. thanks the French Ministry of Research for a Ph.D. fellowship. This research was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC), the Fonds de Recherche du QuébecNature et Technologies (FRQNT), the Centre Québéquois des Matériaux Fonctionnels (CQMF), and the Centre d’Etudes des Matériaux Optiques et Photoniques de l’Université de Sherbrooke (CEMOPUS).

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DOI: 10.1021/acs.inorgchem.6b01594 Inorg. Chem. XXXX, XXX, XXX−XXX