Note Cite This: J. Org. Chem. 2018, 83, 5282−5287
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Porphyrin-Oligopyridine Triads: Synthesis and Optical Properties Nuno M. M. Moura,*,†,‡ Inês F. A. Mariz,§ José A. S. Cavaleiro,† Artur M. S. Silva,† Carlos Lodeiro,‡,∥ José M. G. Martinho,§ Ermelinda M. S. Maçôas,§ and Maria G. P. M. S. Neves*,† †
QOPNA and Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal BIOSCOPE Group, LAQV@REQUIMTE, Chemistry Department, Faculty of Science and Technology, University NOVA of Lisbon, 2829-516, Monte da Caparica, Portugal § CQFM and IN-Institute of Nanoscience and Nanotechnology, Instituto Superior Técnico, University of Lisbon, Av. Rovisco Pais, 1049-001 Lisbon, Portugal ∥ ProteoMass Scientific Society, Madan Parque, Rua dos Inventores 2825-182, Monte da Caparica, Portugal ‡
S Supporting Information *
ABSTRACT: The synthesis of two triads with two porphyrinyl units linked by oligopyridine derivatives and a new βfunctionalized porphyrin-dihydroazepine is described. One of the porphyrin-oligopyridine triads has a quinquepyridine unit connecting the porphyrins β-pyrrolic positions, while the other one has an asymmetric quaterpyridine with one of the pyridines fused to the porphyrin. All compounds have fluorescence emission quantum yields in the range of meso-tetraphenylporphyrin (16−22%).
P
porphyrin-2-ylpyridines.10 The procedure involved the condensation of β-formyl-5,10,15,20-tetraphenylporphyrin (βCHOTPP)14 with aryl methyl ketones in the presence of ammonium acetate. In this communication, we report an efficient synthetic approach giving access to triads 6 and 7 (Scheme 1). In triad 6, the spacer is a quaterpyridine unit with one of the pyridines fused to one of the porphyrin units, while, in triad 7, two porphyrins are linked by β-pyrrolic positions to a quinquepyridine. The optical properties of triads 6 and 7 are discussed and compared with those of the parent compound and of the relevant intermediates produced. Having in mind their potentialities in functional materials for therapy and imaging applications, the two-photon absorption spectra in the near-infrared (NIR) were measured. The photophysical properties are also dependent on the adopted distorted geometry. In the strategy outlined in Scheme 1, it is envisaged that the symmetrical bis-porphyrin derivative 2 could be an excellent template to reach in each chalcone unit Krö hnke-type porphyrin-2-ylpyridines. This template was obtained through the condensation of free base β-CHOTPP 1 with 0.5 equiv of 2,6-diacetylpyridine in the presence of piperidine and catalytic amounts of La(OTf)3. The reaction was performed in refluxing
yridines are relevant N-heterocycles playing a key role in several fields, namely, as precursors of functional materials, agrochemicals, and pharmaceuticals.1 Molecules bearing oligopyridine units are important building blocks for polymer science and supramolecular chemistry, affording systems with potential applications in organic solar cells, functional materials, catalysis, sensors, and medicine.2−5 The most popular synthetic strategies used to prepare oligopyridines are based on (i) condensation, (ii) cycloaddition, and (iii) metal-mediated coupling reactions.2−4,6 In general, these methodologies afford symmetrical oligopyridines with a C2v symmetry.7 However, the number of reports describing the synthetic access to oligopyridines bearing other chromophores is limited due to the multistep synthetic pathways required.8 Tetrapyrrolic macrocycles are an attractive class of compounds due to their unique physicochemical features and their use in a wide range of applications. Porphyrins have been successfully used as catalysts, in the development of advanced biomimetic models for photosynthesis, as components of electronic devices, sensors, and drugs.9 In the literature, the scarce number of porphyrinic derivatives bearing terpyridine units located at meso- and β-positions is lacking considering their recently recognized potential as sensors and photosensitizers.10−13 In 2012, we reported a strategy giving access to a βfunctionalized porphyrin bearing a terpyridine unit directly attached to one of the pyrrolic units, the Kröhnke-type © 2018 American Chemical Society
Received: January 23, 2018 Published: April 12, 2018 5282
DOI: 10.1021/acs.joc.8b00208 J. Org. Chem. 2018, 83, 5282−5287
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The Journal of Organic Chemistry Scheme 1. Synthetic Route to Porphyrin Derivatives 6 and 7
Figure 1. Structures of other compounds isolated during the synthesis of template 2.
by its 13C NMR spectrum which shows a signal near δ 189.0 ppm corresponding to the two carbonyl carbons from the α,βunsaturated ketone moieties. Compound 3 ([M + H]+ ion at m/z = 788.3) shows two signals at δ 199.7 and δ 188.5 ppm due to the resonances of the carbonyl carbon from the α,βunsaturated ketone moiety and of the acetyl group, respectively. Compound 5 is an interesting compound resulting from a parallel reaction of β-CHOTPP 1 with piperidine. The structure was unambiguously supported by its mass spectrum, which shows the [M + H]+ ion at m/z = 708.2 and by 1D and 2D NMR studies (see the Supporting Information, Figures S16−S23). The 1H NMR spectrum in addition to the characteristic signals of the porphyrinic macrocycle shows two broad signals at δ 7.6 ppm and δ 6.5 ppm; these are due to the resonances of the double bond H-2′ and H-6′ from the dihydroazepine moiety. In the aliphatic region, two triplets at δ 3.7 ppm and δ 2.8 ppm due to the resonances of H-3′ and H-5′ are displayed and also a quintet at δ 1.8 ppm which is due to the resonance of H-4′. The formation of this unexpected derivative can be explained by the formation of an iminium salt between piperidine and the porphyrin formyl group, followed
toluene, and after the usual workup, the desired chalcone 2 was isolated in 32% yield, being accompanied by the mono derivative 3 (30%) (Figure 1). Further reaction of this derivative with β-CHOTPP can also afford the bis-chalcone 2 in 71%. In these syntheses, two minor derivatives from the reaction of β-CHOTPP 1 with piperidine were also isolated, the dimer 4 (8%) previously reported by us15 and the unexpected new porphyrin-dihydroazepine derivative 5 in 15% (Figure 1). The structures of all compounds were unambiguously confirmed by 1D, and 2D NMR studies and their molecular formulas were confirmed by HRMS (Supporting Information). The mass spectrum of the desired compound 2 showed a peak at m/z = 1412.5 corresponding to the expected [M + H]+ molecular ion. Important features in its 1H NMR spectrum are the singlet at δ 9.0 ppm corresponding to the resonance of the β-pyrrolic protons H-3, and a doublet at ca. δ 8.3 ppm due to the resonance of the two β-protons from the α,β-unsaturated ketone moieties with a coupling constant of 15.6 Hz. These obtained results confirm the trans configuration of both double bonds.16 The high symmetry of this molecule is also confirmed 5283
DOI: 10.1021/acs.joc.8b00208 J. Org. Chem. 2018, 83, 5282−5287
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The Journal of Organic Chemistry Scheme 2. Mechanistic Pathway Proposed for the Synthesis of Compound 6
Figure 2. Absorption (A and B) and emission (C and D) spectra of 1−7 in DMF.
fused at the β-porphyrin position. The mass spectrum shows a peak at m/z = 1509.5 corresponding to the molecular ion [M + H]+ of 6, and the proposed structure was unambiguously established by NMR spectroscopy (1D and 2D). The 1H NMR of compound 6 shows two singlets at δ −2.55 ppm and δ −2.72 ppm, corresponding to the resonances of inner core N-H, which demonstrates the presence of two different free base porphyrinic moieties. The asymmetry in the molecule is also proved by the signals assigned to the resonances of H-3′ and H5′ of the tri-substituted pyridine ring, which appear as doublets with small coupling constants (J = 1.5 Hz). The presence of the β-fused pyrido[2,3-b]porphyrin moiety was also confirmed by the absence of the H-3 signal of one of the porphyrinic units in the 1H NMR spectrum low field region. The proton assignments were performed with the support by 2D COSY NMR (see the Supporting Information, Figures S24−S32). The synthesis of compound 6 shows that, after the formation of the first terpyridine unit, the intermediate can react with NH3 from ammonium acetate, affording the corresponding imine. The obtained intermediate can then suffer an intramolecular aza-Diels−Alder cycloaddition, followed by thermal dehydrogenation (Scheme 2).
by ring-opening and further closure to a seven-membered ring. After this ring expansion, an oxidative step takes place, affording derivative 5 (see Scheme S1 in the Supporting Information). The condensation of 2 with 2-acetylpyridine was performed in the presence of ammonium acetate and La(OTf)3 under experimental conditions that favor the synthesis of Kröhnketype pyridines. The reaction was performed in refluxing toluene under a N2 atmosphere, and after 18 h, the total consumption of 2 was seen by TLC and two more polar compounds were obtained. After the workup and purification, the spectroscopic data of the more polar and major product (obtained in 52% yield) confirmed the synthesis of derivative 7. Its mass spectrum showed a base peak at m/z = 1612.5 corresponding to the [M + H]+ ion, and the 1H NMR spectrum was in accordance with a symmetric molecule (see the Supporting Information, Figures S33−S36), as it is shown by the resonances of H-3 and N-H protons of both porphyrin units as being two singlets, respectively, at δ 9.0 and δ −2.6 ppm. The duplet with a coupling constant of J 1.6 Hz centered at δ 8.1 due to the resonance of H-3′ from the two tri-substituted pyridine rings also support a highly symmetric structure. The less polar compound isolated in 21% yield was identified as the quaterpyridine triad 6 which contains one pyridine unit 5284
DOI: 10.1021/acs.joc.8b00208 J. Org. Chem. 2018, 83, 5282−5287
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The Journal of Organic Chemistry
decays possibly due to a distribution of ground state conformers that originate a distribution of lifetimes. Within our observation window (790−920 nm), the twophoton absorption (TPA) spectra are similar in all the compounds with a relatively unstructured band increasing in intensity toward the lower wavelengths (Figure S38 in the Supporting Information). The maximum TPA cross-sectional values estimated at 790 nm range between 3.5 and 17 GM. These values are in good agreement with those reported for the TPP standard (12 GM at 790 nm).18 Compounds 2 and 3 with a vinyl group attached to the β-position have the highest TPA cross section. The fact that the bichromophoric compounds do not show a higher two-photon absorption cross section compared to the parent compounds reflects the limited πelectronic delocalization due to the deviation from planarity of the molecules. The various strategies that can be followed to create high TPA in porphyrin arrays have been reviewed earlier.19,20 Ensuring planarity between the meso-substituents and the porphyrin core is known to provide a large enhancement of the TPA cross section in bis(porphyrin)substituted squarines with a TPA cross section higher than 103 GM.21 In summary, a synthetic approach was developed leading to new oligopyridines bearing porphyrin units in good yields. This synthetic methodology can be easily modified to obtain other triads with planar geometry and an extended conjugation length. All compounds have high fluorescence quantum yields. The triads (2, 4, 6, and 7) were shown to have similar optical properties to those of the single chromophoric compounds (1 and 3) due to the reduced π-conjugation between the porphyrin moieties and the β-pyrrolic substituents. The porphyrin-oligopyridines triads described in this work show a high potential to be explored in supramolecular chemistry via grid formation or complexation at pyridines nitrogens.
Considering the interesting features of the isolated compounds, the one-photon and two-photon absorption of all derivatives 2−7 was studied and compared with those of βCHOTPP 1. The linear and nonlinear optical properties of the porphyrin and bis-porphyrin derivatives in DMF are summarized in Table S1 (Supporting Information). Figure 2 shows the absorption and emission spectra corresponding to the mono-porphyrin derivatives (panels A and C on the left) and to the bis-porphyrin derivatives (panels B and D on the right). All the synthesized compounds show typical absorption features of the meso-tetraarylporphyrins, with intense Soret bands in the 417−436 nm region and the weak quartet of Qbands in the 500−700 nm region. The relative intensity of the Q-bands quartet is expected to be sensitive to the type and position of the substituents in the macrocyclic ring, with a pattern of IV > III > II > I typical of β-substitution with groups containing π-electrons, carbonyl or vinyl groups, and a pattern of the IV > II > III > I expected upon substitution on the mesopositions. In all the synthesized compounds, the observed relative intensity of the Q-bands follows the IV > III ≈ II > I trend as a consequence of substitution of all the meso-positions with phenyl groups and one of the β-positions with groups containing π-electrons. The absorption spectra agree well with that of the tetraphenylporphyrin standard (TPP). On average, the maximum absorption cross sections of the Soret band of the mono-porphyrin derivatives is 5 × 10−16 cm−2 [4.9 × 10−16 cm−2 (1), 4.2 × 10−16 cm−2 (3), and 7.1 × 10−16 cm−2 (5)]. Bisporphyrins 4 and 7 have maximum absorption cross sections that are twice than those of the mono-porphyrins [14.8 × 10−16 cm−2 (4) and 10.1 × 10−16 cm−2 (7)]. Similar trends are obtained from the integrated absorption cross section in the 350−500 nm region. This additive effect on the absorption cross section is due to the reduced conjugation between the porphyrin macrocycle and the β-substituents. All compounds are emissive with fluorescence quantum yields between 16 and 22%, in accordance with the values reported for the TPP standard (Table S1 in the Supporting Information).17 The higher energy band in the emission spectrum of each one of the derivatives with carbonyl or vinyl groups directly attached to the β-position appears red-shifted if compared with the one due to TPP by about 10 nm (674−676 nm for 1, 2, and 3 and 665 nm for TPP). This relatively small red-shift is indicative of a limited, but non-negligible, conjugation between the macrocycle and the substituents at the β-position. The conjugation is limited by the steric hindrance between the β-substituents and the phenyl substituent at the adjacent meso-position. Analysis of the calculated dihedral angles between the pyrrole rings of the macrocycle and the substituents connected to the pyrrole provides quantitative information about the distortion from planarity and gives further support to the reduced conjugation between the porphyrin macrocycle and the β-substituents (Figure S37 in the Supporting Information). In agreement with their red-shifted emission, the lowest distortion from planarity is predicted for compounds 1, 2, and 3 with dihedral angles of 19−28°. Compounds 6 and 7 suffer the strongest distortion from planarity with dihedrals above 50° found in all the conformers analyzed. In 4, the alkyl bridge connecting the pyridine to the porphyrin macrocycle prevents any electronic delocalization effect. The fluorescence decay curve of 4 can be fitted with a single exponential with 10.2 ns lifetime, very similar to that of TPP (10.8 ns). All the other compounds have multiexponential
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EXPERIMENTAL SECTION
General Remarks. 1H and 13C solution NMR spectra were recorded on Bruker Avance 300 (300.13 and 75.47 MHz, respectively) and Avance 500 (500.13 and 125.76 MHz, respectively) spectrometers. CDCl3 was used as solvent and tetramethylsilane (TMS) as the internal reference; the chemical shifts are expressed in δ (ppm) and the coupling constants (J) in hertz (Hz). Unequivocal 1H assignments were made using 2D COSY (1H/1H), while 13C assignments were made based on 2D HSQC (1H/13C) and HMBC (delay for long-range JC/H couplings were optimized for 7 Hz) experiments. Mass spectra were recorded using a MALDI TOF/TOF 4800 Analyzer, Applied Biosystems MDS Sciex, with CHCl3 as solvent and without matrix. Mass spectra HRMS were recorded on an APEXQe FT-ICR (Bruker Daltonics, Billerica, MA) mass spectrometer using CHCl3 as solvent, in m/z (rel. %). Preparative thin-layer chromatography was carried out on 20 × 20 cm glass plates coated with silica gel (0.5 mm thick). Column chromatography was carried out using silica gel (Merck, 35− 70 mesh). Analytical TLC was carried out on precoated sheets with silica gel (Merck 60, 0.2 mm thick). All the chemicals were used as supplied. Solvents were purified or dried according to the literature procedures.22 Experimental Procedures and Characterizations. Synthesis of the Starting Porphyrin TPP-CHO. The 2-formyl-5,10,15,20-tetraphenylporphyrin (TPP-CHO) was prepared from 5,10,15,20-tetraphenylporphyrinato copper(II), N,N′-dimethylformamide (DMF) and phosphorus oxychloride (POCl3), according to literature procedure.23 Synthesis of Compounds 2−5. To a solution of 2,6-diacetylpyridine (12.7 mg, 7.8 × 10−5 mol) in dry toluene (1 mL) was added piperidine (36.9 μL, 3.7 × 10−4 mol), and the mixture was stirred for 30 min at room temperature. After this period, 2-formyl-5,10,15,20tetraphenylporphyrin 1 (100 mg, 1.56 × 10−4 mol) and La(OTf)3 5285
DOI: 10.1021/acs.joc.8b00208 J. Org. Chem. 2018, 83, 5282−5287
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The Journal of Organic Chemistry (18.2 mg, 3.1 × 10−5 mol) were added to the mixture, and it was heated at reflux for 2.5 h. After cooling, the reaction mixture was washed with water and extracted with dichloromethane. The organic phase was dried (Na2SO4), and the solvent was evaporated under reduced pressure. The crude mixture was submitted to column chromatography (silica gel) using toluene/dichloromethane (1:2) and dichloromethane as eluent. The fractions obtained were fully characterized by NMR, mass, and spectroscopic techniques after crystallization in a CH2Cl2/hexane mixture. The spectroscopic data of compound 4 are in accordance with the literature.15 2,2′-Bis[3-oxo-3-(pyridin-2,6-yl)prop-1-en-1-yl]-5,10,15,20-tetraphenylporphyrin 2. Purple solid, 35.2 mg, 32% yield. Mp > 300 °C. 1 H NMR (300 MHz, CDCl3): δ 1H NMR (300 MHz, CDCl3) δ 9.02 (2H, s, H-3), 8.86 (2H, d, J 4.9 Hz, H-β), 8.82 (2H, d, J 4.9 Hz, H-β), 8.73 and 8.72 (4H, AB, J 4.9 Hz, H-β), 8.50 (2H, d, J 4.9 Hz, H-β), 8.36 (2H d, J 7.8 Hz, H-3′′,5′′), 8.35 (2H, d, J 15.6 Hz, H-1′), 8.24 (2H, dd, J 7.7 and 1.7 Hz, H-o-Ph), 8.17−8.13 (4H, m, H-o-Ph), 8.11− 8.07 (5H, m, H-o-Ph and H-4′′), 8.04 (2H, d, J 4.9 Hz, H-β), 7.84− 7.65 (21H, m, H-m,p-Ph and H-2′), 7.33 (4H, d, J 7.1 Hz, H-o-Ph), 6.46 (2H, t, J 7.5 Hz, H-p-Ph), 6.25 (4H, t, J 7.6 Hz, H-m-Ph), −2.63 (4H, s, N-H) ppm. 13C NMR (75 MHz, CDCl3): δ 189.0, 154.4, 153.6, 141.9, 141.6 (C-2′), 141.2, 134.52, 134.46, 134.36, 133.9, 132.1, 131.0−128.8 (C-β), 127.8, 127.7, 127.3, 126.9, 126.7, 125.8, 122.4 (C1′), 120.4 ppm. UV−vis (DMF): λmax = 426.0, 523.0, 566.0, 604.0, 659.0 nm. MS (MALDI): 1412.5 [M + H]+. HRMS-ESI(+): m/z calcd (%) for C95H66N9O2: 1412.5334 [M + H]+; found: 1412.5353. 2-[3-(6-Acetylpyridin-2-yl)-3-oxoprop-1-en-1-yl]-5,10,15,20-tetraphenylporphyrin 3. Purple solid, 36.8 mg, 30% yield. Mp > 300 °C. 1 H NMR (300 MHz, CDCl3): δ 9.21 (1H, s, H-3), 8.90−8.80 (6H, m, H-β), 8.46 (1H, d, J 15.7 Hz, H-1′), 8.33 (1H, d, J 7.7 Hz, H-3′′), 8.28−8.25 (2H, m, H-o-Ph), 8.24−8.15 (6H, m, H-o-Ph), 8.04 (1H, t, J 7.7 Hz, H-4′′), 7.84−7.71 (13H, m, H-m,p-Ph and H-5′′), 7.66 (1H, d, J 15.7 Hz, H-2′), 2.83 (3H, s, CH3), −2.55 (2H, s, N-H) ppm. 13C NMR (75 MHz, CDCl3): δ 199.7, 188.5, 153.6, 152.4, 142.2, 142.0, 141.7, 141.5, 141.0 (C-2′), 138.1, 134.7, 134.59, 134.56, 134.3, 132.2− 130.5 (C-β), 128.9, 128.0, 127.9, 127.2, 126.9, 126.8, 126.7, 126.1, 124.3, 122.4 (C-1′), 120.7, 120.5, 120.3, 25.8 (−CH3) ppm. UV−vis (DMF): λmax = 433.0, 526.0, 570.0, 605.0, 663.0 nm. MS (MALDI): 788.3 [M + H]+. HRMS-ESI(+): m/z calcd (%) for C54H38N5O2: 788.3020 [M + H]+; found: 788.3016. 2-(4,5-Dihydro-3H-azepin-7-yl)-5,10,15,20-tetraphenylporphyrin 5. Purple solid, 16.5 mg, 15% yield. Mp > 300 °C. 1H NMR (300 MHz, CDCl3): δ 8.87−8.79 (6H, m, H-β), 8.71 (1H, s, H-3), 8.24− 8.19 (6H, m, H-o-Ph), 8.06−8.04 (2H, m, H-o-Ph), 7.84−7.67 (12H, m, H-m,p-Ph), 7.60 (1H, brs, H-2′), 6.53 (1H, brs, H-6′), 3.72 (2H, t, J 5.7 Hz, H-3′), 2.82 (2H, t, J 5.7 Hz, H-5′), 1.82 (2H, q, J 5.7 Hz, H4′), −2.67 (2H, s, N-H) ppm. 13C NMR (75 MHz, CDCl3) δ 164.0, 142.2, 142.0, 141.9, 141.7, 134.6, 134.5, 134.0, 132.2−130.3 (C-β), 128.7, 127.9, 127.8, 127.2, 126.8, 126.70, 126.67, 120.6, 120.2, 120.0, 49.2, 24.5, 21.6 ppm. (3.70). UV−vis (DMF): λmax = 423.0, 521.0, 554.0, 598.0, 653.0 nm. MS (MALDI): 708.3 [M + H]+. HRMSESI(+): m/z calcd (%) for C50H38N5: 708.3020 [M + H]+; found: 708.3114. Synthesis of Compounds 6 and 7. To a solution of 2acetylpyridine (4.9 μL, 4.4 × 10−5 mol) in dry toluene (1 mL) was added ammonium acetate (25 mg, 8.8 × 10−5 mol), and the mixture was stirred for 30 min at room temperature. After this period, bisporphyrin-chalcone type derivative 2 (68.2 mg, 1.8 × 10−5 mol) and La(OTf)3 (2.1 mg, 3.5 × 10−6 mol) were added to the mixture, and it was heated at reflux for 2.5 h. After cooling, the reaction mixture was washed with water and extracted with dichloromethane. The organic phase was dried (Na2SO4), and the solvent was evaporated under reduced pressure. The crude mixture was submitted to column chromatography (silica gel) using dichloromethane and dichloromethane/methanol (2%) as eluent. From this chromatography were isolated, after crystallization in CH2Cl2/Hexane, compounds 6 and 7 in 21% and 52% yield, respectively. The fractions obtained were fully characterized by NMR, mass, and UV−vis techniques. 2-{2,2′:6′,2′′-[6′′-(2−5,10,15,20-Tetraphenylpyrido[2,3-b]porphyrin)]-terpyridin-4′-yl}-5,10,15,20-tetraphenylporphyrin 6.
Purple solid, 16.8 mg, 21% yield. Mp > 300 °C. 1H NMR (300 MHz, CDCl3): δ 8.99 (1H, s, H-3), 8.94 and 8.92 (2H, AB, J 5.0 Hz, H-β), 8.91−8.86 (3H, m, H-β), 8.82−8.78 (3H, m, H-β), 8.76−8.72 (3H, m, H-β and H-6′′), 8.69−8.65 (3H, m, H-β and H-3′′), 8.58 (1H, d, J 1.5 Hz, H-5′), 8.45−8.42 (2H, m, H-o-Ph and H-3′), 8.32− 8.13 (13H, m, H-o-Ph), 8.04−7.89 (9H, m, H-o,m,p-Ph and H-4′′), 7.82−7.81 (4H, m, H-m,p-Ph, H-3′′′ and H-5′′′), 7.76−7.66 (12H, m, H-m,p-Ph and H-4′′′), 7.41−7.33 (4H, m, H-m,p-Ph, H-5′′ and H3′′′′), 7.20 (1H, d, J 7.5 Hz, H-4′′′′), 7.02−6.93 (3H, m, H-m,p-Ph), −2.55 (2H, s, N-H), −2.71 (2H, s, N-H) ppm. 13C NMR (125 MHz, CDCl3): δ 159.4, 156.6, 155.6, 155.2, 154.3, 154.2, 153.9, 149.2, 149.0, 148.8, 143.3, 142.3, 142.2, 142.0, 141.92, 141.85, 141.76, 140.3, 137.1, 136.9, 135.5, 134.7, 134.6, 134.51, 134.47, 134.3, 133.9, 133.3, 132.4− 131.0 (C-β), 128.9, 128.5, 128.2, 127.9, 127.84, 127.80, 127.7, 127.5, 127.1, 126.9, 126.8, 126.5, 126.1, 123.6, 123.3, 122.1, 121.9, 121.5, 121.2, 121.1, 120.5, 120.4, 120.3, 117.8, 117.7, 117.6 ppm. UV−vis (DMF): λmax = 423.0, 427, 518.0, 551.0, 594.0, 645.0 nm (3.70). MS (MALDI): 1509.5 [M]+•. HRMS-ESI(+): m/z calcd (%) for C106H69N12: 1510.5796 [M + H]+; found: 1510.5814. 2,2′-Bis[2,2′:6′,2′′:6′′,2′′′-quinquepyridin-4′,4′′′-yl]-5,10,15,20tetraphenylporphyrin 7. Purple solid, 44.5 mg, 52% yield. Mp > 300 °C. 1H NMR (300 MHz, CDCl3): δ 9.05 (2H, s, H-3), 8.87−8.81 (6H, m, H-β and H6′′), 8.77−8.69 (9H, m, H-β and H-3′′), 8.38 (2H, d, J 8.0 Hz, H-o-Ph), 8.28−8.21 (11H, m, H-o-Ph and H-5′), 8.09 (2H, d, J 1.6 Hz, H-3′), 8.00−7.94 (5H, H-o-Ph), 7.85−7.72 (22H, m, Hm,p-Ph, H-4′′ and H-5′′), 7.38−7.30 (4H, m, H-m-Ph), 7.07−6.96 (5H, m, H-p-Ph, H-3′′′, H-4′′′ and H-5′′′), −2.59 (4H, s, N-H) ppm. 13 C NMR (125 MHz, CDCl3): δ 156.2, 155.7, 155.0, 150.00, 149.96, 149.4 149.1, 149.0, 146.4, 142.4, 142.3, 141.9, 140.7, 136.9, 136.7, 135.7, 134.6, 132.0−129.8 (C-β), 127.8, 127.7, 127.3, 127.2, 126.8, 126.69, 126.65, 125.8, 123.60, 123.57, 123.50, 121.9, 121.34, 121.25, 120.4, 120.3, 120.0, 115.7 ppm.” UV−vis (DMF): λmax = 416.0, 510.0, 547.0, 588.0, 645.0 nm. MS (MALDI): 1612.5 [M]+•. HRMS-ESI(+): m/z calcd (%) for C113H74N13: 1613.6216 [M + H]+; found: 1613.6199. Spectroscopic Measurements. The linear absorption spectra were recorded on a JASCO V-540 spectrophotometer. The fluorescence spectra were recorded using a Horiba Jobin Yvon Fluorlog 3-22 Spectrofluorimeter with a xenon lamp of 450 W. The spectra were recorded in spectroscopic grade dioxane using 5 × 5 mm quartz cells. The fluorescence quantum yields were determined using tetraphenylporphyrin in acetonitrile (ϕ = 0.15, λdem = 640−740) upon excitation of the Soret/Q-band.17 Two-photon absorption (TPA) spectra were measured in 5−10 μM dimethylformamide (DMF) solutions by two-photon fluorescence (TPF) using tetraphenylporphyrin in carbon tetrachloride as standard to account for collection efficiency and pulse characteristics.18 A modified setup that follows loosely the one described by Xu and Webb was used to estimate the TPA cross section in the range 710−990 nm region.24 The twophoton emission (TPE) was measured within a narrow wavelength bandwidth selected by the H20Vis Jobin Yvon monochromator placed at the entrance of a PMC-100-4 photomultiplier tube (Becker and Hickl GmbH). The integrated TPF over the entire emission band was extrapolated using the emission spectra corrected by the detector sensitivity. The excitation source was a Ti:sapphire laser (Tsunami BB, Spectra-Physics, 710−990 nm, 1.7 W, 100 fs, 82 MHz). The twophoton absorption cross section was calculated from the equation
⎛ F ⎞ ⎛ ϕCnσ2 ⎞ σ2 = ⎜ 2 ⎟ ⎜ ⎟ ⎝ ϕCn ⎠s⎝ F2 ⎠ref
(1)
where F2 stands for fluorescence intensity, ϕ is the fluorescence quantum yield, n refers to the refractive index in solution, C is the concentration, and s and ref are relative to the sample and the TPA reference, respectively. The emission intensity dependence of the excitation power was checked. The relative error of the cross sections values is at most ±20%. The fluorescence decays were measured in 5 mm quartz cuvettes by the Single-Photon Timing technique under excitation at 580 nm by collecting the emission at 670 nm. The excitation source was a 5286
DOI: 10.1021/acs.joc.8b00208 J. Org. Chem. 2018, 83, 5282−5287
Note
The Journal of Organic Chemistry
(7) Ziener, U.; Lehn, J.-M.; Mourran, A.; Möller, M. Chem. - Eur. J. 2002, 8, 951. (8) Sasaki, I.; Daran, J. C.; Commenges, G. Beilstein J. Org. Chem. 2015, 11, 1781−1785. (9) Kadish, K. M., Smith, K. M., Guilard, R., Eds. Handbook of Porphyrin Science; World Scientific Publishing Company Co: Singapore, 2010; Vols.1−12. (10) Moura, N. M. M.; Faustino, M. A. F.; Neves, M.; Paz, F. A. A.; Silva, A. M. S.; Tome, A. C.; Cavaleiro, J. A. S. Chem. Commun. 2012, 48, 6142. (11) Moura, N. M. M.; Ramos, C. I. V.; Linhares, I.; Santos, S. M.; Faustino, M. A. F.; Almeida, A.; Cavaleiro, J. A. S.; Amado, F. M. L.; Lodeiro, C.; Neves, M. G. P. M. S. RSC Adv. 2016, 6, 110674. (12) Lanzilotto, A.; Buldt, L. A.; Schmidt, H. C.; Prescimone, A.; Wenger, O. S.; Constable, E. C.; Housecroft, C. E. RSC Adv. 2016, 6, 15370. (13) Liew, J. Y.; Brown, J. J.; Moore, E. G.; Schwalbe, M. Chem. - Eur. J. 2016, 22, 16178. (14) Cerqueira, A. F. R.; Moura, N. M. M.; Serra, V. V.; Faustino, M. A. F.; Tomé, A. C.; Cavaleiro, J. A. S.; Neves, M. G. P. M. S. Molecules 2017, 22, 1269. (15) Moura, N. M. M.; Nunez, C.; Santos, S. M.; Faustino, M. A. F.; Cavaleiro, J. A. S.; Paz, F. A. A.; Neves, M.; Capelo, J. L.; Lodeiro, C. Chem. - Eur. J. 2014, 20, 6684. (16) Baas, P.; Cerfontain, H. Tetrahedron 1977, 33, 1509. (17) Gradyushko, A. T.; Sevchenko, A. N.; Solovyov, K. N.; Tsvirko, M. P. Photochem. Photobiol. 1970, 11, 387. (18) Makarov, N. S.; Drobizhev, M.; Rebane, A. Opt. Express 2008, 16, 4029. (19) Kim, K. S.; Lim, J. M.; Osuka, A.; Kim, D. J. Photochem. Photobiol., C 2008, 9, 13. (20) Aratani, N.; Kim, D.; Osuka, A. Chem. - Asian J. 2009, 4, 1172. (21) Odom, S. A.; Webster, S.; Padilha, L. A.; Peceli, D.; Hu, H.; Nootz, G.; Chung, S. J.; Ohira, S.; Matichak, J. D.; Przhonska, O. V.; Kachkovski, A. D.; Barlow, S.; Bredas, J. L.; Anderson, H. L.; Hagan, D. J.; Van Stryland, E. W.; Marder, S. R. J. Am. Chem. Soc. 2009, 131, 7510. (22) Armarego, W. L. F.; Chai, C. Purification of Laboratory Chemicals, 7th ed.; Butterworth-Heinemann: Oxford, U.K., 2013. (23) Moura, N. M. M.; Faustino, M. A. F.; Neves, M.; Duarte, A. C.; Cavaleiro, J. A. S. J. Porphyrins Phthalocyanines 2011, 15, 652. (24) Xu, C.; Webb, W. W. J. Opt. Soc. Am. B 1996, 13, 481.
Coherent Radiation Dye laser 700 series (laser dye Rhodamine6G, 560−610 nm, 130 mW, 5 ps, 4 MHz). The emission at the maximum was collected at the magic angle using a Jobin Yvon HR320 monochromator (Horiba Jovin Ivon Inc.). The instrument response functions for deconvolution (35−80 ps fwhm) were generated by scattering dispersions of colloidal silica in water. The solutions were kept under gentle stirring during the data collection. Blank decays were acquired to ensure that dark photon counts were negligible. Decay curves were stored in 1024 channels with 48.8 ps per channel and an accumulation of 20k counts in the peak channel. The fluorescence decays were analyzed by a nonlinear least-squares deconvolution method using the TRFA DP software by SSTC (Scientific Software Technologies Center, Belarusian State University, Minsk, Belarus).
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.joc.8b00208. Proposed mechanism for the synthesis of compound 5, copies of NMR and MS spectra, optical properties data, and B3LYP data (PDF)
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AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected] (N.M.M.M.). *E-mail:
[email protected] (M.G.P.M.S.N.). ORCID
Nuno M. M. Moura: 0000-0002-9373-7006 José A. S. Cavaleiro: 0000-0001-5495-5126 Artur M. S. Silva: 0000-0003-2861-8286 Carlos Lodeiro: 0000-0001-5582-5446 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS Thanks are due to FCT and FEDER for funding the QOPNA unit (project PEst-C/QUI/UI0062/2013) and the Portuguese National NMR Network. The CQFM unit is also supported by FCT (UID/NAN/50024/2013). We also thank the Associate Laboratory for Green Chemistry LAQV which is financed by national funds from FCT/MEC (UID/QUI/50006/2013) and co-financed by the ERDF under the PT2020 Partnership Agreement (POCI-01-0145-FEDER-007265) and the Scientific Society PROTEOMASS (General Funds) (Portugal). FCT is acknowledged for the individual support given to N.M.M.M. (SFRH/BPD/84216/2012), I.F.A.M. (SFRH/BPD/75782/ 2011), and E.M.S.M. (IF/00759/2013).
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REFERENCES
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DOI: 10.1021/acs.joc.8b00208 J. Org. Chem. 2018, 83, 5282−5287
