Trimeric Assembly of Dendritic Light-Harvesting Antenna with Two

Aug 7, 2017 - These absorption and fluorescence studies are compatible with solvent-dependent conformation; the extended forms of the trimers are favo...
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Trimeric Assembly of Dendritic Light-Harvesting Antenna with Two Kinds of Porphyrin Cores Ryo Kimura, Shuichi Suzuki,† Keiji Okada, and Masatoshi Kozaki* Graduate School of Science, Osaka City University, 3−3−138, Sugimoto, Sumiyoshi-ku, Osaka 558−8585, Japan S Supporting Information *

ABSTRACT: A trimeric assembly of light-harvesting antennas was prepared using a copper-catalyzed Hüisgen 1,3-dipolar cycloaddition reaction between a dendrimer having a zinc diethynyldiphenylporphyrin core (ZnDEDPP) with two azide terminals and two equivalents of dendrimers having a zinc tetraphenylporphyrin core (ZnTPP) with one ethynyl terminal. The absorptions of the trimer appear in a longer-wavelength region compared to monomeric references in toluene; however, there is almost no shift in wavelength in 1,1,2,2-tetrachloroethane (TCE). Fluorescence spectra of the trimer show that the singlet energy transfer from ZnTPP to ZnDEDPP takes place more effectively in toluene than in TCE. These absorption and fluorescence studies are compatible with solvent-dependent conformation; the extended forms of the trimers are favored by solvation in polar TCE, and the folded conformation is stabilized by the attractive van der Waals and dipole−dipole interactions between the dendritic chains in nonpolar toluene.

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INTRODUCTION The regulation of energy-transfer efficiency in light-harvesting antenna systems in plants is essential to avoid potentially damaging reactions caused by excess light energy.1 This lightharvesting adjustment is also important for artificial photosynthesis to maintain the solar energy conversion and stable photochemical production of redox and energetic raw materials.2 Dendrimers are valuable frameworks for artificial light-harvesting systems, and a variety of light-harvesting dendrimers3 and their assemblies4 have been reported. However, only a limited number of approaches have been reported for the regulation of the energy-transfer process in dendritic light-harvesting systems.5 Recently, rearrangement of antenna complexes around reaction center core complexes in a thylakoid membrane was shown to be involved in energy-transfer regulation in plants.6 Although such a rearrangement of the light-harvesting dendrimers seems to be an attractive bioinspired approach for regulating of the light-harvesting ability of dendritic antenna systems, no reliable methodology to change the arrangement of the light-harvesting dendrimers has been reported. Recently, we prepared linear oligomers of dendrimers that take a folded or an extended conformation depending on temperature and solvents.7 This unique conformational transformation has stimulated us to construct a dendritic antenna assembly whose light-harvesting ability is adjustable by changing its higher-order structure. In this study, as a proof of concept, we prepared trimer 1 containing two kinds of lightharvesting dendrimers (Figure 1).8 The peripheral and central dendrimers have a zinc tetraphenylporphyrin core (ZnTPP) © 2017 American Chemical Society

and a zinc diethynyldiphenylporphyrin core (ZnDEDPP), respectively. Our spectroscopic investigation of higher-order structures of the trimer establishes that the trimer prefers a folded conformation in toluene and an extended conformation in 1,1,2,2-tetrachloroethane (TCE). Fluorescence spectra of 1 showed the effect of higher-order structure on the energy transfer from ZnTPP to ZnDEDPP.

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RESULTS AND DISCUSSION Synthesis of Dendrimers 1−3. The synthetic routes for dendrimers 2 and 3 are shown in Schemes 1 and 2, respectively. Dendron 4 was prepared according to our reported procedures.9 Sonogashira coupling reactions of 4 and 5 were carried out to afford 6 in nearly quantitative yield. After the TMS group in 6 was removed by treatment with TBAF in THF, the resulting hydroxyl group was reacted with excess 1,4dibromobutane to produce 8. Dendron 10 was obtained by the condensation reaction of 4 and 3-bromo-1-trimethylsilyl-1propyne (9) under Williamson ether synthesis conditions. The Sonogashira coupling reaction between 8 and 10 afforded dendrimer 2 as a purple solid in 84% yield. In this coupling reaction, the copper-free condition is essential to gain 2 in high yield. When we carried out the Sonogashira coupling reaction of 8 and 10 using PdCl2(PPh3)2 and CuI as catalysts, 2 was obtained in only 38% yield. The terminal TMS group was removed under basic conditions in the presence of 18-crown-6 to afford dendrimer 11 as a purple solid in 90% yield. Dendron Received: May 23, 2017 Published: August 7, 2017 8917

DOI: 10.1021/acs.joc.7b01275 J. Org. Chem. 2017, 82, 8917−8926

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The Journal of Organic Chemistry

Figure 1. Chemical structure of trimer 1.

4 was attached with both ethynyl terminals in 1210 by Sonogashira coupling to give dendrimer 13 in 71% yield. Both hydroxyl terminals in 13 were reacted with excess of 1,4dibromobutane to produce dendrimer 3 as a green solid in 90% yield. Both bromo groups were substituted by azide groups by treatment with excess sodium azide in DMF to afford dendrimer 14 as a green solid in 82% yield. The coppercatalyzed acetylene-azide cycloaddition (CuAAC) reaction of the alkyne terminal in 11 (2.2 equiv) and each azide group in 14 (1.0 equiv) was performed using copper sulfate (3.0 equiv) and sodium ascorbate (10 equiv) in dry DMF at room temperature for 2 days to afford trimer 1 as a black solid in 36% yield. After several trials to improve the yield, we found that addition of a large excess of copper sulfate (10 equiv) and sodium ascorbate (45 equiv) led to an improvement in the yield of 1 (66%) (Scheme 3). Trimer 1 was sufficiently purified by preparative recycling gel permeation chromatography (GPC) using chloroform as eluent. Trimer 1 was soluble in common organic solvents like THF, dichloromethane, chloroform, DMF, and toluene. Interestingly, the solubility of 1 in ethyl acetate is quite limited. NMR Spectra and MALDI-TOF MS. Dendrimer 2 gives sharp and well-resolved NMR signals in CDCl3 at room temperature (Figure S15). Two characteristic doublets of βprotons on ZnTPP in 2 are observed at 8.90 and 8.80 ppm. On the other hand, the NMR spectra of 3 in CDCl3 containing one drop of pyridine-d5 at room temperature features sharp and well-resolved signals (Figure S18).11 Four β-protons of ZnDEDPP close to the ethynyl units at the meso-positions

resonate in the downfield region at 9.64 ppm compared to the other β-protons which appear at the higher field of 8.68 ppm due to the anisotropic effect of the benzene rings. These characteristic signals of β-protons on each porphyrin ring are also observed in the NMR spectrum of trimer 1 in CDCl3 with a drop of pyridine-d5 at room temperature (Figure 2). In addition, the formation of the triazole rings is undoubtedly confirmed by the NMR spectra. Unfortunately, the signal of the proton directly attached to the triazole ring is buried in the intense signals of the aromatic protons in the dendritic chains. The methylene protons adjacent to the triazole ring are clearly observed as a singlet at 5.11 (Ha) and as a broad triplet at 4.42 ppm (Hb).7 On the other hand, trimer 1 gave broad NMR signals at room temperature in toluene-d8 with a drop of pyridine-d5 (Figure S11). Well-resolved signals were observed at 60 °C. In addition, dendrimers 2 and 3 are clearly identified by MALDI-TOF MS through the detection of the molecular ion peaks at m/z = 4620 (calcd for C316H305BrN4O18SiZn; 4 545 , F i gur e S 1 ) a n d m/ z = 4 4 9 3 ( c a l c d f o r C302H294N10O18Zn; 4493, Figure S2), respectively. Formation of 1 was corroborated by the detection of the molecular ion peak at m/z = 13515 (calcd for C928H888Br2N18O54Zn3; 13513) in MALDI-TOF MS (Figure 3). In addition, a series of fragment ions generated by the cleavage of ether bond in dendritic chains was detected. UV−vis Spectra. Figure 4a shows UV−vis spectra of 1, 2, and 3 in TCE at room temperature. Compound 2 shows a Soret band at λmax = 428 nm (log ε = 5.70) and Q bands at λmax = 551 (log ε = 4.41) and 594 nm (log ε = 3.88) which are 8918

DOI: 10.1021/acs.joc.7b01275 J. Org. Chem. 2017, 82, 8917−8926

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The Journal of Organic Chemistry Scheme 1. Synthesis of Dendrimer 2

(log ε = 4.76), 594 (log ε = 4.49), and 659 nm (log ε = 4.96) in the Q-band region are reasonably assigned as the Q-band of ZnTPP, overlapped absorption of Q-bands of ZnTPP and ZnDEDPP, and the Q-band of ZnDEDPP, respectively, based on the comparison of 2 and 3. The absorption spectrum of 1 is satisfactorily reproduced using the spectra of 2 and 3,

characteristic for ZnTPP. Soret and Q bands of ZnDEDPP in 3 are observed at λmax = 464 (log ε = 5.60) and 657 nm (log ε = 4.90), respectively.12 Trimer 1 exhibits two sharp high-energy absorption bands at λmax = 429 (log ε = 5.96) and 466 nm (log ε = 5.67) which are assigned as the Soret bands of ZnTPP and ZnDEDPP, respectively. Three absorption bands at λmax = 551 8919

DOI: 10.1021/acs.joc.7b01275 J. Org. Chem. 2017, 82, 8917−8926

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The Journal of Organic Chemistry Scheme 2. Synthesis of Dendrimer 3

interaction at low concentration (10−5−10−7 M) in toluene. The observed spectral change in Figure 4b is mostly attributed to the intramolecular interaction between the dendrimer units in 1. We reported in our prior communication that the linear assemblies of the dendrimers with conjugated backbones have a strong preference for folded conformation in toluene due to the attractive interaction between dendritic wedges.7 These results suggest that trimer 1 has a stable, folded conformation in toluene, in which porphyrin units are located in close proximity (Figure S10b). To see the stability of the folded conformation of trimer 1, absorption spectra of 1, 2, and 3 were obtained in toluene with temperatures varying from 20 to 90 °C. The observed spectral changes of 1 are summarized in Figure 5 and Table S1. The corresponding data for 2 and 3 are shown in Figure S4. As temperature increases, the molar absorptivities of the Soret and the Q-band absorption of 2 and 3 decrease slightly. Negligible shift in wavelength at the absorption maximum is observed for both 2 and 3. In contrast, the absorption spectrum of 1 has substantial temperature dependence. The toluene solution of trimer 1 exhibits the Soret bands of ZnTPP and ZnDEDPP at λmax = 428 and 466 nm, respectively, and three absorption

suggesting negligible interaction between the dendrimer units in TCE.13 Therefore, 1 has an extended conformation and each dendrimer unit behaves independently in TCE (Figure S10a). On the other hand, trimer 1 in toluene has a couple of sharp absorption bands at λmax = 431 (log ε = 5.92) and 476 nm (log ε = 5.58), in addition to the absorption bands at λmax = 554 (log ε = 4.68), 602 (log ε = 4.43), and 686 nm (log ε = 4.97) in the Q-band region (Figure 4b). Minor bathochromic shifts were observed for the absorption bands mainly due to ZnTPP in 1 (λmax = 431 and 554 nm) compared to the corresponding absorption bands of 2 (λmax = 428 and 551 nm). In contrast, the Soret (λmax = 476 nm, δλmax = 9 nm) and the Q-band (λmax = 686 nm, δλmax = 25 nm) of ZnDEDPP in 1 showed significant red shift compared to the corresponding absorption bands of 3 (λmax = 467 and 661 nm), suggesting considerable interaction between the dendrimer units in toluene.14 To estimate the contribution of intermolecular interaction for these spectral changes, the absorption spectra of 1 was obtained at 20 °C with varying concentrations from 1.58 × 10−5 M to 1.58 × 10−7 M in toluene. A small concentration dependence was observed (Figure S3a), indicating the presence of a minor contribution (δλmax < 14 nm for the longest Q-band) of intermolecular 8920

DOI: 10.1021/acs.joc.7b01275 J. Org. Chem. 2017, 82, 8917−8926

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The Journal of Organic Chemistry Scheme 3. Synthesis of Trimer 1

Figure 2. 1H NMR spectrum of 1 in CDCl3 with a drop of pyridine-d5 at room temperature. Py: pyridine; −CH2Br: terminal bromomethy groups; and benzyl protons: benzyl protons in branching chains.

bands (λmax = 551, 594, and 659 nm) in the Q-band region at 90 °C. This spectrum can be reproduced using the observed spectra for 2 and 3 at 90 °C, indicating a negligible intramolecular interaction among the dendrimer units in 1 at 90 °C. Thus, trimer 1 is stable in its extended conformation at this temperature in toluene. When the temperature decreases, the Soret bands of ZnTPP and ZnDEDPP show red shifts of δλmax = 3 and 10 nm, respectively. A similar trend is observed

Figure 3. MALDI-TOF MS of trimer 1 (dithranol).

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DOI: 10.1021/acs.joc.7b01275 J. Org. Chem. 2017, 82, 8917−8926

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The Journal of Organic Chemistry

Figure 4. UV−vis spectra of 1 (black solid line, 6.76 × 10−7 M in TCE, and 1.55 × 10−6 M in toluene), 2 (red broken line), and 3 (blue broken line) (a) in TCE and (b) in toluene at room temperature.

higher-order structure from the extended to the folded form when the temperature decreases from 90 to 20 °C.15 Fluorescence Spectra. The fluorescence spectra of 1, 2, and 3 were measured in TCE and in toluene. The results are summarized in Figure 6 and Table 1. The excitation of ZnTPP in 2 (λEX = 428 nm) in TCE resulted in fluorescence at λEM‑max = 604 and 651 nm (ΦF = 0.10). When ZnDEDPP in 3 was excited at λEX = 465 nm in TCE, fluorescence at λEM‑max = 668 nm (ΦF = 0.39) was observed. Trimer 1 displayed two intense emission bands at λEM‑max = 604 and 667 nm (ΦF = 0.17) upon excitation at 428 nm in TCE, at which incident light is predominantly absorbed by ZnTPP (the molar absorptivity ratio of 2 × ε(2):ε(3) = 95:5) (Figure 6a). The emission at 604 and 667 nm can be assigned to the fluorescence from ZnTPP and ZnDEDPP in 1, respectively, as suggested by the fluorescence spectra of 2 and 3. These results indicate that singlet excited-state energy transfer occurred from ZnTPP to ZnDEDPP in 1. To quantify the quantum efficiency of the energy transfer, the fluorescence spectrum of 1 (λEX = 428 nm) was simulated using a linear combination of the spectra of 1 (λEX = 466 nm, direct excitation of ZnDEDPP, ΦF = 0.35) and 2, indicating that the fluorescence of 1 can be divided into two components with an area ratio of 1 (ZnTPP):2.48 (ZnDEDPP) (Figure S8). Therefore, the chromophore-dependent quantum yields in 1 are determined as ΦF = 0.049 for ZnTPP and ΦF = 0.12 for ZnDEDPP. When ZnTPP in 1 was excited in TCE, the fluorescence quantum yields for ZnTPP and ZnDEDPP in 1 is

Figure 5. Variable-temperature UV−vis absorption spectra of 1 in toluene (1.55 × 10−6 M).

for the thermochromic behavior in the Q-band region; upon cooling, moderate red shifts (δλmax = 3 nm) are observed for the band at λmax = 551 nm (at 90 °C) where the ZnTPP absorption has a dominant contribution. In contrast, the Qband mainly due to ZnDEDPP progressively shifts from λmax = 659 nm to λmax = 686 nm when the temperature decreases from 90 to 20 °C. These results suggest that 1 gradually changes its

Figure 6. (a) Fluorescence spectra of 1 (black line for λEX = 428 nm, green line for λEX = 466 nm, 1.99 × 10−7 M), 2 (red line for λEX = 428 nm), and 3 (blue line for λEX = 465 nm) in TCE and (b) 1 (black line for λEX = 429 nm, green line for λEX = 468 nm, 1.54 × 10−7 M), 2 (red line for λEX = 428 nm), and 3 (blue line for λEX = 466 nm) in toluene. 8922

DOI: 10.1021/acs.joc.7b01275 J. Org. Chem. 2017, 82, 8917−8926

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The Journal of Organic Chemistry Table 1. Emission Data of 1, 2, and 3 in TCE and Toluene fluorescence assignment compd 1 1 1 2 3 a

ZnTPP ZnDEDPP ZnDEDPP ZnTPP ZnDEDPP

TCE

toluene

λEM‑max (λEX)/nm

ΦFa

λEM‑max (λEX)/nm

ΦFa

604 (428) 667 (428) 668 (466) 604, 651 (428) 668 (465)

0.049 0.12 0.35 0.10 0.39

603 (429) 678 (429) 679 (468) 604, 651 (428) 668 (466)

0.022 0.18 0.34 0.11 0.49

Fluorescence quantum yields are relative to tetraphenylporphyrin as the external standards.16

49% of that of 2 (ΦF = 0.10) and 34% of that of 1 (λEX = 466 nm, ΦF = 0.35), respectively. Figure 6b shows the fluorescence spectra of 1 (λEX = 429 nm and λEX = 468 nm), 2 (λEX = 428 nm), and 3 (λEX = 466 nm) in toluene. The change of the solvent led to negligible shifts in the emission bands (Table 1). The selective excitation of ZnDEDPP in 1 at 468 nm (2 × ε(2):ε(3) = 2:98) in toluene results in the broad emission band at λEM‑max = 679 nm (ΦF = 0.34) (Figure 6b). The observed broadening of ZnDEDPP emission suggests significant intramolecular interaction in 1 in toluene. When ZnTPP in 1 was selectively excited at 429 nm (2 × ε(2):ε(3) = 96:4) in toluene, the weak emission band at λEM‑max = 603 and broad intense emission band at 678 nm (ΦF = 0.20) were observed (Figure 6b). The spectrum was successfully reproduced with a linear combination of the spectra of 1 (λEX = 468 nm, direct excitation of ZnDEDPP) and 2 and divided into two components with an area ratio of 1 (ZnTPP emission):8.05 (ZnDEDPP emission) (Figure S9). The chromophore-dependent quantum yields in 1 are estimated as ΦF = 0.022 for ZnTPP and ΦF = 0.18 for ZnDEDPP. The fluorescence quantum yield for ZnTPP in 1 in toluene is 20% of that of 2 (ΦF = 0.11). This ratio is much smaller than the corresponding ratio (49%) obtained in TCE. In addition, the fluorescence quantum yield for ZnDEDPP in 1 in toluene is 53% of that of 1 (λEX = 468 nm, ΦF = 0.34). This value is larger than the corresponding value (34%) in TCE. These results suggest that the energy transfer from ZnTPP to ZnDEDPP in 1 takes place in the higher quantum efficiency in toluene than in TCE. According to the Förster theory, singlet energy-transfer rate is strongly dependent on the distance between an energy donor and an acceptor.17 The superior energy-transfer efficiency from ZnTPP to ZnDEDPP in toluene indicates that the small distance between ZnTPP and ZnDEDPP in 1 is due to the folded conformation. In contrast, the poor energy-transfer efficiency in TCE can be assigned to the stable extended conformation of 1.

changing their higher-order structures. Thus, a variety of stimuli-responsive light-harvesting systems could be constructed by the incorporation of antenna chromophores into the dendritic branches.

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EXPERIMENTAL SECTION

General. Melting points were taken on a Yanako MP J-3 apparatus and are uncorrected. 1H NMR and 13C NMR spectra were recorded at room temperature on a JEOL Lambda 300, JEOL Lambda 400, JEOL JNM-ECZ 400, Bruker AV 300N, Bruker AV III HD 400, Bruker AV III HD 600 spectrometers. Chemical shifts were recorded in units of parts per million downfield from tetramethylsilane as an internal standard and all coupling constants are reported in Hz. Standard abbreviations indicating multiplicities are given: br = broad, d = doublet, m = multiplet, q = quartet, s = singlet, t = triplet. Some carbons have only undetectable difference in magnetic environment. As the results, some carbon signals in 13C NMR are missing due to overlapping. IR spectra were obtained on a Shimadzu FTIR-8700 spectrometer. UV−vis spectra were obtained on a Shimadzu UV2550PC spectrometer. The ESI-TOF mass spectra were recorded on a JEOL AccuTOF LC-plus JMS-T100LP spectrometer. MALDI-TOF mass was measured on a Shimadzu-Kratos AXIMA-CFR Plus and BURUKER solariX spectrometers using dithranol as a matrix reagent. Elemental analyses were obtained from the Analytical Center in Osaka City University. TLC was carried out using 0.2 mm thick Merck silica gel (60 F254). Merck silica gel 60 (0.063−0.200 mm) and Kanto kagaku silica gel 60 (spherical) were used as the stationary phase for column chromatography. Recycling preparative GPC (gel permeation chromatography) was carried out using Japan Analytical Industry LC9210 with JAIGEL-2H and -3H GPC columns. Commercially available reagents and solvents were purified and dried when necessary. Porphyrin 5. To a solution of meso-(mesityl)dipyrromethane (412 mg, 1.56 mmol), 4-[2-(trimethylsilyl)ethynyl]benzaldehyde (159 mg, 0.784 mmol), and 4-ethynylbenzaldehyde (102 mg, 0.784 mmol) in dry CH2Cl2 (100 mL) was added under nitrogen BF3 etherate (0.04 mL, 0.3 mmol). After the solution was stirred at room temperature for 1 h, DDQ (531 mg, 2.34 mmol) was added. The solution was stirred for further 1 h at room temperature and filtered through a pad of silica gel. The filtrate was concentrated under reduced pressure. The resulting purple solid was dissolved in CH2Cl2 and CH3OH was slowly added. The solution was left overnight. The precipitation was filtered off and dissolved in CH2Cl2 (30 mL). After the addition of Zn(OAc)2 (148 mg, 0.808 mmol) in CH3OH (10 mL), the solution was stirred at room temperature for 6 h. The mixture was washed with water and brine and dried over anhydrous Na2SO4. The solvent was evaporated under reduced pressure to afford purple solid (265 mg). The solid was separated by column chromatography on silica gel (hexane:CH2Cl2 = 7:3 (v/v)) to afford 5 as a purple solid (119 mg, 17%). 5: purple solid; mp >300 °C; 1H NMR (400 MHz, CDCl3): δ (ppm) 8.86−8.77 (m, 8H), 8.21−8.17 (m, 4H), 8.86−8.77 (m, 4H), 7.28 (s, 4H), 3.31 (s, 1H), 2.63 (s, 6H), 1.82 (s, 12H), 0.37 (s, 9H); 13C NMR (100 MHz, CDCl3): δ (ppm) 150.0, 149.8, 149.7, 143.5, 143.1, 139.2, 138.9, 137.6, 134.33, 134.31, 132.14, 132.10, 131.0, 130.4, 130.2, 127.7, 122.2, 121.3, 119.6, 119.3, 105.2, 95.3, 83.8, 78.1, 21.6, 21.5, 0.1; IR (KBr/cm−1) 3296, 2960, 2156, 1605, 1492, 1336, 1250, 1205, 1066, 999, 863, 798, 721, 660, 542; MS (ESI+-TOF) m/z 880.2 [M+];

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CONCLUSIONS In conclusion, we prepared a trimer of porphyrin dendrimers as a light-harvesting system using the CuAAC reaction. The terminal and the central dendrimer in the trimer possess ZnTPP and ZnDEDPP cores, respectively. The absorption spectra suggest that the stable higher-order structure of the trimer is the folded conformation in toluene and the extended conformation in TCE. Fluorescence spectra show that singlet excitation energy transfer from ZnTPP to ZnDEDPP in toluene occurrs at higher quantum efficiency than that in TCE, due to the smaller distance between ZnTPP and ZnDEDPP in the folded conformation. These results demonstrate that energy transfer in light-harvesting systems can be regulated by 8923

DOI: 10.1021/acs.joc.7b01275 J. Org. Chem. 2017, 82, 8917−8926

Article

The Journal of Organic Chemistry HRMS (ESI+-TOF) calcd for C57H48N4Si64Zn m/z 880.2940; found m/z 880.2941. Porphyrin 6. Dendron 4 (207 mg, 108 μmol), porphyrin 5 (140 mg, 158 μmol), Pd2(dba)3·CHCl3 (15.4 mg, 14.9 μmol), and AsPh3 (34.7 mg, 113 μmol) in degassed iPr2EtN (10.0 mL) and degassed CH2Cl2 (20.0 mL) were stirred at room temperature for 2 days. The mixture was filtered through Celite and the solvent was evaporated under reduced pressure. The residue was dissolved in CH2Cl2 and washed with water and brine and dried over anhydrous Na2SO4. The solvent was evaporated under reduced pressure. The resulting purple solid was separated by column chromatography on silica gel (hexane:CH2Cl2 = 1:3 (v/v) and CH2Cl2) to afford 6 as a purple solid (264 mg, 92%). 6: purple solid; mp 183−184 °C; 1H NMR (300 MHz, CDCl3): δ (ppm) 8.91−8.78 (m, 8H), 8.25−8.17 (m, 4H), 7.93 (d, J = 8.3 Hz, 2H), 7.86 (d, J = 8.3 Hz, 2H), 7.72 (d, J = 8.7 Hz, 4H), 7.69 (s, 2H), 7.58 (d, J = 8.7 Hz, 4H), 7.42−7.31 (m, 24H), 7.28 (s, 4H), 7.13 (s, 2H) 7.12 (d, J = 8.9 Hz, 4H), 7.02 (d, J = 8.7 Hz, 4H), 6.95 (d, J = 8.9 Hz, 2H), 6.75 (d, J = 2.3 Hz, 4H), 6.65 (d, J = 8.7 Hz, 2H), 6.57 (t, J = 2.3 Hz, 2H), 5.03 (s, 4H), 4.97 (s, 8H), 4.88 (s, 4H), 4.84 (s, 1H), 2.63 (s, 6H), 1.83 (s, 12H) 1.32 (s, 18H), 1.30 (s, 36H), 0.37 (s, 9H); 13C NMR (100 MHz, CDCl3): δ (ppm) 160.2, 158.52, 158.49, 155.6, 151.0, 150.9, 150.0, 149.7, 144.9, 144.0, 143.2, 143.1, 139.3, 139.2, 138.9, 137.5, 134.5, 134.3, 133.8, 133.6, 133.2, 133.0, 132.7, 132.2, 132.1, 131.1, 130.9, 130.7, 130.4, 130.2, 129.9, 127.7, 127.61, 127.55, 125.47, 125.45, 123.2, 122.7, 122.17, 122.15, 120.2, 119.5, 119.4, 115.6, 115.3, 114.3, 114.0, 106.2, 105.2, 101.6, 97.4, 97.3, 95.3, 91.5, 91.3, 90.3, 88.0, 70.0, 69.9, 69.8, 34.5, 31.34, 31.30, 21.6, 21.4, 0.1; IR (KBr/cm−1) 3452, 3032, 2960, 2906, 2868, 2204, 2156, 1606, 1508, 1460, 1363, 1246, 1225, 1153, 999, 832, 722, 535; MS (MALDI-TOF) m/z 2664.2 [M+]; HRMS (MALDI-TOF) calcd for C183H172N4O9Si64Zn m/z 2661.2180; found m/z 2661.2161. Porphyrin 7. To a solution of 6 (24.8 mg, 9.31 μmol) in THF (3.0 mL) was added TBAF (1.0 M THF solution, 0.01 mL, 10 μmol). The solution was stirred at room temperature for 10 min. After the addition of a drop of acetic acid, the solution was washed with water and brine and dried over anhydrous Na2SO4. The solvent was evaporated under reduced pressure. The resulting purple solid was separated by column chromatography on silica gel (hexane:CH2Cl2 = 1:2 (v/v)) to afford 7 (24.1 mg, quantitative) as a purple solid. 7: purple solid; mp 178 °C; 1 H NMR (300 MHz, CDCl3): δ (ppm) 8.91−8.78 (m, 8H), 8.25− 8.17 (m, 4H), 7.93 (d, J = 8.1 Hz, 2H), 7.87 (d, J = 7.9 Hz, 2H), 7.72 (d, J = 8.5 Hz, 2H), 7.69 (s, 2H), 7.57 (d, J = 8.7 Hz, 2H), 7.41−7.31 (m, 24H), 7.28 (s, 4H), 7.13−7.10 (m, 6H), 7.01 (d, J = 8.7 Hz, 4H), 6.94 (d, J = 8.3 Hz, 2H), 6.74 (d, J = 1.9 Hz, 4H), 6.63 (d, J = 8.1 Hz, 2H), 6.57 (t, J = 1.9 Hz, 2H), 5.02 (s, 4H), 4.99 (s, 1H), 4.96 (s, 8H), 4.87 (s, 4H), 3.30 (s, 1H), 2.63 (s, 6H), 1.83 (s, 12H) 1.32 (s, 18H), 1.30 (s, 36H); 13C NMR (100 MHz, CDCl3): δ (ppm) 160.2, 158.54, 158.50, 155.5, 151.0, 150.9, 149.97, 149.96, 149.8, 149.7, 144.9, 144.0, 143.5, 143.1, 139.3, 139.2, 138.9, 137.5, 134.5, 134.3, 133.8, 133.6, 133.2, 133.0, 132.7, 132.2, 132.1, 131.1, 131.0, 130.9, 130.7, 130.3, 129.9, 127.7, 127.61, 127.55, 125.48, 125.46, 123.1, 122.7, 122.2, 121.2, 120.20, 120.18, 119.5, 119.3, 115.7, 115.3, 114.3, 114.0, 106.2, 101.6, 97.4, 97.3, 91.5, 91.3, 90.3, 88.0, 83.8, 78.1, 70.0, 69.9, 69.8, 34.54, 34.52, 31.33, 31.30, 21.6, 21.5; IR (KBr/cm−1) 3288, 3032, 2960, 2906, 2867, 2204, 1606, 1508, 1460, 1363, 1226, 1153, 999, 832, 722, 535; MS (MALDI-TOF) m/z 2592.2 [M+]; HRMS (MALDITOF) calcd for C180H164N4O964Zn m/z 2589.1784; found m/z 2589.1789. Porphyrin 8. Porphyrin 7 (64.0 mg, 24.7 μmol), K2CO3 (13.6 mg, 98.4 μmol), and 1,4-dibromobutane (0.03 mL, 300 μmol) in dry DMF (5.0 mL) were stirred at room temperature under nitrogen for 9 h. The mixture was washed with saturated solution of NH4Cl, water, and brine and dried over anhydrous Na2SO4. The solvent was evaporated under reduced pressure. The resulting purple solid was separated by column chromatography on silica gel (hexane:CH2Cl2 = 1:3 (v/v)) to afford 8 (54.0 mg, 80%) as a purple solid. 8: purple solid; mp 165−167 °C; 1H NMR (400 MHz, CDCl3): δ (ppm) 8.90−8.77 (m, 8H), 8.23− 8.17 (m, 4H), 7.93 (d, J = 8.2 Hz, 2H), 7.85 (d, J = 7.8 Hz, 2H), 7.72 (d, J = 8.7 Hz, 2H), 7.69 (s, 2H), 7.57 (d, J = 8.7 Hz, 2H), 7.40−7.30 (m, 24H), 7.27 (s, 4H), 7.13 (s, 2H) 7.10 (d, J = 8.7 Hz, 4H), 7.00 (d,

J = 8.7 Hz, 4H), 6.97 (d, J = 8.7 Hz, 2H), 6.73 (d, J = 1.8 Hz, 4H), 6.68 (d, J = 8.7 Hz, 2H), 6.55 (brt, 2H), 5.00 (s, 4H), 4.95 (s, 8H), 4.87 (s, 4H), 3.91 (t, J = 5.9 Hz, 2H), 3.44 (t, J = 6.4 Hz, 2H), 3.27 (s, 1H), 2.62 (s, 6H), 2.05−1.98 (m, 2H), 1.91−1.87 (m, 2H), 1.82 (s, 12H) 1.32 (s, 18H), 1.30 (s, 36H); 13C NMR (100 MHz, CDCl3): δ (ppm) 160.3, 158.7, 158.60, 158.56, 151.01, 150.97, 150.0, 149.8, 149.7, 144.9, 144.0, 143.6, 143.2, 143.0, 139.3, 139.2, 139.0, 137.5, 134.5, 134.4, 133.9, 133.7, 133.2, 133.0, 132.6, 132.2, 132.0, 131.1, 130.9, 130.8, 130.4, 130.3, 129.9, 127.7, 127.61, 127.58, 125.51, 125.49, 123.2, 122.7, 122.2, 122.0, 121.2, 120.2, 119.5, 119.2, 115.7, 114.3, 114.0, 106.2, 101.6, 97.44, 97.42, 91.5, 91.3, 90.3, 88.2, 83.8, 78.1, 70.0, 69.9, 69.8, 66.8, 34.58, 34.56, 33.3, 31.4, 31.3, 29.3, 27.8, 21.7, 21.5; IR (KBr/cm−1) 3415, 3288, 3033, 2960, 2868, 2206, 1605, 1508, 1363, 1244, 1154, 999, 831, 725, 538; MS (MALDI-TOF) m/z 2727.2 [M+]; HRMS (MALDI-TOF) calcd for C184H17179BrN4O964Zn m/z 2723.1515; found m/z 2723.1531. Dendrimer 2. Porphyrin 8 (108 mg, 40.0 μmol), dendron 10 (86.1 mg, 42.6 μmol), Pd2(dba)3·CHCl3 (6.2 mg, 5.9 μmol), and AsPh3 (12.1 mg, 40 μmol) in degassed iPr2EtN (5.0 mL) and degassed CH2Cl2 (10.0 mL) were stirred at room temperature overnight. The mixture was filtered through Celite and the solvent was evaporated under reduced pressure. The residue was dissolved in CH2Cl2 and washed with water and brine, and dried over anhydrous Na2SO4. The solvent was evaporated under reduced pressure. The resulting purple solid was separated by column chromatography on silica gel (hexane:CH2Cl2 = 3:4 (v/v) and CH2Cl2) to afford 2 (156 mg, 84%) as a purple solid. 2: purple solid; mp 245−247 °C; 1H NMR (300 MHz, CDCl3): δ (ppm) 8.90 (d, J = 4.7 Hz, 4H), 8.80 (d, J = 4.5 Hz, 4H), 8.24 (d, J = 8.3 Hz, 4H), 7.89 (d, J = 8.1 Hz, 4H), 7.72 (d, J = 8.7 Hz, 8H), 7.69 (s, 4H), 7.58 (d, J = 8.7 Hz, 8H), 7.42−7.31 (m, 48H), 7.29 (s, 4H), 7.13−7.10 (m, 12H), 7.03−6.96 (m, 12H), 6.79 (d, J = 9.1 Hz, 2H), 6.75 (d, J = 2.1 Hz, 8H), 6.70 (d, J = 8.9 Hz, 2H), 6.57 (t, J = 2.1 Hz, 4H), 5.02 (s, 8H), 4.96 (s, 16H), 4.88 (s, 8H), 4.62 (s, 2H), 3.94 (t, J = 5.8 Hz, 2H), 3.46 (t, J = 6.4 Hz, 2H), 2.63 (s, 6H), 2.08−1.99 (m, 2H), 1.95−1.88 (m, 2H), 1.83 (s, 12H) 1.32 (s, 36H), 1.30 (s, 72H), 0.16 (s, 9H); 13C NMR (100 MHz, CDCl3): δ (ppm) 160.3, 158.7, 158.60, 158.58, 158.56, 157.6, 151.00, 150.97, 150.95, 150.0, 149.8, 144.9, 144.1, 144.0, 143.1, 139.3, 139.2, 138.9, 137.5, 134.5, 133.9, 133.8, 133.7, 133.2, 133.02, 133.00, 132.5, 132.4, 131.1, 130.9, 130.8, 130.4, 129.9, 127.7, 127.63, 127.60, 127.57, 125.50, 125.48, 123.2, 122.8, 122.7, 122.2, 120.2, 120.1, 119.50, 119.46, 116.4, 115.7, 114.8, 114.3, 114.0, 106.2, 101.6, 99.5, 97.4, 97.2, 93.0, 91.5, 91.3, 90.3, 88.4, 88.2, 70.0, 69.9, 69.8, 66.8, 56.6, 34.6, 33.3, 31.4, 31.3, 29.3, 27.8, 21.7, 21.5, −0.3; IR (KBr/cm−1) 3290, 3031, 2960, 2868, 2206, 1605, 1508, 1462, 1364, 1244, 1154, 999, 831, 722, 549; MS (MALDI-TOF) m/z 4620.1 [M+]; Anal. Calcd for C316H305BrN4O18SiZn·H2O: C, 81.83; H, 6.67; N, 1.21; Found: C, 81.50; H, 6.63; N, 1.12. Dendrimer 11. Dendrimer 2 (30.1 mg, 6.55 μmol), K2CO3 (19.0 mg, 137 μmol), and 18-crown-6 (8.1 mg, 30 μmol) in CH3OH (6.0 mL) and CH2Cl2 (24.0 mL) was stirred at room temperature for 3 h. The mixture was washed with saturated solution of NH4Cl, water, and brine and dried over anhydrous Na2SO4. The solvent was evaporated under reduced pressure. The resulting purple solid was separated by column chromatography on silica gel (hexane:CH2Cl2 = 3:4 (v/v)) to afford 11 as a purple solid (26.7 mg, 90%). 11: purple solid; mp 243− 245 °C; 1H NMR (400 MHz, CDCl3): δ (ppm) 8.90 (d, J = 4.6 Hz, 4H), 8.80 (d, J = 5.0 Hz, 4H), 8.23 (d, J = 8.2 Hz, 4H), 7.93 (d, J = 7.8 Hz, 4H), 7.72 (d, J = 8.2 Hz, 8H), 7.69 (s, 4H), 7.57 (d, J = 8.7 Hz, 4H), 7.57 (d, J = 8.7 Hz, 4H), 7.41−7.32 (m, 48H), 7.28 (s, 4H), 7.13−7.10 (m, 12H), 7.03−6.97 (m, 12H), 6.79 (d, J = 8.7 Hz, 2H), 6.75 (d, J = 2.3 Hz, 8H), 6.69 (d, J = 9.1 Hz, 2H), 6.57 (t, J = 2.3 Hz, 4H), 5.02 (s, 8H), 4.96 (s, 16H), 4.88 (s, 8H), 4.63 (d, J = 2.3 Hz, 2H), 3.93 (t, J = 6.0 Hz, 2H), 3.46 (t, J = 6.4 Hz, 2H), 2.49 (t, J = 2.3 Hz, 1H), 2.63 (s, 6H), 2.07−2.00 (m, 2H), 1.94−1.89 (m, 2H), 1.83 (s, 12H) 1.32 (s, 36H), 1.30 (s, 72H); 13C NMR (100 MHz, CDCl3): δ (ppm) 160.3, 158.7, 158.63, 158.61, 158.58, 157.3, 151.03, 150.99, 150.0, 149.8, 144.9, 144.1, 144.0, 143.1, 139.4, 139.2, 138.9, 137.6, 137.5, 134.5, 133.87, 133.85, 133.7, 133.2, 133.03, 132.99, 132.6, 132.5, 131.1, 131.0, 130.9, 130.8, 130.4, 129.9, 127.7, 127.64, 127.62, 8924

DOI: 10.1021/acs.joc.7b01275 J. Org. Chem. 2017, 82, 8917−8926

Article

The Journal of Organic Chemistry

of pyridine-d5): δ (ppm) 9.65 (d, J = 4.6 Hz, 4H), 8.69 (d, J = 4.6 Hz, 4H), 7.98 (s, 4H) 7.80 (d, J = 8.7 Hz, 8H), 7.60 (d, J = 8.2 Hz, 8H), 7.42−7.33 (m, 48H), 7.28 (s, 4H), 7.17 (s, 4H), 7.16 (d, J = 8.7 Hz, 8H), 7.03 (d, J = 8.7 Hz, 8H), 6.96 (d, J = 8.7 Hz, 4H), 6.78 (d, J = 2.3 Hz, 8H), 6.65 (d, J = 8.7 Hz, 4H), 6.60 (t, J = 2.3 Hz, 4H), 5.04 (s, 8H), 4.98 (s, 16H), 4.88 (s, 8H), 3.86 (t, J = 5.9 Hz, 4H), 3.32 (t, J = 6.4 Hz, 4H), 2.63 (s, 6H), 1.84−1.69 (m, 20H), 1.32 (s, 36H), 1.30 (s, 72H); 13C NMR (100 MHz, CDCl3 with a drop of pyridine-d5): δ (ppm) 160.3, 158.70, 158.67, 158.6, 151.9, 150.99, 150.95, 149.8, 145.1, 144.1, 139.4, 139.0, 138.9, 137.4, 133.9, 133.7, 133.3, 133.0, 132.5, 131.3, 131.0, 130.8, 130.4, 127.7, 127.62, 127.58, 125.51, 125.48, 124.2, 122.8, 121.1, 120.2, 120.0, 115.7, 114.4, 114.3, 114.0, 106.2, 101.6, 100.1, 97.6, 97.5, 96.2, 95.7, 91.6, 88.2, 70.1, 69.9, 69.8, 67.1, 51.1, 34.6, 31.4, 31.3, 26.4, 25.6, 21.6, 21.5; IR (KBr/cm−1) 3034, 2960, 2906, 2868, 2203, 2095, 1605, 1508, 1461, 1413, 1364, 1244, 1154, 1016, 1001, 830, 545; MS (MALDI-TOF) m/z 4416.2 [M+]; Anal. Calcd for C302H294N10O18Zn: C, 82.12; H, 6.71; N, 3.17; Found: C, 81.74; H, 6.71; N, 3.40. Trimer 1. Dendrimer 11 (29.2 mg, 6.42 μmol), dendrimer 14 (11.7 mg, 2.65 μmol), copper(II) sulfate pentahydrate (6.8 mg, 27 μmol), and sodium L-ascorbate (23.8 mg, 120 μmol) in DMF (8.0 mL) were stirred under nitrogen at room temperature for 2 days. CH2Cl2 was added to the mixture. The solution was washed with water and brine and dried over anhydrous Na2SO4. After filtration the solvent was evaporated under reduced pressure and the residue was separated by column chromatography on silica gel (CH2Cl2 and CH2Cl2:ethyl acetate = 1:1 (v/v)) to afford a crude product. The product was further separated by preparative recycling GPC (JAIGEL 3H-4H columns, chloroform) to afford 1 as a black solid (23.8 mg, 66%). 1: black solid; mp 270 °C (decomposition); 1H NMR (300 MHz, CDCl3 with a drop of pyridine-d5): δ (ppm) 9.62 (d, J = 4.5 Hz, 4H), 8.81− 8.77 (m, 8H), 8.71−8.68 (m, 12H), 8.20 (d, J = 8.1 Hz, 4H), 8.12 (d, J = 7.4 Hz, 2H), 7.98−7.92 (m, 6H), 7.89 (d, J = 8.1 Hz, 4H), 7.81− 7.64 (m, 36H), 7.62−7.52 (m, 24H), 7.43−7.30 (m, 146H), 7.26 (s, 12H), 7.18−7.08 (m, 36H), 7.06−6.92 (m, 36H), 6.81−6.63 (m, 36H), 6.60−6.54 (m, 12H), 5.11 (s, 4H), 5.03 (s, 24H), 4.97 (s, 48H), 4.91−4.83 (m, 24H), 4.42 (t, J = 5.7 Hz, 4H), 3.97−3.82 (m, 8H), 3.46 (t, J = 6.4 Hz, 4H), 2.62 (s, 18H), 2.14−1.98 (m, 8H), 1.96−1.72 (m, 44H), 1.32−1.30 (m, 324H); 13C NMR spectrum of trimer 1 was not obtained because of its poor solubility.; IR (KBr/cm−1) 3033, 2959, 2867, 2203, 1727, 1605, 1507, 1460, 1364, 1243, 1153, 1015, 997, 830, 729, 537; MS (MALDI-TOF) m/z 13515.3 [M+]; Anal. Calcd for C928H888Br2N18O54Zn3·4(H2O): C, 82.05; H, 6.65; N, 1.86; Found: C, 81.72; H, 6.69; N, 2.05. Electronic and Emission Spectra Measurement. Electronic and emission spectra were recorded on a Shimadzu UV-2550, and Hitachi F-7000 spectrometers, respectively, using 1 cm × 1 cm quartz cuvettes. For the investigation of energy-transfer efficiency, fluorescence quantum yields are relative to tetraphenylporphyrin as the external standards.16

127.59, 125.53, 125.50, 123.2, 122.8, 122.7, 122.2, 120.2, 120.1, 119.6, 119.5, 116.7, 115.7, 114.8, 114.3, 114.0, 106.2, 101.6, 97.4, 97.1, 91.5, 91.4, 90.3, 88.4, 88.2, 78.1, 75.8, 70.0, 69.9, 69.8, 66.8, 55.7, 34.6, 33.4, 31.4, 31.3, 29.4, 27.8, 21.6, 21.5; IR (KBr/cm−1) 3036, 2960, 2867, 2206, 1605, 1507, 1364, 1242, 1154, 1016, 999, 831, 538; MS (MALDI-TOF) m/z 4548.1 [M+]; Anal. Calcd for C313H297BrN4O18Zn·5(H2O): C, 81.05; H, 6.67; N, 1.21; Found: C, 80.94; H, 6.59; N, 1.37. Dendrimer 13. Dendron 4 (263 mg, 134 μmol), porphyrin 12 (45.3 mg, 68.8 μmol), Pd2(dba)3·CHCl3 (9.3 mg, 8.9 μmol), and AsPh3 (21.5 mg, 70.2 μmol) in degassed Et3N (5 mL) and degassed CH2Cl2 (10 mL) were stirred at room temperature overnight. The mixture was evaporated under reduced pressure. The residue was dissolved in CH2Cl2 and washed with water and brine and dried over anhydrous Na2SO4. The solvent was evaporated under reduced pressure. The resulting green solid was separated by column chromatography on silica gel (hexane:CH2Cl2 = 1:3 (v/v) and CH2Cl2:ethyl acetate = 1:1 (v/v)) to afford 13 as a green solid (206 mg, 71%). 13: green solid; mp 250 °C (decomposition); 1H NMR (300 MHz, CDCl3 with a drop of pyridine-d5): δ (ppm) 10.89 (brs, 2H), 9.63 (d, J = 4.5 Hz, 4H), 8.68 (d, J = 4.5 Hz, 4H), 7.98 (s, 4H) 7.80 (d, J = 8.7 Hz, 8H), 7.60 (d, J = 8.7 Hz, 8H), 7.40−7.28 (m, 52H), 7.15 (d, J = 8.7 Hz, 8H), 7.15 (s, 4H), 7.02 (d, J = 8.7 Hz, 8H), 6.95 (d, J = 8.5 Hz, 4H), 6.77 (d, J = 2.1 Hz, 8H), 6.72 (d, J = 8.5 Hz, 4H), 6.58 (t, J = 2.1 Hz, 4H), 5.04 (s, 8H), 4.97 (s, 16H), 4.87 (s, 8H), 2.63 (s, 6H), 1.82 (s, 12H), 1.31 (s, 36H), 1.30 (s, 72H); 13C NMR (100 MHz, CDCl3 with a drop of pyridine-d5): δ (ppm) 160.3, 158.7, 158.6, 158.3, 151.9, 151.0, 150.9, 149.8, 145.1, 143.9, 139.4, 139.0, 138.9, 137.4, 133.9, 133.7, 133.3, 133.1, 132.7, 131.3, 131.0, 130.8, 130.4, 127.69, 127.65, 127.6, 125.51, 125.47, 124.2, 122.5, 121.1, 120.5, 120.1, 115.8, 114.4, 114.0, 106.2, 101.6, 100.1, 98.2, 97.7, 96.2, 95.6, 91.5, 87.5, 70.1, 69.9, 69.8, 34.5, 31.34, 31.31, 21.6, 21.5; IR (KBr/cm−1) 3033, 2960, 2904, 2867, 2200, 1606, 1508, 1460, 1363, 1233, 1153, 1015, 997, 831, 532; MS (MALDI-TOF) m/z 4223.0 [M+]; Anal. Calcd for C294H280N4O18Zn· 2(H2O): C, 82.91; H, 6.72; N, 1.32; Found: C, 82.57; H, 6.74; N, 1.35. Dendrimer 3. Dendrimer 13 (31.1 mg, 7.36 μmol), K2CO3 (9.0 mg, 65.1 μmol), and 1,4-dibromobutane (0.02 mL, 200 μmol) in dry DMF (5.0 mL) were stirred at room temperature under nitrogen overnight. The mixture was washed with water and brine and dried over anhydrous Na2SO4. The solvent was evaporated under reduced pressure. The resulting green solid was separated by column chromatography on silica gel (hexane:CH2Cl2:NEt3 = 2:3:0.1 (v/v/ v)) to afford 3 as a green solid (30.0 mg, 90%). 3: green solid; mp 285 °C (decomposition); 1H NMR (300 MHz, CDCl3 with a drop of pyridine-d5): δ (ppm) 9.64 (d, J = 4.5 Hz, 4H), 8.68 (d, J = 4.5 Hz, 4H), 7.98 (s, 4H) 7.80 (d, J = 8.7 Hz, 8H), 7.59 (d, J = 8.7 Hz, 8H), 7.42−7.28 (m, 52H), 7.16 (d, J = 8.7 Hz, 8H), 7.15 (s, 4H), 7.03 (d, J = 8.9 Hz, 8H), 6.98 (d, J = 8.9 Hz, 4H), 6.77 (d, J = 2.3 Hz, 8H), 6.69 (d, J = 8.9 Hz, 4H), 6.59 (t, J = 2.3 Hz, 4H), 5.04 (s, 8H), 4.98 (s, 16H), 4.89 (s, 8H), 3.93 (t, J = 5.8 Hz, 4H), 3.46 (t, J = 6.4 Hz, 4H), 2.63 (s, 6H), 2.07−1.88 (m, 8H), 1.83 (s, 12H), 1.32 (s, 36H), 1.30 (s, 72H) ; 13C NMR (100 MHz, CDCl3 with a drop of pyridine-d5): δ (ppm) 160.3, 158.71, 158.67, 158.6, 151.9, 151.00, 150.96, 149.8, 145.1, 144.1, 139.4, 139.0, 138.93, 138.92, 133.9, 133.7, 133.3, 133.0, 132.5, 131.3, 131.0, 130.8, 130.4, 127.61, 127.58, 125.52, 125.49, 124.2, 121.1, 120.2, 120.0, 115.7, 114.4, 114.3, 114.0, 106.2, 101.6, 100.0, 97.6, 97.4, 96.2, 95.70, 95.67, 91.6, 88.2, 70.1, 69.9, 69.8, 66.8, 34.6, 33.3, 31.4, 31.3, 29.3, 27.7, 21.6, 21.5; IR (KBr/cm−1) 3456, 3034, 2960, 2868, 2203, 1605, 1508, 1461, 1364, 1244, 1154, 1016, 1001, 831, 543; MS (MALDI-TOF) m/z 4493.0 [M+].; Anal. Calcd for C302H294Br2N4O18Zn·2(H2O): C, 80.09; H, 6.63; N, 1.24; Found: C, 79.91; H, 6.56; N, 1.24. Dendrimer 14. Dendrimer 3 (29.1 mg, 6.48 μmol) and NaN3 (10.7 mg, 165 μmol) in dry DMF (5.0 mL) were stirred at 80 °C under nitrogen for 35 min. The mixture was washed with water and brine and dried over anhydrous Na2SO4. The solvent was evaporated under reduced pressure. The resulting green solid was separated by column chromatography on silica gel (hexane:CH2Cl2 = 1:2 (v/v) and CH2Cl2) to afford 14 as a green solid (23.4 mg, 82%). 14: green solid; mp 275 °C (decomposition); 1H NMR (400 MHz, CDCl3 with a drop

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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.7b01275. UV−vis absorption and emission spectra and NMR, MS data (PDF)

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AUTHOR INFORMATION

Corresponding Author

*[email protected] ORCID

Keiji Okada: 0000-0002-2817-9335 Masatoshi Kozaki: 0000-0002-9737-5639 Present Address †

Graduate School of Engineering Science, Osaka University, Machikaneyama, Toyonaka, Osaka 560−8531, Japan 8925

DOI: 10.1021/acs.joc.7b01275 J. Org. Chem. 2017, 82, 8917−8926

Article

The Journal of Organic Chemistry Notes

(15) The additional change of the absorption was continuously observed, when temperature decreased from 20 °C to −50 °C (Figure S6). Intermolecular interaction may have contribution for the spectral change at lower temperature. (16) Goll, J. G.; Moore, K. T.; Ghosh, A.; Therien, M. J. J. Am. Chem. Soc. 1996, 118, 8344−8354. (17) Lakowicz, J. R. Principles of Fluorescence Spectroscopy, 3 ed; Springer: New York, 2006; pp 443−475.

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was partially supported by Grant-in-Aid for Scientific Research from JSPS KAKENHI (No. JP17K05790 for M.K. and K.O., No. JP26288041 and No. JP15H00956 for K.O., and No. JP26102005 for S.S.).

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REFERENCES

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DOI: 10.1021/acs.joc.7b01275 J. Org. Chem. 2017, 82, 8917−8926