Functionalization of SWNTs with Porphyrin Dendrons
A R T I C L E S
or VWR and were used as received. For synthesis, CH2Cl2 (CaH2,
N2), toluene (K/benzophenone, N2), THF (K/benzophenone, N2)
were distilled before use. 5,10,15-Tris-(4-tert-butylphenyl)-20-(4-
aminophenyl)porphyrin56 and 3,5-(dipropargyloxy)benzyl chloride
859 were synthesized according to the literature procedure.
Synthesis. Porphyrin 7. To a solution of zinc porphyrin 5 (100
mg, 0.116 mmol) in dry THF (40 mL) was added tert-butylnitrite
(28 µL, 0.232 mmol) and azidotrimethylsilane (31 µL, 0.232 mmol)
at 0 °C under Ar. The solution was stirred for 30 min and checked
by TLC (eluent toluene). The completion of the reaction sometimes
requires the addition of 2 additional equivalents of tert-butylnitrite
and azidotrimethylsilane. Then water was added, and the mixture
was extracted with CH2Cl2; the organic phase was filtered through
hydrophobic paper filter (Phase Separator Whatman filter) and
evaporated to dryness. Purification of the residue by column
chromatography (eluent toluene) gave pure 6 (73 mg, 71% yield)
as a pink powder. 1H NMR (300 MHz, CDCl3) δ 9.00 (d, 2H, arom
H), 8.98 (s, 4H, arom H), 8.91 (d, 2H, arom H), 8.21 (d, 2H, arom
H), 8.16 (d, 6H, arom H), 7.76 (d, 6H, arom H), 7.38 (d, 2H, arom
H), 1.62 (s, 27H, C(CH3)3). FT-IR (KBr) υ (cm-1) 2959, 2901,
2863, 2120, 2083, 1601, 1525, 1493, 1461, 1392, 1337, 1288, 1266,
1205, 1179, 1107, 1066, 998, 852, 800, 721, 694, 528. UV-vis
(toluene) λmax (nm) 425, 552, 592. MALDI-TOF MS C56H51N7Zn
(885.35) m/z ) 885.34 [M+].
p-SWNTs 4. Raw SWNT material (40 mg) was sonicated in
nitric acid (35 vol %) (150 mL) with a sonic bath (160 W max)
(100% for 5 min and then 40% for 15 min) and then heated at 100
°C for 4 h. The suspension was then cooled and vacuum filtered
through a PTFE membrane (Sartorius, 0.2 µm pore). While pursuing
vacuum filtration, the thick SWNT layer formed on the filtration
membrane (buckypaper) was washed by 200 mL of deionized water;
the pH was monitored during the washing and was about 7 at the
end of the process. The nanotubes were redispersed in NaOH 2 M
(100 mL) using the sonic bath (100% for 10 min) and then filtered
through a PTFE membrane and washed with NaOH 2 M, deionized
water, and then HCl 1 M followed by deionized water until the
filtrate was neutral. Finally, the buckypaper was redispersed in
hydrogen peroxide (30%) (150 mL) using the sonic bath (100%
for 5 min and then 40% for 10 min). The suspension was heated at
100 °C for 1 h, cooled down to room temperature, and then vacuum
filtered through a PTFE membrane. The nanotubes were washed
by 200 mL of deionized water and then dried at 50 °C under high
vacuum. The overall yield of the purification process was 45% (18
mg).
f-SWNTs 5. A suspension of purified SWNTs 4 (15 mg) in NMP
(50 mL) was first sonicated for 10 min and then 4-(2-trimethylsi-
lyl)ethynylaniline57 (475 mg, 2.5 mmol, 2 equiv C) and isoamyl
nitrite (335 µL, 2.5 mmol, 22 equiv C) were added. The reaction
mixture was stirred at 70 °C overnight under Ar. After cooling to
room temperature, the suspension was filtered on a PTFE membrane
(0.2 µm), and the black solid was washed several times with NMP.
The nanotubes were redispersed in NMP (50 mL), and the entire
procedure was repeated two times more. The SWNTs reacted in
total with 6 equiv C of 4-(2-trimethylsilyl)ethynylaniline. A small
part (less than 1.0 mg) of the solid on the filter was collected for
analysis; the rest was redissolved and kept in NMP (90 mL; 1 mg
SWNT per 6 mL of NMP).
SWNT-ZnP 1. To a suspension of f-SWNTs 5 (4 mg) in NMP
(24 mL) at 0 °C was added a solution of tetrabutylammonium
fluoride (1 M in THF) (10 µL). The reaction mixture was stirred at
room temperature for 1 h, and then porphyrin 7 (10 mg, 11.0 µmol),
Cu(MeCN)4PF6 (3 mg, 8.0 µmol), 2,6-lutidine (50 µL), and THPTA
(a spatula tip) were added; then oxygen in the mixture was removed
by several cycles of vacuum/argon. The reaction mixture was stirred
at room temperature for 48 h and then filtered on a PTFE membrane
(0.2 µm), washed with NMP, deionized water, saturated NH4Cl
solution, and then water and NMP. In order to remove the eventual
products absorbed on the nanotubes, the buckypaper was redispersed
in NMP, then refiltered and washed with NMP, THF, and CH2Cl2.
These operations were repeated until the filtrate contained no
porphyrin (checked by UV-vis absorption).
Porphyrin 3. To a solution of porphyrin 7 (15 mg, 0.017 mmol)
in a mixture THF/water (10/1 mL) were added phenylacetylene (4
µL, 0.034 mmol), Cu(MeCN)4PF6 (3 mg, 0.008 mmol), 2,6-lutidine
(100 µL), and THPTA (a spatula tip). The reaction mixture was
frozen, and the oxygen was removed by several cycles of vacuum/
argon. Finally, the solution was stirred at 60 °C for 20 h, then water
was added, and the mixture was extracted with CH2Cl2; the organic
phase was filtered through hydrophobic paper filter (Phase Separator
Whatman filter) and evaporated to dryness. Purification of the
residue by column chromatography (eluent CH2Cl2) gave pure 7
(10 mg, 60% yield) as a purple powder. 1H NMR (300 MHz,
CDCl3) δ 8.04 (d, 2H, arom H), 9.00 (s, 4H, arom H), 8.95 (d, 2H,
arom H), 8.53 (s, 1H, arom H), 8.43 (d, 2H, arom H), 8.21 (d, 2H,
arom H), 8.16 (d, 6H, arom H), 8.05 (d, 2H, arom H), 7.77 (d, 2H,
arom H), 7.55 (t, 2H, arom H), 7.48-7.40 (m, 1H, arom H), 1.63
(s, 27H, C(CH3)3). FT-IR (KBr) υ (cm-1) 2958, 2901, 2865, 1525,
1492, 1461, 1394, 1362, 1338, 1267, 1205, 1109, 1070, 998, 853,
811, 796, 758, 719, 692, 582. UV-vis (toluene) λmax (nm) 425,
550, 589. MALDI-TOF MS C64H57N7Zn (987.40) m/z ) 987.42
[M+].
Compound 9. To a solution of porphyrin 7 (50 mg, 0.056 mmol)
in THF (10 mL) were added 3,5-(dipropargyloxy)benzyl chloride
8 (6.6 mg, 0.028 mmol), Cu(MeCN)4PF6 (5 mg, 0.014 mmol), 2,6-
lutidine (100 µL), and water (1 mL). The reaction mixture was
frozen, and the oxygen was removed by several cycles of vacuum/
argon. Finally, the solution was stirred at 60 °C overnight, water
was added, and the mixture was extracted with CH2Cl2; the organic
phase was filtered through hydrophobic paper filter (Phase Separator
Whatman filter) and evaporated to dryness. Purification of the
residue by column chromatography (eluent first CH2Cl2, then
CH2Cl2/Et2O 100/5) gave pure 9 (27 mg, 48% yield) as a purple
powder. Note that about 10 mg of monoadduct (compound
containing only 1 porphyrin) was recovered from column chroma-
1
tography. H NMR (300 MHz, toluene-d8, 60 °C) δ 9.15 (d, 4H,
arom H), 9.11-9.06 (m, 8H, arom H), 8.94 (d, 4H, arom H), 8.31
(d, 4H, arom H), 8.26 (d, 8H, arom H), 8.05 (d, 4H, arom H), 7.05
(d, 4H, arom H), 6.79 (s, 2H, arom H), 6.57 (broad d, 2H, arom
H), 6.25 (broad signal, 1H, arom H), 4.25 (s, 2H, CH2Cl), 3.61
(broad s, 4H, OCH2), 1.49 (s, 54H, C(CH3)3). FT-IR (KBr) υ (cm-1
)
2957, 2924, 2901, 2865, 1595, 1524, 1490, 1459, 1394, 1362, 1338,
1267, 1205, 1150, 1109, 1067, 1039, 998, 853, 811, 796, 719, 582.
UV-vis (toluene) λmax (nm) 424, 550, 590. MALDI-TOF MS
C125H113ClN14O2Zn2 (2004.74) m/z ) 2004.68 [M+].
Compound 10. To a solution of porphyrin 9 (20 mg, 0.010
mmol) in THF (5 mL) was added sodium azide (6.5 mg, 0.100
mmol) in water (1 mL). The reaction mixture was stirred under
reflux for 1 day, and then water was added, and the mixture was
extracted with CH2Cl2; the organic phase was filtered through
hydrophobic paper filter (Phase Separator Whatman filter) and
evaporated to dryness. Purification of the residue by column
chromatography (eluent first CH2Cl2, then CH2Cl2/Et2O 100/5) gave
1
pure 10 (17 mg, 85% yield) as a purple powder. H NMR (300
MHz, toluene-d8, 60 °C) δ 9.14 (d, 4H, arom H), 9.10-9.05 (m,
8H, arom H), 8.93 (d, 4H, arom H), 8.30 (d, 4H, arom H), 8.25 (d,
8H, arom H), 8.06 (d, 4H, arom H), 7.15 (d, 4H, arom H), 6.91 (s,
2H, arom H), 6.44 (broad d, 2H, arom H), 6.35 (broad signal, 1H,
arom H), 3.82 (broad signal, 6H, CH2N and OCH2), 3.61 (broad s,
4H, CH2N), 1.49 (s, 54H, C(CH3)3). FT-IR (KBr) υ (cm-1) 2954,
2924, 2901, 2864, 2095, 1594, 1523, 1490, 1458, 1393, 1362, 1338,
1266, 1204, 1150, 1108, 1066, 1039, 997, 852, 810, 796, 719, 581.
UV-vis (toluene) λmax (nm) 425, 552, 592. MALDI-TOF MS
C125H113N17O2Zn2 (2011.78) m/z ) 2011.84 [M+].
SWNT-ZnP 2. To a suspension of f-SWNTs 5 (3 mg) in NMP
(18 mL) at 0 °C was added a solution of tetrabutylammonium
fluoride (1 M in THF) (10 µL). The reaction mixture was stirred at
room temperature for 1 h, and then porphyrin dendron 10 (10 mg,
5.0 µmol), Cu(MeCN)4PF6 (3 mg, 8.0 mmol), 2,6-lutidine (20 µL),
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J. AM. CHEM. SOC. VOL. 131, NO. 42, 2009 15401