Meso-meso linked diporphyrin functionalized single-walled carbon nanotubes

Article abstract of DOI:10.1016/j.jphotochem.2010.09.001

Meso-meso linked diporphyrins ([H₂Por]₂) covalently functionalized soluble single-walled carbon nanotubes ([H₂Por] ₂-SWNTs) have been successfully prepared. As a light-harvesting chromophore, meso-meso linked di

Full text of DOI:10.1016/j.jphotochem.2010.09.001

Journal of Photochemistry and Photobiology A: Chemistry 216 (2010) 15–23
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Meso-meso linked diporphyrin functionalized single-walled carbon nanotubes
Lin He , Yi-Zhou Zhu , Jian-Yu Zheng , Yan-Feng Ma , Yong-Sheng Chenb
a
a
a,∗
b
a
State Key Laboratory and Institute of Elemento-Organic Chemistry, Nankai University, 94 Weijin Road, Nankai District, Tianjin 300071, China
Center for Nanoscale Science and Technology and Key Laboratory for Functional Polymer Materials, Institute of Polymer Chemistry,
b
College of Chemistry, Nankai University, Tianjin 300071, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 April 2010
Received in revised form 17 August 2010
Accepted 3 September 2010
Available online 15 September 2010
Meso-meso linked diporphyrins ([H Por] ) covalently functionalized soluble single-walled carbon
2
2
nanotubes ([H2Por]2-SWNTs) have been successfully prepared. As a light-harvesting chromophore, meso-
meso linked diporphyrins have been incorporated into a photosynthetic electron-transfer model with
SWNTs as an electron-acceptor. The steady emission characteristics revealed the existence of the effective
energy and electron transfer between the excited porphyrin moiety and SWNTs, and the electron transfer
process wasconfirmedby electrochemicalstudy. The charge separation quenching process was supported
by the results of time-resolved transient absorption spectra, and the lifetime of charge-separation state
was observed to be 145 ns, which was 2.5 times of that of monoporphyrin modified SWNTs (TPP-SWNTs).
Key words:
Meso-meso linked diporphyrin
Single-walled carbon nanotube
Charge separate
Photoinduced electron transfer
© 2010 Elsevier B.V. All rights reserved.
1
. Introduction
Carbon nanotubes are actively being investigated for producing
an 86% reduction of fluorescence quantum yield in the nanohybrid
employing amide linkage between SWNTs and porphyrin [43],
while more than 97% reduction with a direct linkage mode [42].
Obviously, the direct linkage mode facilitated the effective energy
and electron transfer between the excited porphyrin moiety and
SWNTs. We report here the preparation of the meso-meso linked
diporphyrin functionalized SWNTs with a direct linkage. The
replacement of monoporphyrin with meso-meso linked dipor-
phyrin can result in a broader absorption, which attributes to the
exciton coupling of the porphyrin subunits [47–54]. Furthermore,
meso-meso linked diporphyrin has prolonged charge-separation
(CS) lifetime of porphyrin–acceptor system compared with
monoporphyrin [50]. Therefore, meso-meso linked diporphyrin
functionalized SWNTs ([H Por] -SWNTs) (Scheme 1) is rationally
photoelectronic and photovoltaic devices [1–6] because of their
high delocalized, extended ␲-electron system [7,8]. Especially,
most single-walled carbon nanotubes (SWNTs) have the diameter
of approximately 1 nm, which results in a higher aspect ratio
and a greater curvature of the sidewall. That further alters the
extent of orbital overlap and the electronic density [9], and makes
them be natural electron acceptor [10–12]. SWNTs have thus
been widely used combining with light absorbing antenna chro-
mophores to construct photovoltaic devices [1,13–17]. Porphyrins
are known chromophores, which play an important role in natural
photosynthetic system due to their unique photophysical and elec-
trochemical properties [18–20]. In the past decades, porphyrins
have been broadly applied in the research of artificial photosyn-
thetic mimic systems [21–29]. In view of the distinct advantages
of porphyrin and SWNTs, a number of SWNTs–porphyrin nanohy-
brids, constructed by ␲–␲ and Van der Waals [30–34], polymer
wrapping [35,36], electrostatic interaction [37–40] or covalent
bond [41–46], have been built to be photoelectron transfer models.
As mentioned above, porphyrins functionalized SWNTs
have attracted extensive attention as excellent candidates for
nanoscale photovoltaic devices. Some covalently linked porphyrin-
functionalized SWNTs [42–44] have previously been synthesized in
our group for the research of energy and electron transfer. We found
2
2
expected to be an improved photon-to-electron conversion system.
2. Results and discussion
2.1. Synthesis and characterization
The meso-meso linked diporphyrin functionalized SWNTs
([H Por] -SWNTs) was prepared by the reaction of octadecylamine
2
2
modified SWNTs (ODA-SWNTs) with the corresponding dipor-
phyrin diazonium compound generated from diporphyrin amino
compound in situ (Scheme 2) [42,55]. The diporphyrin was obtained
via a Suzuki-coupling reaction (Scheme 3) [56].
The Raman spectrum of [H Por] -SWNTs was significantly
2
2
different from that of ODA-SWNTs (Fig. 1). Compared to ODA-
SWNTs, more structure information could be found except for
∗ Corresponding author. Tel.: +86 22 23505572; fax: +86 22 23505572.
E-mail address: jyzheng@nankai.edu.cn (J.-Y. Zheng).
−
1
the tangential mode at ∼1590 cm
(G-band) and the disorder
1
010-6030/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jphotochem.2010.09.001

1
6
L. He et al. / Journal of Photochemistry and Photobiology A: Chemistry 216 (2010) 15–23
Scheme 1. Structures of porphyrin–SWNTs dyads and reference compounds.
−
1
mode at ∼1350 cm (D-band). The additional peaks at 819, 1002,
octadecylamine. These Raman and IR data indicate a successful
functionalization of SWNTs with diporphyrins.
−1
1
082, 1234, 1454, 1494, and 1553 cm could be assigned to the
covalently attached porphyrin moiety [57]. Meanwhile, the FTIR
spectrum of [H Por] -SWNTs (see ESI, Fig. S1) exhibited the char-
Consisting with Raman and FTIR results, the transmission
electron microscopy (TEM) images showed more direct evidence
for the successful modification. Fig. 2 shows the typical surface
morphology of SWNTs before and after porphyrin functionaliza-
tion. The sidewall of the SWNTs was significantly roughened by
the coverage of soft materials, indicating the presence of porphyrin
attached to the SWNTs surface. The content of porphyrin moiety
2
2
acteristic porphyrin absorptions at 3306, 3060, 1537, 1419, 1022,
−1
−1
7
92, and 684 cm . The absorption bands at 3306 and 3060 cm
could be separately assigned to the stretching vibration of the
pyrrole N–H and aromatic C–H of the diporphyrins. The bands at
−1
3
343, 2921, 2850, and 1646 cm
derived from the moieties of
◦
Scheme 2. Preparation of [H2Por]2-SWNTs: (i) 70 C, isoamyl nitrite, ODCB.

L. He et al. / Journal of Photochemistry and Photobiology A: Chemistry 216 (2010) 15–23
17
◦
Scheme 3. Preparation of meso-meso linked diporphyrin: (i) NBS, CHCl3/MeOH; 91%; (ii) NBS, CH2Cl2/MeOH; (iii) 90 C, 4,4,5,5-tetramethyl-1,3,2-dioxaborolane, Pd(PPh3)2Cl2,
◦
triethylamine, 1,2-dichloroethane; 40% (two steps); (iv) 80 C, Pd(PPh3)4, Cs2CO3, DMF/toluene; 68%; (v) 5% Pd/C, NaBH4, CH2Cl2/MeOH; (vi) CF3COOH, CHCl3; 67% (two steps).
Soret band than the absorption spectrum of monoporphyrin func-
tionalized SWNTs (TPP-SWNTs) (Fig. 3). Compared to [H Por] -ref,
2
2
there were 4–7 nm red-shift for both Soret bands and Q-bands, and
simultaneously with notable broadening of the Soret bands. Those
reflect that the covalent bonding to SWNTs causes a change of the
electronic states of diporphyrin, and there is notable electronic
communication between SWNTs and diporphyrin in the ground
state [58]. The absorption spectra of [H Por] -SWNTs with differ-
2
2
ent concentrations were measured, and the absorption values at
19 and 459 nm were plotted against concentrations to get a stan-
4
−
1
dard curve (in mg L , Fig. 4). On the basis of Beer’s law, the effective
extinction coefficient of [H Por] -SWNTs was determined to be
2
2
−
1
−1
0
.03 L mg cm in accordance with the slope of the linear least-
squares fit. The absorption values of [H Por] -SWNTs at different
2
2
wavelengths were well in line with the correlative concentrations,
proving that the solution was homogeneous. The solubility could
−
1
be calculated to be 355 mg L according to the Beer’s law, and the
solution in ODCB was stable for several months (Fig. 5). The good
solubility indicates the exfoliating of nanotube bundles.
Fig. 1. Raman spectra of [H2Por]2-SWNTs (A) and ODA-SWNTs (B).
in [H Por] -SWNTs nanohybrid could be estimated in the light of
2
2
the elemental composition of ODA-SWNTs and [H Por] -SWNTs
2
2
2
.3. Steady state emission spectroscopy
(
(
Table 1), determined by X-ray photoelectron spectroscopy
XPS). The content of diporphyin unit in [H Por] -SWNTs, one
2
2
The excited state interactions between SWNTs and diporphyrins
diporphyrin unit per ∼600 C atoms, is similar to the content of
were explored by steady state fluorescence spectra of [H Por] -ref
and [H Por] -SWNTs. [H Por] -SWNTs exhibited complete fluores-
2
2
monoporphyrin unit in TPP-SWNTs nanohybrid.
2
2
2
2
cence quenching (100%, Fig. 6), upon excitation of the porphyrin
moiety at 419 and 453 nm. Even when the absorption of SWNTs
was subtracted from the absorbance of [H Por] -SWNTs, the fluo-
rescence also exhibited almost complete quenching (99%) (see ESI,
Fig. S2). The complete luminescence quenching indicates that there
is a strong interaction between the excited diporphyrin and SWNTs
2
.2. Steady state absorption spectroscopy
2
2
The steady state absorption spectrum of [H Por] -SWNTs in
2
2
ODCB (Fig. 3) showed two split Soret bands (423 and 459 nm) and
four Q-bands (530, 569, 601, and 662 nm). There was one more
[
42]. Possible pathways for the deactivation of excited porphyrins
Table 1
may be attributed to two competitive processes, energy transfer
(ET) and photoinduced electron transfer (PET). The emission band
XPS elemental composition for o-SWNTs, ODA-SWNTs, TPP-SWNTs and [H2Por]2-
SWNTs.
of [H Por]2 (between 620 and 800 nm) overlaps with the absorp-
2
Sample
XPS elemental compositiona
tion band of SWNTs, which enables singlet–singlet energy transfer
from diporphyrin to SWNTs [59]. Nevertheless, the fluorescence
quantum yield of [H Por] -SWNTs significantly decreased against
C1s
N1s
O1s
2
2
o-SWNTsb
ODA-SWNTs
TPP-SWNTs
83.41
86.50
84.72
92.01
0.00
1.18
1.49
1.86
16.59
12.32
13.79
6.13
increasing solvent polarity (Table 2), which indicates that the
quenching process in [H Por] -SWNTs nanohybrid is mainly dom-
2
2
[H2Por]2-SWNTs
inated by the excited state electron transfer, because the energy
transfer commonly does not depend on solvent polarity while the
electron transfer tends to be sensitive to medium effects [42,60,61].
a
The elemental composition was measured as atomic conc.
o-SWNTs is the abbreviation of oxide SWNTs.
b

1
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L. He et al. / Journal of Photochemistry and Photobiology A: Chemistry 216 (2010) 15–23
Fig. 2. TEM images of ODA-SWNTs (A) and [H2Por]2-SWNTs (B).
2.4. Electrochemistry analysis
with a cathodic shift of ∼340 mV, which can be attributed to the
fast electron transfer in [H Por] -SWNTs as a result of limited
2
2
Electrochemical studies with cyclic voltammetry (CV) were
access of the SWNTs bound redox probes to the electrode surface
performed to understand the overall redox behavior of [H Por] -
[63]. One more reduction peek at −0.49 V appeared in [H Por] -
2
2
2
2
SWNTs, evaluate the electronic properties of the nanohybrid, and
also visualize the existence of any electronic interaction between
diporphyrins and SWNTs. The CV of [H Por] -ref showed two oxi-
SWNTs, which corresponded to the reduction potential of SWNTs
[63]. The change of redox properties of porphyrin moiety indicates
the diporphyrin becomes easier to be oxidized. The free-energy
changes for charge separation (ꢀGcs) was calculated according to
the Rehm–Weller method (Eq. (1)), by employing the first oxida-
2
2
dation and one reduction processes (see ESI, Fig. S3). The first
+
reduction peak was observed at −1.57 V versus Ag/Ag , and the two
1
oxidation peaks were seen at +0.66 and +0.90 V, respectively. The
redox properties of the mixture of ODA-SWNTs and [H Por] -ref
tion potential of diporphyrin (E ), the first reduction potential
ox
of SWNTs (E1 ), and the singlet excitation energy of [H Por] -ref
2
2
2
2
red
(
ODA-SWNTs + [H Por] -ref) did not show any significant vari-
(ꢀE0–0) [64]:
2
2
ations compared to [H Por] -ref (Table 3). However, obvious
2
2
1
1
ꢀ
GCS = E − E − ꢀE0–0
(1)
variations were found in the oxidation and reduction potentials of
H Por] -SWNTs. The first oxidation peek was observed at +0.32 V
ox
red
[
2
2
Herein, ꢀE0–0 (1.81 eV) was determined by the 0–0* absorption.
•
+
The ꢀG value for generating the radical ion pair [H Por]2
-
CS
2
•
−
SWNTs was found to be −1.00 eV, which indicates the possibility
of photoinduced charge separation in the nanohybrid. It should
be noted that the Coulombic terms in the present donor–acceptor
systems are negligible, especially in solvents with moderate or
high polarity, because of the relatively long edge-to-edge distance
(
Ree > 11 A˚ ) employed [65–70].
2.5. Transient absorption spectroscopy
Time-resolved transient absorption spectrum, following
nanosecond laser pulses, was employed to examine the photody-
namics of [H Por] -SWNTs nanohybrid. It provided evidence for
2
2
charge separation and allowed us to estimate the charge recom-
bination rates, kCR. Fig. 7 shows a broad absorption band between
4
[
60 and 680 nm, which is the typical absorption of radical cation
•
H Por]2 of [H Por] -SWNTs nanohybrid [50]. Meanwhile, a net
2 2 2
+
decrease was observed around 420, 460, 570, 600, and 650 nm
due to 1[H Por] *, which are dominated by the ground state
2
2
absorption of diporphyrin. Therefore, the photoinduced electron
transfer process involved from 1[H2Por]2* to SWNTs and, in turn,
Fig. 3. UV–vis spectra of [H2Por]2-ref (a), ODA-SWNTs (b), [H2Por]2-SWNTs (c), and
TPP-SWNTs (d) in ODCB. The inset showed the Soret-band region in more details.

L. He et al. / Journal of Photochemistry and Photobiology A: Chemistry 216 (2010) 15–23
19
Fig. 4. Absorption spectra of [H2Por]2–SWNTs in ODCB (concentrations are 15, 30, 45, 60, 75, 90 mg L−1, respectively). Shown in the inset are the plots of absorbency at 419
and 459 nm versus concentration. The straight lines are linear least-square fit to the data.
Table 2
Relative fluorescence quantum yields of [H2Por]2-SWNTs in solvents of different
polarity.
Solvent
Dielectric constanta
Relative ˚fb
Toluene
THF
ODCB
2.38
7.58
9.93
1.0
0.48
0.28
Solutions were deoxygenated by purging with N2 before quantum yields were deter-
mined.
a
From Ref. [62].
Measured at 298 K.
b
created the [H Por]2 +-SWNTs•− state, as shown in Scheme 4.
•
2
The time-resolved transient absorption spectrum confirmed the
existence of electron transfer. The lifetime of the charge separation
•
+
•−
state ([H Por]2 -SWNTs ) was evaluated to be 145 ns from
2
transient absorption kinetics measurement at 620 nm (Fig. 7), and
Fig. 5. The state of [H2Por]2-SWNTs (A) and ODA-SWNTs (B) solutions in ODCB after
two months.
6
−1
the kCR was calculated to be 6.9 × 10 S . However, the CS lifetime
of TPP-SWNTs and the corresponding k were determined to
CR
7
−1
be 57 ns and 1.8 × 10 S separately. The significant decrease of
charge recombination rate, compared to TPP-SWNTs nanohybrid,
makes it more feasible to build photovoltaic device.
3. Experimental
3.1. Instruments and measurements
UV–vis spectra were recorded on a VARIAN Cary 300 spec-
trophotometer using a quartz cell with a path length of 10 mm.
Fluorescence spectra were obtained with a Cary Eclipse spec-
trometer. FTIR spectra were obtained with a BRUKER TENSOR 27
Table 3
Redox potentials (versus Ag/Ag+) of [H2Por]2-ref, SWNTs + [H2Por]2-ref, and
[
H2Por]2-SWNTs.
2
1
Sample
E
/V
E
/V
Ered/V
ox
ox
[
H2Por]2-ref
SWNTs + [H2Por]2-ref
H2Por]2-SWNTs
0.90
0.91
0.66
0.66
0.32
−1.57
−1.58
−0.49
Fig. 6. Fluorescence spectra of [H2Por]2-ref (dotted) and [H2Por]2-SWNTs (solid) in
ODCB excited at 419 and 453 nm (the inset), respectively.
[

2
0
L. He et al. / Journal of Photochemistry and Photobiology A: Chemistry 216 (2010) 15–23
employing a monochromated Al-Ka X-ray source (hꢁ = 1486.6 eV),
hybrid (magnetic/electrostatic) optics and a multi-channel plate
and delay line detector (DLD). All XPS spectra were recorded using
an aperture slot of 300 ␮m × 700 ␮m, survey spectra were recorded
with a pass energy of 160 eV, and high resolution spectra with a pass
energy of 40 eV. Transmission electron microscope (TEM) images
were obtained on a FEI TECNAI-20 instrument operated at 100 kV.
Sample preparation involved sonicating materials in THF for 30 min
and dropping the resulting suspension onto carbon-coated copper
grids. Redox potentials were measured by cyclic voltammetry on
a BAS electrochemical analyzer model 660. All experiments were
carried out using a conventional three-electrode system employ-
ing a glassy carbon electrode as the working electrode, Ag/Ag+
electrode as the reference electrode, and a Pt wire as the counter
electrode. The redox potentials were measured by cyclic voltam-
metry in ODCB, using 0.04 M n-Bu NPF as supporting electrolyte
4
6
−
1
with a scan rate of 100 mV s . Nanosecond transient absorption
measurements were carried out using the third (532 nm) harmonic
of Q-switched Nd:YAG laser (Continuum Surelite I, fwhm 7 ns) as
excitation source and a Germanium Photodiode (Edinburgh Lp900)
was used as a detector. All of the sample were dissolved in THF, and
deaerated with Ar bubbling for 30 min at room temperature.
3.2. Materials
The pristine carbon nanotube was purchased from Shen-
zhen Nanotech Port Co., individual tubes of SWNTs have
diameter range of <2 nm. All of solvents were purified
according to standard methods. Acetonitrile, o-dichlorobenzene
ODCB), chloroform, dichloromethane, 1,2-dichloroethane and
a
(
N,N-dimethylformamide (DMF) were distilled from calcium
hydride before use. THF and toluene were dried and distilled
from sodium. All other chemicals (AR) obtained from commercial
sources were used without any further purification.
3
.3. Preparation
Fig. 7. Nanosecond transient absorption spectra of TPP-SWNTs (A) and [H2Por]2-
SWNTs (B) observed by laser irradiation at 532 nm in THF. The insets showed the
time profiles of absorbance at 620 nm.
5
,15-Di(3,5-di-tert-butyl)phenylporphinatozinc
,15-di(3,5-di-tert-butyl)phenyl-10-(4,4,5,5-tetramethyl-
,3,2-dioxaborolan-2-yl)porphinatozinc (4),
3-Zn,
5
1
and
instrument. All IR samples were prepared as films on pellets of spec-
troscopic grade KBr with solution in CH Cl . Raman spectra were
5-(p-aminophenyl)-10,15,20-triphenylporphyrin
were prepared according to the literature [72,73].
(TPP-NH2),
2
2
measured by a Reinishaw via Raman microscope at room tempera-
ture with the 514.5 nm line of an Ar ion laser as an excitation source.
3.3.1. Synthesis of 5,15-di(3,5-di-tert-butylphenyl)-10-
(4-nitrophenyl)porphyrin (1)
1
13
H NMR and C NMR spectra were recorded on Bruker (300 MHz
or 400 MHz) or VARIAN (400 MHz) spectrometer using TMS as the
internal standard. Mass spectra were recorded on a FTICR-MS, using
ESI ionization method. Separations of SWNTs from the impurities
were performed with a centrifuge (Eppendorf 5810R), and filtration
was performed through a nylon membrane (Whatman Interna-
tional Ltd., England/MAGNA, 0.22/0.1 ␮m). Ultrasonication was
done in a KQ-400KDE (400 W, 40 kHz, Kunshan Sonicator Instru-
ment Co. Inc.) bath sonicator. X-ray photoelectron spectroscopy
To
a
solution of 4-nitrophenyldipyrromethane (1.06 g,
3.2 mmol) and 3,5-di-tert-butylbenzaldehyde (1.21 g, 5.6 mmol)
in 950 mL dry dichloromethane pumped with N2 for 15 min,
TFA (0.73 g, 6.4 mmol) was added, then dipyrromethane (0.41 g,
2.8 mmol) in 75 mL dry dichloromethane was added dropwise for
30 min. The mixture was stirred at room temperature for 1 h, then
treated with DDQ (1.41 g, 6.2 mmol) and stirred for another 2 h.
Removal of solvent and chromatography afforded a purple solid
(185 mg, 8%). 1H NMR (CDCl3): ı 10.28 (s, 1H), 9.38 (d, J = 4.5 Hz,
(
XPS) were recorded using a Kratos Axis Ultra DLD spectrometer
2H), 9.09 (d, J = 4.5 Hz, 2H), 9.00 (d, J = 4.5 Hz, 2H), 8.76 (d, J = 4.5 Hz,
2H), 8.64 (d, J = 8.7 Hz, 2H), 8.41 (d, J = 8.4 Hz, 2H), 8.11 (d, J = 1.5 Hz,
4H), 7.83 (t, J = 1.5 Hz, 2H), 1.55 (s, 36H), −2.96 ppm (s, 2H).
3.3.2. Synthesis of 5-bromo-15-(4-nitrophenyl)-10,20-di(3,5-di-
tert-butylphenyl)-porphyrin
2
NBS (5 mg, 0.028 mmol) was added to a stirred solution of 1
(
21 mg, 0.026 mmol) in 50 mL CHCl /MeOH (9:1) at room tem-
3
perature. After 10 min, the reaction was quenched with acetone
2 mL). Removal of solvent and the residue was crystalled with
CHCl3/MeOH to afford the product as a purple solid (21 mg, 91%).
(
Scheme 4. Photo-reaction route of [H2Por]2-SWNTs in THF (the energy of excited
SWNT is from Ref. [71]).

L. He et al. / Journal of Photochemistry and Photobiology A: Chemistry 216 (2010) 15–23
21
1
H NMR (CDCl ): ı 9.70 (d, J = 4.8 Hz, 2H), 8.96 (d, J = 4.8 Hz, 2H),
with nitrogen for 15 min, isoamyl nitrite (5 ␮L, 0.037 mmol) was
quickly added and the suspension was stirred in the dark at 70 C
3
◦
8
8
1
.88 (d, J = 4.8 Hz, 2H), 8.69 (d, J = 4.8 Hz, 2H), 8.63 (d, J = 8.4 Hz, 2H),
.37 (d, J = 8.4 Hz, 2H), 8.05 (d, J = 1.6 Hz, 4H), 7.83 (t, J = 1.6 Hz, 2H)
.54 (s, 36H), −2.72 ppm (s, 2H).
for 48 h. During the period, another 90 mg (0.060 mmol) 7 and 25 ␮L
(0.19 mmol) isoamyl nitrite were added in 5 portions (total 5×
1
8 mg 7 and 5× 5 ␮L isoamyl nitrite) to ensure a high degree of
II
3
.3.3. Synthesis of Zn -free base hybrid diporphyrin 5
functionalization. The suspension was diluted with 10 mL DMF, fil-
tered over a nylon membrane (0.1 ␮m), and washed repetitively
with DMF. The filtered product was sonicated in DMF and filtered
repeatedly. Ultimately, the product was washed with CH2Cl2 and
Bromoporphyrin 2 (119 mg, 0.134 mmol), porphyrin boronate
4
(117.5 mg, 0.134 mmol), Cs CO3 (65.6 mg, 0.201 mmol), and
2
Pd(PPh3)4 (15.5 mg, 0.0134 mmol) were dissolved in a mixture of
dry DMF (9 mL) and dry toluene (18 mL). The solution was deoxy-
genated via three freeze–pump–thaw degassing cycles and the
resulting mixture was heated at 80 C for 12 h under Ar. The mix-
ture was extracted with CH Cl , and the organic layer was dried
◦
dried in vacuum at 80 C for 10 h to give [H2Por]2-SWNTs (6.1 mg).
◦
4. Conclusion
2
2
with anhydrous Na SO . Removal of solvent and chromatogra-
2
4
In conclusion, we have prepared covalently linked [H Por] -
2
2
1
phy afforded a purple solid (142 mg, 68%). H NMR (CDCl ): ı
3
SWNTs nanohybrid for the first time, where meso-meso linked
diporphyrin is successfully incorporated into a charge separation
unit as a photosynthetic electron-transfer model. The nanohy-
brid reveals photoinduced electron-transfer from the diporphyrin
excited singlet state to the SWNTs, which resulted in the genera-
1
0.41 (s, 1H), 9.51 (d, J = 4.8 Hz, 2H), 9.20 (d, J = 4.8 Hz, 2H), 8.97
(
d, J = 4.8 Hz, 2H), 8.81 (d, J = 4.8 Hz, 2H), 8.79 (d, J = 4.8 Hz, 2H),
8
8
8
1
.69 (d, J = 8.4 Hz, 2H), 8.60 (d, J = 4.8 Hz, 2H), 8.50 (d, J = 8.4 Hz, 2H),
.19 (d, J = 4.8 Hz, 2H), 8.11 (d, J = 1.6 Hz, 4H), 8.06 (d, J = 1.6 Hz, 4H),
.03 (d, J = 4.8 Hz, 2H), 7.72 (t, J = 1.6 Hz, 2H), 7.70 (t, J = 1.6 Hz, 2H),
•+
•−
tion of [H Por]2 -SWNTs radical ion pair with 145 ns lifetime.
2
.45 (d, J = −13.2 Hz, 72H), −2.15 ppm (s, 2H); ESI-MS m/z: 1554.83
It should be emphasized here that the CS lifetime of the nanohy-
brid has been prolonged substantially by replacing monoporphyrin
with diporphyrin. The present results demonstrate that meso-meso
linked diporphyrin is an outstanding electron donor to build SWNTs
involving light-energy conversion and photovoltaic devices.
+
(
[M+H] ); calcd for C
H
N O Zn 1554.79.
1
02 108 9 2
3
.3.4. Synthesis of meso-meso linked diporphyrin 7
Zn -free base hybrid diporphyrin 5 (142 mg, 0.091 mmol) was
II
dissolved in CH Cl (13 mL) and methanol (9 mL), to which 5% Pd/C
2
2
(
54 mg) was added. Then, NaBH4 (47 mg, 1.175 mmol) was added
Supplementary data
to the solution by portions, and the resulting reaction mixture was
stirred for 2 min at room temperature. Pd/C was filtered off and the
filtrate was washed with water and the organic layer was dried over
anhydrous Na SO . The desiccant was filtered off and the filtrate
was treated with TFA at room temperature for an hour. The mix-
ture was washed with saturation Na CO , and the organic layer was
FTIR spectra, absorption and emission spectra and cyclic
voltammograms of the nanohybrid and reference compounds. The
preparation of the reference compound [H Por] -ref.
2
4
2
2
2
3
dried with anhydrous Na SO . The solvent was removed by a rotary
Acknowledgements
2
4
evaporator and the residue was separated by silica gel chromatog-
raphy with CH Cl to give purple solid 7 (90 mg, 68%). 1H NMR
We would like to thank Associate Professor Yuping Liu for her
work on XPS measurement. This work is supported by the 973 Pro-
gram (2006CB932900), NSFC (Nos. 20721062 and 20802038) and
Tianjin Natural Science Foundation (07QTPTJC29700).
2
2
(
CDCl ): ı 10.37 (s, 1H), 9.45 (d, J = 4.8 Hz, 2H), 9.13 (d, J = 4.8 Hz,
3
2
2
H), 9.04 (d, J = 4.8 Hz, 2H), 8.94 (d, J = 4.8 Hz, 2H), 8.70 (d, J = 4.8 Hz,
H), 8.62 (d, J = 4.8 Hz, 2H), 8.12 (m, 12H), 8.05 (d, J = 4.8 Hz, 2H), 7.74
(
t, J = 1.6 Hz, 2H), 7.71 (t, J = 1.6 Hz, 2H), 7.11 (d, J = 8.4 Hz, 2H), 4.05
s, 2H), 1.47 (d, J = −10.8 Hz, 72H), −2.09 (s, 2H), −2.32 ppm (s, 2H);
(
Appendix A. Supplementary data
1
3
C NMR: ı 149.08, 148.86, 146.25, 141.287, 140.81, 135.82, 132.95,
1
1
30.09, 130.02, 129.95, 129.85, 122.47, 122.08, 121.67, 121.31,
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jphotochem.2010.09.001.
21.22, 118.39, 117.87, 113.71, 31.97 ppm; ESI-MS m/z: 1462.9027
+
(
[M+H] ); calcd for C102H112N9 1462.9035.
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