Functionalization of diameter-sorted semiconductive SWCNTs with photosensitizing porphyrins: Syntheses and photoinduced electron transfer

Article abstract of DOI:10.1002/chem.201200970

Covalent functionalization of diameter sorted SWCNTs with porphyrins (MP), and photochemistry to establish nanotube diameter-dependent charge separation efficiencies are reported. The MP-SWCNT(n,m) [M=2 H or Zn, and (n,m)=(7,6) or (6,5)] nanohybrids are c

Full text of DOI:10.1002/chem.201200970

FULL PAPER
DOI: 10.1002/chem.201200970
Functionalization of Diameter Sorted Semi-conductive SWCNTs with
Photosensitizing Porphyrins: Syntheses and Photoinduced Electron Transfer
[
a]
[b]
[a]
Sushanta K. Das, Atula S. D. Sandanayaka, Navaneetha K. Subbaiyan,
[
c]
[d]
[a, c]
Melvin E. Zandler, Osamu Ito,* and Francis DꢀSouza*
Abstract: Covalent functionalization of
diameter sorted SWCNTs with por-
phyrins (MP), and photochemistry to
establish nanotube diameter-dependent
charge separation efficiencies are re-
the SWCNT surface. The MO results
suggest charge separation (CS) via the
excited state of MP. Time-resolved
fluorescence studies reveal quenching
of the singlet excited state of the MP
transient absorption measurements
confirm the charge-separated radical
+
cation and the radical anion as [MPC
À
–SWCNTC ] with their characteristic
absorption bands in the visible and
near-IR regions. The charge separated
states persist for about 70–100 ns thus
giving an opportunity to utilize them to
build photoelectrochemical cells, which
allowed us to derive the structure–reac-
tivity relationship between the nature
of porphyrin and diameter of the em-
ployed nanotubes.
ported. The MP–SWCNT
A
H
U
G
R
N
U
G
with SWCNT
ACHTUNGERTNNUNG( n,m), giving the rate con-
2
H or Zn, and (n,m)=(7,6) or (6,5)]
stants of charge separation (k ) in the
CS
9
À1
nanohybrids are characterized by a vari-
ety of spectroscopic, thermogravimet-
ric, TEM imaging techniques, and also
by DFT MO calculations. The ther-
mogravimetric, Raman and fluores-
cence studies reveal the presence of
a moderate number of porphyrins on
range of (4–5)ꢁ10 s . Nanosecond
Keywords: charge separation · elec-
tron
transfer
·
light-energy
harvesting · photoelectrochemistry ·
porphyrins
Introduction
and drug delivery systems), in electronics (transistors), and
opto-electronics (photodetectors and photovoltaic devi-
[1]
[4–9]
Single wall carbon nanotubes (SWCNTs) are well known
for their extraordinary mechanical, electronic and optical
ces).
Notably, the application of SWCNTs to energy con-
version is fundamentally connected to the role as electron
acceptors and/or electron donors. Consequently, carbon
nanotube-based nanohybrids/conjugates with electron
[
2]
properties. These SWCNTs with novel properties are pre-
dicted to be highly useful for a large number of innovative
applications, especially when they are incorporated into new
donors and acceptors have been the focus of several studies
[
2,3]
[6–10]
functional materials.
Among these applications, the most
in recent years.
Such association with electron–donor or
promising are in material science (ultralight and robust com-
posite materials), in biology (imaging, sensing, biosensing
electron–acceptors is shown to modulate the electronic
properties of SWCNTs.
The structures and properties of SWCNT relate to a pair
of indices (n,m) referring to their diameter and chirality;
that is, when n and m are different, SWCNTs are semicon-
ducting, when n and m are a multiple of three, these are
[
a] S. K. Das, Dr. N. K. Subbaiyan, Prof. F. DꢂSouza
Department of Chemistry, University of North Texas
1
155 Union Circle, 305070, Denton, TX 76203-5017 (USA)
[2]
metallic. To derive better structure–activity relations for
the above-mentioned wide applications, it is essential to use
sorted nanotubes according to their (n,m) indices, since the
physicochemical properties, including optical absorption and
E-mail: Francis.DSouza@UNT.edu
[
[
b] Dr. A. S. D. Sandanayaka
School of Materials Science
Japan Advanced Institute of Science and Technology (JAIST)
Nomi, Ishikawa, 923-1292 (Japan)
[11]
emission, redox properties and band gaps vary as a func-
[12]
[
c] Prof. M. E. Zandler, Prof. F. DꢂSouza
Department of Chemistry, Wichita State University
Wichita, KS 67260-0051 (USA)
tion of (n,m) indices of SWCNTs. The bulk separation of
nanotubes according to their (n,m) indices is still being de-
ꢀ
veloped; efforts to sort the HiPCO nanotubes by using den-
d] Prof. O. Ito
sity gradient centrifugation and gel electrophoresis, and Co-
CarbonPhotoScience Laboratory, Kita-Nakayama 2-1-6
Izumi-ku, Sendai, 981-3215 (Japan)
ꢀ
MoCAT catalytic method of growing SWCNTs of narrow
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201200970. These include The
distribution of tube diameter by South West Nano Technolo-
gies are noteworthy accomplishments.
[13–15]
Raman spectra [pristine SWCNT
plots, TEM images [ZnP–SWCNT
spectra [UV/Vis/NIR for ZnP–SWCNT
energy levels of ZnP–SWCNT(7,6), and nanosecond transient spectra
of H P–SWCNT(n,m) in DMF.
A
H
U
G
R
N
U
G
2
P–SWCNT ACHTUTGNRNENUG( 6,5)], TGA
Recently, by developing elegant self-assembled supra-
molecular approaches, we formed nanohybrids comprised of
various electron–donor or electron–acceptor photosensitiz-
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
[16,17]
2
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
ers and diameter-sorted single-wall carbon nanotubes.
Chem. Eur. J. 2012, 00, 0 – 0
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By using these donor–acceptor nanohybrids, we were suc-
cessful in demonstrating the effects of the nanometer diame-
ter on photoinduced electron transfer leading to charge sta-
bilization, photocatalytic electron pooling to accumulate
redox products, and photoelectrochemical solar cells for
lently connected porphyrin can be recognized as a dyad, the
molecular orbital calculations were performed to visualize
the frontier orbitals, from which an intramolecular charge-
separation mechanism was elucidated.
[16,17]
direct conversion of light-into-electricity.
However, to date, such investigations have not been per-
formed on covalently functionalized SWCNT(n,m) with
Results and Discussion
AHCTUNGTRENNUNG
photosensitizer molecules, which will provide information
on the effect of nanotube diameter on fine-tuned physico-
chemical properties. In the present study, we have accom-
plished this task by covalent functionalization of SWCNT-
Synthesis of MP–SWCNT AHCTUNGTERNNUN(G n,m) donor–acceptor nanohy-
brids: Scheme 2 presents the multistep synthesis strategy
adopted for the preparation of the MP–SWCNT nanohy-
brids; further details of the synthesis are given in the Exper-
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(7,6) and SWCNT
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(6,5) using a well-known photosensitizer
imental Section. Briefly, H -5(p-carboxyphenyl)-10,15,20-tri-
ACHTUNGTRENNUNG( 4-propyl)phenylporphyrin was synthesized by treating stoi-
chiometric amounts of methyl-4-formylbenzoate, pyrrole
and 4-propylbenzaldehyde in refluxing propionic acid fol-
lowed by chromatographic separation. The methyl benzoate
2
[18]
electron donor: porphyrin. In order to attach the porphyr-
ins, we have employed Pratoꢂs method, that is, dipolar cyclo-
addition of azomethine ylide to produce pyrrolidine ring on
the nanotube surface, as this method is mild enough to con-
trol the number of addends to a minimum number without
group was subjected to base hydrolysis to obtain H -5(p-car-
2
[19]
significantly altering the electronic structure of the tubes.
boxyphenyl)-10,15,20-tri ACHTUNGTREUNNN(G 4-propyl)phenylporphyrin (1). The
The expected structures of these newly synthesized photoac-
tive nanohybrids are shown in Scheme 1; a sufficient
number of alkyl groups on the porphyrin periphery and
ether chain on the pyrrolidine ring are introduced to in-
crease the solubility. These nanohybrids have been charac-
terized by using several optical, thermal, microscopic, and
theoretical methods, and finally photoinduced electron
transfer leading to charge separation and photoelectrochem-
ical behavior has been systematically demonstrated. Further-
acid chloride form of porphyrin obtained by SOCl treat-
ment was reacted with hydroxybenzaldehyde followed by
2
chromatographic separation to yield H -5-{4“-formyl-hy-
2
droxyphenyl-4’-phenylester}-10,15,20-tri ACHUTNGRNENGU( 4-propyl)phenyl-
porphyrin (2). In a separate experiment, N-[2-(N-Boc)2,2’-
(ethylenedioxy)diethylamino]glycine (3) was synthesized
(Scheme 2); Boc=ÀC(=O)ÀOÀC
ACHTUNGENTRNUNG( CH ) . For the synthesis
3 3
of H P–SWCNT (4), pristine SWCNT, 2 and 3 were refluxed
2
in DMF at 1208C for 24 h, yielding 4 as a black powder,
which was dissolved in DMF, sonicated, centrifuged and fil-
tered until all the unreacted components were washed away.
more, since each SWCNT ACHUTNERGNNUG( 7,6) and SWCNT CAHTUNGTRNENUNG( 6,5) with cova-
Finally, H P–SWCNTACHTUNGTRENNUNG
2
SWCNT
ACHTUNGTRENNUNG
Raman and TEM imaging studies: Figure 1 shows the
Raman spectra of pristine and H P–SWCNT(n,m) hybrids.
(7,6) revealed a main band corresponding to
AHCTUNGTRENNUNG
2
The SWCNT
the tangential mode (the graphitic G band) at 1584 cm ,
whereas for H P–SWCNT(7,6), a weak band appeared at
ACHTUNGTRENNUNG
À1 [2]
AHCTUNGTRENNUNG
2
Scheme 1. Structures of MP–SWCNT
A
H
U
G
R
N
N
(n,m) [M=2H, Zn, and (n,m)=
Figure 1. Raman spectra of: (i) pristine SWCNT
ACHTUNGTRENNUNG( 7,6), and (ii) dried
(
6,5) and (7,6)] donor–acceptor nanohybrids synthesized by using Pratoꢂs
sample of H P–SWCNT(7,6) excited by using a 532 nm laser light; both
spectra are normalized to the G band position.
2
ACHTUNGTRENNUNG
[
19]
method of dipolar cycloaddition of azomethine ylide.
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Semi-conductive SWCNTs with Photosensitizing Porphyrins
FULL PAPER
plots). For the H P–SWCNT-
2
AHCTUNGTERNNUNG( 7,6) hybrid, this weight loss
was 17% at this temperature
range. Using this information,
for every 270 carbon atoms of
SWCNT ACTHUNGTERNNGN(U 6,5) one H P–pyrroli-
2
dine moiety was estimated,
whereas for every 150 carbon
atoms of SWCNT ACHNTUGRNENUG( 7,6) one
H P–pyrrolidine moiety was es-
2
timated. These results indicate
higher chemical reactivity of
the SWCNT
ACHTUNGTRENNU(GN 7,6) compared to
the SWCNT(6,5).
AHCTUNGTRENNUNG
Figure 2 shows the TEM
images of the dry samples of
pristine
H P–SWCNT
2
SWCNT
A
H
U
G
E
N
N
and
the
A
H
U
G
R
N
U
H P–SWCNT
2
A
H
U
G
R
N
U
G
SWCNT ACHUTNGRNEGUN( n,m) bundles were
found to be loosened by the co-
valent connection of H P,
2
although some intertwining
during sample preparation on
the grid was observed. Similar
TEM images were seen for
ZnP–SWCNT ACHUTNGRENNUG( n,m) (see Sup-
porting Information Figure S3).
An apparent difference be-
tween MP–SWCNT
MP–SWCNT(7,6)
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
found in the TEM images. No
significant nanocarbon particle
or the catalyst impurities used
in the synthesis of the tubes
were
observed,
indicating
higher purity upon functionali-
zation of SWCNTs in the pres-
ent study.
Scheme 2. Synthesis procedures for MP–SWCNT nanohybrids.
À1
1
340 cm , corresponding to the disorder mode (D band).
Since the D band results from the chemical disruption of the
Absorption spectral studies: Figure 3 shows the optical ab-
sorption spectra of H P–SWCNTAHCNUTGTERNNUNG
2
2
sp hybridized carbon atoms in the hexagonal framework of
[20]
the nanotube walls, the appearance of the D band is evi-
ACHTUNGTRENNUNG
dence for the covalent attachment of H P–pyrrolidine
2
moiety onto the sidewalls of SWCNT
crease in the D band after functionalization of SWCNT
was observed compared to pristine SWCNT(6,5) (see Sup-
porting Information Figure S1). The higher D band intensity
observed for H P–SWCNT(7,6) indicates enhanced degree
of functionalization compared to H P–SWCNT(6,5), a result
A
H
U
G
R
N
U
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
A
H
U
G
R
N
U
G
ACHTUNGTRENNUNG
H P moieties appear in the UV/Vis regions (main band in
the 415–420 nm region and weak bands in the 500–550 nm
region; the 300 nm band may be due to the MP moieties).
2
A
H
U
G
R
N
U
G
2
AHCTUNGTRENNUNG
2
that readily agrees with the thermogravimetric data dis-
cussed below.
The absorption bands of SWCNT AHCTNUGTERNNUN(G n,m) in the nanohybrids
À1
were red-shifted by about 400 cm from that of the pristine
SWCNT(n,m) peaks, due to the interaction with the p elec-
trons of the H P moiety and chemical functionalization.
[21]
The thermogravimetric analyses (TGA)
were per-
ACHTUNGTRENNUNG
[22,23]
formed on H P–SWCNT(n,m) hybrids; for the H P–
AHCTUNGTRENNUNG
2
2
2
SWCNT
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(6,5) hybrid, nearly 11% of the weight loss was ob-
From the longest absorption sharp peaks, the band gaps can
be evaluated to be 1.21 and 1.05 eV for SWCNT(6,5) and
SWCNT(7,6), respectively, which show narrowing of 0.06–
served in the 400–4508C range corresponding to the organic
fragments (see Supporting Information Figure S2 for TGA
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
Chem. Eur. J. 2012, 00, 0 – 0
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O. Ito, F. DꢂSouza et al.
nanotube hybrids, DFT energy optimization was performed
[26]
by using the B3LYP/3-21G(*) basis set on these computa-
tionally challenging systems. In these calculations, 318 car-
bons for SWCNT ACHUNTGRENNU(G 6,5) and 268 carbons for SWCNT ACHTUNGTRENNUNG( 7,6) in
building the nanotube with one porphyrin unit were used
for better understanding of the donor–acceptor hybrid elec-
tronic structure. Hydrogen atoms were bonded to the termi-
nal carbons of the open tubes. Figure 4 shows the optimized
Figure 2. TEM images of: a) SWCNT
2
ACHTUNGTNERNUNG( 6,5), b) SWCNT ACHTUNGTRENNUNG( 7,6), c) H P–
SWCNT(6,5), and d) H P–SWCNT(7,6); scale bars 50 nm.
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
2
ACHTUNGTRENNUNG
Figure 4. B3LYP/3-21G(*) optimized structure of: a) ZnP–SWCNT
in which a connected bond is seen at the upper surface, and b) ZnP–
SWCNT(7,6), in which a connected bond is seen on the lower middle.
Two views are shown for better visualization.
ACHTUNGTRENNUNG( 6,5),
AHCTUNGTRENNUNG
structures of the ZnP–SWCNT
hybrids in two views, in which a pyrrolidine ring is bonded
to a C=C bond on SWCNT
(n,m), converting to CÀC bonds.
The calculated diameter and length were 7.55 and 34.32 nm
for SWCNT(6,5), and 8.98 and 24.48 nm for SWCNT(7,6),
respectively; the diameters are in good agreement with the
ACTHUNGTRENNUNG( 6,5) and ZnP–SWCNT ACHTUNGTRENNUNG( 7,6)
AHCTUNGTRENNUNG
Figure 3. Steady-state absorption spectra of H
with: (i) SWCNT(6,5), and (ii) SWCNT(7,6).
2
P–SWCNT ACHTUTGNRNENUG( n,m) in DMF
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
A
H
U
G
E
N
N
A
H
U
G
E
N
N
ACHTUNGTRENNUNG
[14]
earlier reported STM and AFM images.
In both struc-
0
.08 eV, due to chemical functionalization. Quite similar ab-
tures, close association of the ZnP to the surface of the
SWCNT was predicted, which is possible from the bent ester
bond connecting MP moiety and the pyrrolidine ring. The
distance between the Zn atom to the closest carbon of
SWCNT was found to be approximately 3.4 ꢄ for both opti-
mized structures. The alkoxy chain of the pyrrolidine ring
was also close to the nanotube surface revealing some inter-
actions. As shown in the edge-on-view of the hybrids on the
right-hand side of each Figure, the ZnP positioning on the
SWCNT surface was symmetric and almost flat in the case
sorption spectra were observed for ZnP–SWCNT(n,m), in
AHCTUNGTRENNUNG
which the ZnP moiety showed a main band at 420–425 nm
and weak bands in the 500–550 nm region (see Supporting
Information Figure S4).
From the absorbance of about 0.1 of the MP-main band,
the concentrations of ZnP and H P were evaluated to be (1–
3
to one MP in every 150–250 carbons of SWCNT, which are
in good agreement with the result from TGA data. Com-
2
À7
)ꢁ10 mol on 0.1 mg of SWCNT
A
H
U
G
R
N
U
G
pared with the reported noncovalent MP–SWCNT
brids,
A
H
U
G
R
N
U
G
of ZnP–SWCNT
ZnP was slightly off and bent due to the smaller diameter of
SWCNT(6,5). Although these optimized structures are cal-
ACTHUNGTRENNUN(G 7,6), whereas for ZnP–SWCNT ACHTUNGTRENNUNG( 6,5) the
[16,17,24,25]
A
H
U
G
R
N
U
ACHTUNGTRENNUNG
culated in “vacuum”, they provide fairly good visualization
of the donor–acceptor structures in solution, in which slight-
ly different structures and interactions would be anticipated.
AHCTUNGTRENNUNG
[19]
extent.
Structure optimization by DFT calculations: In order to vis-
Energy level diagram: The MO energy levels were also cal-
ualize the geometry of the covalently linked porphyrin–
culated by the DFT calculations by using the optimized
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Semi-conductive SWCNTs with Photosensitizing Porphyrins
FULL PAPER
[12]
structures in Figure 4. Some of the representative
tials of SWCNTs in DMF
corresponding to the LUMO
HOMOÀn and LUMO+n (n=0, 1, 2, …) of ZnP–SWCNT-
and HOMO, respectively, are added to the energy level dia-
gram in Figure 5. By photoexcitation of the ZnP moiety, an
electron from the HOMOÀ3 level is elevated to the
LUMO+10 level within the ZnP moiety; thus, the reduc-
tion potential of ZnP is evaluated from the excitation
energy (2.03 eV) from HOMOÀ2. From the excited state of
the ZnP moiety (LUMO+10), the electron can transfer to
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(6,5) are shown in Figure 5. HOMO and HOMOÀ1 have
the electron density mainly on SWCNT
ACHTUNGTRENNUNG( 6,5), corresponding
to the valence band of SWCNT(6,5). The electron distribu-
AHCTUNGTRENNUNG
+
À
the LUMO on SWCNT
formed, which is denoted as charge-separation pro
(CS-1) in Figure 5. Similar MO distributions and energy
levels were calculated for ZnP–SWCNT(7,6); some of them
are shown in the Supporting Information (Figure S5).
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
1
AHCTUNGTRENNUNG
+
À
The energy of MPC –SWCNTC can be evaluated from the
difference of the LUMO energy [ERed of SWCNT(n,m)] and
the HOMO energy (E of MP). Then, the free energy of
AHCTUNGTRENNUNG
Ox
28]
[
the charge separation
(DGCS-1) from the lowest excited
singlet state ( ZnP*) can be evaluated to be À0.71 and
À0.72 eV for SWCNT(6,5) and SWCNT(7,6), respectively.
Similarly, DG values for H P–SWCNT via H P*
1
A
H
U
G
R
N
U
G
ACHTUNGTRENNUNG
1
CS-1
2
2
(
1.81 eV) can be evaluated to be À0.52 and À0.50 eV for
SWCNT(6,5) and SWCNT(7,6), respectively [see Supporting
Information Figure S5 for energy diagram with MO of ZnP–
SWCNT(7,6)].
From the energy level diagram in Figure 5, the other CS
process from the HOMO levels of SWCNT(n,m) to the
A
H
U
G
R
N
U
G
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
1
half-vacant HOMO of MP* generated after the photoexci-
tation is also possible, denoted as the CS-2 process, and
gives MPC –SWCNTC . The free-energies for this process
Figure 5. Energy diagrams with MOs of ZnP–SWCNT
duced charge separation. Left: MO energy levels of the ZnP moiety
(nꢁ10); center: MO energy levels of the SWCNT(6,5) moiety; right: the
electron distributions of some representative MOs. The EOx and ERed
values of ZnP and SWCNT(6,5) versus Ag/AgCl.
ACHTUNGTRENNUN(G 6,5) for photoin-
À
+
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
A
H
U
G
R
N
U
G
1
(
DGCS-2) were estimated to be À0.17–À0.31 eV via ZnP*
AHCTUNGTRENNUNG
1
and 0.04–À0.11 eV via H P* for SWCNT
ACHTUNGTRENNU(GN 6,5) and SWCNT-
2
AHCTUNGTRENNUNG( 7,6), respectively. Considering lower exothermicity of CS-2
tions of HOMO and HOMOÀ1 are higher on the middle
part of SWCNT(6,5) just under the ZnP compared with
processes, CS-1 may be the predominant route for the occur-
rence of photoinduced electron transfer. From the energy
diagram, sequential occurrence of CS-1 and CS-2 results in
energy transfer; however, the widely distributed electron
and hole along the SWCNTs may retain the CS states for
a period.
ACHTUNGTRENNUNG
both sides; in addition, some electron distributions are also
found on the ZnP moiety, suggesting occurrence of weak
charge-transfer interactions in the ground state. On the
other hand, HOMOÀ2 has the electron density predomi-
nantly localized on the ZnP moiety, corresponding to the
local HOMO of the ZnP moiety, whereas HOMOÀ3 has
Fluorescence measurements: Photochemistry and photo-
physical events via the excited state of the MP moiety of the
the electron density localized on SWCNT
A
H
U
G
R
N
U
G
LUMO and LUMO+1 have the electron density localized
on the whole SWCNT(6,5), corresponding to the conduction
band of SWCNT(6,5). These LUMOs are also typical for
covalently linked MP–SWCNT ACHNUTGERTNNUNG( n,m) (M=Zn and H ) were
2
probed by fluorescence measurements. Figure 6a shows the
steady-state fluorescence spectra and the time-profiles of
A
H
U
G
R
N
U
G
ACHTUNGTRENNUNG
LUMO+n (ꢀ10), although the ranges of the distributions
vary with n, as shown for the LUMO+2 as an example, in
which the electron densities gather under ZnP. At higher
LUMOs the electron density was localized on the ZnP
moiety corresponding to the local LUMO of the ZnP
moiety, although n=10 is not an exact number due to the
the fluorescence intensity of the H P–SWCNTACHTUNGTERNNUNG
2
ZnP–SWCNTACTHUNGTRENNUNG
citation of the porphyrin moiety. H P samples exhibited
2
a main fluorescence peak at 650 nm with an additional one
at 720 nm. In the hybrids with SWCNT, the H P fluores-
2
cence intensities [H P–SWCNT ACTHUNGTERNN(UNG 6,5), curve (i); H P–
2
2
delocalization both to ZnP and SWCNT
A
H
U
G
R
N
N
(6,5).
SWCNT ACHTUNGTNERNUNG( 7,6), curve (ii)] were found to be quenched over
The energy diagram in Figure 5 was constructed on com-
bination of these MO energy levels and the observed redox
potentials for the components, since the calculated values
for such huge and distorted carbon p-electron systems are
quite qualitative. Therefore, the reported oxidation potential
30% of its original intensity (data not shown), suggesting
1
[29]
occurrence of some events via the H P* state. Similarly,
2
ZnP–SWCNT ACHTUNGRNENUG( n,m) showed sharper peaks at 620 and
660 nm characteristic of ZnP fluorescence (Figure 6b). In
the hybrids with SWCNT, the ZnP fluorescence intensity
was found to be quenched over 40% of its original intensity
[27]
of ZnP corresponding to HOMOÀ2 and the redox poten-
Chem. Eur. J. 2012, 00, 0 – 0
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
5
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ÞÞ
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O. Ito, F. DꢂSouza et al.
From the picosecond fluorescence time-profile measure-
ments with the streak-scope method (insets in Figure 6), it
can be seen that the presence of SWCNT
ACHTUNGTRENNU(GN 6,5) and SWCNT-
AHCTUNGTREG(NNUN 7,6) in the hybrids accelerated the ZnP and H P fluores-
2
cence decays. By curve-fitting the time profiles with a bi-ex-
ponential decay function, the MP-fluorescence lifetimes
[
(tf)hybrid] were evaluated to be 80–330 ps with major frac-
tions (F) of 82–92% (Table 1). The minor fractions may be
Table 1. Observed fluorescence lifetimes [(t
f
)
hybrid] and estimated rate pa-
(n,m) hy-
rameters (kCS and FCS) for charge separation of MP–SWCNTACHTUNGTRENNUNG
[
a]
brids in DMF.
MP–SWCNT(n,m)
(6,5)
(7,6)
(6,5)
(7,6)
[
a]
À1
A
H
U
G
R
N
U
(t
f
)
hybrid [ps] (F [%])
k
CS [s
]
FCS (ꢁF)
9
9
9
9
ZnP–SWCNT
ZnP–SWCNTACHTUNGTRENNNUG
P–SWCNT
P–SWCNTAHCUTNGTRENNUNG
A
H
U
T
E
N
N
110 (89)
80 (92)
330 (82)
220 (90)
9.5ꢁ10
12.0ꢁ10
2.5ꢁ10
4.2ꢁ10
0.99 (0.88)
0.99 (0.92)
0.84 (0.68)
0.89 (0.80)
H
H
2
2
A
H
U
G
E
N
N
[
1
a] kCS =(1/t
450 ps for ZnP and 2000 ps for H
f
)
hybrid
À
A
H
U
G
R
N
U
G
f
)
ref
;
F
CS =[(1/t
f
)
hybrid f f hybrid f ref
ACHTUNGTRNEGUN( 1/t )ref]/ CATHUNGTRENNGNU( 1/t ) ; (t ) =
À
2
P in DMF.
attributed to no-interacting MPs, because their lifetimes are
similar to those of the pristine MPs. From the short (tf)hybrid
values, the rate constant and quantum yield for the MP fluo-
rescence quenching can be calculated; on combining the
above considerations, these values can be attributed to
Figure 6. Steady-state fluorescence of MP–SWCNT
A
H
U
G
R
N
U
(n,m) in DMF; lex
=
5
50 nm, where the absorbance of the MP moiety is normalized for these
charge separation rate constant (k ) and quantum yield
solutions. Inset: fluorescence decay time profiles; lex =408 nm. a) H
SWCNT(n,m) (650–720 nm), and b) ZnP–SWCNT
i) SWCNT(6,5), and (ii) SWCNT(7,6).
2
P–
CS
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
A
H
U
G
R
N
U
G
(F ), which are listed in Table 1.
CS
(
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
ACHTUNGTRENNUNG
The evaluated kCS and FCS for ZnP–SWCNT
DMF were found to be in the ranges of (9.5–12.0)ꢁ10 s
and 0.88–0.92 (including interacting fraction), which are
larger than those of H P–SWCNT(n,m) in the rage of (2.5–
ACHTUNGTRENNUNG( n,m) in
9
À1
(
data not shown), suggesting occurrence of events via
ACHTUNGTRENNUNG
2
1
9
À1
ZnP*.
The fluorescence quenching for MP–SWCNT
found to be more efficient than that of MP–SWCNT
must be noted here that the steady-state quenching experi-
ments of the MP–SWCNT(n,m) are quite qualitative, be-
cause some broad absorptions of the SWCNT(n,m) overlap
4.2)ꢁ10 s for kCS and 0.68–0.80 for F . This trend is in
CS
A
H
N
T
E
N
G
agreement with the exothermic trends in both the CS-1 and
A
H
U
G
R
N
N
CS-2 processes evaluated from both DGCS-1 and DGCS-2
,
which are mainly determined by small E . The values of
Ox
A
H
U
G
R
N
N
kCS and FCS for MP–SWCNT
those for MP–SWCNT(6,5), suggesting that SWCNT
with the higher conduction band level is more favorable for
ACHTUNGTRENNUNG
A
H
N
T
N
U
G
A
H
U
G
R
N
U
G
ACHTUNGTRENNUNG
with the MP absorption in the visible region, making it diffi-
cult to normalize the MP excitation intensity. Therefore, it is
essential to measure the fluorescence time profiles (see
insets in Figure 6 and analyses in the following paragraphs),
which are independent of MP concentration in a relatively
wide range.
1
charge separation via MP* compared with SWCNT
ACHTUNGTRENNUNG( 6,5)
with the lower conduction band level.
Nanosecond transient absorption studies: Evidence for
charge separation and the rate constant of charge recombi-
nation, kCR, were obtained from transient absorption spec-
tral studies by using a 532 nm laser light to excite the ZnP
1
As for photophysical events via the MP* state in polar
solvents, such as DMF, electron transfer may be more favor-
[
30]
able than energy transfer.
rence of energy transfer from MP* to SWCNT
NIR emission of the SWCNT(n,m) was monitored by the
excitation of the MP moieties in MP–SWCNT(n,m). No in-
crease in the emission intensity from SWCNT(n,m) in the
In order to check the occur-
and H P moieties predominantly. Figure 7 shows the nano-
2
1
A
H
U
G
R
N
U
G
second transient absorption spectra of ZnP–SWCNT ACHTUNGTRENNUNG( n,m)
nanohybrids in Ar-saturated DMF. Noticeably, a main tran-
A
H
U
G
R
N
N
AHCTUNGTRENNUNG
sient absorption peak was observed at 620–650 nm, which
+
[16]
A
H
N
T
N
U
G
can be attributed to the formation of ZnPC . In the NIR
NIR region upon MP excitation was observed in DMF, elim-
inating energy transfer as one of the quenching mechanisms.
region, the broad absorption bands were observed, which
À
+
can be ascribed to SWCNT
moiety, since both the band intensities decrease at the same
rates. Indeed, the NIR band observed for SWCNT(6,5) (Fig-
ure 7a) is slightly sharper than that of SWCNT(7,6) (Fig-
ure 7b), suggesting these NIR bands are characteristic of
ACHTUNGTRENNUNG
(n,m)C , as a partner of the ZnPC
Hence, in polar DMF, electron transfer (charge separation)
1
via MP* in MP–SWCNT
A
H
U
G
E
N
N
(n,m) is considered as a main
ACHTUNGTRENNUNG
origin of fluorescence quenching, which is supported by the
evaluated negative DGCS values.
ACHTUNGTRENNUNG
&
6
&
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Semi-conductive SWCNTs with Photosensitizing Porphyrins
FULL PAPER
ed from the ZnP fluorescence lifetimes. The decays of the
+
ZnPC mostly persists until about 500 ns; from the first-
order fitting to the decay curves until about 500 ns, the k
values were evaluated to be (5–6)ꢁ10 s (Table 2).
CR
6
À1
[
a]
Table 2. Estimated rate parameters for charge recombination in DMF.
[
a]
À1
[a]
Nanohybrids
k
CR [s
]
t
RIP [ns]
kCS/kCR
6
ZnP–SWCNT
ZnP–SWCNTACHTUNGTRENNNUG
A
H
U
G
R
N
U
G
4.9ꢁ10
5.8ꢁ10
6.4ꢁ10
7.5ꢁ10
210
170
160
130
1950
2070
390
6
6
6
H
H
2
2
P–SWCNT
P–SWCNT
ACHTUNGTRENNUNG
A
H
U
G
R
N
U
G
550
[
1
a] kCS =(1/t
450 ps for ZnP and 2000 ps for H
f
)
hybrid
À
A
H
U
G
R
N
N
(1/t
f
)
ref
;
F
CS =[(1/t
f
)
hybrid
À
A
H
U
G
R
N
U
G
f
)
ref]/
A
H
U
T
E
N
N
(1/t
f
)
hybrid
;
(t
f
)
ref
=
2
P in DMF.
+
From these k values, the lifetimes of ZnPC –SWCNT-
CR
À
A
H
U
G
R
N
U
G
RIP
+
À
ilarly, the kCR and t
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(n,m)C
RIP
2
6
À1
+
À
À
+
+
À
À
2
2
+
CS CR
[10]
for ZnP–SWCNT
SWCNT(n,m) (390–550), suggesting higher charge stabiliza-
tion of ZnPC –SWCNTC (or ZnPC –SWCNTC ). In both
cases, SWCNT(7,6) had slightly larger k /k values than
SWCNT(6,5), indicating that the best pair as the photoin-
ACHTUNGTNERUNNG( n,m), which are larger than those of H P–
2
AHCTUNGTRENNUNG
+
À
À
+
AHCTUNGTRENNUNG
CS CR
AHCTUNGTRENNUNG
duced charge-separation system was ZnP–SWCNT
DMF.
ACHTUNGTRENNUNG( 7,6) in
Figure 7. Nanosecond transient absorption spectra of ZnP–SWCNT
observed by 532 nm (ca. 3 mJ per pulse) laser irradiation in Ar-saturated
DMF. Inset: absorption–time profile at 650 nm. a) ZnP–SWCNT(6,5),
and b) ZnP–SWCNT(7,6). Spikes at 542 and 1064 nm are scattered light
from SHG and fundamental of YAG laser.
ACHTUNGTNERNUNG( n,m)
AHCTUNGTRENNUNG
Photoelectrochemical studies: The photoinduced charge-
separation rates and stabilization observed in the investigat-
ACHTUNGTRENNUNG
ed MP–SWCNT ACHNTUGRNENUG( n,m) impelled us to perform photoelectro-
[31]
chemical studies to visualize their ability to convert light
energy into electricity. To this aim, the MP–SWCNT(n,m)
ACHTUNGTRENNUNG
SWCNT
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(6,5) and SWCNT
A
T
N
T
E
N
N
(7,6). Similarly, H P–SWCNT-
nanohybrids in DMF solution were drop-coated on nano-
2
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(n,m) nanohybrids showed transient absorption spectra (see
clustered SnO /FTO electrode surface (FTO; fluorine doped
2
Supporting Information Figure S6) in which two broad ab-
sorption bands appear in the visible region (at 500 and 600–
tin oxide), in which FTO/SnO was selected due to its E
2
Red
as low as those of SWCNT
ACHTUNGTNERNUNG( n,m). The photocurrent action
7
00 nm) and also in the NIR region. Although they are
spectra based on incident photon conversion efficiency
[32]
broader, the former VIS bands support the assignments to
H PC , and the latter NIR bands to SWCNT
(IPCE%) values in the wavelength region covering up to
700 nm show a peak near 420–440 nm (Figure 8) corre-
sponding to the absorption of the MP moieties, although the
overall IPCE% values were low, which could be due to
a lower number of porphyrin entities and quenching of por-
phyrin emission in the donor–acceptor hybrids. Among the
earlier reported nanohybrids assembled with the porphyrin
+
À
A
H
U
G
R
N
U
G
2
From these broad transient bands, it was difficult to sepa-
rately recognize two kinds of radical-ion pairs (RIPs), such
+
À
À
+
as MPC –SWCNTC and MPC –SWCNTC . Compared with
the non-covalent MP–SWCNT(n,m) hybrids in our previous
these transient spectra of the covalently bonded
AHCTUNGTRENNUNG
[16,17]
reports,
À
+
[16]
MPC –SWCNT
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(n,m)C do not exhibit any distinct maxima; it
derivatives by some supramolecular approaches, the pres-
can be noted here that the covalent bonding on SWCNT-
(n,m) considerably disturbs the p-electronic structures of
the SWCNT(n,m).
ent IPCEs look to be moderate. The photoswitching re-
sponses shown in the inset of Figure 8 revealed quick re-
sponse and light stability of these nanohybrids. The maximal
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
+
The time profiles of ZnPC at 650 nm are shown in the
IPCE values follow the trends of k /k in Table 2, suggest-
CS CR
+
insets of Figure 7. The increases in ZnPC are fast within the
ing that the photovoltaic cell efficiency strongly depends
upon the charge separation stability. Consequently, higher
values for SWCNT ACHTUNGRENNU(G 7,6) compared to SWCNT ACHTUNGERTNNUNG( 6,5) derived
nanosecond laser pulse (6 ns); such quick rises correspond
to the fast charge separation within about 100 ps as estimat-
Chem. Eur. J. 2012, 00, 0 – 0
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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O. Ito, F. DꢂSouza et al.
charge-separated state stabilization evaluated by time-re-
solved spectral data.
Experimental Section
ꢀ
Chemicals: The (6,5 and 7,6) enriched SWCNTs were from CoMoCAT ,
[
15]
SourthWest Nano Technologies, Inc., (Norman, OK) marketed by Al-
drich Chemicals (Milwaukee, WI). The bulk solvents utilized in the spec-
tral and photophysical measurements were from Aldrich.
Synthesis of MP–SWCNT
-5(p-methoxycarbonylphenyl)-10,15,20-tri
1a): This compound was synthesized according to Adler et al. A mix-
ture of methyl-4-formylbenzoate (1.2 g, 7.3 mmol), pyrrole (1.99 mL,
9.2 mmol) and 4-propylbenzaldehyde (3.23 mL, 21.9 mmol) was refluxed
ACHTUNGTRENNUNG
H
(
2
ACHTUNGTRENNUNG
[
33]
2
in propionic acid (200 mL) for 8 h. The propionic acid was removed
under reduced pressure and the crude product was purified on basic alu-
mina column by using hexane: CH
2
Cl
-d): d=8.9–8.75 (m, 8H, b-pyrrolic H), 8.45 (d, 2H,
phenyl H), 8.3 (d, 2H, phenyl H), 8.14–8.06 (m, 6H, o-phenyl H), 7.53–
.58 (m, 6H, m-phenyl H), 4.3 (s, 3H, methoxy H), 2.9 (t, 6H, propyl À
CH H), 1.9 (sextet, 6H, propyl-CH H), 1.18 (t,9H, propyl-CH H),
calcd for
2
(1:1 v/v). Yield: 1.38 g, 25%;
1
H NMR (CHCl
3
Figure 8. IPCE spectra and (inset) light-current switching curves for the
photoelectrochemical cells of: (i) ZnP–SWCNT(7,6), (ii) ZnP–SWCNT-
(6,5), (iii) H P–SWCNT(7,6), and (iv) H P–SWCNT(6,5) coated on SnO
modified FTO electrode surface in acetonitrile containing LiI (0.5m) and
(0.1m) mediator.
7
AHCTUNGTRENNUNG
2
2
3
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
2
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
2
A
T
G
R
N
U
G
2
-
À2.78 ppm (s, br, 2H, imino H); ESI mass in CHCl
3
+
+
C
55
H
50
N
4
O
2
, 799.01; found: m/z (%): 799.6 [M ] (100), 800.5 [M ] (60),
I
2
+
8
01.5 [M ] (15).
H
2
-5(p-carboxyphenyl)-10,15,20-tri AHCTUNGRETNNUN(G 4-propyl)phenylporphyrin (1): A mix-
ture of 1a (200 mg, 0.25 mmol) in THF (20 mL) and excess of KOH (5 g,
saturated solution in water) was refluxed for 20 h. After being cooled,
nanohybrids, and higher values for ZnP over H P derived
nanohybrids were observed.
2
the mixture was diluted with CH
tracted. The organic layer was washed with saturated NaHCO
and dried over anhydrous Na SO . Solvent was evaporated and the crude
product was purified on silica gel column by using CHCl /CH OH (95:5
-d): d=8.94–8.78 (m, 8H, b-
pyrrolic H), 8.6 (d, 2H, phenyl H), 8.3 (d, 2H, phenyl H), 8.18–8.08 (m,
o-phenyl H), 7.6–7.53 (m, 6H, m-phenyl H), 2.9 (t, 6H, propyl-CH H),
.9 (sextet, 6H, propyl-CH H), 1.18 (t, 9H, propyl-CH
H), À2.78 ppm (s,
br, 2H, ÀNH); ESI mass in CHCl calcd for C H N O , 784.98; found:
2
Cl
2
, acidified with conc. HCl and ex-
3
solution
2
4
3
3
1
v/v). Yield: 0.158 g, 80%; H NMR (CHCl
3
Conclusion
2
Light energy harvesting donor–acceptor nanohybrids com-
prised of porphyrins and diameter-sorted SWCNT ACHTUNGRNENUG( n,m)
were newly synthesized and characterized. In order to con-
nect the porphyrins (MP) covalently to the side walls of
1
2
3
3
54 48
4
+
2
+
+
m/z (%): 785.5 [M ] (100), 786.5 [M ] (62), 787.5 [M ] (17).
-5-{4“formylhydroxyphenyl-4’-phenylester}-10,15,20-tri(4-propyl)phe-
nylporphyrin (2): A solution of 1 (150 mg, 0.19 mmol), SOCl (150 mL,
.9 mmol) and pyridine (1 mL) in dry toluene (40 mL) was refluxed
H
2
ACHTUNGTRENNUNG
2
SWCNT
azomethine ylide was employed, which largely preserved the
p electronic structure of SWCNT(n,m) after functionaliza-
ACHTUNGTRENNUNG( n,m), Pratoꢂs method of dipolar cycloaddition of
1
under argon for 3 h. After being cooled, the solvent was evaporated and
the resultant mixture was redissolved in dry toluene (40 mL). Then pyri-
dine (1 mL) was added followed by 4-hydroxybenzaldehyde (46 mg,
AHCTUNGTRENNUNG
tion, which were evident from the TGA and Raman studies.
The theoretical DFT-MO calculations of the MP–SWCNT-
ACHTUNGTRENNUNG( n,m) nanohybrids provided the optimized structures and
the MO energy levels; on combining the redox values, possi-
ble mechanisms of electron transfer and the free-energy cal-
culations were estimated. The steady-state and time-re-
solved fluorescence studies revealed efficient quenching of
0
.38 mmol). Reaction mixture was stirred at room temperature under
argon for 12 h. Solvent was evaporated and the crude compound was pu-
rified by column chromatography on silica gel by using hexane/CH Cl
-d): d=10.1 (s, 1H, À
2
2
1
(
10:90 v/v). Yield: 0.118 g, 70%; H NMR (CHCl
3
CHO H), 8.94–8.8 (m, 8H, b-pyrrolic H), 8.6 (d, 2H, phenyl H), 8.4
(d,2H, phenyl H), 8.14–8.10 (m, o-phenyl H), 8.08 (d, 2H, phenyl H), 7.6
(
d, 2H, phenyl H), 7.52–7.58 (m, 6H, m-phenyl H), 2.9 (t, 6H, propyl-
CH H), 1.9 (sextet, 6H, propyl-CH H), 1.18 (t, 9H, propyl-CH H),
): d=190.0,
64.8, 155.8, 148.5, 142.2, 139.3, 134.9, 134.5, 134.1, 131.4, 128.5, 128.1,
2
2
3
the singlet excited states of the ZnP and H P moieties; the
13
2
À2.78 ppm (s, br, 2H, ÀNH); C NMR (400 MHz, CDCl
3
nanosecond transient absorption technique confirmed an
1
+
À
electron transfer process, producing MPC –SWCNTC (or
126.8, 122.6, 120.9, 120.5, 117.7, 38.0, 24.7, 14.1 ppm; ESI mass in CHCl
3
À
+
+
MPC –SWCNTC ) charge separation species. The merit of
charge-separated state stabilization, which were calculated
from the rates of charge separation, kCS and rate of charge
recombination, kCR were found to be higher for ZnP than
calcd for C61
H
52
N
4
O
3
, 889.09; found: m/z (%): 889.5 [M ] (100), 890.5
+
+
[
M ] (70), 891.5 [M ] (22).
N-Boc-[{2-amino}2,2’-(ethylenedioxy)]diethylamine (3a): This compound
[34]
was prepared according to Muller et al. A solution of di-tert-butyl bi-
carbonate (7.5 g, 0.034 mol) dissolved in dry CHCl (100 mL) was added
3
H P and slightly higher for the MP–SWCNT
2
A
H
U
G
R
N
U
G
to a solution of 2,2’-(ethylenedioxy)diethylamine (50 mL, 0.34 mol) in
SWCNT
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
CHCl
then allowed to stir for another 24 h at room temperature. It was then
washed with water, extracted with CHCl and dried over anhydrous
Na SO . Solvent was the evaporated and the organic layer yielded the de-
sired compound as pale yellow oil. Yield: 1.68 g, 20%; H NMR (CHCl
d): d=5.2 (s, br, 1H, ÀNH), 3.64 (d, 4H), 3.5 (m, 4H), 3.3 (m, 2H), 2.85
3
(300 mL) in 2.5 h with stirring in an ice-bath. The reaction was
AHCTUNGTRENNUNG
3
2
4
A
H
U
G
R
N
U
G
1
3
-
&
8
&
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ÝÝ
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Semi-conductive SWCNTs with Photosensitizing Porphyrins
FULL PAPER
(
m, 2H), 1.6–1.4 ppm (m, 9H, Boc-H); ESI mass in CHCl
3
calcd for
fluorine doped indium tin oxide (FTO; Pilkington TEC-8, 6–9 W per
square) and dried in air. The electrodes were annealed in an oven for 1 h
in air at 673 K. The estimated thickness of the electrode was around 1–
+
+
C
11
H
24
N
2
+
O
4
, 248.32; found: m/z (%): 249.0 [M ] (100), 250 [M ] (15),
49 [M , reactant amine] (35).
Benzyl-N-[{2-(N-Boc)}2,2’-(ethylenedioxy)diethylamino]glycinate (3b):
1
2
mm.
[
35]
This compound was prepared according to Kordatos et al. A solution
of benzyl 2-bromoacetate (0.64 mL, 4.02 mmol) in 1,4-dioxane (20 mL)
was added slowly over a period of 1 h to a solution of 3a (3 g, 0.012 mol)
in 1,4-dioxane (20 mL) cooled at 08C. The reaction mixture was then
stirred, overnight. The solvent was then evaporated under reduced pres-
sure and the residue was dissolved in water and extracted with ethyl ace-
Instrumentation: The UV/Vis spectral measurements were carried out
with a Shimadzu Model 2550 double monochromator UV/Vis spectro-
photometer. The steady-state fluorescence spectra were measured by
using a PerkinElmer (LS-55) and a Horiba Jobin Yvon Nanolog UV/Vis–
NIR spectrofluorometer equipped with PMT (for UV/Vis) and InGaAs
(for NIR) detectors. All the solutions were purged prior to spectral meas-
1
13
tate. The organic extract was dried over anhydrous Na
2
SO
4
and the sol-
urements by using Ar gas. H and C NMR spectra were obtained by
vent was evaporated under reduced pressure. The crude compound was
purified by column chromatography on silica gel by using petroleum
using a Varian 400 MHz instrument. Tetramethylsilane (Si
used as an internal standard.
3 4
ACHTUNGTRNENUG( CH ) ) was
ether/ethyl acetate (70:30 to 50:50 v/v). Evaporation of the solvent yield-
Thermogravimetric analyses were run by using a Texas Instruments TGA
Q50 instrument. All the samples for the analysis were dried under
1
ed the desired product. Yield: 1.19 g, 75%; H NMR (CHCl
3
-d): d=7.42–
7
6
.39 (m, 5H, phenyl H), 5.22 (s, br, 1H, ÀNH), 5.18 (s, 2H), 3.6–3.51 (m,
vacuum. Samples ramp test were performed under nitrogen atmosphere
H), 3.5–3.46 (m, 4H), 3.28 (m, 2H), 2.8 (t, 2H), 1.45 ppm (s, 9H, Boc-
À1
at 108Cmin
.
1
3
H); C NMR (400 MHz, CD
3
OD): d=180.0, 155.2, 79.0, 70.3, 69.9, 53.4,
calcd for C20 , 396.48;
Transmission electron micrograph (TEM) measurements were recorded
by applying a drop of the sample to a copper grid. Images were recorded
on a Hitachi H7100 transmission electron microscope at an accelerating
voltage of 100 kV for imaging.
4
9.3, 40.7, 27.4 ppm; ESI mass in CHCl
3
32 2 6
H N O
+
found: m/z (%): 397.1 [M ] (18).
N-[2-(N-Boc)2,2’-(ethylenedioxy)diethylamino]glycine (3): Pd/C (80 mg,
%) was added to a methanolic solution of 3b (1.25 g, 3.15 mmol), and
5
The Raman spectra were measured by using Enwave Optronics, Inc.,
ProRaman-L instrument with 532 nm laser source. IR experiments were
performed with a PerkinElmer Spectrum One FT-IR Spectrometer with
universal ATR sampling accessory.
the reaction mixture was stirred under hydrogen atmosphere for 24 h.
The catalyst was then removed by filtration by using Celite and solvent
was evaporated. The residue was triturated in diethyl ether to give the
1
desired product as a white solid. Yield: 0.77 g, 80%; H NMR (CHCl
3
-d):
The time-resolved fluorescence spectra were measured by single photon
counting method by using a streakscope (Hamamatsu Photonics, C5680)
as a detector and the laser light (Hamamatsu Photonics M10306, laser
diode head, 408 nm, pulse width=71.5 ps) as an excitation source. Life-
d=3.8 (t, 2H), 3.7–3.55 (m, 8H), 3.5 (t, 2H), 1.40 ppm (s, 9H, Boc-H);
ESI mass in H
2
O calcd for N13
H
26
N
2 6
O , 306.36; found: m/z (%): 306.4
À
À
À
[
M ] (55), 305.5 [M ] (40), 307.3 [M ] (33).
Covalent functionalization of SWCNT
A
H
U
G
R
N
U
G
A
H
U
G
E
N
N
[40]
times were evaluated with software attached to the equipment.
phyrins (4): The synthesis of covalently functionalized carbon nanotube
Nanosecond transient absorption measurements were carried out by
using THG (532 nm) of a Nd:YAG laser (Spectra-Physics, Quanta-Ray
GCR-130, 5 ns fwhm) as an excitation source. For transient absorption
spectra in the near-IR region (600–1200 nm) and the time-profiles, moni-
toring light from a pulsed Xe lamp was detected with a Ge-APD (Hama-
matsu Photonics, B2834). For the measurements in the visible region
was carried out by 1,3-dipolar cycloaddition via azomethine ylide forma-
[
36–38]
tion.
In a typical experiment, pristine SWCNT AHCTUNGTERNNNU(G 7,6) (40 mg) was
taken in DMF (40 mL) and the mixture was sonicated for 15 min by
using a Mesonix ultrasonicator at 4 W power output. To the dispersed
carbon nanotube/DMF solution were added porphyrin aldehyde
2
(
10 mg) and Boc protected amino acid 3 (40 mg) and the reaction mix-
(
400–1000 nm), a Si-PIN photodiode (Hamamatsu Photonics, S1722-02)
ture was heated at 1208C. After 24 h, porphyrin aldehyde 2 (10 mg) and
Boc protected amino acid 6 (40 mg) were again added to the reaction
flask. Another lot of the same amount was again added after 48 h and
the reaction mixture was heated for 4 days in total. After being cooled to
room temperature, the solution was filtered on a Millipore nylon mem-
brane filter (0.2 mm). The black nanotube on the filter was washed with
[
42]
was used as a detector.
Photoelectrochemical experiments were performed in a two-electrode
configuration by using desired donor–acceptor nanohybrids drop coated
onto FTO/SnO
2
electrode and a platinized FTO electrode as counter
(0.1m) as
redox mediator. The photocurrent–photovoltage characteristics of
electrode in acetonitrile solution containing LiI (0.5m) and I
I /I
2
À
À
3
2 2
DMF, CH CH , MeOH. The residue was time and again sonicated, cen-
the solar cells were measured by using a Model 2400 Current/Voltage
Source Meter of Keithley Instruments, Inc. (Cleveland, OH) under illu-
mination with an AM 1.5 simulated light source with a Model 9600 of
trifuged and filtered until all the unreacted components were washed
away. The final functionalized nanotube sample was then dried and used
for further characterization by using UV/Vis/NIR, NIR fluorescence,
Raman, TGA, TEM studies.
1
50-W Solar Simulator of Newport Corp. (Irvine, CA).
Energy minimization calculations and the MO distributions and their
energy levels by using B3LYP/3-21G(*) basis set of the nanohybrids were
performed with Gaussian-09 software. The frontier orbitals were gener-
ated by using the Gauss View program.
For the synthesis of covalently functionalized porphyrin–SWCNT
ACHTUNGTRNENUNG( 6,5),
a similar procedure as above was followed. Finally, the H P–SWCNT hy-
2
[
26]
brids (4) were converted to ZnP–SWCNT hybrids (5) by standard zinc-
insertion reactions by using zinc acetate in methanol. The progress of the
reaction was followed spectroscopically. After completion of the reaction,
excess zinc acetate was removed by washing the reaction product with
methanol.
À1
ATR-IR analysis of functionalized nanohybrids: Peaks at 2800–3000 cm
corresponding to aliphatic CÀH stretching, peaks in the range 3020–
Acknowledgements
À1
3
1
1
100 cm attributed to aromatic ring stretch, strong, broad hump at
À1
300–1600 cm corresponding to phenyl ring stretch, peaks around 980–
This work was financially supported by the National Science Foundation
(Grant No. 1110942, to F.D.). A.S.D.S thanks Prof. H. Murata of JAIST
for his kind support for this study.
À1
À1
050 cm corresponding to CÀO stretch, weak band at 3000–3200 cm
À1
corresponding to NÀH stretch, a peak at 1050 cm due to CÀN stretch,
À1
a band in the range 1600–1710 cm attributed to carbonyl (C=O) stretch
[
39–40]
were observed in agreement with literature results.
Preparation of nanocrystalline SnO electrodes: These were prepared ac-
cording to the literature procedure with few changes. An SnO
dal solution (10 mL; Alfa Aesar, 15%) was dissolved in ethanol (10 mL);
NH OH (500 mL) was added to this solution for stability. About 0.5 mL
of the colloidal solution was placed on an optically transparent electrode,
2
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These are not the final page numbers!

Semi-conductive SWCNTs with Photosensitizing Porphyrins
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Published online: && &&, 0000
Chem. Eur. J. 2012, 00, 0 – 0
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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These are not the final page numbers!

O. Ito, F. DꢂSouza et al.
Size matters! Diameter dependent effi-
ciencies of photoinduced electron
transfer leading to charge stabilization,
and photoelectrochemical response of
solar cells is demonstrated in porphy-
rin covalently linked to (7,6) and (6,5)
enriched single wall carbon nanotube
donor–acceptor nanohybrids (see
figure).
Photoelectrochemistry
S. K. Das, A. S. D. Sandanayaka,
N. K. Subbaiyan, M. E. Zandler,
O. Ito,* F. DꢀSouza* ......... &&&& — &&&&
Functionalization of Diameter Sorted
Semi-conductive SWCNTs with Photo-
sensitizing Porphyrins: Syntheses and
Photoinduced Electron Transfer
&
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www.chemeurj.org
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!