Tin(IV) porphyrin functionalization of electrochemically active fluoride-doped tin-oxide (FTO) via Huisgen [3+2] click chemistry

Article abstract of DOI:10.1142/S1088424611002970

A novel tetra-alkyne terminated tin(IV) porphyrin 3 was synthesized in good yields and characterized using NMR spectroscopy, high resolution mass spectrometry and X-ray crystallography, the latter revealing interactions with hexane molecules that stabiliz

Full text of DOI:10.1142/S1088424611002970

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2011; 15: 75–82
DOI: 10.1142/S1088424611002970
Published at http://www.worldscinet.com/jpp/
Tin(IV) porphyrin functionalization of electrochemically
active fluoride-doped tin-oxide (FTO) via Huisgen [3+2]
click chemistry
Shiva Prasada, Mohan Bhadbhadeb and Pall Thordarson*a
a School of Chemistry, The University of New South Wales, Sydney, NSW 2052, Australia
b Analytical Centre, The University of New South Wales, Sydney, NSW 2052, Australia
Received 5 November 2010
Accepted 15 January 2011
ABSTRACT: A novel tetra-alkyne terminated tin(IV) porphyrin 3 was synthesized in good yields and
characterized using NMR spectroscopy, high resolution mass spectrometry and X-ray crystallography,
the latter revealing interactions with hexane molecules that stabilize the crystal structure of the tin(IV)
porphyrin 3. It was then linked to a conductive fluorine-doped tin oxide (FTO) surfaces using Huisgen
[3+2] click chemistry. The attachment of the tin(IV) porphyrin to the FTO surface 6 was characterized
by X-ray photoelectron spectroscopy (XPS), indicating the presence of the 1,2,3-triazole unit. Electro-
chemical measurements of the tin(IV) porphyrin modified FTO surface 7 show that it is still electro-
chemically active with oxidation (Epa) and reduction peaks (Epc) for the ferricyanide redox couple
observed at Epc and Epa of -0.144 and +0.568 V vs. Ag|AgCl respectively, representing a modest shift of
ca. +/- 0.1–0.15 V, compared to unmodified FTO.
KEYWORDS: surface functionalization, tin(IV) porphyrin, XPS, FTO, electrochemistry.
nickel [15], rhodium [16] and iron [17] porphyrins. In
INTRODUCTION
particular, zinc(II) and tin(IV) metalloporphyrins are
Currently, there is an extensive amount of workfocused
most commonly used as photosensitizers as they have
on the study of photo-driven processes and devices, par-
most of the above properties for a good photocatalyst.
ticularly in the field of renewable energy research in the
This includes a number of recent demonstration of the
form of solar cells [1–6]. Most of this effort is focused
use of zinc(II) porphyrins in dye-sensitized solar cells
on searching for chromophores capable of efficiently
[18–20] and the application of tin(IV) porphyrins as pho-
generating photocurrent on appropriately designed elec-
tocatalyst to generate metallic nanostructures [21, 22].
trodes. The ideal chromophores for this purpose requires
To be useful in photo-driven devices such as light
a combination of unique electronic [7], photonic [8] and
activated biosensors, biofuel cells and solar cells prefer-
catalytic properties [9, 10]. One particular class of chro-
ably requires the metalloporphyrin chromophores to be
mophores that has drawn a lot of interest are metallopor-
attached to transparent conductive electrodes. Recent
phyrins. Metalloporphyrins are long been known to act
studies show that electrodes functionalized with free-
as good photosensitizers due to their long-lived excited
base porphyrin chromophores can generate photocurrent
states, good quantum yields of excitation and excellent
in the presence of light and a sacrificial electron donor.
visible light absorption and redox properties [11, 12].
The free-base tetraphenyl porphyrin-fullerene dyad mod-
Representive examples of frequently used metallopor-
ified indium tin oxide (ITO) surface reported by Fuku-
phyrins as photosensitizers include zinc [13], tin [14],
zumi and coworkers showed up to 100 nA photocurrent
in the presence of triethanolamine as an electron donor
and an applied potential bias [23]. Similarly, Hirano
SPP full member in good standing
and coworkers have been able to generate photocurrent
with a mesoporous silica-porphyrin hybrid coated on a
*Correspondence to: Pall Thordarson, email: p.thordarson@
unsw.edu.au, tel: +61 2-9385-4478
Copyright © 2011 World Scientific Publishing Company

76
S. PraSaD et al.
TMS
fluorine-doped tin oxide (FTO) electrode [24]. When the
system is exposed to a switching light source under a bias
of -0.4 to 0.3 V, a photocurrent is detected.
TMS
Here we describe the synthesis of novel tin(IV) por-
phyrin that has been linked to a FTO surface using the
Huisgen [3+2] click reaction. The resulting tin(IV) por-
phyrin modified FTO surface were characterized by
X-ray photoelectron spectroscopy (XPS) and shown to
be electrochemically active. This represents an effective
and generic way to generate metalloporphyrin modified
electrodes for use in photo-driven devices.
N
H
N
N
H
N
1
TMS
TMS
TMS
TMS
RESUlTS AND DISCUSSION
i)
Synthesis and characterization of tin(IV) porphyrins
The tin(IV) porphyrin 3 was obtained in three steps
as shown in Scheme 1. The precursor trimethylsilane
(TMS) protected free-base porphyrin 1 was synthesized
in 37% yield following the method reported by McDon-
ald and coworkers [25]. The subsequent metalation to
afford dichlorotin(IV) porphyrin 2 was achieved using
the Rothemund method [26] where 1 was refluxed with
an excess of tin(II) chloride to afford 2 in 97% yield.
The TMS-groups were then removed to afford the target
tetra-alkyne tin(IV) porphyrin 3 in 30% yield by reflux-
ing potassium carbonate with tin(IV) porphyrin 2 in a
dichloromethane/methanol mixture (Scheme 1) [27].
In each step of this synthesis, the porphyrins were
isolated in good purity by precipitation or by washing
the organo-soluble porphyrins (1–3) with water. The
structureofthesecompoundswasdeterminedbyacombi-
nation of spectroscopic techniques, including 1H and high
resolution mass spectrometry. The UV-vis (Fig. 1a) and
1H NMR spectra for 2 (Fig. 1b) and 3 (Fig. 1c) are similar
to previously reported tin(IV) porphyrins [28]. Following
N
Cl
N
N
Cl
Sn
N
2
97%
TMS
TMS
ii)
N
Sn
N
Cl
N
N
Cl
1
the metalation, H NMR the -2.83 ppm resonance for
the inner pyrrolic N-H in 1 disappeared and the inser-
tion of the tin metal was confirmed by MS (1000.53 m/z)
and UV-vis with a Soret band at 430 nm and two
Q-bands at 602 and 561 nm, respectively. After removal
of the TMS-group to form 3, the coupling constant of
the 119Sn NMR (-590.08) suggested that the axial ligands
were chlorides [28]. This was somewhat unexpected as
the conditions used for converting 2 and 3 have been
reported to result in ligand exchange from a chloride to
a hydroxide. It is possible that chloroform, which was
used as a solvent for recrystallatization, could have
degraded to form phosgene and hydrochloric acid. The
resulting chlorides from hydrochloric acid could then
exchange with the labile hydroxyl ligands, accounting
for the observed chlorides in 3. Signs of 3 converted to
the dihydroxy ligated species did show in MALDI-TOF
mass spectrometry analysis but this ligand exchange
may have happened during sample preparation or in situ
in the mass spectrometer.
3
30%
Scheme 1. Reagents and conditions: (i) tin(II) dichlo-
ride, pyridine, reflux, overnight; (ii) potassium carbonate,
methanol:dichloromethane (1:4), reflux, 16 h
Single crystals of tin(IV) porphyrin 3 were grown for
X-ray crystallography by slow diffusion of hexane into
a solution of 3 in chloroform. Due to the small crys-
tal size, acquisition of data for X-ray crystallographic
analysis was carried out at the synchrotron X-ray
source at the Australian Synchrotron Centre. The data
was collected with 10223 reflections with an R factor of
0.1143. The quality of the data obtained was sufficient
to confirm the main structural features of the tin(IV)
porphyrin 3, including the nature of the axial ligands
as chlorides.
Copyright © 2011 World Scientific Publishing Company
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TIn(IV) POrPhyrIn funCTIOnalIzaTIOn Of eleCTrOChemICally aCTIVe fluOrIDe-DOPeD TIn-OxIDe (fTO)
77
Fig. 3. A perspective view of the tin(IV) porphyrin 3 along
the crystallographic a-axis. The hydrogen atoms are excluded
for clarity. The packing of tin(IV) porphyrin 3 (wireframe) is
shown in the presence of hexane (spacefill)
crystals. These hexane molecules are important for the
Fig. 1. Spectra of 2 and 3; (a) UV-vis spectra (CHCl3) of 2 and
3. 1H NMR (300 MHz, CDCl3) of (b) 2 and (c) 3 (solvent impu-
stability of the crystal lattice of tin(IV) porphyrin 3.
Along the crystallographic a-axis, these porphyrin mol-
ecules pack as close to each other as possible, with the
hexane molecules sitting in between each porphyrin. The
axial chlorides of the porphyrin interacts with the hydro-
gen of the C3-hexane molecules, while the phenyl ring of
an adjacent porphyrin molecule interacts with the same
hexane, however at the C1-position, causing the alkyne
group (CaC−C) to be slightly kinked (178°). Along the
crystallographic b-axis, each tin(IV) porphyrin mac-
rocycle sits approximately 40° to the following tin(IV)
porphyrin, creating a unique form of packing.
rities are labeled with *)
As illustrated in Fig. 2a, the tin metal ion sits expect-
edly within the porphyrin macrocycle with a N-Sn-N
bond angle of 180° and a N-Sn bond length of 2.1 Å.
The Cl-Sn-N bond angle, which is expected to be approx-
imately 90°, was observed to be 87°. This is because the
axial chloride ligand sits next to the hexane molecule.
Moreover, the meso-porphyrin phenyl rings of the tin(IV)
porphyrin 3 are rotated approximately 79° to the plane of
the porphyrin macrocycle. The tin(IV) porpyhrin mac-
rocycles packs in a unique way, where one macrocycle
is approximately 40° to the following tin(IV) porphyrin
macrocycle (Fig. 2b). The three-dimensional packing of
tin(IV) porphyrin 3 is shown in Fig. 3.
Synthesis and characterization of tin(IV) porphyrin-
modified FTO surfaces
The porphyrin packs into a crystal lattice in the pres-
ence of hexane that was used during the growth of these
The tin(IV) porphyrin modified surface 7 was pre-
pared using the copper(I) catalyzed Huisgen [3+2] click
Fig. 2. X-ray crystallographic analysis of tin(IV) porphyrin 3. (a) Front view and (b) the unique packing of tin(IV) porphyrin 3 along
the crystallographic b-axis. The hydrogen atoms are excluded for clarity
Copyright © 2011 World Scientific Publishing Company
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78
S. PraSaD et al.
OH
OH
amount of copper(II) sulfate, ascorbic acid and tin(IV)
porphyrin 3 in N,N-dimethylformamide and water to
yield the tin(IV) porphyrin triazole-modified FTO sur-
face 7. Scheme 2 outlines a step-wise modification of
tin(IV) porphyrin to FTO surfaces.
OH
OH
OH
4
The tin(IV) porphyrin-modified FTO surface 7 was
analyzed using XPS (Fig. 4a,b) and surface reflectance
UV-vis spectroscopy (Fig. 4c). The N1s XPS spectra of
the azide-modified FTO surface 6 (Fig. 4a) show two dis-
tinct peaks at 404.7 eV and 400.6 eV in a 1:2 ratio which
correspond to the center electron deficient azide nitro-
gen and the two nearly equivalent terminal azide nitro-
gen atoms as previously reported in the literature [32].
Following the Huisgen [3+2] click chemistry reaction to
form the tin(IV) porphyrin triazole-modified FTO surface
7, the 404.7 eV peak disappears (Fig. 4b), leaving one
peak at 400.4 eV for the near-equivalent 1,2,3-triazole
nitrogens, indicating that the reaction of the azide with
the terminal alkyne of tin(IV) porphyrin 3 to a 1,2,3-
triazole was successful and therefore effectively linking
the tin(IV) porphyrin 3 to the surface [32]. In addition,
surface reflectance UV-vis spectral data (Fig. 4c) shows
the characteristic Soret peak of the tin(IV) porphyrin chro-
mophore at 432 nm following the attachment of tin(IV)
OEt
OEt
OEt
i)
N3
Si
5
N3
Si
O
O
O
6
ii)
Cl
N
Sn
N
N
N
N
N
Cl
N
Si
O
O
O
7
Scheme 2. (Left) the attachment of tin(IV) porphyrin 3 to the
azide-modified FTO surface 6; (i) (3-azidopropyl)triethoxysi-
lane 5 (40 mM), toluene, 2 h, room temperature; (ii) tin(IV)
porphyrin 3, copper(II) sulfate, ascorbic acid, N,N-dimethyl-
formamide, water, overnight (the presence of chloride axial
ligands are assumed but cannot be verified by XPS or UV-vis
spectroscopy)
chemistry approach [29] outlined in Scheme 2. The
(3-azidopropyl)triethoxysilane 5 precursor was initially
synthesized in 95% yields using methods adopted from
Khoukhi and coworkers [30]. The azide linker 5 was
added to the activated FTO surface 4 in a solution of
toluene (Scheme 2). The resulting azide-modified FTO
surface 6 was washed and sonicated in dichloromethane,
chloroform, methanol and acetone to clean the surface
of any absorbed compounds. The tetra-alkyne terminated
tin(IV) porphyrin 3 was then attached to surface 6 using
the copper(I) catalyzed Huisgen [3+2] click chemistry
method adopted from Ortega-Munoz [31]. The azide-
modified FTO surface 6 was reacted with a catalytic
Fig. 4. Characterization spectra for FTO modified surfaces;
the N1s XPS spectra of FTO modified surfaces (a) 6 and (b) 7.
(c) The UV-vis reflectance of FTO modified surface 7 showing
the porphyrin peak at 432 nm (absorption below ≈ 380 nm is
due to the glass in FTO)
Copyright © 2011 World Scientific Publishing Company
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TIn(IV) POrPhyrIn funCTIOnalIzaTIOn Of eleCTrOChemICally aCTIVe fluOrIDe-DOPeD TIn-OxIDe (fTO)
79
porphyrin 3 to the azide-modified FTO surface 6. It should
be noted that surface reflectance UV-vis spectroscopy
does not distinguish between covalently attached ligands
or surface absorbed molecules. However, the absorbance
spectrum observed for the tin(IV) porphyrin triazole-
modified FTO surface 7 did not change even after con-
tinuous sonication to remove adhered contaminants in
solvents such as dichloromethane, chloroform, toluene,
acetone, methanol and N,N-dimethylformamide.
and +0.006 V vs. Ag|AgCl respectively, consistent with
an accessible electrode surface. After modification, this
response decreases, consistent with a surface blocking
layer. The azide-modified FTO surface 6 (Fig. 5, thick
gray line) has an Epc at +0.084 V vs. Ag|AgCl and an Epa
at +0.384 V vs Ag|AgCl. Following the attachment of the
tin(IV) porphyrin 3 chromophore, peaks with Epc and Epa
of -0.144 and +0.568 V vs. Ag|AgCl were detected on the
tin(IV) porphyrin triazole-modified FTO surface 7 respec-
tively (Fig. 5, thick black line). The change in Epc and
Epa are attributed to the increased distance from the FTO
surface to the terminal tin(IV) porphyrin chromophores.
As the length of the monolayer increases from surface
6 to 7, the rate of electron transfer from the redox probe to
the surface decreases, resulting in an increase in ∆E. The
ratio of the area under the reduction and oxidation peaks
for surfaces 6 and 7 (ipa/ipc) was calculated to be approxi-
mately 1, indicating the redox processes are reversible and
stable under the working conditions (0.05–0.60 V/s). The
tin(IV) porphyrin triazole-modified FTO surface 7 also
shows a reduction in current when compared to the azide-
modified precursor FTO surface 6. The azide-modified
FTO surface 6 has a cathodic peak current (ipc) and an
anodic peak current (ipa) of -77 and +51 μA respectively,
whilst the tin(IV) porphyrin triazole-modified FTO sur-
face 7 has an ipc and ipa of -51 and +25 μA.
Electrochemical characteristics of surface 7
Cyclic voltammetry (CV) measurements of the tin(IV)
porphyrin-modified FTO electrodes were performed in
an effort to gain information about the electroactivity of
the modified FTO surfaces, using a ferricyanide probe.
Previous electrochemical studies of tin(IV) porphy-
rins suggest that the first reduction of tin(IV) porphyrins
occurs at about -0.7 V vs. SCE [33, 34]. However, this
falls outside the linear current region of unmodified FTO
surfaces, as reduction of tin in FTO surfaces occurs at
approximately -0.5 to -0.6 V vs. Ag|AgCl (Fig. 5, thin
black line). For this reason, the reduction peak of tin(IV)
porphyrin-modified on FTO surfaces was not observed
directly. In order to obtain information about the porphy-
rin layers, ferricyanide (Fe(CN)63+) was used as a probe
to measure the changes in response during each modifi-
cation step. The cyclic voltammogram (-0.4 to 1.0 V vs.
Ag|AgCl) for each modification step leading up to the
synthesis of tin(IV) porphyrin triazole-modified FTO
surface 7, using ferricyanide as a redox probe, is shown
in Fig. 4. The activated FTO surface 4 (Fig. 5, thin gray
line) shows large reversible ferricyanide with oxidation
(Epa) and reduction peaks (Epc) at +0.441 V vs. Ag|AgCl
ExpERImENTAl
Chemicals and instruments
All chemicals were purchased from Sigma Aldrich
with the exception of propionic acid, potassium carbon-
ate, pyridine, anhydrous sodium sulfate (Ajax Finchem
Pty. Ltd.) and tin(II) chloride dihydrate (Merck). Solvents
were used as is from the manufacturers. Dichloromethane
and methanol were distilled before use or obtained from
Pure Solv dry solvent system (Innovative Technology
Inc. #PS-MD-7). Pyrrole was purchased from Merck
and freshly distilled or purified over aluminum oxide
1
before use. The H Nuclear Magnetic Resonance (1H
NMR) spectra were recorded on a Bruker Avance DPX
200 Bruker Avance DPX 300 or on an Avance III 400
MHz spectrometers at 300 K. Signals were reported in
ppm relative to tetramethylsilane (SiMe4, (1H) = 0). The
119Sn NMR spectra were obtained on a Bruker Avance III
400 MHz spectrometer as stated, quoted in ppm relative
to tetramethyltin (Sn(CH3)4, 119Sn = 0 ppm) as an external
standard. Infra-red (IR) spectroscopy was recorded on a
ThermoNicolet Avatar model 370 FT-IR spectrometer or
on a Shimadzu FTIR-8400S by solid state. UV-vis spec-
tra were recorded either on a Varian Cary 5E UV-vis-NIR
or a Varian Cary 50Bio UV-visible spectrophotometer.
Electrospray ionisation (ESI) mass spectra were recorded
on a ThermoQuest Finnigan LCQ-DECA electrospray
instrument equipped with a Xcaliber processing software
Fig. 5. Cyclic voltammograms for the bare activated FTO sur-
face 4, FTO with ferricyanide, the azide-modified FTO surface
6 and the tin(IV) porphyrin triazole-modified FTO surface 7.
These results were obtained using ferricyanide (1 mM) and
potassium chloride (200 mM) as supporting electrolyte in
phosphate buffer (100 mM, pH 7.0) with platinum counter and
Ag|AgCl reference electrodes at a scan rate of 0.1 mV/s
Copyright © 2011 World Scientific Publishing Company
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80
S. PraSaD et al.
or on a Waters Micromass ZQ 2000 ESCi equipped with
MassLynx version 4.1. Matrix assisted laser desorption
ionisation (MALDI) was performed on a Applied Bio-
systems Voyager DE STR MALDI (reflectron mode)
with the matrix trans-2-[3-(4-tert-butylphenyl)-2-methyl-
2-propenylidene]-malononitrile. High resolution ESI
(HR-MS) mass spectrometry was performed on a Thermo
Linear Quadropole Ion Trap Fourier Transform Ion
Cyclotron Resonance (LQT FT Ultra) mass spectrometer
in electrospray mode with a 7 T superconducting magnet
at the BMSF, Analytical Centre at the University of New
South Wales. Melting points were recorded using a Mel-
Temp II melting point apparatus and are uncorrected.
standard. Cyclic Voltammetry was performed on either
a Electrochemical Analyzer BAS100B (BASi) utilizing
BAS100W software or on aAutolab Potentiostat PGSTAT
12 equipped with GPES version 4.9. Surface modi-
fied electrodes were analyzed in a solution of 100 mM
phosphate buffer (pH 7.0) with 200 mM potassium chlo-
ride and 1 mM ferrocyanide with Ag|AgCl reference and
platinum counter electrodes. Each sample was deoxygen-
ated by bubbling dry nitrogen for 5 min prior to elec-
trochemical analysis. X-ray Crystallography work in this
research was undertaken on the macromolecular crystal-
lography beamline at the Australian Synchrotron, Victo-
ria, Australia. Surface analysis by X-ray photoelectron
spectroscopy (XPS) was performed on a VG ESCALAB
220-IXL imaging XPS microscope with an Al Ka X-ray
(1486.6 eV) anode source. Surface UV-vis absorption
measurements were made using a Cary 5 UV-vis-NIR fit-
ted with a diffuse reflectance apparatus. The 5,10,15,20-
tetrakis[(4-trimethylsilyl)ethynyl-phenyl]porphyrin1was
synthesized according to literature procedure [25]. UV-
vis (CH2Cl2): λmax, nm (log ε) 422 (5.65), 516 (4.38),
as fine purple crystals (347 mg, 97%), mp > 300 °C. UV-
vis (CH2Cl2): λmax, nm (log ε) 431 (5.74), 562 (4.29), 603
(4.27). 1H NMR (300 MHz, CDCl3, Me4Si): δH, ppm 0.39
(36H, s, Si(CH3)3), 7.93 and 8.25 (16H, ABq, J = 8.2 Hz,
Ph), 9.19 (8H, s, satellites, 4J1H-Sn = 14.8 Hz, pyrrole-H).
119Sn NMR (149 MHz, CDCl3, Me4Sn): δSn, ppm -590.08
(Sn). FTIR (KBr): ν, cm-1 2956 (m), 2898 (w), 2157 (s),
1499 (m), 1249 (s), 1030 (s), 864 (s). MS (MALDI):
m/z 1116.26 (calcd. for [M - 2Cl]+ 1116.29). HR-MS
(FT-ESI): m/z 1147.3091 (calcd. for C65H63N4OSi4Sn:
[M - 2Cl + OCH3]+ 1147.2836), 1133.2935 (calcd. for
C64H61N4OSi4Sn: [M - 2Cl + OH]+ 1133.2958.
Dichloro[5,10,15,20-tetrakis(4-ethynylphenyl)
porphyrinato]tin(IV) (3). The dichloro[5,10,15,20-
tetrakis((4-trimethylsilyl)ethynylphenyl)porphyrinato]
tin(IV) porphyrin 2 (84.3 mg, 71.0 μmol) was dissolved
in dichloromethane (40 mL). To this was added a solution
of potassium carbonate (1.10 g, 7.97 mmol) in metha-
nol (10 mL) and the mixture was refluxed for 16 h in
the absence of light. After cooling, the solvents were
removed under reduced pressure and the crude solid was
redissolved in dichloromethane (200 mL). The solution
was washed with water (3 × 100 mL) and the organic
layer dried over anhydrous sodium sulfate. The final
product was recovered by filtration and solvent removed
under reduced pressure to give the dichloro[5,10,15,20-
tetrakis(4-ethynylphenyl)porphyrinato]tin(IV) porphy-
rin 3 as a purple crystalline solid (22.1 mg, 29%),
mp>300°C. UV-vis(CH2Cl2):λmax, nm(logε)430(5.84),
561(4.37),602(4.29).1HNMR(300MHz,CDCl3,Me4Si):
δH, ppm 3.37 (4H, s, C≡CH), 7.97 and 8.29 (ABq, 16H,
J = 8.2 Hz, Ph), 9.21 (8H, s, satellites, 4J1H-Sn = 14.8 Hz,
pyrrole-H). 119Sn NMR (149 MHz, CDCl3, Me4Sn): δSn,
ppm -588.77 (Sn). FTIR (KBr): ν, cm-1 3289 (m), 2107
(w), 1498 (m), 1234 (s), 1029 (s), 856 (s), 813 (s). MS
(MALDI): m/z 861.72 (calcd. for [M - 2Cl + 2OH]+
861.53), 828.15 (calcd. for [M - 2Cl]+ 828.13). HR-MS
(FT-ESI): m/z 859.1528 (calcd. for C53H31N4OSn
[M - 2Cl + OCH3]+ 859.1532).
1
551 (4.18), 589 (3.88), 645 (3.86). H NMR (200 MHz,
CDCl3, Me4Si): δH, ppm -2.83 (2H, s, pyrrole-NH), 0.38
(36H, s, Si(CH3)3), 7.79 and 8.16 (16H, ABq, J = 9.0 Hz,
Ph), 8.81 (8H, s, pyrrole-H). FTIR (KBr): ν, cm-1 3313
(w), 2956 (m), 2156 (s), 1497 (s), 1474 (s), 1249 (s), 966
(s), 869 (s). MS (ESI): m/z 1000.53 (calcd. for [M + H]+
999.55).
Activating FTO surface electrodes [38]. The FTO
slides were washed by sonicating in acetone for 5 min
followed by isopropanol for 5 min. The resulting slides
were treated with a solution of H2O2:H2O (30%) and
NH4OH:H2O (25%) at 80 °C for 20 min. The activated
transparent slides were again rinsed with water and dried
under nitrogen prior to use.
Dichloro[5,10,15,20-tetrakis((4-trimethylsilyl)
ethynylphenyl)porphyrinato] tin(IV) (2). The 5,10,
15,20-tetrakis[(4-trimethylsilyl)ethynylphenyl]porphy-
rin 1 (300 mg, 300 μmol) was dissolved in pyridine
(100 mL) and heated to reflux. Tin(II) chloride dihy-
drate (270 mg, 1.20 mmol) was added and the solution
was allowed to reflux in air for 12 h in the absence of
light. After cooling, dichloromethane was evaporated and
water (150 mL) was added. The aqueous layer was then
extracted with dichloromethane (3 × 100 mL). The com-
bined organic extracts were then washed with water (3 ×
100mL)andaqueoushydrochloricacid(1M,2×100mL).
The organic layers were combined, dried over anhydrous
sodium sulfate and filtered. The dichloro[5,10,15,20-
tetrakis((4-trimethylsilyl)ethynylphenyl)porphyrinato]-
tin(IV) porphyrin 2 was collected under reduced pressure
(3-azidopropyl)triethoxysilane (5) [31, 39]. To a
pre-heated solution (60°C) of sodium azide (1.01g,
15.5 mmol) in dimethyl sulfoxide was added (3-chlo-
ropropyl)triethoxysilane (2.00g, 8.33mmol) and stirred
overnight. After cooling, water (100 mL) was added and
the aqueous phase was extracted with diethyl ether (3 ×
100 mL), dried over anhydrous sodium sulfate and fil-
tered. The (3-azidopropyl)triethoxysilane 5 was retrieved
under reduced pressure as a clear yellow oil (1.96 g,
1
95%). H NMR (CDCl3, 200 MHz): δ, ppm 3.86–3.79
(m 2H, CH3CH2Si), 3.26 (t, 2H, N3CH2CH2, J = 7.1 Hz),
Copyright © 2011 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2011; 15: 80–82

TIn(IV) POrPhyrIn funCTIOnalIzaTIOn Of eleCTrOChemICally aCTIVe fluOrIDe-DOPeD TIn-OxIDe (fTO)
81
1.74–1.68 (m, 2H, -CH2CH2CH2), 1.23 (t, 3H, CH3CH2Si,
J = 7.1 Hz), 0.71–0.65 (m, 2H, SiCH2CH2). These
results were in good agreement with those found in
literature [31].
P-1, a = 12.185(2) Å, b = 12.512(3) Å, c = 18.173(4) Å,
a = 71.95(3)º, β = 70.69(3)º, γ = 80.68(3)º. Z = 2,
ρ
calcd = 1.260 Mg/m3. μ = 0.661 mm-1. F(000) = 954.0. A
total of 30,826 reflections were measured, 10,223 unique.
The structure was refined on F2 to 0.1143, with R(F)
equal to 0.2723 and a goodness of fit, S = 1.902.
(3-azidopropyl)triethoxysilane-modified FTO (6).
To a pre-washed activated fluorine-doped tin oxide sur-
face (ethanol then water, sonicated twice, each for 5 min)
was added a solution of (3-azidopropyl)triethoxysilane
3 (98 mg, 396 μmol) in toluene (10 mL). The mixture
was left to stand for 1.5 h and washed with toluene, then
sonicated twice (5 min each) with toluene, ethanol and
water. The resulting (3-azidopropyl)triethoxysilane-mod-
ified FTO surface 6 was then dried under nitrogen. XPS
(orbital) eV: Si2p (102.29, OSiC), C1s (285.01 C-C) C1s
(286.61, C-N), C1s(288.01, C-Hx), N1s(400.73, N=N-N),
N1s (404.74, N=N-N), O1s (531.01, O-C), O1s (532.14,
O-Si), O1s (533.24, O-H). The XPS spectral data were in
good agreement with those reported in literature [32].
Dichloro[5,10,15,20-tetrakis(4-(ethynylphenyl))
porphyrinato]tin(IV) porphyrin-modified FTO (7).
The (3-azidopropyl)triethoxysilane-modified FTO sur-
face 6 was pre-washed in toluene, water, ethanol and
acetone, then nitrogen dried prior to use. The FTO sur-
face 6 was then sonicated in dry N,N-dimethylforma-
mide. Separately, ascorbic acid (105 mg, 0.60 mmol) and
copper(II) sulfate (100 mg, 626 μmol) were pre-dissolved
in dry N,N-dimethylformamide (20 mL) and allowed to
stir with 3 (35.9 mg, 41.6 μmol) for 15 min. The FTO
surface 6 was then added and the deep purple mixture
was allowed to stand overnight at room temperature in
the absence of light. The surface was then washed with
N,N-dimethylformamide, water, ethanol and acetone
(sonicated, each for 5 min) and nitrogen dried to afford
the tin(IV) porphyrin-modified FTO surface 7. UV-vis
surface reflectance spectroscopy: 432 nm; XPS (orbital)
eV: C1s (285.06 C-C) C1s (286.55, C-N), C1s (288.23,
C-Hx), N1s (400.38, N-C), Sn3d5 (487.20, Sn-O), O1s
(531.22, O-C), O1s (532.34, O-Si), O1s (533.47, O-H).
CONClUSION
We were successful in the preparation and character-
ization of a novel alkyne-terminated tin(IV) porphyrin 3,
including obtain a crystal structure for 3. We also described
the successful synthesis of tin(IV) porphyrin modified FTO
transparent electrode 7. The tetra-alkyne terminated tin(IV)
porphyrin 3 was attached to a transparent FTO electrode
using Huisgen [3+2] click chemistry to link the porphy-
rin to the electrode via a 1,2,3-triazole structure. Electro-
chemical measurements of surface 7 using a ferricyanide
probe show oxidation and reduction peaks at -0.144 and
+0.568 V vs. Ag|AgCl, respectively. Following the suc-
cessful attachment of tin(IV) porphyrin to the FTO sur-
faces described here, future studies will focus on the use of
these electrodes in the photocatalytic generation of hydro-
gen which has been demonstrated by Shelnutt and cowork-
ers using tin(IV) porphyrin–platinum nanoaggregates [22,
35]. We are also currently exploring the use of these FTO
surfaces for the regeneration of the oxidatively active bio-
logical markers such as the coenzyme NAD+ and FAD but
the reductive power of photoexcited tin(IV) porphyrins is
well-placed to reduce these coenzymes [34].
Acknowledgements
We thank the Australian Research Council for a dis-
covery grant and an Australian Research Fellowship
(DP0666325) to Pall Thordarson and the University of
Sydney for a PhD scholarship to Shiva Prasad. We thank
Dr. Tom Caradoc-Davies (Australian Synchrotron) for
assistance. We would also like to thank Dr. Bill Bin Gong
for XPS analysis and Prof. J.J. Gooding for access and
assistance with electrochemical equipment.
x-ray structure determination
The X-ray diffraction measurement for 3 were car-
ried out at the Australian Synchrotron Facility using
graphite-monochromated synchrotron X-ray radiation
(λ = 0.65253 Å) at 120(2) K. The crystal, mounted on the
goniometer using cryo loops for intensity measurements,
was coated with paraffin oil and then quickly transferred
to the cold stream using Oxford Cryo stream attachment.
Symmetry related absorption corrections using the pro-
gram XDS were applied and the data were corrected for
Lorentz and polarization effects using the XDS software
[36]. All structures were solved by Direct methods and
the full-matrix least-squares refinements were carried out
using SHELXL [37].
Supporting information
Crystallographic data for compound 3 have been
deposited at the Cambridge Crystallographic Data Center
(CCDC) under deposition number CCDC 759436. Cop-
ies can be obtained on request, free of charge, via www.
ccdc.cam.ac.uk/conts/retrieving.html or from the Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK (fax: +44 1223-336-033 or
email: deposit@ccdc.cam.ac.uk).
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J. Porphyrins Phthalocyanines 2011; 15: 82–82