[60]Fullerene-porphyrin-ferrocene triad self-assembled monolayers (SAMs) for photovoltaic applications

Article abstract of DOI:10.1016/j.jorganchem.2014.02.022

A new triad array, C₆₀-triosmium cluster-zinc porphyrin-ferrocene complex 1, Os₃C₆₀ZnPFc, was prepared by the decarbonylation of Os₃(CO)₉(μ₃- η²:η²:η²-C₆₀) (9) and subsequent reaction with an isocyanide ligand containing porphyrin and ferrocene. This novel triad array exhibits well-defined and stable electrochemical properties in solution due to a robust bonding mode between the C₆₀ and the triosmium cluster. Compound 2, Os₃C ₆₀SiZnPFc was prepared in a manner similar to that of compound 1 from Os₃(CO)₈(CN(CH₂)₃Si(OEt) ₃)(μ₃-η²:η²: η²-C₆₀) (10) and an isocyanide ligand containing porphyrin and ferrocene. The SAM of triad 2 (2/ITO) was fabricated by immersion of an ITO electrode into a chlorobenzene solution of 2 and diazabicyclooctane (2:1 equiv.), and characterized by UV-Vis absorption spectroscopy and cyclic voltammetry. The triad SAM exhibited ideal, well-defined electrochemical responses and high stability due to the stable C₆₀ π-delocalized system via a linkage with the metal cluster center as well as a robust bonding mode. The photoelectrochemical properties of the 2/ITO triad were investigated by a standard three-electrode system in the presence of an ascorbic acid sacrificial electron donor. Reproducible photocurrent was generated by excitation of the porphyrin moiety in the triad SAM with visible light.

Full text of DOI:10.1016/j.jorganchem.2014.02.022

Journal of Organometallic Chemistry 761 (2014) 20e27
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
[60]Fullereneeporphyrineferrocene triad self-assembled monolayers
(SAMs) for photovoltaic applications
,
Min Hyung Lee a, Jung Won Kim b, Chang Yeon Lee c
*
a Department of Applied Chemistry, Kyung Hee University, Yongin, Gyeonggi 446ꢀ701, Republic of Korea
b Department of Chemical Engineering, Kangwon National University, 346 Joongang-ro, Samcheok, Gangwon-do 245-711, Republic of Korea
c Department of Energy and Chemical Engineering, Incheon National University, Incheon 406-772, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
A new triad array, C60etriosmium cluster-zinc porphyrineferrocene complex 1, Os3C60ZnPFc, was pre-
pared by the decarbonylation of Os3(CO)9(m3- : :h
h2 h2 2-C60) (9) and subsequent reaction with an iso-
Received 9 January 2014
Received in revised form
20 February 2014
cyanide ligand containing porphyrin and ferrocene. This novel triad array exhibits well-defined and
stable electrochemical properties in solution due to a robust bonding mode between the C60 and the
triosmium cluster. Compound 2, Os3C60SiZnPFc was prepared in a manner similar to that of compound 1
Accepted 26 February 2014
from Os3(CO)8(CN(CH2)3Si(OEt)3)(m3- : :h
h2 h2 2-C60) (10) and an isocyanide ligand containing porphyrin
Keywords:
and ferrocene. The SAM of triad 2 (2/ITO) was fabricated by immersion of an ITO electrode into a
chlorobenzene solution of 2 and diazabicyclooctane (2:1 equiv.), and characterized by UVeVis absorption
spectroscopy and cyclic voltammetry. The triad SAM exhibited ideal, well-defined electrochemical re-
sponses and high stability due to the stable C60 p-delocalized system via a linkage with the metal cluster
center as well as a robust bonding mode. The photoelectrochemical properties of the 2/ITO triad were
investigated by a standard three-electrode system in the presence of an ascorbic acid sacrificial electron
donor. Reproducible photocurrent was generated by excitation of the porphyrin moiety in the triad SAM
with visible light.
Fullerene
Metal-cluster
Photovoltaic device
Self-assembled monolayer (SAMs)
Ó 2014 Elsevier B.V. All rights reserved.
Introduction
a covalently linked fullereneeporphyrineferrocene triad system
was prepared explosively to obtain a long-lived charge separation
Photoinduced electron transfer (PET) between nanocarbon ar-
chitecture and photosensitizers has received considerable attention
due to its potential applications for optoelectronics, photonics,
sensors, and other functional nanoscale molecular devices [1e3].
The chemically functionalized fullerene systems for PET processes
often combine with electron donors, such as porphyrin [4e7],
ferrocene [8e10], thiophene [11], and carbon nanotubes [12], and
additional light harvesting antenna molecules. In these systems,
fullerene acts as an efficient electron acceptor because of its
intriguing characteristics that allow for the acceleration of photo-
induced charge separation and a charge recombination decelera-
tion in the electron transfer process [13]. Numerous molecular
donoreacceptor arrays containing accessory pigments, from dyads
to hexads, have been synthesized to address the detailed kinetics of
energy and electron transfer; in a few cases, these have been suc-
cessfully applied to solar energy conversion [14e18]. Among them,
state. A lifetime extension can be achieved by the addition of a
secondary intermolecular electron transfer to a porphyrin cation
radical on the ferrocene, which acts as an additional electron donor
in this system. Imahori and coworkers reported long-lived charge
separated states of 10
ms in triad systems containing ferrocene,
porphyrin, and fullerene [19].
For the purpose of demonstrating a photovoltaic device, mo-
lecular donoreacceptor arrays should be immobilized on the
various electrodes. Recent progress in covalent fullerene function-
alization has led to the advance of electrode-immobilized fullerene
and nanocarbon architectures on various surfaces. Numerous
electrode-immobilized systems, including porphyrinefullerene,
ferroceneeporphyrinefullerene
triad,
ferroceneeporphyrine
fullereneeboron dipyrrin tetrad, and organometallic fullerene on
gold and indium-tin oxide (ITO) surfaces, have been studied with
respect to solar energy conversion [20e26]. However, direct cova-
lent functionalization disturbs the fullerene
p-conjugation system
by the formation of an -bond; therefore, the prepared fullerene
s
SAMs show poorly defined electrochemical properties and insta-
bility in reduced states, which causes severe limitations for
* Corresponding author.
E-mail address: cylee@incheon.ac.kr (C.Y. Lee).
http://dx.doi.org/10.1016/j.jorganchem.2014.02.022
0022-328X/Ó 2014 Elsevier B.V. All rights reserved.

M.H. Lee et al. / Journal of Organometallic Chemistry 761 (2014) 20e27
21
technological applications. To address this issue, our group utilized
60-metal cluster complexes with a face-capping m3
h2 h2 2-C60
bonding mode for the immobilization of donoreacceptor arrays on
an indium tin oxide (ITO) surface [27,28]. The m3
h2 h2 2-C60
MeCN followed by treatment with 8 in chlorobenzene at 55 ꢁC
C
-
:
:
h
afforded Os3(CO)7(CNR)(CNR0)(m3
(OEt)3, R0 ¼ ZnPFc) in 50% yield.
-
h2
:
h2
:h
2-C60) (2; R ¼ (CH2)3Si
-
:
:h
Both Compounds 1 and 2 were formulated by molecular ion
isotope multiplets (m/z (highest peak): 2613 (1); 2814 (2)) in the
MADI-TOF mass spectrum. The IR spectrum of 1 shows a similar
bonding mode stabilizes the C60 hybridization such that the intact
electrochemical properties of fullerene can be directly transferred
to the electrode surface via a linkage to the metal cluster [27].
With our continued interest in photovoltaic devices containing a
fullereneeporphyrineferrocene triad system, herein we report the
preparation of two novel C60eporphyrineferrocene triad struc-
pattern to that of Os3(CO)8(CNCH2Ph)(m3- : :h
h2 h2 2-C60) [29], sug-
gesting that the isocyanide ligand in 1 is terminally coordinated at
an equatorial site of the Os center. The IR spectrum of 2 exhibits two
NC stretches (RNC: 2188 cmꢀ1; R0NC: 2146 cmꢀ1) and an essentially
tures, Os3(CO)8(CNR0)(m3
(CO)7(CNR)(CNR0)(m3 h2 h2
-
h2
:
h2
:
h
2-C60) (1, Os3C60ZnPFc) and Os3
identical CO stretching pattern to that of Os3(CO)7(CNCH2Ph)2(m3
h2 h2 2-C60) [29], implying that the two isocyanide ligands in 2
occupy equatorial positions on adjacent osmium atoms. The CO
-
-
:
:h
2-C60) (2, Os3C60SiZnPFc) R ¼ (CH2)3
:
:h
Si(OEt)3, R0 ¼ ZnPFc (Scheme 2). The triosmium cluster moiety in
compound 1 links a C60 and a porphyrineferrocene unit without
stretching bands appear in the typical range of 2080e1950 cmꢀ1
,
disturbance of the fullerene
p-conjugation system and 3-(trie-
and shift to the low energy region by w20 cmꢀ1 as the two iso-
cyanide ligands are coordinated, reflecting the stronger electron-
donor effect of the isocyanide ligand relative to the carbonyl
ligand (Fig. 1).
thoxysilyl)propyl isocyanide was acts as a surface anchoring ligand
in compound 2, which is also linked to C60 through a triosmium
cluster moiety. The triad system forms ideal self-assembled
monolayers (SAMs) on the ITO in the presence of dia-
zabicyclooctane (DABCO), which exhibits well-defined electro-
chemical responses and reproducible photoelectrochemical
properties.
Fig. 2 shows absorption and fluorescence spectra of various
chromophores in dichloromethane. Compound 8 exhibits charac-
teristic porphyrin absorption peaks with a strong soret band at
426 nm and moderate Q bands at 552 and 593 nm. These absorp-
tion bands are preserved in compound 1 and additional charac-
teristic broad bands from absorption of the C60 moiety appeared
between 325 nm and 375 nm. Since there was no significant ab-
sorption of ferrocene in the visible region, the porphyrin moiety
acts as the primary chromophore for harvesting solar energy in the
triad system. The fluorescence spectra of 1 and 8 are provided in
Fig. 2b. Porphyrin excitation of 8 at 426 nm in CH2Cl2 resulted in
typical porphyrin fluorescence with emission maxima at 609 nm
and 650 nm. When the porphyrin chromophore of 1 was excited in
CH2Cl2, 93% of the porphyrin fluorescence from 1 was quenched by
the additional attached fullerene, as compared with 8. Considering
that there was no noticeable fullerene emission in the range of
600e700 nm, this result clearly shows that an efficient electron
transfer occurred from ZnP to C60 in 1.
Results and discussion
Synthesis and characterization of 1e8
The synthetic methods for isocyanide ligand (8, ZnPFc) con-
taining porphyrin and ferrocene are summarized in Scheme 1 and
the synthetic routes for triad compounds 1 and 2 are depicted in
Scheme 2. The synthetic intermediate 4 was prepared in 50% yield
from a dipyrromethane 3 condensation with benzaldehyde in the
presence of trifluoroacetic acid, followed by a reduction of the nitro
group. Compound 5 was synthesized by esterification of 4 with
trifluoroacetic anhydride. Hydrolysis of one of the ester groups of 5
under basic conditions, followed by reductive amination with for-
mylphenyl ferrocene and deprotection of the remaining ester
group, afforded compound 7. Isocyanide functionalized Zne
porphyrineferrocene ligand (8, ZnPFc) was prepared by a reductive
amination reaction of 4-isocyano benzaldehyde with 7 followed by
Electrochemical properties of 8, 1, and 2
Solution electrochemical properties of 8,1, and 2 were measured
using cyclic voltammetry in chlorobenzene solution with tetrabu-
tylammonium perchlorate as the supporting electrolyte. Cyclic
voltammograms (CVs) are depicted in Fig. 3 and the corresponding
half-wave potentials (E1/2) are listed in Table 1. Compound 8
exhibited two reversible one-electron redox waves in the reduction
metalation with Zn(OAc)2. Decarbonylation of Os3(CO)9(m3
-
h2 h2 2-C60) (9) with Me3NO/MeCN and subsequent reaction with
:
:h
8 in chlorobenzene at 60 ꢁC afforded Os3(CO)8(CNR0)(m3 h2 h2 h2
- : : -
C
60) (1; R0 ¼ ZnPFc) in 40% yield. As an alternative, decarbonylation
of Os3(CO)8(CN(CH2)3Si(OEt)3)(m3- : :h
h2 h2 2-C60) (10) with Me3NO/
Scheme 1. Synthesis of 8.

22
M.H. Lee et al. / Journal of Organometallic Chemistry 761 (2014) 20e27
Scheme 2. Synthesis of 1 and 2.
Fig. 1. IR spectra (carbonyl and NC stretching region) of 10, 1, and 2.
region, which were obviously attributed to redox reactions at the
zinc porphyrin center. The CV of 10 revealed four reversible one-
electron redox waves, with the third and fourth waves over-
lapping. These overlapping waves have been similarly observed in
redox potentials of the porphyrin center, reflecting the electron-
donor nature of the isocyanide ligand. The CVs of 1 and 2 in the
oxidation region exhibited three reversible one-electron oxidation
waves (see Supplementary data). The first one-electron oxidation
was assigned to the oxidation of ferrocene, whereas the second and
third oxidations were assigned to a stepwise abstraction of two
electrons from the porphyrin center.
various known complexes including Os3(CO)8(PMe3)(m3- : : -
h2 h2 h2
C
60) and Os3(CO)9-n(CNCH2Ph)n(m3
-
h2
:
h2
:h
2-C60) (n ¼ 2, 3, and 4)
[29], due to C60 reductions combined with electronic communica-
tion between C60 and the metal cluster centers. As expected, the
general feature of the CV of 1 was the sum of those of 8 and 10. The
1 CV showed seven redox waves that consisted of five reversible
redox waves corresponding to redox reactions at the C60 center and
two reversible redox waves corresponding to the porphyrin center.
Although the CV of 2 was similar to that of 1, the C60 center redox
potential in 2 was shifted in the negative direction with preserved
Formation and photovoltaic properties of 2/ITO SAM
The SAM of 2 (2/ITO) was prepared by the immersion of an ITO
electrode into a chlorobenzene solution of 2 and DABCO (2:1 equiv.)
at 100 ꢁC for 7 h, followed by washing with chlorobenzene and
dichloromethane (Scheme 3). The presence of DABCO in the SAM

M.H. Lee et al. / Journal of Organometallic Chemistry 761 (2014) 20e27
23
Fig. 2. a) UVeVis spectra of 1, 8, and 9 in CH2Cl2. b) Fluorescence spectra of 1 and 8 in
CH2Cl2 with excitation at 426 nm.
Fig. 3. Cyclic voltammograms of 8, 10, 1, and 2 in dry, deoxygenated chlorobenzene
(0.1 M [(n-Bu)4N][ClO4]) at a scan rate of 10 mV/s.
formation resulted in a well-ordered structural confinement due to
the strong interaction between ZnP and the bifunctional DABCO
base, which may lead to high surface coverage as shown in previ-
ously reported studies [17,28]. The absorption spectrum of 2/ITO
(Fig. 5) showed a characteristic soret (438 nm) band, which was
broader and red-shifted by w12 nm compared with that of 2 in
solution due to stacking of the porphyrin moieties on the surface.
The CV of 2/ITO (Fig. 4) in deoxygenated dichloromethane exhibited
three well resolved and electrochemically stable redox waves
at ꢀ1.21, ꢀ1.52, and ꢀ2.02 V (E1/2) with a relative area of 1:1:3.2.
Importantly, the overall features of the 2/ITO CV were similar to
that of 2 in solution. The first and second waves were successive,
one-electron reductions of 2 localized on C60. The third wave cor-
responded to an overlapping pattern of two-electron reductions of
the C60etriosmium cluster moiety and one electron reduction of
the porphyrin moiety. Three successive waves due to the oxidation
of ferrocene and the porphyrin moiety were also observed at 0, 0.19,
and 0.38 V (E1/2) for 2/ITO (see Supplementarydata). The monolayer
Photocurrent measurement was carried out for 2/ITO in a 0.1 M
Na2SO4 solution containing 50 mM ascorbic acid (AsA) as an elec-
tron sacrificer by the three electrode system of the modified ITO
substrate as a working electrode, a Pt counter electrode, and a Ag/
AgCl (3 M NaCl) reference electrode, denoted as ‘ITO/2/AsA/Pt’. The
solution was controlled at pH 3.5. A stable anodic photocurrent was
observed immediately upon irradiation of the ITO electrode with
l
¼ 435 nm light (0.96 mW cmꢀ2) at an applied potential of 100 mV
and the response was reversibly repeated, as shown in Fig. 6. The
ITO/2/AsA/Pt cell action spectrum (solid blue line with circles in
Fig. 5) matched well with the absorption spectrum of 2/ITO in the
380e700 nm region, indicating that the porphyrin unit acted as a
real photoactive center for photocurrent generation. The quantum
yield was estimated to be 11% for 2/ITO, based on the amount of
photons absorbed by the chromophores.
Concluding remarks
surface
coverage
(
G
)
of
2/ITO
was
estimated
as
1.8 ꢂ 10ꢀ10 mol cmꢀ2 from the integrated charge of the first
reduction peak at ꢀ1.21 V, which was comparable to
w1.9 ꢂ 10ꢀ10 mol cmꢀ2 for a closed packed monolayer of C60. The
ideal, well-defined electrochemical responses in 2/ITO may be
We prepared a new triad system containing C60, porphyrin, and
ferrocene using a triosmium cluster as a linker. The triad array
exhibited well-defined and stable electrochemical properties in
solution due to robust bonding between C60 and the triosmium
cluster. We also successfully constructed a highly ordered, nearly
fully covered [60]fullerene triosmium cluster-zinc porphyrine
ferrocene triad SAM on the ITO surface with the aid of DABCO. The
triad SAM exhibited ideal, well-defined electrochemical responses
ascribed to the fact that
by the -type coordination of C60 on the metal cluster and the C60
moiety remained intact during SAM formation by confining the
60emetal cluster complex to the electrode surface via a linkage to
the metal center.
p-delocalization of C60 was not perturbed
p
C
and high stability due to the stability of the C60
p-delocalized

24
M.H. Lee et al. / Journal of Organometallic Chemistry 761 (2014) 20e27
Table 1
Half-wave potential (E1/2 vs. Eo (Fc/Fcþ)) in C60, 8, 1, 2, and 2/ITO CVs.
ZnPþ/2þ
ZnP0/þ
Fc0/þ
C
C
C
C
ZnP0/ꢀ
ZnPꢀ/2ꢀ
C
Solvent
0/ꢀ
ꢀ/2ꢀ
2ꢀ/3ꢀ
3ꢀ4ꢀ
4ꢀ/5ꢀ
5ꢀ/6ꢀ
C
60
Compound
60
60
60
60
60
C60
8
1
ꢀ1.06
ꢀ1.43
ꢀ1.91
ꢀ2.38
CB
CB
CB
CB
ꢀ1.96
ꢀ1.94
ꢀ1.94
ꢀ2.29
ꢀ2.32
ꢀ2.32
0.29
0.29
0.12
0.14
0
0
ꢀ1.03
ꢀ1.10
ꢀ1.37
ꢀ1.45
ꢀ1.73
ꢀ1.84
ꢀ2.44
ꢀ2.53
ꢀ2.73
2
SAM
ZnPþ/2þ
ZnP0/þ
Fc0/þ
C
C
C
C
ZnP0/ꢀ
ZnPꢀ/2ꢀ
C
Solvent
0/ꢀ
ꢀ/2ꢀ
2ꢀ/3ꢀ
3ꢀ4ꢀ
4ꢀ/5ꢀ
5ꢀ/6ꢀ
C
60
60
60
60
60
60
2/ITO
0.38
0.19
0
ꢀ1.21
ꢀ1.52
ꢀ2.02
DM
2/ITO
Scheme 3. Preparation of 2/ITO.
system via a linkage to the metal cluster center as well as a robust
bonding mode between C60 and the metal cluster. The photovoltaic
cell based on the triad SAMs revealed a reproducible and stable
photocurrent when it was irradiated by visible light. The present
successful application of C60emetal cluster complexes in photo
electrochemical cells promises other useful technological applica-
tions of C60emetal cluster based SAMs for molecular electronic
device fabrication. Efforts are currently underway using these triad
and triad-based SAMs to investigate the detailed kinetics involved
in electron transfer in solution and on electrodes.
Fig. 5. Absorption spectrum of 2/ITO (solid red line) and action spectrum of ITO/2/AsA/
Pt (solid blue line with circles) with 0.7 mW cmꢀ2 light; applied potential, 100 mV vs.
Ag/AgCl (3 M NaCl). (For interpretation of the references to color in this figure legend,
the reader is referred to the web version of this article.)
Fig. 4. Cyclic voltammograms of 2 (dashed line) and 2/ITO (solid line) containing 0.1 M
Bu4NPF6 as an electrolyte (scan rate ¼ 0.5 V sꢀ1).

M.H. Lee et al. / Journal of Organometallic Chemistry 761 (2014) 20e27
25
Synthesis of 5
A portion of 4 (200 mg, 0.283 mol), triethylamine (0.1 mL,
0.849 mmol), and trifluoroacetic anhydride (178 mg, 0.849 mmol)
were stirred in chloroform (20 mL) at room temperature for 20 min.
TLC analysis indicated total consumption of the starting material.
The reaction mixture was quenched with water and extracted with
chloroform, and extracts were dried (Na2SO4). The solvent was
removed by evaporation at reduced pressure and the crude product
was purified by flash column chromatography on silica gel with
hexaneeethyl acetate (2:1) as the eluent to give 213 mg (90%) of the
desired compound. 1H NMR (400 MHz, CDCl3)
d
ꢀ2.74 (br s, 2H),
7.76 (m, 6H), 7.97 (d, J ¼ 8.3 Hz, 4H), 8.18 (d, J ¼ 6.2 Hz, 4H), 8.24 (d,
J ¼ 8.3 Hz, 4H), 8.29 (s, 2H), 8.80 (d, J ¼ 4.8 Hz, 4H), 8.85 (d,
J ¼ 4.8 Hz, 4H). MS (FABþ) m/z 837 [M þ H]þ.
Fig. 6. Photocurrent response of ITO/2/AsA/Pt irradiated with 435 nm light
(0.96 mW cmꢀ2); applied potential, 100 mV vs. Ag/AgCl (3 M NaCl).
Synthesis of 7
Compound 5 (320 mg, 0.382 mmol) was dissolved in a mixture
of 35 mL methanol, 20 mL THF, and 2 mL of aqueous 10% KOH. The
reaction mixture was stirred at 75 ꢁC for 90 min, after which it was
poured into a separatory funnel containing water (50 mL). The
aqueous phase was extracted with chloroform and extracts were
dried (Na2SO4). The solvent was removed by evaporation at
reduced pressure and the crude product was purified by flash
column chromatography on silica gel with hexaneeethyl acetate
(1:1) as the eluent to give 141 mg (50%) of the desired compound 6.
Five drops of acetic acid (96%) were added to an ethanol solution
(40 mL) of 6 (170 mg, 0.229 mmol), 4-formylphenylferrocene
(73.0 mg, 0.252 mmol), and anhydrous Na2SO4 at room tempera-
ture and then the reaction mixture was stirred at reflux for 2 h.
After evaporation of the solvent in vacuo, the residue was redis-
solved in THF/MeOH (1/1, 40 mL). To the resulting solution, a 1.0 M
THF solution (0.688 mL) of NaBH3CN was added at 0 ꢁC for 15 min.
The solvent was evaporated and the residue was purified by column
chromatography (silica gel, hexane/ethyl acetate ¼ 2:1) to afford a
deep violet solid. The obtained violet solid (150 mg, 0.148 mmol)
was dissolved in a mixture of 20 mL methanol, 10 mL THF, and 2 mL
of aqueous 10% KOH. The reaction mixture was stirred at 75 ꢁC for
90 min, after which it was poured into a separatory funnel con-
taining water (20 mL). The aqueous phase was extracted with
chloroform and extracts were dried (Na2SO4). The solvent was
removed by evaporation at reduced pressure and the crude product
was purified by flash column chromatography on silica gel with
hexaneeethyl acetate (2:1) as the eluent to give 120 mg (90%) of 7.
Experimental section
General comments
All reactions were carried out under a nitrogen atmosphere with
the use of standard Schlenk techniques. Solvents were dried over
appropriate drying agents and distilled immediately before use. C60
(99.5%, Southern Chemical Group, LLC.) was used without further
purification. Anhydrous trimethylamine N-oxide (m.p. 255e230 ꢁC)
was obtained from Me3NO$2H2O (98%, Aldrich) by sublimation
(three times) at 90e100 ꢁC under vacuum. Dipyrromethane 3 [30]
and Os3(CO)8(CN(CH2)3Si(OEt)3)(m3- : :h
h2 h2 2-C60) [27] were pre-
pared according to published methods. Infrared spectra were ob-
tained on a Bruker EQUINOX-55 FT-IR spectrophotometer. 1H
(400 MHz) NMR spectra were recorded on a Bruker AVANCE-400
spectrometer. Positive ion FAB mass spectra (FABþ) and MALDI-
TOF were obtained at the Korea Basic Science Institute.
Synthesis of 1e8
Synthesis of 4
A solution of dipyrromethane 3 (2 g, 7.48 mmol) and benzal-
dehyde (0.794 g, 7.48 mmol) in chloroform (750 mL) was degassed
by bubbling with nitrogen for 1 h. The reaction vessel was shielded
from ambient light. Trifluoroacetic acid (1.04 mL, 7.48 mmol) was
then added to one portion. The solution was stirred for 2 h at room
temperature under a nitrogen atmosphere. To the reddish black
reaction mixture, p-chloranil (2.76 g, 11.2 mmol) was added with
overnight stirring. Triethylamine was added and then the reaction
mixture was concentrated. Flash column chromatography on silica
gel (CH2Cl2) yielded the desired porphyrin from the mixture as the
third major band. Reprecipitation with chloroformemethanol
afforded a vivid reddish purple solid. SnCl2 (1.5 g, 7.9 mmol) was
added to a suspension of the above crude product (550 mg,
0.780 mmol) in concentrated HCl solution (116 mL). The reaction
mixture was stirred for 45 min at room temperature and main-
tained at 95e100 ꢁC for an additional 30 min. After cooling, the
reaction was quenched by the slow addition of 25% ammonia. The
organic layer was extracted with CHCl3 and washed with water.
After standing over anhydrous Na2SO4, the organic extract was
concentrated to dryness. Flash column chromatography on silica
gel with CH2Cl2eethyl acetate (30:1) as the eluent and subsequent
reprecipitation from CHCl3eCH3OH gave 4 as a deep violet solid
1H NMR (400 MHz, THF-d8)
d
ꢀ2.59 (s, 2H), 4.01 (s, 5H), 4.29 (t,
J ¼ 1.7 Hz, 2H), 4.49 (d, J ¼ 5.5 Hz, 2H), 4.69 (t, J ¼ 1.7 Hz, 2H) 4.94 (s,
2H) 5.82 (t, J ¼ 5.5 Hz,1H), 6.98 (d, J ¼ 8.3 Hz, 2H), 7.04 (d, J ¼ 8.3 Hz,
2H), 7.45 (d, J ¼ 8.1 Hz, 2H), 7.55 (d, J ¼ 8.1 Hz, 2H), 7.75 (m, 6H), 7.88
(d, J ¼ 8.3 Hz, 2H), 7.95 (d, J ¼ 8.3 Hz, 2H), 8.21 (m, 4H), 8.77 (d,
J ¼ 4.5 Hz, 4H), 8.94 (d, J ¼ 4.5 Hz, 4H). MS (FABþ) m/z 798 [M þ H]þ.
Synthesis of 8
Five drops of acetic acid (96%) were added to a THF solution
(40 mL) of 7 (220 mg, 0.239 mmol), 4-isocyano benzaldehyde
(38.0 mg, 0.362 mmol), and anhydrous Na2SO4 at room tempera-
ture, and then the reaction mixture was stirred at reflux for 2 h.
After evaporation of the solvent in vacuo, the residue was redis-
solved in THF/MeOH (1/1, 40 mL). To the resulting solution, a 1.0 M
THF solution (0.718 mL) of NaBH3CN was added at 0 ꢁC for 15 min.
The solvent was evaporated and the residue was purified by column
chromatography (silica gel, CH2Cl2/methanol ¼ 99:1) to afford a
deep violet solid. A 5 mL saturated methanol solution of Zn(OAc)2
(87.5 mg, 0.477 mmol) was added to a CHCl3 solution (40 mL) of
violet solid, which was obtained from the above reaction, at room
temperature and the resulting solution was stirred for 30 min. The
solvent was evaporated and the residue was purified by column
(200 mg, 0.283 mmol, 4%). 1H NMR (400 MHz, CDCl3)
d
ꢀ2.75 (br s,
2H), 3.99 (br s, 4H), 7.03 (d, J ¼ 8.3 Hz, 4H), 7.74 (m, 6H), 7.98 (d,
J ¼ 8.3 Hz, 4H), 8.21 (d, J ¼ 9.3 Hz, 4H), 8.81 (d, J ¼ 4.8 Hz, 4H), 8.92
(d, J ¼ 4.8 Hz, 4H). MS (FABþ) m/z 645 [M þ H]þ.

26
M.H. Lee et al. / Journal of Organometallic Chemistry 761 (2014) 20e27
chromatography (silica gel, CH2Cl2/methanol ¼ 99:1). Recrystalli-
zation from THF/hexane resulted in 8 as a purple crystalline solid
Electrochemical measurements of 8, 1, and 2
Cyclic voltammetry was carried out on an AUTOLAB (PGSTAT 10,
Eco Chemie, Netherlands) electrochemical analyzer using the con-
ventional three-electrode system of a platinum working electrode
(1.6-mm-diameter disk, Bioanalytical Systems, Inc.), a platinum
counter wire electrode (5-cm length of 0.5-mm-diameter wire), and
a Ag/Agþ reference electrode (0.1 M AgNO3/Ag in acetonitrile with a
VycorÔ salt bridge). All measurements were performed at ambient
temperature under nitrogen atmosphere in a dry, deoxygenated
0.1 M chlorobenzene solution of [(n-Bu)4N]ClO4. The concentration
of the compounds was w3 ꢂ 10ꢀ4 M. All potentials were referenced
to the standard ferrocene/ferrocenium (Fc/Fcþ).
(160 mg, 0.146 mmol, 61%).
d
4.02 (s, 5H), 4.29 (t, J ¼ 1.7 Hz, 2H),
4.50 (d, J ¼ 5.3 Hz, 2H), 4.54 (d, J ¼ 5.7 Hz, 2H), 4.69 (t, J ¼ 1.7 Hz, 2H)
5.70 (t, J ¼ 5.5 Hz,1H), 5.85 (t, J ¼ 5.8 Hz,1H), 6.93 (d, J ¼ 8.3 Hz, 2H),
7.03 (d, J ¼ 8.3 Hz, 2H), 7.46 (d, J ¼ 8.1 Hz, 4H), 7.55 (d, J ¼ 8.1 Hz,
2H), 7.59 (d, J ¼ 8.1 Hz, 2H), 7.72 (m, 6H), 7.92 (d, J ¼ 8.3 Hz, 2H), 7.95
(d, J ¼ 8.3 Hz, 2H), 8.21 (m, 4H), 8.82 (m, 4H), 8.94 (d, J ¼ 4.6 Hz, 2H),
8.99 (d, J ¼ 4.6 Hz, 2H). MS (FABþ) m/z 975 [M þ H]þ.
Synthesis of Os3(CO)8(CNR0)(m3
-
h2
:
h2
:
h
2-C60) (1; R0 ¼ ZnPFc)
An acetonitrile solution (1.2 mL) of anhydrous Me3NO (5.35 mg,
0.071 mmol) was added dropwise to a chlorobenzene solution
(60 mL) of Os3(CO)9(m3- : :h
h2 h2 2-C60) (100 mg, 0.064 mmol) at 0 ꢁC.
Electrochemical measurements of SAM
The reaction mixture was allowed to warm to room temperature for
40 min. After evaporation of the solvent in vacuo, the residue was
dissolved in chlorobenzene (60 mL). A chlorobenzene solution of 8
(71.1 mg, 0.065 mmol) was added to the resulting solution and the
reaction mixture was stirred at 60 ꢁC for 2 h. The solvent was
evaporated and the residue was purified by column chromatog-
raphy (silica gel, CS2:CH2Cl2, 1:3) to result in compound 1 (67.7 mg,
0.026 mmol, 40%) as a brown solid. IR (CH2Cl2) v(NC) 2155(m);
v(CO) 2067(vs), 2037(s), 2019(s), 1997(m) cmꢀ1; 1H NMR (400 MHz,
Cyclic voltammetry was carried out using an AUTOLAB (PGSTAT
10, Eco Chemie, Netherlands) electrochemical analyzer with a
conventional three-electrode system of a modified ITO working
electrode (electrode area 0.36 cm2), a platinum counter wire elec-
trode (5-cm length of 0.5-mm-diameter wire), and a Ag QRE
reference electrode. All measurements were performed at ambient
temperature under nitrogen atmosphere in dry 0.1 M dichloro-
methane solution of [(n-Bu)4N]PF6. All potentials were referenced
to the standard ferrocene/ferrocenium (Fc/Fcþ). Surface coverage
was calculated using the real surface areas of the electrodes, which
were determined by the electrochemical method based on mass
transfer and adsorption processes.
CDCl3)
d
4.01 (s, 5H), 4.29 (t, J ¼ 1.7 Hz, 2H), 4.51 (d, J ¼ 5.4 Hz, 2H),
4.58 (d, J ¼ 5.6 Hz, 2H), 4.70 (t, J ¼ 1.7 Hz, 2H) 5.72 (t, J ¼ 5.5 Hz, 1H),
5.91 (t, J ¼ 5.8 Hz, 1H), 6.90 (d, J ¼ 8.3 Hz, 2H), 7.03 (d, J ¼ 8.3 Hz,
2H), 7.43 (d, J ¼ 8.4 Hz, 2H), 7.48 (d, J ¼ 8.1 Hz, 2H), 7.56 (d,
J ¼ 8.1 Hz, 2H), 7.63 (d, J ¼ 8.4 Hz, 2H), 7.71 (m, 6H), 7.89 (d,
J ¼ 8.3 Hz, 2H), 7.95 (d, J ¼ 8.3 Hz, 2H), 8.18 (m, 4H), 8.76 (d,
J ¼ 4.6 Hz, 2H), 8.78 (d, J ¼ 4.6 Hz, 2H), 8.87 (d, J ¼ 4.6 Hz, 2H), 8.96
(d, J ¼ 4.6 Hz, 2H). MALDI-TOF m/z 2613 [M]þ.
Photoelectrochemical measurements
Photoelectrochemical measurements were performed in
a
designed Teflon cell. The cell was illuminated with monochromatic
excitation light through a monochromator (Thermo Oriel, model
77250) by a 300-W xenon lamp (Thermo Oriel, model 6259) on a
SAM of 0.36 cm2. The photocurrent was measured in a three-
electrode arrangement (AUTOLAB, PGSTAT 10): a modified ITO
working electrode, a platinum wire counter electrode, and a Ag/
AgCl (3 M NaCl) reference electrode. Light intensity was monitored
by an optical power meter (Anritsu ML9002A) and corrected.
Quantum yields were calculated based on the number of photons
absorbed by the chromophore on the ITO electrodes at each
wavelength using the input power, the photocurrent density, and
the absorbance determined from the absorption spectrum on the
ITO electrode.
Synthesis of Os3(CO)7(CNR)(CNR0)(m3
R ¼ (CH2)3Si(OEt)3, R0 ¼ ZnPFc)
- : :h
h2 h2 2-C60) (2;
An acetonitrile solution (1 mL) of anhydrous Me3NO (4.70 mg,
0.063 mmol) was added dropwise to a chlorobenzene solution
(60 mL) of Os3(CO)8(CN(CH2)3Si(OEt)3)(m3- : :h
h2 h2 2-C60) (100 mg,
0.057 mmol) at 0 ꢁC. The reaction mixture was allowed to warm to
room temperature for 40 min. After evaporation of the solvent in
vacuo, the residue was dissolved in chlorobenzene (60 mL). A chlo-
robenzene solution of 8 (62.6 mg, 0.057 mmol) was added to the
resulting solution and the reaction mixture was stirred at room
temperature for 2.5 h. The solvent was evaporated and the residue
was purified by column chromatography (silica gel, CS2:CH2Cl2, 1:2)
to result in compound 2 (80.3 mg, 0.029 mmol, 50%) as a brown solid.
IR (CH2Cl2) v(NC) 2188(m), 2146(m); v(CO) 2047(vs), 2016(s),
Acknowledgments
This work was supported by the Incheon National University
(501100002628) Research Grant in 2012.
2001(s), 1983(m) cmꢀ1 1H NMR (400 MHz, CDCl3)
; d 0.65 (m, 2H),
1.15 (t, J ¼ 7.0 Hz, 9H), 1.79 (m, 2H), 3.75 (q, J ¼ 7.0 Hz, 6H), 3.98 (t,
J ¼ 6.7 Hz, 2H), 4.01 (s, 5H), 4.29 (t, J ¼ 1.7 Hz, 2H), 4.51 (d, J ¼ 5.4 Hz,
2H), 4.56 (d, J ¼ 5.6 Hz, 2H), 4.69 (t, J ¼ 1.7 Hz, 2H), 5.70 (t, J ¼ 5.5 Hz,
1H), 5.86 (t, J ¼ 5.8 Hz,1H), 6.92 (d, J ¼ 8.3 Hz, 2H), 7.03 (d, J ¼ 8.3 Hz,
2H), 7.41 (d, J ¼ 8.4 Hz, 2H), 7.47 (d, J ¼ 8.1 Hz, 2H), 7.55 (d, J ¼ 8.1 Hz,
2H), 7.61 (d, J ¼ 8.4 Hz, 2H), 7.72 (m, 6H), 7.93 (d, J ¼ 8.3 Hz, 2H), 7.97
(d, J ¼ 8.3 Hz, 2H), 8.20 (m, 4H), 8.80 (m, 4H), 8.91 (d, J ¼ 4.6 Hz, 2H),
8.98 (d, J ¼ 4.6 Hz, 2H). MALDI-TOF m/z 2814 [M]þ.
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2014.02.022.
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