Photoinduced electron transfer in a ferrocene-distyryl BODIPY dyad and a ferrocene-distyryl BODIPY-C60 triad

Article abstract of DOI:10.1002/cphc.201200167

A ferrocene-distyryl BODIPY dyad and a ferrocene-distyryl BODIPY-C ₆₀ triad are synthesized and characterized. Upon photoexcitation at the distyryl BODIPY unit, these arrays undergo photoinduced electron transfer to form the corresponding charge-separated species. Based on their redox potentials, determined by cyclic voltammetry, the direction of the charge separation and the energies of these states are revealed. Femtosecond transient spectroscopic studies reveal that a fast charge separation (k _CS=1.0×10¹⁰ s^-1) occurs for both the ferrocene-distyryl BODIPY dyad and the ferrocene-distyryl BODIPY-C₆₀ triad, but that a relatively slow charge recombination is observed only for the triad. The lifetime of the charge-separated state is 500 ps. Charge recombination of the dyad and triad leads to population of the triplet excited sate of ferrocene and the ground state, respectively.

Full text of DOI:10.1002/cphc.201200167

DOI: 10.1002/cphc.201200167
Photoinduced Electron Transfer in a Ferrocene–Distyryl
BODIPY Dyad and a Ferrocene–Distyryl BODIPY–C60
Triad**
Jian-Yong Liu,[a] Mohamed E. El-Khouly,[b, c] Shunichi Fukuzumi,*[b, d] and Dennis K. P. Ng*[a]
A ferrocene–distyryl BODIPY dyad and a ferrocene–distyryl
BODIPY–C60 triad are synthesized and characterized. Upon pho-
toexcitation at the distyryl BODIPY unit, these arrays undergo
photoinduced electron transfer to form the corresponding
charge-separated species. Based on their redox potentials, de-
termined by cyclic voltammetry, the direction of the charge
separation and the energies of these states are revealed. Fem-
tosecond transient spectroscopic studies reveal that a fast
charge separation (kCS =1.0ꢀ1010 sÀ1) occurs for both the ferro-
cene–distyryl BODIPY dyad and the ferrocene–distyryl BODIPY–
C60 triad, but that a relatively slow charge recombination is ob-
served only for the triad. The lifetime of the charge-separated
state is 500 ps. Charge recombination of the dyad and triad
leads to population of the triplet excited sate of ferrocene and
the ground state, respectively.
1. Introduction
Solar-light conversion is a promising strategy to address the in-
creasing energy requirements in the future.[1] Intensive work
has been carried out to develop highly efficient solar cells
based on inorganic semiconductors with a narrow band gap.[2]
As an alternative approach, artificial photosynthetic models
have also received considerable attention, in which different
chromophores and redox-active units are carefully selected
and assembled to mimic the primary events of natural photo-
synthesis.[3–11] The ultimate goal is to convert solar energy into
fuels effectively via a series of photochemical processes.
triad are described in detail. The combination of DSBDP, Fc,
and C60 enables the construction of excellent photosynthetic
reaction center models that absorb over a wide range of visi-
ble light. The Fc-DSBDP-C60 triad is of particular interest as it
undergoes sequential electron transfer resulting in charge sta-
bilization.
2. Results and Discussion
Scheme 1 shows the synthetic route used to prepare these
DSBDP-based arrays. Condensation of the phenol-containing
BODIPY 1[21] with one equivalent of aldehyde 2[22] in the pres-
Being a versatile class of functional dyes, boron dipyrrome-
thenes (BODIPYs) are promising candidates for the construc-
tion of such models as a result of their desirable photophysical
and electrochemical properties.[12] In fact, a substantial number
of BODIPY-based light-harvesting[13] and electron donor–ac-
ceptor[14] systems have been reported. By extending the p-con-
jugation via condensation with aryl aldehydes at the 3- and 5-
positions, the resulting distyryl BODIPYs, labeled as DSBDPs,
absorb and emit strongly in the near-infrared region (ca.
650 nm). In addition, they have reasonably long excited-state
lifetimes and possess good solubility and stability in many sol-
vent systems. As a result, apart from their application as fluo-
rescent probes for metal ions,[15] components for molecular
logic gates,[15c,16] and photosensitizers for photodynamic thera-
py,[17] these compounds have also been used to construct pho-
tosynthetic models[13c,g,18] and dye-sensitized solar cells.[19]
We have recently reported a dyad of DSBDP and C60, which
undergoes photoinduced electron transfer to give a charge-
separated state with a lifetime of 476 ps in benzonitrile.[20] We
report herein a related dyad and a related triad having DSBDP
as an antenna, electron acceptor, and electron mediator, as
well as ferrocene (Fc) and C60 as an electron donor and accept-
or, respectively. The preparation and photoinduced electron-
transfer properties of the Fc-DSBDP dyad and Fc-DSBDP-C60
[a] Dr. J.-Y. Liu,+ Prof. D. K. P. Ng
Department of Chemistry
The Chinese University of Hong Kong
Shatin, N. T., Hong Kong (China)
Fax: (+852)2603-5057
E-mail: dkpn@cuhk.edu.hk
[b] Dr. M. E. El-Khouly,+ Prof. S. Fukuzumi
Department of Materials and Life Sciences
Graduate School of Engineering
Osaka University, ALCA (JST)
Suita, Osaka 565-0871 (Japan)
E-mail: fukuzumi@chem.eng.osaka-u.ac.jp
[c] Dr. M. E. El-Khouly+
Department of Chemistry, Faculty of Science
Kafr El-Sheikh University
Kafr El-Sheikh 33516 (Egypt)
[d] Prof. S. Fukuzumi
Department of Bioinspired Science
Ewha Womans University
Seoul 120-750 (Korea)
[+] These two authors contributed equally to this work.
[**] BODIPY: Boron Dipyrromethene
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cphc.201200167.
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S. Fukuzumi, D. K. P. Ng et al.
Figure 1a shows the absorp-
tion spectra of Fc-DSBDP dyad 6
and Fc-DSBDP-C60 triad 8 in ben-
zonitrile. The spectrum of the
non-Fc-containing analogue 9[20]
is also included for comparison.
The spectrum of
9 exhibited
a
strong S0–S1 transition at
649 nm and a higher-energy S0–
S2 transition at 376 nm. From the
S0–S1 transition, the energy of
the singlet-excited state of
DSBDP (1DSBDP*) was estimated
as 1.91 eV. This transition was
red-shifted by about 150 nm
compared to that of the BODIPY
derivatives as a result of the ex-
tended conjugation. The S0–S1
transition band of the unsym-
metrical Fc-DSBDP dyad 6 was
significantly broadened and red-
shifted by about 20 nm com-
pared to that of 9, while the
higher-energy S0–S2 transition
was blue-shifted by about
15 nm. Under these conditions,
the absorption of the Fc unit
was not observed due to its low
molar extinction coefficient.
These observations suggested
the presence of ground-state in-
teractions between the Fc and
DSBDP entities in the dyad. For
Fc–DSBDP–C60 triad 8, the ab-
sorption spectrum resembled
that of dyad 6, except for the
occurrence of two additional
Scheme 1. Synthesis of the DSBDP-based arrays.
characteristic absorption bands
of C60 at 330 and 432 nm. The
ence of piperidine and acetic acid gave the monostyryl
BODIPY 3, which could be isolated from the reaction mixture
by column chromatography. Treatment of this compound with
ferrocenecarboxaldehyde (4) under the same conditions led to
the formation of Fc-DSBDP dyad 5.
latter was partially overlapped with the S0–S2 absorption band
of DSBDP.
Upon excitation at the DSBDP unit at 380 nm, DSBDP 9 gave
a strong fluorescence band at 670 nm together with a weak
one at 591 nm. The fluorescence quantum yield (Ff) was
found to be 0.54. The presence of the Fc moiety in dyad 6 and
This compound was then treated
1
with 1,3-dibromopropane and 4-
triad 8 effectively quenched DSBDP* (Ff =1ꢀ10À3), leading to
hydroxybenzaldehyde successively
virtually invisible fluorescence emission (Figure 1b).
in the presence of K2CO3 in N,N-di-
To establish the relative energy levels, electrochemical stud-
ies were performed for these compounds in benzonitrile using
cyclic voltammetry. Figure 2 shows the voltammograms of
DSBDP 9, dyad 6, and triad 8. The voltammogram of DSBDP 9
showed an one-electron reduction couple at À1050 mV and an
one-electron oxidation couple at 800 mV, both relative to the
saturated calomel electrode (SCE). For the dyad 6, the first re-
duction potential shifted cathodically to À996 mV (vs. SCE). An
additional couple due to the one-electron oxidation of the Fc
unit also appeared at 504 mV (vs. SCE), which is shifted to the
methylformamide (DMF) to afford
aldehyde 7 via the bromo com-
pound 6. The Fc-DSBDP-C60 triad 8
was prepared by treating 7 with
C60 and sarcosine according to the
Prato procedure.[23] All the new
compounds were characterized
with various spectroscopic meth-
ods.
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Electron Transfer in Dyads and Triads
Figure 2. Cyclic voltammograms of DSBDP 9, Fc-DSBDP dyad 6, and Fc-
DSBDP-C60 triad 8 (from top to bottom) in deaerated benzonitrile in the
presence of 0.1m [nBu4N][ClO4]. Scan rate=20 mVsÀ1
.
·À
-DSBDP·À and Fc+-DSBDP-C60 were estimated to be À1.50
and À1.08 eV, respectively.[26] By comparing the energy level of
1
these charge-separated states with that of DSBDP* (1.91 eV),
Figure 1. a) Electronic absorption and b) fluorescence spectra of DSBDP 9,
Fc-DSBDP dyad 6, and Fc-DSBDP-C60 triad 8 in benzonitrile (all at 9 mm)
(lex =380 nm).
the driving forces of the charge-separation process (DGCS) for
·À
Fc+-DSBDP·À and Fc+-DSBDP-C60 were determined to be
À0.41 and À0.83 eV, respectively.[26] The negative values of
DGCS for these processes suggested that the generation of
charge-separated state via 1DSBDP* is thermodynamically fa-
vorable for these arrays in polar benzonitrile.
positive potential by about 30 mV as compared with that of
ferrocene.[24] For the triad 8, the position of the Fc/Fc+ couple
was virtually the same as that for the dyad 6. Two reduction
processes were also revealed at À996 and À576 mV (vs. SCE),
which can be ascribed to the DSBDP and C60 moieties, respec-
tively. Hence, the first reduction potential of the C60 unit is
cathodically shifted by 420 mV as compared with that of the
DSBDP unit.
The excited-state properties of dyad 6 and triad 8 in benzo-
nitrile were studied by femtosecond transient absorption spec-
troscopy using an excitation light source of 390 nm to selec-
tively excite the DSBDP unit. As a reference, DSBDP 9 was first
studied and the spectrum is shown in Figure 3. It can be seen
that two absorption bands at 480 and 965 nm appear, which
1
These results clearly revealed the electron-donating nature
of the Fc unit and the electron-accepting property of the
DSBDP and C60 moieties in the dyad and triad. The energies of
the charge-separated states were calculated by the Rehm–
Weller equation[25] using the above spectroscopic and redox
data. Based on the redox potentials of the first oxidation of Fc
and the first reduction of DSBDP and C60 moieties, the driving
forces of the charge-recombination process (DGCR) for Fc+
can be attributed to DSBDP*. By monitoring the decay of the
near-infrared band at 965 nm, it was found that it decayed
slowly with a rate constant of 7.1ꢀ108 sÀ1 to populate the cor-
responding triplet manifold. The transient absorption spectra
of the Fc-DSBDP dyad 6 (Figure 4) also showed the characteris-
tic absorptions of 1DSBDP*. However, the absorption at
844 nm decayed much faster with a rate constant of 9.8ꢀ
1
109 sÀ1, showing that DSBDP* in the dyad is much short-lived
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was also not observed due to its low molar extinction coeffi-
cient (e=330mÀ1 cmÀ1 at 620 nm).[27] For these reasons, we
could not determine accurately the rate of charge recombina-
tion of Fc+-DSBDP·À.
The complementary nanosecond transient absorption spec-
tra of Fc-DSBDP dyad 6 in deaerated benzonitrile were also re-
corded by utilizing a laser source of 600 nm, which excited the
DSBDP entity. The spectra (Figure S2 in the Supporting Infor-
mation) showed no transient absorptions for the triplet excited
state of DSBDP (3DSBDP*) and Fc (3Fc*) in the microsecond
region. Energetically, the decay of Fc+-DSBDP·À to populate
the 3DSBDP* (1.15 eV)[20] and/or 3Fc* (1.16 eV)[28] is possible.
However, as 3DSBDP* was not detected, it is likely that Fc+
3
-DSBDP·À decays mainly to populate Fc*, which is extremely
difficult to detect in the microsecond region, as well as to the
ground state.
For Fc-DSBDP-C60 triad 8, the transient absorption spectrum
1
at 10 ps showed the characteristic absorption of DSBDP* at
840 nm, which decayed rapidly with a rate constant of 1.0ꢀ
1010 sÀ1. For the transient spectra at time intervals between
Figure 3. Femtosecond transient absorption spectral traces at different time
intervals for DSBDP 9 in benzonitrile (lex =390 nm). Inset: Decay profile of
the transient band of DSBDP* at 965 nm.
·À
30–1500 ps, the characteristic absorption of C60 at 1000 nm
1
could also be seen (Figure 5). These observations suggest the
Figure 5. Femtosecond transient absorption spectral traces at different time
intervals for Fc-DSBDP-C60 triad 8 in benzonitrile (lex =390 nm). Inset: Decay
profile of the transient band of C60·À at 1000 nm.
Figure 4. Femtosecond transient absorption spectral traces at different time
intervals for Fc-DSBDP dyad 6 in benzonitrile (lex =390 nm). Inset: Decay
profile of the transient band of DSBDP* at 844 nm.
1
1
than that in 9. This observation is in accord with the occur-
rence of electron transfer from Fc to DSBDP* in the dyad, as
occurrence of electron transfer from Fc to DSBDP* to form the
initial charge-separated species Fc+-DSBDP·À-C60, which is fol-
lowed by a fast electron mediation (EM) from DSBDP·À to the
C60 to generate the final charge-separated species Fc+-DSBDP-
1
suggested by the effective fluorescence quenching and the
negative calculated value of DGCS. The short distance between
the iron center of Fc and the boron center of DSBDP (6.2 ꢂ as
found in the optimized structure shown in Figure S1 in the
Supporting Information) may rationalize the extremely fast
electron-transfer process from Fc to 1DSBDP*. The expected
absorption band of DSBDP·À was embedded by the strong
C60·À. The transient band of C60 at 1000 nm showed a fast
·À
decay within the initial 500 ps, followed by a slow decay up to
3 ns (inset of Figure 5). While the fast decay is quite similar to
1
the decay of DSBDP*, the slow decay can be assigned to the
decay of Fc+-DSBDP-C60·À. From the fitting of the slow decay,
1
bleaching of DSBDP*. The transient absorption band of Fc+
the rate of charge-recombination (kCR) and lifetime (tCS) of the
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Electron Transfer in Dyads and Triads
on silica gel (Macherey–Nagel, 70–
230 mesh) columns with the indi-
cated eluents. Compounds 1,[21]
2,[22] and 9[20] were prepared as de-
scribed.
1H and 13C{1H} NMR spectra were
recorded on a Bruker AVANCE II
400 spectrometer (1H, 400; 13C,
100.6 MHz) in CDCl3. Spectra were
referenced internally using the re-
sidual solvent (1H: d=7.26 ppm) or
solvent (13C: d=77.0 ppm) reso-
nance relative to SiMe4. Electro-
spray ionization (ESI) mass spectra
were measured on a Thermo Finni-
gan MAT 95 XL mass spectrometer.
Steady-state fluorescence spectra
were measured on a Shimadzu RF-
5300
PC
spectrofluorometer
Figure 6. Energy-level diagrams showing the photoinduced intramolecular events of a) Fc-DSBDP dyad 6 and
b) Fc-DSBDP-C60 triad 8 in benzonitrile.
equipped with a photomultiplier
tube having high sensitivity in the
700–800 nm region. The fluores-
cence quantum yields were mea-
·À
charge-separated state Fc+-DSBDP-C60 were found to be 2.0ꢀ
sured with a Hamamatsu C9920-0X(PMA-12) U6039-05 spectro-
fluorometer with an integrated sphere adapted to a right angle
configuration. The diffuse reflectance spectra of the samples were
recorded and the measured results were corrected for the detector
response as a function of wavelength.
109 sÀ1 and 500 ps, respectively. The latter is comparable with
·À
that of the closely spaced Fc+-BODIPY-C60 triad (416 ps)[14b]
·À
and the DSBDP·+-C60 dyad (476 ps)[20] reported by us earlier.
Charge recombination resulted in population of the ground
state. The photoinduced intramolecular processes of dyad 6
and triad 8 in benzonitrile are summarized in the energy-level
diagrams shown in Figure 6.
Cyclic voltammograms were recorded on a BAS CV-50W voltam-
metric analyzer. A platinum disk electrode was used as the working
electrode, while a platinum wire served as a counter electrode. The
SCE electrode was used as the reference electrode. All measure-
ments were carried out in deaerated benzonitrile containing 0.1m
[nBu4N][ClO4] as the supporting electrolyte. The scan rate was set
3. Conclusions
as 20 mVsÀ1
.
We have reported the preparation and photoinduced electron-
transfer processes of an Fc-DSBDP dyad and an Fc-DSBDP-C60
triad in benzonitrile. Upon excitation at the DSBDP unit, both
of these systems undergo rapid electron transfer to form the
charge-separated species Fc+-DSBDP·À, Fc+-DSBDP·À-C60, and
Fc+-DSBDP-C60·À. Steady-state emission and femtosecond laser
flash photolysis studies have provided tangible evidence for
the occurrence of photoinduced electron transfer in these
donor-acceptor systems. Free-energy calculations have also re-
vealed that these charge-separation processes are thermody-
namically favorable. The Fc-DSBDP-C60 triad 8 undergoes a fast
For laser flash photolysis, the studied compounds were excited by
a Panther OPO pumped by an Nd:YAG laser (Continuum SLII-10,
4–6 ns fwhm) with a power of 1.5 or 3.0 mJpulseÀ1. The transient
absorption measurements were performed using a continuous
xenon lamp (150 W) as the probe light and an InGaAs-PIN photo-
diode (Hamamatsu 2949) as the detector. The output from the
photodiode and a photomultiplier tube was recorded with a digitiz-
ing oscilloscope (Tektronix TDS3032, 300 MHz). Femtosecond tran-
sient absorption spectroscopic experiments were conducted using
an ultrafast source: Integra-C (Quantronix Corp.), an optical para-
metric amplifier: TOPAS (Light Conversion Ltd.), and a commercially
available optical detection system: Helios provided by Ultrafast
Systems LLC. The source for the pump and probe pulses was de-
rived from the fundamental output of Integra-C (780 nm,
2 mJpulseÀ1, fwhm=130 fs) at a repetition rate of 1 kHz. 75% of
the fundamental output of the laser was introduced into TOPAS,
which has optical frequency mixers resulting in tunable range from
285 to 1660 nm, while the rest of the output was used for white
light generation. Typically, 2500 excitation pulses were averaged
for 5 s to obtain the transient spectrum at a set delay time. Kinetic
traces at appropriate wavelengths were assembled from the time-
resolved spectral data. All measurements were conducted at 298 K.
The transient spectra were recorded using fresh solutions in each
laser excitation.
charge separation (1.0ꢀ1010 À1) and a relatively slow charge
s
recombination (2.0ꢀ109 sÀ1). The wide absorption of this triad
in the visible region and its high kCS/kCR ratio suggest that this
novel triad is a promising light-harvesting system.
Experimental Section
Materials
All the reactions were performed under nitrogen atmosphere. Tet-
rahydrofuran (THF), toluene, and DMF were distilled from sodium
benzophenone ketyl, sodium, and barium oxide, respectively. Ben-
zonitrile used for spectroscopic studies was of analytical grade (Al-
drich). All other solvents and reagents were of reagent grade and
used as received. Chromatographic purifications were performed
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S. Fukuzumi, D. K. P. Ng et al.
16.0 Hz, 1H, CH=CH), 7.21 (d, J=8.4 Hz, 2H, ArH), 7.20 (d, J=
16.0 Hz, 1H, CH=CH), 7.10 (d, J=16.0 Hz, 1H, CH=CH), 7.02 (d, J=
8.4 Hz, 2H, ArH), 6.94 (d, J=8.4 Hz, 2H, ArH), 6.60 (s, 1H, pyrrole-
H), 6.57 (s, 1H, pyrrole-H), 4.64 (t, J=1.6 Hz, 2H, Fc-H), 4.44 (t, J=
1.6 Hz, 2H, Fc-H), 4.13–4.21 (m, 9H, Fc-H + CH2), 3.89 (t, J=4.8 Hz,
2H, CH2), 3.74–3.79 (m, 2H, CH2), 3.61–3.73 (m, 6H, CH2), 3.55–3.59
(m, 2H, CH2), 3.39 (s, 3H, OCH3), 2.38 (quintet, J=6.0 Hz, 2H, CH2),
1.50 (s, 3H, CH3), 1.47 ppm (s, 3H, CH3); 13C{1H} NMR: d=159.4,
159.1, 152.9, 151.9, 142.0, 141.0, 137.5, 136.9, 134.9, 133.5, 133.2,
129.7, 129.6, 128.8, 127.6, 117.3, 116.8, 114.9, 114.8, 81.9, 71.8, 70.8,
70.6, 70.5, 69.7, 69.6, 68.1, 67.4, 65.4, 59.0, 32.3, 29.9, 29.6,
14.8 ppm; MS (ESI): isotopic clusters peaking at m/z 929 {100%,
[M+Na]+}, 908 {75%, [M]+}, and 889 {35%, [MÀF]+}; HRMS (ESI):
m/z calcd for C47H50BBrF2FeN2NaO5 [M+Na]+: 929.2206, found
929.2183.
Monostyryl BODIPY 3
A mixture of the phenol-containing BODIPY 1 (0.34 g, 1.0 mmol),
aldehyde
2 (0.27 g, 1.0 mmol), glacial acetic acid (2.0 mL,
34.9 mmol), piperidine (2.4 mL, 24.3 mmol), and a small amount of
Mg(ClO4)2 in toluene (60 mL) was refluxed for 3 h. The water
formed during the reaction was removed azeotropically with
a Dean–Stark apparatus. The mixture was concentrated under re-
duced pressure, then the residue was purified by column chroma-
tography using CH2Cl2/ethyl acetate (10:1 v/v) as the eluent. The
pink colored fraction was collected and rotary evaporated to yield
1
the desired product (0.15 g, 26%). H NMR: d=7.52 (d, J=16.4 Hz,
1H, CH=CH), 7.49 (d, J=8.8 Hz, 2H, ArH), 7.15 (d, J=16.4 Hz, 1H,
CH=CH), 7.07 (d, J=8.8 Hz, 2H, ArH), 6.94 (d, J=8.8 Hz, 2H, ArH),
6.88 (d, J=8.8 Hz, 2H, ArH), 6.55 (s, 1H, pyrrole-H), 6.34 (br s, 1H,
OH), 5.98 (s, 1H, pyrrole-H), 4.15 (t, J=4.8 Hz, 2H, CH2), 3.87 (t, J=
4.8 Hz, 2H, CH2), 3.73–3.78 (m, 2H, CH2), 3.64–3.72 (m, 4H, CH2),
3.54–3.59 (m, 2H, CH2), 3.39 (s, 3H, OCH3), 2.58 (s, 3H, CH3), 1.47 (s,
3H, CH3), 1.45 ppm (s, 3H, CH3); 13C{1H} NMR: d=159.5, 156.7,
154.3, 153.2, 142.7, 142.2, 140.2, 135.9, 133.2, 132.0, 129.6, 129.5,
128.9, 126.8, 120.9, 117.4, 117.0, 116.0, 114.9, 71.8, 70.8, 70.6, 70.5,
69.7, 67.4, 59.0, 14.8, 14.7, 14.5 ppm; MS (ESI): isotopic clusters
peaking at m/z 613 {100%, [M+Na]+}, 590 {17%, [M]+}, and 571
{52%, [MÀF]+}; HRMS (ESI): m/z calcd for C33H37BF2N2NaO5 [M+
Na]+: 613.2656, found 613.2659.
Fc-DSBDP Dyad 7
Potassium carbonate (0.16 g, 1.2 mmol) was added to a mixture of
6 (0.18 g, 0.2 mmol) and 4-hydroxybenzaldehyde (0.07 g, 0.6 mmol)
in DMF (30 mL). The resulting mixture was stirred at 808C for 8 h,
then the solvent was removed under reduced pressure. The resi-
due was then mixed with CH2Cl2 (50 mL) and water (50 mL). The
aqueous layer was separated and extracted with CH2Cl2 (50 mL ꢀ
3). The combined organic fractions was dried over anhydrous
MgSO4, then evaporated to dryness. The residue was subject to
column chromatography using CH2Cl2 as the eluent to give 7 as
Fc-DSBDP Dyad 5
1
a blue solid (0.17 g, 89%). H NMR: d=9.90 (s, 1H, CHO), 7.85 (d,
According to the above procedure, the monostyryl BODIPY 3
(0.59 g, 1.0 mmol) was treated with ferrocenecarboxaldehyde (4)
(0.42 g, 2.0 mmol), glacial acetic acid (2.0 mL, 34.9 mmol), piperi-
dine (2.4 mL, 24.3 mmol), and a small amount of Mg(ClO4)2 in re-
fluxing toluene (60 mL) for 24 h. The crude product was purified
by column chromatography using CH2Cl2/ethyl acetate (2:1 v/v) as
the eluent. The blue-colored fraction was collected and rotary
J=8.8 Hz, 2H, ArH), 7.58 (d, J=16.0 Hz, 1H, CH=CH), 7.56 (d, J=
8.8 Hz, 2H, ArH), 7.32 (d, J=16.0 Hz, 1H, CH=CH), 7.21 (d, J=
8.8 Hz, 2H, ArH), 7.19 (d, J=16.0 Hz, 1H, CH=CH), 7.10 (d, J=
16.0 Hz, 1H, CH=CH), 7.05 (d, J=8.8 Hz, 2H, ArH), 7.02 (d, J=
8.8 Hz, 2H, ArH), 6.94 (d, J=8.8 Hz, 2H, ArH), 6.59 (s, 1H, pyrrole-
H), 6.56 (s, 1H, pyrrole-H), 4.64 (t, J=1.6 Hz, 2H, Fc-H), 4.44 (t, J=
1.6 Hz, 2H, Fc-H), 4.31 (t, J=6.0 Hz, 2H, CH2), 4.23 (t, J=6.0 Hz, 2H,
CH2), 4.15–4.20 (m, 7H, Fc-H + CH2), 3.89 (t, J=4.8 Hz, 2H, CH2),
3.73–3.78 (m, 2H, CH2), 3.65–3.72 (m, 4H, CH2), 3.55–3.59 (m, 2H,
CH2), 3.39 (s, 3H, OCH3), 2.34 (quintet, J=6.0 Hz, 2H, CH2), 1.48 (s,
3H, CH3), 1.46 ppm (s, 3H, CH3); 13C{1H} NMR: d=190.7, 163.8,
159.4, 159.2, 153.0, 151.6, 141.9, 140.9, 137.5, 137.0, 135.0, 133.5,
133.3, 132.0, 130.0, 129.8, 129.7, 128.8, 127.6, 117.4, 117.2, 116.8,
114.9, 114.8, 114.7, 81.9, 71.9, 70.8, 70.6, 70.5, 69.7, 68.1, 67.4, 64.8,
64.2, 59.0, 29.1, 14.8 ppm; MS (ESI): isotopic clusters peaking at m/
z 971 {52%, [M+Na]+} and 948 {100%, [M]+}; HRMS (ESI): m/z
calcd for C54H55BF2FeN2O7 [M]+: 948.3414, found 948.3411.
1
evaporated to yield the desired product (0.25 g, 32%). H NMR: d=
7.58 (d, J=16.0 Hz, 1H, CH=CH), 7.55 (d, J=8.8 Hz, 2H, ArH), 7.32
(d, J=16.0 Hz, 1H, CH=CH), 7.19 (d, J=16.0 Hz, 1H, CH=CH), 7.15
(d, J=8.8 Hz, 2H, ArH), 7.10 (d, J=16.0 Hz, 1H, CH=CH), 6.95 (d,
J=8.4 Hz, 2H, ArH), 6.93 (d, J=8.4 Hz, 2H, ArH), 6.59 (s, 1H, pyr-
role-H), 6.56 (s, 1H, pyrrole-H), 5.36 (s, 1H, OH), 4.64 (t, J=1.8 Hz,
2H, Fc-H), 4.43 (t, J=1.8 Hz, 2H, Fc-H), 4.14–4.20 (m, 7H, CH2 + Fc-
H), 3.89 (t, J=4.8 Hz, 2H, CH2), 3.74–3.79 (m, 2H, CH2), 3.65–3.73
(m, 4H, CH2), 3.54–3.59 (m, 2H, CH2), 3.39 (s, 3H, OCH3), 1.50 (s, 3H,
CH3), 1.47 ppm (s, 3H, CH3); 13C{1H} NMR: d=159.3, 156.6, 152.9,
151.7, 142.0, 141.1, 137.7, 136.9, 135.0, 133.6, 133.4, 129.9, 129.7,
128.9, 127.0, 117.3, 116.8, 115.9, 114.8, 82.0, 71.9, 70.8, 70.6, 70.5,
70.4, 69.7, 68.1, 67.4, 59.0, 14.8 ppm; MS (ESI): an isotopic cluster
peaking at m/z 786 {100%, [M]+}; HRMS (ESI): m/z calcd for
C44H45BF2 FeN2O5 [M]+: 786.2734, found 786.2729.
Fc-DSBDP-C60 Triad 8
Dyad 7 (47 mg, 0.05 mmol) and sarcosine (44 mg, 0.50 mmol) were
added to a solution of C60 (72 mg, 0.10 mmol) in toluene (50 mL).
The mixture was heated under reflux for 12 h. After cooling slowly
to room temperature, the solvent was removed under reduced
pressure. The residue was purified by column chromatography
using toluene, and then toluene/ethyl acetate (10:1 v/v) as the elu-
ents. The product was obtained as a dark purple solid (43 mg,
51%). 1H NMR: d=7.73 (br s, 2H, ArH), 7.58 (d, J=16.0 Hz, 1H,
CH=CH), 7.56 (d, J=8.8 Hz, 2H, ArH), 7.31 (d, J=16.0 Hz, 1H, CH=
CH), 7.19 (d, J=16.0 Hz, 1H, CH=CH), 7.18 (d, J=8.8 Hz, 2H, ArH),
7.09 (d, J=16.0 Hz, 1H, CH=CH), 6.97–7.03 (m, 4H, ArH), 6.94 (d,
J=8.8 Hz, 2H, ArH), 6.58 (s, 1H, pyrrole-H), 6.55 (s, 1H, pyrrole-H),
4.98 (d, J=9.2 Hz, 1H, pyrrolidine-H), 4.89 (s, 1H, pyrrolidine-H),
4.63 (t, J=1.8 Hz, 2H, Fc-H), 4.44 (t, J=1.8 Hz, 2H, Fc-H), 4.16–4.27
(m, 12H, Fc-H, pyrrolidine-H, and CH2), 3.89 (t, J=4.8 Hz, 2H, CH2),
3.74–3.78 (m, 2H, CH2), 3.66–3.72 (m, 4H, CH2), 3.55–3.58 (m, 2H,
Fc-DSBDP Dyad 6
Potassium carbonate (0.55 g, 4.0 mmol) was added to a mixture of
5 (0.15 g, 0.2 mmol) and 1,3-dibromopropane (0.81 g, 4.0 mmol) in
DMF (15 mL). The resulting mixture was stirred at room tempera-
ture overnight. The volatiles were then evaporated under reduced
pressure and the residue was mixed with CH2Cl2 (40 mL) and water
(40 mL). The aqueous layer was separated and extracted with
CH2Cl2 (40 mL x 3). The combined organic fractions were dried
over anhydrous MgSO4, then evaporated to dryness. The residue
was purified by column chromatography using CH2Cl2 as the
1
eluent to give 6 as a blue solid (0.17 g, 94%). H NMR: d=7.59 (d,
J=16.0 Hz, 1H, CH=CH), 7.56 (d, J=8.4 Hz, 2H, ArH), 7.32 (d, J=
&6
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These are not the final page numbers!

Electron Transfer in Dyads and Triads
A. A. Sarjeant, S. T. Nguyen, J. T. Hupp, J. Am. Chem. Soc. 2011, 133,
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2H, CH2), 1.47 (s, 3H, CH3), 1.45 ppm (s, 3H, CH3); MS (ESI): an iso-
topic cluster peaking at m/z 1697 {100%, [M+H]+}; HRMS (ESI):
m/z calcd for C116H61BF2FeN3O6 [M+H]+: 1697.3999, found
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Acknowledgements
This work was supported by a Grant-in-Aid (No. 20108010),
a Global COE program “the Global Education and Research
Center for Bio-Environmental Chemistry” from the Japan Society
of Promotion of Science, and the NRF/MEST of Korea through the
WCU (R31-2008-000-10010-0) and GRL (2010-00353) programs.
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Keywords: boron
dipyrromethenes
·
donor–acceptor
systems · electron transfer · ferrocene · fullerenes
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Received: February 25, 2012
Published online on && &&, 2012
ChemPhysChem 0000, 00, 1 – 8
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemphyschem.org
&
7
&
ÞÞ
These are not the final page numbers!

ARTICLES
J.-Y. Liu, M. E. El-Khouly, S. Fukuzumi,*
D. K. P. Ng*
Promising dyes: The photoinduced
electron-transfer properties of a ferro-
cene–distyryl BODIPY dyad and a ferro-
cene–distyryl BODIPY–C60 triad (BODIPY:
boron dipyrromethene) are studied. The
triad undergoes a relatively slow charge
recombination, giving a charge-separat-
ed state with a lifetime of 500 ps.
&& – &&
Photoinduced Electron Transfer in
a Ferrocene–Distyryl BODIPY Dyad
and a Ferrocene–Distyryl BODIPY–C60
Triad
&8
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www.chemphyschem.org
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemPhysChem 0000, 00, 1 – 8
ÝÝ
These are not the final page numbers!