Synthesis and photophysics of silicon phthalocyanine-perylenebisimide triads connected through rigid and flexible bridges

Article abstract of DOI:10.1002/chem.201100320

Three new bisperylenebisimide-silicon phthalocyanine triads [(PBI) ₂-SiPcs 1, 2, and 3] connected with either rigid or flexible bridges were synthesized and characterized. A new synthetic approach to connect SiPc and PBI moieties through click chemistry produced triad 3 with an 80 % yield. In (PBI)₂-SiPc 1, PBI and SiPc are orthogonal and were connected with a rigid connector; triads 2 and 3 bear flexible aliphatic bridges, resulting in a tilted (2) or nearly parallel arrangement (3) of PBI and SiPc. Photoinduced intramolecular processes in these (PBI)₂-SiPcs were studied and the results are compared with those of the reference compounds SiPc-ref and PBI-ref. The occurrence of electron-transfer processes between the SiPc and PBI units was confirmed by time-resolved emission and transient absorption techniques. Charge-separated (CS) states with lifetimes of 0.91, 1.3 and 2.0 ns for triads 1, 2, and 3, respectively, were detected using femtosecond laser flash photolysis. Upon the addition of Mg(ClO₄)₂, an increase in the lifetime of the CS states to 59, 110 and 200 μs was observed for triads (PBI)₂-SiPcs 1, 2, and 3, respectively. The energy of the CS state (SiPc⁺-PDI^-/Mg²⁺) is lower than the energy of both silicon phthalocyanine (³SiPc*-PDI) and perylenebisimide (SiPc-³PDI*) triplet excited states, which decelerates the metal ion-decoupled electron-transfer process for charge recombination to the ground state, thus increasing the lifetime of the CS state. The photophysics of the three triads demonstrate the importance of the rigidity of the spacer and the orientation between donor and acceptor units.

Full text of DOI:10.1002/chem.201100320

FULL PAPER
DOI: 10.1002/chem.201100320
Synthesis and Photophysics of Silicon Phthalocyanine–Perylenebisimide
Triads Connected through Rigid and Flexible Bridges
F. Javier Cꢀspedes-Guirao,[a] Luis Martꢁn-Gomis,[a] Kei Ohkubo,[b]
Shunichi Fukuzumi,*[b, c] Fernando Fernꢂndez-Lꢂzaro,*[a] and ꢃngela Sastre-Santos*[a]
Dedicated to Prof. Dr. Dr. h.c. Michael Hanack on the occasion of his 80th birthday
Abstract: Three new bisperylenebis-
imide–silicon phthalocyanine triads
[(PBI)2–SiPcs 1, 2, and 3] connected
with either rigid or flexible bridges
were synthesized and characterized. A
new synthetic approach to connect
SiPc and PBI moieties through click
chemistry produced triad 3 with an
80% yield. In (PBI)2–SiPc 1, PBI and
SiPc are orthogonal and were connect-
ed with a rigid connector; triads 2 and
3 bear flexible aliphatic bridges, result-
ing in a tilted (2) or nearly parallel ar-
rangement (3) of PBI and SiPc. Photo-
induced intramolecular processes in
these (PBI)2–SiPcs were studied and
the results are compared with those of
the reference compounds SiPc-ref and
PBI-ref. The occurrence of electron-
transfer processes between the SiPc
and PBI units was confirmed by time-
resolved emission and transient absorp-
tion techniques. Charge-separated (CS)
states with lifetimes of 0.91, 1.3 and
2.0 ns for triads 1, 2, and 3, respective-
ly, were detected using femtosecond
laser flash photolysis. Upon the addi-
lifetime of the CS states to 59, 110 and
200 ms was observed for triads (PBI)2–
SiPcs 1, 2, and 3, respectively. The
+
C
Cꢀ
energy of the CS state (SiPc –PDI /
Mg2+) is lower than the energy of both
silicon phthalocyanine (3SiPc*–PDI)
and perylenebisimide (SiPc–3PDI*)
triplet excited states, which decelerates
the metal ion-decoupled electron-trans-
fer process for charge recombination to
the ground state, thus increasing the
lifetime of the CS state. The photophy-
sics of the three triads demonstrate the
importance of the rigidity of the spacer
and the orientation between donor and
acceptor units.
tion of MgACTHUNRGTNEUNG(ClO4)2, an increase in the
Keywords: click chemistry · peryl-
enebisimide · photoinduced elec-
tron transfer · photophysics · silicon
phthalocyanine
Introduction
interest for photochemical energy conversion and storage[2]
and for the construction of optoelectronic devices.[3] In these
cases, not only the selection of the building block matters,[4]
but also the distance,[5] the electronic coupling mediated by
the connecting unit,[6] the solvent polarity,[7] and the aggre-
gation status[8] can play an important role. Over the years,
we have been working with different electron-poor moiet-
ies,[9] especially with perylenebisimide (PBI), owing to its
strong absorption in the 450–600 nm region, its chemical
and thermal stabilities, and its ease of chemical modifica-
tion.[10,11] For this study, and in order to increase the electron
affinity, we have selected the 1,6,7,12-tetrachloro-substituted
PBI (Cl4PBI).
The art of designing and constructing molecular architec-
tures in the search for a controlled transfer of energy and/or
electrons has been developed by smart selection from a rela-
tively small number of building blocks,[1] thus leading to a
deeper knowledge of the photophysical insights, which is of
[a] F. J. Cꢀspedes-Guirao, Dr. L. Martꢁn-Gomis,
Prof. Dr. F. Fernꢂndez-Lꢂzaro, Prof. Dr. ꢃ. Sastre-Santos
Divisiꢄn de Quꢁmica Orgꢂnica Instituto de Bioingenierꢁa
Universidad Miguel Hernꢂndez, Elche 03202 (Spain)
Fax : (+34)966658351
E-mail: fdofdez@umh.es
As the electron-rich counterpart we use phthalocyanines
(Pcs),[12] which are the synthetic analogues of naturally oc-
curring porphyrins. Phthalocyanines have excellent light-har-
vesting abilities, at wavelengths at which the maximum of
the solar photon flux occurs, and are also chemically and
thermally stable. Among the phthalocyanines, zinc Pcs[11,13]
have been extensively investigated, because of their long-
lived and low-lying triplet excited states, which are of great
interest for use in energy-transfer systems, such as in photo-
dynamic therapy (PDT) for cancer treatment.[14] Silicon Pcs
also attract increasing interest because of their low tendency
to aggregate, which accounts for their high solubilities and
asastre@umh.es
[b] Dr. K. Ohkubo, Prof. Dr. S. Fukuzumi
Department of Material and Life Science
Graduate School of Engineering
Osaka University and ALCA (JST)
2–1 Yamada-oka, Suita, Osaka 565-0871 (Japan)
Fax : (+81)6-6879-7370
E-mail: fukuzumi@chem.eng.osaka-u.ac.jp
[c] Prof. Dr. S. Fukuzumi
Department of Bioinspired Science
Ewha Womans University, Seoul, 120-750 (Korea)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201100320.
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better photophysical properties (e.g., longer fluorescence
lifetimes), and the ease of chemical modification at the axial
positions.[15] SiPcs are one of the most promising classes of
Pc-based photosensitizers for PDT.[16,17] Recently, it has
been demonstrated that the use of bis(trihexylsilyl oxide)sili-
con–phthalocyanine and bis(trihexylsilyl oxide)silicon–naph-
thalocyanine as near-IR dyes in multicolored dye-sensitized
polymer/fullerene solar cells, enhances the power conversion
efficiency up to 4.3% compared to individual ternary blend
solar cells with a single dye. This behavior is probably due
to the fact that both dye molecules are located at the inter-
face where no unfavorable aggregation occurs.[18] Despite all
of these special characteristics, SiPcs have hardly been ex-
plored as donor compounds in photoinduced electron-trans-
fer processes.
For the purpose of this study, we axially link two Cl4PBI
electron-demanding units to a SiPc. This combination leads
to strong light absorption over the whole visible spectrum,
while allowing selective excitation of the desired subunits, as
the absorption ranges for each moiety are separated. This is
the first example of a covalently linked axial PBI–Pc system,
which can be compared with previously synthesized coordi-
natively linked axial[19] and covalently linked non-axial sys-
tems.[11a–c,20] Three different connecting units have been se-
lected that vary the orientation and rigidity between the two
different moieties, to gain further insight into the role of
these issues in the electron-transfer processes.
To date, the synthesis of SiPcs functionalized in the axial
positions has been mainly carried out by nucleophilic dis-
placement of chlorine atoms by hydroxy or carboxy substi-
tuted moieties, resulting in compounds with low to moderate
yields.[15] In this paper we have developed a new strategy to
connect SiPcs with PBI units in high yields using click
chemistry.
We report herein the synthesis and photophysics of three
new (PBI)2–SiPc triads 1–3. (PBI)2–SiPc triad 1 is connected
through a rigid benzene ring in such a way that the PBI and
the SiPc are orthogonal, while triads 2 and 3 bear flexible
aliphatic bridges. In the case of (PBI)2–SiPc 2 both units are
connected through a flexible linker that allows a tilted ori-
entation, while in (PBI)2–SiPc 3, the PBI and the SiPc moi-
eties are connected by means of a Huisgen reaction where
the 1,3-substitution in the triazole ring allows a nearly paral-
lel orientation between both moieties. To the best of our
knowledge, this is the first time that a SiPc has been func-
tionalized using a click chemistry reaction which opens a
new way for the functionalization of SiPcs.
between the tetrachloroperylene bisanhydride and equimo-
lar quantities of the corresponding aniline compounds.
Then, nucleophilic displacement of the two chlorine atoms
from the dichlorosilicon phthalocyanine afforded (PBI)2–
SiPc triads 1 and 2 in 5 and 15% yields, respectively.
The synthesis of (PBI)2–SiPc triad 3 relied on a well-
known click reaction, namely the copper-catalyzed [3+2]
Huisgen cycloaddition reaction between the alkyne 6 and
azide 7 (Scheme 2). The best results were obtained using
10% mol of sodium ascorbate and 5% of CuSO4·5H2O in a
4:1 THF:H2O mixture, and heating at 608C for 24 h. Under
these conditions, the desired (PBI)2–SiPc triad 3 was ob-
tained in 80% yield. SiPc 6 was obtained by reaction of the
SiPcCl2 with 5-hexynoic acid in 30% yield. PBI 7 was af-
forded by condensation of 3-azidopropylamine and 2-ethyl-
hexylamine with tetrachloroperylene bisanhydride, in 35%
yield.
Results and Discussion
Synthesis: The synthesis of triads 1–3 was accomplished
using different strategies. A conventional approach to the
axial functionalization of dichlorosilicon phthalocyanine
compounds was used for triads 1 and 2 (Scheme 1). First we
prepared the asymmetrically substituted carboxylic acid PBI
derivatives 4 and 5[21] by a one-step statistical condensation
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Silicon Phthalocyanine–Perylenebisimide Triads
FULL PAPER
Figure 1. 1H NMR spectrum (CDCl3, 300 MHz, 258C) of (PBI)2–SiPc
triad 3.
1
nine ring. Figure 1 shows, as an example, the H NMR spec-
trum of (PBI)2–SiPc triad 3 in deuterated chloroform. The
peaks corresponding to the two different sets of aromatic
protons of the phthalocyanine are located around 9.6–9.7
and 8.3–8.4 ppm, while the peaks corresponding to the pro-
tons of the perylenebisimide moiety are centered at 8.69
and 8.55 ppm. The integration of these signals, together with
the characteristic singlet of the triazole linker (6.20 ppm),
clearly indicate the success in the coupling between the
alkyne-substituted silicon phthalocyanine 6 and the azide-
substituted tetrachloroperylene 7 through a click reaction.
Scheme 1. Synthesis of (PBI)2–SiPc triads 1 and 2. a) 4-Aminobenzoic
acid, 2,6-diisopropylaniline, propionic acid, 1408C. b) 4-(4-Aminophe-
nyl)butyric acid, 2,6-diisopropylaniline, propionic acid, 1408C. c)
DichloroACHTUNGTRENNUNGsilicon phthalocyanine, dyglime, 1608C.
Spectroscopic and redox properties: Figure 2 shows the
comparison of the absorption spectra of (PBI)2–SiPc triads
1–3 with SiPc and PBI reference compounds 6 and 7. We
can clearly see a set of absorption bands between 486 and
520 nm, corresponding to the PBI moiety, and a sharp Q
band, centered at 685 nm, characteristic of non-aggregated
phthalocyanine compounds. A decrease in the extinction co-
efficient of the phthalocyanine Q-band is observed for triads
Scheme 2. Synthesis of (PBI)2–SiPc triad 3. a) 5-Hexynoic acid, dyglime,
1608C. b) 3-Azidopropylamine, 2-ethylhexylamine, toluene, 1108C. c)
Copper(II) sulfate pentahydrate, sodium ascorbate, tetrahydrofurane,
H2O, 60 8C.
1
All new compounds were characterized by H NMR, UV/
Vis, and FT-IR spectroscopies, mass spectrometry, and ele-
1
mental analysis. The good resolution of the H NMR spectra
of (PBI)2–SiPc triads 1–3 registered in deuterated chloro-
form clearly indicates the lack of aggregation phenomena in
solution, mainly due to the presence of the bulky perylene-
bisimide moieties in the axial positions of the phthalocya-
Figure 2. UV/Vis spectra in CHCl3 of SiPc 6, PBI 7 and (PBI)2–SiPc 1–3
triads.
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1 and 2, but not for triad 3. This effect could be explained
by a possible p–p interaction between the PBI units and the
phthalocyanine core as a consequence of the close distance
of both moieties; this interaction decreases as the length of
the linker between the electroactive units becomes longer.
Taking this into account, the absorption spectra of triads 1–3
can be considered as a reasonable superposition of the ab-
sorption spectrum of each component, which indicates a
weak, or inexistent, electronic interaction between the elec-
troactive chromophores in the ground state.
SiPc units, confirming the lack of electronic interaction be-
tween the electroactive moieties in the ground state, as al-
ready observed in the absorption spectra.
Theoretical calculations: HOMO and LUMO orbitals of
(PBI)2–SiPc triads 1–3 calculated with the optimized struc-
ture using the DFT method[22] are shown in Figure 4. The re-
sults indicate that the HOMO is localized on the SiPc
moiety, the LUMO is on one PDI moiety, and the LUMO+
1 is localized on the other PDI moiety.
The cyclic voltammograms in benzonitrile (PhCN) of
(PBI)2–SiPc triads 1–3, together with those of the reference
compounds, SiPc 6 and PBI 7, are shown in Figure 3. From
the shape of the voltammograms and the calculated reduc-
tion and oxidation potential values, we infer that the elec-
tronic interaction between the electroactive moieties is very
weak for all compounds. Only in triad 1, which has the
shortest linker of all the studied compounds, the interaction
could be slightly more intense due to the rigid nature of the
aromatic linker and the close distance between electroactive
moieties as previously detected by UV/Vis spectroscopy. In
all cases the one-electron oxidation and reduction waves are
virtually the superposition of those of the unlinked PBI and
Photoinduced charge separation: The photophysical behav-
ior of triads 1–3 was qualitatively investigated in PhCN by
steady-state fluorescence using 361 and 522 nm light excita-
tion, which selectively excites the SiPc and PBI entities, re-
spectively. As shown in Figure 5, the fluorescence spectrum
of SiPc reference 6 exhibits an emission band centered at
Figure 3. Cyclic voltammograms of a) SiPc 6, b) PBI 7, c) (PBI)2–SiPc
triad 1, d) (PBI)2–SiPc triad 2 and e) (PBI)2–SiPc triad 3, in deaerated
PhCN containing 0.10m Bu4NPF6.
Figure 4. HOMO, LUMO and LUMO+1 of a) (PBI)2–SiPc triad 1, b)
(PBI)2–SiPc triad 2 and c) (PBI)2–SiPc triad 3, calculated using DFT at
the B3LYP/3-21G level.
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Silicon Phthalocyanine–Perylenebisimide Triads
FULL PAPER
1
ty, suggests that the deactivation of PBI* occurs through a
non-radiative process as well, but its first step involves
energy transfer from the perylenebisimide to the phthalo-
cyanine unit. Photoinduced electron transfer was examined
by femtosecond laser flash photolysis measurements.
Figure 7 shows that 430 nm excitation of PBI 7 with a fem-
tosecond laser pulse yields a transient with absorptions at
830 nm and 980 nm which corresponds to the singlet excited
1
state PBI*.
Figure 5. Fluorescence spectra of SiPc 6 and (PBI)2–SiPc 1–3 in deaerat-
ed PhCN. Excitation wavelength=361 nm.
693 nm (1.79 eV). The axial linkage with the PBI units effi-
ciently quenches this emission band (Figure 5) suggesting a
non-radiative deactivation of the singlet excited state of
SiPc (1SiPc*; * denotes the excited state) according to previ-
ously reported data for singlet excited state values of PBI
and SiPc units.[15] The quenching rate constant for (PBI)2–
SiPc triads 1–3 is >5ꢆ1010 sꢀ1 from the efficient fluores-
cence quenching (>99%) and the fluorescence lifetime of
SiPc 6 (8.5 ns) (see Supporting Information Figure S1). The
intensity of the 1PBI* emission, centered at 550 nm
(2.25 eV) after 522 nm light excitation (selective excitation
of the PBI unit), dramatically decreases for triads 1–3, com-
pared to the emission intensity observed by exciting the PBI
reference compound 7 (Figure6). Such fluorescence quench-
ing in a polar solvent suggests either an energy- or electron-
transfer process.
Figure 7. Femtosecond transient absorption spectrum of PBI 7 in deaerat-
ed PhCN taken at 10 ps after 430 nm laser excitation.
The behavior of the (PBI)2–SiPc triads 1–3 is similar (Fig-
ures 8–10) to that of PBI 7. Thus, photoexcitation of a de-
aerated PhCN solution containing (PBI)2–SiPc
1 with
430 nm excitation affords, initially, the singlet excited state
of the perylene moiety, as indicated by the broad absorp-
tions centered at 830 and 980 nm (see Figure 8a). These ab-
sorptions slowly vanish, leaving sharper peaks at 580 and
+
C
850 nm, which are indicative of the presence of the SiPc
Interestingly, in the case of triad 1, a concomitant appear-
ance of a fluorescence emission band can be distinguished in
the area where the 1SiPc* emission maximum appears
(Figure 6, inset). The appearance of this fluorescence emis-
radical cation.[15d,e,h,23] The broad absorption around 980 nm
obscures the detection of the SiPc singlet excited state,
which should absorb at 950 nm;[15h] however, the fluores-
cence quenching results for triad 1 and our previous experi-
ence[15] support its formation. Thus, the transient absorption
1
sion band assigned to SiPc*, together with its weak intensi-
spectra in Figures 8–10 clearly indicate the formation of the
+
C
Cꢀ
CS state [PBI–SiPc –PBI ], in which one of the two PBI
units becomes the radical anion by electron transfer from
1SiPc* to PBI in the triads.
The energy-transfer rate constant from 1PBI* to 1SiPc*
was determined from the decay of the band at 980 nm for
triads 1–3. Rate constants of 6.0ꢆ1010 sꢀ1 for (PBI)2–SiPc
triad 1, 1.0ꢆ1011 sꢀ1 for (PBI)2–SiPc triad 2, and 1.2ꢆ1011 sꢀ1
for (PBI)2–SiPc triad 3 were determined, with lifetimes of
17, 10 and 8.3 ps, respectively (Figures 8b–10b). These data
are in accordance with the fluorescence quenching results.
The results indicate that the compounds with flexible
spacers, which allow a non-perpendicular orientation be-
tween the SiPc and the PDI moieties (2, 3), afford faster
energy-transfer rate constants (1.0–1.2ꢆ1011 sꢀ1).
The formation and decay profiles of the CS state of SiPc
triad 1 are different from those of triads 2 and 3. The rate
constants of formation and decay of the CS state of (PBI)2–
Figure 6. Fluorescence spectra of PBI 7 and (PBI)2–SiPc 1–3 in deaerated
PhCN. Excitation wavelength=522 nm.
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SiPc 1, determined from the rise and decay of the absorb-
ance at 850 nm (Figure 8c), are 1.3ꢆ109 and 1.1ꢆ109 sꢀ1,
respectively, leading to a CS lifetime of 0.91 ns. The ab-
sorbance decays of (PBI)2–SiPc triads 2 and 3 are fitted
to tri-exponential functions, as shown in Figures 9c and
10c, respectively. From the fast decay component in the
absorbance at 850 nm, due to SiPc·+, the rate constants of
formation of the CS state for triads 2 and 3 were deter-
mined to be 9.4ꢆ109 and 5.7ꢆ109 sꢀ1 respectively, which
is in agreement with the value determined from the fluo-
1
rescence quenching of SiPc* (>5ꢆ1010 sꢀ1). The lifetimes
of the CS state in PhCN for triads 2 and 3 are 1.3 and
2.0 ns respectively, obtained from the slow component of
the absorbance decay at 850 nm.
The presence of a flexible linker in the (PBI)2–SiPc
triads, together with a tilted orientation of the PDI units
versus the SiPc, affords high electron-transfer rate con-
stants to generate the CS state, but low recombination
rate constants. Hence the CS lifetime is the longest in
triad 3 (2.1 ns), followed by triad 2, (1.3 ns) and then
triad 1 (0.9 ns).
The results of nanosecond laser flash photolysis with
photoexcitation at 355 nm indicate that the same photo-
physical decay pathways are followed in the three
(PBI)2–SiPc triads. As shown in Figure 11a for triad 3,
the absorption bands at 530 and 760 nm corresponding to
Figure 8. a) Femtosecond transient absorption spectra of (PBI)2–SiPc 1 in de-
aerated PhCN at 298 K after 430 nm laser excitation. b) Time profile of absorb-
ance at 980 nm. c) Time profile of absorbance at 850 nm. Gray lines represent
a tri-exponential fit.
3
3
the triplet excited states, SiPc* and PBI*, respectively,
are detected at 10 ms after laser excitation. The decay of
3
3SiPc* at 530 nm is significantly faster than that of PBI*.
3
The transient absorption band of PBI* remains at 70 ms
(grey plot in Figure 11a). From the decay of the band of
3SiPc* (for triad 3 see Figure 11b) the lifetime of the
(PBI)2–3SiPc* species for triads 1–3 are determined to be
50, 51 and 100 ms, respectively (see Supporting Informa-
tion Figures S2 and S3 for triads 1 and 2, respectively).
This decay process is assigned to the energy transfer from
3SiPc* to PBI forming SiPc–3PBI*.
Nanosecond laser flash photolysis with photoexcitation
at 355 nm, of (PBI)2–SiPc triads 1–3 in PhCN after the
addition of magnesium perchlorate [MgACHTNURTGNE(UNG ClO4)2], yielded
quite different results from the previous ones. As shown
in Figure 12a for (PBI)2–SiPc triad 3, the bands observed
at 580 and 850 (SiPc·+) confirm the formation of the CS
state. From the decay of the bands at 850 nm the CS-
state lifetimes are calculated to be 59, 110 and 210 ms for
(PBI)2–SiPc triads 1–3, respectively (see Figure 12b for
triad 3 and Supporting Information Figures S4 and S5 for
triads 1 and 2, respectively). Again, the longer lived CS
state corresponds to the (PBI)2–SiPc triad 3, confirming
that the quasi-parallel location of the two moieties
through a non-rigid linker hinders the back electron-
transfer process. According to the literature,[15d,e,h] the
energy of the triplet excited state of SiPc is 1.26 eV. The
CS-state energy for (PBI)2–SiPc 3 (1.38 eV), determined
from Eox of SiPc (0.96 V vs. SCE) and Ered of PBI
(ꢀ0.42 V vs. SCE), is higher than the energy of the triplet
excited state of SiPc [3SiPc*–(PBI)2]. The triplet excited-
Figure 9. a) Femtosecond transient absorption spectra of (PBI)2–SiPc 2 in de-
aerated PhCN at 298 K after 430 nm laser excitation. b) Time profile of absorb-
ance at 980 nm. c) Time profile of absorbance at 850 nm. Gray lines represent
a tri-exponential fit.
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Silicon Phthalocyanine–Perylenebisimide Triads
FULL PAPER
Scheme 3. Energy diagram for (PBI)2–SiPc triads 1–3.
Conclusion
We have synthesized, for the first time, triad systems
based on SiPc and PBI building blocks. A new strategy
using click chemistry has been developed to connect SiPc
and PBI in triad 3 in a high yield (80%). This strategy
opens a new route to the functionalization of SiPc. The
Figure 10. a) Femtosecond transient absorption spectra of (PBI)2–SiPc 3 in de-
aerated PhCN at 298 K after 430 nm laser excitation. b) Time profile of absorb-
ance at 980 nm. c) Time profile of absorbance at 850 nm. Gray lines represent
a tri-exponential fit.
state energy of PBI (PBI–SiPc–3PBI*, 1.07 eV)[24] is also
lower than the energy of the CS state. The CS-state energies
for (PBI)2–SiPc 1 (1.38 eV) and (PBI)2–SiPc 2 (1.34 eV) are
also higher in energy than 3SiPc*–(PBI)2 and PBI–
SiPc–3PBI*. In the presence of magnesium ions, however,
the one-electron reduction potential of PBI is shifted from
ꢀ0.44 V versus SCE to +0.14 V (Figure 13).
+
The energy of the CS state (PBI–SiPc –PBI /Mg2+) is
0.81 eV, which is now lower than the energy of the SiPc trip-
let excited state, and results in the deceleration of the metal
ion-decoupled back electron transfer to the ground state
which increases the lifetime of the CS state.[1b]
C
Cꢀ
Scheme 3 summarizes the energy diagram of the photoin-
duced events in (PBI)2–SiPc 1–3 triads, in which one accept-
or unit is omitted for clarity. In each case, energy transfer
1
1
occurs from the PBI* to the SiPc*, followed by photoin-
1
duced electron transfer from the SiPc* unit to the acceptor
moiety to produce the CS state. There are three pathways
for the charge recombination (CR): CR to 3PBI*, CR to
3SiPc*, and CR to the ground state. The third pathway is un-
likely to occur because, as previously described, the decay
of the CS state affords the phthalocyanine triplet excited
3
state SiPc*.[15e]
The rate constants and CS state lifetimes for the (PBI)2–
SiPc triads are listed in Table 1. According to the data, the
back electron transfer for triad 3 is slower as a consequence
of the flexible linker and the orientation of the two electro-
active subunits.
Figure 11. a) Nanosecond transient absorption spectra of (PBI)2–SiPc 3 in
deaerated PhCN at 298 K after 355 nm laser excitation. b) Time profile
of absorbance at 530 nm. Gray line represents a mono-exponential fit.
Chem. Eur. J. 2011, 17, 9153 – 9163
ꢅ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
9159

ꢃ. Sastre-Santos, S. Fukuzumi, F. Fernꢂndez-Lꢂzaro et al.
Table 1. Rate constants of singlet energy transfer (k1), electron transfer
(k2), back electron transfer (k3) and triplet energy transfer of (PBI)2–SiPc
Upon the addition of MgACHTNUGTRNEUGN(ClO4)2, an increase in the CS life-
times of 1, 2, and 3 was observed, with values of 59, 110,
triads 1–3 and CS lifetimes (t) with and without Mg2+
.
and 210 ms, respectively. The energy of the CS state (PBI-
SiPc –PBI /Mg2+) becomes lower than the energy of the
silicon phthalocyanine triplet excited state (PBI–3SiPc*–
PBI), resulting in deceleration of the metal-ion-decoupled
back-electron-transfer process to the ground state, thus in-
creasing the lifetime of the CS state. The photophysics of
the three triads demonstrate the importance in photoin-
duced events of the rigidity of the spacer and the orientation
between donor and acceptor units.
C
Cꢀ
A
E
N
+
k1 [sꢀ1
k2 [sꢀ1
k3 [sꢀ1
k4 [sꢀ1
]
]
]
]
6.0ꢆ1010
1.3ꢆ109
1.1ꢆ109
2.0ꢆ104
0.9
1.0ꢆ1011
9.4ꢆ109
8.0ꢆ108
2.0ꢆ104
1.3
1.2ꢆ1011
5.7ꢆ109
5.0ꢆ108
9.6ꢆ103
2.0
t(CS) [ns]
t(CS) with Mg2+ [ms]
59
110
210
Experimental Section
General: All chemicals were reagent-grade, purchased from commercial
sources, and used as received, unless otherwise specified. Column chro-
matography was performed using SiO2 (40–63 mm) TLC plates coated
with SiO2 60F254 and visualized by UV light. NMR spectra were mea-
sured with a Bruker AC 300. UV/Vis spectra were recorded with a
Helios Gamma spectrophotometer. Fluorescence spectra were recorded
with a Perkin–Elmer LS 55 Luminescence Spectrometer and IR spectra
with a Nicolet Impact 400D spectrophotometer. Mass spectra were ob-
tained from a Bruker Reflex III matrix-assisted laser desorption/ioniza-
tion time of flight (MALDI-TOF) and from a VG AutoSpec instrument
(FAB). Elemental analyses were performed on a LECO CHNS-932 ele-
mental analyzer.
PBI derivative 4: A mixture of 1,6,7,12-tetrachloroperylene-3,4:9,10-tet-
racarboxyanhydride (3 g, 5.66 mmol) and propionic acid (120 mL) was
stirred at RT for 15 min, then 2,6-diisopropylaniline (1.01 mg, 5.7 mmol)
and 4-aminobenzoic acid (782 mg, 5.7 mmol) were added. The mixture
was stirred at 1408C under argon atmosphere for 24 h. After cooling, the
crude product was poured over an ice/water mixture, filtered, washed
with cold water several times and, finally, purified twice by flash chroma-
tography (SiO2, CH2Cl2!CH2Cl2/acetone 8:2), to yield an orange solid
(690 mg, 24% yield). 1H NMR (300 MHz, CDCl3, 258C, TMS): d=8.78
(s, 2H; 2ꢆH-PBI), 8.77 (s, 2H; 2ꢆH-PBI), 8.35 (d, J=8.5 Hz, 2H; 2ꢆH-
Ar), 7.52 (t, J=8.1 Hz, 1H; H-Ar’), 7.48 (d, J=8.5 Hz, 2H; 2ꢆH-Ar),
7.38 (d, J=8.1 Hz, 2H; 2ꢆH-Ar’), 2.80–2.68 (m, 2; 2ꢆCH-(CH3)2), 1.24–
1.16 ppm (m,12H; 4ꢆCH3); 13C NMR (75 MHz, CDCl3 9:1 CD3CN,
258C, TMS): d=166.4, 161.9, 161.8, 145.3, 138.6, 135.2, 135.1, 132.9,
132.8, 131.3, 131.2, 130.7, 130.3, 129.7, 129.5, 128.6, 128.5, 123.8, 123.5,
123.3, 122.9, 122.8, 116.3, 28.8, 23.5 ppm; IR (KBr): n˜ =2962, 2928, 1715
(C=O acid), 1677 (C=O imide) 1588, 1411, 1382, 1314, 1293, 1240, 1189,
801, 748, 686, 546 cmꢀ1; UV/Vis (CH2Cl2): lmax (log e)=231 (4.89), 269
(4.47), 427 (3.96), 487 (4.40), 521 nm (4.56); MS (MALDI-TOF): m/z:
807 [M+H]+; elemental analysis calcd (%) for C43H26Cl4N2O6.H2O: C
62.47, H 3.42, N 3.39; found C 62.24, H 3.82, N 3.23.
Figure 12. a) Nanosecond transient absorption spectra of (PBI)2–SiPc 3 in
deaerated PhCN containing 10 mm Mg(ClO4)2 at 298 K after 355 nm
laser excitation. b) Time profile of absorbance at 850 nm. Gray line rep-
resents a mono-exponential fit.
AHCTUNGTRENNUNG
AHCTUNTGERNGUN(N PBI)2–SiPc 1: SiPcCl2 (40 mg, 0.065 mmol) and PBI 4 (230 mg,
0.28 mmol) in dyglime (5 mL) were stirred at 1608C under argon atmos-
phere for 12 h. After cooling, the crude product was poured over water,
filtered, washed with water several times and, finally, purified by flash
chromatography (SiO2, CH2Cl2/acetone 20:1!CH2Cl2/MeOH 10:1) to
yield a dark green solid (7 mg, 5% yield). 1H NMR (300 MHz, CDCl3,
258C, TMS): d=9.80–9.76 (m, 8H; 8ꢆH-Pc), 8.68 (s, 4H; 4ꢆH-PBI),
8.45–8.41 (m, 8H; 8ꢆH-Pc), 8.41 (s, 4H; 4ꢆH-PBI), 7.50 (t, J=7.6 Hz,
2H; 2ꢆH-Ar’), 7.33 (d, J=7.6 Hz, 4H; 4ꢆH-Ar’), 6.22 (d, J=8.6 Hz,
4H; 4ꢆH-Ar), 5.39 (d, J=8.6 Hz, 4H; 4ꢆH-Ar), 2.74–2.61 (m, 4H; 4ꢆ
CH-(CH3)2), 1.19–1.12 ppm (m, 24H; 8ꢆCH3); 13C NMR (75 MHz,
CDCl3, 258C, TMS): d=162.2, 161.5, 158.3, 150.3, 145.5, 136.5, 135.6,
135.5, 135.3, 133.4, 133.3, 133.0, 131.6, 131.5, 131.4, 131.3, 129.8, 128.8,
128.7, 127.4, 126.9, 124.2, 124.1, 123.8, 123.3, 123.1, 122.8, 29.3, 24.0 ppm;
IR (KBr): n˜ =2961, 1716 (C=O acid), 1679 (C=O imide) 1588, 1431,
1380, 1336, 1291, 1240, 1188, 1166, 1123, 1082, 914, 805, 761, 737, 686,
546 cmꢀ1; UV/Vis (CH2Cl2): lmax (log e)=232 (5.23), 267 (4.89), 359
Figure 13. Cyclic voltammogram of PBI 7 (1.0 mm) in the presence of
MgACHTUNGTRENNUNG .
(ClO4)2 (10 mm) in deaerated PhCN at 298 K. Sweep rate: 0.1 Vsꢀ1
photoinduced electron-transfer processes between SiPc and
the PBI were measured by time-resolved emission and tran-
sient absorption techniques. By using femtosecond laser
flash photolysis, the CS lifetimes of the triads (PBI)2-SiPc 1–
3 were determined to be 0.91, 1.3, and 2.0 ns, respectively.
9160
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ꢅ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 9153 – 9163

Silicon Phthalocyanine–Perylenebisimide Triads
FULL PAPER
(4.79), 427 (4.31), 488 (4.72), 521 (4.88), 617 (4.47), 655 (4.41), 686 nm
PBI derivative 7: 1,6,7,12-Tetrachloroperylene-3,4:9,10-tetracarboxyanhy-
dride (2 g, 3.77 mmol), 3-azidopropylamine (517 mg, 4 mmol), 2-ethylhex-
ylamine (517 mg, 4 mmol) and 25 mL of dry toluene, were stirred at
1108C under argon atmosphere for 24 h. After cooling, the solvent was
evaporated and the crude product was purified twice by flash chromatog-
raphy (SiO2, CH2Cl2!CH2Cl2/acetone 20:3) to yield an orange solid
(950 mg, 35% yield). 1H NMR (300 MHz, CDCl3, 258C, TMS): d=8.69
(s, 2H, 2xH-PBI), 8.68 (s, 2H; 2ꢆH-PBI), 4.33 (t, J=7.1 Hz, 2H; N-CH2-
CH2-CH2-N3), 4.23–4.08 (m, 2H; N-CH2-CH-R’), 3.47 (t, J=6.7 Hz, 2H;
-CH2-N3), 2.66 (q, J=6.9 Hz, 2H; N-CH2-CH2-CH2-N3), 2.00–1.88 (m,
1H; -CH-), 1.49–1.22 (m, 8H; 4ꢆ-CH2-), 1.02–0.86 ppm (m, 6H; 2ꢆ
CH3); 13C NMR (75 MHz, CDCl3, 258C, TMS): d=162.6, 162.3, 135.5,
135.3, 133.1, 133.0, 131.5, 131.4, 128.8, 128.5, 123.4, 123.3, 122.9, 49.4,
44.6, 38.4, 38.0, 30.7, 28.7, 28.6, 27.6, 24.0, 23.1, 14.1, 10.6 ppm; IR (KBr):
n˜ =2957, 2928, 2096 (N3), 1704 (C=O imide), 1665 (C=O imide), 1588,
1493, 1434, 1392, 1368, 1349, 1286, 1236, 1172, 911, 805, 748, 686,
547 cmꢀ1; UV/Vis (CH2Cl2): lmax (log e)=232 (4.83), 278 (4.44), 426
(4.05), 486 (4.45), 519 nm (4.61); MS (MALDI-TOF): m/z: 721 [M]+ and
722 [M+H]+; elemental analysis calcd (%) for C35H27Cl4N5O4.1/2H2O: C
57.31, H 3.85, N 9.55; found C 57.35, H 3.71, N 9.67.
(5.22); HRMS (MALDI-TOF): m/z: calcd for
2150.2195 [M]+; found: 2150.2209; elemental analysis calcd (%) for
118H66Cl8N12O12Si.6H2O: C 62.61, H 3.47, N 7.43; found C 62.65, H 3.67,
C118H66Cl8N12O12Si:
C
N 6.93.
PBI derivative 5:[21] A mixture of 1,6,7,12-tetrachloroperylene-3,4:9,10-
tetracarboxyanhydride (3 g, 5.66 mmol) and 100 mL of propionic acid
was stirred at RT for 15 min, then 2,6-diisopropylaniline (1 g, 5.66 mmol)
and 4-(4-aminophenyl)-butyric acid (1.05 mg, 5.66 mmol) were added.
The mixture was stirred at 1408C under argon atmosphere for 24 h. After
cooling, the crude product was poured over an ice/water mixture, filtered,
washed with cold water several times and, finally, purified twice by flash
chromatography (SiO2, CH2Cl2!CH2Cl2/acetone 10:1), to yield an
orange solid (1.2 g, 25% yield). 1H NMR (300 MHz, CDCl3, 258C,
TMS): d=8.77 (s, 2H; 2ꢆH-PBI), 8.75 (s, 2H; 2ꢆH-PBI), 7.53 (t, J=
7.8 Hz, 1H; H-Ar), 7.43 (d, J=8.3 Hz, 2H; 2ꢆH-Ar’), 7.37 (d, J=7.8 Hz,
2H; 2ꢆH-Ar), 7.25 (d, J=8.3 Hz, 2H; 2ꢆH-Ar’), 2.87–2.66 (m, 4H; Ar-
CH2- + 2ꢆCH-(CH3)2), 2.49 (t, J=7.30 Hz, 2H; CH2-CO2H), 2.16–2.01
(m, 2H; Ar-CH2-CH2-CH2-CO2H) 1.23–1.15 ppm (m, 12H; 4ꢆCH3);
13C NMR (75 MHz, CDCl3, 258C, TMS): d=178.1, 162.5, 162.3, 145.6,
142.4, 135.6, 135.5, 133.4, 133.3, 132.4, 131.7, 131.6, 130.0, 129.9, 129.7,
128.9, 128.8, 128.4, 124.3, 123.9, 123.7, 123.5, 123.2, 34.8, 33.2, 29.3, 26.0,
24.0. ppm; IR (KBr): n˜ =2962, 2929 1713 (C=O acid), 1677 (C=O imide)
1588, 1512, 1411, 1382, 1315, 1297, 1241, 1191, 1149, 843, 805, 747, 687,
547 cmꢀ1; UV/Vis (CH2Cl2): lmax (log e)=232 (4.9), 271 (4.63), 427 (4.05),
487 (4.47), 521 nm (4.63); MS (MALDI-TOF): m/z: 848 [M]+; elemental
analysis calcd (%) for C46H32Cl4N2O6.H2O: C 63.61, H 3.95, N 3.23;
found C 63.44, H 3.94, N 3.30.
AHCTUNGRTEG(NUNN PBI)2-SiPc 3: SiPc 6 (15 mg, 0.02 mmol) and PBI 7 (32 mg, 0.04 mmol)
were suspended in a 4:1 THF/H2O mixture (5 mL), and treated with
CuSO4.5H2O (5% mol, 0.54 mg, 0.002 mmol) and sodium ascorbate
(10% mol, 0.85 mg, 0.004 mmol). The mixture was stirred at 608C for
24 h. After cooling, the solvent was evaporated and the crude product
was purified by flash chromatography (SiO2, CH2Cl2/acetone 20:2!
CH2Cl2/acetone 20:3) to yield a dark green solid (35 mg, 80% yield).
1H NMR (300 MHz, CDCl3, 258C, TMS): d=9.72–9.63 (m, 8H; 8ꢆH-
Pc), 8.69 (s, 4H; 4ꢆH-PDI), 8.55 (s, 4H; 4ꢆH-PDI), 8.40–8.30 (m, 8H;
8ꢆH-Pc), 6.20 (s, 2H; 2ꢆH-triazole), 4.22–4.06 (m, 12H; 6ꢆN-CH2),
2.23–2.11 (m, 4H; 2ꢆN-CH2-CH2), 2.03–1.90 (m, 2H; 2ꢆCH), 1.49–1.20
ACHTUNGTRENNUNG(PBI)2-SiPc 2: SiPcCl2 (50 mg, 0.082 mmol) and PBI 5 (278 mg,
0.33 mmol) in dyglime (3 mL) were stirred at 1608C under argon atmos-
phere for 12 h. After cooling, the crude product was poured over water,
filtered, washed with water several times and, finally, purified by flash
chromatography (SiO2, CH2Cl2/acetone 20:1!CH2Cl2/acetone/MeOH
(m, 16H; 8ꢆCH2), 1.03–0.75 (m, 16H; 4ꢆCH3
+ 2ꢆCH2-triazole),
ꢀ0.46 (m, 4H; 2ꢆO2C-CH2-CH2). 0.61 ppm (t, J=7.5 Hz, 4H; 2ꢆO2C-
CH2-CH2); 13C NMR (75 MHz, CDCl3, 258C, TMS): d=166.7, 162.6,
162.1, 150.0, 146.4, 135.6, 135.5, 135.3, 133.0, 132,9, 131.5, 131.3, 128.8,
128.4, 124.0, 123.3, 123.2, 123.1, 122.7, 120.0, 47.7, 44.6, 38.0, 33.1, 30.7,
28.6, 28.4, 24.0, 23.9, 23.1, 23.0, 22.5, 14.1, 10.6 ppm; IR (KBr): n˜ =2955,
2928, 1705 (C=O imide), 1666 (C=O imide), 1589, 1432, 1391, 1337, 1288,
1237, 1165, 1123, 1082, 914, 805, 738, 686, 546 cmꢀ1; UV/Vis (CH2Cl2):
lmax (log e)=230 (5.28), 279, (4.88), 360 (4.87), 426 (4.37), 486 (4.74), 520
(4.90), 616 (4.56), 655 (4.49), 686 nm (5.35); HRMS (MALDI-TOF): m/z:
calcd for C114H84Cl8N18O12Si: 2204.3787 [M]+; found: 2204.3788; elemen-
tal analysis calcd (%) for C114H84Cl8N18O12Si.2H2O: C 60.97, H 3.95, N
11.23; found C 60.92, H 3.83, N 11.29.
9:1:0.2) to yield
a
dark green solid (27 mg, 15% yield). 1H NMR
(300 MHz, CDCl3, 258C, TMS): d=9.76–9.69 (m, 8H; 8ꢆH-Pc), 8.77 (s,
4H; 4ꢆH-PBI), 8.72 (s, 4H; 4ꢆH-PBI), 8.43–8.37 (m, 8H; 8ꢆH-Pc),
7.54 (t, J=7.9 Hz, 2H; 2ꢆH-Ar’), 7.34 (d, J=7.9 Hz, 4H; 4ꢆH-Ar’), 6.81
(d, J=8.3 Hz, 4H; 4ꢆH-Ar), 6.31 (d, J=8.3 Hz, 4H; 2ꢆH-Ar), 2.75 (m,
4H; 4ꢆCH-(CH3)2), 1.24–1.13 (m, 24H, 8ꢆCH3), 0.88 (t, J=7.2 Hz, 4H;
2ꢆAr-CH2), ꢀ0.34 to ꢀ0.54 ppm (m, 8H, 2ꢆ-CH2-CH2-CO2H);
13C NMR (75 MHz, CDCl3, 258C, TMS): d=166.8, 162.4, 162.3, 150.1,
145.6, 142.0, 135.6, 135.7, 135.6, 135.5, 133.4, 133.2, 131.7, 131.6, 134.5,
131.4, 130.1, 129.8, 128.9, 128.8, 128.7, 127.6, 124.3, 124.1, 123.9, 123.6,
123.5, 123.2, 33.8, 33.0, 29.3, 24.3, 24.0 ppm; IR (KBr): n˜ =2960, 2926,
1715 (C=O acid), 1678 (C=O imide) 1588, 1431, 1381, 1337, 1314, 1292,
1240, 1190, 1123, 1082, 914, 805, 737, 687, 546 cmꢀ1; UV/Vis (CH2Cl2):
lmax (log e)=231 (5.28), 269 (4.93), 360 (4.85), 426 (4.38), 487 (4.80), 520
(4.95), 616 (4.56), 654 (4.49), 685 nm (5.26); HRMS (MALDI-TOF): m/z:
calcd for C124H78Cl8N12O12Si: 2234.3165 [M]+; found: 2234.3134; elemen-
tal analysis calcd (%) for C124H78Cl8N12O12Si.4H2O: C 64.50, H 3.90, N
7.22; found C 63.14, H 3.93, N 7.02.
Laser flash photolysis: A solution of ZnPc–PBI in MeCN was excited by
a Panther OPO pumped by Nd:YAG laser (Continuum, SLII-10, 4–6 ns
fwhm, 1.5 and 3.0 mJpulseꢀ1) at l=531 nm. The transient absorption
measurements were performed using a continuous xenon lamp (150 W)
and an InGaAs-PIN photodiode (Hamamatsu 2949) as the probe light
and detector, respectively. The output from the photodiodes and a photo-
multiplier tube was recorded with a digitized oscilloscope (Tektronix,
TDS3032, 300 MHz). Femtosecond transient absorption spectroscopy ex-
periments were conducted using an ultrafast source (Integra-C, Quantro-
nix Corp.), an optical parametric amplifier (TOPAS, Light Conversion
Ltd.) and a commercially available optical detection system (Helios, Ul-
trafast Systems LLC). The source for the pump and probe pulses were
derived from the fundamental output of Integra-C (780 nm, 2 mJpulseꢀ1
and 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 fre-
quency mixers, resulting in a 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 as-
sembled from the time-resolved spectral data. All measurements were
conducted at 298 K. The transient spectra were recorded using fresh solu-
tions in each laser excitation.
SiPc 6: SiPcCl2 (100 mg, 0.16 mmol) and 5-hexynoic acid (1.02 g,
9.06 mmol) in dyglime (2 mL) were stirred at 1608C under argon atmos-
phere for 6 h. After cooling, the crude product was poured over water,
filtered, washed with water several times and, finally, purified by flash
chromatography (SiO2, CH2Cl2) to yield a dark blue solid (39 mg 31%
yield). 1H NMR (300 MHz, CDCl3, 258C, TMS): d=9.75–9.65 (m, 8H;
ꢁ ꢀ
8ꢆH-Pc), 8.42–8.34 (m, 8H; 8ꢆH-Pc), 1.18 (t, J=2.7 Hz, 2H; 2ꢆC C
ꢀ ꢁ ꢀ
H), 0.49–0.42 (m, 4H; 2ꢆCH2 C C H), ꢀ0.53–(ꢀ0.61) ppm (m, 8H; 2ꢆ
-CH2-CH2-CO2H); 13C NMR (75 MHz, CDCl3, 258C, TMS): d=166.3,
150.0, 135.6, 131.3, 124.0, 82.5, 67.7, 32.8, 21.7, 16.1 ppm; IR (KBr): n˜ =
ꢀ ꢁ ꢀ
3304 ( C C H), 2964, 1680, 1528, 1474, 1426, 1351, 1336, 1288, 1236,
1161, 1122, 1081, 1059, 914, 762, 732, 664, 536 cmꢀ1; UV/Vis (CH2Cl2):
lmax (log e)=360 (4.87), 615 (4.59), 653 (4.52), 684 nm (5.35); MS
(MALDI-TOF): m/z: 762 [M]+; elemental analysis calcd (%) for
C44H30N8O4Si.1/2H2O: C 68.38, H 4.04, N 14.50; found C 68.39, H 4.02, N
14.61.
For nanosecond laser flash photolysis experiments, deaerated solutions of
the dyad were excited by a Panther OPO equipped with a Nd:YAG laser
Chem. Eur. J. 2011, 17, 9153 – 9163
ꢅ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
9161

ꢃ. Sastre-Santos, S. Fukuzumi, F. Fernꢂndez-Lꢂzaro et al.
(Continuum, SLII-10, 4–6 ns fwhm) at l=430 nm with the power of
10 mJpulseꢀ1. The photochemical reactions were monitored by continu-
ous exposure to a Xe-lamp (150 W) as a probe light and a photomultipli-
er tube (Hamamatsu 2949) as a detector. The transient spectra were re-
corded using fresh solutions for each laser excitation. The solution was
deoxygenated by argon purging for 15 min prior to the measurements.
[8] a) P. Samorꢇ, X. Yin, N. Tchebotareva, Z. Wang, T. Pakula, F.
Jꢈckel, M. D. Watson, A. Venturini, K. Mꢉllen, J. P. Rabe, J. Am.
Chem. Soc. 2004, 126, 3567–3575; b) M. J. Ahrens, L. E. Sinks, B.
Rybtchinski, W. Liu, B. A. Jones, J. M. Giaimo, A. V. Gusev, A. J.
Goshe, D. M. Tiede, M. R. Wasielewski, J. Am. Chem. Soc. 2004,
126, 8284–8294; c) F. Wꢉrthner, Z. Chen, F. J. M. Hoeben, P. Oss-
wald, C-C. You, P. Jonkheijm, J. V. Herrikhuyzen, A. P. H. J. Schen-
ning, P. P. A. M. van der Schoot, E. W. Meijer, E. H. A. Beckers,
S. C. J. Meskers, R. A. J. Janssen, J. Am. Chem. Soc. 2004, 126,
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sen, J. Am. Chem. Soc. 2006, 128, 649–657.
Theoretical calculations: Density-functional theory (DFT) calculations
were performed on a COMPAQ DS20E computer. Geometry optimiza-
tions of (PBI)2–SiPc 1–3 were carried out using the Becke3LYP function-
al and 3-21G basis set,[25–27] with the restricted Hartree–Fock (RHF) for-
malism as implemented in the Gaussian 03 program Revision C.02.
Graphical outputs of the computational results were generated with the
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Acknowledgements
This work was partially supported by Grants-in-Aid from the Ministry of
Education, Culture, Sports, Science and Technology, Japan (Nos.
21750146 and 20108010), KOSEF/MEST through WCU project (R31-
2008-000-10010-0), and by Grants from MICINN, FEDER, and Generali-
tat Valenciana (Consolider-Ingenio 2010 project HOPE CSD2007-00007,
CTQ2007-67888/BQU, CTQ2008-05901/BQU, CTQ2010-20349, ACOMP/
2009/039 and ACOMP/2009/056). F.J.C.-G. thanks the Spanish Govern-
ment MICINN for a FPU fellowship. L.M.G. thanks the Global Educa-
tion and Research Center for Bio-Environmental Chemistry of Osaka
University for stage grants.
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Received: January 28, 2011
Published online: June 28, 2011
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9163