BODIPY-tetrazine multichromophoric derivatives

Article abstract of DOI:10.1002/ejoc.200900874

New dyes based on BODIPY and tetrazine fluorophores con-nected through a phenyl spacer have been synthesized and their absorption, emission and electrochemical properties characterized. BODIPY can be reversibly oxidized into a stable cation radical whereas tetrazine can be reduced to a stable anion radical. The electrochemical and absorption studies demonstrate that both fluorophores behave indepen-dently. The bichromophoric compounds show an expected very weak emission by the BODIPY core that is quenched by the phenoxytetrazine mainly through energy transfer. DFT calculations and spectroelectrochemistry experiments dem-onstrate that photoinduced electron transfer and energy transfer remain possible when the tetrazine moiety is re-duced electrochemically, which prevents switching on of the fluorescence of the BODIPY unit.

Full text of DOI:10.1002/ejoc.200900874

FULL PAPER
DOI: 10.1002/ejoc.200900874
BODIPY-Tetrazine Multichromophoric Derivatives
Cécile Dumas-Verdes,[a] Fabien Miomandre,*[a] Eve Lépicier,[a] Olivier Galangau,[a]
Thanh Truc Vu,[a] Gilles Clavier,[a] Rachel Méallet-Renault,[a] and Pierre Audebert*[a]
Keywords: Heterocycles / Dyes/Pigments / Fluorescence / Electrochemistry / Density functional calculations / Chromo-
phores
New dyes based on BODIPY and tetrazine fluorophores con-
nected through a phenyl spacer have been synthesized and
their absorption, emission and electrochemical properties
characterized. BODIPY can be reversibly oxidized into a
stable cation radical whereas tetrazine can be reduced to a
stable anion radical. The electrochemical and absorption
studies demonstrate that both fluorophores behave indepen-
dently. The bichromophoric compounds show an expected
very weak emission by the BODIPY core that is quenched by
the phenoxytetrazine mainly through energy transfer. DFT
calculations and spectroelectrochemistry experiments dem-
onstrate that photoinduced electron transfer and energy
transfer remain possible when the tetrazine moiety is re-
duced electrochemically, which prevents switching on of the
fluorescence of the BODIPY unit.
tion coefficient of TZ is rather low. Among other possible
candidates as redox-switchable fluorophores, BODIPY (4-
difluoro-4-bora-3a,4a-diaza-s-indacene) derivatives are
interesting because of their very good spectroscopic proper-
ties, namely strong UV/Vis absorption and quite sharp
fluorescence bands with high quantum yields (Φf Ͼ 0.7).
They are also relatively insensitive to the polarity and pH
of their environment and small modifications of their struc-
tures enable tuning of their fluorescence features.[8] Their
synthesis is relatively straightforward starting from pyrrole
heterocycles and they can be post-modified at various posi-
tions even though the synthesis and photophysical proper-
ties of the fully unsubstituted BODIPY core has been re-
ported only very recently.[9] Consequently, these dyes are
widely used to label proteins[10] and DNA.[11] Other appli-
cations use BODIPY dyes as fluorescent switches,[12]
chemosensors,[13] laser dyes[14] and solar cell concentra-
tors.[15] BODIPY is also interestingly used in dyads[16] and
multichromophoric or oligomeric fluorescent com-
pounds[17] in which the intrinsic properties of BODIPY can
be tuned. Cakmak and Akkaya have described some BOD-
IPY oligomers[17b] in which the boradiazaindacene dyes
were converted into phenylethynyl-BODIPY oligomers. As
the number of repeating units increases, peak absorption
and emission wavelengths are shifted to the red end of the
visible spectrum. Such oligomers are very bright red-emit-
ting fluorophores. Arbeloa and co-workers designed multi-
chromophoric dyes with borondipyrromethene (BODIPY)
and poly-p-phenylene (di- and tri-p-phenylene) groups in
the same molecule.[18] One of the bichromophoric dyes ap-
peared to be sensitive to the environmental acidity/basicity
and could be applied as a proton sensor. Thus, the aim of
this work was to present new bichromophoric derivatives
Introduction
The search for new fluorescent multichromophoric sys-
tems attracts much attention because of their potential ap-
plications in various domains such as light-harvesting,[1]
sensors[2] or solar concentrators.[3] One area of interest is
the possibility of controlling the fluorescence output by an
external stimulus such as light, electrical potential or chemi-
cals (proton, metals, etc.). A recent emerging trend is to
control the luminescence through the redox state of the sys-
tem. Several examples of molecular probes based on the
redox modification of a moiety attached to the fluorophore
have been reported.[4] The principle is based on the modula-
tion of photoinduced electron transfer (PET) from or to the
fluorophore. This PET is possible with one state of the side-
group and is cancelled after its redox modification and it
has been reported to be especially sensitive to the linker
length and solvent polarity among other factors.[5] Such ap-
proaches are applicable in areas such as molecular switches
or in the detection of redox-active compounds (e.g., perox-
ides, NOx or metals). In addition, we recently demonstrated
that the fluorescence of tetrazines (TZs) could also be elec-
trochemically switched on and off in a reversible way.[6] TZ
derivatives are presently developed in our laboratory espe-
cially for their long-lifetime emission properties associated
with their high electron affinity giving rise to a very stable
anion radical that is not fluorescent.[7] However, the absorp-
[a] Laboratoire PPSM, CNRS UMR8531, Ecole Normale Supérie-
ure de Cachan, PRES UniverSud,
61 Avenue du Président Wilson, 94235 Cachan, France
Fax: +33-1-47402454
E-mail: mioman@ppsm.ens-cachan.fr
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.200900874.
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F. Miomandre, P. Audebert et al.
FULL PAPER
comprising one or two BODIPY units and one TZ moiety.
The absorption wavelengths of TZ compounds are in the
same range as those of BODIPY, but have much lower ab-
sorption coefficients. Thus, it can be expected that the asso-
ciation of a donor (BODIPY) and an acceptor (TZ) chro-
mophore in the same molecule leads to photoinduced elec-
tron transfer, which, in turn, is likely to be modulated by
the redox state of each moiety. For this reason we have syn-
thesized various BODIPY-TZ derivatives differing from
each other by the nature of the linker and the relative posi-
tions of the two chromophores. The photophysical, electro-
chemical and absorption spectroelectrochemical properties
of these new dyes have been investigated and compared with
their parent monochromophoric derivatives. Theoretical
calculations have also been performed to better understand
the spectroscopic and electrochemical features of these new
compounds.
The second substitution of Cl2TZ is usually more diffi-
cult as once a chlorine has been substituted by an oxygen,
the reactivity of the tetrazine ring decreases due to the elec-
tron-donating mesomeric effect of the oxygen atom. Thus,
the bichromophoric dyes 5a and 5b were synthesized in a
sealed tube. The ortho-coupled bis-BODIPY compound
could not be obtained by this reaction as a result of steric
hindrance.
Results and Discussion
Synthesis
The BODIPY derivatives were synthesized using a classic
one-pot route: condensation of an aldehyde with 2 equiv. of
cryptopyrrole followed by oxidation (either with DDQ or
chloranil), deprotonation with DIPEA and finally complex-
ation with boron trifluoride to give BODIPYs 1a, 1b, 1c
and 2 in overall yields of around 55%.
The main difficulty of this process was to cope with the
partial polymerization of pyrrole when using TFA: the con-
trolled addition of this carbonyl activator circumvented this
Absorption and Emission Spectroscopy
Table 1 shows the spectroscopic features of the various
problem. Another issue was the oxidization step using compounds represented in Scheme 1. The BODIPY deriva-
DDQ as we usually isolated the oxidized cleaved compound tives 1a–c and 2 display standard spectra for such fluoro-
bearing a hydrogen atom at the C-8 (meso) position in large phores with an intense band in the visible region located at
quantities. The use of chloranil was successful in limiting around 525 nm (corresponding to a πǞπ* transition) with
this oxidative cleavage.
a vibrational shoulder at a higher energy. A second, less
The multi-gram synthesis of dichlorotetrazine Cl2TZ has intense band is located in the UV region at around 375 nm.
previously been performed in our laboratory starting from Note that despite the use of different phenols the spectro-
di(pyrazol-1-yl)-s-tetrazine.[7,19] The electron-deficient core scopic features of the BODIPY chromophores 1 and 2 are
of Cl2TZ undergoes nucleophilic substitution with a variety very similar, in agreement with the orthogonal arrangement
of compounds to give mono- or disubstituted products de- of the dipyrrin moiety in relation to the phenol ring.
pending on the nucleophile used. In this work, with the ex-
The absorption spectra of the bichromophoric molecules
ception of 4c (due to steric hindrance), the mono-substitu- 3 and 4 exhibit a broad maximum in the UV domain corre-
tion proceeded at atmospheric pressure in the presence of sponding to transitions located both in the tetrazine core
1 equiv. of 2,4,6-collidine and 1 equiv. of Cl2TZ with yields and the BODIPY unit. A second maximum located in the
of around 36%.
visible region is very similar to those observed in the parent
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BODIPY-Tetrazine Multichromophoric Derivatives
Table 1. Spectroscopic data for the investigated compounds 1–5: values for BODIPY πǞπ* transitions. The nǞπ* transition
absorption wavelengths, absorption coefficients at 530 nm, emis-
sion wavelengths and quantum yields.
of the tetrazine core, which lies in the same wavelength
range, has a much lower absorption coefficient and is thus
Compound[a]
λabs [nm]
ε530 [Lmol–1cm–1] λem [nm][b]
φ[c]
hidden underneath that of BODIPY. The spectra of com-
pounds 3 and 4a–c correspond to the sum of their individ-
ual components (see Figure 1, A), which demonstrates that
no charge transfer state is observed. In the case of com-
pound 5b, the absorption coefficient for the visible band is
nearly twice that of compound 4b, as expected for a bichro-
mophoric species with two independent chromophores.
1a
1b
1c
2
378, 526
372, 525
381, 530
376, 525
375, 528
375, 528
378, 528
384, 533
377, 523
375, 528
56000
82000
83000
74000
69000
63000
78000
66000
n.d.
537
537
544
536
537
538
538
545
534
544
0.80
0.80
0.80
0.70
0.05
0.02
0.04
n.d.
n.d.
0.02
3
4a
4b
4c
5a[d]
5b
164000
[a] All measurements in dichloromethane. [b] Excitation wave-
length: 530 nm. [c] Measured with Rhodamine 590 in methanol as
the standard (φf = 0.83). [d] Determined in acetonitrile.
Figure 1. A) Absorption spectra of: chloromethoxy-s-tetrazine
(from ref.[3]), 1a, 4a and chloromethoxy-s-tetrazine + 1a. B) Com-
parison of the absorption, emission (λexc) and excitation spectra
(λexc) of 4b.
Luminescence spectra were recorded in solution (dichlo-
romethane) and display an emission maximum at around
540 nm, which can be ascribed mainly to the BODIPY flu-
orophore (see Figure 1, B). The luminescence results clearly
evidence fluorescence quenching by the tetrazine moiety.
Indeed the quantum yield changes from 0.70–0.80 in 1 and
2 (classic value for BODIPY) to 0.02–0.04 for BODIPY-TZ
Scheme 1. Structures of the investigated compounds 1–5.
BODIPY compounds 1a–c and 2. Note that the measured compounds 3 and 4. This quenching is due to an intramo-
absorption coefficients for this latter transition are in the lecular process because no variation in the quantum yield
region of 70000 Lmol–1 cm–1, in agreement with classical was observed for pure BODIPY in the presence of added
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F. Miomandre, P. Audebert et al.
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chloromethoxytetrazine. One could expect that the rather cal of BODIPY is less stable under these experimental con-
strong electron-accepting power of the tetrazine ring would ditions than the tetrazine anion radical.
be responsible for the excited-state quenching of the
The redox potentials for the compounds shown in
BODIPY moiety through a redox process (see Figure 3). Scheme 1 are reported in Table 2. A comparison of the data
Nevertheless, the quantum yield measured for 4b in an apo- for compounds 4a–c shows that the various standard poten-
lar solvent such as methylcyclohexane is exactly the same tials are almost insensitive to the position of substitution
as in dichloromethane, which makes the assumption of an on the phenyl ring, especially those of BODIPY. When
energy-transfer mechanism more likely. In addition, exci- comparing the results obtained for BODIPY-TZ com-
tation spectra (Figure 1, B) as well as monoexponential de- pounds 3–5 with those for chloromethoxy-s-tetrazine (E° =
cays with a lifetime of around 5 ns for 4b (from time-re- –0.99 V vs. Fc[7]) and for the parent BODIPYs (compounds
solved fluorescence experiments not shown) clearly evi- 1 and 2), it is clear that the mutual influence of each redox
dence that the residual luminescence is due to BODIPY and moiety on the standard potential of the other one is weak
not the chlorophenoxy-TZ moiety.
but more sensitive for the TZ reduction. This means that
One could have expected an influence of the position of the apparent conjugation between BODIPY and TZ is not
substitution of the tetrazine on the fluorescence quantum effective in the various bichromophoric compounds, first
yield. Indeed, other groups have shown such an effect on a because the ether linker disrupts the conjugation and sec-
BODIPY derivative with a different acceptor, namely malei- ondly because the two subunits are not coplanar (see below
mide.[20] It appears that in our case the fluorescence for details). The more positive values for the tetrazine re-
quenching is similarly efficient in all cases. Because conju- duction potential in the bichromophoric dyes (compared
gation is known to be more efficient through para rather with chloromethoxy-s-tetrazine) can be explained by the
than meta coupling, this result is also in favour of quench- electron-withdrawing character of the BODIPY-phenyl sub-
ing by energy transfer, the similar values for the quantum unit, as previously observed in BODIPY-ruthenium polypy-
yields corroborating the fact that the quenching moiety lies ridine dyes.[16d] This effect is the most sensitive in the case
at approximately the same distance from the BODIPY core of the para linkage in 4b, whereas for 3 it is partially can-
in the meta- and para-linked compounds (actually calcula- celled by the donor character of the methoxy group on the
tions show a difference of 15% for the TZ-BODIPY dis- phenyl ring. In addition, the bis-BODIPY compounds 5a
tances in both 4a and 4b, which is within the uncertainty and 5b also display unexpectedly high values for the re-
for the determination of the quantum yield).
duction potential of TZ compared with dimethoxy-s-TZ
tetrazine (E° = –1.25 V vs. Fc[7]): substituting a chlorine by
a methoxy group on the TZ core leads to a negative poten-
tial shift of about 250 mV, whereas for 5a and 5b the shift
is much lower (140–170 mV), which confirms that the
BODIPY-phenyl unit is much less donating than the methyl
group. This is confirmed by the relative positions of the TZ-
located LUMOs in compounds 4b and 5b compared with
the corresponding BODIPY-located HOMOs (see Table 3):
the difference between 4b and 5b is 0.24 eV, similar to the
corresponding difference in the redox potentials (170 mV).
The BODIPY reduction is nearly not affected by the TZ
subunit, with all the corresponding potentials in the same
range except for 1c in which it is likely a hydrogen bond
Electrochemistry
A typical cyclovoltammogram for a BODIPY-TZ com-
pound is displayed in Figure 2. Three pairs of peaks can be
identified corresponding to the oxidation of BODIPY into
its cation radical (near +0.8 V), the reduction of TZ into its
anion radical (near –0.75 V) and the reduction of BODIPY
into its anion radical (near –1.7 V). The first two peaks are
fully reversible as far as concerns the backward versus for-
ward current, although the peak-to-peak separation is
greater than 60 mV due to both the uncompensated ohmic
drop and sluggish electron transfer, whereas the final peak
is only partially reversible, which shows that the anion radi-
Table 2. Electrochemical data for investigated compounds 1–5. Po-
tentials are referenced to Ag+(0.01 )/Ag. The reference electrode
was checked versus Fc as recommended by IUPAC (between 60
and 90 mV vs. Fc).
Compound[a]
E°ox [V]
E°red1 [V]
E°red2 [V]
1a
1b
1c
2
0.73
0.74
0.75
0.70
0.75
0.76
0.76
0.73
0.75
0.73
–
–
–
–
–1.76
–1.70
–1.52
–1.70[b]
–1.65
3
–0.81
–0.76
–0.71
–0.79
–0.90
–0.88
4a
4b
4c
5a
5b
–1.70
–1.70[b]
–1.70[b]
–1.63
–1.65
Figure 2. Cyclic voltammetry of compound 4a in dichloromethane
+ 0.1  Bu4NPF6. Potentials are referenced to Ag+ (10–2 )/Ag.
Scan rate: 100 mV/s.
[a] All measurements in dichloromethane + TBAPF6 on Pt, except
for 1 which was on Au. [b] Ill-defined because not fully reversible.
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BODIPY-Tetrazine Multichromophoric Derivatives
Table 3. Energy differences (in eV) between the various frontier orbitals of compounds 3–5 and their constitutive fragments.
∆EHOMO–LUMO
∆EHOMO–LUMO (BODIPY) ∆EHOMO–LUMO (TZ) ∆EHOMO(BODIPY) –HOMO(TZ) ∆ELUMO(BODIPY)–LUMO(TZ)
3
4a
4b
4c
1.93
1.80
1.82
1.88
2.04
2.88
2.88
2.88
2.85
2.90
3.69
3.57
3.55
3.61
3.52
1.76
1.77
1.74
1.72
1.48
0.96
1.08
1.06
0.97
0.86
5a–5b
stabilizes the anion radical of BODIPY. Finally, the results its much higher absorption coefficient, the driving force for
of a comparison of the relative current peaks for the TZ PET is only –0.74 eV, which could explain why the quench-
reduction with the BODIPY oxidation in 4b (Figure 2) and ing mechanism is dominated by energy transfer.
5b (see the Supporting Information) are in accord with the
expected 1:1 and 1:2 exchanged electron ratio, which shows
that both moieties maintain their own electroactivity in the
bichromophoric compounds.
Theoretical Calculations
Quantum chemical calculations were carried out on
bichromophores 3 and 4a–c. Density functional theory
(DFT) and time-dependant density functional theory (TD-
DFT) calculations at the B3LYP level of theory and with
the 6-31+G(d) basis set were performed. For all the bichro-
mophores 3 and 4a–c, the three subunits (BODIPY, phenyl
and s-tetrazinyloxy) are found to be more are less perpen-
dicular to each other (see Figure 4). This is due to steric
hindrance in the case of BODIPY and the phenyl. Indeed,
the methyl groups at the 1- and 7-positions of the BODIPY
ring force the meso substituent (i.e., the phenyl ring) out of
the plane of the BODIPY (calculated angle between the
planes is between 81 and 87°). On the other hand, the angle
between the phenyl and the tetrazinyloxy moieties is a result
of the propensity of the oxygen atom to force the two adja-
cent rings to be nearly perpendicular, but this angle is found
to depend on the position of the tetrazinyloxy group on the
phenyl. Indeed, in the case of 4b, the angle is calculated at
87° but decreases to 77° for 4a and 4c. This is due to the
proximity of the BODIPY ring and its methyl substituents,
which causes some steric hindrance. The close proximity of
the tetrazine and BODIPY rings is very pronounced in the
case of 4c, as reflected by the loss of symmetry of the two
fluorine atoms seen in the 19F NMR spectrum. Indeed a
multiplet corresponding to an ABX spin system is observed
instead of the usual quartet. The geometry optimization
also clearly shows that the tetrazine ring lies on one side of
the BODIPY and is approximately 6 Å from one fluorine
atom with no possibility of free rotation around the
BODIPY ring.
The electrochemical and spectroscopic data have allowed
the relative redox properties of the various neutral, ionic
and excited states of both chromophores to be identified.
The results are summarized on a redox scale in Figure 3.
The oxidation potentials of the anion radical of BODIPY
(to the excited BODIPY) and of BODIPY itself (to its cat-
ion radical) are found to be close, consistent with the elec-
tron being removed from the same orbital. Similarly, the
reduction potential of BODIPY (to its anion radical) is
close to that of the BODIPY cation radical (to the excited
BODIPY) as the electron is added to the same orbital in
both cases. The lack of fluorescence of the bichromophoric
species could be predicted when one looks at the redox po-
tentials. Indeed, in any case, the absorption of one photon
leads to an excited state in which an electron-transfer pro-
cess from the BODIPY to the TZ ring is thermodynami-
cally favoured. However, in the case of BODIPY fluores-
cence, which is the main fluorophore in these dyes due to
Figure 4. Calculated geometries of BODIPY-TZ compounds 3, 4a,
4b and 4c (from left to right).
Figure 3. Redox scale for the neutral, ionic and excited-state BOD-
IPY (BDPY) and tetrazine (TZ) couples vs. ferrocene (Fc). The
potentials for the couples involving neutral species are average val-
ues from Table 2. Those involving excited-state species were calcu-
lated from E0–0 values extracted from the spectroscopic data.
The molecular orbitals are found to be localized on each
subunit because electronic interactions are prevented by
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Figure 5. Energy diagram and representation of the main molecular orbitals of the various fragments in compound 4b: LUMO (135),
HOMO (133), HOMO-1 (132), HOMO-2 (131) and HOMO-5 (128) for the BODIPY core. LUMO+1 (136), LUMO (134), HOMO (130)
and HOMO-1 (129) for the TZ core. LUMO (137) and HOMO (217) for the phenyl ring. As shown in the diagram, (133) and (134)
correspond to the HOMO and LUMO, respectively, of compound 4b.
their spatial arrangement (Figure 5). Indeed, sets of orbitals
TD-DFT was also implemented to calculate the wave-
can be extracted that correspond to BODIPY, tetrazine and lengths associated with the electronic transitions in the vari-
the phenyl ring. The highest occupied molecular orbital ous compounds (Table 4). The results for 3–5 reveal the
(HOMO) is always centred on the BODIPY core, which presence of a first transition localized on the tetrazine ring
reflects its electron-donating ability. The non-bonding or- at around 550 nm but its calculated oscillator strength is
bital of the tetrazine is found at a lower energy. Contrari- very small (0.002–0.004). A second intense transition is
wise, the lowest unoccupied molecular orbital (LUMO) is found at around 440–445 nm (f = 0.44–0.47) and is local-
centred on the s-tetrazine ring and the BODIPY centred ized on the BODIPY. Thus, reconstructed spectra only
one is found at a higher energy, which corroborates the elec- show the BODIPY-centred band, which completely over-
trochemistry results. The energy gap between the HOMO shadows that of the tetrazine. This is in agreement with the
and the LUMO centred on BODIPY does not change with experimental UV/Vis results.
the substitution pattern and is found to be 2.88 eV. Only in
the case of 4c is this gap smaller (2.85 eV). Such values are
slightly overestimated compared with those determined
Table 4. Calculated absorption wavelengths and oscillator strengths
(f) using TD-DFT for all investigated compounds 1–5.
Compound
λabs [nm] gaseous (solvated)
f
from the electrochemical and spectroscopic data (2.4 eV).
Nevertheless, the evolution with molecular structure agrees
well with the experimental data. Indeed, the position of the
absorption band does not depend upon substitution. The
small red shift observed for compound 4c compared with
the others is supported by the smaller gap derived from
the calculations. This is probably due to the close spatial
proximity of the TZ ring. On the other hand, the energy
gap between the HOMO and the LUMO centred on the
tetrazine is dependent on the nature of the phenyl ring. In-
deed, in the case of 3, the presence of an additional meth-
oxy substituent increases the energy of the LUMO by ap-
proximately 0.1 eV because of the more electron-donating
nature of the phenyl ring. Hence the BODIPY ring is less
1a
1b
1c
2
437 (450)
437 (450)
439 (452)
437 (453)
439 (452)
440 (452)
439 (452)
443 (455)
431 (n.d.)
431 (n.d.)
0.48
0.49
0.49
0.47
0.47
0.46
0.47
0.44
0.88
0.90
3
4a
4b
4c
5a
5b
UV/Vis Spectroelectrochemistry
The evolution of the spectroscopic features of a bichro-
affected by a change in the position of the substituents than mophoric BODIPY-tetrazine compound upon electrochem-
TZ, which is confirmed by the oxidation potential (and to ical reduction was investigated and compared with those of
a lesser extent by its reduction potential) of BODIPY re- the corresponding individual chromophores. As shown in
maining constant whereas the reduction potential of TZ Figure 6, the UV/Vis spectrum of the bichromophore 4b is
changes from –0.71 V for 4b to –0.81 V for 3. These results largely similar to that of the individual chromophore 1b as
are consistent with the calculated changes in the various a result of the much higher absorption coefficient of the
MO energies.
BODIPY chromophore compared with TZ. Nevertheless,
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BODIPY-Tetrazine Multichromophoric Derivatives
the spectroelectrochemical behaviour upon electrochemical zine shows the same behaviour under similar conditions
reduction is different. Compound 1b exhibits no variation (see Figure 7). In this latter case, the appearance of new
in absorption in the wavelength range explored, whereas 4b bands in the 550–650 nm and near-UV ranges is correlated
displays an increase in absorbance in the 550–650 nm range. to the decrease of the main absorption band, as evidenced
This variation can be ascribed to the absorption of the by the isosbestic points at around 470 and 550 nm. It is
anion radical of the TZ moiety, as chloromethoxy-s-tetra- thus likely that the new growing bands are actually related
Figure 6. Spectroelectrochemical analysis of compounds 1b and 4b in dichloromethane. Top: at open circuit potential (OCP); bottom: at
–1.2 V for the various electrolysis times displayed.
Figure 7. Spectroelectrochemical analysis of chloromethoxy-s-tetrazine under the same conditions as Figure 6. Inset: magnification of the
550–650 nm range.
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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2531

F. Miomandre, P. Audebert et al.
FULL PAPER
and the residue purified by chromatography on silica or alumina
gel or by automatic chromatography to afford BODIPY.
to the electrogenerated anion radical of TZ and not to by-
products (e.g., formed by the counter-electrode reaction).
Further evidence for this rationale comes from the lack of
variation in the absorbance of compound 1b, which is con-
sistent with the fact that the applied potential is not nega-
tive enough to allow electrochemical reduction of the
Synthesis of BODIPY-TZ Derivatives (Procedure B): A dry solution
of BODIPY (1 equiv.) and dichloro-s-tetrazine (Cl2Tz; 1 equiv.) was
stirred and then 2,4,6-collidine (1 equiv.) was added. The mixture
was allowed to stand either under atmospheric pressure or under
BODIPY unit (see Table 2). A consequence of this behav- a higher pressure (in a sealed tube) until no more evolution. The
crude product was purified on silica gel to afford the bifluorophoric
derivatives.
iour is an overlap between the emission band of BODIPY
and the absorption band of the anion radical of TZ. Hence,
quenching by energy transfer is likely to occur when reduc-
ing the TZ in addition to PET from TZ·– to the excited
BODIPY. These two processes could explain the impossi-
bility of switching on the luminescence of the bifluo-
2,6-Diethyl-4,4-difluoro-8-(m-hydroxyphenyl)-1,3,5,7-dimethyl-4-
bora-3a,4a-diaza-s-indacene (1a): The reaction was carried out
using procedure A starting with cryptopyrrole (1500 mg) and 3-hy-
droxybenzaldehyde (750 mg). Purification on silica gel (CH2Cl2) af-
1
rophoric compounds upon reduction of TZ, as evidenced forded 940 mg of 1a (yield 38%). H NMR (400 MHz, CDCl3): δ
= 7.34 (dd, J = 8.2, J = 7.8 Hz, 1 Har), 6.93 (ddd, J = 8.2, J = 2.8,
J = 0.9 Hz, 1 Har), 6.86 (ddd, J = 7.3, J = 2.3, J = 0.9 Hz, 1 Har),
6.77 (dd, J = 2.8, J = 1.4 Hz, 1 Har), 5.01 (br. s, 1 H, OH) 2.53 (s,
6 H, CH3), 2.30 (q, J = 7.8 Hz, 4 H, CH2-CH3), 1.37 (s, 6 H, CH3),
0.98 (t, J = 7.8 Hz, 6 H, CH2CH3) ppm. 13C NMR (100 MHz,
CDCl3): δ = 156.6, 153.5, 139.8, 138.6, 136.8, 134.0, 133.0 (Car),
132.8, 120.2 (Car), 115.6 (Car), 115.1 (Car), 16.9, 14.4, 12.5
by epifluorescence microscopy coupled to electrochemistry
experiments.[21]
Conclusions
Multichromophoric BODIPY-tetrazine derivatives have
been synthesized and their photophysical and electrochemi-
cal properties investigated. It appears that both chromo-
phores behave almost independently from the spectroscopic
and electrochemical points of view. This result is supported
by theoretical calculations that show the absence of conju-
gation through the phenyl ring for geometrical reasons. The
absorption properties are dominated by those of BODIPY,
which is thus the main emitting species. As expected the
bifluorophoric derivatives exhibit very low emission quan-
tum yields, most probably because of energy transfer rather
than PET between the excited BODIPY core and the TZ
moiety. Upon reduction of TZ, the system remains non-
fluorescent due to both PET and a possible energy transfer
from the TZ anion radical to the excited BODIPY, as evi-
denced by absorption spectroelectrochemistry. A detailed
survey is in progress to elucidate the quenching mechanisms
because interactions between the two chromophores seem
to lead to rather complex behaviour.
11.4 ppm. 19F NMR (376 MHz, CDCl3): δ = –145.6 (q, JF-B
=
32.3 Hz) ppm. 11B NMR (128 MHz, CDCl3): δ = –0.17 (t, J =
33.2 Hz) ppm. HRMS: calcd. for C23H27BF2N2O [M + Na]+
419.2082; found 419.2097.
2,6-Diethyl-4,4-difluoro-8-(p-hydroxyphenyl)-1,3,5,7-dimethyl-4-
bora-3a,4a-diaza-s-indacene (1b): The reaction was carried out
using procedure A starting with cryptopyrrole (1.0 g) and 4-hy-
droxybenzaldehyde (500 mg). Purification on silica gel (CH2Cl2) af-
forded 900 mg of 1b (yield 56 %); m.p. Ͼ290 °C. 1H NMR
(400 MHz, CDCl3): δ = 7.12 (d, J = 8.24 Hz, 2 Har), 6.95 (d, J =
8.24 Hz, 2 Har), 2.53 (s, 6 H, CH3), 2.31 (q, J = 7.5 Hz, 4 H,
CH2 CH3 ), 1.35 (s, 6 H, CH3 ), 0.98 (t, J = 7.5 Hz, 6 H,
CH2CH3) ppm. 13C NMR (100 MHz, CDCl3): δ = 156.48, 153.79,
140.54, 138.64, 132.97, 131.39, 129.93 (Car), 128.17, 116.29 (Car),
17.35, 14.90, 12.76, 12.12 ppm. 19F NMR (376 MHz, CDCl3): δ =
–145.68 (q, J = 32 Hz, BF2) ppm. 11B NMR (128 MHz, CDCl3): δ
= –0.13 (t, J = 32 Hz) ppm. IR: ν = 3473 (OH), 2961, 2926, 2864
˜
(C–H), 1614, 1537, 1474 (C=C, C=N), 1436, 1402, 1370, 1312,
1278, 1266, 1216, 1186 (B–F), 1160, 1114, 1090, 1058 (C–O), 965,
948, 918, 867, 831, 813, 799, 759, 698, 662 cm–1. HRMS: calcd. for
C23H27BF2N2O [M + Na]+ 419.2082; found 419.2097.
Experimental Section
2,6-Diethyl-4,4-difluoro-8-(o-hydroxyphenyl)-1,3,5,7-dimethyl-4-
bora-3a,4a-diaza-s-indacene (1c): The reaction was carried out
using procedure A starting with cryptopyrrole (1.0 g) and salicylal-
dehyde (500 mg). Purification on silica gel (CH2Cl2/petroleum
General: All solvents were dried on an automatic M. Braun SPS-
800 instrument. All compounds were characterized by the usual
analytical methods: 1H, 13C, 19F and 10B NMR spectra were re-
corded with either a Bruker Avance (300 MHz) or a JEOL ECS
(400 MHz) spectrometer. All chemical shifts are referenced to
Me4Si (J values are given in Hz). Melting points were measured
with a Kofler melting-point apparatus. IR spectra were measured
with a Nicolet Avatar 330 FT-IR spectrometer. Mass spectra were
measured at the CNRS Imagif platform (Waters spectrometer).
1
ether, 65:35) afforded 870 mg of 1c (yield 54%); m.p. – (dec.). H
NMR (400 MHz, CDCl3): δ = 7.38 (s, 1 Har), 7.30 (ddd, J = 7.50,
J = 1.65 Hz, 1 Har), 7.06 (dd, Ja = 7.79, Jb = 2 Hz, 1 Har), 6.95
(m, 2 H, Har, OH), 2.48 (s, 6 H, CH3), 2.29 (q, J = 7.5 Hz, 4 H,
CH2 CH3 ), 1.42 (s, 6 H, CH3 ), 0.96 (t, J = 7.5 Hz, 6 H,
CH2CH3) ppm. 13C NMR (100 MHz, CDCl3): δ = 153.81, 153.70,
138.44, 136.42, 132.64, 131.24 (Car), 130.72, 129.71 (Car), 122.45,
121.02 (Car), 116.75 (Car), 17.17, 14.77, 12.47, 11.01 ppm. 19F
NMR (376 MHz, CDCl3): δ = –147 (dq, JF-F = 148.8, JB-F1 = 32,
Synthesis of BODIPY (Procedure A): A few drops of trifluoroacetic
acid were added to a dichloromethane solution of cryptopyrrole
(2 equiv.) and aldehyde (1 equiv.). The dark reaction mixture was JB-F2 = 33.23 Hz) ppm. 11B NMR (128 MHz, CDCl3): δ = –0.37 (t,
stirred at room temperature until total disappearance of the alde-
hyde. The oxidising agent (DDQ or chloranil, 1 equiv.), then 5 min
later DIPEA (7 equiv.) and finally trifluoroborate etherate
(11 equiv.) were successively added. The mixture was filtered
through a pad of silica or used crude. The filtrate was concentrated
J = 33.22 Hz) ppm. IR: ν = 3488 (OH), 2964, 2928, 2870, 1533,
˜
1474 (C=C, C=N), 1448, 1403, 1388, 1376, 1368, 1312, 1287, 1273,
1260, 1183 (B–F), 1160, 1115, 1104, 1056, 963, 869, 831, 800, 760,
710, 659 cm–1. HRMS: calcd. for C23H27BF2N2O [M]+ 396.2165;
found 396.2179.
2532
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2010, 2525–2535

BODIPY-Tetrazine Multichromophoric Derivatives
2,6-Diethyl-4,4-difluoro-8-(m-hydroxy-p-methoxyphenyl)-1,3,5,7-di- TzCl2 (113 mg) in a sealed tube at 125 °C. Purification by
methyl-4-bora-3a,4a-diaza-s-indacene (2): The reaction was carried
out using procedure A starting with cryptopyrrole (750 mg) and 3-
hydroxy-4-methoxybenzaldehyde (460 mg). Purification on silica
chromatography on silica gel (CH2Cl2/petroleum ether, 5:5) af-
forded 145 mg of 4c (yield 37 %); m.p. – (dec.). 1H NMR
(400 MHz, CDCl3): δ = 7.91 (ddd, Jg = 8.24, Jm = 7.33, 4J =
4
gel (CH2Cl2) afforded 450 mg of 2 (yield 35 %). 1H NMR 1.83 Hz, 1 H, Har), 7.78 (ddd, Jg = 7.79, Jm = 7.33, J = 0.92 Hz,
4
(400 MHz, CDCl3): δ = 6.92 (d, J = 8.2 Hz, 1 H, Har), 6.82 (d, J 1 H, Har), 7.73 (dd, Jg = 7.33, J = 1.83 Hz, 1 H, Har), 7.68 (dd,
4
= 1.8 Hz, 1 H, Har), 6.73 (dd, J = 8.2, J = 1.8 Hz, 1 H, Har), 3.95
(s, 3 H, O-CH3), 2.50 (s, 6 H, CH3), 2.29 (q, J = 7.4 Hz, 4 H,
Jg = 8.24, J = 0.92 Hz, 1 H, Har), 2.78 (s, 6 H, CH3), 2.59 (q, J =
7.5 Hz, 4 H, CH2CH3), 1.78 (s, 6 H, CH3), 1.28 (t, J = 7.5 Hz, 6 H,
CH2 CH3 ), 1.37 (s, 6 H, CH3 ), 0.96 (t, J = 7.4 Hz, 6 H, CH2CH3) ppm. 13C NMR (100 MHz, CDCl3): δ = 167.40, 165.35,
CH2CH3) ppm. 13C NMR (100 MHz, CDCl3): δ = 153.56, 146.99, 154.87, 150.17, 138.23, 133.36, 132.79, 130.62, 131.40, 131.10,
146.37, 140.03, 138.55, 132.68, 131.09, 128.70, 120.16, 114.82, 128.33, 127.42, 122.39, 17.41, 14.86, 12.88, 11.80 ppm. 19F NMR
111.03, 56.05, 17.16, 14.73, 12.57, 11.84 ppm. IR: ν = 2967, 2923, (376 MHz, CDCl3): δ = –145.6 (large multiplet) ppm. 11B NMR
˜
1540, 1476, 1405, 1190, 1066, 1057, 978, 756 cm–1. HRMS: calcd.
for C24H29BF2N2O2 [M + Na]+ 449.2188; found 449.2190.
(128 MHz, CDCl ): δ = –0.40 (t, J = 33 Hz) ppm. IR: ν = 2966,
˜
3
2928, 2871 (C–H), 1535, 1473 (C=C, C=N), 1434, 1404, 1389, 1371,
1352, 1319, 1272, 1186 (B–F), 1157, 1114, 1080 (C–Cl), 1059, 1035,
1019, 972, 933, 890, 852, 817, 764, 720, 695, 659 cm–1. HRMS:
calcd. for C25H26BClF2N6O [M]+ 510.1898; found 510.1912.
8-[m-(p-Chloro-s-tetrazinyloxy)-p-methoxyphenyl]-2,6-diethyl-4,4-di-
fluoro-1,3,5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene (3): The reac-
tion was carried out using procedure B starting with 2 (285 mg)
and TzCl2 (100 mg, 1 equiv.) Purification by chromatography on
silica gel (CH2Cl2/petroleum ether, 6:4) afforded 200 mg of 3 (yield
2,6-Diethyl-4,4-difluoro-1,3,5,7-dimethyl-8-[o-phenyloxy-p-(pPCB)-
s-tetrazine]-4-bora-3a,4a-diaza-s-indacene (5a): Compound 5a was
prepared along with 4a in the reaction described above to give
200 mg of 4a (yield 39%) and 130 mg of 5a (15%); m.p. – (dec.).
1H NMR (300 MHz, CDCl3): δ = 7.64 (dd, J = 7.7, J = 8.0 Hz, 2
H, Har), 7.42 (dd, J = 7.8, J = 2.0 Hz, 2 H, Har), 7.32 (d, J =
8.0 Hz, 2 H, Har), 7.25 (s, 2 H, Har), 2.56 (s, 12 H, CH3) 2.34 (q, J
= 7.3 Hz, 8 H, CH2CH3), 1.43 (s, 12 H, CH3), 1.02 (t, J = 7.3 Hz,
12 H, CH2CH3) ppm. 13C NMR (75 MHz, CDCl3): δ = 167.35,
154.24, 153.01, 138.18, 137.87, 137.69, 132.99, 130.94, 130.37,
126.52, 121.17 (Car), 121.16 (Car), 16.98, 14.40, 12.35, 11.64 ppm.
1
55%); m.p. – (dec.). H NMR (300 MHz, CDCl3): δ = 7.10 (m, 3
H, Har), 3.68 (s, 3 H, O-CH3), 2.72 (s, 6 H, CH3), 2.14 (m, 4 H,
CH2CH3), 1.28 (s, 6 H, CH3), 0.81 (m, 6 H, CH2CH3) ppm. 13C
NMR (75 MHz, CDCl3): δ = 167.71, 165.29, 153.98, 152.64,
141.02, 138.37, 137.94, 133.01, 130.86, 127.96 (Car), 125.39 (Car),
122.22 (Car), 113.46 (Car), 56.15, 17.00, 14.62, 12.47, 12.06 ppm.
IR: ν = 2969, 2900, 1542, 1476, 1441, 1354, 1321, 1191, 1066,
˜
979 cm–1. HRMS: calcd. for C26H28BClF2N6O2 [M + Na]+
563.1921; found 563.1931.
IR: ν = 2969, 2901, 1541, 1475, 1406, 1382, 1320, 1190, 1066,
˜
8-[m-(p-Chloro-s-tetrazinyloxy)phenyl]-2,6-diethyl-4,4-difluoro-
1,3,5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene (4a): The reaction
was carried out using procedure B starting with 1a (400 mg) and
TzCl2 (150 mg, 1 equiv.). Purification by chromatography on silica
gel (CH2Cl2/petroleum ether, 95:5) afforded 200 mg of 4a (yield
979 cm–1. HRMS: calcd. for C48H52B2F4N8O2 [M + Na]+
893.4233; found 893.4258.
2,6-Diethyl-4,4-difluoro-1,3,5,7-dimethyl-8-[o-phenyloxy-p-(pPCB)-
s-tetrazine]-4-bora-3a,4a-diaza-s-indacene (5b): The reaction was
carried out using procedure B starting with 2 (630 mg) and TzCl2
(90 mg) in a sealed tube at 125 °C. Purification by chromatography
on alumina gel (CH2Cl2/petroleum ether, 5:5) afforded 92 mg of 5b
1
39%) and 130 mg of 5a (15%); m.p. – (dec.). H NMR (300 MHz,
CDCl3): δ = 7.67 (dd, J = 8.1, J = 7.4 Hz, 1 H, Har), 7.43 (d, J =
8.1 Hz, 1 H, Har), 7.36 (d, J = 7.4 Hz, 1 H, Har), 7.28 (s, 1 H, Har),
2.53 (s, 6 H, CH3), 2.33 (q, J = 7.5 Hz, 4 H, CH2CH3), 1.45 (s, 6
H, CH3), 1.01 (t, J = 7.5 Hz, CH2CH3) ppm. 13C NMR (75 MHz,
CDCl3): δ = 167.57, 165.35, 154.31, 152.32, 138.15, 138.10, 137.43,
133.07, 131.08, 130.33, 127.08, 121.25, 121.20, 16.96, 14.51, 12.43,
11.77 ppm. HRMS: calcd. for C25H26BF2N6O [M + Na]+ 533.1815;
found 533.1827.
1
(yield 18%); m.p. – (dec.). H NMR (400 MHz, CDCl3): δ = 7.12
(d, J = 7.79 Hz, 4 H, Har), 6.94 (d, J = 7.79 Hz, 4 H, Har), 2.54 (s,
12 H, CH3), 2.32 (q, J = 7.33 Hz, 8 H, CH2CH3), 1.38 (s, 12 H,
CH3), 0.99 (t, J = 7.30 Hz, 12 H, CH2CH3) ppm. 13C NMR
(100 MHz, CDCl3): δ = 167.54, 154.47, 153.09, 138.79, 138.48,
134.40, 133.36, 131.00, 130.54 (Car), 121.82 (Car), 27.93, 22.86,
15.52, 14.86 ppm. 19F NMR (376 MHz, CDCl3): δ = –145.64 (q,
J = 33 Hz) ppm. 11B NMR (128 MHz, CDCl3): δ = –15 (t, J =
8-[p-(p-Chloro-s-tetrazinyloxy)phenyl]-2,6-diethyl-4,4-difluoro-
1,3,5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene (4b): The reaction
was carried out using procedure B starting with 1b (200 mg) and
TzCl2 (76 mg). Purification by chromatography on silica gel
(CH2Cl2/petroleum ether, 5:5) afforded 92 mg of 4b (yield 36%);
m.p. – (dec.). 1H NMR (400 MHz, CDCl3): δ = 7.44 (m, 4 H, Har),
2.53 (s, 6 H, CH3), 2.32 (q, J = 7.5 Hz, 4 H, CH2CH3), 1.38 (s, 6
H, CH3), 0.99 (t, J = 7.5 Hz, CH2CH3) ppm. 13C NMR (100 MHz,
CDCl3): δ = 167.55, 165.45, 154.24, 152.09, 138.31, 138.21, 134.67,
133.14, 130.68, 130.40 (Car), 121.73 (Car), 17.08, 14.63, 12.54,
33 Hz) ppm. IR: ν = 2965, 2925, 2870 (C–H), 1540, 1474 (C=C,
˜
C=N), 1404, 1373, 1318, 1262, 1187 (B–F), 1115, 1063 (C–O),
1019, 978, 924, 885, 849, 808, 783, 758, 734, 701 cm–1. MS (TOF
ES+): calcd. for [C48H52B2F4N8O2 +Na]+· 893.4233; found
893.425.
Photophysical Measurements: The solvents used were purchased
from Sigma–Aldrich and were all of spectroscopic grade. Excitation
and emission spectra were measured with a SPEX Fluorolog-3
(Jobin–Yvon) spectrometer. A right-angle configuration was used
and the optical density was adjusted to below 0.1 to avoid reab-
sorption artefacts. Fluorescence decay curves in solution were ob-
tained using a time-correlated single-photon counting method
using a titanium-sapphire laser pumped by an argon ion laser (Tsu-
nami, by Spectra-Physics, 82 MHz, 1 ps pulse width, repetition rate
lowered to 4 MHz with a pulse-peaker, a doubling crystal was used
to reach 495 nm excitation). The Levenberg–Marquardt algorithm
was used for the non-linear least-squares fit.
11.95 ppm. 19F NMR (376 MHz, CDCl3): δ = –145.61 (q, JF-B
=
=
33 Hz) ppm. 11B NMR (128 MHz, CDCl3): δ = –0.21 (t, JB-F
33 Hz) ppm. IR: ν = 2968, 2928, 2870 (C–H), 1536, 1474 (C=C,
˜
C=N), 1434, 1389, 1371, 1353, 1319, 1273, 1186 (B–F), 1114, 1157,
1080 (C–Cl), 1059 (C–O), 1034, 1019, 972, 933, 890, 851, 817, 802,
763, 720, 694, 661 cm–1. HRMS: calcd. for C25H26BF2N6O [M +
Na]+ 533.1815; found 533.1826.
8-[o-(p-Chloro-s-tetrazinyloxy)phenyl]-2,6-diethyl-4,4-difluoro-
1,3,5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene (4c): The reaction
was carried out using procedure B starting with 1b (600 mg) and
Electrochemistry and Absorption Spectroscopy: Solvents (SDS,
HPLC grade) and electrolyte salts (tetrabutylammonium hexafluo-
Eur. J. Org. Chem. 2010, 2525–2535
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2533

F. Miomandre, P. Audebert et al.
FULL PAPER
[8]
[9]
a) A. Loudet, K. Burgess, Chem. Rev. 2007, 107, 4891; b) T. E.
Wood, A. Thompson, Chem. Rev. 2007, 107, 1831.
a) I. J. Arroyo, R. Hu, G. Merino, B. Zhong Tang, E. Pea-Cab-
rera, J. Org. Chem. 2009, 74, 5719; b) A. Schmitt, B. Hinkeldey,
M. Wild, G. Jung, J. Fluoresc. 2009, 19, 755; c) K. Trama, H.
Yana, H. A. Jenkins, S. Vassiliev, D. Bruce, Dyes Pigm. 2009,
82, 392.
a) J. Karolin, L. B.-A. Johansson, L. Strandberg, T. Ny, J. Am.
Chem. Soc. 1994, 116, 7801; b) R. P. Haugland, Handbook of
Fluorescent Probes and Research Chemicals, 6th ed., Molecular
Probes, Eugene, OR, 1996; c) K. Tan, L. Jaquinod, R. Paolesse,
S. Nardis, C. Di Natale, A. Di Carlo, L. Prodi, M. Montalti,
N. Zaccheroni, K. M. Smith, Tetrahedron 2004, 60, 1099; d)
M.-c. Yee, S. C. Fas, M. M. Stohlmeyer, T. J. Wandless, K. A.
Cimprich, J. Biol. Chem. 2005, 280, 29053; e) R. W. Wagner,
J. S. Lindsey, Pure Appl. Chem. 1996, 68, 1373.
rophosphate from Fluka, puriss.) were used without further purifi-
cation. Cyclic voltammetry was performed in a three-electrode cell
with a potentiostat (CH Instruments 600) driven by a PC. Platinum
or gold disk electrodes (1 mm diameter) were used as working elec-
trodes, whereas platinum wire and Ag+ (0.01  in acetonitrile)/Ag
were used, respectively, as the counter and reference electrodes. All
the investigated solutions were deaerated by argon-bubbling for at
least 5 min before performing the electrochemical measurements.
[10]
Absorption spectra were recorded with a Cary 500 (Varian) spec-
trophotometer in 1 cm optical length quartz cuvettes. Absorption
spectroelectrochemistry was performed in the same cuvette using
an ITO plate as the working electrode, a Mg wire as a sacrificial
anodic counter-electrode and an Ag wire as a pseudo-reference
electrode.
[11]
[12]
M. L. Metzker, WO Patent WO/2003/066812, 2003.
a) T. A. Golovkova, D. V. Kozlov, D. C. Neckers, J. Org. Chem.
2005, 70, 5545; b) C. Trieflinger, K. Rurack, J. Daub, Angew.
Chem. Int. Ed. 2005, 44, 2288; c) H. Rohr, C. Trieflinger, K.
Rurack, J. Daub, Chem. Eur. J. 2006, 12, 689; d) A. Ambroise,
R. W. Wagner, P. D. Rao, J. A. Riggs, P. Hascoat, J. R. Diers,
J. Seth, R. K. Lammi, D. F. Bocian, D. Holten, J. S. Lindsey,
Chem. Mater. 2001, 13, 1023; e) G. Beer, C. Niederalt, S.
Grimme, J. Daub, Angew. Chem. Int. Ed. 2000, 39, 3252.
a) K. Yamada, Y. Nomura, D. Citterio, N. Iwasawa, K. Suzuki,
J. Am. Chem. Soc. 2005, 127, 6956; b) J. D. Blakemore, R.
Chitta, F. D’Souza, Tetrahedron Lett. 2007, 48, 1977.
a) M. Álvarez, A. Costela, I. García-Moreno, F. Amat-Guerri,
M. Liras, R. Sastre, F. López Arbeloa, J. Bañuelos Prieto, I.
López Arbeloa, Photochem. Photobiol. Sci. 2008, 7, 802; b) A.
Costela, I. Garcia-Moreno, J. Photochem. Photobiol. A: Chem.
2008, 198, 192; c) I. García-Moreno, F. Amat-Guerri, M. Liras,
A. Costela, L. Infantes, R. Sastre, F. López Arbeloa, J.
Bañuelos Prieto, Í. López Arbeloa, Adv. Funct. Mater. 2007,
17, 3088.
Quantum Chemical Calculations: Calculations were performed with
the Gaussian 03 software[22] at the MESO calculation centre of the
ENS Cachan (Nec TX7 with 32 processors of type Itanium 2). All
calculations were performed at the B3LYP/6-31+G(d) of theory.
Supporting Information (see also the footnote on the first page of
this article): S1: CV of compound 5b in dichloromethane (scan
rate: 100 mV/s). S2: Spin density from B3LYP calculations per-
formed on the cation radical, anion radical and dianion of 4b.
[13]
[14]
[1] a) L. Flamigni, J. P. Collin, J. P. Sauvage, Acc. Chem. Res. 2008,
41, 857; b) A. Sautter, B. K. Kaletas, D. G. Schmid, R. Dob-
rawa, M. Zimine, G. Jung, I. H. M. Van Stokkum, L. De Cola,
R. M. Williams, F. Wurthner, J. Am. Chem. Soc. 2005, 127,
6719; c) J. Baffreau, S. Leroy-Lhez, N. Van Anh, R. M. Wil-
liams, P. Hudhomme, Chem. Eur. J. 2008, 14, 4974; d) J. Baf-
freau, S. Leroy-Lhez, P. Hudhomme, M. M. Groeneveld,
I. H. M. Van Stokkum, R. M. Williams, J. Phys. Chem. A 2006,
110, 13123; e) F. Würtner, Chem. Commun. 2004, 1564.
[2] a) A. P. De Silva, N. H. Q. Gunaratne, T. Gunnlaugsson,
A. J. M. Huxley, C. P. McCoy, J. T. Rademacher, T. E. Rice,
Chem. Rev. 1997, 97, 1515; b) B. K. Kaleta, R. M. Williams, B.
König, L. De Cola, Chem. Commun. 2002, 776; c) A. P.
De Silva, N. H. Q. Gunaratne, C. P. McCoy, Nature 1993, 364,
42.
[3] a) W. G. J. H. M. Van Sark, K. W. J. Barnham, L. H. Slooff,
A. J. Chatten, A. Buchtemann, A. Meyer, S. J. McCormack, R.
Koole, D. J. Farrell, R. Bose, E. E. Bende, A. R. Burgers, T.
Budel, J. Quilitz, M. Kennedy, T. Meyer, C. D. M. Donega, A.
Meijerink, D. Vanmaekelbergh, Optics Express 2008, 16,
21773; b) M. J. Currie, J. K. Mapel, T. D. Heidel, S. Goffri,
M. A. Baldo, Science 2008, 321, 226.
[4] a) R. L. Zhang, Z. L. Wang, Y. S. Wu, H. B. Fu, J. N. Yao, Org.
Lett. 2008, 10, 3065; b) T. Suzuki, A. Migita, H. Higushi, H.
Kawai, T. Fujiwara, K. Tsuji, Tetrahedron Lett. 2003, 44, 6837;
c) A. C. Benniston, G. Copley, K. J. Elliot, R. W. Harrington,
W. Clegg, Eur. J. Org. Chem. 2008, 2705; d) S. Leroy-Lhez, L.
Perrin, J. Baffreau, P. Hudhomme, C. R. Chim. 2006, 9, 240.
[5] a) H. Oevering, M. N. Paddon-Row, M. Heppener, A. M. E.
Oliver, E. Cotsaris, J. W. Verhoeven, N. S. Hush, J. Am. Chem.
Soc. 1987, 109, 3258; b) R. M. Williams, J. M. Zwier, J. W. Ver-
hoeven, J. Am. Chem. Soc. 1995, 117, 4093; c) M. T. Indelli, C.
Chiorboli, F. Flamigni, L. De Cola, F. Scandola, Inorg. Chem.
2007, 46, 5630; d) T. Nakamura, J. Ikemoto, M. Fujitsuka, Y.
Araki, O. Ito, K. Takimiya, Y. Aso, T. Otsubo, J. Phys. Chem.
B 2005, 109, 14365.
[15]
[16]
T. Rousseau, A. Cravino, T. Bura, G. Ulrich, R. Ziessel, J. Ron-
cali, Chem. Commun. 2009, 1673.
a) R. Ziessel, B. D. Allen, D. B. Rewinska, A. Harriman, Chem.
Eur. J. 2009, 15, 7382; b) S. Hattori, K. Ohkubo, Y. Urano, H.
Sunahara, T. Nagano, Y. Wada, N. V. Tkachenko, H. Lemme-
tyinen, S. Fukuzumi, J. Phys. Chem. B 2005, 109, 15368; c)
A. C. Benniston, G. Copley, A. Harriman, D. B. Rewinska,
R. W. Harrington, W. Clegg, J. Am. Chem. Soc. 2008, 130,
7174; d) M. Galleta, F. Puntoriero, S. Campagna, C. Chior-
bolli, M. Quesada, S. Goeb, R. Ziessel, J. Phys. Chem. A 2006,
110, 4348.
a) M. Broring, R. Kruger, S. Link, C. Kleeberg, S. Kohler, X.
Xie, B. Ventura, L. Flamigni, Chem. Eur. J. 2008, 14, 2976; b)
Y. Cakmak, E. U. Akkaya, Org. Lett. 2009, 11, 85.
J. Banuelos, F. Lopez Arbeola, T. Arbeloa, S. Salleres, F. Amat-
Guerri, M. Liras, I. Lopez Arbeaola, J. Phys. Chem. A 2008,
112, 10816.
[17]
[18]
[19]
[20]
[21]
D. E. Chavez, R. D. Gilardi, M. A. Hiskey, Angew. Chem. Int.
Ed. 2000, 39, 1791.
T. Matsumoto, Y. Urano, T. Shoda, H. Kojima, T. Nagano,
Org. Lett. 2007, 9, 3375.
F. Miomandre, E. Lépicier, O. Galangau, C. Dumas-Verdes, P.
Audebert, R. Méallet-Renault, R. B. Pansu, manuscript sub-
mitted.
[22]
M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, J. A. Montgomery Jr., T.
Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar,
J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N.
Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y.
Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P.
Hratchian, J. B. Cross, C. Adamo, J. Jaramillo, R. Gomperts,
R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pom-
elli, J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P.
[6] a) Y. Kim, E. Kim, G. Clavier, P. Audebert, Chem. Commun.
2006, 3612; b) F. Miomandre, R. Meallet-Renault, J. J. Vachon,
R. B. Pansu, P. Audebert, Chem. Commun. 2008, 1913.
[7] P. Audebert, F. Miomandre, G. Clavier, M. C. Vernières, S.
Badré, R. Méallet-Renault, Chem. Eur. J. 2005, 11, 5667.
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BODIPY-Tetrazine Multichromophoric Derivatives
Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich,
A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D.
Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui,
A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu,
A. Liashenko, P. Piskorz, I. Komaromi, R. L. Martin, D. J.
Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara,
M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M. W.
Wong, C. Gonzalez, J. A. Pople, Gaussian 03, Revision C.02,
Gaussian Inc., Wallingford, CT, 2004.
Received: July 31, 2009
Revision Received: January 13, 2010
Published Online: March 26, 2010
Eur. J. Org. Chem. 2010, 2525–2535
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
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