Bis(BF2)-2,2′-bidipyrrins (BisBODIPYs): Highly fluorescent BODIPY dimers with large stokes shifts

Article abstract of DOI:10.1002/chem.200701912

Four new dimeric bis(BF₂)-2,2′-bidipyrrins (bisBODIPYs), and their corresponding BODIPY monomers, have been prepared and studied with respect to their structural and photophysical properties. The solidstate molecular structure of the dimers and the relative orientation of the subunits have been revealed by an X-ray diffraction study, which showed that the molecules contain two directly linked BODIPY chromophores in a conformationally fixed, almost orthogonal arrangement. Two of the fluorine atoms are in close contact with each other and the ¹⁹F NMR spectra show a characteristic through-space coupling in solution. The new chromophores all exhibit a clear exciton splitting in the absorption spectra with maxima at about 490 and 560 nm, and are highly luminescent with an intense emission band at around 640 nm. The Stokes shift, which is the difference between the maximum of the lowest-energy absorption band and the maximum of the emission band, has a typical value of 5 to 15 nm for simple BODIPYs, whereas this value increases to 80 nm or more for the dimers, along with a slight decrease in fluorescence quantum yields and lifetimes. These properties indicate potential uses of these new fluorophoric materials as functional dyes in biomedical and materials applications and also in model compounds for BODIPY aggregates.

Full text of DOI:10.1002/chem.200701912

DOI: 10.1002/chem.200701912
Bis(BF2)-2,2’-Bidipyrrins (BisBODIPYs): Highly Fluorescent BODIPY
G
Dimers with Large Stokes Shifts
Martin Brçring,*[a] Robin Krüger,[a] Stephan Link,[a] Christian Kleeberg,[a] Silke Kçhler,[a]
Xiulian Xie,[a] Barbara Ventura,[b] and Lucia Flamigni[b]
Abstract: Four new dimeric bis
G
atoms are in close contact with each
other and the 19F NMR spectra show a
characteristic through-space coupling
in solution. The new chromophores all
exhibit a clear exciton splitting in the
absorption spectra with maxima at
about 490 and 560 nm, and are highly
luminescent with an intense emission
band at around 640 nm. The Stokes
shift, which is the difference between
the maximum of the lowest-energy ab-
sorption band and the maximum of the
emission band, has a typical value of 5
to 15 nm for simple BODIPYs, where-
as this value increases to 80 nm or
more for the dimers, along with a slight
decrease in fluorescence quantum
yields and lifetimes. These properties
indicate potential uses of these new flu-
orophoric materials as functional dyes
in biomedical and materials applica-
tions and also in model compounds for
BODIPY aggregates.
2,2’-bidipyrrins (bisBODIPYs), and
their corresponding BODIPY mono-
mers, have been prepared and studied
with respect to their structural and
photophysical properties. The solid-
state molecular structure of the dimers
and the relative orientation of the sub-
units have been revealed by an X-ray
diffraction study, which showed that
the molecules contain two directly
linked BODIPY chromophores in a
conformationally fixed, almost orthog-
onal arrangement. Two of the fluorine
Keywords: bidipyrrins
·
boron
·
·
dyes/pigments
porphyrinoids
·
fluorescence
Introduction
different approaches. The introduction of functional sub-
stituents on the carbon framework, enlargement of the chro-
mophore, substitution of the fluorine atoms for O- or C-
donors, or replacing the meso CH position with a nitrogen
bridge has produced a plethora
of interesting fluorophores
from this class of molecule.
Very recently, two comprehen-
Boron dipyrrins (BODIPYs, also called boron dipyrrome-
thene or boraindacene) constitute a class of boron chelates
with a dipyrrin ligand[1] that are currently attracting multifa-
cetted interest in many research areas owing to their advan-
tageous photophysical properties. BODIPYs are very versa-
tile and are used as light-stable functional dyes in a variety
of different fields, such as laser dyes,[2,3] light harvesters,[4–6]
fluorescent switches,[7] biomolecular labels,[8] cation sen-
sors,[9–17] and so on.[18–24] The fluorescence properties of
BODIPYs can be fine-tuned preparatively by using several
sive reviews of the field have
appeared in the literature.[25,26]
Despite
the
enormous
number of publications about
different aspects of BODIPY dyes, reports on other oligo-
pyrrolic boron complexes have remained scarce. Macrocyclic
tetra-,[27–31] hexa-, and octapyrroles[29] have only been used as
ligands for BF2 groups during the last decade, and in two in-
stances open-chain tetrapyrroles of the bilin and urobilin
type have been employed.[32,33] Oligomeric dipyrrins would
be of interest as ligands for BF2 groups because of their po-
tential to form covalent BODIPY aggregates.[34–36] Formal
dipyrrin dimers, such as 2,2’-bidipyrrins, are particularly ap-
pealing in this context owing to their straightforward synthe-
sis, high stability, and known ability to form mono- and di-
nuclear transition-metal chelates of different structures.[37–43]
[a] Prof. Dr. M. Brçring, R. Krüger, Dr. S. Link, Dr. C. Kleeberg,
Dr. S. Kçhler, Dr. X. Xie
Fachbereich Chemie
Philipps-Universität Marburg
Hans-Meerwein-Straße
35043 Marburg (Germany)
Fax : (+49)6421-282-5653
E-mail: Martin.Broering@chemie.uni-marburg.de
[b] Dr. B. Ventura, Dr. L. Flamigni
Istituto ISOF-CNR
Via P. Gobetti 101
40129 Bologna (Italy)
2976
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Chem. Eur. J. 2008, 14, 2976 – 2983

FULL PAPER
We have successfully used 2,2’-bidipyrrins as starting materi-
als for conceptually new bisBODIPY fluorophores and
report herein the preparation, structural determination, and
basic photophysical characterization of these dyes.
formed at ambient temperature in a mixture of dichlorome-
thane and triethylamine. For 2,2’-bidipyrrins 1, 2, 9, and 10,
however, the desired bisBODIPYs were only formed in a
yield of about 10% under these conditions, and no improve-
ment in yield was observed upon changing the reaction
time, solvent, or reagent concentration. Indeed, a larger
excess of boron trifluoride and an increased reaction tem-
perature were found to decompose the product with time.
The meso-unsubstituted bisBODIPYs (3 and 4) were partic-
ularly sensitive to these conditions.
We assumed that the formation of basic fluoride anions in
the reaction mixture, and their attack at the meso-position
of both the free-base ligands and the bisBODIPYs, was re-
sponsible for the observed decomposition processes. There-
fore, water-saturated diethyl ether was employed as the re-
action medium to reduce the basicity of the fluoride ions.
The yields improved significantly and after some further op-
timization the desired dimeric BODIPYs were obtained in
reasonable yields of up to 65% (Schemes 1and 2). The new
compounds were obtained as analytically pure ruby-colored
powders after chromatographic purification on silica gel. In
solution the novel fluorophores are characterized by a violet
color and an intense red fluorescence.
Results and Discussion
Preparation of fluorophores: The syntheses of dimeric bis-
BODIPYs 3, 4, 11, and 12 were achieved by a two-fold BF2-
coordination of the free-base ligands 1, 2, 9, and 10, as de-
picted in Schemes 1and 2. Two different types of 2,2 ’-bidi-
Scheme 1. Preparation of meso-unsubstituted bisBODIPYs 3 (44% yield)
and 4 (45% yield). i) BF3·Et2O, 2,6-lutidine, diethyl ether.
For comparison, monomeric BODIPYs 13–16, which have
similar peripheral substituents as dimeric 3, 4, 11, and 12,
were also studied herein. The monomers were prepared ac-
cording to published procedures for meso-unsubstituted (13
and 14)[44] or meso-aryl substituted compounds (15 and
16).[45] Analytical and spectroscopic data were as previously
reported for known compound 14 and are similar to litera-
ture analogues for the new derivatives.
Scheme 2. Preparation of meso-aryl-substituted bisBODIPYs 11 and 12.
i) N-4-Methylbenzoylmorpholine, POCl3, 1,2-dichloroethane, 48%;
ii) POCl3, D, 70 (7) and 67% (8); iii) BF3·Et2O, 2,6-lutidine, diethyl ether,
65%.
pyrrins were employed for this study, namely, those with
and without meso-aryl substituents. Tetrapyrroles 1 and 2
(Scheme 1) have been reported previously, whereas meso-
arylated ligands 9 and 10 (Scheme 2) were unknown, but
were easily prepared by known procedures from bipyrrole 5
via two-fold-substituted compound 6 and trialkylpyrroles 7
or 8 with an overall yield of 34 and 32%, respectively.
Conformation of bisBODIPYs: Single crystals suitable for
X-ray diffraction studies were grown from 12, 13, and 16.
The results of this study are presented in Figures 1, 2, and 3,
and crystallographic and molecular details are summarized
in Tables 1and 2. The C 9BN2 frameworks of 13 and 16
(Figure 1) are essentially flat, with the boron atom displaced
from the median plane by only 0.07 and 0.092 Š, respective-
ꢀ
ꢀ
The preparation of BODIPYs in high yields from dipyr-
rins and excess boron trifluoride etherate is usually per-
ly. Typical B N and B F bond lengths of 1.54–1.55 and
1.39–1.40 Š, respectively, are present throughout, and as ex-
Chem. Eur. J. 2008, 14, 2976 – 2983
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2977

M. Brçring et al.
Table 1. Selected crystallographic data for 12, 13, and 16.
Table 2. Selected bond lengths [Š], distances [Š], and bond angles [8]
for 13, 16, and 12.
12
13
16
13
16
12[a]
formula
C48H56B2F4N4
786.59
P1
C16H21BF2N2
290.16
P21/n
8.8728(8)
11.9386(14)
14.0937(13)
90
90.313(11)
90
1492.9(3)
4
1.291
0.093
2.71–25.89
11117
C26H33BF2N2
422.35
P21/n
11.1044(9)
18.348(2)
11.9364(11)
90
109.857(6)
90
2287.4(4)
4
(B1)
(B2)
Mr [gmolꢀ1
]
[b]
¯
ꢀ
space group
a [Š]
b [Š]
c [Š]
a [8]
B N1
ꢀ
B N2
1.546(3)
1.538(3)
1.394(3)
1.402(2)
1.348(2)
1.391(2)
1.378(3)
1.378(3)
1.396(2)
1.356(2)
02.9613.01
2.492
107.76(15)
110.37(17)
109.90(16)
109.51(16)
110.28(17)
109.01(16)
1.5461(19)
1.5457(19)
1.3935(15)
1.3951(18)
1.3502(17)
1.4014(17)
1.4084(19)
1.4008(19)
1.4016(16)
1.3483(17)
1.544(3)
1.540(3)
1.384(3)
1.383(3)
1.341(3)
1.402(3)
1.387(3)
1.405(3)
1.401(3)
1.365(3)
1.538(3)
1.535(3)
1.368(3)
1.384(4)
1.344(3)
1.403(3)
1.383(3)
1.413(3)
1.400(3)
1.361(3)
13.6933(16)
17.1625(18)
19.050(2)
94.680(14)
98.435(14)
103.149(13)
4281.6(9)
4
1.220
0.083
1.73–26.23
34034
ꢀ
B F1
ꢀ
B F2
ꢀ
C2 N1
N1 C5
C5 C6
C6 C7
C7 N2
N2 C10
B···C6
N1···N2
N1-B-N2
N1-B-F1
N1-B-F2
N2-B-F1
N2-B-F2
F1-B-F2
ꢀ
b [8]
ꢀ
g [8]
V [Š3]
Z
ꢀ
ꢀ
1calcd [gcmꢀ3
]
1.226
0.082
ꢀ
m [mmꢀ1] (MoKa
2q limits [8]
)
2.992
2.478
2.987
2.13–25.90
11740
2.480
107.1(2)
2.475
107.3(2)
measured reflns
106.55(10)
110.29(11)
110.28(11)
110.58(11)
109.94(11)
109.18(11)
independent reflns
observed reflns[a]
no. parameters
R1[b]
15769
9097
1088
0.0559
0.1604
0.878/ꢀ0.352
2847
1839
196
0.0444
0.1306
0.287/ꢀ0.240
4399
2860
287
109.2(2)
108.8(2)
110.8(2)
111.0(2)
109.9(2)
110.7(2)
108.5(2)
110.8(2)
110.5(2)
109.0(2)
0.0324
0.0644
0.180/ꢀ0.172
wR2[c] (all data)
max/min peaks
[a] Data given for molecule B only. (B1) and (B2) denominate the mono-
meric subunit that contains atom B1or B2, respectively. [b] A unified
numbering system, which was analogous to the BODIPY system, was
used for the subunits of dimer 12. For a better comparison, see Figures 1
and 2.
[a] Oberservation criterion: I>2s(I).
P
P
ꢀ
ꢁ
2
jjFojꢀjFcjj
½wðF2oꢀF2cÞ ꢁ
1/2
P
[b] R1=
. [c] wR2=
P
2
2
jFoj
½wðFoÞ ꢁ
Figure 1. Molecular structure of BODIPYs 13 and 16 (ellipsoids set at
the 50% probability level; hydrogen atoms omitted for clarity).
Figure 2. Molecular structure of bisBODIPY 12 (molecule B; ellipsoids
set at the 50% probability level; hydrogen atoms omitted for clarity).
pected the angles around the boron atom have values close
to the tetrahedral angle of 109.58 (Table 2). The influence of
the 4-methylphenyl substituent of 16 on the molecular struc-
ture is very small. The mean plane of this group is at a dihe-
dral angle of 82.888 with respect to the mean C9BN2 plane,
which means that these subunits are electronically decou-
pled. The steric influence is mainly visible in the metrics of
the central six-membered C3BN2 ring, in which 16 has
general, the monomeric subunits of 12 follow the structural
behavior of the monomers described above. However, an el-
ꢀ
ement of asymmetry is present within the Cmeso Cpyrrole
ꢀ
ꢀ
bonds. The C6 C7 and C15 C16 bond lengths are 0.018 and
ꢀ
ꢀ
0.030 Š longer than C5 C6 and C16 C17, respectively
(Figure 2), and the planarity of the two slightly different
C9BN2 subunits is less pronounced in 12 than it is in 13 or
16. However, all other bond lengths, angles, and distances
within the BODIPY subunits of 12, which includes the
almost perpendicular orientation of the 4-methylphenyl sub-
stituents (B1subunit: 89.07 8; B2 subunit: 85.108), are very
similar to the results from the monomers, particularly 16
(Table 2).
ꢀ
ꢀ
longer C5 C6 and C6 C7 bonds, a larger C6···B distance, a
smaller N1···N2 distance, and a slightly reduced N1-B-N2
ꢀ
ꢀ
angle than 13. The C C and C N bond lengths within the
dipyrrin backbone of 13 and 16 indicate strongly delocalized
and almost symmetric p-systems, without any clear distinc-
tion between single and double bonds. These findings are
characteristic for most BODIPYs and have been reported
previously.[46]
The intramolecular interactions of the monomeric subu-
nits of 12 deserve special attention. The subunits are joined
ꢀ
BisBODIPY 12 crystallizes with two independent (though
very similar) molecules, A and B, in the asymmetric unit,
but only molecule B will be discussed herein (Figure 2). In
at C11 C12 with a bond length of 1.471 Š, which is typical
2
for a single C
N
(sp2) bond, and a dihedral angle of
ꢀ
96.528 between the mean C9BN2 planes (Figure 3). In this ar-
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Fluorescent Dimers
FULL PAPER
Figure 4. Top: A 19F NMR spectrum (376 MHz) of 3 obtained experimen-
tally. Bottom: simulated 19F NMR spectrum of 3. Inset: 11B NMR spec-
trum (128 MHz) of 3. Spectra were recorded in CD2Cl2.
Figure 3. Selected views of the molecular conformation of bisBODIPY
12 (substituents removed).
19F NMR spectrum of 3 that assumes an F1,F3 coupling of
25 Hz provides a good first-order fit of the experimental
data (Figure 4, bottom). Therefore, the locked conformation
of the bisBODIPY framework found in the crystalline state
also appears to be present and stable under ambient condi-
tions in solution.
rangement, the inward-pointing fluorine atoms F1and F3
are situated in close contact (a distance of only 2.968 Š),
and the BF2 subunits are displaced outwards from the mean
C9BN2 planes by 0.049 and 0.145 Š to reduce the steric in-
teraction in the center of the molecule. The other two fluo-
rine atoms, F2 and F4, show short F···H distances to a
methyl group proton of the same subunit (2.482 (F2···H)
and 2.541Š (F4···H), compared with 2.481 and 2.561Š for
13 and 16, respectively) and to an ethyl group proton of the
other subunit (2.552 (F2···H) and 2.479 Š (F4···H)). This
data indicates very intimate interactions, but also the ab-
sence of significant intermolecular strain between the
locked subunits of 12.
Photophysical characterization: BisBODIPYs 3, 4, 11, and
12 were examined by absorption and steady-state fluores-
cence spectroscopy in toluene. For comparison, data for
monomers 13 to 16 were recorded under identical condi-
tions, and the results are summarized in Table 3. Figure 5
shows typical spectra of both monomeric and dimeric BOD-
IPYs.
BODIPYs, such as 13–16, show very characteristic 19F and
11B NMR spectra, with a quartet signal at dꢂꢀ140 ppm in
the 19F NMR spectrum, a triplet at dꢂ0.5 ppm in the
The absorption spectrum of 12 is characterized by two
major bands at 490 and 559 nm, and similar spectra are ob-
tained for all dimers (see Table 3). A comparison of the ex-
tinction coefficient and the energy of the longest-wavelength
absorption band with those of 16, which is a similarly substi-
tuted monomer, at 529 nm clearly indicates the presence of
exciton splitting for bisBODIPYs. Such behavior was ex-
pected for the dimer, given the close spatial relationship of
the subchromophores of 12 and the fact that, in the ob-
served conformation, the transition dipole moments of the
component units do not cancel each other out.[51] To confirm
that the observed phenomenon have a molecular origin
rather than a supramolecular one, several control experi-
ments were performed at a range of concentrations from 3”
10ꢀ4 to 7”10ꢀ6 molLꢀ1. Identical spectra were observed and
it can be safely assumed that no dimerization or other ag-
gregation phenomena are present under the working condi-
tions.
11B NMR spectrum, and a coupling constant of 1J
(B,F)
R
ꢂ34 Hz. However, owing to the reduced local symmetry in
bisBODIPYs 3, 4, 11, and 12, the fluorine atoms are no
longer magnetically equivalent and show a strong 2J
(F,F’)
G
coupling of 103 to 106 Hz. This leads to two complex mul-
tiplet signals in the 19F NMR spectra at dꢂꢀ140 and
ꢀ147 ppm and the observation of a doublet of doublets
signal in the 11B NMR spectra (Figure 4). A more detailed
analysis of the 19F signals reveals that the low-field absorp-
tion can be fully explained as a doublet of quartets signal
1
2
ACHTREUNG
with J
signal displays a more complex pattern. This pattern can be
understood if the presence of a second J(F,F) coupling be-
A
AHCTREUNG
tween the spatially related F1and F3 atoms is assumed.
Such through-space coupling (as opposed to through-bond
coupling) is known for inflexible systems such as this, in
which a fluorine atom is locked at a van der Waals distance
from a second NMR-active nucleus.[47–50] A simulation of the
The luminescence spectra of the bisBODIPYs display a
broad emission band that is notably shifted by a Stokes shift
of 79 to 83 nm with respect to the lowest-energy absorption
Chem. Eur. J. 2008, 14, 2976 – 2983
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2979

M. Brçring et al.
Table 3. Spectroscopic and luminescence data for compounds 3, 4, and
11–16 in toluene.
Compound
Absorption
lmax [nm]
Emission
lmax[a] [nm]
[b]
e [104 mꢀ1 cmꢀ1
]
Ffl
bisBODIPY 3
393
492
565
393
494
567
394
489
558
395
490
559
1.66
6.44
7.36
1.55
6.46
7.15
1.62
6.71
7.71
1.70
7.20
8.26
648
650
638
638
0.71
0.76
0.67
0.69
bisBODIPY 4
bisBODIPY 11
bisBODIPY 12
BODIPY 13
BODIPY 14
BODIPY 15
BODIPY 16
3810.74
534
380
535
378
526
380
529
.05040
8.20
0.78
8.89
0.70
7.26
0.71538
7.75
1
540
538
1.00
0.88
0.80
[a] Derived from corrected emission spectra. [b] Luminescence quantum
yields in air-free toluene, determined by comparing corrected emission
spectra and using N,N’-bis(1-hexylheptyl)-3,4:9,10-perylenebis(dicarbox-
imide) in aerated dichloromethane as a standard (Ffl =0.99).[52] Excita-
tion at 490 nm.
Figure 5. The spectroscopic properties of bisBODIPY 12 and BODIPY
16 in toluene. Top: absorption spectra of 12 (c) and 16 (g). To
allow a better comparison, the absorption coefficient of 16 is multiplied
by two. Bottom: absorption (g) and emission spectra (c) of 12 after
excitation at 490 nm. The normalized excitation spectrum recorded at
640 nm is also shown (gray line).
transition. Excitation spectra registered on the emission
maxima of the bisBODIPYs perfectly match the absorption
spectra, which indicates a genuine emission of the dimeric
species. The large Stokes shift of the emission, which for
simple monomeric BODIPYs is typically in the range of 5
to 15 nm, and the relatively broad shape of the emission
band are indicative of a large geometric displacement of the
excited state with respect to the ground state and/or of some
excimer-like character in the excited state of the covalent
dimers. The fluorescence quantum yields (Ffl) of dimers 3,
4, 11, and 12 have been determined to be between 0.67 and
0.76 (Table 3). These values are lower than those of the
analogous monomers (13–16, Table 3), but still remarkably
high. An enhancement of the intersystem crossing efficiency,
with a consequent loss of fluorescence yield, has been re-
ported for composite molecules that exhibit exciton split-
ting, and this situation could also apply here.[51] The pres-
ence of aryl substituents decreases the luminescence of the
bisBODIPYs and that of the corresponding BODIPY mo-
nomer models by around 10%, which is likely to be caused
by an enhancement of the nonradiative rate constants of the
singlet excited state.[53,54] Exchanging methyl for ethyl sub-
stituents, on the other hand, does not markedly influence
the photophysics. These observations are well-known for
monomeric BODIPYs.[26] The time evolution of the lumines-
cence is described by a single exponential decay under an
experimental resolution of 10 ps and the measured lifetime
is (3.4ꢃ0.1) ns for all dimers. The luminescence lifetime of
the monomers is exponential and ranges from 4 to 6 ns. The
shorter lifetime of the dimers can be accounted for by en-
hanced intersystem crossing, which is the result of the popu-
lation of an exciton-split excited state, as discussed above.
To fully characterize the systems, in-depth spectroscopic and
photophysical studies under different conditions are under-
way. It should be stressed that the monomers and dimers
show very high photostability, both in air-equilibrated and
air-free solutions. Indeed, the dimers are even more stable
than the monomers under high-power laser irradiation.
Conclusion
In summary, we have reported the preparation, structure de-
termination, and spectroscopic characterization of a set of
highly fluorescent covalent BODIPY dimers (bisBODIPYs).
As a result of the specific conformation of these species,
which is present in the solid state and in solution, the photo-
physical properties deviate significantly from those of the
monomers. In particular, the increased Stokes shift and the
reduced fluorescence lifetime of the novel fluorophores are
of interest in this context. These properties indicate poten-
tial uses of these new fluorophoric compounds as functional
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Chem. Eur. J. 2008, 14, 2976 – 2983

Fluorescent Dimers
FULL PAPER
until the blue color of the solution faded (ꢂ2 mL). After stirring for 1h,
the product was filtered off and washed with cold MeOH until the wash-
ings were colorless. Recrystallization from MeOH/CH2Cl2 gave 9 or 10 as
fine, dark green powders with a metallic sheen.
dyes for biomedical applications and materials and also in
model compounds for BODIPY aggregates.
2,2’-Bidipyrrin 9: Prepared from 7 (562 mg, 70%). 1H NMR (300 MHz,
CDCl3): d=13.38 (s, 2H; NH), 7.25–7.21(m, 8H; Har), 2.82 (q, J=
7.5 Hz, 4H; CH2CH3), 2.45 (s, 6H; CH3), 2.28 (s, 6H; CH3), 1.84 (s, 6H;
CH3), 1.31 (s, 6H; CH3), 1.23 (s, 6H; CH3), 1.20 ppm (t, J=7.5 Hz, 6H;
CH2CH3); 13C NMR (100 MHz, CDCl3): d=159.2, 141.9, 138.0, 137.9,
137.2, 136.7, 135.9, 134.6, 132.7, 130.7, 129.8, 129.3, 128.7, 21.6, 18.3, 15.6,
15.4, 12.8, 11.4, 9.8 ppm; HRMS (ESI+): m/z: calcd for C44H51N4
[M+H]+: 635.4108; found: 635.4099; elemental analysis calcd (%) for
C44H50N4·1.5MeOH: C 80.02, H 8.26, N 8.20; found: C 80.43, H 7.96, N
8.40.
2,2’-Bidipyrrin 10: Prepared from 8 (588 mg, 67%). 1H NMR (400 MHz,
CDCl3): d=13.53 (brs, 2H; NH), 7.29 (d, J=7.9 Hz, 4H; Har), 7.22 (d,
J=7.9 Hz, 4H; Har), 2.84 (q, J=7.4 Hz, 4H; CH2CH3), 2.45 (s, 6H; CH3),
2.30 (s, 6H; CH3), 2.29 (q, J=7.5 Hz, 4H; CH2CH3), 1.60 (q, J=7.3 Hz,
4H; CH2CH3), 1.26 (s, 6H; CH3), 1.18 (t, J=7.4 Hz, 6H; CH2CH3), 1.04
(t, J=7.5 Hz, 6H; CH2CH3), 0.671ppm (t, J=7.3 Hz, 6H; CH2CH3);
13C NMR (100 MHz, CDCl3): d=156.9, 143.6, 139.8, 138.9, 138.0, 137.4,
135.9, 135.6, 133.9, 133.6, 131.6, 130.0, 128.8, 21.6, 19.0, 18.4, 17.8, 16.8,
15.6, 15.2, 15.1, 11.5 ppm; HRMS (ESI+): m/z: calcd for C48H59N4
[M+H]+: 691.4734; found: 691.4727; elemental analysis calcd (%) for
C48H58N4·1.5MeOH: C 80.44, H 8.73, N 7.58; found: C 80.66, H 8.46, N
7.70.
Experimental Section
General: Solvents were dried according to standard procedures and then
saturated with argon. All reagents were purchased from commercial sour-
ces and used as received, unless stated otherwise. Compounds 1,[55] 2,[56]
5,[57] 7,[58] 8,[59] and 14[60] were prepared as previously reported. NMR
spectra were obtained by using Bruker ARX-300 or Bruker DRX-400
spectrometers. Chemical shifts (d) are given in ppm relative to residual
solvent resonances (1H, 13C NMR spectra) or to external standards
(BF3·Et2O for 11B and CFCl3 for 19F NMR spectra). High-resolution ESI
mass spectra were recorded by using an IonSpec Ultima or a QStar Pul-
sar i. Combustion analyses (C,H,N) were performed by using an Elemen-
tar Vario EL instrument. Spectroscopic-grade toluene was used for pho-
tophysical and spectroscopic determinations. A Perkin–Elmer Lambda 9
UV/Vis spectrophotometer and a Spex Fluorolog II spectrofluorimeter
were used to acquire absorption and emission spectra. Reported lumines-
cence spectra are corrected for the photomultiplier response. Emission
quantum yields were determined after correction for the photomultiplier
response, with reference to an air-equilibrated toluene solution of N,N’-
bis(1-hexylheptyl)-3,4:9,10-perylenebis(dicarboximide) in aerated CH2Cl2
with a Ffl value of 0.99.[52] Luminescence lifetimes were recorded by
using IBH single-photon counting equipment (excitation at l=465 nm
from a pulsed diode source; resolution 0.3 ns). The presence of fast com-
ponents was excluded by exciting the sample with the second harmonic
of a picosecond Nd/YAG laser (l=532 nm) and collecting the emissions
with a Streak Camera; the overall resolution of the system was 10 ps.
Further details on the spectroscopy/photophysics experimental setup can
be found in the literature.[61,62] Single-crystal X-ray diffraction studies
were performed by using Stoe IPDS-1( 12, 13) or Stoe IPDS-2 (16) in-
struments. Suitable crystals were obtained by layering solutions of the
compounds in CH2Cl2 with hexane and allowing slow diffusion at ꢀ208C.
All of the structures were solved and refined by using the SHELXS pro-
grams for crystal structure determination[63] and refinement.[64] Crystal
data and experimental details are given in Table 1. CCDC 669710,
669711, and 669712 contain the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
General procedure for 3, 4, 11, and 12: 2,6-Lutidine (5 mL), and then
BF3·Et2O (12 mL), were added dropwise to an ice-cooled solution of 1, 2,
9, or 10 (0.12 mmol) in Et2O (100 mL). Then the ice bath was removed
and the mixture was stirred for 10 min. The ice bath was then replaced
and the reaction was quenched by addition of a saturated aqueous solu-
tion of NaHCO3 (50 mL). The aqueous layer was extracted with Et2O,
then the combined organic layers were washed with a saturated aqueous
solution of Na2CO3 (3”20 mL), dried over MgSO4, and evaporated to
dryness in vacuo. The reddish residue was purified by column chromatog-
raphy on silica gel (CH2Cl2). The strongly fluorescent red fraction con-
tained the product. Recrystallization from CH2Cl2/hexane gave 3, 4, 11,
or 12 as analytically pure ruby-colored powders.
BisBODIPY 3: Prepared from 1 (29 mg, 44%). 1H NMR (300 MHz,
CD2Cl2): d=7.17 (s, 2H; CHmeso), 2.36 (s, 6H; CH3), 2.33 (q, J=7.6 Hz,
4H; CH2CH3), 2.31(s, 6H; C H3), 2.19 (s, 6H; CH3), 1.92 (s, 6H; CH3),
1.03 ppm (t, J=7.6 Hz, 6H; CH2CH3); 13C NMR (100 MHz, CD2Cl2): d=
160.7, 142.8, 140.0, 134.9, 134.7, 133.6, 132.7, 127.7, 120.2, 18.1, 13.8, 13.0,
9.9, 9.5, 8.8 ppm; 19F NMR (376 MHz, CD2Cl2): d=ꢀ140.2 (dq, J
(F1,F2)=
3,3’-Diethyl-4,4’-dimethyl-5,5’-di-4-methylbenzoyl-2,2’-bipyrrole (6): N-4-
Methylbenzoylmorpholine (16.42 g, 80 mmol) and phosphorous oxytri-
chloride (16 mL, 171 mmol) were mixed under an argon atmosphere and
heated at 658C for 3.5 h. Then, a solution of 3,3’-diethyl-4,4’-dimethyl-
2,2’-bipyrrole (4.32 g, 20 mmol) in 1,2-dichloroethane (80 mL) was added
at RT and the mixture was heated at reflux for 4 h. The reaction was
quenched with saturated Na2CO3 solution (600 mL) and heated for an
additional hour at 808C. After phase separation, the aqueous layer was
extracted thoroughly with dichloromethane. The combined organic ex-
tracts were dried (Na2SO4) and evaporated to dryness in vacuo. The
brownish residue was purified by column chromatography on silica gel
(CH2Cl2/diethyl ether 1:0 to 20:1). The brownish-yellow fraction was col-
lected and gave 6 as a shiny yellow powder after recrystallization from di-
chloromethane/hexane (4.26 g, 48%). 1H NMR (300 MHz, CDCl3): d=
8.80 (s, 2H; NH), 7.61(d, J=8.0 Hz, 4H; Har), 7.27 (d, J=8.0 Hz, 4H;
Har), 2.53 (q, J=7.6 Hz, 4H; CH2CH3), 2.43 (s, 6H; CH3), 2.11 (s, 6H;
CH3), 1.11 ppm (t, J=7.6 Hz, 6H; CH2CH3); 13C NMR (100 MHz,
CDCl3): d=186.2, 142.1, 137.0, 129.2, 129.1, 128.7, 127.8, 127.5, 125.6,
21.7, 18.0, 15.6, 11.7 ppm; HRMS (ESI+): m/z: calcd for C30H32N2O2Na
[M+Na]+: 475.2356; found: 475.2358.
103 Hz,
J
U
F1,BF2); 11B NMR (128 MHz, CD2Cl2): d=0.52 ppm (dd,
J
(B,F1), J-
(B,F2)=34 Hz; 2B); HRMS (ESI+): m/z: calcd for C30H36B2F4N4Na
[M+Na]+: 573.2954; found: 573.2957; elemental analysis calcd (%) for
C30H36B2F4N4: C 65.48, H 6.59, N 10.18; found: C 65.21, H 6.33, N 10.23.
BisBODIPY 4: Prepared from 2 (34 mg, 45%). 1H NMR (300 MHz,
CD2Cl2): d=7.15 (s, 2H; CHmeso), 2.74 (q, J=7.6 Hz, 4H; CH2CH3), 2.63
(q, J=7.6 Hz, 4H; CH2CH3), 2.39 (s, 6H; CH3), 2.41–2.32 (m, 8H; 2”
CH2CH3), 1.29 (t, J=7.6 Hz, 6H; CH2CH3), 1.21 (t, J=7.6 Hz, 6H;
CH2CH3), 1.06 (t, J=7.6 Hz, 6H; CH2CH3), 1.04 ppm (t, J=7.6 Hz, 6H;
CH2CH3); 13C NMR (75 MHz, CD2Cl2): d=160.4, 145.8, 143.3, 141.5,
133.7, 133.3, 133.1, 132.1, 120.2, 18.3, 18.1, 17.9, 17.2, 16.8, 16.7, 14.7, 14.3,
12.9 ppm; 19F NMR (376 MHz, CD2Cl2): d=ꢀ140.4 (dq,
J
(F1,F2)=
A
103 Hz, J
A
11B NMR (128 MHz, CD2Cl2): d=1.10 ppm (dd, J(B,F1), J(B,F2)=34 Hz;
2B); HRMS (ESI+): m/z: calcd for C36H48B2F4N4Na [M+Na]+:
657.3893; found: 657.3898; elemental analysis calcd (%) for
C36H48B2F4N4: C 68.16, H 7.63, N 8.83; found: C 67.85, H 7.64, N 8.77.
BisBODIPY 11: Prepared from 9 (57 mg, 65%). 1H NMR (300 MHz,
CD2Cl2): d=7.37–7.25 (m, 8H; Har), 2.47 (s, 6H; CH3), 2.42 (s, 6H;
CH3), 2.29–2.21(m, 4H; C H2CH3), 1.85 (s, 6H; CH3), 1.44 (s, 6H; CH3),
1.35 (s, 6H; CH3), 0.95 ppm (t, J=7.6 Hz, 6H; CH2CH3); 13C NMR
(75 MHz, CD2Cl2): d=158.7, 142.6, 142.2, 141.4, 139.1, 136.8, 134.8, 132.8,
132.6, 131.7, 129.9, 129.8, 128.4 (2C), 128.2, 21.2, 18.1, 13.9, 13.0, 12.3,
General procedure for 9 and 10: A solution of 6 (575 mg, 1.27 mmol) and
7 or 8 (3.80 mmol) in phosphorous oxytrichloride (10 mL) was heated at
reflux for 5 h. After cooling to 608C and removal of all volatile com-
pounds in vacuo, the residual dark-green tar was redissolved in methanol
(300 mL). The product was precipitated by slow addition of triethylamine
Chem. Eur. J. 2008, 14, 2976 – 2983
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
2981

M. Brçring et al.
12.2, 8.8 ppm; 19F NMR (376 MHz, CD2Cl2): d=ꢀ137.2 (dq, J
C
132.6, 132.0, 130.2, 128.9, 128.7, 21.3, 18.6, 17.0, 16.3, 14.9, 12.4 ppm;
103 Hz, J
C
19F NMR (376 MHz, CD2Cl2): d=ꢀ145.7ppm (q, J
ACHTREUNG
ACHTREUNG
11B NMR (128 MHz, CD2Cl2): d=1.00 ppm (dd, J
G
C
BF); 11B NMR (128 MHz, CD2Cl2): d=0.23 ppm (t, J
BF); HRMS (ESI+): m/z: calcd for C26H33BF2N2Na [M+Na]+: 445.2597;
found: 445.2604; elemental analysis calcd (%) for C26H33BF2N2·1.5H2O:
C 69.49, H 8.02, N 6.24; found: C 69.37, H 7.76, N 5.96.
2B); HRMS (ESI+): m/z: calcd for C44H48B2F4N4Na [M+Na]+:
753.3893; found: 753.3893; elemental analysis calcd (%) for
C44H48B2F4N4: C 72.34, H 6.62, N 7.67; found: C 71.91, H 6.81, N 7.58.
BisBODIPY 12: Prepared from 10 (61mg, 65%). 1H NMR (300 MHz,
CD2Cl2): d=7.40–7.32 (m, 8H; Har), 2.47 (s, 6H; CH3), 2.43 (s, 6H;
CH3), 2.32 (q, J=7.5 Hz, 4H; CH2CH3), 2.28–2.21(m, 4H; C H2CH3),
1.79–1.66 (m, 4H; CH2CH3), 1.39 (s, 6H; CH3), 1.02 (t, J=7.5 Hz, 6H;
CH2CH3), 0.94 (t, J=7.6 Hz, 6H; CH2CH3), 0.72 ppm (t, J=7.5 Hz, 6H;
CH2CH3); 13C NMR (100 MHz, CD2Cl2): d=158.8, 147.5, 142.8, 142.2,
139.1, 137.1, 134.9, 134.4, 132.2, 131.9, 131.8, 129.4, 129.3, 128.7, 128.5,
21.2, 18.7, 18.1, 17.0, 16.1, 14.6, 13.9, 12.8, 12.2 ppm; 19F NMR (376 MHz,
Acknowledgements
Funding of this work by the Deutsche Forschungsgemeinschaft (DFG),
CNR of Italy (PM.P04.10, Project MACOL), and the Volkswagen Foun-
dation is gratefully acknowledged.
CD2Cl2): d=ꢀ139.2 (dq, J
U
N
0.05 ppm (dd, J
A
C
[1] T. E. Wood, A. Thompson, Chem. Rev. 2007, 107, 1831–1861.
[2] T. Chen, J. H. Boyer, M. L. Trudell, Heteroat. Chem. 1997, 8, 51–54.
[3] G. Sathyamoorthi, L. T. Wolford, A. M. Haag, J. H. Boyer, Heteroat.
Chem. 1994, 5, 245–249.
for C48H56B2F4N4Na [M+Na]+: 809.4519; found: 809.4526; elemental
analysis calcd (%) for C48H56B2F4N4: C 73.29, H 7.18, N 7.12; found: C
72.90, H 7.25, N 6.95.
[4] F. Li, S. I. Yang, Y. Ciringh, J. Seth, C. H. Martin III, D. L. Singh, D.
Kim, R. R. Birge, D. F. Bocian, D. Holten, J. S. Lindsey, J. Am.
Chem. Soc. 1998, 120, 10001–10017.
[5] R. K. Lammi, A. Amboise, T. Balasubramanian, R. W. Wagner, D. F.
Bocian, D. Holten, J. S. Lindsey, J. Am. Chem. Soc. 2000, 122, 7579–
7591.
[6] A. Amboise, C. Kirmaier, R. W. Wagner, R. S. Loewe, D. F. Bocian,
D. Holten, J. S. Lindsey, J. Org. Chem. 2002, 67, 3811–3826.
[7] T. A. Golovkova, D. V. Kozlov, D. C Neckers, J. Org. Chem. 2005,
70, 5545–5549.
[8] R. P. Haugland in Handbook of Molecular Probes and Research
Products, Molecular Probes, Eugene, OR, 9th edition, 2002.
[9] R. W. Wagner, J. S. Lindsey, Pure Appl. Chem. 1996, 68, 1373–1380.
[10] G. Beer, K. Rurack, J. Daub, Chem. Commun. 2001, 1138–1139.
[11] G. Beer, C. Niederalt, S. Grimme, J. Daub, Angew. Chem. 2000, 112,
3385–3388; Angew. Chem. Int. Ed. 2000, 39, 3252–3255.
[12] M. Kollmannsberger, K. Rurack, U. Resch-Genger, W. Rettig, J.
Daub, Chem. Phys. Lett. 2000, 329, 363–369.
[13] F. Sancenón, R. Martínez-MµÇez, J. Soto, Angew. Chem. 2002, 114,
1474–1477; Angew. Chem. Int. Ed. 2002, 41, 1416–1419.
[14] Y. Gabe, Y. Urano, K. Kikuchi, H. Kojima, T. Nagano, J. Am.
Chem. Soc. 2004, 126, 3357–3367.
[15] T. Ueno, Y. Urano, H. Kojima, T. Nagano, J. Am. Chem. Soc. 2006,
128, 10640–10641.
[16] Y. Mei, P. A. Bentley, W. Wang, Tetrahedron Lett. 2006, 47, 2447–
2449.
[17] N. Basaric, M. Baruah, W. Qin, B. Metten, M. Smet, W. Dehaen, N.
Boens, Org. Biomol. Chem. 2005, 3, 2755–2761.
[18] C. McCusker, J. B. Carroll, V. M. Rotello, Chem. Commun. 2005,
996–998.
[19] R. Y. Lai, A. J. Bard, J. Phys. Chem. B 2003, 107, 5036–5042.
[20] J. M. Brom, Jr., J. L. Langer, J. Alloys Compd. 2002, 338, 112–115.
[21] A. Hepp, G. Ulrich, R. Schmechel, H. von Seggern, R. Ziessel,
Synth. Met. 2004, 146, 1 1 –1 5.
[22] S. Hattori, K. Ohkubo, Y. Urano, H. Sunahara, T. Nagano, Y. Wada,
N. V. Tkchanko, H. Lemmetyinen, S. Fukuzumi, J. Phys. Chem. B
2005, 109, 15368–15375.
[23] M. P. Debreczeny, W. A. Svec, M. R. Wasielewski, Science 1996, 274,
584–587.
[24] Y. Teki, H. Tamekuni, J. Takeuchi, Y. Miura, Angew. Chem. 2006,
118, 4782–4786; Angew. Chem. Int. Ed. 2006, 45, 4666–4670.
[25] R. Ziessel, G. Ulrich, A. Harriman, New J. Chem. 2007, 31, 496–
501.
[26] A. Loudet, K. Burgess, Chem. Rev. 2007, 107, 4891–4932.
[27] W. J. Belcher, M. Breede, P. J. Brothers, C. E. F. Richard, Angew.
Chem. 1998, 110, 1133–1135; Angew. Chem. Int. Ed. 1998, 37, 1 1 1 2–
1114.
Preparation of BODIPY 13: NEt3 (9.6 mL) and BF3·Et2O (12 mL) were
added to a solution of 4-ethyl-3,3’,4’,5,5’-pentamethyldipyrrin hydrobro-
mide[65] (647 mg, 2 mmol) in CH2Cl2 (200 mL). After stirring for 1h, the
mixture was added to a saturated solution of Na2CO3. After phase sepa-
ration, the aqueous layer was extracted with CH2Cl2. The combined or-
ganic layers were washed with a saturated aqueous solution of Na2CO3
(3”20 mL), dried over Na2SO4, and evaporated to dryness in vacuo. The
residue was purified by column chromatography on silica gel (CH2Cl2/
pentane 1:2). Compound 13 was obtained as a red powder after recrystal-
lization (CH2Cl2/MeOH) of the residue obtained from the strongly fluo-
rescent greenish-yellow fraction (403 mg, 69%). 1H NMR (400 MHz,
CD2Cl2): d=7.06 (s, 1H; CHmeso), 2.49 (s, 3H; CH3), 2.48 (s, 3H; CH3),
2.44 (q, J=7.6 Hz, 2H; CH2CH3), 2.22 (s, 3H; CH3), 2.20 (s, 3H; CH3),
1.97 (s, 3H; CH3), 1.11 ppm (t, J=7.6 Hz, 3H; CH2CH3); 13C NMR
(100 MHz, CD2Cl2): d=155.1, 154.4, 137.6, 137.0, 132.3, 131.8, 125.5
(2C), 118.8, 17.3, 14.4, 12.5, 12.3, 9.4, 9.2, 8.7 ppm; 19F NMR (376 MHz,
CD2Cl2): d=ꢀ146.4 ppm (q,
J
ACHTREUNG
(128 MHz, CD2Cl2): d=0.73 ppm (t, J
AHCTREUNG
(ESI+): m/z: calcd for C16H22BF2N2 [M+H]+: 291.1839; found: 291.1838;
elemental analysis calcd (%) for C16H21BF2N2: C 66.23, H 7.29, N 9.65;
found: C 66.11, H 7.23, N 9.76.
General procedure for meso aryl-substituted BODIPYs: A mixture of 7
or 8 (6 mmol) and 4-methylbenzoylchloride (3 mmol) in CH2Cl2 (60 mL)
was stirred at RT for 4 d. NEt3 (18 mmol) and BF3·Et2O (24 mmol) were
added and the mixture was stirred for an additional day. The mixture was
then poured into a saturated aqueous solution of NaHCO3. After phase
separation, the aqueous layer was extracted with CH2Cl2. The combined
organic layers were washed with
a saturated aqueous solution of
NaHCO3 (3”20 mL), dried with Na2SO4, and evaporated to dryness in
vacuo. The residue was purified by column chromatography on silica gel
(CH2Cl2/pentane 1:1). The product was obtained as orange needles after
recrystallization (CH2Cl2/MeOH) of the residue obtained from the
strongly fluorescent greenish-yellow fraction.
BODIPY 15: Prepared from 7 (423 mg, 42%). 1H NMR (300 MHz,
CD2Cl2): d=7.34–7.27 (m, 4H; Har), 2.48 (s, 6H; CH3), 2.44 (s, 3H;
CH3), 1.86 (s, 6H; CH3), 1.31 (s, 6H; CH3); 13C NMR (75 MHz, CD2Cl2):
d=153.7, 140.8, 139.2, 138.9, 132.7, 130.9, 129.8, 128.2, 126.5, 21.2, 12.5,
11.9, 8.7 ppm; 19F NMR (376 MHz, CD2Cl2): d=ꢀ146.2 ppm (q, J
ACHTREUNG
34 Hz, 2F; BF); 11B NMR (128 MHz, CD2Cl2): d=0.03 ppm (t, J
AHCTREUNG
34 Hz, 1B; BF); HRMS (ESI+): m/z: calcd for C22H25BF2N2Na
[M+Na]+: 389.1971; found: 389.1973; elemental analysis calcd (%) for
C22H25BF2N2·0.25H2O: C 71.27, H 6.93, N 7.56; found: C 71.10, H 6.72, N
7.65.
BODIPY 16: Prepared from 8 (570 mg, 45%). 1H NMR (300 MHz,
CD2Cl2): d=7.36–7.17 (m, 4H; Har), 2.48 (s, 6H; CH3), 2.44 (s, 3H;
CH3), 2.32 (q, J=7.6 Hz, 4H; CH2CH3), 1.61 (q, J=7.5 Hz, 4H;
CH2CH3), 1.04 (t, J=7.6 Hz, 6H; CH2CH3), 0.68 ppm (t, J=7.5 Hz, 6H;
CH2CH3); 13C NMR (75 MHz, CD2Cl2): d=154.2, 145.6, 140.9, 139.1,
[28] A. Weiss, H. Pritzkow, P. J. Brothers, W. Siebert, Angew. Chem.
2001, 113, 4311–4313; Angew. Chem. Int. Ed. 2001, 40, 4182–4184.
2982
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Chem. Eur. J. 2008, 14, 2976 – 2983

Fluorescent Dimers
FULL PAPER
[29] T. Kçhler, M. C. Hodgson, D. Seidel, J. M. Veuthier, S. Meyer, V.
Lynch, P. D. W. Boyd, P. J. Brothers, J. L. Sessler, Chem. Commun.
2004, 1060–1061.
[30] W. J. Belcher, P. D. W. Boyd, P. J. Brothers, M. J. Liddell, C. E. F.
Rickard, J. Am. Chem. Soc. 1994, 116, 8416–8417.
[31] A. Weiss, M. C. Hodgson, P. D. W. Boyd, W. Siebert, P. J. Brothers,
Chem. Eur. J. 2007, 13, 5982–5993.
[32] A. Gossauer, F. Fehr, F. Nydegger, H. Stçckli-Evans, J. Am. Chem.
Soc. 1997, 119, 1599–1608.
10, 4853–4871; c) R. Bandichhor, C. Thivierge, N. S. P. Bhuvanesh,
K. Burgess, Acta Crystallogr. E 2006, 62, o4310–o4311.
[47] F. B. Mallory, C. W. Mallory, Encyclopedia of Nuclear Magnetic Res-
onance, Wiley, New York, 1996.
[48] F. B. Mallory, C. W. Mallory, W. M. Ricker, J. Org. Chem. 1985, 50,
457–461.
[49] K. L. Servis, K.-N. Fang, J. Am. Chem. Soc. 1968, 90, 6712–6717.
[50] J. Chen, J. Reibenspies, A. Derecskei-Kovacs, K. Burgess, Chem.
Commun. 1999, 2501–2502.
[33] F. Borle, F. Fehr, P. Nesvadba, A. Gossauer, Photochem. Photobiol.
1997, 65, 949–956.
[51] M. Kasha, H. R. Rawls, M. A. El-Bayoumi, Pure Appl. Chem. 1965,
11, 371–392.
[34] F. Bergstroem, I. Mikhalyov, P. Haeggloef, R. Wortmann, T. Ny,
L. B. A. Johansson, J. Am. Chem. Soc. 2002, 124, 196–204.
[35] I. Mikhalyov, N. Gretskaya, F. Bergstroem, L. B. A. Johansson,
Phys. Chem. Chem. Phys. 2002, 4, 5663–5670.
[52] H. Langhals, J. Karolin, L. B.-Š. Johansson, J. Chem. Soc. Faraday
Trans. 1998, 94, 2919–2922.
[53] W. Qin, M. Baruah, M. van der Auweraer, F. C. De Schryver, N.
Boens, J. Phys. Chem. A 2005, 109, 7371–7384.
[36] D. Marushchak, S. Kalinin, I. Mikhalyov, N. Gretskaya, L. B. A. Jo-
hansson, Spectrochim. Acta, Part A 2006, 65, 113–122.
[37] Y. Zhang, A. Thompson, S. J. Rettig, D. Dolphin, J. Am. Chem. Soc.
1998, 120, 13537–13538.
[54] M. Kollmannsberger, K. Rurack, U. Resch-Genger, J. Daub, J. Phys.
Chem. A 1998, 102, 10211–10220.
[55] M. Brçring, D. Griebel, C. Hell, A. Pfister, J. Porphyrins Phthalo-
cyanines 2001, 5, 708–714.
[38] H. S. Gill, I. Finger, I. Bozidarevic, F. Szydlo, M. J. Scott, New J.
Chem. 2005, 29, 68–71.
[39] M. Brçring, S. Link, C. D. Brandt, E. Cónsul Tejero, Eur. J. Inorg.
Chem. 2007, 1661–1670.
[40] M. Brçring, E. Cónsul-Tejero, J. Organomet. Chem. 2005, 690,
5290–5299.
[41] M. Brçring, C. D. Brandt, E. Cónsul-Tejero, Z. Anorg. Allg. Chem.
2005, 631, 1793–1798.
[56] M. Brçring, Synthesis 2000, 1291–1294.
[57] R. Grigg, A. W. Johnson, J. W. F. Wasley, J. Chem. Soc. 1963, 359–
366.
[58] A. Treibs, D. Dinelli, Liebigs Ann. Chem. 1935, 517, 152–169.
[59] J. Tang, J. G. Verkade, J. Org. Chem. 1994, 59, 7793–7802.
[60] H. Fischer, E. Jordan, Z. Physiol. Chem. 1930, 191, 36–64.
[61] L. Flamigni, J. Phys. Chem. 1992, 96, 3331–3337.
[62] B. Ventura, A. Degli Esposti, B. Koszarna, D. T. Gryko, L. Flamigni,
New J. Chem. 2005, 29, 1559–1566.
[63] G. M. Sheldrick, SHELXS-97, Program for Crystal Structure Deter-
mination, University of Gçttingen, Gçttingen (Germany), 1997.
[64] G. M. Sheldrick, SHELXL-97, Program for Crystal Structure Re-
finement, University of Gçttingen, Gçttingen (Germany), 1997.
[65] J. H. Boyer, A. M. Haag, G. Sathyamoorthi, M. L. Soong, K. Than-
garaj, T. G. Pavlopoulos, Heteroat. Chem. 1993, 4, 39–49.
[42] M. Brçring, C. D. Brandt, J. Bley-Escrich, J.-P. Gisselbrecht, Eur. J.
Inorg. Chem. 2002, 910–917.
[43] M. Brçring, C. D. Brandt, J. Lex, H.-U. Humpf, J. Bley-Escrich, J.-P.
Gisselbrecht, Eur. J. Inorg. Chem. 2001, 2549–2556.
[44] H. Falk, O. Hofer, H. Lehner, Monatsh. Chem. 1974, 105, 169–178.
[45] R. Ziessel, L. Bonardi, P. Retailleau, G. Ulrich, J. Org. Chem. 2006,
71, 3093–3102.
[46] For examples, see: a) Y.-H. Yu, A. B. Descalzo, Z. Shen, H. Rçhr,
Q. Liu, Y.-W. Wang, M. Spieles, Y.-Z. Li, K. Rurack, X.-Z. You,
Chem. Asian J. 2006, 1, 176–187; b) Z. Chen, H. Rçhr, K. Rurack,
H. Uno, M. Spieles, B. Schulz, G. Reck, N. Ono, Chem. Eur. J. 2004,
Received: December 4, 2007
Published online: February 27, 2008
Chem. Eur. J. 2008, 14, 2976 – 2983
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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2983