Synthesis and optical properties of 2-(Benzo[b]thiophene-3-yl)pyrroles and a new bodipy fluorophore (BODIPY = 4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene)

Article abstract of DOI:10.1002/chem.200802467

2-(Benzo[b]thiophene-3-yl)-1-vinylpyrrole has been synthesized directly from 3-acetylbenzo[b]thiophene oxime and acetylene (flow system, KOH-DMSO, 120 °C, 5 h) in 68% yield. Devinylation of the synthesized pyrrole (Hg(OAc)CU₂, NaBH₄, 50 °C) led to the corresponding 2-(benzo[b]thio-phene-3-yl)pyrrole in 63% yield. Tri-fluoroacetylation of both the pyrroles with trifluoroacetic anhydride (80 °C, 1 h) gave the corresponding 5-trifluor-oacetyl pyrroles in 97% and 76% yields, respectively. 2-(Benzo[b]thio-phene-3-yl)pyrrole was reacted subsequently with mesityl aldehyde, 2,3-di-chloro-5,6-dicyano-1,4-benzoquinone (DDQ), and BF ₃·OEt₂ to afford 4,4-di-fluoro-3,5- diT(benzo[CAGHRUENb]thiophene-3-yl)-8-mesityl-4-bora-3a,4a-diaza-s-inda-cene, a representative of the novel BODIPY fluorophore family (BODIPY = 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene), in 34% overall yield. The synthesized pyrroles exhibit promising optical properties (absorption and emission spectra, nonlinear optical (NLO) features), superior to existing analogues. The BODIPY fluorophore displays an intense red-shifted fluorescence emission in CH₂Cl₂(625 nm, 0.84 fluorescence quantum yield) that is fully preserved in the solid state.

Full text of DOI:10.1002/chem.200802467

FULL PAPER
DOI: 10.1002/chem.200802467
Synthesis and Optical Properties of 2-(Benzo[b]thiophene-3-yl)pyrroles and a
New BODIPY Fluorophore (BODIPY=4,4-Difluoro-4-bora-3a,4a-diaza-s-
indacene)
Elena Yu. Schmidt,[a] Boris A. Trofimov,*[a] Alꢀbina I. Mikhaleva,[a]
Nadezhda V. Zorina,[a] Nadezhda I. Protzuk,[a] Konstantin B. Petrushenko,[a]
Igor A. Ushakov,[a] Marina Yu. Dvorko,[a] Rachel Mꢁallet-Renault,[b] Gilles Clavier,[b]
Thanh Truc Vu,[b] Ha Thanh Thao Tran,[b] and Robert B. Pansu[b]
Abstract: 2-(Benzo[b]thiophene-3-yl)-
1-vinylpyrrole has been synthesized di-
rectly from 3-acetylbenzo[b]thiophene
oxime and acetylene (flow system,
KOH-DMSO, 1208C, 5 h) in 68%
yield. Devinylation of the synthesized
yields, respectively. 2-(Benzo[b]thio-
phene-3-yl)pyrrole was reacted subse-
quently with mesityl aldehyde, 2,3-di-
chloro-5,6-dicyano-1,4-benzoquinone
(DDQ), and BF3·OEt2 to afford 4,4-di-
fluoro-3,5-diACTHNUGRTENUNG(benzo[b]thiophene-3-yl)-
8-mesityl-4-bora-3a,4a-diaza-s-inda-
cene, a representative of the novel
(BODIPY=4,4-difluoro-4-bora-3a,4a-
diaza-s-indacene), in 34% overall
yield. The synthesized pyrroles exhibit
promising optical properties (absorp-
tion and emission spectra, nonlinear
optical (NLO) features), superior to
existing analogues. The BODIPY fluo-
rophore displays an intense red-shifted
fluorescence emission in CH2Cl2
(625 nm, 0.84 fluorescence quantum
yield) that is fully preserved in the
solid state.
pyrrole (Hg
N
to the corresponding 2-(benzo[b]thio-
phene-3-yl)pyrrole in 63% yield. Tri-
fluoroacetylation of both the pyrroles
with trifluoroacetic anhydride (808C,
1 h) gave the corresponding 5-trifluor-
oacetyl pyrroles in 97% and 76%
BODIPY
fluorophore
family
Keywords: acetylene
·
chromo-
phores · fluorescence · pyrroles
Introduction
phene-tailored dyestuffs (aza- and thioindigoid dyes) are of
industrial importance.[2] Benzothiophene and its 3-chloro
and 6-methoxy derivatives exhibit liquid-crystal features.[3]
Combination of the benzo[b]thiophene structural unit with a
pyrrole nucleus leads to molecules with useful optical prop-
erties. Benzothiophene systems fused with the pyrrole nu-
The benzothiophene moiety is a subunit of a number of pro-
spective advanced materials. The fusion of benzene and
thiophene nuclei gives monomers that allow low band gap
conducting polymers to be synthesized.[1] The benzo[b]thio-
cleus, 2H-[1]benzothienoACTHNURGTNE[UNG 3,2-b]pyrroles, have been em-
ployed for the synthesis of merocyanine dyes, which now at-
tract attention as nonlinear optical chromophores for photo-
refractive materials.[4]
[a] Dr. E. Y. Schmidt, Prof. Dr. B. A. Trofimov,
Prof. Dr. A. I. Mikhaleva, Dr. N. V. Zorina, Dr. N. I. Protzuk,
Dr. K. B. Petrushenko, Dr I. A. Ushakov, M. Y. Dvorko
A. E. Favorsky Irkutsk Institute of Chemistry
Siberian Branch of the Russian Academy of Sciences
1 Favorsky Str., Irkutsk 664033 (Russian Federation)
Fax : (+7)3952-41-93-46
Despite the benefits of combination of the benzo[b]thio-
phene–pyrrole structures, such compounds still remain rare
because of the lack of their expedient and general synthesis.
To our knowledge, only two representatives of functional-
ized 2-(benzothiophene-2-yl)pyrroles, namely 4-[5-(4,7-di-
methylbenzothiophene-2-yl)pyrrole-2-yl]- and 4-[5-(5,7-di-
methylbenzothiophenyl-2-yl)pyrrole-2-yl] benzoic acids,[5]
have as yet been reported. These compounds were synthe-
sized from the corresponding benzothiophene-2-yl-carbalde-
hydes and enones, followed by the condensation of the 1,4-
diketones formed with ammonium acetate, the yields being
E-mail: boris_trofimov@irioch.irk.ru
[b] Prof. Dr. R. Mꢀallet-Renault, Dr. G. Clavier, T. T. Vu, H. T. T. Tran,
Prof. Dr. R. B. Pansu
PPSM, ENS Cachan, CNRS
UniverSud, 61 av President Wilson
94230 Cachan (France)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200802467.
Chem. Eur. J. 2009, 15, 5823 – 5830
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
5823

14 and 26%, respectively. These compounds were consid-
ered as prospective immunosuppressive agents.[5] The 3,2-
linked benzothiophene–pyrrole ensembles remain unknown.
At the same time it might be expected that such compounds,
owing to the dye-related benzothiophene entity, will possess
special optical properties, particularly providing fluores-
cence with substantial red shifts and high quantum yields.
Apart from their sound medicinal prospects, such benzothio-
phene–pyrrole ensembles are especially promising as start-
ing materials for the synthesis of fluorophores of the
BODIPY family (BODIPY=4,4-difluoro-4-bora-3a,4a-
diaza-s-indacene), due to extension of the overall conjuga-
tion.[6]
The objective of the present work, therefore, was to de-
velop a straightforward and general approach to the synthe-
sis of unknown 2-(benzo[b]thiophene-3-yl)pyrroles by devel-
oping the Trofimov reaction[7] of ketones (via oximes) with
acetylene as applied to 3-acylbenzo[b]thiophenes, for exam-
ple, 3-acetylbenzo[b]thiophene 1 (via oxime 2), leading to
the synthesis of pyrroles 3 and 4 (Scheme 1).
Results and Discussion
Our experiments have shown that the reaction of oxime 2
with acetylene does follow Scheme 1: when carried out in
KOH–DMSO at 1208C (excess acetylene was passed
through the reaction mixture under atmospheric pressure
for 5 h) it led selectively to 2-(benzo[b]thiophene-3-yl)-1-vi-
nylpyrrole (4) in 68% yield (Scheme 1).
Interestingly, the reaction of the oxime of 2-acetylthio-
phene with acetylene (KOH–DMSO, 1008C, 6.5 h, atmos-
pheric pressure) gave 2-(thiophene-2-yl)pyrrole in only 34%
yield.[9] To synthesize 2-(thiophene-2-yl)-1-vinylpyrrole from
the same starting materials, harsher conditions (KOH–
DMSO, 1208C, 3 h, excess acetylene under 16 atm initial
pressure) were required, and the yield was 62%.
The more facile pyrrole formation from oxime 2 as com-
pared to the oxime of 2-acetylthiophene may be rationalized
in thermodynamics terms: pyrrole 4 possesses a more devel-
oped conjugation system. The same, even more pronounced
effect was observed for the oxime of 2-acetylbenzo[b]furan,
which was converted to the corresponding pyrrole, 2-(ben-
zo[b]furan-2-yl)pyrrole, in 24% yield (KOH–DMSO, 708C,
5 min, acetylene under 14 atm pressure),[10] while the oxime
of 2-acetylfuran reacted with acetylene under more forced
conditions (KOH–DMSO, 70–788C, 6 h, acetylene under
14 atm pressure) to give 2-(2-furyl)pyrrole in 11% yield.[11]
Variation of the reaction conditions (Scheme 1) by using
acetylene under pressure (initial pressure 14–16 atm at RT,
reaching 25–30 atm at the reaction temperature), 90–1208C,
1–1.5 h did not allow the yield of pyrrole 4 to be improved.
Amazingly, the unvinylated pyrrole 3 was not detected at all
(1H NMR spectroscopy). Under milder conditions (808C,
30 min), the only isolable product was O-vinyloxime 5 in
55% yield (Scheme 3).
Scheme 1. Synthesis of 2-(benzo[b]thiophene-3-yl)pyrroles 3 and 4.
The result was neither evident nor predictable, since the
close analogue of the ketone 1, 3-acetylindole (in a form of
its oxime), under common conditions gave the anticipated
pyrrole only in negligible yields, whereas the major product
O-Vinyloximes were assumed to be the key intermediates
in the pyrrole synthesis from ketoximes and acetylene.[12]
According to this mechanism, 3,3-sigmatropic rearrange-
ment of a tautomeric form of O-vinyloxime 5 should lead to
was
3-acetyl-1-vinylindole
along
with
d-carboline
(Scheme 2).[8]
unvinylated
pyrrole
3
(Scheme 3). Indeed, the smooth
rearrangement of O-vinyloxime
5 to pyrrole 3 was observed
under conditions of 1208C for
30 min in DMSO, a minor side
product being the ketone
1
(5:1, 1H NMR spectroscopy).
Apparently, in this special case,
pyrrole 3 was unusually prone
to vinylation and was trapped
by acetylene just at the moment
of its formation (Scheme 4).
Scheme 2. Reaction of 3-acetylindole oxime with acetylene.
The unvinylated pyrrole 3,
further required for the synthe-
sis of the BODIPY dye was
also prepared in 63% yield
through devinylation (deprotec-
tion) of pyrrole 4 by using sub-
Scheme 3. Synthesis of O-vinyloxime 5 and its rearrangement to pyrrole 3.
5824
www.chemeurj.org
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 5823 – 5830

Properties of Pyrroles and BODIPY Fluorophore
FULL PAPER
Scheme 4. Vinylation of pyrrole 3 with acetylene.
sequent treatment with mercury acetate and sodium boro-
ACHTUNGTRENNUNGhydrate (Scheme 5).
Scheme 7. Synthesis of BODIPY 8.
1
signments of H and 13C NMR spectra were performed by
COSY, NOESY, HSQC, and HMBC experiments.
The electronic absorption and fluorescent properties of
pyrroles 3, 4, 6, and 7 have been studied (Figure 1, Table 1).
Scheme 5. Deprotection of 1-vinylpyrrole 4.
Pyrroles 3 and 4 are compounds that combine the pyrrole
nucleus and condensed heteroaromatic system (the benzo-
thiophene moiety) in a single-conjugation chain; as in the
cases of pyrenoACHTUNGTRENNUNG ,
[2,1-b]pyrroles[13] and naphthodithiophenes[1]
this secures a small HOMO–LUMO energy gap, decreases
ionization potential and redox activity, and enhances elec-
trochromic and photochromic responses. The N-vinyl sub-
stituent in pyrrole 4 provides a useful handle for further
functionalization and polymerization.
Figure 1. Normalized electronic absorption (1–3, 2ꢂ10ꢀ3 molLꢀ1
) and
fluorescence (4–6, 4ꢂ10ꢀ5 molLꢀ1) spectra (in hexane): 2,4: 3; 1,5: 4; 3,6:
6.
The trifluoroacetylation of pyrroles 3 and 4 was readily ef-
fected with trifluoroacetic anhydride in pyridine (808C, 1 h)
to give regiospecific trifluoroacetyl derivatives 6 and 7 in
97% and 76% yields, respectively, at the 5-position of the
pyrrole ring (Scheme 6).
Table 1. Electronic absorption and fluorescent spectra of pyrroles 3, 4, 6,
and 7 in hexane (acetonitrile).
Pyrrole
Absorption
emax [Lmolꢀ1 cmꢀ1
Fluorescence
Stokes shift
Dn [cmꢀ1
lmax [nm]
]
lmax [nm]
]
3
4
6
7
309 (310)
300 (300)
345 (350)
325 (332)
6800 (7900)
5800 (4500)
18000 (21000)
13000 (12500)
363 (387)
363 (383)
385 (437)
–
4800 (6400)
5800 (7200)
3000 (5700)
–
The relatively large Stokes shifts for pyrroles 3 and 4 are
probably due to their nonplanar structure. According to
quantum chemical calculations (DFT/B3LYP/6-31+G(d)),
the dihedral angles between the pyrrole and benzothiophene
cycles in the ground state (S0) are 38 and 488, respectively,
corresponding to the steric effect of the N-vinyl group,
which further distorts the coplanarity. For the first excited
singlet state (S1) these angles decrease to 158 and 238, re-
spectively (CIS//6-31G). The increase of torsion angle
caused by the N-vinyl substituent is accompanied by a small
hypsochromic shift of the longest band in the absorption
Scheme 6. Trifluoroacetylation of pyrroles 3 and 4.
Pyrrole 3 was further involved in the synthesis of 4,4-di-
fluoro-3,5-diACHTUNGTRENNUNG(benzo[b]thiophene-3-yl)-8-mesityl-4-bora-
3a,4a-diaza-s-indacene (8; BODIPY), a prospective fluoro-
phore. To reach this goal, pyrrole 3 was treated with 2,4,6-
trimethylbenzaldehyde in the presence of trifluoroacetic
acid. The dipyrromethane thus formed was oxidized in situ
with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) to
yield dipyrromethene, which, after reaction with BF3 ether-
ate, afforded the target BODIPY 8 in 34% overall yield
(Scheme 7).
spectra and simultaneously by
(Figure 1, Table 1).
a hypochromic effect
The calculated energy values of vertical transitions for the
!
!
absorption (S1 S0) and fluorescence (S0 S1) spectra for
pyrroles 3 and 4 (Table 2) and experimental data (Table 1,
in hexane) match well. The major contributions to these
The structures of all the compounds synthesized were
confirmed by their NMR (1H, 13C) and IR spectra; the as-
Chem. Eur. J. 2009, 15, 5823 – 5830
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5825

B. A. Trofimov et al.
!
Table 2. TD-DFT calculation results for electronic transitions S1 S0 and
S0 S1 of pyrroles 3 and 4.
role 7, because of complications imposed by its photodegra-
dation.
!
!
!
S0 S1
[a]
[b]
S1 S0
f[c]
The pyrroles 3, 4, and 6 were preliminarily shown to pos-
sess NLO properties. For example, when pyrrole 3 was irra-
diated with an IR laser (1064 nm), the second harmonic gen-
erated (532 nm) was approximately eight times lower in in-
tensity than that of LiIO3, known as having high NLO effi-
ciency (deff =4.1ꢂ10ꢀ12 mVꢀ1),[14] whereas pyrrole 6 was ꢁ15
times less effective. The NLO properties of the vinylpyrrole
4 were hardly discernible.
l [nm]
Main
l [nm]
f
Main
configuration
configuration
3
4
316.91
308.75
0.115
0.082
H-L (0.650[d]
H-L (0.627)
)
374.08
366.80
0.185
0.230
H-L (0.619)
H-L (0.629)
[a] In optimal geometry of the ground state (B3LYP/6-31+G(d)). [b] In
optimal geometry of the excited state (CIS/6–31G): H=HOMO, L=
LUMO. [c] Oscillator strength. [d] Coefficients.
The spectral properties of compound 8 (BODIPY) were
studied both in dichloromethane (Figure 3, Table 3) and
solid state (thin amorphous film, see Figures 5, and 6, later).
transitions belong to the configurations corresponding to the
electron transfer from the HOMO to the LUMO. The struc-
ture of these molecular orbitals (Figure 2) allows these tran-
Figure 3. Absorption (black line) and emission (black dotted line, lexc
581 nm) spectra of compound 8 in dichloromethane (6ꢂ10ꢀ6 molLꢀ1).
=
Figure 2. B3LYP/6-31+G(d) molecular orbitals (LUMO top, HOMO
bottom) of 3 (left) and 4 (right).
Table 3. Spectroscopic features of BODIPY 8 in dichloromethane.
[a]
e581 [Lmolꢀ1 cmꢀ1
]
labs [nm]
lem [nm]
fF
tF ꢂ0.2[b] [ns]
63800
581
625
0.84
[c]
kr[c] [108 sꢀ1
]
knr [108 sꢀ1
]
R0[d] [nm]
5.43
Stokes shift Dn [cmꢀ1
]
sitions to be assigned as pp*-type transitions. This confirms
the inference about the more planar structure of pyrroles 3
and 4 in the excited state. In this case, the HOMOs are anti-
bonding for the intercyclic bonds that preclude the coplanar-
ity of the ground state, whereas the LUMOs for these re-
gions are pronouncedly bonding. Hence, the population of
the LUMOs should planarize the excited S1 state.
1.40
0.27
1200
[a] lexc =581 nm; sulforhodamine 101 in ethanol was used as a reference,
fF =0.9.[15] [b] Experimental data.[16] [c] Calculated values from fF =
(kr+knr). [d] Calculated Fçrster radius.[17,18]
(kr/ACHTNUGTRENN(UG kr+knr); tF =1/HCATUNGTRENNGUN
For trifluoroacetyl derivative 6, a broad, structureless,
highly intense long-wave absorption band, as well as a large
bathochromic shift of the fluorescent band maximum in
MeCN as compared to that in hexane (Figure 1, Table 1), is
indicative of a charge transfer pp* transition. The smaller
Stokes shift for pyrrole 6 relative to that of pyrrole 3
(Table 1) is evidence for the extra planarization of the mo-
lecular skeleton owing to the introduction of the CF3CO
substituent to the pyrrole moiety (the effect of through-con-
jugation).
From DFT/B3LYP/6-31+G(d) calculations, the dihedral
angle between BODIPY and benzothiophene moieties in
the ground state (S0) was found to be 408, which is very sim-
ilar to that calculated for pyrrole 3 (see above).
!
The shape of the absorption band is typical of the S1 S0
transition found in other BODIPYs,[19] with a high extinction
coefficient (Table 3). Table 4 summarizes the data calculated
by the TD-DFT method, which are consistent with the ob-
served band.
The long wavelength absorption band of pyrrole 7 is ob-
served in a shorter wavelength region than that of pyrrole 6,
and is of lower intensity (Table 1), thus corresponding to the
coplanarity distortion due to the vinyl group steric effect. It
was impossible to register the fluorescent spectrum of pyr-
!
Table 4. TD-DFT calculated electronic transition (S1 S0) of BODIPY 8.
l [nm]
f
Main configuration
H-L (0.613)
8
545
0.510
5826
www.chemeurj.org
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 5823 – 5830

Properties of Pyrroles and BODIPY Fluorophore
FULL PAPER
!
The second band (l=417 nm) corresponds to the S2 S0
transition (e417=11400 Lmolꢀ1 cmꢀ1). Three other UV bands
appear at 333, 300, and 254 nm, but these cannot be easily
attributed. Compared to alkyl-substituted derivatives[20] (labs
!
ꢁ515–530 nm) the absorption of the main band (S1 S0) is
shifted to a longer wavelength (labs=581 nm), which is con-
sistent both with the calculated partial charge transfer and
conjugation of the benzothiophene nuclei with the BODIPY
core.
Whatever the excitation wavelength is (lexc=254, 300, 333,
417, or 581 nm), only one fluorescence emission band is ob-
!
served at 625 nm. It corresponds to the classical S0 S1 tran-
sition typical for BODIPY derivatives. A high fluorescence
quantum yield was found (fF =0.84 at lexc =581 nm). As
found previously, the emission maximum of 3,5-diaryl-substi-
tuted BODIPYs is shifted to longer wavelength (lem =588–
626 nm)[21,22] as the 3,5-aryl groups extend the conjugation of
the BODIPY core. It is worth noting that fluorophore 8 ex-
hibits the same absorption and emission wavelengths as a
BODIPY with a p-electron-donating group (methoxy) in
the aryl substituent, but has a much higher fluorescence
quantum yield (Table 5). Such a difference comes from the
Figure 4. Calculated electron density changes accompanying the first
electronic excitation of fluorophore 8. The grey and black lobes signify
decreases and increases in electron density accompanying the electronic
transition. Their areas indicate the magnitude of the electron density
change.
Table 5. Comparison of fluorescent properties of fluorophore 8 with 3,5-
di(4-methoxyphenyl) substituted BODIPY.
Figure 5. Absorption spectra (1,3, dotted line) and fluorescence emission
spectra (2,4, solid line) of BODIPY 8 in CH2Cl2 (1,2) and an amorphous
deposit of 8 (3,4).
CHCl3 fF 0.42
labs 582 nm
CH2Cl2 fF 0.84
labs 581 nm
lem 626 nm
lem 625 nm
to longer wavelengths by 8 nm is observed for the absorp-
tion band, which arises from intermolecular interactions.[25]
As the bathochromic shift is small, we may postulate that in-
teractions between chromophores are quite weak. Looking
at the emission properties, the fluorescence band is located
at the same position as in solution (625 nm) with a shoulder
at 652 nm. The 625 nm emission may arise from the mono-
mer and the 652 nm shoulder from the aggregates.
The photostability of compound 8 was investigated in cast
film. The fluorescence intensity remains nearly constant
(less than 3% loss) under laser irradiation (1.3 mW) at
515 nm for 2500 s (see data in Supporting Information).
We made an attempt to eval-
mesityl group in the meso-position[23] and from the bulky
benzothiophene moiety, both of which prevent the free rota-
tion of the substituents.
The measured fluorescence lifetime (5.99 ns) and calculat-
ed radiative (kr =1.40ꢂ10ꢀ8 sꢀ1) and nonradiative (knr =
0.27ꢂ10ꢀ8 sꢀ1) constants are typical of BODIPY deriva-
tives.[24] The Stokes shift (1200 cmꢀ1) is larger compared to
3,5-alkyl-substituted BODIPY derivatives (350–400 cmꢀ1).
This may be rationalized by the large change in electronic
density between the ground (S0, v0) and the excited (S1, v0)
states (Figure 4). A partial charge transfer from the benzo-
thiophene moiety to the BODIPY core takes place.
Amorphous films were prepared by evaporation of a solu-
tion of BODIPY 8 in dichloromethane (0.2 mmolLꢀ1). They
were studied by microscopy imaging. Typical transmission
and fluorescence images are shown in the Supporting Infor-
mation.
uate
a
relative fluorescence
quantum yield in the solid state.
We prepared amorphous films
from a simple 3,5-dialkyl-substi-
tuted BODIPY [from 2,4-di-
methyl-3-ethylpyrrole (krypto-
pyrrole), shown here] and com-
The interesting spectroscopic properties of the amorphous
spots are close to those for the solution (Figure 5). A shift
Chem. Eur. J. 2009, 15, 5823 – 5830
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5827

B. A. Trofimov et al.
pared it to amorphous deposits of compound 8. To evaluate
the number of emitted photons versus the number of ab-
sorbed photons, we plotted the surface of the fluorescence
emission spectra (denoted as Area) as a function of the ab-
sorbance value (denoted as A515) at the excitation wave-
length (515 nm) (Figure 6). It is quite striking that BODIPY
Experimental Section
NMR spectra were recorded at RT on a Bruker DPX 400 spectrometer
(400.13 MHz, 1H; 101.61 MHz, 13C) with HMDS as an internal standard.
The assignments of 1H and 13C NMR spectra were performed by COSY,
NOESY, HSQC, and HMBC experiments. The NMR spectrum of
BODIPY 8 was recorded on a 400ECS spectrometer from JEOL. IR
spectra were obtained on a Bruker IFS25 instrument. UV/Vis absorption
spectra were measured with a Varian CARY 500 spectrophotometer. Ex-
citation and emission spectra were measured on a SPEX Fluorolog-3
(Jobin-Yvon). The solvent used was dichloromethane (spectroscopic
grade) from Sigma-Aldrich. For liquid samples, a right-angle configura-
tion was used and optical density was adjusted below 0.1 to avoid reab-
sorption artifacts. Fluorescence decay curves were obtained with a time-
correlated single-photon-counting method using a titanium-sapphire laser
pumped by an argon ion laser (82 MHz, 1 ps pulse width, repetition rate
lowered to 4 MHz using a pulse-peaker; a doubling crystal was used to
reach 495 nm excitation).[29] The Levenberg–Marquardt algorithm was
used for the nonlinear least-square fit.[30] Fluorescence properties of com-
pound 8 and kryptoBODIPY were studied on cast films (amorphous de-
posits) prepared by evaporation of a droplet of the dye in solution
(about 0.1 to 1 mmolLꢀ1 in CH2Cl2) onto microscope slides. For one se-
lected position (on a film), the transmission and fluorescence images
were recorded as well as the related absorption and emission spectra
with a fiber multichannel spectrophotometer (Ocean Optics, Inc.). From
four or five different positions, we could plot the surface of the each
emission spectrum as a function of the related absorbance at 515 nm and
estimate a relative fluorescence quantum yield (comparison between 8
and kryptoBODIPY). Fluorescence stability measurements on cast films
were performed using an excitation at 515 nm from a frequency-doubled
femtosecond laser (t-Pulse 200 Amplitude, l=1030 nm, 10 MHz, 100 fs
FWHM). The detector was a fluorescence imaging setup, which has been
described previously.[31] Calculations were performed by using the Gaus-
sian software[32] at the MESO calculation center of the ENS Cachan (Nec
TX7 with 32 processors Itanium 2). The ground-state minimum was de-
termined by B3LYP/6-31+G(d). Excited states were obtained with
TDDFT B3LYP/6-31+G(d). The density difference was calculated by
subtraction of the first excited state electron density (CIS state 1 one-par-
ticle Total Density) from the ground state one (SCF Total Density).
Second harmonic generation was carried out in powders according to the
method proposed by Kurtz and Perri.[33] Harmonic intensity was com-
pared with that of powder prepared from nonlinear LiIO3 crystals. The
second harmonic was generated by the neodime–yttrium–aluminum
garnet (Nd:YAG) laser with Q-switching at the operating wavelength of
l=1064 nm. The excitation impulse intensity was ꢁ107 Wcmꢀ2. The spec-
tral composition and amplitude of the second harmonic impulse was con-
Figure 6. Plot of the fluorescence emission band area as a function of the
absorbance value at 515 nm (A515). BODIPY 8 (+) and kryptoBODIPY
*
).
(
8 has a higher fluorescence quantum yield (five times
higher) compared to the kryptoBODIPY. p-Stacking is con-
sidered to be the principal culprit behind the loss of fluores-
cence in crystalline form.[26,27] Here we have demonstrated
that developing a new fluorophore in which the BODIPY
core is separated from its neighbors in the solid state by
bulky substituents gives rise to a stronger fluorescence emis-
sion compared to lower alkyl-substituted BODIPY. Similar
conclusions have been deduced by other research.[28]
Conclusion
To summarize, with the example of 3-acetylbenzo[b]thio-
phenes, the first facile and expedient synthesis of 2-(ben-
zo[b]thiophene-3-yl)pyrroles from available 3-acylbenzo[b]-
thiophenes (through their oximes) and acetylene has been
developed. The electronic absorption and fluorescent spec-
tra of benzo[b]thiophene-pyrroles and their derivatives
show the pyrroles to possess properties prospective for opto-
electronic materials and devices such as highly efficient fluo-
rescent sensors. A new BODIPY fluorophore has been de-
rived from 2-(benzo[b]thiophene-3-yl)pyrrole, which shows
promising spectroscopic properties in solution (bathochro-
mic shift, high fluorescence quantum yield). Notably, these
properties are transposed to the solid state; the positions of
the absorption and emission bands are preserved and the
fluorescence remains intense despite the close packing. This
result emphasizes the importance of the incorporation of a
steric group in the BODIPY fluorophore to maintain good
emission properties in the solid state. Work is currently in
progress to develop, using this original BODIPY, highly
emissive nanomaterials for sensing applications.
trolled using
MDR-23.
a
photomultiplier and
a
diffractional monochromator
3-Acetylbenzo[b]thiophene oxime (2):
A
mixture of (1.00 g,
1
5.67 mmol), H2NOH·HCl (0.49 g, 7.09 mmol) and pyridine (15 mL) was
heated (808C) for 5 h and then poured into water (80 mL). The crystal-
line precipitate was filtered off, washed with water and dried in vacuo to
afford 0.99 g (yield 91%) of 2 as a white powder (m.p. 118–1208C).
3
1H NMR (400.13 MHz, CDCl3): d=8.50 (d, J4’-5’ =7.9 Hz, 1H; 4’-H), 7.84
(d, 3J
ACTHNUTRGNEUNG(7’,6’)=7.9 Hz, 1H; 7’-H), 7.69 (brs, 1H; OH), 7.60 (s, 1H; 2’-H),
7.43–7.34 (m, 2H; 5’-H, 6’-H), 2.38 ppm (s, 3H; Me); 13C NMR
(101.61 MHz, CDCl3): d=153.6 (C=N), 140.4 (C-7a’), 136.4 (C-4a’), 133.0
(C-3’), 127.1 (C-2’), 125.6 (C-4’), 124.8 (C-5’,C-6’), 122.5 (C-7’), 13.3 ppm
(Me); IR (KBr): n˜ =3430, 1637, 1456, 1425, 1377, 1232, 1067, 986, 903,
757, 721, 687, 426 cmꢀ1; elemental analysis calcd (%) for C10H9NOS
(191.25): C 62.80, H 4.74; N 7.32, S 16.76; found: C 62.95, H 5.04, N 7.45,
S 16.86.
2-(Benzo[b]thiophene-3-yl)pyrrole (3): Mercury acetate (2.12 g,
6.66 mmol) in aqueous acetonitrile (15 mL, 10%) was added to 4 (0.50 g,
2.22 mmol) in acetonitrile (15 mL) while stirring. The reaction mixture
was stirred for 30 min at 508C, then NaBH4 (0.38 g, 10.00 mmol) was
added in small portions. After gas evolution was complete, the residue
was filtered off. The filtrate was diluted with brine (50 mL), extracted
5828
www.chemeurj.org
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 5823 – 5830

Properties of Pyrroles and BODIPY Fluorophore
FULL PAPER
with diethyl ether (3ꢂ15 mL), and the combined ether extracts were
dried over K2CO3 overnight. Diethyl ether was removed to give 0.28 g
removal of benzene and vacuum sublimation, the residue of 6 or 7 was
obtained. Column chromatography (basic Al2O3, hexane) of the residue
after evaporation of the hexane gave pure 6 or 7.
(yield 63%) of
(400.13 MHz, CDCl3): d=8.37 (brs, 1H; NH), 8.05 (d, 3J
1H; 7’-H), 7.87 (d, 3J
(4’,5’)=8.4 Hz, 1H; 4’-H), 7.42–7.35(m, 2H; 5’-H,
3
as white crystals (m.p. 78–808C). 1H NMR
AHCTUNGTREG(NNUN 6’,7’)=8.4 Hz,
Compound 6: Yield 0.14 g (97%), yellow crystals (m.p. 178–1808C);
1H NMR (400.13 MHz, CDCl3): d=9.73 (brs, 1H; NH), 8.01 (d, 3J-
ACHTUNGTRENNUNG
ACHUTNGRENNUG HCATUNGTREN(NUGN 4’,5’)=7.8 Hz, 1H; 4’-H,), 7.71 (s,
(6’,7’)=7.7 Hz, 1H; 7’-H,), 7.92 (d, 3J
6’-H), 7.29 (s, 1H; 2’-H), 6.89–6.88 (m, 1H; 5-H), 6.54–6.55 (m, 1H; 3-
H), 6.36–6.35 ppm (m, 1H; 4-H); 13C NMR (101.61 MHz, CDCl3): d=
140.6 (C-7ꢃ’), 137.4 (C-4a’), 129.8 (C-2), 126.9 (C-3’), 124.7, 124.6 (C-5’,
C-6’), 123.1, 123.0 (C-4’, C-7’), 120.9 (C-2’), 118.4 (C-5), 109.7 (C-3),
107.7 ppm (C-4); IR (KBr): n˜ =3372, 1417, 1342, 1097, 1041, 982, 827,
805, 759, 730, 569, 418 cmꢀ1; elemental analysis calcd (%) for C12H9NS
(199.27): C 72.33, H 4.55, N 7.03, S 16.09, found: C 72.45, H 4.47, N 7.20,
S 16.27.
1H; 2’-H), 7.46–7.42 (m, 2H; 5’-H, 6’-H), 7.34–7.33 (m, 1H; 4-H), 6.74–
6.73 ppm (m, 1H; 3-H); 13C NMR (101.61 MHz, CDCl3): d=170.1 (C=
O), 142.4 (C-5), 140.6 (C-7a’), 137.5 (C-4a’), 136.4 (C-2), 126.8 (C-3’),
126.0 (C-2’), 125.3 (C-5’, C-6’), 123.2ACTHNUGTRNEUNG(C-4’), 122.8 (C-4), 122.4 (C-7’),
117.1 (CF3), 111.8 ppm (C-3); IR (KBr): n˜ =3372, 1417, 1342, 1097, 1041,
982, 827, 805, 759, 730, 569, 418 cmꢀ1; elemental analysis calcd (%) for
C14H8F3NOS (295.28): C 56.95, H 2.73, F 19.30, N 4.74, S 10.86; found: C
57.01, H 2.99, F 18.97, N 4.70, S 10.67.
Compound 7: Yield 0.16 g (76%), yellow oil (n2d0 =1.6365); 1H NMR
(400.13 MHz, CDCl3): d=7.88–7.87 (m, 1H; 7’-H), 7.59–7.58 (m, 1H; 4’-
2-(Benzo[b]thiophene-3-yl)-1-vinylpyrrole (4): A mixture of 2 (1.00 g,
5.23 mmol) was dissolved in DMSO (20 mL) in a 50 mL flask equipped
with a stirrer and then KOH (0.66 g, 10.15 mmol) was added. At 1208C,
pure, dry acetylene was fed under vigorous stirring at the rate of 4–
6 mLminꢀ1 for 6 h. The reaction mixture, after cooling, was diluted with
a threefold volume excess of ice water and extracted with diethyl ether
(5ꢂ15 mL). The ether extracts were washed with cold water (3ꢂ10 mL)
to remove dissolved DMSO and dried over K2CO3 overnight. Column
chromatography (basic Al2O3, hexane) of the residue (1.26 g) after evap-
oration of the hexane gave 0.80 g (yield 68%) of 4 as white crystals (m.p.
68–708C). 1H NMR (400.13 MHz, CDCl3): d=7.88–7.87 (m, 1H; 7’-H),
7.72–7.71 (m, 1H; 4’-H), 7.37–7.36 (m, 2H; 5’-H, 6’-H), 7.35 (s, 1H; 2’-
H), 7.51 (s, 1H; 2’-H), 7.40–7.37 (m, 4H; X-H, 4-H, 5’-H, 6’-H), 6.50 (d,
3
3J
(d, 3J
(3,4)=4.2 Hz, 1H; 3-H), 4.95 (d, J
N
AHCTUNGTRENNUNG
(B,X)=15.6 Hz, 1H; B-H); 13C NMR (101.61 MHz, CDCl3): d=
169.4 (C=O), 148.9 (C-5), 139.9 (C-7a’), 139.0 (C-4a’), 137.4 (C-2), 131.7
(C-a), 127.9 (C-2’), 126.9 (C-3’), 125.1, 124.9 (C-5’, C-6’), 124.3 (C-4),
123.2 (C-4’), 122.9 (C-7’), 116.7 (CF3), 114.3 (C-3), 113.2 ppm (C-b); IR
(film): n˜ =3349, 3097, 1644, 1572, 1520, 1510, 1422, 1381, 1349, 1251,
1219, 1191, 1141 cmꢀ1; elemental analysis calcd (%) for C16H10F3NOS
(321.32): C 59.81, H 3.14, F 17.74, N 4.36, S 9.98; found: C 59.85, H 2.99,
F 17.44, N 4.20, S 9.87.
3
3
H), 7.19–7.18 (m, 1H; 5-H), 6.77 (dd, J
1H; X-H), 6.36–6.35 (m, 2H; 4-H, 3-H), 5.14 (d, 3J
B-H), 4.60 ppm (d, 3J(A,X)=8.8 Hz, 1H; A-H); 13C NMR (101.61 MHz,
G
ACHTUNGTREN(NUNG B,X)=15.7 Hz,
AHCTUNGTRENNUNG
4,4-Difluoro-3,5-diACHTNUTGRNEUNG(benzo[b]-thiophen-3-yl)-8-mesityl-4-bora-3a,4a-diaza-
ACHTUNGTRENNUNG
s-indacene (8): Pyrrole 3 (0.12 g, 0.6 mmol) and 2,4,6-trimethylbenzalde-
hyde 9 (0.044 g, 0.3 mmol) were dissolved in degassed CH2Cl2 (25 mL),
then two drops of TFA were added and the obtained solution was stirred
for 23 h under argon at room temperature. Then DDQ (0.06 g,
0.26 mmol) was added and the reaction mixture was stirred for 0.5 h.
After that, diisopropylethylamine (0.37 mL, 0.27 g, 2.1 mmol) and boron
trifluoride etherate (0.42 mL, 0.47 g, 3.3 mmol) were added with subse-
quent stirring of the obtained fluorescent solution for 0.5 h. After evapo-
ration of the solvent at ambient temperature in vacuo, chromatography
was performed on the residue under nitrogen on silica (CH2Cl2/petrole-
um ether=1:3) to afford BODIPY 8 (0.058 g, 34%). The deep violet
crystals did not melt above 3008C; 1H NMR (400.13 MHz, CDCl3): d=
8.36 (s, 2H; 2’-H), 7.90–7.85 (m, 4H; 4’-H, 7’-H), 7.37–7.33 (m, 4H; 5’-H,
6’-H), 7.02 (s, 2H; 3’’-H), 6.76–6.74 (m, 4H; 6-H, 7-H), 2.40 (s, 3H; CH3-
4’’-C), 2.26 ppm (s, 6H; CH3-2’’-C); 13C NMR (101.61 MHz, CDCl3): d=
151.8 (C-2, C-5), 143.1 (C-8), 140.1 (C-4a’, C-7a’), 138.8 (C-4’’), 138.3 (C-
4a’, C-7a’), 137.0 (C-1’’), 136.3 (C-1a, C-7a), 131.0 (C-2’), 130.4 (C-2’’),
129.3 (CH pyrrole), 128.3 (C-3’’), 127.6 (C-3’), 124.7 and 124.6 (C-5’ and
C-6’), 123.2 and 123.0 (C-4’ and C-7’), 120.9 (CH pyrrole), 21.3 (CH3-
C4’’), 20.4 ppm (CH3-C-2’’); 19F (376 MHz, CDCl3): d=ꢀ133.9 ppm (q, J-
CDCl3): d=139.9 (C-7a’), 139.0 (C-4a’), 131.7 (C-a), 128.1 (C-3’), 127.5
(C-2), 126.2 (C-2’), 124.7, 124.6 (C-5’, C-6’), 123.6 (C-4’), 122.8 (C-7’),
117.8 (C-5), 111.3, 110.3 (C-3, C-4), 98.4 ppm (C-b); IR (KBr): n˜ =3093,
1711, 1640, 1582, 1449, 1432, 1414, 1336, 1280, 1255, 1233, 1161, 1075,
1062, 973, 922, 870, 858, 825, 790.2, 757, 740, 733, 664, 595, 567, 489,
428 cmꢀ1; elemental analysis calcd (%) for C14H11NS (225.31): C 74.63, H
4.92, N 6.22, S 14.23; found: C 74.85, H 4.99, N 6.20, S 14.27.
O-Vinyloxime of 3-acetylbenzo[b]thiophene (5): A mixture of 2 (1.00 g,
5.23 mmol) and KOH·0.5H2O (0.66 g, 10.15 mmol) was dissolved under
heating (708C) in DMSO (50 mL). The solution of potassium oximate
thus obtained was placed into a 0.25 L steel rotating autoclave. Then
acetylene gas was transferred to the autoclave to remove air and the au-
toclave was charged with acetylene again from a cylinder at room tem-
perature (initial pressure 14 atm). The autoclave was heated upon rotat-
ing (808C) for 30 min. The reaction mixture, after cooling to room tem-
perature, was extracted with pentane (7ꢂ10 mL). The pentane extracts
were washed with cold water (3ꢂ10 mL) to remove dissolved DMSO.
The mixture was dried over K2CO3 overnight and the pentane was re-
moved to yield a residue (1.93 g). After column chromatography (basic
Al2O3, hexane) pure 5 was obtained (0.63 g, 55%) as an oil (n2d0 1.6166).
1H NMR (400.13 MHz, CDCl3): d=8.63–8.62 (m, 1H; 4’-H), 7.84–7.83
(m, 1H; 7’-H), 7.68 (s, 1H; 2’-H), 7.43–7.42 (m, 1H; 5’-H), 7.34–7.33 (m,
ACHUTNGRENNUG ACHTUTGNREN(NUGN F,B)=32 Hz).
(F,B)=32.3 Hz); 11B (128 MHz, CDCl3): d=0.5 ppm (t, J
1H; 6’-H), 7.10 (dd, 3J
(dd, 3J(B,X)=14.2 Hz, 2J
6.6 Hz, 2J(A,B)=1.7 Hz, 1H; A-H), 2.42 ppm (s, 3H, Me); 13C NMR
A
ACHTUNGTRENNUNG
A
R
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
Acknowledgements
(101.61 MHz, CDCl3): d=154.6 (C=N), 152.8 (C-a), 140.5 (C-7a’), 136.2
(C-4a’), 132.2 (C-3’), 128.6 (C-2’), 126.2 (C-4’), 125.1 (C-5’, C-6’), 122.6
(C-7’), 88.4 (C-b), 14.5 ppm (Me); IR (film): n˜ =3106, 3065, 2926, 2854,
1668, 1636, 1601, 1504, 1458, 1426, 1375, 1241, 1165, 1146, 1068, 993, 888,
859, 759, 735, 667, 479, 422 cmꢀ1; elemental analysis calcd (%) for
C12H11NOS (217.29): C 66.33, H 5.10, N 6.45, S 14.75; found: C 65.98, H
5.45, N 6.33, S 14.79.
This work was supported by the Russian Foundation for Basic Research
(Grants 07–03–92162-PICS and 08–03–00002) and the French Centre
AHCTUNGTREGNNNUN ational de la Recherchꢀ Scientifique (PICS 3922).
[1] Handbook of Conducting Polymers, (Eds.: T. A. Skotheim, J. R.
Reynolds), 3rd ed., CRC Press Taylor & Francis Group, Boca,
Raton, London, New York, 2007.
[2] T. Hihara, Y. Okada, Z. Morita, Dyes Pigm. 2002, 53, 153–177.
[3] M. Kurfꢄrst, V. Kozmꢅk, J. Svoboda, V. Novotnꢆ, M. Glogarov,
Liquid Crystals 2008, 35, 21–31.
[4] A. A. Shimkin, V. Z. Shirinian, D. M. Nikalin, M. M. Krayushkin,
T. S. Pivina, N. A. Troitsky, L. G. Vorontsova, Z. A. Starikova, Eur.
J. Org. Chem. 2006, 2087–2092.
2-(Benzo[b]thiophene-3-yl)-5-trifluoroacetylpyrrole (6) and 2-(benzo[b]-
thiophene-3-yl)-5-trifluoroacetyl-1-vinylpyrrole (7) (general procedure):
Trifluoroacetic anhydride (0.16 g, 0.75 mmol) was added dropwise to a
mixture of 3 or 4 (0.5 mmol) and pyridine (0.06 g, 0.75 mmol) in benzene
(5 mL), for 1 h at 808C. The reaction mixture was poured into a saturated
aqueous solution of NaHCO3 (30 mL). The organic layer was separated
and the aqueous layer extracted with benzene (5ꢂ5 mL). The combined
extracts were washed with water (3ꢂ5 mL) and dried over K2CO3. After
Chem. Eur. J. 2009, 15, 5823 – 5830
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5829

B. A. Trofimov et al.
[5] H. Yoshimura, K. Kikuchi, Sh. Hibi, K. Tagami, T. Satoh, T. Yamau-
chi, A. Ishibahi, K. Tai, T. Hida, N. Tokuhara, M. Nagai, J. Med.
Chem. 2000, 43, 2929–2937.
[22] A. Burghart, H. Kim, M. B. Welch, L. H. Thoresen, J. Reibenspies,
K. Burgess, F. Bergstrçm, L. B.-A. Johansson, J. Org. Chem. 1999,
64, 7813–7819.
[6] a) A. Loudet, K. Burgess, Chem. Rev. 2007, 84, 4891–4932; b) R.
Ziessel, G. Ulrich, A. Harriman, New J. Chem. 2007, 31, 496–501;
c) G. Ulrich, R. Ziessel, A. Harriman, Angew. Chem. 2008, 120,
1202–1219; Angew. Chem. Int. Ed. 2008, 47, 1184–1201; d) L. Bo-
nardi, G. Ulrich, R. Ziessel, Org. Lett. 2008, 10, 2183–2186.
[7] a) G. P. Bean in The Chemistry of Heterocyclic Compounds, Vol. 48
(Ed.: R. A. Jones), Wiley, New York, 1992, pp. 105–130; b) R. J. Te-
deschi in Encyclopedia of Physical Science and Technology, Vol. 1,
Academic Press, San Diego, 1992, pp. 27–65; c) F. Bellina, R. Rossi,
Tetrahedron 2006, 62, 7213–7256.
[8] B. A. Trofimov, E. Yu. Schmidt, A. I. Mikhaleva, N. V. Zorina, I. A.
Ushakov, A. V. Afonin, A. M. Vasilꢇtsov, Mendeleev Commun. 2007,
17, 40–42.
[9] S. E. Korostova, A. I. Mikhaleva, R. N. Nesterenko, N. V. Maznaya,
V. K. Voronov, N. M. Borodina, Zh. Org. Khim. 1985, 21, 405–411.
[10] A. B. Zaitsev, E. Yu. Schmidt, A. I. Mikhaleva, A. M. Vasiltsov, I. A.
Ushakov, A. V. Afonin, D. S.-D. Toryashinova, Chem. Heterocycl.
Compd. 2005, 41, 444–448.
[11] O. A. Tarasova, S. E. Korostova, A. I. Mikhaleva, L. N. Sobenina,
R. N. Nesterenko, S. G. Shevchenko, B. A. Trofimov, Zh. Org. Khim.
1994, 30, 810–816.
[12] B. A. Trofimov, Curr. Org. Chem. 2002, 6, 1121–1162.
[13] S. Selvi, S.-C. Pu, Y.-M. Cheng, J.-M. Fang, P.-T. Chou, J. Org.
Chem. 2004, 69, 6674–6678.
[14] W. Koechner, Solid State Lasers Engineering, Vol. 1, Springer,
Berlin, 1996, p. 708.
[15] M. Sauer, K.-T. Han, R. Muller, S. Nord, A. Schulz, S. Seeger, J.
Wolfrum, J. Arden-Jacob, G. Deltau, N. J. Marx, C. Zander, K. H.
Drexhage, J. Fluoresc. 1995, 5, 247–263.
[23] A. B. Zaitsev, R. Mꢀallet-Renault, E. Y. Schmidt, A. I. Mikhaleva, S.
Badrꢀ, C. Dumas, A. M. Vasil’tsov, N. V. Zorina, R. B. Pansu, Tetra-
hedron 2005, 61, 2683–2688.
[24] C. Goze, G. Ulrich, L. J. Mallon, B. D. Allen, A. Harriman, R. Zies-
sel, J. Am. Chem. Soc. 2006, 128, 10231–10239.
[25] M. Kasha, Radiat. Res. 1963, 20, 55–70.
[26] H. Langhals, R. Ismael, O. Yꢄrꢄk, Tetrahedron 2000, 56, 5435–5441.
[27] S. Yokohama, A. Otomo, T. Nakahama, S. Mashiko, Thin Solid
Films 2001, 393, 124–128.
[28] a) H. Langhals, S. Kirner, Eur. J. Org. Chem. 2000, 365–380; b) G. J.
Mohr, U. E. Spichiger, W. Jona, H. Langhals, Anal. Chem. 2000, 72,
1084–1087.
[29] L. Schoutteten, P. Denjean, R. B. Pansu, J. Fluoresc. 1997, 7, 155–
165.
[30] K. A. Levenberg, Appl. Math II 1944, 2, 164–168.
[31] J.-A. Spitz, R. Yasukuni, M. Takano, J.-J. Vachon, R. Mꢀallet-Re-
nault, R. B. Pansu, J. Microscopy Part I 2008, 229, 104–114.
[32] Gaussian 03 (Revision C.02), M. J. Frisch, G. W. Trucks, H. B. Schle-
gel, 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. Pomelli, J. W. Ochterski, P. Y. Ayala, K.
Morokuma, G. A. Voth, P. Salvador, J. J. Dannenberg, V. G. Zakr-
zewski, 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. Challa-
combe, P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong, C. Gonza-
lez, J. A. Pople, Gaussian, Inc., Pittsburgh, PA, 2004.
[16] L. Schoutteten, P. Denjean, R. B. Pansu J. Fluoresc. 1997, 7, 159–
166.
[17] M. N. Berberan-Santos, M. J. E. Prieto, J. Chem. Soc. Faraday Trans.
2 1987, 83, 1391–1409.
[18] M. N. Berberan-Santos, J. Canceill, J. C. Brochon, L. Jullien, J.-M.
Lehn, J. Pouget, P. Tauc, B. Valeur, J. Am. Chem. Soc. 1992, 114,
6427–6435.
[33] S. K. Kurtz, T. T. Perry, J. Appl. Phys. 1968, 39, 3798–3813.
[19] J. Karolin, L. B.-A. Johansson, L. Strandberg, T. Ny, J. Am. Chem.
Soc. 1994, 116, 7801–7806.
[20] A. Loudet, K. Burgess, Chem. Rev. 2007, 84, 4891–4932.
[21] L. H. Thoresen, H. Kim, M. B. Welch, A. Burghart, K. Burgess, Syn-
lett 1998, 1276.
Received: November 26, 2008
Revised: January 29, 2009
Published online: April 25, 2009
5830
www.chemeurj.org
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 5823 – 5830