Fullerene-coumarin dyad as a selective metal receptor: Synthesis, photophysical properties, electrochemistry and ion binding studies

Article abstract of DOI:10.1002/chem.201001665

A coumarin derivative with a malonate unit has been synthesized and used for the preparation of a fullerene-coumarin dyad through the Bingel cyclopropanation method. The newly synthesized dyad is soluble in organic solvents and has been fully characterized with traditional spectroscopic techniques. Electronic interactions between the two components of the dyad were probed with the aid of UV/Vis spectroscopy, fluorescence emission, and electrochemistry measurements. Our studies clearly show the presence of electronic interactions between C₆₀ and modified coumarin in the ground state; efficient electron-transfer quenching of the singlet excited state of the coumarin moiety by the appended fullerene sphere was also observed. Time-resolved fluorescence measurements revealed lifetimes for the coumarin-C₆₀ dyad at a maximum of 50 ps, while the quantum yield was reaching unity. Additionally, the redox potentials of the C₆₀- coumarin dyad were determined and the energetics of the electron-transfer processes were evaluated. Finally, after alkaline treatment of C ₆₀-coumarin, which resulted in the deprotection of carboxylate units, the dyad was tested as a metal receptor for divalent metal cations; ion competition studies and fluorescence experiments showed binding selectivity for lead ions. Lead along by fullerene: A coumarin derivative with a malonate unit has been synthesized and used for the preparation of a fullerene-coumarin dyad through the Bingel cyclopropanation method (see scheme). The dyad was tested as a metal receptor for divalent metal cations and showed binding selectivity for lead ions.

Full text of DOI:10.1002/chem.201001665

FULL PAPER
DOI: 10.1002/chem.201001665
Fullerene–Coumarin Dyad as a Selective Metal Receptor: Synthesis,
Photophysical Properties, Electrochemistry and Ion Binding Studies
Georgia Pagona,[a] Solon P. Economopoulos,[a] George K. Tsikalas,[b]
Haralambos E. Katerinopoulos,[b] and Nikos Tagmatarchis*[a]
Abstract: A coumarin derivative with a
malonate unit has been synthesized
and used for the preparation of a full-
erene–coumarin dyad through the
Bingel cyclopropanation method. The
newly synthesized dyad is soluble in or-
ganic solvents and has been fully char-
acterized with traditional spectroscopic
techniques. Electronic interactions be-
tween the two components of the dyad
were probed with the aid of UV/Vis
spectroscopy, fluorescence emission,
and electrochemistry measurements.
Our studies clearly show the presence
of electronic interactions between C60
and modified coumarin in the ground
while the quantum yield was reaching
unity. Additionally, the redox poten-
tials of the C60–coumarin dyad were de-
termined and the energetics of the
electron-transfer processes were evalu-
ated. Finally, after alkaline treatment
of C60–coumarin, which resulted in the
deprotection of carboxylate units, the
dyad was tested as a metal receptor for
divalent metal cations; ion competition
studies and fluorescence experiments
showed binding selectivity for lead
ions.
state;
efficient
electron-transfer
quenching of the singlet excited state
of the coumarin moiety by the append-
ed fullerene sphere was also observed.
Time-resolved fluorescence measure-
ments revealed lifetimes for the cou-
marin–C60 dyad at a maximum of 50 ps,
Keywords: coumarin
·
dyes/pig-
ments · fullerenes · hybrid materi-
als · metal receptors
Introduction
low reduction potential, extended p-electron system, and
low reorganization energy.[2] In view of exploring practical
applications, such hybrid fullerene-based materials are con-
sidered as key components in molecular electronic,[3] optoe-
lectronic,[4] photonic,[5] and sensor[6] devices, to name a few.
Organic dyes, such as coumarin derivatives, are attractive
molecules due to their extended spectral range, high emis-
sion quantum yields, and photostability.[7] Moreover, cou-
marin derivatives are frequently encountered as receptors
and signaling units in sensors and biosensors[8] as well as in
advanced photophysical systems.[9] Coumarin-based ion indi-
cators generally do not have large extinction coefficients in
comparison with the more common fluorescein- and rhoda-
mine-based fluorescent ion indicators. However, the fluores-
cence intensity per dye molecule is proportional to the prod-
uct of epsilon and the quantum yield. The respective values
of coumarin-based dyes allow for ion detection at low indi-
cator concentrations. Additionally, coumarin indicators can
be introduced to cells either by microinjection or as mem-
brane permeable derivatives without causing cell death. The
fact that aminocoumarins undergo photoinduced charge
transfer upon excitation has been exploited in the design
and synthesis of ratiometric fluorescent ion indicators exhib-
iting blue- or redshifts in their spectra upon ion binding.
Fullerenes provide an interesting platform for designing
novel materials with diverse functions. However, direct ap-
plication of intact fullerenes in devices is limited due to
poor solubility, particularly in polar solvents. Among the dif-
ferent approaches explored to overcome the solubility issue
is organic functionalization. Developments in the organic
modification of fullerenes led to the construction of ad-
vanced materials incorporating photo- and/or electroactive
units, thus forming novel donor–acceptor dyads,[1] in which
fullerene acts as an electron acceptor due to its relatively
[a] Dr. G. Pagona, Dr. S. P. Economopoulos, Dr. N. Tagmatarchis
Theoretical and Physical Chemistry Institute
National Hellenic Research Foundation
48 Vassileos Constantinou Avenue
11635 Athens (Greece)
Fax : (+30)210-7273794
E-mail: tagmatar@eie.gr
[b] Dr. G. K. Tsikalas, Prof. H. E. Katerinopoulos
Department of Chemistry, University of Crete
71003, Heraklion (Greece)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201001665.
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The shift depends on the interaction of the ion with the ami-
nocoumarin donor or acceptor moiety, respectively.[7]
In principle, in fullerene–coumarin dyads not only the
characteristic intrinsic properties of the individual compo-
nents, namely, fullerene and coumarin, would be integrated,
but also intriguing behavior, function, and properties, based
on intermutual interactions between the individual units,
may arise. With only a couple of related reports published
from a single group, fullerene–coumarin dyads remained
almost unexplored.[10] In this light, herein, we initially fo-
cused on the synthesis and characterization of a C60–coumar-
in dyad. Then, optical measurements, in terms of steady-
state electronic absorption and fluorescence emission spec-
troscopy, as well as time-resolved fluorescence emission,
combined with electrochemistry, were performed and al-
lowed us to gain insight in electron-transfer processes within
the fullerene–coumarin dyad. Finally, the newly prepared
dyad was tested for ion-binding ability and found to be se-
lective for lead.
acetate, as the active component for the Knoevenagel-type
reaction, was accomplished through the reaction of zinc ace-
tate dihydrate and o-aminothiophenol followed by treat-
ment with malonylchloride monomethyl ester.[14] Eventually,
the malonate–coumarin derivative 8 was obtained by treat-
ment of 7 with methyl malonyl chloride. The structure of 8,
as well as all synthetic intermediates, was confirmed by stan-
dard analytical and spectroscopic techniques (see the Sup-
porting Information). The formation of the ring system and
1
the malonate side chain in 8 was verified by the H NMR
signals of the vinyl proton at d=8.96 ppm and the malonyl
unit protons at d=3.76 and 3.48 ppm. Additionally, the two
signals at d=166.3 and 166.7 ppm in the 13C NMR spectrum
verified the presence of the malonyl moiety carbonyls. The
MALDI-TOF mass spectrum, in the positive mode, shows a
signal at m/z 598.12, corresponding to the molecular ion
[M+] of 8.
With 8 in hand, we then turned our attention to covalent-
ly link it with the fullerene sphere. We followed the litera-
ture procedure of the Bingel cyclopropanation,[11,12] in which
a-halomalonates were generated in situ by direct treatment
with carbon tetrabromide in the presence of 1,8-
Results and Discussion
diazabicycloACTHUNTGRNEUNG[5.4.0]undec-7-ene (DBU) as a base and then
Synthesis: The methodology employed for the preparation
of the targeted C60–coumarin hybrid material is based on
the well-established protocol of the Bingel cyclopropanation
reaction.[11,12] To this end, cou-
marin derivative 8 with a malo-
nate unit was synthesized ac-
cording to the procedure given
in Scheme 1. Briefly, 4-(benzy-
loxy)-2-nitrophenol (1)[13] was
alkylated under typical Wil-
liamson conditions with 1-[(2-
bromoethoxy)methyl]benzene
reacted with C60. To this end, derivative 8 (1 equiv), carbon
tetrabromide (1.15 equiv), and DBU (1.35 equiv) were
added to a solution of C60 (1.3 equiv) in toluene. After stir-
to generate 4-(benzyloxy)-1-[2-
(benzyloxy)ethoxy]-2-nitroben-
zene (2) in 92% yield. Then,
catalytic hydrogenation of 2 re-
sulted in the formation of ani-
line derivative 3, which was
subsequently alkylated with
methyl bromoacetate (2 equiv)
to give compound 4 in 32%
yield. Vilsmayer formylation of
4, followed by deprotection of
the benzyl moieties under cata-
lytic conditions led to the for-
mation of salicylaldehyde 6 in
73% yield. Knoevenagel-type
reaction allowed the incorpora-
tion of the benzothiazol chro-
mophore unit as an extension
of the p-conjugated system of
the coumarin skeleton, thus
giving derivative 7. The synthe-
sis of methyl 2-benzothiazolyl Scheme 1. Synthetic route of 8. Bn=benzyl.
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Fullerene–Coumarin Dyad
FULL PAPER
ring at 258C for 24 h, the corresponding fullerene–coumarin
dyad 9 was isolated in moderate yield (19%), according to
Scheme 2. The structure of 9 was confirmed by 1H NMR
ature down to ꢀ108C is required to recover the original en-
dothermic peak when the temperature was cycled back from
temperatures much above the transition temperature. Col-
lectively, the transition temper-
ature (Tc), the transition enthal-
py (DH), and the transition en-
tropy (DS) of 9 are summarized
in Table 1.
Ground-state electronic absorp-
tion spectra: The absorption
spectrum of 9 disclose features
of both species, namely, the
fullerene and the coumarin.
The UV/Vis spectra of dyad 9,
precursor 8, and C60, obtained
in toluene, are depicted in
Figure 2. The spectrum of 8 is
Scheme 2. Synthesis of 9.
Table 1. Transition temperature (Tc), transition enthalpy (DH) and tran-
sition entropy (DS) of dyad 9.
spectroscopy and MALDI-TOF mass spectrometry. The
1H NMR spectrum of 9 is similar to that of 8, with some of
the signals shifted downfield due to the deshielding effect of
the fullerene core. The mass of 9 was found by MALDI-
TOF mass spectrometry (negative mode) to be m/z 1317.16,
a value that corresponds to the molecular ion of [M+], thus
unambiguously verifying the successful formation of 9.
Figure 1 shows typical differential scanning calorimetry
(DSC) thermograms for dyad 9. An endothermic “sub-
peak” (i.e., change in the baseline) at 33.58C is present.
During subsequent heating–cooling cycles at a rate of
108Cminꢀ1, reversibility of the transition was found. Since a
main transition peak could not be detected, the transition
found in dyad 9 is different from the ones observed in lipo-
somal and synthetic lipid bilayer membranes.[15] Multiscan
DSC measurements revealed that the transition at 33.58C is
recovered when the temperature was cycled back after heat-
ing up to 2008C. On the other hand, ageing of 9 at a temper-
Dyad
Tc [8C]
DH [kJmolꢀ1
]
DS [Jmolꢀ1 Kꢀ1
]
9
33.5
33.9
12.6
characterized by a broad absorption band in the visible
region, with a maximum at 431 nm, while intact C60 has a
characteristic sharp absorption at 330 nm. On the other
hand, in the absorption spectrum of dyad 9, the absorption
band due to the fullerene unit appears broadened, while ad-
ditional changes are observed in the shape and absorption
intensity of the coumarin chromophore (i.e., blueshifted at
429 nm). These results indicate not only the successful func-
tionalization of C60 with 8, but also intradyad ground-state
electronic interactions between the coumarin chromophore
and C60.
Figure 2. Electronic absorption spectra of 9 (black line), 8 (dashed line),
Figure 1. Differential scanning calorimetry thermograms of 9.
and C60 (dotted line), obtained in toluene.
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N. Tagmatarchis et al.
Excited-state fluorescence emission spectra: Meaningful in-
sight into the excited-state interactions between the photo-
and redox-active units in 9, arose from fluorescence emis-
sion measurements. In Figure 3, the steady-state emission
spectra of dyad 9 and precursor 8 are compared when excit-
ed at 430 nm in toluene. In the spectrum of 9, the coumarin
emission band, with a maximum at 478 nm and a shoulder
at 501 nm, is 98% quenched by the C60 unit, relative to that
of the reference coumarin malonate 8 (the spectra obtained
with matching absorbances at the excitation wavelength).
Moreover, the coumarin emission maxima in dyad 9 are
blueshifted by 10 and 7 nm, respectively, compared with
those of the reference compound 8, mirroring the batho-
chromic shifts observed in the UV/Vis spectra. It should be
noted that the characteristic fluorescence emission of C60 at
710 nm is masked by the strong emission of the coumarin
unit due to the low quantum yield of C60 (FC60 =6ꢁ10ꢀ4).[16]
Collectively, these observations suggest efficient quenching
of the singlet excited state of the coumarin moiety by the
appended fullerene sphere. Changing the solvent from non-
polar toluene to polar THF or dichloromethane, similar
fluorescence emission spectral changes for dyad 9, however,
with enhanced fluorescence quenching, were observed. This
is attributed to the better solvation the radical ion pairs ex-
perience in the polar environment of THF or dichlorome-
thane than in toluene, resulting in lower energies of the de-
veloping charge-separated states. From this solvent depend-
ence, efficient electron-transfer quenching the excited sin-
glet state of the coumarin moiety by C60 is inferred.
To probe the photophysical dynamics of the singlet excit-
ed state of coumarin in dyad 9, time-resolved fluorescence
emission studies were performed by the time-correlated
single photon counting (TCSPC) method. Time-resolved
fluorescence decay profiles of coumarin in the absence, ref-
erence compound 8, and presence of C60, dyad 9, are shown
in Figure 3b. The fluorescence decay of 1coumarin* in 8
either in nonpolar toluene or polar solvents, such as THF
and dichloromethane, is exclusively monoexponentially
fitted with a lifetime of 2.43 ns. On the other hand, upon
photoexcitation at 441 nm of a toluene solution of dyad 9,
analysis of the time profiles for the decay at 492 nm yielded
two exponentially decayed components (i.e., a fast and a
slow decay) with lifetimes of 58 ps (94%) and 2.41 ns (6%).
It should be mentioned that the lifetime of about 58 ps is
only an upper limit of the actual lifetime due to the time-
resolution limitation our instrument (i.e., 50 ps). Therefore,
the fast-decay in dyad 9, with a lifetime almost 50 times
shorter than that of 8, is attributed to the singlet excited
state of coumarin (1coumarin*). This is consistent with what
was observed in the steady-state fluorescence emission
measurements, in which strong quenching of coumarin due
to C60 in dyad 9 was observed (see above and Figure 3a).
Then, by attributing the fast-decaying component to the
charge separation in 9, the rate constant for charge separa-
tion (kCS) was determined to be 1.7ꢁ1010, according to
Equation (1). Additionally, the quantum yield FCS for
charge separation was calculated to be 0.98, according to
Equation (2):
kCS ¼ ð1=tfÞꢀð1=t0Þ
ð1Þ
ð2Þ
FCS ¼ ½ð1=tfÞꢀð1=t0Þꢁ=ð1=tfÞ
in which tf refers to the lifetime of the faster-decaying com-
ponent in the biexponential fitting function and t0 refers to
the coumarin fluorescence lifetime.
Time-resolved fluorescence studies performed in polar
THF and dichloromethane solvents gave similar results. All
photophysical data are collected and presented in Table 2.
Figure 3. a) Steady-state fluorescence spectra of 9 (black line) compared
with 8 (dashed line). Inset: Magnified emission spectra of 9, showing
1) hypsochromic shift in the emission band of its coumarin chromophore
(black line) compared with the precursor 8 (dashed line), and 2) the
emission of C60 at 710 nm (black line). Measurements performed in tolu-
ene at lexc =430 nm. b) Fluorescence lifetime decay of 9 (black line) com-
pared with 8 (gray line). Measurements performed at room temperature
in toluene at lexc =430 nm and lem =492 nm.
Electrochemistry: The determination of the redox potentials
of 9 is important for the evaluation of the energetics of the
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Fullerene–Coumarin Dyad
FULL PAPER
Table 2. Fluorescence decay lifetime data for dyad 8 and 9.
Solvent
CH2Cl2
THF
Material
tf [ps]
kCS
FCS
8
9
8
9
8
9
2680
51 (84%) 2600 (16%)
2630
48 (88%) 2570 (12%)
2430
1.9ꢁ1010
2.1ꢁ1010
1.7ꢁ1010
0.97
0.99
0.98
toluene
58 (94%) 2410 (6%)
electron-transfer processes. In this direction, to enlighten
the intramolecular interaction between the coumarin moiety
and C60, the electrochemical properties of C60, derivative 8,
and dyad 9 were investigated by differential pulse voltam-
metry (DPV) as well as cyclic voltammetry (CV). The meas-
urements were performed in a mixture of ortho-dichloro-
benzene (ODCB)/acetonitrile 5:1, with tetrabutylammonium
hexafluorophosphate (TBAPF6) as the electrolyte in a stan-
dard three-electrode cell with platinum as the working and
counter electrode. As shown in Figure 4, DPV and CV
measurements revealed that 9 undergoes three reversible
one-electron reduction and a one-electron oxidation pro-
cesses. Comparison of the redox data of C60 and 8 with
those of 9 indicate that the two reductions of dyad 9 at
ꢀ0.91 and ꢀ1.26 V are due to the presence of C60, while the
reduction of coumarin moiety at ꢀ1.82 V is overlapping
with the third reduction peak of C60 at ꢀ1.75 V. On the
other hand, the oxidation process at 0.94 V, due to the pres-
ence of the coumarin moiety, is anodically shifted by 50 mV,
compared with the reference compound 8. The small catho-
dic shift observed for the reduction potential of dyad 9 rela-
tive to C60 is rationalized in terms of the decreased electron
affinity monosubstituted fullerenes show relative to intact
C60.
Figure 4. a) Differential pulsed voltammograms (scan rate 20 mVsꢀ1) of
~
*
the C60–coumarin dyad 9 ( ) as compared with pristine C60
( ) and the
coumarin malonate derivative 8 (black), and b) cyclic voltammogram
Ion-binding studies: To explore the ability of 9 to bind to
metals, it was necessary to unmask the methyl ester groups
and liberate the carboxylate anions. Treatment of dyad 9
with tBuOK/DMSO[8f] quantitatively gave probe 10, as de-
scribed in Scheme 3.
(scan rate 100 mVsꢀ1) of the C60–coumarin dyad 9 ( ) as compared with
*
~
pristine C60
( ) and the coumarin derivative 8 (black). Conditions:
ODCB/MeCN 5:1, 0.1m nBu4NPF6 as the electrolyte, Pt wires as working
and counter electrodes, and Ag/AgNO3 as reference electrode.
As expected,[8g] probe 10 ex-
hibited moderate affinity to
Zn2+ ions in contrast to a far
stronger interaction with Pb2+
.
We therefore studied the fluo-
rescence profile of 10 in solu-
tions of increasing Pb2+ concen-
trations, as shown in Figure 5.
The ion-free fullerene–coumar-
in probe 10 exhibits an excita-
tion maximum at 470 nm, which
shifts to 468 nm upon Pb2+
binding. When excited, the ion-
free form of 10 shows an emis-
Scheme 3. Deprotection of 9 to give 10.
sion maximum at 503 nm,
which shifts to 500 nm upon Pb2+ binding with a small de-
crease in fluorescence intensity at Pb2+ saturation levels.
The dissociation constant of probe 10 was calculated accord-
ing to Tsienꢂs algorithm[17] as 72 mm.
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N. Tagmatarchis et al.
of Pb2+ results in a decrease of fluorescence intensity when
the system is excited at 470 nm, the fluorescence ratio F400
/
F470 is expressed in positive numbers. In the first set of meas-
urements, the fluorescence ratio after addition of 50 mm Pb2+
is shown (black bar) and compared with that of 50 mm of the
free dye (gray bar). The rest of the measurement sets indi-
cate a fluorescence ratio of the dye in the presence of one
equivalent of metal (gray bars) versus the fluorescence ratio
after addition of one equivalent of Pb2+ to the same sample
(black bars). Binding by these metal ions appears to be
weak, since subsequent addition of Pb2+ to these solutions
increases the fluorescence ratio of the dye–metal solution to
the same extent as in the case of the first measurement
(competitive ion-free solution).
Conclusion
The preparation of 9 has been carried out by following the
established cyclopropanation Bingel protocol via suitably
functionalized coumarin–malonate 8. The electronic proper-
ties of the newly synthesized dyad 9 were probed by elec-
tronic absorption and fluorescence spectroscopy, which sug-
gest the existence of electronic interactions between the full-
erene and the coumarin of the dyad, in the ground and the
excited states. The characteristic emission of coumarin was
quenched in dyad 9 following intramolecular electron trans-
fer, from the coumarin to C60, as inferred by photolumines-
cence experiments performed in apolar and polar solvents.
Time-resolved fluorescence measurements revealed lifetimes
for the 9 at a maximum of 50 ps, while the quantum yield
reached unity. Moreover, electrochemistry revealed the
redox potentials of dyad 9, where a cathodic shift observed
for the reduction potential of 9 compared with intact C60.
Lastly, the methyl esters in dyad 9 have been cleaved to lib-
erate free carboxylate moieties in dyad 10. The latter was
tested for binding divalent metal cations, while ion competi-
tion studies demonstrated that probe 10 is selective for Pb2+
complexation. Thus, such C60–coumarin dyads may find in-
teresting applications as selective artificial receptors in a
wide range of biological, environmental, and chemical pro-
cesses.
Figure 5. a) Excitation and b) emission spectra of 10 in solutions of in-
creasing Pb2+ concentrations in nanopure water. The excitation wave-
length was set at 470 nm.
The potential use of dyad 10 as a Pb2+ probe in biological
or environmental systems is shown in an ion competition
study of a range of metals. Materials were excited at the iso-
sbestic point (400 nm) and 470 nm, and the fluorescence in-
tensity ratio was calculated (Figure 6). Given that addition
Experimental Section
General: All chemicals were purchased from chemical suppliers and used
without further purification. Dry solvents were prepared by using cus-
tomary literature procedures.[18] TLC: Riedel-de Haꢃn silica gel F254.
Detection: UV lamp and iodine chamber. Flash chromatography (FC):
Aldrich silica gel 60 (230–400 mesh, 0.04–0.063 nm). NMR spectra were
recorded on a Bruker AC 300 FT-NMR spectrometer; the chemical shifts
are given in parts per million relative to tetramethylsilane. Differential
scanning calorimetry (DSC) measurements were performed on a Q 200
differential scanning calorimeter from TA Instruments. In a typical ex-
periment, the sample was placed in hermetically closed aluminum pan
under helium flow. Standard DSC heating and cooling scans were per-
formed at 108Cminꢀ1. Electrochemistry studies were performed by using
a standard three-electrode cell. Platinum wires were used as counter and
Figure 6. Ion competition study of 10.
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Fullerene–Coumarin Dyad
FULL PAPER
working electrodes. Silver/silver nitrate (Ag/AgNO3 0.1m in acetonitrile)
was used as a reference electrode. TBAPF6 (98%) was used as the elec-
trolyte and was recrystallized three times from acetone and dried in a
vacuum at 1008C. Before each experiment the cell was purged with high
purity N2 for 5 min. Before the start of the measurement the inert gas
was turned to “blanket mode”. Measurements were recorded by using an
EG&G Princeton Applied Research potensiostat/galvanostat Model 2273
connected to a personal computer running PowerSuite software. The
working electrode was cleaned before each experiment through polishing
using a cloth and 6, 3, and 1 mm diamond pastes. The Ag/AgNO3 elec-
trode was calibrated before each experiment by running cyclic voltamme-
try on ferrocene. .Mass spectra were recorded on a MALDI-TOF mass
spectrometer. UV/Vis spectra were recorded on a Perkin–Elmer UV/
VIS/NIR spectrometer Lamda 19. Mid-IR spectra in the region 550–
4000 cmꢀ1 were obtained on a Fourier-transform IR spectrometer (Equi-
nox 55 from Bruker Optics) equipped with a single reflection diamond
ATR accessory (DuraSamp1IR II by SensIR Technologies). A drop of
the solution was placed on the diamond surface, followed by evaporation
of the solvent, in a stream of nitrogen, before recording the spectrum.
Typically, 100 scans were acquired at 4 cmꢀ1 resolution. Fluorescence
spectra were taken on an Aminco Bowman spectrofluorimetre (Spectro-
nocs Co., USA) and a Fluorolog-3 Jobin Yvon-Spex spectrofluorometer
(model GL3–21). Picosecond time-resolved fluorescence spectra were
measured by the time-correlated single-photon counting (TCSPC)
method on a NanoLog spectrofluorometer (Horiba Jobin Yvon), using a
laser diode as an excitation source (NanoLED, 441 nm, 200 ps pulse
width). Lifetimes were evaluated with the DAS6 Fluorescence-Decay
Analysis Software. All measurements were performed at room tempera-
ture.
4.65 (s, 2H), 5.02 (s, 2H), 6.54 (dd, J1 =8.7 Hz, J2 =3.5 Hz, 1H), 6.59 (d,
J1 =2.5 Hz, 1H), 6.83 (d, J1 =9 Hz, 1H),7.47–7.34 ppm (m, 10H);
13C NMR (500 MHz, CDCl3): d=51.4 (2C), 53.1 (2C), 68.4, 68.7, 70.1,
72.9, 106.4, 107.1, 115.2, 127.3 (2C), 127.4 (3C), 127.6, 128.1 (3C), 128.2,
137.0, 137.9, 140.1, 144.6, 153.5, 171.4 ppm (2C); MALDI-TOF MS (di-
thranol as matrix): m/z: 493 [M+].
Preparation of 5: This compound was prepared according to a previously
described method[13] using 4 (0.215 g, 0.45 mmol) and phosphoryl chloride
(0.064 mL, 0.70 mmol) in DMF (5 mL) to give the product after workup
and purification (0.175 g, 72%). UV/Vis (CH2Cl2): l=325, 292, 251 nm;
ATR-IR: 3085–2850, 1745, 1664, 1600, 1517 cmꢀ1 1H NMR (500 MHz,
;
CDCl3): d=3.67 (s, 6H), 3.71 (t, J1 =3 Hz, J2 =8 Hz, 2H), 4.09 (t, J1 =
3 Hz, J2 =8 Hz, 2H), 4.18 (s, 4H), 4.53 (s, 2H), 5.07 (s, 2H), 6.24 (s, 1H),
7.36–7.28 (m, 11H), 10.27 ppm (s, 1H); 13C NMR (500 MHz, CDCl3): d=
51.9, 53.8, 68.1, 68.3, 71.1, 73.0, 102.5, 111.3, 117.9, 127.2 (2C), 127.56
(2C), 127.59, 128.1, 128.3 (2C), 128.6 (2C), 136.3, 137.9, 143.8, 146.1,
157.3, 171.0 (2C), 187.5; MALDI-TOF MS (dithranol as matrix): m/z:
521 [M+].
Preparation of 6: This compound was prepared according to a previously
described method[13] using compound 5 ( 0.175 g, 0.33 mmol), 10% Pd/C
(0.02 g) as the hydrogenation catalyst and ethyl acetate (10 mL) as the
solvent to give the product after workup and purification (0.112 g, 98%).
UV/Vis (CH2Cl2): l=357, 309, 255 nm; ATR-IR (): 3454, 2950–2850,
1
1735, 1629, 1575, 1510 cmꢀ1; H NMR (300 MHz, CDCl3): d=3.71 (t, J1 =
3 Hz, J2 =4.8 Hz, 2H), 3.80 (s, 6H), 4.04 (t, J1 =3 Hz, J2 =4.8 Hz, 2H),
4.20 (s, 4H), 6.13 (s1H), 6.85 (s, 1H), 9.57 (s, 1H), 11.17 ppm (s, 1H);
13C NMR (300 MHz, CDCl3): d=51.9, 52.4, 53.8, 54.1, 71.7, 72.8, 104.2,
107.2, 113.2, 115.6, 117.9, 118.4, 171.5, 172.3, 193.2 ppm; MALDI-TOF
MS (dithranol as matrix): m/z: 341 [M+].
Preparation of 2: K2CO3 (415 mg, 3 mmol) was added to a suspension of
1[13] (7350 mg, 3 mmol) in anhydrous DMF (60 mL). After 20 min, benzyl
2-bromomethyl ether (935 mg, 4.3 mmol, 688 mL) was added to the reac-
tion mixture. After heating the suspension for 14 h at 1108C under nitro-
gen, the reaction was complete. The system was cooled to room tempera-
ture, dissolved in H2O, and extracted with ethyl acetate. The organic
phase was dried over Na2SO4, filtered, and then the solvent was evapo-
rated to dryness in vacuum, yielding a yellow solid (1.055 g, 92%). UV/
Preparation of 7: Compound 6 (0.112 mg, 0.33 mmol) was added to a so-
lution of methyl a-benzothiazolyl acetate[14] (0.07 g, 0.33 mmol) and pi-
peridine(0.028 g, 0.33 mmol) in dry methanol (3 mL) and the yellow/
orange suspension was heated to 708C for 1 h. The system was then
cooled to 08C and the precipitated yellow solid filtered by suction and
washed with diethyl ether to give the product (0.139 g, 85%). UV/Vis
(CH2Cl2): l=433 nm; ATR-IR: 3400–3165, 2950–2850, 1737, 1708, 1617,
1550, 1510, 1411, 1230–1163 cmꢀ1 1H NMR (300 MHz, CDCl3): d=3.72
;
Vis (CH2Cl2): l=358, 260 nm; ATR-IR: n˜ =3085–2850, 1525, 1496 cmꢀ1
;
(s, 2H), 3.84 (s, 6H) 4.09 (s,2H), 4.24 (s, 4H), 6.64 (s, 1H), 6.98 (s, 1H),
7.39(t, J=5.2 Hz, 1H), 7.50 (t, J=5.2 Hz, 1H), 7.60 (d, J=7.8 Hz, 1H),
8.03 (d, J=8.1 Hz, 1H), 8.92 ppm (s, 1H); 13C NMR (300 MHz, CDCl3):
d=52.5 (2C), 54.2 (2C), 60.8, 61.0, 104.1, 110.5, 112.1, 116.4, 121.6, 122.4,
124.9, 126.3, 136.5, 141.1, 145.0, 147.2, 150.5, 152.4, 160.4, 160.7,
171.6 ppm (2C); MALDI-TOF MS (dithranol as matrix): m/z: 498 [M+].
1H NMR (300 MHz, CDCl3): d=3.86 (t, J1 =4.5 Hz, 2H), 4.24 (t, J1 =
4.5 Hz, 2H), 4.65 (s, 2H), 5.05 (s, 2H), 7.07 (s, 1H), 7.13 (d, J=3 Hz,
1H), 7.36–7.42 (m, 10H), 7.48 ppm (d, J=3 Hz, 1H); 13C NMR
(300 MHz, CDCl3) d=64.9, 68.2, 69.8, 72.9, 110.9, 117.1, 121.4, 127.6
(2C), 127.7 (2C), 128.3, 128.4 (3C), 128.7 (2C), 137.6, 137.9, 140.0, 146.7,
152.1 ppm; MALDI-TOF-MS (dithranol as matrix): m/z: 379 [M+].
Preparation of 8: Pyridine (0.137 mg, 1.74 mmol) was added to a solution
of coumarin dye 7 (0.038 m, 0.076 mmol) in dry CH2Cl2 (4 mL), under an
N2 atmosphere. After stirring at room temperature for 10 min, the mix-
ture was cooled to 08C and a solution of methyl malonyl chloride
(0.023 g, 0.168 mmol) in dry CH2Cl2 (2 mL) was added dropwise. The re-
action mixture was stirred at room temperature for 24 h and monitored
by TLC (ethyl acetate/petroleum ether 50/50). At the end of the reaction,
the solvent was removed under reduced pressure and the residue was fur-
ther purified by column chromatography (silica gel, ethyl acetate/petrole-
um ether 70/20) to afford the product (0.036 mg, 79%). UV/Vis
(CH2Cl2): l=430 nm; ATR-IR: 3400–3165, 2950–2850, 1745, 1730, 1705,
Preparation of 3: Powdered 10% Pt/C (10 mg) was added to a solution
of 2 (1.040 g, 2.8 mmol) in dry ethanol under an N2 atmosphere at room
temperature. Removal of N2 in vacuo followed by addition of H2 and stir-
ring of the reaction mixture for 17 h led to the formation of the product.
The reaction was monitored by TLC (ethyl acetate/petroleum ether 30/
70). The solution was filtered and the solvent was removed under re-
duced pressure. The remained residue was further purified via column
chromatography (silica gel, ethyl acetate/petroleum ether 20/80) to give 3
(800 mg, 80%). UV/Vis (CH2Cl2): l=366, 304, 251 nm; ATR-IR: 3475,
1
3370, 3085–2860, 1617, 1509, 1452 cmꢀ1; H NMR (300 MHz, CDCl3): d=
1614, 1550, 1510, 1411, 1240, 1207–1150 cmꢀ1
;
1H NMR (300 MHz,
3.82 (t, J1 =4.5 Hz, 2H), 4.13 (t, J1 =4.5 Hz, 2H), 4.64 (s, 2H), 5.00 (s,
2H), 6.32(dd, J1=9 Hz, J2 =3 Hz, 1H) 6.43 (d, J=2.7 Hz, 1H), 6.76(d,
J=9 Hz, 1H), 7.33–7.45 ppm (m, 10H); 13C NMR (300 MHz, CDCl3): d=
68.4, 69.0, 69.8, 72.8, 102.4, 102.7, 114.2, 127.1 (2C), 127.45 (3C), 127.40,
128.18(2C), 128.12 (2C), 137.2, 137.8, 138.2, 140.5, 153.9; MALDI-TOF
MS (dithranol as matrix): m/z: 349 [M+].
CDCl3): d=3.48 (s, 2H), 3.79 (s, 3H) 3.80 (s, 6H), 4.24 (dd, J1 =J2 =
4.5 Hz, 2H), 4.26 (s, 4H), 4.46 (dd, J1 =J2 =4.5 Hz, 2H), 6.66 (s, 1H),
7.00 (s, 1H), 7.40 (t, J=7.2 Hz, 1H), 7.51 (t, J=7.8 Hz, 1H), 7.96 (d, J=
8.1 Hz, 1H), 8.05 (d, J=8.4 Hz, 1H), 8.96 ppm (s, 1H); 13C NMR
(300 MHz, CDCl3): d=41.0, 52.3 (2C), 52.6, 53.8 (2C), 63.3, 66.9, 104.1,
110.7, 111.8, 116.3, 121.7, 122.5, 124.9, 126.3, 136.5, 141.1, 144.9, 146.6,
150.7, 152.4, 160.4, 160.7, 166.5, 166.7, 170.7 (2C); MALDI-TOF MS (di-
thranol as matrix): m/z: 598 [M+].
Preparation of 4: This compound was prepared by following a previously
published procedure[13] using 3 (0.500 g, 1.43 mmol), tert-butyl bromoace-
tate (0.875 g, 5.72 mmol), diisopropylethylamine (0.740 g, 5.72 mmol),
and sodium iodide (0.215 g, 1.43 mmol) in DMF (5 mL) as the solvent to
give the product after workup and purification (0.215 g, 30%). UV/Vis
(CH2Cl2): l=362, 300, 250 nm; ATR-IR: 3085–2850, 1745, 1606, 1506,
Preparation of 9: DBU (0.005 g, 0.035 mmol) was added dropwise to a
suspension containing C60 (0.025 g 0.034 mmol), CBr4 (0.010 g
0.030 mmol), and 8 (0.016 g, 0.026 mmol) in dry toluene (100 mL) under
N2 atmosphere. The reaction mixture was stirred at room temperature
for 24 h, and the progress of the reaction was monitored by TLC (ethyl
1454 cmꢀ1
;
1H NMR (500 MHz, CDCl3): d=3.72 (s, 6H), 3.82 (t, J1 =
4.5 Hz, J2 =5 Hz, 2H), 4.16 (t, J1 =5.5 Hz, J2 =4.5 Hz, 2H), 4.25 (s, 4H),
Chem. Eur. J. 2010, 16, 11969 – 11976
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
11975

N. Tagmatarchis et al.
acetate/toluene 30/70). The product was isolated by flash chromatography
(silica gel, toluene) and dried in vacuo to give the product (0.007 g,
19%). UV/Vis (CH2Cl2): l=429 nm; ATR-IR: 2950–2850, 1739, 1705,
Castanas, T. G. Deligeorgiev, H. E. Katerinopoulos, Cell Calcium
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1610, 1550, 1512, 1456, 1267, 1236–1163 cmꢀ1
.
1H NMR (300 MHz,
CDCl3): d=3.85 (s, 6H), 4.07 (s, 3H), 4.27 (s, 4H), 4.41 (dd, 2H), 4.83
(dd, 2H), 6.90 (s, 1H), 7.09 (s, 1H), 7.44 (t, 1H), 7.56 (t, 1H), 7.96 (d,
1H), 8.15 (d, 1H), 9.28 ppm (s, 1H); MALDI-TOF MS (dithranol as
matrix): m/z: 1316 [M+].
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Received: June 11, 2010
Published online: September 10, 2010
11976
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ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 11969 – 11976