From Dark to Light to Fluorescence Resonance Energy Transfer (FRET): Polarity-Sensitive Aggregation-Induced Emission (AIE)-Active Tetraphenylethene-Fused BODIPY Dyes with a Very Large Pseudo-Stokes Shift

Article abstract of DOI:10.1002/chem.201503457

The work presented herein is devoted to the fabrication of large Stokes shift dyes in both organic and aqueous media by combining dark resonance energy transfer (DRET) and fluorescence resonance energy transfer (FRET) in one donor-acceptor system. In this

Full text of DOI:10.1002/chem.201503457

DOI: 10.1002/chem.201503457
Full Paper
&
Donor–Acceptor Systems
From Dark to Light to Fluorescence Resonance Energy Transfer
(FRET): Polarity-Sensitive Aggregation-Induced Emission (AIE)-
Active Tetraphenylethene-Fused BODIPY Dyes with a Very Large
Pseudo-Stokes Shift**
Esra S¸en,[a] Kadem Meral,[b] and Serdar Atılgan*[a]
Abstract: The work presented herein is devoted to the fabri-
cation of large Stokes shift dyes in both organic and aque-
ous media by combining dark resonance energy transfer
(DRET) and fluorescence resonance energy transfer (FRET) in
one donor–acceptor system. In this respect, a series of
donor–acceptor architectures of 4,4-difluoro-4-bora-3a,4a-
diaza-s-indacene (BODIPY) dyes substituted by one, two, or
three tetraphenylethene (TPE) luminogens were designed
and synthesised. The photophysical properties of these
three chromophore systems were studied to provide insight
into the nature of donor–acceptor interactions in both THF
and aqueous media. Because the generation of emissive TPE
donor(s) is strongly polarity dependent, due to its aggrega-
tion-induced emission (AIE) feature, one might expect the
formation of appreciable fluorescence emission intensity
with a very large pseudo-Stokes shift in aqueous media
when considering FRET process. Interestingly, similar results
were also recorded in THF for the chromophore systems, al-
though the TPE fragment(s) of the dyes are non-emissive.
The explanation for this photophysical behaviour lies in the
DRET. This is the first report on combining two energy-trans-
fer processes, namely, FRET and DRET, in one polarity-sensi-
tive donor–acceptor pair system. The accuracy of the dark-
emissive donor property of the TPE luminogen is also pre-
sented for the first time as a new feature for AIE phenom-
ena.
Introduction
properties, and thus, they are found in a wide range of applica-
tions, such as nucleic acid and ion analysis, signal transduction,
light harvesting, and metallic nanomaterials.[5] On the other
hand, the change in the efficiency of energy transfer in FRET
arising from changes in the donor–acceptor separation dis-
tance enables enormous opportunities for the identification of
biological molecules and their interactions both in vivo and in
vitro.[6] To demonstrate the importance of FRET in these areas,
it is useful to consider the limitations of single fluorophores,
particularly, traditional organic dyes, such as 4,4-difluoro-4-
bora-3a,4a-diaza-s-indacene (BODIPY), rhodamine and coumar-
in. One of the major limitations of these fluorophores is
a small Stokes shift, which can lead to re-absorption or an
inner filter effect and self-quenching that hamper the applica-
tions of dyes.[4,6] In addition to these undesired photophysical
processes, their tuneable emissions also hinder the use of fluo-
rophores in single excitation techniques, which are applicable
for multicolour fluorescent labelling approaches.[6] Thus, the
FRET technique provides a valuable solution to these challeng-
es through the formation of a large Stokes shift, as a result of
substantial overlap between the donor emission and acceptor
absorption.[4–6d] The requirements in applications for achieving
effective energy transfer, by taking advantage of large Stokes
shift, have attracted immense interest. One complementary ap-
proach that intends to minimise inadequacies associated with
FRET is through-bond energy transfer (TBET), which is a struc-
ture-based approach, in which a donor fluorophore and an ac-
Fluorescent molecules, which provide insights into solutions
for current challenges towards widespread applications and ex-
panding the horizons of many processes with their judiciously
designed architecture, constitute an attractive sub-discipline in
the broader field of supramolecular chemistry.[1] This is mostly
due to several potential medicinal and bioimaging applica-
tions, as well as materials science.[2] Fluorescence resonance
energy transfer (FRET), is an attractive spectroscopic technique
used in these supramolecular architectures.[3] FRET is explained
as a process that describes energy transfer between an excit-
ed-state donor fluorophore and a ground-state acceptor fluo-
rophore linked together by a non-conjugated spacer.[3,4] The
materials generated by the FRET approach are of special inter-
est thanks to their highly promising optical and electronic
[a] E. S¸en, Dr. S. Atılgan
Department of Chemistry, Suleyman Demirel University
32000, Isparta (Turkey)
E-mail: serdaratilgan@sdu.edu.tr
[b] Dr. K. Meral
Department of Chemistry, Ataturk University
25240, Erzurum (Turkey)
[**] BODIPY=4,4-difluoro-4-bora-3a,4a-diaza-s-indacene.
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201503457.
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ceptor fluorophore are connected to each other by electroni-
cally conjugated linkers, thereby opening up the way to im-
prove energy-transfer efficiency.[7] The recently developed dark
resonance energy transfer (DRET) process is another encourag-
ing approach for a better energy-transfer process between
chromophores.[8a] Accordingly, this complementary approach is
identical, in terms of molecular designs and energy-transfer
mechanism, to FRET and TBET. However, it differs from them in
that the donor molecule, which might be aptly called a “dark
donor”, is non-fluorescent or weakly fluorescent.[8c] One attrac-
tive feature of using a dark donor in molecular designs is that
the energy-transfer efficiency is relatively high, which results
from the fact that possible fluorescence leakage is eliminated.[8]
When considering the effectiveness and efficiencies of FRET-
and DRET-based mechanisms as useful tools for various areas,
they not only provide improved applications, but also help in
the development of more specific strategies for energy trans-
fer; thus satisfying different applications. On the other hand,
since their practical use is essential in biological applications
and solar energy systems, which cover a wide range of polarity
of solvents, one should consider polarity during the design of
FRET- or DRET-based systems to increase the feasibility and ac-
ceptability of the molecules.[5c]
Herein, we present a novel approach to preparing energy-
transfer systems by taking advantage of AIE methodology to
improve energy-transfer efficiency, and thus, increase the
adaptability of energy-transfer systems to different applica-
tions. The strategy developed herein provides a more promis-
ing approach for making full use of energy-transfer systems in
both organic and aqueous media with a single donor–acceptor
interaction. For this purpose, a series of BODIPY derivatives
containing TPE substituents at the meso-phenyl moiety have
been designed and synthesised by means of copper(I)-cata-
lysed 1,3-dipolar cycloaddition. Contrary to our previous stud-
ies, herein, a long chain of alkyl groups is positioned between
the BODIPY and TPE moieties to form non-conjugated systems.
In the molecular design, the TPE chromophore acts as a donor
and BODIPY acts as an acceptor. Based on the AIE activity of
the TPE units, we carried out photophysical experiments to ex-
plore the potential of its donor ability through energy-transfer
studies in both polar and non-polar media. The fluorescence
investigations showed that all desired BODIPY–TPE (hereafter
represented as BTn, in which n represents the number of TPE
units substituted on the BODIPY core) chromophores displayed
large pseudo-Stokes shifts between absorbed and emitted
light with a high emission intensity in both organic and aque-
ous media; this indicated substantial energy transfer between
the donor and acceptor groups. A schematic illustration of the
energy-transfer processes on one of the designed chromo-
phore structures is shown in Figure 1. It must be noted that
Tetraphenylethene (TPE) and its derivatives have been inves-
tigated intensively since the early discovery of aggregation-in-
duced emission (AIE) phenomena due to its good AIE efficien-
cy with high emission intensity, simple synthetic routes, and
facile modifications with various functionalities.[9] The fluores-
cence enhancement of these chromophores in poor solvents is
attributed to the restriction of intramolecular rotation of
phenyl rings, in parallel with the definition of AIE methodolo-
gy. Thus, these chromophores are used as functional units in
applications such as organic light-emitting diodes (OLEDs)[10] or
as probes for the detection of biomolecules,[11] ions,[12] and ex-
plosive compounds.[13]
BODIPY dyes are among the most advantageous fluoro-
phores owing to their excellent spectroscopic features, such as
large molar extinction coefficients, high fluorescence quantum
yields, and narrow absorption–emission bands.[14] However,
many BODIPY derivatives suffer from aggregation because
their emission is quenched by p–p interactions in the packing
of dyes in polar media.[15] Thus, several strategies, such as the
introduction of bulky groups on the dye skeleton, which pre-
vents close packing of the dyes,[16] and the generation of AIE-
compatible dyes that emerge from either the formation of
emissive J-type aggregates[17] or incorporation of AIE-active lu-
minogens,[18] were proposed to reduce the influence of aggre-
gation on BODIPY dyes. In our previously reported study, we
demonstrated a series of conjugated TPE-fused BODIPY deriva-
tives.[18b] Theoretical and experimental investigations into the
photophysical properties of these conjugated BODIPY–TPE
couples clearly demonstrated that the addition of the AIE fea-
ture to the chromophore by incorporating TPE units made
these dyes highly emissive in both organic and aqueous
media, although BODIPY skeleton was highly hydrophobic and
its emission was quenched due to the formation of aggregate
in aqueous medium.
Figure 1. The structure of BT3 and its operation in energy-transfer systems.
the AIE effect, through an energy-transfer event in which the
TPE units act as a fluorescent donor molecule, seems to be
suitable to explain the photophysical results for the BTn mole-
cules in aqueous media. Although the results obtained in
aqueous media could be accounted for by the formation of
aggregated fluorescent BTn, it is unlikely to account for the re-
sults of such similar energy-transfer efficiencies recorded in or-
ganic media.
By considering the in situ solvolysis of non-fluorescent TPE
units in desired molecules by organic solvents, the observation
of a high fluorescence intensity of BTn at lꢀ500 nm clearly
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implies that the TPE units act as a dark donor. Thus, DRET is
the only process capable of explaining the formation of an effi-
cient energy-transfer system in organic medium between TPE,
a dark donor, and BODIPY, a fluorescent acceptor. Accordingly,
for the first time, two resonance energy transfer (RET) process-
es, namely, FRET and DRET, were combined in one molecule.
Furthermore, the work addressed herein has revealed a novel
feature of AIE-active TPE, that is, the formation of a non-lumi-
nescent TPE chromophore when molecularly dissolved in good
solvents, which could function as a dark donor in energy-trans-
fer systems. On the other hand, this is the first report of an AIE
approach being applied to a FRET approach with a very large
pseudo-Stokes shift.
role was used as a reactant. Mono-, di- and trialkyne-function-
alised BODIPY fluorophores, 1–3, respectively, were also used
in photophysical investigations to elucidate the role of the ac-
ceptor in energy-transfer efficiencies. The synthesis of the
energy-donor moiety, TPE, was achieved in two steps. Firstly,
the precursor, TPE-Br (4), was synthesised by lithiation of di-
phenylmethane in THF at À788C, which was followed by the
addition of 4-bromobezophenone and a condensation reaction
in which p-toluenesulfonic acid (PTSA) was used as a catalyst.
Further reaction between 4 and sodium azide in THF yielded 5
in 75% yield. Finally, copper(I)-catalysed 1,3-dipolar cycloaddi-
tion reaction between 5 and 1, 2, and 3 afforded the desired
donor–acceptor BTn chromophores, BT1, BT2, and BT3, re-
spectively, in excellent yield. Following the same strategy,
(prop-2-yn-1-yloxy)benzene was reacted with 5 to demonstrate
the donor functionality in subsequent photophysical studies.
The UV/Vis absorption spectra of donor–acceptor com-
pounds BT1, BT2, and BT3, along with a plot of the separated
BODIPY chromophore 1 (see Supporting Information for the
absorbance spectrum of 2, 3 and 7, Figures S1 and S2 in the
Supporting Information), in THF are shown in Figure 2. A
narrow band with a maximum at lꢀ500 nm is characteristic
of the BODIPY chromophore, whereas the broad band be-
tween l=310 and 330 nm corresponds to the TPE chromo-
phore. The recorded absorption intensity in the range of l=
310–330 nm clearly reflects the number of TPE units on BTn
chromophores. Accordingly, chromophore BT3 has a higher
absorption intensity in the range of l=310–330 nm than
those of BT2 and BT1, of which BT1 has the smallest value.
Meanwhile, in accordance with the molecular architectures for
Results and Discussion
The synthesis of the molecules in the energy-transfer systems
and their structures are illustrated in Scheme 1. The criteria
and synthetic pathways used in the molecular designs are as
follows. BODIPY, which is a well-known fluorophore on account
of its intense absorption and emission bands in the visible
region accompanied by high photochemical stability, is used
as an energy acceptor. Our synthetic studies towards the con-
struction of acceptor BODIPY units commenced with the syn-
thesis of mono-, di-, and trialkyne-functionalised benzaldehyde
derivatives by a simple nucleophilic substitution reaction be-
tween relevant hydroxybenzaldehyde derivatives and proparg-
yl bromide in CH3CN in the presence of K2CO3 as a base. The
resulting products were then transformed into BODIPY deriva-
tives 1–3 by a common procedure in which 2,4-dimethylpyr-
Scheme 1. Synthesis of TPE-fused BODIPY chromophores BT1, BT2, and BT3 and control compound 7. TFA =trifluoroacetic acid, DDQ=2,3-dichloro-5,6-dicya-
no-1,4-benzoquinone, TosN3 =tosyl azide.
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BTn (3-, 6-, and 12-fold increase for BT1, BT2 and BT3, respec-
tively, with respect to 1, 2 and 3 when excited at l=315 nm).
On the basis of these results, it was concluded that the DRET
process, in which TPE groups and BODIPY chromophores acted
as a dark donor and emissive acceptor, respectively, took place
in BTn chromophores with very large pseudo-Stokes shifts
(lꢀ200 nm, the largest shift ever observed for DRET). Depend-
ing on the number of TPE groups, different energy-transfer ef-
ficiencies were observed for BTn chromophores. The increase
in the energy-transfer efficiencies is directly proportional to the
increase in the number of photons absorbed by the donor.
Chromophore BT3 contains three dark donor TPE substituents,
and thus, yields the most efficient energy transfer in THF. Thus,
chromophore BT3 is possibly the best donor–acceptor combi-
nation of all BT derivatives in terms of the DRET process (Fig-
ure 3D). The photophysical properties (quantum yield and life-
time) of all chromophores are also in agreement with the fluo-
rescence changes observed in Figure 3. The preferred standard
fluorescent chromophores, rhodamine 6G and quinine sulfate,
are consistent with the absorption maxima of dyes 1–3 and
the donor sites of BTn series, respectively. However, due to the
large pseudo-Stokes shift of the BTn series, the emission wave-
length of the chromophores does not overlap with the emis-
sion wavelength of quinine sulfate. Thus, the measured quan-
tum yields are lower than the expected results for the BTn
series. The increase in emission lifetime and fluorescence quan-
tum yield of BTn chromophores, sequentially, when excited at
the dark donor, TPE (l=315 nm), provide further evidence to
support the number of TPE units fused to the BODIPY chromo-
phores. The measured quantum yields of BT1, BT2, and BT3
are 0.09, 0.13, 0.18, respectively, and the fluorescence lifetimes
were calculated to be 3.43 ns for BT1, 4.80 ns for BT2, and
5.58 ns for BT3. Furthermore, a very good fit was obtained
with single-exponential values for the fluorescence decays of
BT1, BT2 and BT3. Thus, a heterogeneous lifetime distribution,
according to multiple quantum yield formation, was eliminated
from the analysis. In addition to these attractive results, re-
markably, high fluorescence intensity increments were ob-
served for BT2 and BT3 in DRET studies when compared with
Figure 2. Normalised absorption spectra of 1, BT1, BT2 and BT3.
BTn chromophores, herein, the BODIPY bands remains the
same.
In parallel to DRET, which was one of the aforementioned
energy-transfer processes addressed herein, fluorescence stud-
ies were also performed on the BTn chromophores and related
molecules in THF. Thus, experimentally determined photophys-
ical properties of the chromophores are summarised in Table 1.
Figure 3 depicts the fluorescence spectra of the chromophores.
Owing to the AIE nature of the TPE chromophores, as antici-
pated, no emission was recorded for 7 when excited at l=
315 nm in THF (Figure S1 in the Supporting Information). Fluo-
rescence studies with compounds 1, 2 and 3, for which the ex-
citation wavelength was set at l=450 nm, impressively dem-
onstrated the unique emission properties of the BODIPY fluo-
rophore at l=505 nm (Figure 3). When excited at l=450 nm,
chromophores BT1, BT2 and BT3 also displayed similar fluores-
cence intensities to the corresponding BODIPY derivatives 1–3,
as expected (Figure 3). The outstanding fluorescence signals of
BTn at l=505 nm are very unusual when the chromophores
are excited at l=315 nm. Very high fluorescence intensities,
relative to the related BODIPY derivatives, were recorded for
Table 1. Photophysical properties of the BODIPY dyes 1–3 and BTn chromophores as 1.0”10À5 m solutions in THF.
[b]
[d]
labs[a] [nm]
labs [nm]
lem [nm]
t[c] [ns] (lexc [nm])
c2
f[c] (lexc [nm])
Dlem–ab [nm]
f
1
–
500
505
3.28 (337)
3.14 (457)
3.43 (337)
3.18 (457)
4.50 (337)
4.54 (457)
4.80 (337)
4.62 (457)
5.48 (317)
5.46 (457)
5.58 (337)
5.50 (457)
0.88
0.95
0.93
0.85
0.88
0.92
1.03
0.87
0.90
0.94
0.86
0.88
0.52 (450)
0.09 (317)
0.70 (450)
0.13 (317)
0.78 (450)
0.18 (317)
5
181
5
BT1
2
325
–
500
501
501
504
504
506
506
506
510
511
BT2
3
320
–
186
6
BT3
318
193
[a] The absorption maximum of the donor (TPE). [b] The absorption maximum of the acceptor (BODIPY). [c] Rhodamine 6G and quinine sulfate were used
as standard dyes for the determination of fluorescence quantum yields of 1–3 and BTn chromophores, respectively. [d] Stokes shift of 1–3 and pseudo-
Stokes shift of BTn chromophores.
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Figure 3. Emission spectra of 1.0”10À5 m solutions in THF of A) 7(D1), 1 and BT1; B) 7(D2) (2.0”10À5 m), 2 and BT2; C) 7(D3) (3.0”10À5 m), 3 and BT3, when
excited at l=315 (solid lines) and 450 nm (dotted lines). D) Comparative emission maxima of 7(D1)-7(D3), 1–3 and BT1–BT3 (the front coloured bars and
back dotted bars indicate the dyes excited at l=315 and 450 nm, respectively).
the emission intensity of 2 and 3 in THF. These results can be
regarded as a sign of the elimination of a deleterious effect,
self-quenching, and the lack of fluorescence leakage in BTn
systems based on the formation of a large pseudo-Stokes shift.
Considering the importance of the fluorescence intensity in
practical applications, we believe that BTn chromophores with
higher fluorescence intensity in organic solvents may attract
significant attention towards potential applications.
medium due to the aggregation-caused quenching effect.[15]
This is also what we observed experimentally for 1, 2, and 3 in
THF/water (2:98 (v/v)), as depicted in Figure 4. The decrease
and broadening in emission intensities of three BODIPY deriva-
tives, 1–3, when excited at their absorption maxima, l=
450 nm, with respect to their sharp and high emission intensi-
ties in THF, as shown in Figure 3, clearly provide scientific evi-
dence for the formation of aggregates, as reported in the liter-
ature.[15c] Apart from these photophysical events, intriguing re-
sults were obtained for the BTn chromophores in a 98% mix-
ture of water/THF. This is the second striking part of our study
that we focus on.
Based on the strong polarity-dependent photoluminescence
behaviour of AIE-active TPE chromophores,[9] it is not surprising
that chromophore 7 has a high emission intensity with good
stability in aqueous media due to the restriction of phenyl ring
rotation and the formation of aggregated species[9] (Figure S3
in the Supporting Information). The increase in the concentra-
tion of 7 (adjusted by considering the lower absorbance
maxima of the BTn series) in THF/water (2:98 (v/v)) leads to
a notable increase in the emission intensity owing to the AIE
methodology, as expected. In contrast, it is known from similar
analyses of the BODIPY fluorophore that there is a decrease in
the emission intensity with an increase in the polarity of the
In aqueous media, upon excitation of the emissive donor(s),
TPE, at its absorption maxima, l=315 nm, a strong fluores-
cence emission maximum centred at lꢀ525 nm, which was
equal to the emission wavelength of BODIPY fluorophore, and
a complete disappearance of TPE emission signal were record-
ed for BTn chromophores (Figure 4). These results clearly indi-
cate the existence of a FRET system between the emissive TPE
donor and emissive BODIPY acceptor in aqueous media. Inci-
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Figure 4. Emission spectra of 1.0”10À5 m A) 7(D1), 1 and BT1; B) 7(D2) (2.0”10À5 m), 2 and BT2; C) 7(D3) (3.0”10À5 m) 3 and BT3, when excited at l=315
(solid lines) and 450 nm (dotted lines), in THF/water (2:98 (v/v)). D) Comparative emission maxima of 7(D1)–7(D3), 1–3 and BT1–BT3 (the front coloured bars
and back dotted bars indicate the dyes excited at l=315 and 450 nm, respectively).
dentally, we speculate that the BODIPY chromophores in the
BTn systems, which are highly fluorescent in aqueous media
due to the presence of bulky TPE substituents on the BTn sys-
tems, suppress close stacking of BODIPY fluorophores. Our pre-
vious studies and other investigations clearly support our pre-
diction on this issue.[16] In FRET studies, chromophore BT3 still
showed the highest emission intensity, which could be attrib-
uted to the highest number of emissive TPE donors on the
chromophore skeleton (Figure 4d). On the other hand, all BTn
chromophores exhibit higher emission intensities than the cor-
responding BODIPY series 1–3. Similar photophysical studies to
those used to observe the DRET process were also carried out
to demonstrate the FRET process by using the BTn chromo-
phores as a donor–acceptor system in aqueous media. The re-
sults of these studies are presented in Table 2.
profiles were collected in aqueous media and fitted to a single
exponential for the FRET process. To gather information about
spectral overlap between the donor and acceptor, intramolecu-
lar energy-transfer rate constants and energy-transfer efficien-
cies in the BTn systems were calculated. Fast energy-transfer
rate constants were obtained from fluorescence intensity data
of BT1, BT2 and BT3 to give values of are 35.5, 39.1 and
39.6 nsÀ1, respectively. The energy-transfer efficiencies were
calculated by using the amount of quenching of the donor
chromophores. Thus, the complete disappearance of the char-
acteristic emission band of the TPE moiety at lꢀ470 nm with
an increase in the emission intensity of acceptor BODIPY fluo-
rophores in the BTn series demonstrated nearly 100% energy-
transfer efficiencies for all chromophores.[8c] The calculated
energy-transfer efficiencies for the BTn series in the FRET pro-
cess is also consistent with the prediction of experimental the
values shown in Table 2. These values further demonstrate the
superior overlap between TPE and BODIPY chromophores.
Briefly, a relatively large pseudo-Stokes shift of lꢀ200 nm was
further recorded for BTn systems in aqueous media based on
The quantum yields of the BTn compounds are 0.09 (BT1),
0.13 (BT2) and 0.18 (BT3) and the lifetime of the compounds
were recorded as 3.43, 4.80 and 5.58, respectively. The increas-
es in these two data sets are compatible with the results re-
corded for the DRET process (Table 1). The fluorescent decay
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Table 2. Photophysical properties of 1.0”10À5 m aqueous solutions (THF/water 2:98 (v/v)) of the BODIPY dyes 1–3, BTn chromophores, and 7.
[b]
labs[a] [nm]
labs [nm]
lemi [nm]
t[c][ns] (lexc [nm])
c2
f[c] (lexc [nm])
Dl[d]
[nm]
em–ab
E [%]
f
1
–
500
500
501
501
504
504
–
505
3.28 (337)
3.14 (457)
3.43 (337)
3.18 (457)
4.50 (337)
4.54 (457)
4.80 (337)
4.62 (457)
5.48 (317)
5.46 (457)
5.58 (337)
5.50 (457)
2.53 (315)
0.88
0.95
0.93
0.85
0.88
0.92
1.03
0.87
0.90
0.94
0.86
0.88
0.52 (450)
0.09 (317)
0.70 (450)
0.13 (317)
0.78 (450)
0.18 (317)
0.03 (315)
5
BT1
2
325
–
506
506
506
510
511
475
181
5
99
BT2
3
320
–
186
6
ꢀ100
ꢀ100
BT3
7
318
320
193
105
[a] The absorption maximum of the donor (TPE). [b] The absorption maximum of the acceptor (BODIPY). [c] Rhodamine 6G was used as the standard dye
to determine the fluorescence quantum yields of 1–3, and quinine sulfate was used as the standard dye for the determination of the fluorescence quan-
tum yields of BTn chromophores and 7. [d] Stokes shifts of 1–3 and pseudo-Stokes shifts of the BTn chromophores.
FRET, similar to that reported for DRET in organic media. To
show the influence of the polarities of solutions on the
energy-transfer processes, the fluorescence emission experi-
ments were further carried out for each BTn chromophores
and acceptors (1–3) in different mixtures of THF/water. As ex-
pected, higher emission intensities were observed for each
BTn chromophore compared with the emission intensities of
the corresponding acceptors (1–3) in solutions with different
polarities when the excitation wavelength was l=315 nm.
Briefly, energy-transfer processes take place efficiently without
being influenced by the polarities of the solvent for BTn chro-
mophores (Figures S4–S6 in the Supporting Information).
clearly indicate the novel, important properties of the multi-
functional AIE-active TPE chromophore, that is, it can act as
both a dark and emissive donor, depending on the polarity of
the solvent used to dissolve the energy-transfer systems. This
is also the first study to apply the AIE methodology to a FRET
process with a spectacular Stokes shift in aqueous media.
Taken all together, we believe that the presented novel assign-
ments will be useful and efficient tools for the purposes of
energy-transfer studies and their applications in organic and
aqueous media. Moreover, the topics addressed herein, in gen-
eral, focus on the developments of novel energy-transfer sys-
tems, and thus, can be extended to further interesting studies
in the field of non-conjugated water-soluble and -insoluble
chromophores.
Conclusion
We have designed and synthesised a family of amphiphilic,
non-conjugated chromophore systems based on a BODIPY
core fused with varying numbers of AIE-active TPE luminogens
from one to three by copper-catalysed azide–alkyne cycloaddi-
tion reactions. In THF, which provides a soluble state for both
chromophores, a remarkable large pseudo-Stokes shift of l=
200 nm was observed for all BTn systems when excited at the
absorption wavelength of non-emissive TPE chromophores to
provide evidence for the existence of the DRET process be-
tween the emissive acceptor BODIPY and dark donor TPE chro-
mophores. Similar photophysical behaviour to that recorded
for the DRET process was also observed in aqueous (THF/water
2:98 (v/v)) studies of the BTn chromophores with the FRET
process. The AIE-active TPE chromophore serves as a unique
dual activator in aqueous media. On one hand, it acts as an
emissive donor based on its aggregation characteristics in
polar media, whereas, on the other hand, it prevents intermo-
lecular p–p stacking of BODIPY fluorophores due to its sterical-
ly bulky molecular structure, and thus, provides an emissive ac-
ceptor. Therefore, this is the first time that two energy-transfer
processes have been combined in one molecule to give high
fluorescence with very large pseudo-Stokes shifts in both solu-
ble and aggregated states. Furthermore, these results also
Experimental Section
Materials and instrumentation
All chemicals and solvents purchased from Aldrich were used with-
1
out further purification. H and 13C NMR spectra were recorded in
CDCl3 with tetramethylsilane (TMS) as an internal reference by
using a Bruker DPX-400 spectrometer. THF was dried by heating at
reflux over metallic sodium in the presence of benzophenone until
a persistent blue colour was obtained and then it was distilled
under an argon atmosphere. Absorption spectroscopy was per-
formed by using a Shimadzu spectrophotometer. Steady-state fluo-
rescence measurements were conducted by using a Shimadzu RF-
5301PC spectrofluorometer. The time-resolved measurements were
carried out with a LaserStrobeModel TM3 spectrofluorophotome-
ter; the light source was a combination of a pulsed nitrogen laser/
tuneable dye laser. The pulse width was about 800 ps and had
a repetition rate of up to 20 pulsessÀ1. The decay curves of the
samples were collected over 200 channels by using a non-linear
timescale, with the time increment increasing according to arith-
metic progression. To determine the lifetime of the samples, the
fluorescence decays were fitted by using the instrument response
function (IRF). The goodness of fits was assessed by the value of
c2. Column chromatography of all products was performed by
using Merck silica gel 60 (particle size: 0.040–0.063 mm, 230–400
Chem. Eur. J. 2016, 22, 736 – 745
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mesh ASTM). Reactions were monitored by TLC. Solvents were pur-
chased from Sigma, and solvents used for spectroscopy experi-
ments were of spectrophotometric grade. (Prop-2-yn-1-yloxy)ben-
zene,[1] 2,3,4-tris(prop-2-yn-1-yloxy)benzaldehyde,[1] 3,5-bis (prop-2-
yn-1-yloxy) benzaldehyde,14-(prop-2-yn-1-yloxy) benzaldehyde,[8e]
The THF/H2O ratio was 1/1 (v/v). The mixture was stirred overnight.
The solvent was then evaporated and extracted with dichlorome-
thane, and the crude product was purified by column chromatog-
raphy on silica gel (CH2Cl2) as the eluent to afford product BT1 as
a light-orange solid (95 mg, 80%). 1H NMR (400 MHz, CDCl3): d=
8.03 (s, 1H), 7.52–7.49 (d, J=11.6 Hz, 2H), 7.23–7.20 (m, 4H), 7.18–
7.11 (m, 11 H), 7.10–7.03 (m, 6H), 6.00 (s, 2H, pyrrole-H), 5.33 (s,
2H), 2.57 (s, 3H), 1.43 ppm (s, 3H); 13C NMR (100 MHz, CDCl3): d=
159.0, 155.5, 145.0, 144.5, 143.4, 143.4, 143.1, 142.6, 141.8, 139.5,
135.1, 133.2, 132.9, 131.5, 131.4, 129.9, 129.6, 128.5, 128.2, 128.1,
128.0, 127.1, 127.03, 126.98, 121.4, 121.1, 119.9, 115.7, 68.2, 25.8,
14.8 ppm (overlapping was observed for some aromatic carbon
atoms); HRMS (MALDI-TOF): m/z calcd for [BT1+H]+: 752.33722;
found: 752.35817.
[9i]
4,[18b] and TPE-N3 were synthesised according to procedures re-
ported in the literature.
Synthesis and characterisation
Compound 1: 4-(Prop-2-yn-1-yloxy)benzaldehyde, (300 mg,
1.88 mmol) and 2,4-dimethylpyrrole, (530 mg, 5.62 mmol) were dis-
solved in CH2Cl2 (750 mL), and purged with argon in a 1000 mL
flask before TFA (1–2 drops) was added as a catalyst and the mix-
ture was stirred overnight. The red solution was treated with p-
chloranil (526 mg, 2,147 mmol) stirred for 1 h, then Et3N (3 mL) and
BF3·Et2O (3 mL) were added. Immediately after the addition of
BF3·Et2O, bright-green fluorescence was observed. The organic
phase was separated, dried (Na2SO4), filtered, and concentrated.
The residue was purified by column chromatography (CH2Cl2); the
first green fluorescent fraction afforded the expected BODIPY chro-
Synthesis of BT2: The same procedure as that described for BT1
was applied, except twice as much 2 was used as a reagent to syn-
thesise BT2. Purification of the crude product by column chroma-
tography on silica gel (CH2Cl2) afforded compound BT2 (160 mg,
85%). 1H NMR (400 MHz, CDCl3): d=7.99 (s, 2H, triazole-H), 7.46–
7.44 (d, J=8.8 Hz, 4H), 7.19–7.17 (m, 5H), 7.14–7.11 (m, 20H), 7.06–
7.01 (m, 12H), 5.94 (s, 2H; pyrrole-H), 5.23 (s, 4H), 2.54 (s, 6H),
1.46 ppm (s, 6H); 13C NMR (100 MHz, CDCl3): d=160.4, 155.9, 144.2,
143.4, 143.3, 139.5, 137.1, 135.0, 132.9, 131.5, 131.4, 128.2, 128.1,
127.9, 127.1, 127.03, 126.98, 121.4, 121.2, 120.0, 107.8, 103.0, 62.3,
30.5, 14.4 ppm (overlapping was observed for some aromatic
carbon atoms); HRMS (MALDI-TOF): m/z calcd for [BT2+Na]+:
1201.48763; found: 1201.48530.
mophore
1
as an orange–red solid (158 mg, 22%). 1H NMR
(400 MHz, CDCl3): d=7.20–7.18 (d, J=8.8 Hz, 2H; ArH), 7.09–7.07
(d, d=8.8 Hz, 2H; ArH), 5.97 (s, 2H; pyrrole-H), 4.76–4.75 (d, d=
2.4 Hz, 2H), 4.70-4.69 (t, J=2.4 Hz, 1H), 2.55 (s, 6H), 1.42 ppm (s,
6H); 13C NMR (100 MHz, CDCl3): d=158.3, 155.4, 143.4, 129.4,
128.2, 121.4, 121.3, 119.1, 115.8, 76.1, 56.3, 46.9, 14.7 ppm; HRMS
(MALDI-TOF): m/z calcd for [1+H]+: 379.17933; found: 379.19998
Compound 2: The same procedure as that described for 1 was ap-
plied, except 3,5-bis(prop-2-yn-1-yloxy)benzaldehyde was used as
a reagent to synthesise BODIPY derivative 2. Purification of the
crude product by column chromatography on silica gel (CHCl3/
CH3OH (99/1, v/v)) afforded 2 (200 mg, 25%). 1H NMR (400 MHz,
CDCl3): d=6.70–6.69 (t, J=2.4 Hz, 1H), 6.59–6.58 (d, J=2.0 Hz, 2H),
5.98 (s, 2H, pyrrole-H), 4.69–4.68 (d, J=2.4 Hz, 4H), 2.55 (s, 6H),
2.50–2.49 (t, J=2.4 Hz, 2H), 1.54 ppm (s, 6H); 13C NMR (100 MHz,
CDCl3): d=159.6, 155.9, 143.3, 140.9, 136.9, 131.2, 121.4, 107.8,
103.9, 78.2, 76.2, 56.2, 14.8, 14.4 ppm; HRMS (MALDI-TOF): m/z
calcd for [2+H]+: 433.18989; found: 433.19510.
Synthesis of BT3: Compound BT3 was obtained from 3 with three
times the concentration of 3 in the same procedure as that used
for the synthesis of BT1. The crude product was purified by
column chromatography on silica gel (CH2Cl2) to yield BT3 as
1
a yellow solid (210 mg, 86%). H NMR (400 MHz, CDCl3): d=8.54 (s,
1H; triazole-H), 8.28 (s, 1H; triazole-H), 8.13 (s, 1H; triazole-H),
7.62–7.60 (d, J=8.8 Hz, 2H), 7.42–7.39 (m, 6H), 7.16–6.96 (m, 51H),
5.80 (s, 2H), 5.38 (s, 2H), 5.32 (s, 2H), 5.26 (s, 2H), 2.36 (s, 6H),
1.38 ppm (s, 6H); 13C NMR (100 MHz, CDCl3): d=155.6, 153.9, 150.1,
145.2, 144.7, 144.6, 144.5, 143.6, 143.52, 143.49, 143.44, 143.39,
142.9, 142.4, 142.3, 141.8, 139.8, 139.7, 139.6, 135.1, 132.9, 132.8,
132.7, 131.6, 131.50, 131.47, 131.45, 128.2, 128.10, 128.08, 128.06,
127.9, 127.13, 127.09, 127.04, 126.99, 126.93, 124.4, 122.1, 121.5,
121.2, 119.8, 119.7, 110.5, 67.5, 66.4, 63.7, 25.8, 14.4 ppm (overlap-
ping was observed for some aromatic carbon atoms); HRMS
(MALDI-TOF): m/z calcd for [BT3+H]+: 1607.67750; found:
1607.69337.
Compound 3: Following the same procedure as that used for the
synthesis of compound 1, but with 2,3,4-tris(prop-2-yn-1-yloxy)ben-
zaldehyde as an reagent, BODIPY derivative 3 was obtained. The
product was purified by column chromatography on silica gel
(CH2Cl2) to give 3 (180 mg, 20%). 1H NMR (400 MHz, CDCl3): d=
6.88–6.81 (dd, J=28 Hz, 2H; AB system), 5.89 (s, 2H; pyrrole-H),
4.77–4.76 (d, J=2.4 Hz, 2H), 4.75–4.74 (d, J=2.4 Hz, 2H), 4.66–4.65
(d, J=2.4 Hz, 2H), 2.50 (s; part of 6H for -CH3, part of 1H for
acetyl-H), 2.38–2.37 (t, J=2.4 Hz, 1H), 2.26–2.25 (t, J=2.4 Hz, 1H),
1.48 ppm (s, 6H); 13C NMR (100 MHz, CDCl3): d=155.5, 153.0, 149.6,
142.9, 141.1, 124.7, 122.9, 121.3, 111.0, 79.0, 78.0, 76.5, 76.0, 75.8,
61.1, 60.6, 57.3, 29.9, 14.8, 14.6 ppm; HRMS (MALDI-TOF): m/z calcd
for [3+H]+: 487.20045; found: 487.22620.
Synthesis of 7: Following the same procedure as that used for the
synthesis of BT1, with (prop-2-yn-1-yloxy)benzene as a reagent,
TPE derivative 7 was obtained. The product was purified by
column chromatography on silica gel (CH2Cl2/hexane (6:4)) to
1
afford 7 (66.0 mg, 84%). H NMR (400 MHz, CDCl3): d=7.96 (s, 1H;
triazole-H), 7.48–7.46 (d, J=8.0 Hz, 2H), 7.32–7.28 (m, 2H), 7.18–
7.16 (d, J=8.0 Hz, 2H), 7.13–7.10 (m, 9H), 7.04–6.96 (m, 9H),
5.28 ppm (s, 2H); 13C NMR (100 MHz, CDCl3): d=158.4, 145.2, 144.9,
143.42, 143.40, 143.3, 142.5, 139.6, 135.2, 132.9, 131.51, 131.48,
131.43, 129.8, 128.2, 128.1, 127.9, 127.1, 127.0, 126.9, 121.6, 120.9,
120.0, 115.0, 62.2 ppm (overlapping was observed for some aro-
matic carbon atoms); HRMS (MALDI-TOF): m/z calcd for [7+H]+:
506.22324; found: 506.23549.
Synthesis of BT1: Compounds 1 (60 mg, 0,157 mmol, 1.0 equiv)
and 5 (63.3 mg, 0,156 mmol, 1.1 equiv) were added to freshly dis-
tilled THF (50 mL). After 15 min, triethylamine (TEA; 10–30 mol%
per triple bond) was added to this mixture, and stirred for 10 min.
A mixture containing 10–30 mol% per triple bond of sodium ascor-
bate and 5–15 mol% of CuSO4·5H2O per triple bond (a stock solu-
tion of sodium ascorbate and CuSO4·5H2O in water prepared at
a concentration of 100 mgmLÀ1) was added to the reaction vessel.
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[5] a) J. Szollosi, S. Damjanovich, L. Matyus, Cytometry 1998, 34, 159–179;
b) R. B. Sekar, A. Periasamy, J. Cell Biol. 2003, 160, 629–633; c) S. R.
Adams, A. T. Harootunian, Y. J. Buechler, S. S. Taylor, R. Y. Tsien, Nature
1991, 349, 694–697; d) K. E. Sapsford, L. Berti, I. L. Medintz, Angew.
Chem. Int. Ed. 2006, 45, 4562–4589; Angew. Chem. 2006, 118, 4676–
4704; e) R. M. Clegg, Curr. Opin. Biotechnol. 1995, 6, 103–110; f) K. E.
Sapsford, L. Berti, I. L. Medintz, Minerva Biol. 2005, 16, 253–279; g) W. S.
Li, T. Aida, Chem. Rev. 2009, 109, 6047–6076; h) R. Ziessel, G. Ulrich, A.
Haefele, A. Harriman, J. Am. Chem. Soc. 2013, 135, 11330–11344; i) O. A.
Bozdemir, S. Erbas-Cakmak, O. O. Ekiz, A. Dana, E. U. Akkaya, Angew.
Chem. Int. Ed. 2011, 50, 10907–10912; Angew. Chem. 2011, 123, 11099–
11104; j) R. Guliyev, A. Coskun, E. U. Akkaya, J. Am. Chem. Soc. 2009,
131, 9007–9013; k) S. Atilgan, T. Ozdemir, E. U. Akkaya, Org. Lett. 2010,
12, 4792–4795; l) O. A. Bozdemir, M. D. Yilmaz, O. Buyukcakir, A. Sie-
miarczuk, M. Tutas, E. U. Akkaya, New J. Chem. 2010, 34, 151–155.
[6] a) Y. N. Teo, E. T. Kool, Chem. Rev. 2012, 112, 4221–4245; b) S. Li, M. S.
Langenegger, R. Häner, Chem. Commun. 2013, 49, 5835–5837; c) R. T.
Ranasinghe, T. Brown, Chem. Commun. 2005, 5487–5502; d) D. M. J.
Lilley, T. J. Wilson, Curr. Opin. Chem. Biol. 2000, 4, 507–517; e) T. Terai, T.
Nagano, Curr. Opin. Chem. Biol. 2008, 12, 515–521.
Photophysical calculations
Quantum yield measurements and calculations were performed by
using rhodamine 6G (f =0.95 in ethanol, at l=480 nm excitation
f
wavelength) and quinine sulfate (f =0.546 in a 0.5m aqueous so-
lution of H2SO4, at l=310 nm excitation wavelength) as standard
dyes with Equation (1):
f
ꢀ
ꢁꢀ
ꢁ ꢀ
ꢁ
2
Aref
A
nD
nD,ref
aref
a
ð1Þ
ꢀf ¼ ꢀf,ref
in which f is the fluorescence quantum yield of the reference
f,ref
dye, A is the absorbance of the solution at the excitation wave-
length, nD is the refraction index of the solvent and a is the area
under the fluorescence spectrum.[19, 20]
The Fçrster distances (Ro), energy-transfer efficiencies (E) and
energy-transfer rate constants (kT(r)) were calculated by using
Equations (2)–(4), respectively:
[7] a) H. Oevering, M. N. Paddon-Row, M. Heppener, A. M. Oliver, E. Cotsaris,
J. W. Verhoeven, N. S. Hush, J. Am. Chem. Soc. 1987, 109, 3258–3269;
b) M. R. Roest, J. M. Lawson, M. N. Paddon-Row, J. W. Verhoeven, Chem.
Phys. Lett. 1994, 230, 536–542; c) G. S. Jiao, L. H. Thoresen, K. Burgess, J.
Am. Chem. Soc. 2003, 125, 14668–14669; d) J. Y. Han, J. Jose, E. Mei, K.
Burgess, Angew. Chem. Int. Ed. 2007, 46, 1684–1687; Angew. Chem.
2007, 119, 1714–1717.
1=6
Ro ¼ 0:211½K2nÀ4ꢀDJðlފ
ð2Þ
ð3Þ
ð4Þ
E ¼ 1ÀðFDA=FDÞ ¼ ðRoÞ =½ðRoÞ þ r6Š
6
6
6
kTðrÞ ¼ ð1=tDÞðRo=rÞ
[8] a) D. Su, J. Oh, S. C. Lee, J. M. Lim, S. Sahu, X. Yu, D. Kim, Y. T. Chang,
Chem. Sci. 2014, 5, 4812–4818; b) D. Su, C. L. Teoh, N. Y. Kang, X. Yu, S.
Sahu, Y. T. Chang, Chem. Asian J. 2015, 10, 581–585; c) E. Aydin, B. Ni-
sanci, M. Acar, A. Dastan, O. A. Bozdemir, New J. Chem. 2015, 39, 548–
554.
in which fD is the quantum yield of the donor, n is the refractive
index of the medium, r is the distance between the donor and ac-
ceptor, and tD is the lifetime of the donor. K2 is generally assumed
to be equal to 2/3. The overlap integral (J(l)) states the degree of
spectral overlap between the emission of donor and the absorp-
tion of acceptor. FD and FDA are the relative fluorescence intensities
of the donor in the absence and presence of the acceptor, respec-
tively.[21, 22]
[9] a) Z. Zhao, S. Chen, X. Shen, F. Mahtab, Y. Yu, P. Lu, J. W. Y. Lam, H. S.
Kwoka, B. Z. Tang, Chem. Commun. 2010, 46, 686–688; b) H. Tong, Y.
Hong, Y. Dong, M. Haussler, J. W. Y. Lam, Z. Li, Z. Guo, Z. Guo, B. Z. Tang,
Chem. Commun. 2006, 3705–3707; c) Y. Dong, J. W. Y. Lam, A. Qin, J.
Liu, Z. Li, B. Z. Tang, Appl. Phys. Lett. 2007, 91, 011111; d) Z. J. Zhao, P.
Lu, J. W. Y. Lam, Z. M. Wang, C. Y. K. Chan, H. H. Y. Sung, I. D. Williams,
Y. G. Ma, B. Z. Tang, Chem. Sci. 2011, 2, 672–675; e) Z. J. Zhao, S. M.
Chen, J. W. Y. Lam, Z. M. Wang, P. Lu, F. Mahtab, H. H. Y. Sung, I. D. Wil-
liams, Y. G. Ma, H. S. Kwok, B. Z. Tang, J. Mater. Chem. 2011, 21, 7210–
7216; f) Z. Zhao, S. Chen, J. W. Y. Lam, P. Lu, Y. Zhong, K. S. Wong, H. S.
Kwok, B. Z. Tang, Chem. Commun. 2010, 46, 2221–2223; g) Q. Zhao, S.
Zhang, Y. Liu, J. Mei, S. Chen, P. Lu, A. Qin, Y. Ma, J. Z. Sun, B. Z. Tang, J.
Mater. Chem. 2012, 22, 7387–7394; h) Z. Wang, Y. Liu, H. S. Kowk, Y. Ma,
B. Z. Tang, Adv. Mater. 2010, 97–101, 2159–2162; i) Y. Cai, L. Li, Z. Wang,
J. Z. Sun, A. Qin, B. Z. Tang, Chem. Commun. 2014, 50, 8892–8895.
[10] a) B. Z. Tang, X. W. Zhan, G. Yu, P. P. S. Lee, Y. Q. Liu, D. B. Zhu, J. Mater.
Chem. 2001, 11, 2974–2978; b) J. W. Chen, C. C. W. Law, J. W. Y. Lam,
Y. P. Dong, S. M. F. Lo, I. D. Williams, D. B. Zhu, B. Z. Tang, Chem. Mater.
2003, 15, 1535–1546; c) Z. Zhao, C. Deng, S. Chen, J. W. Y. Lam, W. Qin,
P. Lu, Z. Wang, H. S. Kwok, Y. Ma, H. Qiub, B. Z. Tang, Chem. Commun.
2011, 47, 8847–8849.
Acknowledgements
This research was financially supported by the Süleyman Demi-
rel University BAP (scientific research project) project. We
˘
thank Dr. Ö. Altan Bozdemir and Dr. Tugba Özdemir Kütük for
their contributions to this work.
Keywords: aggregation · donor–acceptor systems · dyes/
pigments · dark resonance energy transfer (DRET) · FRET
[1] a) A. W. Czarnik, Fluorescent Chemosensors for Ion and Molecule Recogni-
tion, ACS Symposium Series 358, American Chemical Society, Washing-
ton, DC, 1993; b) B. Valeur, J. R. Lakowicz, in Probe Design and Chemical
Sensing, Topics in Fluorescence Spectroscopy, Plenum, New York,
1994;c) A. P. de Silva, H. Q. N. Gunaratne, T. Gunnlaugsson, A. J. M.
Huxley, C. P. McCoy, J. T. Rademacher, T. E. Rice, Chem. Rev. 1997, 97,
1515–1566; d) X. Chen, Y. Zhou, X. Peng, J. Yoon, Chem. Soc. Rev. 2010,
39, 2120–2135; e) G. Ulrich, R. Ziessel, A. Harriman, Angew. Chem. Int.
Ed. 2008, 47, 1184–1201; Angew. Chem. 2008, 120, 1202–1219.
[11] a) I. Caplia, R. J. Linhardt, Angew. Chem. Int. Ed. 2002, 41, 390–412;
Angew. Chem. 2002, 114, 426–450; b) H. Tong, Y. N. Hong, Y. Q. Dong,
M. Haeussler, Z. Li, J. W. Y. Lam, Y. P. Dong, H. H. Y. Sung, I. D. Williams,
B. Z. Tang, J. Phys. Chem. B 2007, 111, 11817–11823; c) M. Wang, D. Q.
Zhang, G. X. Zhang, Y. L. Tang, S. Wang, D. B. Zhu, Anal. Chem. 2008, 80,
6443–6448; d) M. Wang, X. G. Gu, G. X. Zhang, D. Q. Zhang, D. B. Zhu,
Anal. Chem. 2009, 81, 4444–4449; e) K. Shiraishi, T. Sanji, M. Tanaka, Tet-
rahedron Lett. 2010, 51, 6331–6333.
[2] a) L. D. Lavis, R. T. Raines, ACS Chem. Biol. 2008, 3, 142–155; b) J. Chan,
S. C. Dodani, C. J. Chang, Nat. Chem. 2012, 4, 973–984; c) M. Schäferl-
ing, Angew. Chem. Int. Ed. 2012, 51, 3532–3554; Angew. Chem. 2012,
124, 3590–3614; d) X. Chen, T. Pradhan, F. Wang, J. S. Kim, J. Yoon,
Chem. Rev. 2012, 112, 1910–1956; e) B. K. An, D. S. Lee, J. S. Lee, Y. S.
Park, H. S. Song, S. Y. Park, J. Am. Chem. Soc. 2004, 126, 10232–10233.
[3] a) J. R Lakowicz, Principles of Fluorescence Spectroscopy, 2nd ed., Kluwer,
New York, 1999; b) J. Wu, W. Liu, J. Ge, H. Zhang, P. Wang, Chem. Soc.
Rev. 2011, 40, 3483–3495.
[12] a) L. Peng, M. Wang, G. Zhang, D. Zhang, D. Zhu, Org. Lett. 2009, 11,
1943–1946; b) S. J. Toal, K. A. Jones, D. Magde, W. C. Trogler, J. Am.
Chem. Soc. 2005, 127, 11661–11665; c) L. Liu, G. X. Zhang, J. F. Xiang,
D. Q. Zhang, D. B. Zhu, Org. Lett. 2008, 10, 4581–4584.
[13] Z. Li, Y. Dong, B. X. Mi, Y. H. Tang, M. Haussler, H. Tong, Y. P. Dong,
J. W. Y. Lam, Y. Ren, H. H. Y. Sung, K. S. Wong, P. Gao, I. D. Williams, H. S.
Kwok, B. Z. Tang, J. Phys. Chem. B 2005, 109, 10061–10069.
[14] A. Loudet, K. Burgess, Chem. Rev. 2007, 107, 4891–4932.
[15] a) S. L. Niu, G. Ulrich, R. Ziessel, A. Kiss, P.-Y. Renard, A. Romieu, Org. Lett.
2009, 11, 2049–2052; b) S.-L. Niu, C. Massif, G. Ulrich, P.-Y. Renard, A.
[4] J. Fan, M. Hu, P. Zhan, X. Peng, Chem. Soc. Rev. 2013, 42, 29–43.
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Romieu, R. Ziessel, Chem. Eur. J. 2012, 18, 7229–7242; c) D. Zhang, V.
Martin, I. Garcia-Moreno, A. Costela, M. E. Perez-Ojeda, Y. Xiao, Phys.
Chem. Chem. Phys. 2011, 13, 13026–13033.
[20] A. Costela, I. Garcıa-Moreno, C. Gomez, R. Sastre, F. Amat-Guerri, M.
Liras, F. L. Arbeloa, J. B. Prieto, I. L. Arbeloa, J. Phys. Chem. A 2002, 106,
7736–7742.
[16] a) T. Ozdemir, S. Atilgan, I. Kutuk, L. T. Yildirim, A. Tulek, M. Bayindir, E. U.
Akkaya, Org. Lett. 2009, 11, 2105–2107; b) S. Frein, F. Camerel, R. Ziessel,
J. Barbera, R. Deschenaux, Chem. Mater. 2009, 21, 3950–3959.
[17] S. Choi, J. Bouffard, Y. Kim, Chem. Sci. 2014, 5, 751–755.
[18] a) R. Hu, C. F. Azael Gomez-Duran, J. W. Y. Lam, J. L. Belmonte-Vazquez,
C. Deng, S. Chen, R. Ye, E. Pena-Cabrera, Y. Zhong, K. S. Wong, B. Z.
Tang, Chem. Commun. 2012, 48, 10099–10101; b) M. Baglan, S. Ozturk,
B. Gur, K. Meral, U. Bozkaya, O. A. Bozdemir, S. Atılgan, RSC Adv. 2013, 3,
15866–15874.
[21] a) N. Boens, V. Leen, W. Dehaen, Chem. Soc. Rev. 2012, 41, 1130–1172;
b) A. C. Benniston, G. Copley, Phys. Chem. Chem. Phys. 2009, 11, 4124–
4131.
[22] a) D. Tleugabulova, Z. Zhang, J. D. Brennan, J. Phys. Chem. B 2002, 106,
13133–13138; b) Y. Tokoro, A. Nagai, Y. Chujo, Tetrahedron Lett. 2010,
51, 3451–3454.
Received: August 30, 2015
[19] a) R. P. Haughland, Handbook of Fluorescent Probes and Research Prod-
ucts, 9th ed., Molecular Probes, Eugene, 2002; b) M. S. T. GonÅalves,
Chem. Rev. 2009, 109, 190–212.
Revised: November 3, 2015
Published online on November 30, 2015
Chem. Eur. J. 2016, 22, 736 – 745
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