Rational design of new thiazolo-thiazole dyes as input energy units in molecular dyads

Article abstract of DOI:10.1002/chem.201203121

Bridge over troubled water: Highly fluorescent thiazolo-thiazole dyes with quantum yields of up to 60 % were prepared in a facile synthesis from dithiooxamide and various aldehydes. When adequately engineered, such dyes could be used as fluorescent bridges with other dyes. A sequence of highly efficient, intramolecular electronic-energy-transfer steps followed from selective illumination of the fluorescent centre in the molecular triads. Copyright

Full text of DOI:10.1002/chem.201203121

COMMUNICATION
DOI: 10.1002/chem.201203121
À
Rational Design of New Thiazolo Thiazole Dyes as Input Energy Units in
Molecular Dyads
Raymond Ziessel,*[a] Adela Nano,[a] Elodie Heyer,[a] Thomas Bura,[a] and
Pascal Retailleau[b]
The demand for readily prepared, generic families of fluo-
rescent molecules that contain multiple functionalities cur-
rently attracts considerable attention.[1,2] The ever-increasing
interest in such probes has been stimulated by their diverse
applications in energy-conversion devices,[3] sensors,[4] and
biological imaging techniques.[5] Specifically, sulfur-contain-
ing fluorescent probes appear to be useful as photoactive
layers in bulk heterojunction solar cells (BHJ)[6] and as dyes
wire-like molecule occurs in a stepwise manner along the
different electron-accepting stations that are present along
the spacer.[18] It has also been demonstrated that the rate
constant for ET (or eT) is strongly dependent on the nature
and orientation of the spacer.[19] We recently used closo-
para-carborane as an innocent spacing unit to promote
through-space ET between two photoactive modules.[20,21]
Typical rates for different borondipyrromethene (bodipy)
units are in the order of 6ꢀ108 sÀ1 and about 2ꢀ109 sÀ1 with
one DPP group and one bodipy group as acceptor moieties.
The probability of one-way ET between terminals depends
on the length of the spacer but also on the temperature and
applied pressure.[22]
in sensitized solar cells (DSSC).[7] The families of oligothio-
[9]
phenes[8] and thiadiazolo bithienyl dyes have largely con-
À
tributed to the spectacular progress in plastic electronics
and the development of BHJ solar cells. The bis-lactam
framework in diketopyrrolopyrroles (DPP) has also attract-
ed our attention because such dyes offer many opportunities
for chemical transformations and, thus, for tuning their opti-
cal and electrochemical properties, as well as having a
unique propensity to be used as a bridging subunit in
À
Recently, thiazolo thiazole frameworks have aroused in-
terest as semiconducting materials with high carrier mobili-
ty,[23] as components of high-performance co-polymer solar
cells,[24] in organic electronics,[25] in photovoltaics,[26] and as
fluorescent sensors.[27] Very surprisingly, analogues of thia-
À
donor acceptor molecular systems[10] or in Ir complexes.[11]
À
Energy transfer (ET) or electron transfer (eT) properties
in multichromophoric arrays have been largely studied so
far.[12,13] These purely organic or metallo-organic frameworks
range from dyads to larger architectures and are classified
as linear, branched, or cyclic structures.[14] These studies re-
vealed that ET predominantly occurs in a through-bond
manner (as opposed to through space) between, for exam-
ple, closely coupled porphyrins, whereas ET between
ACHTUNGTRENzNUGN olo thiazoles based on fused five-membered rings have not
been used as spacing units in more-sophisticated architec-
tures.[12] It is expected that the use of thiazolo thiazole tem-
À
plates should ensure a rigid backbone with a highly extend-
ed p-electron core, thereby leading to strong p-stacking,
which is favourable for: 1) the preparation of new fluores-
cent dyes; 2) tuning the nature of the donor subunits; and
À
3) the construction of donor acceptor scaffolds by using the
À
second- or third-neighbours utilizes the intervening por
N
thiozalo thiazole subunit as the energy input during irradia-
A
tion.
in the order of 20–30 ps.[15] When identical chromophores
are present in the cyclic arrays, energy hopping is ultrafast
and occurs with a time constant of 1–9 ps.[16,17] The exponen-
In thiazolo thiazole fluorescent bridges, the energy level
À
À
is scaled at higher energy versus both donor acceptor sub-
units, thus rendering the LUMO/HOMO orbitals for
À
À
tial distance dependence of eT in a donor bridge acceptor
through-bond ET inaccessible for classical ET or eT process-
À
es. Herein, we report the design of thiazolo thiazole bridges
[a] Dr. R. Ziessel, A. Nano, E. Heyer, T. Bura
Laboratoire de Chimie Molꢁculaire et Spectroscopies Avancꢁes
LCOSA
that favour through-space ET processes, which is a clear dis-
tinction compared to previously published systems.
A general synthesis of 2,5-diarylthiazoloACHTNUTRGNEUNG[5,4-d]thiazoles
Ecole Europꢁenne de Chimie, Polymꢂres et Matꢁriaux
UMR 7515 associꢁ au CNRS
25 rue Becquerel, 67087 Strasbourg Cedex 02 (France)
E-mail: ziessel@unistra.fr
was performed herein by heating dry dithiooxamide with
the desired aldehyde in anhydrous n-propanol (or DMF for
compound 3) at 1408C. The resulting highly fluorescent
dyes were purified by column chromatography on silica gel
and isolated in acceptable yields (55–83%, Scheme 1). The
FTIR spectra of most of these compounds were quite simple
and consisted of a small number of strong bands, thus re-
flecting the high level of symmetry within the molecules. Be-
cause numerous possible cyclisation products could be envis-
Homepage: http://www-lmspc.u-strasbg.fr/lcosa/
[b] Dr. P. Retailleau
Laboratoire de Crystallochimie, ICSN - CNRS
Bꢃt. 27- 1 avenue de la Terrasse, 91198 Gif-sur-Yvette, Cedex
(France)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201203121.
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analysis on two key derivatives (Figures 1 and 2). Interest-
ingly, the selective mono-deprotection of a single triethylsil-
yl (TES) group in compound 3 was achieved in 55% yield
by using KF in a MeOH/THF mixture (Scheme 2). The reac-
tion was followed by TLC, thus allowing it to be quenched
before double deprotection occurred. The resulting com-
pound (6), which showed a resonance at d=3.23 ppm for
1
the terminal alkyne group in its H NMR spectrum, was a
pivotal starting material for the step-by-step linking of dif-
ferent useful fluorophores (Scheme 2). Precursors A and C
(Scheme 3) were prepared according to literature proce-
dures,[29,30] whereas compound B was prepared by a Knove-
nagel reaction between julolidine aldehyde and tetramethyl-
bodipy (see the Supporting Information).[31] It was possible
to graft dye A onto compound 6 in a single step in the pres-
ence of Pd0, thereby leading to compound 7 in 80% yield.
Deprotection of compound 7 was straightforward, thus lead-
ing to compound 8 in 84% yield. Finally, cross-coupling of
compound 8 with blue dyes B and C readily provided dyes 9
and 10, respectively, in excellent yields.
À
Scheme 1. Synthesis and chemical structures of the new thiazolo thiazole
dyes.
aged[28] and because NMR spectroscopy did not provide un-
ambiguous assignment, conclusive evidence for the thia-
zolo thiazole structure (Scheme 1) was obtained by X-ray
All of these mixed dyes were unambiguously character-
ized by standard NMR and FTIR spectroscopy, MS, and ele-
mental analysis. Tabular orange single crystals of compound
À
A
Scheme 2. a) KF, THF/MeOH (1:1), RT, 55%; b) compound A, benzene/triethylamine (3:1), [Pd
ACHTUNGTRENNUNG
84%; d) compound B, benzene/triethylamine (3:1), [Pd(PPh3)4], 708C, 88%; e) compound C, benzene/triethylamine (3:1), [PdACHTUNGTRENNUNG
N
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Thiazolo Thiazole Dyes
COMMUNICATION
conformation of both N and S atoms around the central
À
double bond of the thiazolo thiazole rings. Both molecules
adopt a distorted quasi-planar conformation around the bis-
ACHUTNGREN(NUG 2-phenyl)thiazoloACHTUNGTRNE[NUGN 5,4-d]thiazole moiety, with some disorder
in the terminal chains. The bond lengths and angles in the
thiazole ring (see legends of Figure 1 and Figure 2) are simi-
À
lar to those of thiazolo
G
been deposited in the Cambridge Structural Database.[32]
À
À
The outer S C bond length is typical of a single S C
À
bond, whilst the inner S C bond has considerable double-
bond character, which is even more pronounced in com-
pound 7. Interestingly, in centrosymmetric dimeric molecule
1, the phenyl rings are twisted from the least-squares plane
of the thiazoloACHTUNTRGNEUNG[5,4-d]thiazole core by 158. This twisting is
less pronounced in compound 7 (dihedral angle of 9.58 with
the phenyl group from the bodipy side, 4.48 on the other
side). The full length of compound 7 is about 35 ꢅ and the
thiazoloACTHNUTRGNE[UNG 5,4-d]thiazole moiety is very close to orthogonal to
À
the C bodipy core (dihedral angle of 87.68), as expected
from the presence of methyl groups at positions C2 and C7.
The bodipy unit is very close to planar, with mean deviation
from the best plane (16 atoms) of 0.026 ꢅ and a maximum
deviation of 0.075 ꢅ for the boron atom. The triethylsilyl
group adopts an eclipsed form with respect to the bodipy
core.
Scheme 3. Structures of compounds A–C.
1 that were suitable for X-ray diffraction were obtained
from a solution in acetone and crystals of compound 7 were
obtained from a mixture of EtOAc and petroleum ether.
The data-collection parameters are available in the Support-
ing Information, Table S1. Representations of both struc-
tures are shown in Figure 1 and Figure 2 and reveal the ex-
pected formulation of these new compounds with an anti-
In the centrosymmetric triclinic crystal packing of com-
pound 1, the molecules are oriented along the [21À2] direc-
tion in corrugated layers that are approximately parallel to
the (021) plane (Figure 3). The shortest distance between
the phenyl rings in adjacent layers is 5.09 ꢅ and the cen-
À
AHCTUNGTREGtNNUN roid centroid distance is above 5.70 ꢅ. N,N-Dibutylaniline
substituents serve as flexible arms to clip adjacent layers to-
gether. The closest S atoms are 5.132 ꢅ apart. In the second
monoclinic P21/c crystal packing, molecules of compound 7
that are related by a centre of inversion stack head-to-tail
À
with a slightly offset overlap between the thiazolo thiazole
group at a general position and the vicinal phenyl group at
À
position Àx,1Ày,1Àz, with a centroid centroid distance of
Figure 1. X-ray crystal structure of compound 1; ellipsoids are set at 30%
probability. Hydrogen atoms are omitted for clarity. Selected bond
À
À
À À
lengths [ꢅ] and angles [8]: S1 C1 1.768(2), S1 C2 1.720(2); C1 S1 C2
À
À
88.64(9), C1 N1 C2 109.0(2).
Figure 2. X-ray crystal structure of compound 7; ellipsoids are set at 30%
probability. Hydrogen atoms are omitted for clarity. Selected bond
À
À
À
lengths [ꢅ] and angles [8]: S1 C20 1.758(8), S2 C23 1.725(8), S1 C22
À
À
À
À
1.695 (7), S2 C21 1.708(7), N1 B1 1.574(10), N2 B1 1.562(10), B1 C1’
À
À
À
À À
1.550(12), B1 C1’’ 1.611 (12); C20 S1 C22 88.2(4), C21 S2 C23 89.4(4),
À
À
À
À
À
À
À
C20 N3 C21 109.6(7), C22 N4 C23 109.8(7), N1 B1 N2 106.0(6), C1’
Figure 3. Packing diagram for compound 1, viewed perpendicular to the
ac plane. Hydrogen atoms are omitted for clarity.
À
B1 C1’’ 110.4 (6).
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R. Ziessel et al.
À
H···O and Csp2 H···N interactions also contribute to stabiliz-
ing the crystal packing.
À
Photophysical parameters for the thiazolo thiazole dyes
1–5 are gathered in Table 1 and selected spectra are shown
in Figure 5. These new dyes exhibit markedly broad absorp-
tion bands and structured emission bands with often poor
mirror symmetry with the absorption bands. This observa-
tion is in keeping with the fact that the ground state is fluc-
tuating between several conformers but the relaxed excited
state is more planar. For all dyes, the extinction coefficients
are high, in the range 40000–70000mÀ1 cmÀ1, and the short
lifetimes (about 1 ns) render the fluorescence insensitive to
O2. Interestingly, changing the polarity of the solvent
changes the shape of the emission bands but not the life-
times, which remain similar. All of these dyes feature sub-
stantial Stokes shifts. Interestingly, an increase in the solvent
polarity increased the photoluminescence quantum yields
(e.g., from 30% in toluene to 62% in DMSO for dye 1).
The highest fem was found for dye 4 in polar conditions and,
in all cases, the excitation spectra matched the absorption
spectra, excluding the formation of aggregates. The optical
signature of these new dyes is remarkable and suggests that,
when appropriately connected to, for example, a bodipy or
Figure 4. Packing diagram for compound 7, viewed along the (0-11)
plane; hydrogen atoms are omitted for clarity. Dotted lines indicate S···S
À
interactions and hydrogen bonds. Hydrogen-bonding geometry: Csp2
À
H···O 2.50 ꢅ, 169.78; Csp2 H···N, 2.60 ꢅ.
À
other units, the thiazolo thiazole frameworks could be used
as an input energy source in directional cascade energy-
transfer processes, owing to the favourable spectroscopic
3.922(4) ꢅ, and the triethylsilyl groups rest on the most-
curved ethynyl arms (Figure 4). The adjacent dimers along
the [100] direction are linked through short common S···S
contacts (<3.5 ꢅ, about 138 between a vector that connects
the S atoms and a normal to the plane of the thiazole
ring),[33] thereby forming infinite undulating molecular strips
parallel to the (011) and (0-11) planes (Figure 4). The dihe-
À
overlap between the emission of the thiazolo thiazole group
(lem =500–600 nm) and the absorption of the bodipy group
(labs =450–520 nm for residue A and 550–650 nm for sub-
AHCTUNGTRENNUNG
units B and C).[12]
Linking the thiazolo thiazole to the bodipy A, leading to
molecule 7, almost results in a linear combination of the ab-
À
À
dral angle between these planes is about 68.58. Weak Csp2
sorption of the respective building blocks (Figure 6a). As
Table 1. Selected spectroscopic data for the relevant dyes.[a]
[b]
[c]
Dye
labs [nm]
e [mÀ1 cmÀ1
]
lem [nm] (lex [nm])
DSS [cmÀ1
]
fF
t [ns] (%)
1
2
3
4
5
7
432
376
388
434
462
396/501
68000
43500
75900
61500
64200
492/517 (396)
417/439/463 (350)
426/451/478 (352)
503/530 (385)
524/559 (420)
513 (382)
2800 (1900)
3800 (1500)
3600 (2300)
4200 (2000)
3800 (1900)
5800
0.60
0.06
0.32
0.58
0.33
0.50
1.34
0.34
0.59
1.52
1.03
3.28
79100/87500
513 (487)
–
0.49
7*
9*
392/500
99500/94700
512 (397)
512 (479)
513/753 (373)
513/755 (490)
750 (600)
6000
0.29
0.34
n.d./0.08
n.d./0.09
0.09
2.92
–
400/501/640
114000/86200/77200
13300
–
–
–
0.84 (86), 3.05 (14)
6.06
10
399/501/638
397/500/634
109800/82100/123000
115500/80100/123000
656 (372)
513/651 (470)
651 (570)
652 (379)
512/647 (468)
647 (583)
9800
0.43
0.10/0.43
0.58
0.37
0.10/0.51
0.58
–
–
0.92 (91), 3.42 (9)
4.12
–
0.92 (91), 3.48 (9)
4.45
–
9900
–
10*
–
[a] Data collected at room temperature, in DMSO/toluene (90:10 v/v), except for dye 9*, for which the data were collected in CH2Cl2/toluene (80:20
v/v), and for dyes 7* and 10*, for which the data were collected in CH2Cl2/toluene (90:10 v/v). [b] Average Stokes Shift (DSS), calculated between the
lmax of the absorption and emission bands (between the l absorption shoulder at low energy and the l emission shoulder at high energy). [c] Quinine sul-
fate was used as a reference for dyes 2 and 3: fF =0.55 in 1m H2SO4 (lex =366 nm);[34] R6G was used as a reference for dyes 1, 4, 5, 7, 7* and the residual
emission of fragment A in triades 9 and 10: fF =0.88 in EtOH (lex =488 nm);[34] tetramethoxydiisoindomethene difluoroborate was used as a reference
in CH2Cl2 for dyes 9 and 10 (fF =0.51 in MeOH);[35] n.d.=not determined.
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À
Thiazolo Thiazole Dyes
COMMUNICATION
Figure 5. Absorption, emission, and excitation spectra of dyes 1 and 3–5 in DMSO/toluene (90:10 v/v) at RT. a) Dye 1: emission lex =396 nm (Do =
0.253); excitation lem =577 nm. b) Dye 3: emission lex =352 nm (Do =0.081); excitation lem =493 nm. c) Dye 4: emission lex =385 nm (Do =0.067); excita-
tion lem =569 nm. d) Dye 5: emission lex =420 nm (Do =0.153); excitation lem =615 nm. For the excitation spectra, each solution was diluted at least ten
times.
expected, only one emission was recorded at 512 nm over
the entire excitation wavelength range. The absence of a re-
À
sidual emission of the thiazolo thiazole unit confirms that
quantitative energy transfer occurred, owing to a pro-
nounced spectroscopic overlap between the absorption of
the bodipy moiety (labs =450–500 nm) and emission of the
À
thiazolo thiazole group (lem =520–600 nm). As a conse-
quence, the Stokes shift increased to 5800 cmÀ1, with respect
to 470 cmÀ1 in bodipy A. By connecting a blue-light-absorb-
ing dye (e.g., B or C) an additional absorption was found at
around 640 nm and the spectra remained a linear combina-
tion of the absorption spectra of the respective modules,
thus highlighting the absence of pronounced electronic inter-
actions between different parts of the triad. By excitation of
the red-light-absorbing bodipy group at about 480 nm, dual
emissions at lem =513 and 651 nm for dye 10 and at lem
=
513 and 755 nm for dye 9, which corresponded to a non-
quantitative energy transfer from fragment A to B or C,
were observed (Figure 6b). This residual emission was weak
(about 10%), thus indicating high energy-transfer efficien-
cies (above 88%), which was not solvent dependent. Inter-
estingly, in all cases, the excitation spectra overlapped with
the whole absorption spectra, thus confirming that the thia-
Figure 6. Absorption, emission, and excitation spectra of dyes 7 and 10 in
CH2Cl2/toluene (90:10 v/v) at RT. a) Dye 7: emission lex =397 nm (Do =
0.112); excitation lem =558 nm. b) Dye 10: emission lex =379 nm (Do =
0.190); excitation lem =675 nm. For the excitation spectra, each solution
was diluted at least ten times.
À
zolo thiazole and bodipy A modules participated in the
energy-transfer process and that aggregate formation was
not an issue with this kind of molecule.
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R. Ziessel et al.
The rate of energy transfer was calculated from the quan-
tum yield, according to Equation (1),[36] to be ken(f) =8.2ꢀ
108 sÀ1 for dye 10, by considering the quantum yield and life-
time of model compound 7 and by taking into account the
amount of light that was used for the direct excitation of
fragment C. The rate that was calculated from the residual
lifetime of fragment A in triad 10 by using Equation (2),[36]
Experimental Section
Synthesis of compound 9: In
a Schlenk tube, compound 8 (30 mg,
0.035 mmol) and compound B (32 mg, 0.042 mmol) were dissolved in a
mixture of benzene (5 mL) and triethylamine (3 mL). Argon gas was
bubbled through the mixture for 30 min; then, [PdACTHNUTRGNE(UNG PPh3)4] (4 mg,
10 mol%) was added and the mixture was stirred at 708C for 12 h. The
solvents were evaporated and the residue was extracted with CH2Cl2 and
washed with water. The organic layer was filtered over hygroscopic
cotton wool and evaporated under reduced pressure. The crude residue
was purified by column chromatography on silica gel (toluene/CH2Cl2,
8:2 to 0:1) and recrystallization from CH2Cl2/EtOAc gave compound 9 as
k
en(t) =7.4ꢀ108 sÀ1, was in excellent agreement with the rate
that was previously calculated from the quantum yields. A
similar energy-transfer rate, ken(t) =8.5 108 sÀ1, was calculated
for triad 9 by using the excited-state lifetimes. The large un-
certainty in the determination of weak quantum yields ex-
cludes the calculation of the energy-transfer rate from these
1
a deep-green solid (46 mg, 88%). H NMR (CD2Cl2, 400 MHz): d=1.0 (t,
3J=7.4 Hz, 3H), 1.33 (s, 6H), 1.43–1.47 (m, 15H), 1.55 (m, 5H), 1.72–
1.75 (m, 4H), 1.85–1.92 (m, 2H), 2.56 (s, 3H), 2.73 (s, 6H), 3.19 (t, 3J=
5.7 Hz, 2H), 3.26 (t, 3J=6.0 Hz, 2H), 3.33 (s, 6H), 3.49–3.52 (m, 4H),
3.59–3.61 (m, 4H), 3.84 (t, 3J=6.7 Hz, 2H), 3.15 (s, 4H), 6.00 (s, 1H),
6.10 (s, 2H), 6.64 (s, 1H), 7.37–7.51 (m, 8H), 7.68–7.73 (m, 8H), 8.04–
8.06 ppm (m, 4H); 13C NMR (CD2Cl2, 50 MHz): d=14.4, 14.6, 14.9, 15.2,
16.3, 19.9, 30.2, 30.9, 32.5, 32.7, 32.9, 36.7, 40.3, 47.2, 47.8, 69.3, 72.2, 76.3,
90.3, 91.8, 113.0, 113.1, 113.2, 117.4, 118.4, 120.5, 120.5, 120.6, 122.1,
122.5, 123.6, 123.9, 123.9, 123.9, 125.6, 125.7, 126.8, 127.3, 129.1, 129.4,
129.6, 132.7, 132.8, 132.9, 134.2, 134.2, 135.5, 136.1, 136.3, 137.6, 140.2,
141.4, 141.8, 143.4, 145.2, 152.0, 152.4, 155.9, 156.5, 158.0, 168.76 ppm;
À
values. Note that, for dye 10, excitation into the thiazolo
thiazole fragment at 379 nm did not show any residual emis-
sion of fragment A. This result implies that direct energy
À
transfer from the thiazolo thiazole to fragment C is effec-
tive and is facilitated by a favourable spectroscopic overlap
À
between the emission of the thiazolo thiazole group at 500–
590 nm and the absorption of styryl dye C in dyad 10 (labs
=
11B NMR (C6D6, 400 MHz): d=1.96 ppm (t, J
ACTHNUTRGNEUNG(B,F)=34.2 Hz); FTIR-
550–650 nm). On irradiation at 379 nm, 3.5% of the light is
ATR : n˜ =2921 (m), 2850 (m), 1580 (s), 1539 (s), 1496 (s), 1291 (s), 1153
(s), 1075 (s), 980 (s), 833 cmÀ1 (s); MS (EI): m/z (%) calcd for [M]:
1485.6; found: 1485.5 (100), 1466.5 (10) [MÀF]; elemental analysis calcd
(%) for C91H91B2F2N7O5S2 (1487.5): C 73.48, H 6.23, N 6.59; found:
C 73.22, H 5.93, N 6.44.
absorbed by group A, 25.9% by group C, and 70.6% by the
À
thioazolo thiazole bridge. No multi-cascade ET from the
À
thiazolo thiazole group to module A and from module A to
module C occurs in this case. Finally, the energy-transfer ef-
ficiency, as well as the rate of energy transfer, were calculat-
Synthesis of compound 10: Compound 10 was prepared according the
same procedure as compound 9 from compound 8 (25 mg, 0.029 mmol),
compound C (23 mg, 0.035 mmol), [PdACHTUNTRGNEUNG(PPh3)4] (3 mg, 10 mmol%), ben-
ed by using PhotochemCAD software[37] with a boron
À
boron distance of 34.5 ꢅ for dye 10, 36.0 ꢅ for dye 9, and
an orientation factor (k2) of 0.5, which is consistent with the
Fçrster energy-transfer theory (kcalcd =9.0ꢀ108 sÀ1 for com-
pound 10 and kcalcd =2.0ꢀ109 sÀ1 for compound 9).[38] Under
these conditions, the Fçrster radius is 43.6 ꢅ for dye 10 and
44.4 ꢅ for dye 9. These calculated rates are in excellent
agreement with the rates that were determined from the re-
sidual quantum yield and excited-state lifetime of donor A
in triads 9 and 10 (see above).
zene (5 mL), and triethylamine (3 mL). The crude residue that was ob-
tained after evaporation of the solvent was recrystallized several times
from THF/EtOH/pentane to give compound 10 as a deep-green solid
(40 mg, 92%). 1H NMR (CD2Cl2, 400 MHz): d=1.47 (s, 6H), 1.54 (s,
6H), 2.39 (s, 6H), 2.73 (s, 6H), 3.33 (s, 6H), 3.50–3.52 (m, 4H), 3.59–3.61
(m, 4H), 4.15 (s, 4H), 6.09 (s, 2H), 6.69 (s, 2H), 7.23–7.31 (m, 6H), 7.36–
7.42 (m, 4H), 7.55 (d, 3J=7.9 Hz, 4H), 7.64–7.74 (m, 10H), 8.03–
8.05 ppm (m, 4H); 13C NMR (CD2Cl2, 100 MHz): d=14.6, 14.7, 14.9,
21.2, 58.6, 59.3, 68.8, 71.7, 89.9, 90.0, 91.2, 91.4, 117.8, 117.9, 121.7, 123.6,
123.7, 125.2, 125.2, 126.3, 127.4, 128.7, 128.9, 129.2, 129.6, 132.3, 132.4,
133.1, 133.8, 135.7, 136.5, 137.9, 139.6, 141.0, 141.4, 142.2, 151.1, 152.7,
155.5, 168.3, 168.3 ppm; 11B NMR (C6D6, 400 MHz): d=2.12 ppm (t, J-
In short, we have successfully constructed a new class of
À
highly fluorescent dyes based on a central thiazolo thiazole
AHCTUNGERTG(NNUN B,F)=33.9 Hz); FTIR-ATR: n˜ =2962 (m), 1603 (m), 1540 (s), 1512 (s),
À
rigid core. These new thiazolo thiazole dyes do not aggre-
1487 (s), 1406 (s), 1367 (s), 1308 (s), 1260 (s), 1151 (s), 1075 (s), 981 (s),
800 cmÀ1 (s); MS (EI): m/z (%) calcd for [M]: 1378.5; found: 1378.4
(100), 1359.4 (20) [MÀF]; elemental analysis calcd (%) for
C86H74B2F2N6O4S2 (1380.3): C 74.83, H 5.48, N 6.09; found: C 74.69,
H 5.18, N 5.72.
gate in apolar or polar solvents and their fluorescence is
fairly insensitive towards solvent polarity, with the best
quantum yields reaching 60%. The post-functionalization of
À
such dyes allows the preparation of donor acceptor systems
CCDC-884442 (1) and CCDC-884443 (7) contain the supplementary crys-
tallographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
À
in a controlled manner, for which the thiazolo thiazole core
can be used as fluorescent bridge and as an input energy
centre to promote cascade electronic energy transfer to a
bodipy energy acceptor. No residual emission of the thia-
À
ACHTUNGTRENNUNGzolo thiazole rings was observed, whereas 10% residual
emission of the tetramethyl-substituted bodipy group was
found in triad 10, thus enabling the calculation of a rate of
electronic energy transfer of about 8ꢀ108 sÀ1. This rate is in
keeping with the calculated rate for Fçrster energy transfer
by using PhotochemCAD. Further work on structural modi-
fication and deeper investigation of the nature of the emis-
Acknowledgements
We acknowledge the CNRS for their provision of research facilities and
financial support and the IMRA Europe S.A.S. (Sophia Antipolis) for a
PhD fellowship (to A.N.). We also thank Prof. Jack Harrowfield (ISIS,
Strasbourg) for critical reading of this manuscript before publication.
À
sion state in the thiazolo thiazole dyes are currently under-
way.
Keywords: aldehydes · bodipy · dyes/pigments · energy
transfer · fluorescence
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Thiazolo Thiazole Dyes
COMMUNICATION
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Received: September 3, 2012
Published online: && &&, 0000
Chem. Eur. J. 2013, 00, 0 – 0
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www.chemeurj.org
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R. Ziessel et al.
Bridge over troubled water: Highly
Dyes/Pigments
À
fluorescent thiazolo thiazole dyes with
quantum yields of up to 60% were
prepared in a facile synthesis from
dithiooxamide and various aldehydes.
When adequately engineered, such
dyes could be used as fluorescent
bridges with other dyes. A sequence of
highly efficient, intramolecular elec-
tronic-energy-transfer steps followed
from selective illumination of the fluo-
rescent centre in the molecular triads.
R. Ziessel,* A. Nano, E. Heyer,
T. Bura, P. Retailleau ........... &&& — &&&
À
Rational Design of New Thiazolo
Thiazole Dyes as Input Energy Units
in Molecular Dyads
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These are not the final page numbers!