New photochromic dithienylethenes through a click chemistry approach

Article abstract of DOI:10.1002/ejoc.201001245

Symmetric dithienylethenes 9-12 bearing a variety of substituents were synthesized by a click chemistry approach. The starting material, diacetylene 4, was obtained through Wittig reaction of dialdehyde 1 with dibromomethyltriphenylphosphonium bromide (2) and subsequent treatment with a lithium base (Corey-Fuchs reaction). Triazoles 11 and 12 with covalently linked fluorophore moieties show reversible quenching of fluorescence in solution. A series of functional photochromic compounds based on dithienylethenes has been synthesized by utilizing a copper-catalyzed azide-alkyne click chemistry approach. Dithienylethenes substituted with fluorophores show reversible photoswitching of fluorescence upon irradiation with UV/Vis light. Copyright

Full text of DOI:10.1002/ejoc.201001245

FULL PAPER
DOI: 10.1002/ejoc.201001245
New Photochromic Dithienylethenes through a Click Chemistry Approach
Oliver Tosic[a] and Jochen Mattay*[a]
Keywords: Sulfur heterocycles / Photochromism / Click chemistry / Fluorescence / Copper
Symmetric dithienylethenes 9–12 bearing a variety of substit-
uents were synthesized by a click chemistry approach. The
starting material, diacetylene 4, was obtained through Wittig
reaction of dialdehyde 1 with dibromomethyltriphenylphos-
phonium bromide (2) and subsequent treatment with a lith-
ium base (Corey–Fuchs reaction). Triazoles 11 and 12 with
covalently linked fluorophore moieties show reversible
quenching of fluorescence in solution.
with a variety of azides and the photochromic properties of
obtained triazoles 9–12.
Introduction
Photochromism describes the light-induced reversible in-
terconversion of two isomers that have different absorption
spectra.[1] Along with their color, photochromic systems
also change their physical and chemical properties, for ex-
ample, structures, refractive indices, or oxidation/reduction
potentials, which makes them interesting candidates for op-
tical memories and switches.[2] Among the numerous photo-
chromic compounds, dithienylethenes specifically have
drawn considerable attention because of their promising
characteristics, such as P-type photochromism, thermal sta-
bility, and high fatigue resistance.[3]
Results and Discussion
Synthesis
The synthetic pathway to diethynyl-substituted dithienyl-
ethene 4 is outlined in Scheme 1. Dialdehyde 1, which
was synthesized in four steps in 44% overall yield starting
from commercially available 5-methyl-2-thiophenecarbal-
dehyde,[12,13] was treated under phase-transfer catalysis con-
ditions[14] with dibromomethyltriphenylphosphonium bro-
mide (acetonitrile complex, 2)[15] to give brominated olefin
3 in 77% yield. Subsequent reaction with an excess amount
of n-butyllithium and quenching with water afforded di-
acetylene 4 in 70% yield.
There has been much effort in the past years to coval-
ently combine photochromic dithienylethenes with func-
tionalized building blocks (e.g., crown ethers,[4] terpyrid-
ines,[5] gelators,[6] polymers,[7] liquid crystals,[8] fluoro-
phores[9]) to obtain new photoswitchable functional materi-
als. So far the synthetic strategies used to build up these
photochromic compounds involve the whole bandwidth of
modern synthetic organic chemistry, except for copper-cata-
lyzed azide–alkyne cycloaddition (CuAAC). This powerful
click method (a Huisgen-type 1,3-dipolar cycloaddition[10]
)
has become a very efficient tool in organic synthesis.[11] Al-
though photochromic diacetylene 4 was reported in the lit-
erature almost a decade ago[12] it has surprisingly not been
employed in copper-mediated click reactions with organic
azides so far. Since the availability of a vast number of azide
building blocks makes CuAAC chemistry highly modular,
its combination with a suitable dithienylethene would give
access to various photoswitchable functional materials. In
this paper we present an alternative synthetic pathway to
compound 4, a protocol for its use in CuAAC reactions
Scheme 1. Synthesis of diacetylene 4.
The two-step reaction sequence from 1 to 4 follows the
well-known Corey–Fuchs reaction pathway, a modification
of the Wittig reaction.[16] Classically, the aldehyde compo-
nent is treated directly with triphenylphosphane, zinc, and
tetrabromomethane at low temperatures to obtain the cor-
responding dibromoolefin. Applied to dithienylethene 1,
[a] Organische Chemie I, Universität Bielefeld,
Postfach 100131, 33501 Bielefeld, Germany
Fax: +49-(0)-521-1066417
E-mail: mattay@uni-bielefeld.de
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201001245.
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371

O. Tosic, J. Mattay
FULL PAPER
this procedure unfortunately only led to decomposition of
the starting material. Although the reaction sequence from
5-methyl-thiophenecarboxaldehyde to 4 over six steps is
longer than the route reported by Irie and co-workers (four
steps, 25% overall yield),[12] the overall yield is comparable
(24%). Also, the Corey–Fuchs approach avoids the use of
expensive, air-sensitive palladium-mediated cross-coupling
with trimethylsilylacetylene.
Azides 5–8 (Scheme 2) were prepared from the corre-
sponding chloro or bromo compounds through substitution
of the halide with sodium azide: 4-bromobenzyl azide (5)
was prepared in almost quantitative yield from commer-
cially available 4-bromobenzylbromide following a pro-
cedure describing the analogous synthesis of 4-fluorobenzyl
azide.[17] 3-Azido-1-propanol (6) was synthesized in 70%
yield following the method of Stenzel et al.[18] 4-Azi-
domethyl-7-methoxycoumarin (7)[19] was prepared in 58%
yield from the corresponding 4-chlorocoumarin, which was
prepared in 77% yield from 3-methoxyphenol following a
slightly altered literature procedure.[20] 9-(Bromomethyl)-
anthracene[21] was converted into 9-(azidomethyl)anthra-
Scheme 3. Copper-catalyzed azide–alkyne cycloadditions.
Scheme 4. Photochemical switching of dithienyl triazoles.
Benzyl-substituted triazole
9 (Figure 1a) and hy-
cene (8) in nearly quantitative yield by a similar pro- droxypropyl dithienylethene 10 (Figure 1b) have very sim-
cedure.[19]
ilar absorption spectra with two absorption bands at 230
and 274 nm (Table 1), respectively, and a shoulder above
310 nm (for clarity, spectra in Figure 1 are scaled, see Sup-
porting Information for full-scale spectra). A hypsochromic
shift can be observed compared to the absorption of dialde-
hyde 1[14b] and methyl-substituted 1,2-bis(2,5-dimeth-
ylthien-3-yl)perfluorcyclopentene (see ref.[23]). The open-
ring isomers of 9 and 10 can be converted into the colored
forms by irradiation with 254-nm light and new broad
Scheme 2. Azides applied in click reactions.
The copper-catalyzed azide–alkyne cycloadditions were bands at around 570 nm arise.
carried out in chloroform solution and gave desired tri-
Dicoumarin 11 shows absorption bands at 274 and
azoles 9–12 in moderate to good yields (Scheme 3). We 324 nm, the latter being attributed to the coumarin moieties
chose [Cu(PPh3)3Br] as the catalyst, because it is quickly (Figure 1c).[24] The ring-closing reaction can be triggered
prepared from inexpensive copper(II) bromide and tri- with 300-nm light, and the colored isomer shows the same
phenylphosphane, and it is air stable and easy to handle.[22] broad absorption band at 572 nm as 9 and 10 do. Anthra-
The synthetic protocol for the cycloadditions involved stir- cene-substituted compound 12 has a similar absorption
ring diacetylene 4, the corresponding azide 5–8 (2–8 equiv.), spectrum with a strong band at 260 nm and additionally
and the catalyst (ca. 15 mol-%) in chloroform. All reactions shows the typical anthracene absorption pattern around
were carried out at ambient temperature except for the reac- 370 nm (Figure 1d). Although the dithienylethene scaffold
tion employing 8, which required reflux conditions. Once has only weak absorption at 350 nm, as can be seen in the
the reactions were finished, no workup was necessary: after spectra of 9 and 10 (Figure 1a,b), 12 can be transformed
removal of the solvent the products were directly purified into its colored isomer by irradiation with 365-nm light
by column chromatography on silica gel (see the Experi- where only the fluorophore is expected to absorb. In the
mental Section for details). To show the generality of the closed-ring form, a new broad band at 590 nm arises and
protocol, a benzylic, an aliphatic, and two fluorogenic func- irradiation at this wavelength gives the decolored isomer
tional building blocks were chosen.
again. The UV/Vis data of compounds 9–12 are summa-
rized in Table 1.
The emission spectra of 11 and 12 are given in Figures 2
and 3. Both are excited at isosbestic points to make sure
that the same number of photons is absorbed by the fluoro-
Photochromism
All four triazole-substituted dithienylethenes 9–12 show phore in both open and closed isomers. Dicoumarin 11 is
P-type photochromism in solution. Upon irradiation with excited with 325-nm light and emits at 400 nm in the open
UV light the open-ring isomer is converted into the closed form (Figure 2). When the solution is irradiated with 300-
form (Scheme 4) and the solution becomes blue or purple. nm light for 5 s the closed ring isomer is formed and acts
In all cases decoloration can be achieved by irradiation with as a quencher for the fluorescence. The intensity of emission
590 or 620-nm light.
therefore drops to 35% of the starting value. Additional
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New Photochromic Dithienylethenes through a Click Chemistry Approach
Figure 1. Solid lines: UV/Vis spectra of compounds 9 (a, 3.4ϫ10–6 m), 10 (b, 1.8ϫ10–5 m), 11 (c, 3.5ϫ10–5 m), and 12 (d, 1.4ϫ10–6 m)
in dichloromethane. Dashed lines: after 1 min irradiation with UV light: (a,b) 254 nm, (c) 300 nm, and (d) 365 nm.
Table 1. UV/Vis data of 9–12.
Compound
λmax
ε
Compound[a] λmax
[nm] [103 mcm–1
ε
[nm] [103 mcm–1
]
]
9 open
230
274
67
47
9 irradiated
230
277
572
72
24
5
10 open
11 open
12 open
230
274
95
47
10 irradiated 229
100
31
8
72
24
5
190
13
18
12
9
277
572
274
324
21
15
11 irradiated 230
274
572
258
351
369
389
200
10
13
12 irradiated 258
352
370
389
584
Figure 3. Emission spectra of 12, λex = 295 nm; solid line:
5ϫ10–6 m in dichloromethane, dashed lines: after irradiation with
365 nm (15 and 20 s), dotted lines: after irradiation with 620 nm
(25 and 70 s).
11
[a] For irradiation wavelengths see Figure 1.
irradiation with 300 nm for 5 s and 10 s changes the fluores-
cence insignificantly, suggesting that a photostationary state
like condition was already reached.[25] After irradiation
with 590 nm for 20 s the fluorescence intensity rises again
to a value slightly higher than the original intensity, poss-
ibly due to degradation of 11 under irradiation with energy-
rich 300-nm light. Additional irradiation with 590 nm does
not affect the fluorescence further.
Compound 12 shows a more efficient fluorescence
quenching performance (Scheme 5, Figure 3). When excited
at the isosbestic point with 295-nm light, 12 gives a typical
anthracene emission spectrum with bands centered around
425 nm. After irradiation with 365-nm light for 15 s the an-
thracene fluorescence drops to 10% of the starting value.
Additional irradiation with 365-nm light does not alter the
emission intensity, indicating a photostationary state like
Figure 2. Emission spectra of 11, λex = 325 nm; solid line:
8ϫ10–6 m in dichloromethane, dashed lines: after irradiation with
300 nm (5,10, and 15 s), dotted lines: after irradiation with 590 nm
(20 and 60 s).
Eur. J. Org. Chem. 2011, 371–376
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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373

O. Tosic, J. Mattay
FULL PAPER
Scheme 5. Fluorescence switching of dianthryldithienylethene 12.
LS50B spectrometer. Irradiations at 254 and 300 nm were done in
a rayonet reactor and irradiations at 365, 590, and 620 nm were
carried out with LEDs.
situation. After irradiation with 620 nm for 25 or 60 s the
emission is restored to ca. 95% of the starting value. In
contrast to 11 this cycle can be repeated several times even
in nondegassed solution.
To assess the mechanism of the fluorescence switching
processes, the overlap integrals J and the Förster radii R0
for 11 and 12 were determined from the measured absorp-
tion spectra and the corresponding emission spectra. The
values were calculated to be J = 1.14ϫ1014 nm4 cm–1 m–1
Materials: Triphenylphosphane, tetrabromomethane, 18-crown-6,
4-bromobenzyl bromide, 3-methoxyphenol, and 4-chloroacetoacet-
ate are commercially available and were used as received. 1,2-Bis-
(5-formyl-2-methylthiophen-3-yl)hexafluorocyclopentene
(1),[12]
3-azido-1-propanol (6),[18] 9-(bromomethyl)anthracene,[21] and
[Cu(PPh3)3Br][22] were prepared according to literature procedures.
Solvents were of analytical grade and dried according to standard
procedures prior to use, except for chloroform, which was used as
received.
and R0
=
14 Å for 11 closed and
m
J
=
9.00ϫ104 nm4 cm–1
–1 and R0 = 0.2 Å for 11 open, indicat-
ing that quenching through a resonance energy transfer
(RET) mechanism is possible in the closed isomer. The val-
ues for 12 are J = 7.24ϫ1013 nm4 cm–1 m–1 and R0 = 26 Å
for the closed form and J = 4.22ϫ1013 nm4 cm–1 m–1 and
R0 = 24 Å for the open form, respectively (see ref.[26] and
the Supporting Information for details). This indicates that
for dianthracene 12 fluorescence quenching is not likely to
proceed through RET, but possibly through photoinduced
electron transfer (PET). For 11, a PET mechanism cannot
be excluded, as we did not calculate the exact free energy
change (ΔGPET) for the emission quenching of 11 and 12.[27]
Safety: Azides should always be handled carefully. Organic azides,
particularly those of low molecular weight, or with high nitrogen
content, are potentially explosive.[28] Any reactions with azides
should involve precautions against explosions.
Dibromomethyltriphenylphosphonium Bromide·CH3CN (2):[15] Tri-
phenylphosphane (17.0 g, 64.81 mmol) and tetrabromomethane
(10.0 g, 30.15 mmol) were stirred in dichloromethane (160 mL) for
0.5 h at room temperature. To this solution was added water
(50 mL), and the phases were separated. The aqueous layer was
extracted with dichloromethane (50 mL). The combined organic
layers were washed with brine (50 mL), dried with sodium sulfate,
filtered, and concentrated in vacuo. To the oily residue was added
acetonitrile (100 mL), and the flask was subjected to ultrasonic ir-
radiation until the oil solidified (ca. 30 min). The solid was filtered,
washed with acetonitrile several times, and dried to give 2 as a
solvate with one equivalent of acetonitrile. Yield: 15.7 g,
Conclusions
In summary we have synthesized the previously known
dithienylethene 4 by an alternative synthetic route. For the
first time we have used this precursor in alkyne–azide click
reactions to obtain novel photochromic materials including
fluorophores. Specifically, photoswitchable fluorophore 12
showed efficient reversible quenching of fluorescence in
solution possibly through a PET mechanism.
1
28.2 mmol, 88%; colorless solid. H NMR (CD2Cl2): δ = 1.97 (s,
3 H, acetonitrile), 7.70–7.74 (m, 6 H, ArH), 7.84–7.87 (m, 3 H, 4Ј-
ArH), 8.14–8.20 (m, 6 H, ArH), 10.37 (d, J = 1.9 Hz, 1 H, PCHBr2)
ppm. MS (ESI+): m/z = 434.9 [M – CH3CN – Br]+.
1,2-Bis[5-(2,2-dibromoethenyl)-2-methylthiophen-3-yl]hexafluoro-
cyclopentene (3): Dialdehyde 1 (0.424 g, 1.00 mmol), phosphonium
salt 2 (1.67 g, 3.00 mmol), and 18-crown-6 (0.010 g, 0.04 mmol)
were suspended in dichloromethane (30 mL). To this mixture was
added freshly ground potassium hydroxide (0.360 g, 6.00 mmol),
and the mixture was stirred at room temperature for 1 h. After
filtration, the solvent was removed in vacuo. The remainder was
passed through a pad of silica gel (cyclohexane/ethyl acetate, 7:3)
until a sample of the last filtrate showed no color change on TLC
material upon irradiation with UV light. The solvent was removed
in vacuo to give 3 as a yellow green solid. Yield: 0.570 g,
Experimental Section
General Remarks: NMR spectra were measured at room tempera-
ture with a Bruker DRX 500 spectrometer (500 MHz). CDCl3,
CD2Cl2, and [D6]DMSO were used as internal standards for 1H
and 13C NMR spectra. Mass spectra (ESI) were recorded by using
a Fourier Transform Ion Cyclotron Resonance (FTICR) mass spec-
trometer Bruker APEX III. EI mass spectra were recorded by using
an Autospec X magnetic sector mass spectrometer with EBE geom-
etry equipped with a standard EI source. Absorption spectra were
recorded with Perkin–Elmer Lamda 25 and Lamda 40 spectrome-
ters. Fluorescence spectra were recorded with a Perkin–Elmer
1
0.77 mmol, 77%. H NMR (CDCl3): δ = 1.87 (s, 6 H, CH3), 7.14
(s, 2 H, ArH), 7.53 (s, 2 H, CHCBr2) ppm. 13C NMR (CDCl3): δ
= 14.7, 88.3, 124.5, 128.7, 129.6, 130.3, 132.1, 132.3, 132.4,
133.1 ppm. HRMS (EI): calcd. for C19H10S2Br4F6 [M]+
+
731.68616; found 731.68860.
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New Photochromic Dithienylethenes through a Click Chemistry Approach
1,2-Bis(5-ethynyl-2-methylthiophen-3-yl)hexafluorocyclopentene ArH), 8.30 (d, J = 8.5 Hz, 2 H, ArH), 8.51 (s, 1 H, ArH) ppm. MS
(4):[12] Tetrabromide 3 (0.57 g, 0.77 mmol) was dissolved in dry
ethyl ether (30 mL) under an argon atmosphere. To this solution
was added n-butyllithium (1.6 m in hexanes, 2.50 mL, 4.00 mmol)
at –78 °C, and the mixture was stirred at this temperature for 1.5 h
and additionally for 1 h at room temperature. Water (30 mL) and
a few drops of 2 m hydrochloric acid were added; the phases were
separated, and the aqueous layer was extracted with ethyl ether
(20 mL). The combined organic layers were washed with brine
(50 mL), dried with sodium sulfate, and concentrated in vacuo. The
remainder was passed through a pad of silica gel (cyclohexane/ethyl
acetate, 7:3) until the filtrate was nearly colorless. The dark yellow
solution was concentrated to dryness to give 4 as a sticky dark
brown solid. Yield: 0.223 g, 0.54 mmol, 70%. 1H NMR (CDCl3): δ
= 1.88 (s, 6 H, CH3), 3.34 (s, 2 H, CH), 7.21 (s, 2 H, ArH) ppm.
13C NMR (CDCl3): δ = 14.4, 75.7, 82.3, 120.6, 124.5, 132.54,
143.6 ppm.[29] HRMS (EI): calcd. for C19H10S2F6+ [M]+ 416.01281;
found 416.01256.
(EI, 70 eV): m/z (%) = 233.1 (25) [M]+, 204.1 (80) [M – N2]+, 191.1
(100) [M – N3]+, 176.1 (30) [M – CH2N3]+.
Bis(bromobenzyl)dithienylethene (9): Diacetylene
0.08 mmol) was dissolved in chloroform (20 mL). To this solution
was added (34 mg, 0.16 mmol) and [Cu(PPh3)3Br] (5 mg,
4
(35 mg,
5
0.005 mmol). After 4 h of stirring at room temperature, the solvent
was removed in vacuo, and the residue was purified by chromatog-
raphy on silica gel (cyclohexane/ethyl acetate, 9:1 to 7:3 mixture).
Yield: 30 mg, 0.036 mmol, 45%; grey solid. 1H NMR (CDCl3): δ
= 1.91 (s, 6 H, CH3), 5.50 (s, 4 H, CH2), 7.19 (d, J = 8.3 Hz, 4 H,
ArH), 7.27 (s, 2 H, thiophene), 7.53 (d, J = 8.3 Hz, 4 H, ArH),
7.58 (s, 2 H, triazole) ppm. 13C NMR (CDCl3): δ = 14.7, 53.8,
119.1, 123.3, 123.6, 125.4, 129.9, 131.2, 132.6, 133.4, 141.9,
142.6 ppm.[29] HRMS (ESI): calcd. for C33H23N6S2Br2F6
+
[M + H]+ 838.96911; found 838.96905.
Bis(hydroxypropyl)dithienylethene (10): Diacetylene
4 (52 mg,
0.13 mmol) was dissolved in chloroform (20 mL). To this solution
was added 6 (101 mg, 1.000 mmol) and [Cu(PPh3)3Br] (20 mg,
0.02 mmol). After 16 h of stirring at room temperature the solvent
was removed in vacuo, and the residue was purified by chromatog-
raphy on silica gel (cyclohexane/ethyl acetate, gradient 0 to 100%
ethyl acetate; then ethyl acetate/methanol, 3:1). Yield: 30 mg,
4-Bromobenzyl Azide (5): 4-Bromobenzyl bromide (1.25 g,
5.00 mmol) and sodium azide (0.49 g, 7.50 mmol) were stirred in
water (20 mL) and acetone (80 mL) at room temperature for 60 h.
The mixture was extracted with dichloromethane (3ϫ50 mL), the
combined organic layers were dried with sodium sulfate, and the
solvent was removed in vacuo to give the product as a yellow liquid.
Yield: 1.04 g, 4.90 mmol, 98%. 1H NMR (CDCl3): δ = 4.31 (s, 2
H, CH2), 7.20 (d, J = 8.3 Hz, 2 H, ArH), 7.52 (d, J = 8.4 Hz, 2 H,
ArH) ppm. MS (EI, 70 eV): m/z (%) = 211.0 (30) [M]+, 184.0 (50)
[M – N2]+, 171.0 (100) [M – N3]+, 155.0 (30) [M – CH2N3]+.
1
0.050 mmol, 39%; brown solid. H NMR (CDCl3): δ = 1.98 (s, 6
H, CH3), 2.16 (m, 4 H, CH2CH2CH2OH), 3.68 (t, J = 5.7 Hz, 4
H, CH2CH2CH2OH), 4.56 (t, J = 6.7 Hz, 4 H, CH2CH2CH2OH),
7.25 (s, 2 H, thiophene), 8.01 (s, 2 H, triazole) ppm. 13C NMR
(CDCl3): δ = 14.6, 32.6, 47.3, 58.7, 116.2, 120.1, 123.7, 125.4, 131.3,
136.2, 141.9, 142.0, 162.8 ppm. HRMS (ESI): calcd. for
4-Azidomethyl-7-methoxycoumarin (7)[19]
C25H25N6O2S2F6 [M + H]+ 619.13791; found 619.13927.
+
Pechmann Condensation: 3-Methoxyphenol (2.48 g, 20.00 mmol)
and 4-chloroacetoacetate (3.62 g, 22.00 mmol) were mixed with
concentrated sulfuric acid (15 mL), and the mixture was stirred at
room temperature for 3 h. The mixture was poured into water
(200 mL), and the pink precipitate was collected by filtration,
washed with additional water, dried in air, and recrystallized (etha-
nol) to give 4-chloromethyl-7-methoxycoumarin[20] as a slightly
pink solid. Yield: 3.26 g, 14.55 mmol, 73%. 1H NMR ([D6]-
DMSO): δ = 3.86 (s, 3 H, OCH3), 4.99 (s, 2 H, CH2Cl), 6.50 (s, 1
H, CHC=O), 7.01 (m, 1 H, ArH), 7.04 (d, J = 2.5 Hz, 1 H, ArH),
7.76 (d, J = 8.8 Hz, 1 H, ArH) ppm.
Dicoumaryldithienylethene (11): Diacetylene 4 (52 mg, 0.13 mmol)
was dissolved in chloroform (20 mL). To this solution was added 7
(116 mg, 0.500 mmol) and [Cu(PPh3)3Br] (20 mg, 0.02 mmol). Af-
ter 16 h of stirring at room temperature the solvent was removed
in vacuo, and the residue was purified by chromatography on silica
gel (cyclohexane/ethyl acetate, 9:1 to 1:3). Yield: 93 mg, 0.11 mmol,
1
85%; yellow solid. H NMR ([D6]DMSO): δ = 1.91 (s, 6 H, CH3),
3.86 (s, 6 H, OCH3), 5.96 (s, 4 H, CH2N), 5.98 (s, 2 H, CHC=O),
7.01 (m, 2 H, ArH), 7.07 (d, J = 2.4 Hz, 2 H, ArH), 7.50 (s, 2 H,
thiophene), 7.75 (d, J = 8.9 Hz, 2 H, ArH), 8.72 (s, 2 H, triazole)
ppm. 13C NMR ([D6]DMSO): δ = 14.1, 49.6, 56.1, 101.2, 110.6,
111.6, 112.5, 122.1, 123.1, 124.5, 125.9, 131.5, 141.2, 141.4, 155.2,
159.9, 162.8 ppm.[29] HRMS (ESI): calcd. for C41H29N6O6S2F6+ [M
+ H]+ 879.14887; found 879.14914.
Reaction with Sodium Azide: 4-Chloromethyl-7-methoxycoumarin
(1.00 g, 4.46 mmol) was added to a suspension of sodium azide
(2.60 g, 36.92 mmol) in acetone (60 mL) and acetonitrile (60 mL).
The mixture was heated to reflux for 4 h, and then the volume
was reduced to 50%. Ethyl acetate (50 mL) was added, and the
precipitate was removed by filtration. The filtrate was dried with
sodium sulfate, and the solvents were removed in vacuo. The resi-
due was recrystallized (methanol) to give 7 as a colorless solid.
Yield: 0.60 g, 2.60 mmol, 58%. 1H NMR ([D6]DMSO): δ = 3.87 (s,
3 H, OCH3), 4.84 (d, J = 0.9 Hz, 2 H, CH2N3), 6.36 (s, 1 H,
CHC=O), 7.01 (m, 1 H, ArH), 7.05 (d, J = 2.5 Hz, 1 H, ArH),
7.66 (d, J = 8.8 Hz, 1 H, ArH) ppm. MS (ESI+): m/z = 253.9 [M
+ Na]+, 484.8 [2M + Na]+.
9-(Azidomethyl)anthracene (8): 9-(Bromomethyl)anthracene[21]
(0.81 g, 2.99 mmol) and sodium azide (1.95 g, 30.00 mmol) were
suspended in acetone (60 mL) and acetonitrile (60 mL). The mix-
ture was heated to reflux for 2 h, and the solvents were then re-
moved in vacuo. The residue was passed through a pad of silica gel
(cyclohexane/ethyl acetate, 7:3), and the filtrate was concentrated
to dryness to give 8 as an orange-brown solid. Yield: 0.68 g,
2.91 mmol, 97%. 1H NMR (CDCl3): δ = 5.33 (s, 2 H, CH2N3),
Dianthryldithienylethene (12): Diacetylene 4 (67 mg, 0.16 mmol)
was dissolved in chloroform (20 mL). To this solution was added 8
(150 mg, 0.64 mmol) and [Cu(PPh3)3Br] (20 mg, 0.02 mmol). After
5 h of stirring at reflux, the solvent was removed in vacuo, and the
residue was purified by chromatography on silica gel (cyclohexane/
1
ethyl acetate, 7:3). Yield: 43 mg, 0.05 mmol, 30%; yellow solid. H
NMR (CDCl3): δ = 1.71 (s, 6 H, CH3), 6.56 (s, 4 H, CH2N), 7.02
(s, 2 H, thiophene), 7.17 (s, 2 H, triazole), 7.55 (m, 4 H, ArH), 7.62
(m, 4 H, ArH), 8.10 (d, J = 8.5 Hz, 4 H, ArH), 8.32 (d, J = 8.5 Hz,
4 H, ArH), 8.59 (s, 2 H, ArH) ppm. 13C NMR (CDCl3): δ = 14.4,
46.6, 118.6, 122.8, 123.0, 123.3, 125.0, 125.5, 127.9, 129.6, 130.1,
130.8, 131.2, 131.4, 141.4, 142.0 ppm.[29] HRMS (ESI): calcd. for
C49H33N6S2F6 [M + H]+ 883.21068; found 883.20983.
+
Supporting Information (see footnote on the first page of this arti-
cle): Details on calculations of overlap integrals and Förster radii,
full scale UV/Vis spectra of compounds 9–12, enlarged emission
7.52 (m, 2 H, ArH), 7.49 (m, 2 H, ArH), 8.06 (d, J = 8.8 Hz, 2 H, spectra of compounds 11 and 12.
Eur. J. Org. Chem. 2011, 371–376
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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375

O. Tosic, J. Mattay
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Published Online: November 24, 2010
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Eur. J. Org. Chem. 2011, 371–376