Synthesis and photochromic reactivity of macromolecules incorporating four dithienylethene units

Article abstract of DOI:10.1016/j.tet.2005.09.099

Two macrocycles bearing four dithienylethene units were synthesized. Upon irradiation of the macrocycles 5 and 6 with ultraviolet light, only one or two photo-induced cyclization reaction occurs. Each isomers were isolated and analyzed by ¹H NM

Full text of DOI:10.1016/j.tet.2005.09.099

Tetrahedron 61 (2005) 12256–12263
Synthesis and photochromic reactivity of macromolecules
incorporating four dithienylethene units
Il Jung,a Hyunbong Choi,a Eunkyoung Kim,b Chai-Ho Lee,c Sang Ook Kanga,
*
and Jaejung Koa,
*
aDepartment of Chemistry, Korea University, Jochiwon, Chungnam 339-700, South Korea
bDepartment of Chemical Engineering, Yonsei University 134 Sinchon-dong, Seodaemoon-gu, Seoul 120-749, South Korea
cDepartment of Chemistry, Wonkwang University, Iksan, Jeonbuk 570-749, South Korea
Received 11 August 2005; revised 21 September 2005; accepted 22 September 2005
Available online 25 October 2005
Abstract—Two macrocycles bearing four dithienylethene units were synthesized. Upon irradiation of the macrocycles 5 and 6 with
ultraviolet light, only one or two photo-induced cyclization reaction occurs. Each isomers were isolated and analyzed by 1H NMR spectrum.
The quantum yield of 5 and 6 are 0.58 and 0.64, respectively. The high value is due to the presence of enforced antiparallel conformation in
the macrocycles 5 and 6.
q 2005 Elsevier Ltd. All rights reserved.
1. Introduction
and multi-substituted phthalocyanine and tetraazaporphyrin
hybrids have been introduced in the form of a macrocyclic
photochromic system.12 We envisioned that the strategic
placement of diarylethene units within a macrocyclic
framework would achieve high quantum yield because the
macromolecule has the enforced antiparallel conformation
of the diarylethene units. We now describe (i) the synthesis
of macromolecules having diarylethene units; (ii) their
photochromic reactivities; (iii) the isolation of photo-
cyclized products.
The conformationally rigid and shape-persistent supra-
molecules of nanometer size have attracted much interest
because of their potential in host–guest systems,1 fluor-
escence ion sensor,2 self-aggregation,3 organometallic
coordination,4 and liquid crystal.5 The design of geo-
metrically well-defined supramolecules will play an
important role because the incorporation of orientation-
ally-controlled functional units into molecules can be
utilized as the encoding of information.6 The combination
of the self-assembly and photochromic unit promises to be
useful in optical technological devices.7 Photochromic 1,2-
diarylethene is very suitable for this purpose, due to the
remarkable thermal stability and high fatigue resistance.8
The open-ring isomer of diarylethene has two confor-
mations—antiparallel and parallel—in equal amounts. The
conrotatory cyclization can proceed only from the anti-
parallel conformation. Therefore, the cyclization quantum
yield cannot exceed 50% in solution. To achieve high
quantum yield, it is required to increase the population of
the antiparallel conformers. Thus, diarylethene—backbone
photochromic polymer,9 multi-dithienylethene arrays,10 and
diarylethene in the crystal lattice11 showed a high
cyclization quantum yield due to the geometrical restriction.
In a recent development, new dithienylethene based mono-
2. Results and discussion
Our strategy for the synthesis of macrocycles is to
incorporate the diarylethene units within a macrocyclic
framework. New macromolecules 5 and 6 are conveniently
synthesized in four steps from the 1,2-bis[2-methyl-5-
bromo-3-thienyl]perfluorocyclopentene. The palladium-
catalyzed cross-coupling of 1,3-diethynylbenzene with 1
afforded 2 in 53% yield. The Sonogashira coupling of 2 with
2.2 equiv of trimethylsilylacetylene followed by basic
hydrolysis yielded 4. Our synthesis of macrocycles 5 and
6 was prepared by the cross-coupling reaction of 2 with 4
and coupling reaction13 of the dialkyne 4 with trans-
Pt(PEt3)2Cl2, respectively (Scheme 1). Spectroscopic data
for 5 is completely consistent with its proposed structures.
Four resonances at 2.07, 2.06, 1.96, and 1.95 ppm in the 1H
NMR spectrum and two peaks at 15.6 and 14.5 ppm in 13C
NMR spectrum of 5 for the methyl group are observed. The
Keywords: Photoswitch; Macrocycle; Diarylethene; High quantum yield.
*
Corresponding authors. Tel.: C82 41 860 1337; fax: C82 41 867 5396;
e-mail: jko@korea.ac.kr
0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2005.09.099

I. Jung et al. / Tetrahedron 61 (2005) 12256–12263
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Scheme 1. Reagents and conditions: (i) 1,3-diethynylbenzene, Pd(PPh3)4, CuI in NEt3; (ii) Me3SiC^CH, Pd(PPh3)4, CuI in NEt3; (iii) KOH in MeOH and
THF, then H2O; (iv) 2C4, Pd(PPh3)2Cl2, P(o-tolyl)3, CuI in NEt3; (v) 4, trans-Pt(PEt3)2Cl2, CuCl in Et2NH.
mass spectrum of 5 showed a molecular ion at m/z 1760.
1.85 ppm) and four peaks at 16.5, 15.1, 9.7, and 8.7 ppm
in the 13C NMR spectrum of 6 proved that a macrocycle
is formed in 6. The 31P NMR spectrum of 6 shows a singlet
at 5.84 ppm with a small coupling constant of JPtP
(2348 Hz), which is consistent with the trans configuration
of 6.13
1
Compound 6 was characterized by H, 13C, and 31P NMR,
mass spectroscopy, and elemental analysis. The initial
indication of the macromolecule 6 stemmed for the
observation of an ion in the mass spectrum at m/z 2637.
Three peaks in the 1H NMR spectrum (1.96, 1.95, and
1
Figure 1. Absorption spectral change of 3 in chloroform upon irradiation with 325 nm light (- - -). Total irradiation periods are 0, 10, 20, 30, 40, 50, 60, 70, 80,
90, 100, 110, 120, 130, 150, 200, and 300 s. Steady-state fluorescence spectrum of the 3 (OO) (—) (excitation at 360 nm).

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Figure 2. 1H NMR methyl signals of (a) the 3 (OO) dimer; and (b) the 3 (CO) dimer.
Figure 1 shows a typical absorption spectral change of 3 in
chloroform upon ultraviolet light irradiation. Irradiation of
chloroform solution of 3 at 325 nm light resulted in an
immediate increase in the absorption intensity at 600 nm.
After visible light irradiation (lO532 nm) for 6 h, the
colored solution was completely bleached. In the first 120 s
of irradiation, an absorption band centered at 600 nm grows
in as 3 is converted from the colourless-open form 3 (OO) to
the blue-closed form 3 (CO). The presence of an isosbestic
point at 334 nm indicates that 3 (OO) is cleanly converted to
a second unique photocyclized product. The closed-ring
isomer 3 (CO) was isolated from the blue colored solution
by HPLC. The photogenerated ring-closed form 3 (CO) was
Such an up-field shift was observed in covalently linked
double 1,2-dithienylethenes.10a The dissymmetric nature of
the photogenerated product indicates that only one of the
thienyl units has cyclized to form 3 (CO) (Scheme 2). The
fluorescence band of 3 (OO) (lZ420 nm) shows a
substantial spectral overlap with the absorption band of 3
¨
(CO), and the Forster excitation energy transfer can take
place from the photogenerated 3 (OO) to the colored form 3
(CO). Accordingly, the cyclization reaction of another
open-ring form cannot take place. A similar result has been
observed in the thienylethene dimer.10
Figure 3 shows the absorption spectral change of the
macromolecule 5 in chloroform by photoirradiation. Upon
irradiation with 325 nm light, the colourless solution of the
open-ring isomer 5 (OOOO) with the absorption maximum
at 313 nm turned blue, in which characteristic absorption
maximum was observed at 602 nm. Upon visible
(lO532 nm) light irradiation, the blue color was completely
bleached.
1
stable at room temperature. Figure 2 shows the H NMR
spectrum of methyl protons of 3 in CDCl3 before
photoirradiation and in the ring-closed form, respectively.
In the 1H NMR spectrum of 3 (OO), two methyl resonances
were observed at 1.83 and 1.80 ppm. In the blue isomer 3
(CO), one distinct new band was appeared at 2.16 ppm,
together with two singlets at 1.93 and 1.88 ppm, which are
slightly down-field shifted to those of 3 (OO). The integral
ratio of the two signals was 1:1, which indicates that the
colored isomer is a C– dimer. Another key feature in the 1H
NMR spectrum of 3 (CO) is the presence of four thienyl
signals at 7.24, 7.22, 6.47, and 6.41 ppm. The two new
resonances at 6.47 and 6.41 ppm are significantly up-field
shifted as would be expected for the ring-closed isomer.
The photogenerated products were analyzed with HPLC
chromatograph (silica gel column, eluent: hexane/ethyl
acetate 4:1). When monitored at the isosbestic point of
338 nm, three peaks were observed. The first peak isomer
had the absorption maximum at 610 nm, while the
absorption maximum of the second peak isomer was shifted
Scheme 2. The photochromic reactivity of 3.

I. Jung et al. / Tetrahedron 61 (2005) 12256–12263
12259
Figure 3. Absorption spectra of 5 (OOOO) (—), 5(COOO) (– $ – $ –), and 5(COCO) (- - -) in the photostaionary state under irradiation with 325 nm light, and
fluorescence spectrum of 5 (OOOO) (—) in chloroform.
to 602 nm. The three isomers were isolated and analyzed by
includes four singlets at 7.17, 7.13, 7.09, and 6.48 ppm in
the region of thienyl protons. The new signal at 6.48 ppm is
assigned to the proton of closed-ring thienyl unit. This
indicates that the first peak isomer is due to the isomer
having one closed-ring form 5 (COOO) (Scheme 3). The
methyl protons of the second peak isomer show five
resonances at 2.17, 2.07, 2.05, 1.97, and 1.95 ppm. The
signal at 2.17 ppm is assigned to the protons of the closed-
ring form. The integral ratio of a signal at 2.17 ppm with
1
1H NMR. Figure 4 shows the H NMR spectra of methyl
protons of 5 in CDCl3 before photoirradiation and in the
ring-closed forms. The methyl protons of the first peak
isomer show seven resonances at 2.18, 2.16, 2.07, 2.05,
1.96, 1.94, and 1.92 ppm. The first two signals at 2.18 and
2.16 ppm are assigned to the methyl protons of the closed-
ring form. Other five signals are ascribed to the open-ring
1
form. A characteristic feature in the H NMR spectrum
Figure 4. 1H NMR methyl signals of the (a) 5 (OOOO); (b) 5 (COOO); and (c) 5 (COCO).
Scheme 3. The photochromic reactivity of 5.

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Scheme 4. The photochromic reactivity of 6.
other signals is approximately 1:1. In addition, there are four
distinct bands at 7.13, 7.09, 6.72, and 6.52 ppm in the
thienyl region, in which the signals at 6.72 and 6.52 ppm is
assigned to the closed-ring thienyl units. This indicates that
two closed-ring form units are included in the macro-
molecule 5 (COCO). The methyl protons of the third peak
isomer are identical to those of the open-ring form isomer 5
(OOOO). Excitation of 5 (OOOO) at 315 nm results in light
emission with a maximum at 430 nm. Due to the spectral
overlap of the fluorescence peak of 5 (OOOO) and
26 nm in comparison with 5. Upon exposure of the dark
blue solution to the visible light (lO532 nm) for 3 min, the
colored solution was completely bleached. In the photo-
stationary state, 88% of 6 is converted into the closed form.
The closed-ring isomer 6 (COCO) is stable and isolated
from the blue colored solution by HPLC. Figure 6 shows the
1H NMR spectra of methyl protons of 6 in CDCl3 before
photoirradiation and in the ring-closed form. Before
photoirradiation, three resonances are observed at 1.96,
1.95, and 1.85 ppm. In the ring-closed form, one new
resonance appears at 2.14 ppm along with a decrease of the
intensity of the three resonances. The strong one resonance
at 2.14 ppm is assigned to the methyl protons of the closed
¨
absorption peak of 5 (COCO), followed by the Forster
excitation energy transfer, the second peak isomer has the 5
(COCO) form. Such excited energy transfer is considered to
prohibit the formation of further closed-ring form
(Scheme 4).
1
form. No side reaction was detected from the H NMR
spectra.
Figure 5 shows the absorption spectra of 6 in chloroform
before photoirradiation and in the photostationary state
under irradiation with 325 nm light. Irradiation of chloro-
form solution of 6 at 325 nm light resulted in an immediate
increase in the absorption intensity at 628 nm. The
absorption maximum shifts to longer wavelength by
The quantum yield of this macromolecules 5 and 6 are
measured using 1,2-bis(2-methyl-3-thienyl)perfluorocyclo-
pentene (TF6) as a reference.14 The cyclization quantum
yield of 5 from the all open-ring form 5 (OOOO) to the 5
(COOO) isomer and form 5 (COOO) to the 5 (COCO)
isomer was determined to be 0.33 and 0.25, respectively.
Figure 5. Absorption spectral change of 6 in chloroform upon irradiation with 325 nm light. Total irradiation periods are 0, 10, 20, 30, 40, 50, 60, 70, 80, 90,
100 and 150 s.

I. Jung et al. / Tetrahedron 61 (2005) 12256–12263
12261
1
isolated and analyzed by H NMR spectrum. The quantum
yield of 5 and 6 are 0.58 and 0.64, respectively. The high
value is due to the presence of enforced antiparallel
conformation in the macrocycles 5 and 6.
3. Experimental
All reactions were carried out under an argon atmosphere.
Solvents were distilled from appropriate reagents.
Perfluorocyclopenthene was purchased from Fluorochem.
1,3-Diethynylbenzene15 and 1,2-bis[2-methyl-5-bromo-3-
thienyl]perfluorocyclopentene16 were synthesized using a
modified procedure of previous references. 1H and 13C
NMR spectra were recorded on a Varian Mercury 300
spectrometer. The absorption and photoluminescence
spectra were recorded on a Perkin–Elmer Lambda 2S
UV–vis spectrometer and a Perkin LS fluorescence
spectrometer, respectively. The fluorescence quantum
yields using 9,10-diphenylanthracene as the standard were
determined by the dilution method.17
Figure 6. 1H NMR methyl signals of the (a) 6 (OOOO); and (b) 6 (COCO).
The asterisk denotes unidentified impurity.
The total cyclization quantum yield is 0.58, which is much
higher than that of tetra-dithienylethene array.10d The
coloration quantum yield of 6 was determined to be 0.64.
The high value is due to the presence of enforced
antiparallel conformation in the macromolecule 5. The
cycloreversion quantum yield of the 5 (COCO) and 6
3.1. Determination of quantum yields
The quantum yields of photochromic ring-cyclizaiton of 5
and 6 were determined form the absorption change at lmax in
UV spectra upon excitation with UV-light for the ring-
closure reaction and visible light for the ring-opening
reaction. The molar extinction coefficients of 5 and 6 are
3.11!104 MK1 cmK1 [5 (OOOO)], 2.60!104 MK1 cmK1
[5 (COOO)], 2.33!104 MK1 cmK1 [5 (COCO)], 3.00!
104 MK1 cmK1 [6 (OOOO)], 2.46!104 MK1 cmK1 [6
(COCO)]. Then, the quantum yield was determined
according to the method described in Ref. 14.
(COCO) was measured to be 4.8!10K3 and 9.4!10K3
,
respectively.
In order to obtain the geometrical configuration and
characteristic features of the electronic structure, molecular
orbital calculation of 5 was performed with the semi-
empirical AM1. The optimized calculations show that two
of four diarylethene units have different configurations. The
HOMO is delocalized over the p-conjugated system via the
1,3-diethynylbenzene through two dithienylethene array.
Examination of the HOMO and LUMO of 5 indicates that
photoexcitation results in a net charge transfer from the
p-conjugated system to the dithienylethene array (Fig. 7).
3.1.1. Compound 2. A mixture of 1,2-bis[2-methyl-
5-bromo-3-thienyl]perfluoro-cyclopentene (9.28 g,
17.6 mmol), 1,3-diethynylbenzene (0.7 g, 5.5 mmol),
Pd(PPh3)4 (1.0 g, 1 mmol), and CuI (0.1 g, 0.5 mmol) was
vacuum-dried and added NEt3 (40 ml). The solution was
refluxed for 12 h and then evacuated to dryness. The product
2 was purified by chromatography on a silica gel column
(1:10 methylene chloride/hexane, RfZ0.3) to afford 2
In summary, we have prepared two macromolecules
incorporating four dithienylethene units. Upon irradiation
of 5 and 6 with ultraviolet light, only one or two photo-
induced cyclization reaction occurs. Each isomers were
1
(2.99 g) in 53% yield. Mp: 205 8C. H NMR (CDCl3): d
Figure 7. Representation of (a) HOMO; and (b) LUMO of 5 based on semi-empirical AM1.

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7.64 (s, 1H), 7.45 (d, 2H, JZ8.40 Hz), 7.33 (t, 1H, JZ
8.40 Hz), 7.23 (s, 2H), 7.02 (s, 2H), 1.98 (s, 6H), 1.88 (s,
6H). 13C{1H} NMR (CDCl3): d 147.4, 143.7, 143.5, 134.1,
131.8, 131.3, 129.9, 128.6, 125.3, 124.9, 123.0, 121.6,
155.9, 110.2, 93.0, 82.3, 14.9, 14.6. MS: m/z 1013 [MC].
Anal. Calcd for C40H20Br2F12S4: C, 47.26; H, 1.98. Found:
C, 47.02; H, 1.90.
1.19 (t, 36H, JZ8.4 Hz). 13C{1H} NMR (CDCl3): d 146.9,
143.9, 139.3, 131.5, 129.4, 127.8, 125.4, 124.1, 123.1,
121.1, 116.1, 115.0, 111.4, 108.2, 100.7, 92.8, 92.1, 82.5,
24.6, 16.5, 15.1, 9.7, 8.7, 4.8. 31P{1H} NMR (CDCl3): d
5.84 (s, JZ2348 Hz). MS: m/z 2673 [MC]. Anal. Calcd for
C112H100F24P4S8Pt2: C, 50.33; H, 3.77. Found: C, 50.18; H,
3.69.
3.1.6. Closed-ring isomer of 3 (CO). 1H NMR (CDCl3): d
7.64 (s, 1H), 7.46 (d, 2H, JZ9.0 Hz), 7.36 (t, 1H, JZ
9.0 Hz), 7.24 (s, 1H), 7.22 (s, 1H), 6.47 (s, 1H), 6.41 (s, 1H),
2.16 (s, 6H), 1.93 (s, 3H), 1.88 (s, 3H). 0.24 (s, 18H).
3.1.2. Compound 3. A mixture of 2 (1.0 g, 1 mmol),
Pd(PPh3)4 (0.06 g, 0.05 mmol), and CuI (0.01 g, 0.5 mmol)
was vacuum-dried and added NEt3 (40 ml) and trimethyl-
silylacetylene (0.31 ml, 2.2 mmol). The solution was
refluxed for 12 h and then evacuated to dryness. The pure
product 3 was obtained by chromatography on a silica gel
column (1:10 methylene chloride/hexane, RfZ0.4) to afford
3.1.7. Closed-ring isomer of 5 (COOO). 1H NMR
(CDCl3): d 7.65 (s, 2H), 7.45 (d, 4H, JZ7.2 Hz), 7.34 (t,
2H, JZ7.2 Hz), 7.17 (s, 2H), 7.13 (s, 2H), 7.09 (s, 2H), 6.48
(s, 2H), 2.18 (s, 3H), 2.16 (s, 3H), 2.07 (s, 3H), 2.05 (s, 3H),
1.96 (s, 3H), 1.94 (s, 6H), 1.92 (s, 3H).
1
3 in 81% yield. Mp: 164 8C. H NMR (CDCl3): d 7.58 (s,
1H), 7.35 (d, 2H, JZ8.1 Hz), 7.24 (t, 1H, JZ8.1 Hz), 7.14
(s, 2H), 7.12 (s, 2H), 1.83 (s, 6H), 1.80 (s, 6H). 0.14 (s, 18H).
13C{1H} NMR (CDCl3): d 143.8, 143.5, 136.2, 132.7,
132.2, 131.6, 131.2, 125.0, 124.6, 123.1, 121.9, 121.5,
116.0, 111.0, 100.2, 96.3, 93.0, 82.0, 17.6, 17.2, K0.7. MS:
m/z 1050 [MC]. Anal. Calcd for C50H38F12S4Si2: C, 57.13;
H, 3.64. Found: C, 56.82; H, 3.52.
3.1.8. Closed-ring isomer of 5 (COCO). 1H NMR
(CDCl3): d 7.65 (s, 2H), 7.45 (d, 4H, JZ7.2 Hz), 7.36 (t,
2H, JZ7.2 Hz), 7.13 (s, 2H), 7.09 (s, 2H), 6.72 (s, 2H), 6.52
(s, 2H), 2.17 (s, 12H), 2.07 (s, 3H), 2.05 (s, 3H), 1.97 (s, 3H),
1.95 (s, 3H).
3.1.3. Compound 4. Compound 3 (1.0 g, 0.95 mmol) and
KOH (0.01 g) were dissolved in THF (20 ml) and MeOH
(20 ml) and then added H2O (10 ml). The solution was
stirred for 12 h and evacuated to dryness. The pure product 4
was obtained by chromatography on a silica gel column
(1:10 methylene chloride/hexane, RfZ0.2) to afford 4
3.1.9. Closed-ring isomer of 6 (COCO). 1H NMR
(CDCl3): d 7.65 (s, 2H), 7.46 (d, 4H, JZ7.2 Hz), 7.32 (t,
2H, JZ7.2 Hz), 7.17 (s, 2H), 7.08 (s, 2H), 6.76 (s, 2H), 6.54
(s, 2H), 2.14 (s, 12H), 1.96 (s, 3H), 1.95 (s, 3H), 1.85 (s, 6H).
1
(0.73 g) in 81% yield. Mp: 151 8C. H NMR (CDCl3): d
7.65 (s, 1H), 7.46 (d, 2H, JZ8.4 Hz), 7.34 (t, 1H, JZ
8.1 Hz), 7.26 (s, 2H), 7.24 (s, 2H), 3.36 (s, 2H), 1.92 (s,
12H). 13C{1H} NMR (CDCl3): d 147.7, 143.8, 136.2, 133.2,
132.3, 132.0, 130.8, 124.9, 123.0, 121.6, 120.8, 119.1,
116.0, 111.2, 100.4, 95.4, 93.1, 82.3, 16.2. MS: m/z 906
[MC]. Anal. Calcd for C44H22F12S4: C, 58.27; H, 2.45.
Found: C, 58.01; H, 2.32.
Acknowledgements
This work was supported by the KOSEF through
National Research Laboratory (NRL 2005) program
awarded to J.K.
3.1.4. Compound 5. A mixture of 2 (0.28 g, 0.28 mmol), 4
(0.25 g, 0.28 mmol), Pd(PPh3)4 (0.003 g), and CuI
(0.0005 g) was vacuum-dried and added NEt3 (60 ml).
The solution was refluxed for 12 h and then evacuated to
dryness. The product 5 was separated by chromatography on
a silica gel column (1:2 methylene chloride/hexane) to
afford 5 in 9% yield. 1H NMR (CDCl3): d 7.65 (s, 2H), 7.45
(d, 4H, JZ7.3 Hz), 7.34 (t, 2H, JZ7.3 Hz), 7.19 (s, 2H),
7.17 (s, 2H), 7.12 (s, 2H), 7.09 (s, 2H), 2.07 (s, 6H), 2.06 (s,
6H), 1.96 (s, 6H), 1.95 (s, 6H). 13C{1H}NMR (CDCl3): d
148.0, 146.9, 144.3, 143.8, 136.4, 134.2, 133.3, 131.6,
129.2, 125.0, 123.0, 121.7, 121.1, 116.5, 111.5, 93.1, 86.0,
82.3, 15.6, 14.5. MS: m/z 1760 [MC]. Anal. Calcd for
C84H40F24S8: C, 57.27; H, 2.29. Found: C, 57.01; H, 2.20.
References and notes
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3.1.5. Compound 6. A mixture of 4 (0.45 g, 0.50 mmol),
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(0.001 g). The solution was stirred for 12 h and then
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7.2 Hz), 7.16 (s, 2H), 7.14 (s, 2H), 7.05 (s, 2H), 6.76 (s. 2H),
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