A photochromic diarylethene dyad based on perylene diimide

Article abstract of DOI:10.1016/j.dyepig.2010.03.020

A new photochromic diarylethene dyad based on perylene diimide (PDI-DTE) has been synthesized. The photochromic reaction of PDI-DTE induced the significant change of the absorption spectra and fluorescence intensity. The color of PDI-DTE in THF solution was not changed obviously upon ultraviolet irradiation, while the fluorescence intensity is increased unexpectedly with the photochromic cyclization of the diarylethene units. With not visible change of color accompanied to the enhanced fluorescence, PDI-DTE can be potentially applied to anti-counterfeiting technology.

Full text of DOI:10.1016/j.dyepig.2010.03.020

Dyes and Pigments 89 (2011) 260e265
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
A photochromic diarylethene dyad based on perylene diimide
*
Wenjuan Tan, Xin Li, Junji Zhang, He Tian
Key Laboratory for Advanced Materials and Institute of Fine Chemicals, East China University of Science & Technology, Shanghai 20023, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A new photochromic diarylethene dyad based on perylene diimide (PDI-DTE) has been synthesized. The
photochromic reaction of PDI-DTE induced the significant change of the absorption spectra and fluo-
rescence intensity. The color of PDI-DTE in THF solution was not changed obviously upon ultraviolet
irradiation, while the fluorescence intensity is increased unexpectedly with the photochromic cyclization
of the diarylethene units. With not visible change of color accompanied to the enhanced fluorescence,
PDI-DTE can be potentially applied to anti-counterfeiting technology.
Received 25 January 2010
Received in revised form
11 March 2010
Accepted 16 March 2010
Available online 27 March 2010
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Photochromism
Diarylethene
Perylene
Fluorescence
Anti-counterfeiting
1. Introduction
modified through substitution in the aromatic core and bay
region [9,10]. The modulation of PDIs properties based on
In recent years, many countries and companies research
variety of anti-counterfeiting technology in order to combat fake
and inferior products. Especially, more efforts are focused on the
banknotes and the anti-counterfeiting packaging of brand-name
products. Thus demands promoted the research and development
of the anti-counterfeiting technology. Photochromic materials,
with special ink marker and high anti-counterfeiting features,
have aroused extensive attention. Generally, there are three kinds
of anti-counterfeiting technology: 1) visible without fluores-
cence; 2) visible with significant fluorescence under ultraviolet
light irradiation; 3) not visible with significant fluorescence under
ultraviolet light irradiation. Organic photochromic compounds
just as spiropyran and fulgide derivatives have been applied as
anti-counterfeiting materials, they all belong to the second kind
[1]. But the application used dithienylethene (DTE) is extremely
rare. Diarylethene derivatives, the promising families of photo-
chromic compounds, substituted with fluorescent chromophore,
exhibit fluorescence modulation upon irradiation with ultraviolet
and visible light [2e5]. On the other hand, perylene diimides
(PDIs) are outstandingly versatile fluorescent chromophores [6]
with exceptional thermal and photochemical stability, strongly
absorb visible light and high fluorescence quantum yield [7,8].
Also, the photophysical properties of PDIs can be conveniently
photochromic reactions has been studied [11e15]. Here we report
on a reversible fluorescence modulation by photoinduced reac-
tion with the diarylethene unit linking to the aromatic region of
the perylene unit (Fig. 1). The final product PDI-DTE show
significant fluorescence after ultraviolet irradiation while the
visible color is the same. PDI-DTE can be potentially used as the
third kind of anti-counterfeiting materials.
2. Experimental
2.1. Chemicals and instruments
N-N-(n-butylamino)-1,7-Dibromoperylenetetracarboxylic acid
diimide was synthesized according to the literature [16]. Other
reagents were commercially available and used without further
purification.
1H NMR spectra were recorded on a Bruker AM 400 spectrom-
eter with tetramethyl silane (TMS) as internal reference. MS were
recorded on EI or ESI mass spectroscopy. Absorption spectra were
measured on a Varian Cary500 UVeVis spectrophotometer. Fluo-
rescence spectra were measured on a Varian Cary Eclipse Fluores-
cence spectrophotometer. The optical switch experiments were
carried out using a photochemical reaction apparatus with a 200 W
Hg lamp. Luminescence lifetime measurements were performed on
an Edinburgh FL 900 Fluorescence Spectrometer equipped with
* Corresponding author.
E-mail address: tianhe@ecust.edu.cn (H. Tian).
a blue laser (
l
¼ 440 nm).
0143-7208/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2010.03.020

W. Tan et al. / Dyes and Pigments 89 (2011) 260e265
261
Cl
S
Cl
S
S
S
O
O
N
O
O
N
O
N
O
O
N
O
UV
Vis
O
O
O
O
S
Cl
S
S
Cl
S
ring-closed PDI-DTE
ring-open PDI-DTE
Fig. 1. The photochromic reaction of compound PDI-DTE.
2.2. Synthesis
J ¼ 7.2 Hz, eCH2e), 2.77 (t, 4H, J ¼ 8.0 Hz, eCH2e), 2.09 (m, 4H,
eCH2e), 2.04 (s, 6H, eCH3), 1.92 (s, 6H, eCH3), 1.712 (m, 4H,
eCH2e), 2.45 (m, 4H, eCH2e), 0.99 (t, 6H, J ¼ 7.2 Hz, eCH3), 13C
2.2.1. 1-{(2-methyl-5-(4-hydroxyl)phenyl)thien-3-yl}-2-
(5-chloro-2-methylthien-3-yl) cyclopentene(DTE)
NMR (400 MHz, CDCl3, ppm): d 163.3, 162.9, 155.0, 154.0, 138.6,
To a stirred solution of 1, 2-Bis(5-chloro-2-methylthien-3-yl)
cyclopentene (1 g, 3 mmol) in THF (10 ml) at ꢀ78 ꢁC under Ar in the
absence of light was added dropwise 2.9 M n-BuLi in hexane (0.17 g,
3 mmol), and the reaction mixture was stirred at ꢀ70 ꢁC for further
30 min. Then tributyl borate (0.7 g, 3 mmol) was quickly added in
one portion. This reddish solution was stirred for 1 h at room
temperature, and was then used in the Suzuki coupling reaction
without any workup because the product is deboronized during
isolation.
136.5, 135.2, 135.0, 134.8, 134.0, 133.3, 132.1, 131.7, 130.3, 129.3,
128.9, 127.8, 127.4, 126.8, 125.2, 125.0, 124.1, 123.9, 122.3, 119.8, 40.4,
38.4, 38.3, 31.9, 30.1, 29.7, 22.9, 22.6, 20.3, 14.4, 14.2, 13.8; MOLDI-
TOF: calculated for (C74H60Cl2N2O6S4) 1271.4440, found:1271.3481.
3. Results and discussion
3.1. Design and synthesis of PDI-DTE
A mixture of 4-iodophenol (0.67 g, 3 mmol), the catalyst Pd
(PPh3)4 and 10 ml THF was stirred for 15 min at room temperature.
Then aqueous Na2CO3 (8 mL, 2 M) was added. The reactive mixture
was heated at a temperature of 60 ꢁC, and the solution of bis
(boronic) esters prepared from 1, 2-Bis(5-chloro-2-methylthien-
3-yl) cyclopentene was added dropwise via a syringe. Subse-
quently, the mixture was refluxed for 2 h and cooled to room
temperature. The reactive mixture was poured into H2O and
extracted with ether, and the organic layer was collected and dried
with anhydrous MgSO4. After concentration, the compound was
purified by column chromatography on silica (petroleum ether-
eethyl acetate ¼ 2:1 v/v) to yield compound DTE (0.618 g), yield
56%. 1H NMR (400 MHz, CDCl3, ppm): 7.38 (d, 2H, J ¼ 8.8 Hz, phenyl
CeH), 6.87 (s, H, thienyl CeH), 6.83 (d, 2H, J ¼ 6.8 Hz, phenyl CeH),
6.63 (d, 1H, J ¼ 5.4 Hz, thienyl CeH), 4.84 (s, 1H, hydroxyl eOH),
2.82 (t, J ¼ 5.2 Hz, 2H, eCH2e), 2.79 (t, 2H, J ¼ 5.2 Hz, eCH2e), 2.07
(m, 2H, eCH2e), 1.99 (s, 3H, eCH3), 1.90 (s, 3H, eCH3). 13C NMR
In this work, a photochromic dithieylethene unit was linked to
perylene bisimide and the photochromic behaviors were investi-
gated in detail. Two reference compounds DTE and PDI were also
prepared. PDI-DTE was synthesized from the typical dithienyle-
thene unit, 2-Bis(5-chloro-2-methylthien-3-yl)cyclopentene (DTE)
(Fig. 2). Compound DTE was prepared by a Suzuki coupling reaction
with 4-iodophenol with a yield of 56%. The target compound PDI-
DTE was involved a phenoxylation of N-N-(n-butylamino)-1,7-
Dibromoperylenetetracarboxylic acid diimide [9] by treatment
with phenol function group of DTE [17]. The product was purified
by silica-gel-column chromatography. The structure was identified
by 1H NMR, 13C NMR spectroscopes and MOLDI-TOF (see
Supporting Information).
3.2. Absorption spectral change of DTE and PDI-DTE
The photochromic behavior of dithienylethene compound DTE
and perylene derivative PDI-DTE was examined in THF solution.
The absorption spectra change of DTE upon photoirradiation is
shown in Fig. 3. After 254 nm ultraviolet light irradiation, the THF
solution of DTE turned colorless to orange. The absorption
maximum located at 290 nm for the open form decreased, while
a new absorption band appeared at ca. 490 nm after ultraviolet
(UV) irradiation. The absorption at 300 nm of the open form is
(400 MHz, CDCl3):
d 154.83, 139.63, 136.19, 135.41, 135.18, 133.61,
133.47, 133.25, 127.59, 126.86, 126.82, 124.93, 122.80, 115.67, 38.44,
38.34, 29.69, 22.91, 14.30, 14.17. TOF-MS: calculated for
(C21H19Cl2NOS2) 386.9580, found: 386.0550.
2.2.2. Synthesis of PDI-DTE
N-N-(n-butylamino)-1,7-Dibromoperylenetetracarboxylic acid
diimide (0.33 g, 0.5 mmol) was stirred under argon with compound
DTE (0.407 g, 1.06 mmol) in NMP (20 ml) at 100 ꢁC in a 100 mL
round flask in the presence of powdered anhydrous K2CO3 (400 mg,
3 mmol). The temperature was maintained at 100 ꢁC overnight
under argon. The reaction mixture was allowed to cool to room
temperature and was poured into aqueous hydrochloride acid
(50 ml, 1 M). The precipitated product was filtered under suction,
and was then purified by column chromatography to give a red
solid PDI-DTE (70 mg, 6.8%). 1H NMR (400 MHz, CDCl3, ppm): 9.58
(d, 2H, J ¼ 8.0 Hz, perylene CeH), 8.63 (d, 2H, J ¼ 8.0 Hz, perylene
CeH), 8.37 (s, 2H, perylene CeH), 7.56 (d, 4H, J ¼ 8.7 Hz, phenyl
CeH), 7.53 (d, 4H, J ¼ 8.7 Hz, phenyl CeH), 6.97 (s, 2H, thienyl CeH),
6.65 (s, 2H, thienyl CeH), 4.17 (t, 4H, J ¼ 8.0 Hz, eCH2e), 2.84 (t, 4H,
ascribed to
p /
p* and n / p* transition of the phenol and
thiophene rings. Upon 254 nm irradiation, the new absorption
band appearing at 490 nm was assigned as absorption of the closed
form, resulting from the enlargement of the
photocyclization.
p conjugation by
After introducing photochromic dithienylethene unit into the
aromatic region of perylene diimide, the derivative PDI-DTE is also
shown photochromic behavior in THF solution. Perylene is a well-
known red dye, and the THF solution of PDI-DTE has not changed
the red color after irradiation with 254 nm ultraviolet light. But the
difference after ultraviolet light irradiation is shown obviously in
the absorption and fluorescence spectra (Figs. 4 and 5). Similarly to
DTE, in the UV region the open form of PDI-DTE shows absorption

262
W. Tan et al. / Dyes and Pigments 89 (2011) 260e265
n-BuLi,B(OBu)3
Cl
S
S
Cl
S
Cl
S
I
OH
S
S
Cl
OH
O
DTE
O
N
O
N
O
N
O
O
N
N
O
O
O
NMP,K2CO3
°C
O
O
Br
S
Br
Cl
S
CH2Cl2
Br2
PDI-DTE
N
O
O
O
Bromo-PDI
Fig. 2. The synthetic route of compound PDI-DTE.
band at 290 nm ascribed to dithienylethene unit. And the charac-
teristic absorption band of perylene unit located at 533 nm,
502 nm, 390 nm and 270 nm, just similar to the reference
compound N,N0-di(n-butyl)-1,7-di (4-phenal) perylene-3,4,9,10-
tetracarboxylic acid bisimide (PDI) at 533 nm, 499 nm, 396 nm and
268 nm. After irradiation of 254 nm UV light, the characteristic
absorption band blue-shift to 520 nm and 490 nm with the inter-
action of the photocyclization of the dithienylethene unit. A new
absorption band appeared at about 585 nm ascribed to the
similar to PDI with the fluorescence maximum at 565 nm. After the
irradiation of 254 nm ultraviolet light the intensity increased 750%
[
Fem
(
lex 480 nm)
¼
0.05, Fem
(
lex
open form
closed form
480 nm) ¼ 0.37, using PDI as Fem
(lex 480 nm) ¼ 1]. For the
structure of PDI-DTE, each diarylethene unit is intimately con-
nected to the perylene unit only through one oxygen atom in PDI-
DTE. That conformation leads to the existence of a strong electronic
interaction between the perylene unit and the diarylethene units.
The fluorescence of the open form of PDI-DTE was very weak. After
254 nm UV light irradiation, the fluorescence of PDI-DTE was
increased. The electrons of the diarylethene units flowing towards
enlargement of the
p conjugation. Also the absorption peak at
290 nm increased with the cyclization of the dithienylethene unit.
The transformation ratios corrected for the active conformer for the
photocyclization were determined [DTE, F254 ¼ 0.28, PDI-DTE,
F254 ¼ 0.18], which were found to be comparable to those for
photocycloreversion [DTE, F510 ¼ 0.35, PDI-DTE, F586 ¼ 0.26].
the perylene unit were pulled back due to the forming of the
p
conjugation of the closed diarylethene. As a result, the fluorescence
of the PDI unit was increased. But the fluorescence intensity of PDI-
DTE is still smaller than that of PDI. This was probably due to the
50% of parallel formation of the open form of DTE units without
cyclization process. The fluorescence life time is also measured and
the results are shown in Supporting Information.
3.3. The fluorescence change of PDI-DTE
Since perylene diimide derivatives are well-known with their
excellent ability to accept electrons, standout stability, high molar
extinction coefficient and fluorescence quantum yield, the fluo-
rescence behavior of PDI-DTE is also investigated (Fig. 5). PDI-DTE is
3.4. The computational study of PDI-DTE
To enhance the understanding of the effect of the diarylethene
unit on the PDI-DTE compound, we carried out molecular orbital
calculation on PDI, the open and closed forms of PDI-DTE. These
experimental data were complemented by B3LYP/6-31G(d).
1.0
6min
5min
4min
3min
2min
60s
40min
35min
30min
25min
20min
15min
10min
5min
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0.8
0.6
0.4
0.2
0.0
30s
open-form
PDI-DTE
DTE
0min
300
400
500
600
700
300
400
500
600
700
Wavelength (nm)
Wavelength (nm)
Fig. 3. UVeVis absorption spectral changes of DTE (5 ꢂ 10ꢀ5 M in THF) at 298 K upon
Fig. 4. UVeVis absorption spectral changes of PDI-DTE (5 ꢂ 10ꢀ5 M in THF) at 298 K
irradiation with 254 nm UV light.
upon irradiation with 254 nm UV light.

W. Tan et al. / Dyes and Pigments 89 (2011) 260e265
263
40min
35min
30min
25min
20min
15min
10min
5min
120
100
80
60
40
20
0
40
30
20
10
0
0min
450
500
550
600
650
700
750
550
600
650
700
Wavelength (nm)
Wavelength(nm)
Fig. 5. Emission spectra changes of PDI and PDI-DTE (5 ꢂ 10ꢀ5 M in THF at 298 K) upon excited at 480 nm.
The calculated HOMOs and LUMOs of the geometry optimized
structures are shown in Fig. 6 and indicate qualitatively different
electronic structures for these compounds. In contrast to the open
form of PDI-DTE, the closed form shows a clear spatial separation of
its HOMO and LUMO, consistent with optical excitation resulting in
the formation of an intramolecular charge separated state of the
closed diarylethene unit. The electron at the phenoxyl thiophene
diarylethene unit leads to the electron back to form
of the closed ring [18].
p conjugation
According to the calculation results (Table 1), incorporation of
the open form of diarylethene unit onto the aromatic region of the
perylene unit increases the energy level of LUMO, the energy gap
between HOMO and LUMO is similar to PDI. While after photo-
cyclization of the diarylethene unit, a significant positive shift in
the energy level of the HOMO while the energy level of LUMO
negative shift, leading to a decrease in the HOMOeLUMO gap. The
unit tends to join the large
p conjugation of the perylene unit at
the open form. After irradiation with UV light, the cyclization of the
Fig. 6. The calculated LUMOs (middle) and HOMOs (bottom) for molecules (top).

264
W. Tan et al. / Dyes and Pigments 89 (2011) 260e265
Table 1
Calculated HOMO and LUMO Energy of PDI-DTE and PDI.
Compound
HOMO (eV)
LUMO (eV)
Twisting angle (ꢁ)
PDI
ꢀ5.51
ꢀ5.50
ꢀ4.75
ꢀ3.09
ꢀ3.20
ꢀ3.25
17.5
17.2
17.4
Open form of PDI-DTE
Closed form of PDI-DTE
calculated data is just consistent with the result of the electro-
chemical studies mentioned below.
Time-dependent density functional theory (TDDFT) calculations
are also performed by using the PBE0 functional and the 6-31G(d)
basis set, to further investigate the excited states of the PDI-DTE.
The TDDFT results are listed in Supporting Information(Table S1).
Upon excitation at 480 nm, the fluorescence of the open form of
PDI-DTE is quenched via internal conversion of the excited state.
While in the closed form of PDI-DTE, there is a significant energy
gap between the excited states, which prevents the internal
conversion from the higher excited states to the lower excited
states. And the strong fluorescence of the PDI unit preserves.
A schematic representation of the excitation process of the open
form of PDI-DTE is shown in Fig. 7. Upon excitation at 480 nm, the
open form of PDI-DTE is excited to the S3 (H-2 / L) state which
may convert to S1 (H / L) state via internal conversion. Since the
HOMO of the open form of PDI-DTE is extended over the whole
molecule, the fluorescence from the LUMO / HOMO transition is
expected to be diminished, in accordance with experimental
observations.
Fig. 8 shows the excitation process of the closed form of PDI-
DTE. Upon 480 nm excitation, the closed form of PDI-DTE is excited
to the S5 state, which does not convert to the lowest S1 state due to
the energy gap between the S1/S2 and the S3/S4/S5 excited states,
and the strong fluorescence of the PDI unit preserves. In the closed
form of PDI-DTE, the HOMO and HOMO-1 orbitals are almost
degenerate, which also contribute to the absorption band around
500 nm (see Table S1 and Fig. S3).
Fig. 8. Excitation process of the closed form of PDI-DTE.
Ferrocence is the internal standard. The scan rate is 100 mV/s. The
inconspicuous first reduction potential, with E1
¼ ꢀ0.48 V, and
Red
the second reduction potential E2
¼ ꢀ0.75 V, which are more
Red
positive than those of PDI (E1
¼ ꢀ0.53 V, E1
¼ ꢀ0.82 V), were
Red
Red
closed form of PDI-DTE
open form of PDI-DTE
3.5. The cyclic voltammograms of PDI-DTE and PDI
The redox potentials of PDI-DTE, as well as DTE and PDI, were
measured with cyclic voltammetry in anhydrous tetrahydrofuran
(THF), in a N2 atmosphere, using Bu4NPF6 as the electrolyte, glassy
carbon electrode as work electrode, platinum as the counter elec-
trode, and the Ag/AgCl as the reference electrode (Fig. 9).
-1.0
-0.8
-0.6
-0.4
-0.2
0.0
Potential ( V vs Fc/Fc+ )
PDI
-2.0
-1.5
-1.0
-0.5
0.0
Potential ( V vs Fc/Fc+)
Fig. 9. The cyclic voltammograms of PDI-DTE, PDI in THF(under N2 atmosphere,
scanning rate 100 mV/s) using Bu4NPF6 as electrolyte, glassy carbon electrode as work
electrode, platinum as the counter electrode, and the Ag/AgCl as the reference
electrode (vs Fc/Fcþ).
Fig. 7. Excitation process of the open form of PDI-DTE.

W. Tan et al. / Dyes and Pigments 89 (2011) 260e265
265
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suggested that the DTE and PI units of PDI-DTE strongly interacted
with each other in the ground state. But for the closed form of PDI-
DTE, the first reduction potential E1
¼ ꢀ0.47 V, and the second
Red
reduction potential E2
¼ ꢀ0.82 V. That result also demonstrated
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4. Conclusions
The photochromic and fluorescence properties of a perylene
derivative PDI-DTE with a diarylethene unit at the aromatic region
have been investigated. Successful tuning of the absorption spectra
and fluorescence intensity has been realized by the photochromic
reaction. Consequently, the fluorescence intensity is increased
unexpectedly upon photochromic cyclization. With not visible
change of color accompanied to the enhanced fluorescence, PDI-DTE
can be potentially applied to the anti-counterfeiting technology.
Acknowledgements
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This work is financially supported by NSFC/China, National Basic
Research 973 Program (2006CB806200), Scientific Ministry of
China (2008DFA41390) and partially by Scientific Committee of
Shanghai.
Appendix. Supplementary data
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Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.dyepig.2010.03.020.
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