Carbon dioxide and water as a key for unlocking photochromism of diarylethene derivative

Article abstract of DOI:10.1016/j.jphotochem.2010.08.002

A photochromic diarylethene derivative with 4-(ethylideneamino) phenol group (1a) is prepared, and 1a exhibits ring-opening and ring-closing photoisomerization with UV/vis light irradiation in solution. Addition of base to both solution of ring-open isomer 1a and ring-closed isomer 1b produces deprotonated compounds 2a and 2b, respectively, and both 2a and 2b are photo-inactive and no photochemical reaction is detected in solution in the absence of carbon dioxide and water. Both 2a and 2b are, however, converted back to 1a and 1b when the solution contains carbon dioxide and water, and photochromic reaction is recovered. This may provide a means to generate a gate for non-destructive readout. Meanwhile, the conversion between species is accompanied color change in a wide range by combination of photo-trigger and chemical trigger. The system endowed with multi-responsive functionality for multi-color change is beneficial for applications such as display and camouflage.

Full text of DOI:10.1016/j.jphotochem.2010.08.002

Journal of Photochemistry and Photobiology A: Chemistry 215 (2010) 103–107
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Carbon dioxide and water as a key for unlocking photochromism of
diarylethene derivative
Huan-Huan Liu, Yi Chen∗
Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, The Chinese Academy of Sciences, Beijing 100190, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 28 May 2010
Received in revised form 22 July 2010
Accepted 2 August 2010
Available online 6 August 2010
A photochromic diarylethene derivative with 4-(ethylideneamino) phenol group (1a) is prepared, and
1a exhibits ring-opening and ring-closing photoisomerization with UV/vis light irradiation in solution.
Addition of base to both solution of ring-open isomer 1a and ring-closed isomer 1b produces deprotonated
compounds 2a and 2b, respectively, and both 2a and 2b are photo-inactive and no photochemical reaction
is detected in solution in the absence of carbon dioxide and water. Both 2a and 2b are, however, converted
back to 1a and 1b when the solution contains carbon dioxide and water, and photochromic reaction is
recovered. This may provide a means to generate a gate for non-destructive readout. Meanwhile, the
conversion between species is accompanied color change in a wide range by combination of photo-
trigger and chemical trigger. The system endowed with multi-responsive functionality for multi-color
change is beneficial for applications such as display and camouflage.
Keywords:
Photochromism
Diarylethene
Multi-responsive system
Gate reactivity
Multi-color
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
[20,21] stimuli and to tailor readable output state. Although there
are some impressive examples of multi-addressable switching
Typical bistable molecules are the so-called photochromic com-
pounds, which is defined as a reversible change induced by
light radiation, between two states of a molecule having differ-
ent absorption spectra [1]. Great interest is currently devoted to
bistable molecules presenting two forms whose inter-conversion
can be modulated by an external stimulus. Molecules with switch-
able properties are of considerable practical and fundamental
interest as the development of robust systems will open up new
avenues and possibilities for applications to drug delivery systems,
optical devices and sensor.
Photochromic diarylethenes are one of the most promis-
ing candidates for photoelectronic applications because of their
thermo-irreversible and fatigue-resistant photoisomerization per-
formances [2,3]. A host of applications exist for photochromic
diarylethenes that take advantage of their inherent ability to pro-
duce switches between two isomers by UV–vis photo-trigger [4–7].
Currently, development of diarylethenes that integrate several
switchable functions into a single molecule are of considerable
interest [8–10] due to miniaturize the components of machin-
ery and electronic down to the molecular level. To reach these
goals, it is essential to transform molecular structures between two
or more states in response to external signals such as photonic
[11–15], chemical [16,17], electrochemical [18,19], or magnetic
systems, which composed of different kinds of photochromic
diarylethenes, have been reported [22–24], multi-input/multi-
output response systems with a photochromic diarylethene are
reported rarely [25,26], they have attracted considerable atten-
tion from the viewpoint of potential applications in molecular
sensing and switches. Since multi-input systems are prototypes
of molecular-level logic operators [27,28], the addition of a multi-
output response would endow such systems with the ability to act
as parallel operating logic elements.
Destructive readout is main disadvantage of photochromic
materials [29,30]. Photochromic reactions, in general, proceed in
proportion to the number of photons absorbed the compounds.
Such a linear-response characteristic cannot be used as the basis of
memory media because information is destroyed after many read-
out operations. Several methods have been proposed to avoid the
destructive readout of diarylethenes such as fluorescence [31–35],
infrared absorption [36–38], and optical rotation [39–41]. These
methods are demonstrated to be efficient to non-destructive read-
out, but the destructive readout cannot be dismissed completely
because diarylethenes are photo-active material and have more
or less two-photon or multi-photon absorption. One possible way
for non-destructive readout is to introduce gated reactivity to
diarylethene systems [42,43], in which diarylethenes are photo-
inactive, therefore, the photochromic reaction was prohibited and
the non-destructive readout was achieved completely.
In this paper, we design an artificial gated photochromic
diarylethene system. It is found that the system exhibits pho-
∗
Corresponding author. Tel.: +86 10 82543595; fax: +86 10 62564049.
E-mail address: yichencas@yahoo.com.cn (Y. Chen).
1010-6030/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jphotochem.2010.08.002

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H.-H. Liu, Y. Chen / Journal of Photochemistry and Photobiology A: Chemistry 215 (2010) 103–107
Scheme 1. Outline for the concept of inter-conversion and gated reactivity of photochromic diarylethene system.
tochromic reaction with UV/vis light irradiation. With addition of
base, both ring-open isomer (1a) and ring-closed isomer (1b) con-
verted to deprotonated compounds 2a and 2b, respectively. Both 2a
and 2b are photo-inactive in absence of carbon dioxide and water,
and the photoconversion between 2a and 2b is inhibited. In pres-
ence of carbon dioxide and water, both 2a and 2b are converted
to 1b and 1a, respectively, with UV light and visible light irradia-
tion. The inter-conversion and gated reactivity concept is outlined
in Scheme 1.
tra data were as follows: a mixture of 3,4-bis(5-formyl-2-
methylthien-3-yl)-2,5-dihydrothiophene [44] (100 mg, 0.3 mmol)
and 4-aminophenol (72 mg, 0.66 mmol) in anhydrous ethanol
(10 ml) was refluxed. After no starting material was detected by
TLC plate, the mixture was cooled, and the yellow product was fil-
tered off, washed with EtOH, pure diarylethene 1a was obtained
after vacuum drying. Yield: 45% (70 mg). M.p. = 210–211 ◦C. 1H NMR
(400 MHz, DMSO-d6): 9.48 (s, 2H), 8.58 (s, 2H), 7.43 (s, 2H), 7.14
(d, 4H, J = 8.7 Hz), 6.76 (d, 4H, J = 8.7 Hz), 4.15 (s, 4H), 1.98 (s, 6H).
13C NMR: 156.2, 149.8, 141.9, 139.9, 139.5, 134.3, 133.0, 132.7,
122.5, 115.7, 42.1, 14.6. TOF-MS EI (m/z) calcd. For C28H24N2O2S3:
516.1000, found: 516.1000 (100%).
2. Experimental
2.1. General methods
2.3. Measurement of the ratio of 1a and 1b at photostationary
state
1H NMR spectrum was recorded at 400 MHz with TMS as an
internal reference and CDCl3 as solvent. MS spectra were recorded
with TOF-MS spectrometer. Absorption spectra were measured
with an absorption spectrophotometer (Hitachi U-3010). All chem-
icals for synthesis were purchased from commercial suppliers, and
solvents were purified according to standard procedures. Reaction
monitored by TLC silica gel plates (60F-254). Column chromatog-
raphy was performed on silica gel (Merck, 70–230 mesh). A 360 nm
lamp (36 W) and a Xenon light (500 W), with different wavelength
filters, were used as light sources for photocoloration and photo-
bleaching, respectively.
The ratio of 1a and 1b at photostationary state was measured
by comparing the integral of proton of 1a and 1b in 1H NMR
spectroscopy. Partial 1H NMR spectroscopy of both 1a and pho-
tostationary state (PPS) is presented in Fig. 1.
3. Results and discussion
The ring-opening and ring-closing photoiosmerization of 1a
with UV/vis light are presented in Scheme 1. Upon irradiation
with UV light, the absorption band (ꢀmax = 353 nm, ε = 4.6 × 104, in
CH3CN), which attributes to the ring-open isomer 1a, decreased in
intensity, and a new band (ꢀmax = 590 nm), which corresponds to
the ring-closed isomer 1b, appeared at the same time (Fig. 2). The
band at 590 nm increased in intensity with the increase of irra-
2.2. Chemical
Diarylethene 1a was prepared according to synthetic route
shown in Scheme 2, and the detailed procedures and spec-
Scheme 2. Synthesis of diarylethene 1a.

H.-H. Liu, Y. Chen / Journal of Photochemistry and Photobiology A: Chemistry 215 (2010) 103–107
105
Fig. 1. Partial 1H NMR spectroscopy of 1a and photostationary state (PSS).
derivatives in solution, and the clear isobestic point indicated
that only two isomers existed when the compound underwent
the photoisomerization reaction. The blue solution was bleached
completely back to colorless solution with visible light (≥400 nm)
irradiation, and the coloration and decoloration can be repeated.
Addition of base (NaOH, 50 ␮M) to the solution of 1a (25 ␮M)
produced a deprotonated diarylethene 2a, whose absorption was
bathochromic shifted to 425 nm (Fig. 3a), resulting in the color
change of solution from colorless to yellow. Similar result was
obtained with ring-closed isomer 1b: addition of NaOH (50 ␮M)
to the solution of photostationary state (1b ca. 7.5 ␮M) produced
a new absorption at 655 nm (Fig. 3b), which corresponded to ring-
closed isomer 2b. This process was accompanied by a color change
of solution from blue to green.
Photoreaction of both 2a and 2b was investigated. It is found
that both 2a and 2b are photo-inactive and no photoreaction was
obtained when the solution of 2a or 2b was irradiated with UV
light and visible light in absence of carbon dioxide and water (mois-
ture). The prohibition of photoreaction of 2a and 2b are probably
resulted from the large energy barriers between the ground states
and photoexcited states due to very strong electron-donator of oxy-
gen anion. The strong electron donation produced a large decrease
of energy of 2a and 2b in ground states, which was confirmed by
Fig. 2. Absorption change of diarylethene 1a (25 ␮M, CH3CN) with 365 nm light
irradiation till to photo-trigger state (periods: 0, 2, 4, 6 min).
diation time till the photostationary state was reached, and the
ratio of 1a and 1b at photostationary state is ca. 1.0:0.3 (see Section
2.3). This process was accompanied by a color change of solution
from colorless to blue. As presented in Fig. 2, the figure showed the
typical absorption spectra changes of photochromic diarylethene
Fig. 3. Absorption change of deprotonation of 1a (a) and 1b (b) (25 ␮M, CH3CN) with addition of NaOH (50 ␮M, MeOH).

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H.-H. Liu, Y. Chen / Journal of Photochemistry and Photobiology A: Chemistry 215 (2010) 103–107
Fig. 4. Absorption change of 2a (a) and 2b (b) before (᭹) and after (ꢀ) irradiation with 365 nm light and visible light (ꢀ ≥ 480 nm) till to photo-steady state, respectively.
Fig. 5. Images of cascade color change patterns using photo-trigger and chemical trigger.
a large bathochromic shift (more than 60 nm) of 2a and 2b, and
therefore it increased the energy gap between the ground states
and excited states.
(elute: ethyl acetate), respectively, where are the same as these of
1a and 1b. All confirmed that 2a and 2b were converted to 1a and
1b, respectively, in the presence of CO2 and H2O, and upon irradi-
ation with UV light or visible light, 2a was converted to 1b via 1a
and 2b was converted to 1a via 1b.
Interesting results were obtained when both solution of 2a and
2b with UV and visible light irradiation in presence of carbon diox-
ide and water (moisture). It is found that the absorption of 2a at
425 nm was unexpectedly shifted to 590 nm upon irradiation with
UV light, which is in accordance with absorption of 1b (Fig. 4a).
Similar results were obtained with solution of 2b: upon irradia-
tion with visible light, the absorption of 2b at 655 nm hypochromic
shifted to 353 nm, which corresponded to absorption of 1a (Fig. 4b).
The mechanism and control experiments were also explored. It
is known that sodium phenoxide can be converted to phenol in the
presence of CO2 and H2O [45]. Based on this result, it is supposed
that both 2a and 2b were converted to 1a and 1b, respectively, in
the presence of CO2 and H2O. In order to confirm the supposal,
some control experiments have been done. First, no color change
was observed and no absorption change was detected by UV–vis
absorption spectroscopy when both solution of 2a and 2b, which
were under argon (CO2 and moisture were expelled completely),
were irradiated with UV light and visible light, respectively. It indi-
cated that both 2a and 2b are photo-inactive in absence of CO2
and H2O. Second, both yellow (2a) and green (2b) were gradually
changed (it took about 5 h) to colorless and blue, respectively, in
moisture air without light irradiation, and the speed of color change
above was significantly increased (it took about less than 5 s) when
the solution was bubbled with moisture air or carbon dioxide in a
gas cylinder (carbon dioxide from gas cylinder through water first
before into the solution). Third, both colorless and blue solution
showed photo-active, and photochromic reaction was recovered
with UV/vis light irradiation. Fourth, TLC (thin layer chromatogram)
plate test showed the products, resulted from the conversion of 2a
and 2b in moisture air, appeared at the place with Rf = 0.78 and 0.71
Cascade color change patterns were achieved using both photo-
trigger and chemical trigger. Upon irradiation of 1a with UV light,
followed by deprotonation, the color changed from colorless to
blue to green, the green solution was bleached back to colorless
solution with visible light irradiation in the presence of CO2 and
H2O. As represented in Fig. 5 (pattern I), the color change could
be recycled by combination both photo-trigger and chemical trig-
ger (addition of NaOH). It is worth noting that the recycle was just
performed two to three times due to decompose of 1a in solution
containing water, and during this process, a white solid (Na2CO3)
as by-product was obtained. More complicated color change pat-
terns (colorless → yellow → blue → green), which showed in Fig. 5
(pattern II), were also obtained by changing the order of trigger:
deprotonation first, followed by UV light irradiation and deproto-
nation again. Also, the green solution was bleached back to colorless
solution with visible light irradiation in the presence of CO2 and
H2O, and the color change could be recycled two to three times.
4. Conclusions
An artificial photochromic diarylethene system with multi-
responsive functionality has been developed. The system possesses
ring-opening and ring-closing photoisomerization with UV/vis
light irradiation. Both ring-open isomer and ring-closed isomer are
converted to deprotonated compound, respectively, with addition
of NaOH, whose photochromic reaction is inhibited. The deproto-
nated compounds can be reversed back to original compounds in
moisture air, and photochromic reaction is recovered with UV/vis

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107
light irradiation. The conversion between species is accompanied
with distinct color change, and the cascade color change patterns
are obtained with multi-input. The system with gate reactivity and
multi-color change is beneficial for non-destructive readout and
applications.
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Acknowledgments
This work was supported by National Basic Research Program
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