Diarylethene-based conjugated polymer networks for ultrafast photochromic films

Article abstract of DOI:10.1039/c9nj02596k

Diarylethene polymers are an emerging class of photochromic materials which offer new opportunities for the development of optical data recording and storage. This work reports two diarylethene-based conjugated polymer networks DPP-1 and DPP-2 constructed by Schiff-base polymerization of two-connected photochromic unit 1,2-bis(5-formyl-2-methylthiophen-3-yl)perfluorocyclopentene (DEA-CHO) and tetrahedral four-connected unit tetra(p-aminophenyl)methane (TAPM) or plane three-connected unit 1,3,5-tris(4-aminophenyl)triazine (TAPT). The molecular structures of DPP-1 and DPP-2 were characterized by FT-IR and ¹³C CP-MAS solid state NMR spectroscopy, and the morphology was investigated through scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The model compound was used to indicate the possibility of constructing DPP-1 and DPP-2. DPP-1 and DPP-2 exhibited high chemical stability in the presence of strong acid (6 M HCl) and strong base (6 M NaOH) for 5 days. DPP-1 and DPP-2 showed ultrafast photochromic transformation between the open form (yellow) and closed form (green) with alternate irradiation of ultraviolet and visible light in 50 seconds, which were measured through UV-vis-NIR experiments. X-ray photoelectron spectroscopy (XPS) demonstrated that the electronic arrangement around the sulfur atoms changed during the process of the open form to the closed form. Moreover, DPP-1 and DPP-2 displayed excellent fatigue resistance that the absorbance only lost ca. 5% after three cycles. DPP-1/PMMA and DPP-2/PMMA films fabricated by dispersing diarylethene-based conjugated polymer networks in the poly(methyl methacrylate) (PMMA) matrix also exhibited great photochromic reversibility and fatigue resistance, which provide potential applications towards the development of optical rewritable patterning and information storage devices.

Full text of DOI:10.1039/c9nj02596k

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Received 00th January
20xx,
Diarylethene-based conjugated polymer networks for ultrafast
photochromic films
Qiu-Ting Fu,‡a Xiaodong Yan,‡a Tao Li,a Xin-Yue Zhang,a Yue He,a Wen-Da Zhang,a Yong Liu,a
Yunxing Li,a and Zhi-Guo Gu*a,b
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Diarylethene polymers is an emerging class of photochromic materials which offers new opportunities for the
development of optical data recording and storage. This work reports two diarylethene-based conjugated polymer
networks DPP-1 and DPP-2 constructed by Schiff-base polymerization of two-connected photochromic unit 1,2-bis(5-
formyl-2-methylthiophen-3-yl)perfluorocyclopentene (DEA-CHO) and tetrahedral four-connected unit tetra(p-
aminophenyl)methane (TAPM) or plane three-connected unit 1,3,5-tris(4-aminophenyl) triazine (TAPT). The molecular
structures of DPP-1 and DPP-2 were characterizated by FT-IR and 13C CP-MAS solid state NMR, and the morphology was
investigated through scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Model compound
was used to indicate the possibility of constructing DPP-1 and DPP-2. DPP-1 and DPP-2 exhibited high chemical stability in
the presence of strong acid (6 M HCl) and strong base (6 M NaOH) for 5 days. DPP-1 and DPP-2 showed ultrafast
photochromic transformation between open form (yellow) and closed form (green) with alternate irradiation of ultraviolet
and visible light in 50 seconds, which were measured through UV-vis-NIR experiments. X-ray photoelectron spectroscopy
(XPS) demonstrated the electronic arrangement around the sulfur atoms changed during the process of open form to
closed form. Moreover, DPP-1 and DPP-2 displayed excellent fatigue resistance that the absorbance only lost ca. 5% after
three cycles. DPP-1/PMMA and DPP-2/PMMA films fabricated by dispersing diarylethene-based conjugated polymer
networks in poly(methyl methacrylate) (PMMA) matrix also exhibited great photochromic reversibility and fatigue
resistance, which provide potential applications towards the development of optical rewritable patterning and information
storage devices.
Diarylethenes (DEAs) could reversibly transform between two
thermally stable isomers of open-ring form and closed-ring
form with colour change upon light irradiation. DEAs are
competitive candidates for industrial applications owing to
their rapid response towards light, high photoisomerization
efficiency, and good fatigue resistance.11
Introduction
The past decades have witnessed the rapid development of
photochromic materials, which have potential applications in a
wide range of fields, such as optical memory,1 optical
information storage,2 optoelectronic devices,3 molecular
switches4 and biological systems.5 Organic photochromic
molecules, which can reversibly transform between two
isomers upon light irradiation, usually contain photochromic
functional units such as azobenzene,6 spiropyran,7
furylfulgide,8 diarylethenes9 and so on. Among them, the
photogenerated isomers of azobenzene and spiropyran are
thermally unstable, limiting their practical applications.10
DEA-based polymers have garnered increasing interest due
to their good optical properties and flexibility in design.12
Photochromic polymers are always required to be in the solid
state when applied as optical materials. However, most of the
current DEA-based photochromic polymers are concentrated
on solution state systems and few are involved in solid state
systems.13 Therefore, it is of high significance to develop DEA-
based conjugated polymers and investigate their
photochromic properties in solid state and especially in films.
Inspired by the design strategies of covalent organic
frameworks (COFs),14 we tend to construct DEA-based
conjugated polymer networks through aldehyde amine
condensation reactions. The long-range π-conjugated
structures are connected by DEA-based dialdehyde and
polyamine. The DEA-based conjugated polymer networks
possess following advantages. Firstly, the π-conjugated
skeleton enhances chemical and thermal stability of the
a. Key Laboratory of Synthetic and Biological Colloids, Ministry of Education, School
of Chemical and Material Engineering, Jiangnan University, Wuxi 214122, China
b. International Joint Research Center for Photoresponsive Molecules and Materials,
School of Chemical and Material Engineering, Jiangnan University, Wuxi 214122,
China
† Electronic Supplementary Information (ESI) available: Additional experimental
figures, general characterizations, and X-ray crystallographic data. CCDC: 1912117-
1912118. For ESI and crystallographic data in CIF or other electronic format. See
DOI: 10.1039/x0xx00000x.
‡These authors contributed equally to this work.
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298 K using standard Varian or Bruker software, and chemical
DOI: 10.1039/C9NJ02596K
shifts were reported in parts per milion (ppm) downfield from
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tetramethylsilane. Solid-state 13C cross polarization magic
angle spinning nuclear magnetic resonance (CP/MAS NMR)
measurements were performed on a Bruker Avance III 500
spectrometer. Element analyses were conducted on elementar
corporation vario Micro cube analyzer. Powder X-ray
diffraction (PXRD) patterns were collected on a D8 Advance X-
ray diffractometer (Bruker AXS Germany) with Cu K radiation
in a 2θ range from 5° to 60° at the speed of 2° min-1 at room
temperature. Photoirradiation was carried out at room
temperature using a 200 W mercury-xenon lamp (Moritex
MUV-202) and a visible lamp (> 500 nm, 60 W, TZ-1006) as the
light source. UV-vis-NIR spectra were carried out by using
Shimadzu UV-3600 UV-visible-NIR spectrophotometer with an
integration sphere setup at room temperature. Scanning
electron microscopy (SEM) images were obtained on a Hitachi
S-4800 scanning electron microscope. The samples were
sputter coated with gold prior to the imaging. Transmission
electron microscopy (TEM) images were obtained on a JEOL
model JEM-2100plus transmission electron microscope. The X-
ray photoelectron spectroscopy (XPS) analysis was carried out
by multifunctional imaging electron spectrometer (Thermo
ESCALAB 250XI). The nitrogen sorption isotherms and pore-
size distribution curves were obtained at the temperature of
liquid nitrogen (77 K) by using automatic volumetric
adsorption equipment (Mircomeritics, ASAP2010). Thermal
gravimetric analysis (TGA) measurement was performed on a
TGA/1100SF thermo grabinetric analyzer with a temperature
range of 40-800 °C. The crystal structure was determined on a
Siemens (Bruker) SMART CCD diffractometer using
monochromated Mo K radiation ( = 0.71073 Å). Cell
parameters were retrieved using SMART software and refined
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Scheme 1. Illustration of the synthesis of DPP-1 and DPP-2 by Schiff-base
polycondensation reaction.
photochromic polymers. Secondly, the well-distributed
photochromic units in the polymer networks allow fast
electronic dynamics and improve photochromic effciency.15
Thirdly, the conjugated polymer networks enable the DEA to
switch easily between open and closed forms which improve
the fatigue resistance.
In this paper, DEA-based dialdehyde was chosen as
photochromic unit, and conjugated polyamine tetra(p-
aminophenyl)methane (TAPM) or triazine (TAPT) was selected
as one of the building blocks. DEA-based conjugated
photochromic polymers DPP-1 and DPP-2 were constructed using SAINT16a on all observed reflections. The highly
through [4 + 2] or [3 + 2] imine condensation of 1,2-bis(5-
formyl-2-methylthiophen-3-yl)perfluorocyclopentene (DEA-
CHO) and TAPM or TAPT, respectively (Scheme 1).
Furthermore, poly(methyl methacrylate) (PMMA) was used to
fabricate DPP-1/PMMA and DPP-2/PMMA films, and their
photochemical transitions between open isomers and closed
isomers were investigated by the UV-vis-NIR spectrometer.
redundant data sets were reduced using SAINT16a and
corrected for Lorentz and polarization effects. Absorption
corrections were applied using SADABS16b supplied by Bruker.
Structure was solved by direct methods using the program
SHELXL-9716c. All of the non-hydrogen atoms were refined with
anisotropic thermal displacement coefficients. Hydrogen
atoms were located geometrically and refined in a riding
model.
Experimental section
Materials and measurements
Synthesis
of
1,2-bis(5-formyl-2-methylthiophen-3-
yl)perfluorocyclopentene (DEA-CHO). DEA-CHO was prepared
according to the reported method with slight modifications,
and the synthesis route was shown in Scheme 2. In a 100 mL
round-bottom flask equipped with a stir bar, p-toluenesulfonic
acid (0.4 g), 3-bromo-2-methyl-5-thiophenecarboxyaldehyde
(4.1 g, 20 mmol), neopentylglycol (2.5 g, 24 mmol) and 35 mL
of benzene were added. Under vigorous stirring, the reactants
were refluxed for 5 h. Then, the mixture was cooled to room
temperature, washed with aqueous sodium bicarbonate (3 ×
20 mL), dried by anhydrous MgSO4, filtered and distilled under
vacuum. The yellow solid product was recrystallized from
Reagent grade tetra(p-aminophenyl)methane (TAPM), 1,3,5-
tris(4-aminophenyl)
triazine
(TAPT),
4-
(triphenylmethyl)benzenamine and PMMA were purchased
from commercial sources and used without further
purification. The Fourier transform infrared (FT-IR) spectra
were recorded on a NICOLET 6700 FT-IR spectrometer. The
liquid Chromatograph Mass Spectrometer (LC-MS) analysis
was conducted on a MALDI SYNAPT MS instrument. NMR
spectra were recorded on AVANCE III (400 MHz) instrument at
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Scheme 2. Synthesis of DEA-CHO.
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hexane and collected as an intermediate product acetal A with temperature. Yellow rectangular crystals were obtained within
a yield of 86 %.
5 days by slow evaporation in the dark. FT-IR (KBr, cm-1): 1618,
Dry ice and acetone mixture were used to maintain the 1594, 1490, 1442, 1336, 1267, 1105, 1045, 985, 742, 700, 628.
ether solution (20 mL) containing the acetal A (1.17 g, 4 mmol) UV-vis (CH3OH) λmax: 622 nm. 1H NMR (400 MHz, CD2Cl2, δ
at -78 °C under a nitrogen atmosphere. Then n-butyllithium ppm): 8.51, 7.28, 7.11, 2.04; 13C NMR (100 MHz, CD2Cl2, δ
(1.6 M in hexane, 2.63 mL, 4.2 mmol) was added to trigger the ppm): 15.1, 53.4, 64.8, 114.7, 120.2, 126.1, 127.6, 131.1, 132.0,
reaction. After 3 h, perfluorocyclopentene (0.25 mL, 2 mmol) 141.5, 145.3, 146.7, 148.4, 151.4. MS (EI) m/z = 1060.3 M+. (Fig.
was added to the solution. The mixture then was stirred for 2 h S5-7).
at -78 °C and returned to room temperature. Another 2 h later,
diethyl ether was added into the reaction solution to dilute it,
Synthesis of DPP-1. A customized cleaned glass tube
charged with 17 mg (0.04 mmol) of DEA-CHO, 7.6 mg (0.02
and the resulting mixture was washed with dilute hydrochloric
mmol) of tetra(p-aminophenyl)methane (TAPM), 1.67 mL of
acid (1%, v/v, 3 × 20 mL), saturated aqueous sodium
mesitylene and 0.33 mL of dioxane was sonicated for 10 min,
bicarbonate (5 × 20 mL), and deionized water (3 × 20 mL),
then 0.2 mL of 3 M aqueous acetic acid was added. The
extracted with diethyl ether (2 × 20 mL), dried with MgSO4 and
mixture was ultrasonicated for 5 min to obtain a homogeneous
filtered. The solvent then was removed by rotary evaporation,
mixture. For the purpose of creating a high temperature and
followed by drying under vacuum to achieve a yellow-brown
high pressure environment, the glass tube was degassed
syrup. Diacetal B (0.81 g, 68 %) was obtained by column
through three sequential freeze-pump-thaw technique cycles
chromatography over silica gel using dichloromethane and
and sealed under frame. The sealed tube was placed in an
oven, which was slowly heated to 120 °C at a ramp rate of 40
hexane mixture (3:1) as an eluent.
Tetrahydrofuran (THF, 110 mL), water (30 mL) and diacetal B
°C h−1 and kept at 120 °C for 5 days. Finally, a light yellow
(0.596 g, 1 mmol) were added into a 250 mL round-bottom
precipitate was achieved through filtering, washing with
flask with a stir bar. Then, trifluoacetic acid (TFA, 23 mL) was
dimethyl formamide (DMF) (3 × 30 mL), and extracting by THF
added. The mixture was stirred for
1 hour at room
(200 mL) in a soxhlet extractor for 24 h. The product DPP-1
was finally dried at 80 °C under vacuum for 12 h with a yield of
71%. FT-IR (KBr, cm-1): 3028, 2866, 1616, 1510, 1340, 1270,
1136, 1045. 13C NMR (100 MHz, δ ppm): 14.4, 64.0, 117.5,
129.8, 133.1, 145.7, 169.5. Anal. Calcld (%) for C59H32F12N4S4: C,
61.40; H, 2.78; N, 4.86; Found: C, 61.36; H, 3.04; N, 4.96.
temperature, and then quenched with saturated aqueous
sodium bicarbonate. The organic layer was extracted with
ether (3 × 25 mL), washed with aqueous sodium bicarbonate
(2%, v/v), dried with Na2SO4, and dried under vacuum to
obtain a yellow thick liquid. The product was purified by
column chromatography on silica gel (eluent: dichloromethane
and hexane =3:1) to afford DEA-CHO with a yield of 66%.
Yellow transparent cube crystals suitable for X-ray analysis
were grown on the tube wall after one week by slow
evaporation in the dark. FT-IR (KBr, cm-1): 3107, 2838, 1668,
Synthesis of DPP-2. DEA-CHO (25.5 mg, 0.06 mmol), 1,3,5-
tris(4-aminophenyl) triazine (TAPT) (14.2 mg, 0.04 mmol) and
p-toluenesulfonic acid (22.8 mg, 0.12 mmol) dissolved in a
solution of 0.5 mL of o-dichlorobenzene and 1.5 mL of ethyl
alcohol were used as the starting materials. DPP-2 was
prepared using similar synthesis procedures to those used for
synthesizing DPP-1. DPP-2 was obtained as a yellow powder
with a yield of 74%. FT-IR (KBr, cm-1): 3068, 2968, 1619, 1510,
1357, 1269, 1136, 1047. 13C NMR (100 MHz, δ ppm): 14.1,
110.0, 114.3, 118.0, 126.3, 133.9, 143.3, 147.6, 152.8, 169.5.
Anal. Calcld (%) for C93H48F18N12S6: C, 59.75; H, 2.57; N, 8.99;
Found: C, 59.92; H, 2.86; N, 8.74.
1
1276, 1125. UV-vis (CH3OH) λmax: 531 nm. H NMR (400 MHz,
CDCl3, δ ppm): 2.05 (s, 6H), 7.76 (s, 2H), and 9.87 (s, 2H); 13C
NMR (100 MHz, CDCl3, δ ppm): 15.4, 110.8, 125.9, 135.7,
142.2, 151.6, 181.9. MS (EI) m/z = 425.3 M+. (Fig. S1-3)
Synthesis of model compound (MC). DEA-CHO (0.255 g, 0.6
mmol), 4-(triphenylmethyl)benzenamine (0.47 g, 1.4 mmol)
and dichloromethane (20 mL) were added into a 50 mL round-
bottom flask equipped with
a magnetic stirrer. After
Fabrication of films. The fabrication process was conducted
in the dark to avoid the isomerization. 100 mg of PMMA was
completely dissolved in 2 mL of chloroform. Then 10 mg of
DPP-1 or DPP-2 was added to the solution. The dissolution of
DPP-1 or DPP-2 was assisted by ultrasonication for 10 min. The
films were made on cleaned quartz glass substrates by spin
completely dissolved, the solution was refluxed for one day at
45 °C under a nitrogen atmosphere. Then the solvent was
removed by virtue of a rotary evaporator and the sample was
dried at 40 °C under vacuum for 3 h to obtain a pale yellow
solid with a yield of 81%. The product was dissolved in a
mixture solvent (CH2Cl2: CH3OH= 1:1) and crystallized at room
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Fig. 1 Molecular structures of (a) DEA-CHO and (b) model compound. Grey: C; red:
O; yellow: S; green: F; blue: N.
Fig. 2 (a) FT-IR spectra of DEA-CHO (black), MC (green), DPP-1 (red) and DPP-2
(blue). (b) 13C CP-MAS NMR spectra of DPP-1 (red), DPP-2 (blue) and MC (black).
coating at a spin speed of 200 rpm, followed by drying in the
dark overnight.
Results and discussion
morphology with a diameter of ~10 μm (Fig. 3b). As shown by
the TEM images, DPP-1 is composed of numerous particles (Fig.
3c), and DPP-2 exists as a whole (Fig. 3d).
DPP-1 was synthesized by Schiff-base condensation reaction
between the photochromic building blocks DEA-CHO and
tetra(p-aminophenyl)methane (TAPM) at 120 °C for 5 days,
while DPP-2 was synthesized with DEA-CHO and 1,3,5-tris(4-
aminophenyl) triazine (TAPT) under the same synthesis
conditions. DPP-1 and DPP-2 were isolated as yellow solids
with a high yield of ca. 70%, and they were insoluble in water
and common organic solvents, such as acetone, ethanol,
hexane, THF, and DMF.
A model compound (MC) was synthesized by the imine
reaction between 4-(triphenylmethyl)aniline and DEA-CHO (Fig.
S4). DEA-CHO and MC have been characterized by single-
crystal X-ray diffraction analysis (Fig. 1). DEA-CHO has two
uncoplanar hiophene rings with a dihedral angle of 65.5°.
Besides, the angle between two aldehyde groups which are
not straight stretched is 111° (Fig. 1a). As for the structure of
MC, two C=N bonds were formed between aniline and
thiophene, and two Schiff-base arms extended along two
direction with an angle of 77° (Fig. 1b). From the two
structures, it is valid to infer that DEA-CHO and polyamines
could be used as precursors to construct high-dimensional
conjugated organic polymer networks.
DPP-1 and DPP-2 were characterized by Fourier transform
infrared (FT-IR) and 13C solid-state NMR spectroscopy. In the
FT-IR spectra, the disappearance of the peak at 1666 cm-1
indicates the complete consumption of the aldehyde while the
presence of peak at 1616 cm-1 suggests the formation of the
new C=N bonds. Furthermore, MC and DPP-1 display similar
FT-IR spectra, indicating that they possess similar structures
(Fig. 2a). This is confirmed by their similar NMR spectra (Fig.
2b). The distinct peaks at 169.5, 126.3 and 13.9 ppm for both
polymers are assigned to the substituted aromatic carbon, the
unsubstituted aromatic carbon and the carbon methyl group
of DEA-CHO thiophene, respectively. The peak at 64.0 ppm for
DPP-1 corresponds to the central C atom of TAPM, while the
peak at 169.8 ppm for DPP-2 corresponds to the C atom on the
triazine. These results prove the formation of the polymer
networks.
The powder X-ray diffraction (PXRD) profile of MC was
consistent with the theoretical values (Fig. S8), showing good
crystallinity. The PXRD profiles of DPP-1 and DPP-2 contained
only one broad peak at 10-25° (Fig. S9), demonstrating their
amorphous nature. Although plenty of attempts and a series of
reaction conditions through controlling the solvents
composition, monomer concentration and reaction
temperature have been done to crystallize DPP-1 and DPP-2,
unfortunately the experiment results were disappointing, and
the products checked by the PXRD all shown amorphous
structure (Table S1).
Nitrogen sorption isotherms were collected to study the
porous structure of the polymers. The Brunauer-Emmett-Teller
(BET) surface areas of DPP-1 and DPP-2 are 31.23 and 26.21
m2 g−1, respectively (Fig. S10). This is consistent with the SEM
and TEM observation that DPP-1 and DPP-2 are nonporous.
According to the structure of MC, the small dihedral angle
(about 70°) between two imine arms and multiple times of
interpenetration in polymer structures impelled the irregular
(b)
(a)
(c)
(d)
The scanning electron microscopy (SEM) and transmission
electron microscopy (TEM) were used to characterize the
morphology. DPP-1 exists in the form of irregular sphere of ~5
μm in diameter (Fig. 3a), while DPP-2 has good spherical
Fig. 3 SEM images of (a) DPP-1 and (b) DPP-2. TEM images of (c) DPP-1 and (d)
DPP-2.
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that DPP-1 and DPP-2 both have good thermal stability. The
chemical stability was assessed by submerging 15 mg of DPP-1
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DOI: 10.1039/C9NJ02596K
and DPP-2 in 6 M HCl and NaOH solutions for five days. Their
structures were well maintained as confirmed by the FT-IR
analysis (Fig. S12-S13). The good thermal and chemical stability
of DPP-1 and DPP-2 might be attributed to the highly
conjugated networks with covalent bonds. This feature
enables DPP-1 and DPP-2 to endure various extraction
conditions and lays the foundation for their practical
applications.
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The photochromic properties of DPP-1 and DPP-2 powders
were studied through UV-vis-NIR measurements at room
temperature which were conducted in solid state. Under the
irradiation of 365 nm UV for 50 s, the colour of DPP-1 changed
from pale yellow to grass green (Fig. 4a), while DPP-2 changed
from yellow to olive green (Fig. 4b). In the meantime, the
absorption band appeared at around 656 nm for both
polymers corresponding to the formation of closed form.
Obviously, DPP-1 is much more sensitive in the visible region.
This could be explained as different spatial structures that
DPP-2 tends to form a planar conformation. Therefore, DPP-1
is flexible and could rotate more easily. Upon exposing to
visible light (> 500 nm), the absorption band in the visible
region disappeared within dozens of seconds, indicating that
the polymers underwent reversible photochromism in the
solid state, which was a transition from closed-ring state to
open-ring state. In contrast, the response time for many
polymers based on DEA in solution state to reach its
photostationary state is longer than 120 s upon irradiation.17
The ultrafast photochromic performance could be attributed
to the fairly uniform distributed diarylethene photochromic
groups in the conjugated network structures.
To characterize the fatigue resistance of DPP-1 and DPP-2,
the time-dependent stability test was conducted (Fig. 4c and
4d). After three cycles, the absorption intensity at 656 nm
decreased 10% and 5% for DPP-1 and DPP-2, respectively.
Cycling experiments show that photochromism is reversible for
DPP-1 and DPP-2 although they had a small amount of light
loss and kept basically stable property after three repeated
cycles. Due to some steric resistance inside the polymer
networks, light loss occurred when the polymer switched
between open-ring and closed-ring states.
Fig. 4 Time-dependent UV–vis–NIR absorption spectral changes of (a) DPP-1 and
(b) DPP-2 upon irradiation with 365 nm light. Reversible changes of absorbance at
656 nm of (c) DPP-1 and (d) DPP-2 during alternating irradiation with UV and
visible light irradiation. Reversible photoisomerization of (e) DPP-1, (f) DPP-2. High
resolution XPS spectra of DPP-1 for the S (2p) region before (g) and after (h) UV
irradiation at 365 nm for 5 min.
Fig. 4e and 4f show the reversible photoisomerization
structural changes of DPP-1 and DPP-2 under UV and visible
light. Before UV irradiation, the two thiophene rings were not
looped on either side of the olefin and they were connected to
form a larger extended conjugation structure by exposing to
UV irradiation. During the process of open form to closed form,
the electronic arrangement around the sulfur atoms changed
with the binding energies variation, which could be monitored
by X-ray photoelectron spectroscopy (XPS). The XPS spectra of
DPP-1 in the S (2p) region before and after UV irradiation at
365 nm and least-squares best fit analysis of the peaks were
arrangement and tight stack of DPP-1 and DPP-2 networks,
leading to the small surface area. Furthermore, the amorphous
structure is relatively elastic, making it difficult to measure
their micropore surface area.
The thermal and chemical stability of the polymers were
investigated. The thermogravimetric diagram conveys the
message that DPP-1 has a slight weight loss of 3.7 % from 40
to 150 °C, corresponding to the loss of adsorbed water, and no
considerable weight loss from 150 to 350 °C (Fig. S11a).
Meanwhile, DPP-2 has a 2.3 % weight loss from 40 to 150 °C
and is stable up to 300 °C (Fig. S11b). The TGA analysis reveals
recorded. The
S (2p) spectra of the open form was
characterized by a doublet with the S (2p3/2) component at a
binding energy about 164.1 eV while the doublet at 163.4 eV
assigned to the closed form,18 both doublet with an intensity
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could be reversed upon irradiation of vViisewibAlerticlelOignhlinte.
Photochromic cycling experiments werDeOIp: e10r.f1o0r3m9/eCd9NJo0n25t9h6eK
films. After three cycles, the intensity of the band lost 7% and
5% relative to the initial values of DPP-1/PMMA (Fig. 5e) and
DPP-2/PMMA (Fig. 5f) films, respectively.
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In summary, two thermally and chemically stable
photochromic conjugated polymer networks DPP-1 and DPP-2
were constructed through the aldehyde amine polymerization.
DPP-1 and DPP-2 powders and films have a sensitive
photochromic response towards ultraviolet and visible light. It
is thus concluded that introducing photochromic groups into
the conjugated networks is a feasible and novel strategy for
the development of photochromic polymers. Further practical
applications of optical devices based on DEA-based conjugated
polymers are ongoing in our laboratory.
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (21771089), the Fundamental Research
Funds for the Central Universities (JUSRP51725B, JUSRP 21936,
and JUSRP11930), the project for Jiangsu scientific and
technological innovation team, and MOE & SAFEA for the 111
Project (B13025).
Fig. 5 Optical photographs of photochromic reaction of (a) DPP-1, (b) DPP-2 PMMA
films. Time-dependent UV-vis-NIR absorption spectral changes of (c) DPP-1 and (d)
DPP-2 PMMA films upon irradiation with 365 nm light. Reversible changes of
absorbance at 656 nm of (e) DPP-1 and (f) DPP-2 PMMA films during alternating
irradiation under UV and visible light irradiation.
Notes and references
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To explore the potential applications of DPP-1 and DPP-2,
DPP-1/PMMA and DPP-2/PMMA films were prepared on
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View Article Online
DOI: 10.1039/C9NJ02596K
Graphic abstract
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Diarylethene-based conjugated polymer networks for ultrafast
photochromic films
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Qiu-Ting Fu,‡a Xiaodong Yan,‡a Tao Li,a Xin-Yue Zhang,a Yue He,a Wen-Da Zhang,a
Yong Liu,a Yunxing Li,a and Zhi-Guo Gu*a,b
Synopsis
Two new diarylethene-based conjugated polymers were synthesized, and their films
exhibited ultrafast photochromism properties and excellent fatigue resistance.