Synthesis and properties of photochromic spirooxazine with aggregation-induced emission fluorophores polymeric nanoparticles

Article abstract of DOI:10.1016/j.dyepig.2017.03.068

We designed and synthesized photochromic fluorescent poly (MMA-co-SPO-co-TPE) nanoparticles with pendant spirooxazine (SPO) dye and tetraphenylethylene (TPE) fuorophores attached to poly (methyl methacrylate) (MMA) backbone by semi-continuous polymerizati

Full text of DOI:10.1016/j.dyepig.2017.03.068

Accepted Manuscript
Synthesis and properties of photochromic spirooxazine with aggregation-induced
emission fluorophores polymeric nanoparticles
Xue Li, Chengpeng Li, Sheng Wang, Huan Dong, Xiang Ma, Derong Cao
PII:
S0143-7208(17)30311-X
10.1016/j.dyepig.2017.03.068
DYPI 5906
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 16 February 2017
Revised Date: 13 March 2017
Accepted Date: 18 March 2017
Please cite this article as: Li X, Li C, Wang S, Dong H, Ma X, Cao D, Synthesis and properties of
photochromic spirooxazine with aggregation-induced emission fluorophores polymeric nanoparticles,
Dyes and Pigments (2017), doi: 10.1016/j.dyepig.2017.03.068.
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ACCEPTED MANUSCRIPT
Synthesis and Properties of Photochromic Spirooxazine with
Aggregation-Induce Emission Fluorophores polymeric nanoparticles
a,b
b
a,b,
c
c,
Xue Li , Chengpeng Li , Sheng Wang *, Huan Dong , Xiang Ma **, Derong
a,
Cao **
a
School of Chemistry and Chemical Engineering, State Key Laboratory of
Luminescent Materials and Devices, South China University of Technology,
Guangzhou 510641, China
b
School of Chemistry and Chemical Engineering, Development Center for New
Materials Engineering & Technology in Universities of Guangdong, Lingnan Normal
University, Zhanjiang 524048, China
c
Key Laboratory for Advanced Materials and Institute of Fine Chemicals, East
China University of Science and Technology
Meilong Road 130, Shanghai, 200237, P. R. China
*
Corresponding author: Prof. Dr. Sheng Wang, School of Chemistry & Chemical
Engineering, Lingnan Normal University, Zhanjiang 524048, P.R. China; Tel:
+86-759-318-2515; Fax: +86-759-318-3510; E-mail: dyesws@126.com;
Prof. Dr. Derong Cao, State Key Laboratory of Luminescent Materials and
Devices, South China University of Technology, Guangzhou 510641, P.R. China; Tel:
+
86-020-8711-0245; Fax: +86-020-8711-0245; E-mail: drcao@scut.edu.cn;
Prof. Dr. Xiang Ma, Key Laboratory for Advanced Materials and Institute of
Fine Chemicals, East China University of Science and Technology
Meilong Road 130, Shanghai, 200237, P. R. China; Tel: +86-21-64252288, Fax:
+86-21-64252288; E-mail: maxiang@ecust.edu.cn
1

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Abstract: We designed and synthesized photochromic fluorescent poly
MMA-co-SPO-co-TPE) nanoparticles with pendant spirooxazine (SPO) dye and
(
tetraphenylethylene (TPE) fuorophores attached to poly (methyl methacrylate) (MMA)
backbone by semi-continuous polymerization. The polymerization reactions were
accomplished in water with randomly methylated-β-cyclodextrin (β-CD) at 80ꢀ in
the presence of potassium peroxodisulfate which can be used as free radical initiator.
This new synthetic method leads to uniform and smooth nanoparticles with a narrow
particle size distribution. In addition, the poly (MMA-co-SPO-co-TPE) nanoparticles
exhibit aggregation induced emission (AIE) properties and excellent photochemical
properties because of spirooxazine dyes convert reversibly to merocyanine form upon
ultraviolet (UV) irradiation, which active the intramolecular energy transfer pathway
and quench the fluorescence of TPE in polymers. Consequently, the fluorescence of
the poly (MMA-co-SPO-co-TPE) nanoparticles can be reversibly switched “on” and
“off” upon UV and visible light, which maybe have potential application in biological
fluorescent labeling as well as in optical fields like individually light–addressable
nanoscale devices.
Keywords: spirooxazine dye; photochromism; polymeric nanoparticles;
aggregation-induced emission; tetraphenylethylene derivative.
2

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1
. Introduction
Photochromic compounds display
a
reversible molecular structure
transformation, which result in significant absorption spectra change upon the
stimulation of ultraviolet (UV) and visible light.[1, 2] The special optical property
makes them have high potential application in optical data storage, chemical sensors,
optical switches, ophthalmic lenses, security documents.[3-7] Among a broad variety
of photochromic compounds, spirooxazines have received considerable attention
because of their fast response speed and good fatigue resistant.[8-10]
Photochromic molecules can be engineered to control the emission of
fluorephore-photochrome dyads by energy transefer that caused by reversible
photoinduced transformation.[11-18] So far, a number of photoswitchable fluorescent
polymers containing spirooxazine have been reported[19-23] and their development
have been extended micrometer/nanometersized level.[24] Photoswitchable
fluorescent nanoparticles (PFNs) has been widely studied because of their potential
biological application, such as ultrahigh-resolution imaging,[25] two photon
imaging.[26] Many strategies have been developed to prepare PFNs, such as
precipitation, self-assemble method, and emulsion polymerization. However, the
self-assembly strategy maybe involves a complicated synthesis and the precipitation
strategy often obtained PFNs via doping fluorescence dyes with photochromic
molecules or polymer, which will lead to the leakage and aggregation of dyes over
time.[27-29] In order to overcome these defects, semi-continuous emulsion
polymerization, a facile and simple route was adopted.
3

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Photoswitchable fluororescent materials are often utilized in their solid states,
however, most of the luminophores will lead to aggregation-caused quenching (ACQ).
Fortunately, Tang group[30] firstly discovered a new type of fluorescent molecular
with Aggregation-induced emission. The AIE effect is opposite to the ACQ effect,[31]
which makes it more valuable in practical application. In fact, the studies of polymers
exhibit photochromic fluorescent properties and AIE properties are rarely reported.
Here, we utilized photochromic molecules spirooxazine (SPO) derivative and the
typical AIE molecule tetraphenylethylene (TPE ) derivative to prepare a series of
polymeric nanoparticles with AIE and photochromic properties via semi-continuous
emulsion polymerization. The fluorescence of the polymer nanoparticle can be
switched “on” and “off” with UV and visible light.
2.Experimental
2.1 Materials and instruments
Potassium persulfate (KPS, 99%, Aladdin) was recrystallized from deionized
water three times and dried under vacuum. Methyl methacrylate (MMA, 99.5%,
Aladdin) was washed five times with 5% sodium hydroxide solution to remove the
phenolic inhibitor and then washed with deionized water until the pH was 7. In
addition, it was further purified upon distillation under reduced pressure and keep
refrigerated for later experiment. Methylated-β-cyclodextrin, bromotriphenylethylene,
2
-bromoethanol, methacryloylchloride, tetrabutylammonium bromide, tetrakis
triphenylphosphine) palladium (0) were purchased from Aladdin company. 2,
-dihydroxynaphthalen, 3-trimethyl-2-methyleneindoline,
(
7
1
ꢁ
3
ꢁ
4

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4
-formylphenylboromic, allyl cyanoacetate were purchased from TCI company.
Tetrahydrofuran (THF, A.R) was distilled over CaH . Deionized water was used for
2
all experiments. Other solvents were analytical pure and without any further drying or
purification.
Molecular weight of the polymers were obtained by using gel permeation
1
chromatography (GPC). H NMR spectra were obtained by a Bruker Avance 400
NMR spectrometerꢂUV-Vis spectra were carried out on Agilent 8453 UV-visible
spectroscopy systemꢂFluorescence spectra were measured by Agilent Cary Eclipse
Fluorescence Spectrophotometer. The polymeric nanoparticles diameter distribution
and morphology was determined by Zetasizer Nano-ZS MPT and Hitachi S-4800
scanning electron microscope (SEM).
2.2 Synthesis of compound 4:
Intermediate 3 was prepared according to the literature procedure,[32] the
preparation method of spirooxazine derivative 4 was follow: adding 3 (1.07 g, 3.1
mmol), anhydrous K CO (1.28 g, 9.3 mmol), 2-bromoethyl methacrylate (1.8 g, 9.3
2
3
mmol) and KI (0.515 g, 3.1 mmol) in 50 mL DMF, and the mixture was stirred for
o
4
8h at 85 C. Then dropping them into ice water and filtered. The precipitate was
dissolved into ethyl acetate and washed with water three times. The organic phase was
dried over anhydrous magnesium sulfate. The purified product was obtained by
column chromatography with petroleum ether/ethyl acetate (v/v=10/1) as eluent,
1
white solid (0.6 g, 42% yield). H NMR (400 MHz, CDCl ) δ 7.93 (s, 1H), 7.75 (s,
3
1
H), 7.68 (d, J = 8.9 Hz, 1H), 7.61 (d, J = 8.7, 1H), 7.32-7.21 (m, 1H), 7.11 (t, J = 7.1
5

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Hz, 2H), 6.99-6.84 (m, 2H), 6.61 (d, J = 7.7 Hz, 1H), 6.22 (s, 1H), 5.63 (s, 1H), 4.63
(t, J = 4.7 Hz, 2H), 4.49 (t, J = 4.7 Hz, 2H), 2.80 (s, 3H), 2.01 (s, 3H), 1.39 (t, J = 3.6
1
3
Hz, 6H). C NMR (101 MHz, CDCl3) δ 167.39, 157.88, 150.35, 147.62, 144.91,
36.05, 135.88, 132.28, 129.97, 129.58, 128.04, 126.10, 124.81, 122.41, 121.51,
19.86, 117.10, 114.30, 107.15, 100.68, 98.59, 66.00, 63.16, 51.81, 29.66, 25.47,
20.82, 18.38.
1
1
2
.3 Synthesis of compound 6
.3.1 Synthesis of 4-(1, 2, 2-triphenylvinyl)benzaldehyde 5
2
Bromotriphenylethylene (3.35 g, 0.01 mol), 4-formylphenylboronicacid (2.25 g,
.015 mol), 60mL toluene, anhydrous K CO (4.9 8g, 0.036 mol), TBAB (0.3 g, 0.01
0
2
3
mol) were added to 100mL three-necked, round-bottomed flask in order. The mixtrue
stirred at room temperature under nitrogen atmosphere for 30min. Then, Pd(pph3)4
o
was added to the flask and the solution was heated to 90 C over 24h. The mixture
solution was extracted with dichloromethane and the extract was dried with
anhydrous magnesium sulfate. Further purification was accomplished by silica gel
column chromatography with petroleum ether/ethyl acetate (v/v=20/1) as eluent,
yellow solid (3.16 g, 87.8% yield).
2.3.2 Synthesis of allyl 2-cyano-3-(4-(1, 2, 2-triphenylvinyl) acrylate 6
5
(1.08 g, 3 mmol), allylcyanoacetate (1.13 g, 9 mmol), NH OH (0.7 g, 9 mmol),
4
ACOH 15mL were reflux for 24h in 50mL of toluene. The mixture solution was
extracted with dichloromethane and the extract was washed three times with water,
than dried with anhydrous magnesium sulfate. The purified product was obtained by
6

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column chromatography with petroleum ether/ethyl acetate (v/v=30/1) as eluent,
1
yellow solid (2 g, 90% yield). H NMR (400 MHz, CDCl ) δ 8.17 (s, 1H), 7.78 (d, J =
3
8
.2 Hz, 2H), 7.17 (dd, J = 9.3, 5.4 Hz, 12H), 7.06 (d, J = 7.1 Hz, 6H), 6.01 (m, J =
6.4, 10.8, 5.6 Hz, 1H), 5.45 (d, J = 17.1 Hz, 1H), 5.34 (d, J = 10.4 Hz, 1H), 4.82 (d,
1
1
3
J = 5.5 Hz, 2H). C NMR (101 MHz, CDCl3) δ 162.46, 154.86, 149.82, 143.40,
143.02, 142.95, 142.81, 139.62, 132.22, 131.39, 131.33, 131.30, 131.25, 131.13,
130.75, 129.32, 128.01, 127.99, 127.74, 127.23, 126.94, 119.19, 115.64, 101.42,
66.90.
2.4 Preparation of the poly (MMA-co-SPO-co-TPE) nanoparticles:
10mL water and methylated β-cyclodextrin (β-CD) was added into 50mL flask
equipped with magnetic stirring bars. The solution was heated to 80ꢀ and deaerated
by bubbling with nitrogen for 10min.Then KPS was added and the solution was
heated under stirring for 30min. The spirooxazine compound 4 (SPO),
tetraphenylethylene (TPE) compound 6 were dissolved in MMA and added dropwise
via syringes over a period of 2h to the stirred solution at 80ꢀ. After the addition of
the monomers were completed, the reaction solution were heated at 85ꢀ for another
five hours.
Scheme.1
Table.1
Fig.1
3. Result and discussion:
3.1 Synthesis
7

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The synthetic route of the monomers spirooxazine compound 4 (SPO),
tetraphenylethylene (TPE) compound 6 were presented in Scheme.1, and the
preparation of polymer nanoparticles was shown in Fig. 1. The copolymers were
consisted of three parts: photochrome, fluorogen and connection chains MMA, all the
chemicals and their amounts were listed in Table 1. Among them, the photochrome act
as energy receptor and the fluorogen act as energy donor, thereby the fluorescence of
the polymer can be modulated by the energy transfer. In order to synthesize
photochromic polymeric nanoparticles, we firstly prepared the photochromic
spirooxazine nanoparticles with aggregation-induced emission by semi-continuous
emulsion polymerization. In this preparation, MMA, TPE 6 and SPO 4 act as
copolymerization monomers, KPS act as the initiator, β-CD is a ring moleculer
consisting of a hydrophobic cavity and hydrophilic out side. This structure made it be
able to form host-guest compounds with hydrophobic molecules, the formation
complexs will increase the solubility of guest moleculer in aquese solution
considerably.[33, 34] When the monomers were added to the β-CD aqueous solution
semicontinuously, the concentration ratio of β-CD/monomers was kept in a high level,
which enables fast complexation, and the complexes would become
polymerizationsites. The β-CD plays an important role in increasing the rates of
monomers conversation and polymerization in emulsion polymerization. In addition,
due to the presence of β-CD in all steps only homogeneous nucleation occurs, which
was contributes to the formation of stable uniform colloidal particles with a narrow
8

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PSD.[35, 36] The structures of products were confirmed by NMR, IR spectroscopy
and mass spectrometry.
3.2 Size and morphological of the poly (MMA-co-SPO-co-TPE) nanoparticles
Paticle size and size distribution of P1 to P4 were obtained by dynamic light
scattering (DLS) analysis and shown in Fig. 2. Their size increased from 355 nm to
6
57 nm with the increased in SPO monomer ratio. Morphology was determined by
scanning electron microscopy and displayed in Fig. 3. The results indicated that all
the samples were smooth and uniform. Fig. 4a and Fig.4b showed the images of P2
under general microscope and fluorescence microscope, respectively. The fluorescent
photo illustrated that the AIE fluorophore was incorporated to the nanoparticles
successfully. We can believe that the semi-continous emulsion polymerization is an
appropriate method to preparation nanoparticle polymer.
Fig.2
Fig.3
Fig.4
3.3 Thermal properties of the poly (MMA-co-SPO-co-TPE) nanoparticles
Thermal properties of the four polymers were evaluated by thermogravimetric
analysis (TGA). The decomposition temperature (T ) of these polymers
d
(corresponding to 5% weight loss occurs during heating in nitrogen) were 284.7� ,
2
87.02� , 276.05� , 280.72� , respectively (Fig. 5). The results indicate that the
polymers have a relatively high thermal stability, to the best of our knowledge, a
relatively high T is crucial for emissive materials used for optoelectronic applications.
d
9

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Hence, the synthesized polymers might be used as potential meterials for applications
in fabricated photoelectric devices.
Fig.5
3.4 Photochromism of spirooxazine 4 and AIE properties of the compound 6
Fig. 6 showed the absorption spectra and color change of spirooxazine (SPO) 4
-5
-1
in DMF (2.0×10 mol L ) irradiation with UV and visible light. Before irradiation
with UV light, the spirooxazine (SPO) 4 in DMF solution was colorless and has no
absorbance at about 600 nm. By UV irradiation (365 nm), the sample become blue
and with an increased absorbance intensity at 602 nm, when it was left in the dark or
irradiated with visible light at ambient temperature, the color was fading and the
absorbance was decreased again. The reason is that the structure of spirooxazine (SPO)
4
change from orthogonal closed cycle to opened merocyanine form. The opened
form is usually thermally unstable and spontaneously underwent thermal bleaching to
the close cycle form.
The corresponding emission spectra of the compound 6 in water/DMF mixtures
with different water fraction (f ) are shown in Fig. 7a. As can be seen from the figure,
w
the PL signals of compound 6 in a dilute solution of DMF almost couldn’t be detected
and the luminescence intensity almost unchanged when f was increased to 60%.
w
However, a dramatic enhancement in luminescence was occured when f was beyond
w
6
0%, and it boosted to 530.7 a.u. at the water fraction of 90% while the highest PL
intensity value was measured only about 3.1 a.u. in pure DMF, the maximum increase
in the emission intensity is∼170-fold. Because there is not so solvable for compound
1
0

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6
in water, the molecular become aggeregation formation in the mixtures with higher
water content. Hence, the PL intensity was enhanced remarkably by restricted
intramolecular rotations (RIR) process in the crowed invironment. The absorption
spectra of compound 6 in the DMF/water mixtures were shown in Fig. 7b. The spectra
were significant changed when water fraction was up to 70% or higher. Fig. 7c
showed the images of the compound 6 were taken under room light (top) and 365 nm
UV light (bottom) at room temperature in DMF/water mixtures with different water
fractions.
Fig.6
Fig.7
3.5 Photochromic properties of the poly (MMA-co-SPO-co-TPE) nanoparticles
The spectra changes of polymers (P1, P2, P3, P4) in DMF solution (2.5mg/mL)
upon UV and visible light irradiation were shown in Fig. 8. With the irradiation of UV
light (365 nm) at room temperature, a new absorption band with λmax= 605 nm was
observed and the solution was changed from colorless to blue, corresponding to the
generation of the opened merocyanine form in SPO units. In addition, these studies
also revealed that the absorption intensity increased with the increase of SPO/TPE
ratio. Fig.9a showed the changes in the absorption spectra of P2 in an aqueous
suspension before and after UV illumination. The absorbance band occurs at 525 to
6
75 nm upon UV irradiation, The inset figure showed the color change of P2 latex,
with the irradiation of UV light the latex was turned to blue from milk white. The
absorption spectra change of P2 in film was shown in Fig. 9b. The reversible
1
1

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bleaching process of film was similar to that in the DMF solution. After the irradiation
of UV light an absorption peak appeared at 605 nm, then the peak disappeared upon
the irradiation of the visible light. The polymer film has excellent photochromic
fatigue resistance. Because of the steric effects in solid powder, the photochromic
stability of the polymer powder was enhanced significantly than that of in DMF
solution. The inset figure showed the color change of P2 in solid powder.
Fig.8
Fig.9
3.6 AIE Properties of the poly (MMA-co-SPO-co-TPE) nanoparticles
We detected the fluorescent emission of all the polymers in a mixture of water
and DMF with different water fractions, and the corresponding emission spectra of P1
and P2 are shown in Fig. 10. The fluorescence intensity change of P1 with the
increasingin water fraction was very different from the monomer TPE, when f was
w
increased to 20%, the PL intensity of the solutions stared increase obviously (Fig.
1
0a). The possible reason was that polymer chains were more hydrophobic and have a
higher tendency to aggregate in a polar medium when compared with the monomer
molecules. So the light emission of P1 significantly enhanced in water fraction as low
as 20% by aggregate formation. The emission intensity reached a maximum with
water fraction upto 30%, then PL intensities decreased with higher water content. As
can be seen from Fig. 10b, when f varies from 0% to 70%, the PL intensity of P2
w
increase gradually, however the f is increased to 80% or higher, the PL intensity
w
decreases with increasing water content. This phenomenon was often observed in
1
2

ACCEPTED MANUSCRIPT
some compounds with AIE properties, but the reasons remain unclear.[37] There are
two possible explanations for this phenomenon: First, according to the aggregation
with the increasing of the water fraction in solvent, only the molecules on the surface
of the nanoparticles emitted light and contributed to the fluorescent intensity upon
excitation, leading to the decrease of the fluorescent intensity; but the restriction of
intramolecular rotations (RIR) of the aromatic rings aroundthe carbon-carbon single
bonds in the aggregation state would enhance light emission. The net outcome of
these two antagonistic processes depends on which process plays a predominant role
in affecting the fluorescent behavior of the aggregated molecules. Second, when water
is added, the solute molecules may aggregate into crystal and amorphous particles.
The former leads to an enhancement in the intensity of photoluminescent emission,
while the latter leads to its reduction. Thus, the measured photoluminescent intensity
often shows no regularity for the uncontrollable formation of the nanoparticles in
solutions with high water content.[38-48]
The inset in Fig. 10 showed that the maximum emission wavelength changes and
fluorescence intensity changes with increasing water fraction, the maximum emission
wavelength had a blue shift. Fluorescence emission spectra of P3 in DMF-H O
2
mixture with different f were demonstrated in the Fig. S9, nearly the same trends
w
were observed in the case of P3, however, the maximum PL intensity is weaker than
P1 and P2. Almost no fluorescence signal was detected for P4 no matter in pure DMF
solution or in water/DMF mixtures. The weaker emission was ascrible the low content
of TPECN unit in P3 or P4. UV absorption spectra of all the polymers with different
1
3

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water fraction were displayed in Fig. S10, they all showed a long-wavelength
absorption tail caused by light-scattering effects in the solution. Fig. 11 showed the
images of the P1 and P2 were taken under room light (top) and 365 nm UV light
(bottom) at room temperature in DMF/water mixtures with different water fractions.
Fig.10
Fig.11
3.7 Photocontrolled fluorescence properties of the poly (MMA-co-SPO-co-TPE)
nanoparticles
The fluorescence intensity changes of the P1 and P2 in DMF-H O mixture
2
solution were described in Fig. 12a and Fig. 12b. The two figures indicated that
fluorescence intensity changes were regulated with the irradiation of UV and visible
light both of P1 and P2. The fluorescence quenching rate of P1 was only about 56%
and the fluorescence quenching rate of P2 was about 70% upon irradiation with UV,
which instructed that the fluorescence quenching rate of the polymer may be
adjusted by changing the ratio of SPO and TPE in polymer. After irradiation with
visible light, the fluorescence intensity gradually recovered to the original intensity,
and this process can be recycled many times, which has vast potential application for
photochromic fluorescence switch. Fig. 12c and Fig. 12d showed the fluorescence
intensity changes of P1 and P2 in film, the case of fluorescence quenching were
similar to that of in DMF-H O mixture solution.
2
The absorption of the opened merocyanine form was from 400 nm to 700 nm and
the emission band of fluorophore unit was from 450 nm to 600 nm, that is to say,
1
4

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their spectra exists overlap in the range of 450 nm to 600 nm. Therefore, when the
SPO unit of the polymer from closed form to merocyanine with the irradiation of UV,
it will absorb the emitted light of TPE because of the energy transfer resulting in the
fluorescence quenching of the polymer. With the irradiation of visible light the
merocyanine return to closed cycle form, there is no overlap of the absorption
spectrum and the emission spectrum, the fluorescence intensity recover.
Fig.12
4. Conclusions
In conclusion, four polymeric nanoparticles with spirooxazine derivative and
AIE fluorescent dye were synthesized by semi-continuous polymerization. All the
nanopartice polymers are uniform and display a narrow particle size distribution.
Their photochromic properties and AIE properties have been studied detailedly,
showing that all the polymers exhibit excellent photochromic ability. P1 and P2
exhibit good AIE properties and their fluorescence intensities could be modulated
regularly with irradiation of UV and visible light. Thus indicates that P1 and P2 may
be potential candidate for external stimuli-responsive materials, such as photoswitch,
bioprobe and so on.
Acknowledgements
This work was financially supported by NSFC (21372194ꢁ20802065 and
2
1476075), and the GuangGong Yangfan Talent Plan (2013).
1
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Table 1. List of nanoparticles prepared with different ratio of SPO and TPE
polymer SOMA TPECN MMA RAMEB water
K S O
8
Dm
Mn
PDI
2
2
(
mmol) (mmol) (mol)
(mg)
30
(g)
10
(mg)
30
(nm)
355.0
436.3
540.5
656.9
(g/mol)
64714
59441
45864
54291
P1
P2
P3
P4
0.02
0.04
0.08
0.16
0.02
0.02
0.02
0.02
0.01
0.01
0.01
0.01
2.86
2.04
1.75
2.03
30
10
10
10
30
30
30
30
30
2
3

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Figure captions
Fig 1 Synthesis and photoswitchable process of polymer nanoparticles.
Fig 2 The size distribution of P1, P2, P3 and P4 by DLS at room temperature.
Fig 3 SEM images of P1, P2, P3 and P4.
Fig 4 The image of P2 under general microscope (a) and fluorescence
microscope (b).
Fig 5 TGA curves of the polymers.
Fig 6 Absorption spectrum and color changes of SPO 6 in DMF solutionꢃ2.0×
-5
-1
1
0 mol L ꢄupon irradiation with UV and visible light.
Fig 7 (a) PL spectra changes and (b) absorption spectra changes of TPE 6 in
-
5
DMF/water mixtures with different water fractions. Concentration : 2×10 mol/L, λ
ex
=
374 nm. (inset: the dependence of the fluorescence emission intensity on the water
fraction). (c) the images of TPE in DMF/water mixtures with different water fractions
were taken under room light (top) and 365 nm UV light (bottom).
Fig 8 Absorption spectra changes of polymers in DMF solution (2.5 mg/mL)
before and after UV (365 nm) illumination. (a):P1; (b):P2; (c):P3; (d):P4.
Fig 9 Absorption spectra changes of P2 (a) in an aqueous suspension and P2 (b)
in film before and after UV illumination. (inset: picture of P2 latexes and P2 solid
before and after UV irradiation at 365 nm).
Fig 10 PL spectra change of (a) P1 and (b) P2 in water/DMF mixtures. The inset
depicts the changes of PL peak intensity and maximum PL emission wavelength
(0.5mg/mL).
2
4

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Fig 11 the images of P1 (a) and P2 (b) in DMF/water mixtures with different
water fractions were taken under room light (top) and 365 nm UV light (bottom).
Fig 12 PLspectra change of (a) P1 in water/DMF mixtures with a water fraction
of 30% (0.5mg/ml) and (b) P2 in water/DMF mixtures with a water fraction of 80%
(
0.5mg/ml) upon irradiation with UV and visible light (λ =302nm). PL spectra
ex
change of (c) P1 in film and (d) P2 in film upon irradiation with UV and visible light
λ =302nm).
(
ex
2
5

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Scheme 1
Scheme 1 Synthetic routes for SPO 4 and TPE 6
2
6

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Fig. 1
2
7

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Fig. 2
2
8

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Fig. 3
2
9