Preparation and photochromic behavior of spiropyran-containing

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Preparation and photochromic behavior of spiropyrancontaining fluorinated polyacrylate hydrophobic coatings Yan Yang, Ting Zhang, Jiajin Yan, Liuwa Fu, Hongping Xiang, Yanyan Cui, Jiahui Su, and Xiaoxuan Liu Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.8b03229 • Publication Date (Web): 28 Nov 2018 Downloaded from http://pubs.acs.org on November 29, 2018

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Preparation and photochromic behavior of spiropyran-containing fluorinated polyacrylate hydrophobic coatings Yan Yang,b Ting Zhang,c Jiajin Yan,b Liuwa Fu,b Hongping Xiang,b Yanyan Cui,b Jiahui Su,a,b,* Xiaoxuan Liu,a,b,** a Guangdong

Provincial Key Laboratory of Functional Soft Condensed Matter, Guangdong

University of Technology, Guangzhou, 510006, P. R. China b

Department of Polymeric Materials and Engineering, School of Materials and Energy,

Guangdong University of Technology, Guangzhou, 510006, P. R. China. c Chemistry

& Environment Engineering, Shaoguan University, Shaoguan 512005, China

KEYWORDS: spiropyran, fluorinated polyacrylate, emulsion polymerization, photochromic, hydrophobicity.

ABSTRACT: In this study, spiropyran (SP)-containing fluorinated polyacrylate (F-PA-SP) latex was prepared by emulsion polymerization using fluorinated and SP-based acrylic monomers as raw materials. FT-IR and 1H-NMR demonstrate that the F-PA-SP copolymer has been successfully synthesized, and DLS and TEM analyses indicate that the synthesized latex has presented a uniform particle size of approximately 200 nm. XPS, AFM and water contact angle (WCA) analysis were used to investigate the surface properties of the F-PA-SP coating and demonstrate that its hydrophobicity is enhanced by addition of a fluorinated acrylic monomer.

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The photochromic properties of the coating were investigated by UV-Vis spectroscopy, and the results reveal that the F-PA-SP coating possesses better photo-responsiveness, fatigue resistance, and photo-reversibility under UV/Vis irradiation than the coating prepared using fluorinated polyacrylate/SP blended latex. Moreover, the WCA of the F-PA-SP coating subjected to UV/Vis irradiation shows minimal changes and retains its excellent hydrophobicity. Finally, the F-PA-SP latex was applied to cellulosic paper, and the resulting photochromic paper exhibits outstanding reversible color changes and hydrophobicity.

INTRODUCTION As a novel smart material, photoresponsive material is well known for the tailorability of their chemical and physical properties1 and unique reversible optical-switching2 in response to light, and have attracted considerable attention in the past decades. As an essential photoresponsive material, photochromic coatings are of key importance and present extensive applications in the fields of optical devices,3 photosensitive paper,4,5 anti-counterfeit coating,6 optical data storage,7 and molecular/ion recognition.8-10 Photosensitive materials are generally prepared by introducing photosensitive molecules to polymer matrix via doping4,11,12 or copolymerizing.13-15 Spiropyran (SP) is a photosensitive molecule featuring reversible optical-switching between two forms, namely, the colorless ring-closed SP form and the colored ring-opened merocyanine (MC) form,16-21 which has recently attracted interest in the field of photochromic coatings because of its rapid photoresponsiveness.22-24 In our previous work,6 epoxy resin was thoroughly mixed with an SP derivative to formulate anti-counterfeiting coatings that could be applied to flexible substrates, such as food and medicine packaging. However, due to its poor fatigue resistance,25 SP is susceptible to environmental influences and could show aggregation-induced


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degradation, which severely harms its photochromic behavior. Methods that could effectively introduce SP into coatings without decreasing its optical properties are therefore extremely important in the preparation of SP-based photochromic coatings. In general, incorporation of photosensitive molecules into polymer matrices via covalent bonding is more effective than physical blending to prevent aggregation, which is a key factor to protect SP from environmental degradation and increase its stability. Many studies have reported that copolymerization of photosensitive molecules with other monomers via emulsion or miniemulsion polymerization could be applied to prepare photochromic coatings for various of applications.26-27 For example, Zhu et al.28 prepared a living-cell nanodetector by copolymerizing an SP-based monomer with styrene, divinylbenzene, and N-isopropylacrylamide via emulsion polymerization and investigated the photochromic and luminescent optical switchability of the resulting polymers. Amin et al.4 prepared novel photochromic polymer nanoparticles with epoxy functional groups and self-made SP derivatives by semi-continuous emulsion polymerization and applied the resulting product to photochromic paper. Although the optical properties of SP-based photochromic coatings have been studied extensively, relatively little attention has been paid to their surface properties like low surface free energy and related hydrophobicity. The hydrophobicity of SP-based coatings could be easily decreased on account of its tunable wettability behavior under different light conditions.29 Thus, novel functional photoresponsive coating materials with microstructures or nanostructures on their coating surface have been further investigated to enhance the surface properties of photoresponsive coatings. Fluorinated polymers are commonly used to modify the hydrophobic surfaces of photoresponsive coatings.30-31 For instance, Zhou et al.32,33 synthesized a novel photoresponsive fluorinated gradient brush copolymer with switchable hydrophobicity by atom


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transfer radical polymerization (ATRP) and the grafting-from method to achieve photo-induced controllable wettability in coating. Nonetheless, the synthesis methods employed were relatively complicated and unsuitable for industrialization. As one of the most convenient and effective methods to introduce photoresponsive molecules into polymer matrices to manufacture photoresponsive materials, emulsion polymerization is highly favored. Herein, the advantages of SP-based and the fluorinated acrylic monomers were combined to develop a photoresponsive fluorinated acrylic latex (F-PA-SP) through emulsion polymerization, finally yielding a material with excellent surface and reversible photochromic properties. The properties and structures of the F-PA-SP latex and the corresponding coating were examined in detail, and the effect of SP contents on the photochromic properties of the coating were also investigated. The optical behaviors of the coatings, including theirs fatigue resistance and reversible color changes under UV/Vis irradiation were investigated by using UV-Vis spectroscopy, and changes in the wettability and hydrophobicity of the coating surface under alternating UV/Vis irradiation were compared. Photochromic cellulosic paper was produced by immersing cellulosic paper into the F-PA-SP latex, and the reversible optical and hydrophobic behaviors of the resulting paper were investigated. The obtained photochromic paper possesses excellent hydrophobicity and outstanding color reversibility. EXPERIMENTAL SECTION Materials: Sodium dodecyl sulfate (SDS, RunDa Chemicals Co. Ltd. China), polyethylene glycol tert-octylphenyl ether (OP-10, RunDa Chemicals Co. Ltd.), methyl methacrylate (MMA, Aladdin, China), butyl acrylate (BA, Aladdin), acrylic acid (AA, Aladdin), ammonium hydroxide (NH4OH, Aladdin), sodium hydrogen carbonate (NaHCO3, Aladdin), ammonium


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persulfate (APS, Aladdin), 2-(perfluorohexyl)ethyl methacrylate (PFM, J&K Scientific Co. Ltd.), and a solution of a structured acrylate copolymer with pigment-affine groups (DISPERBYK2015, BKY, Germany) were used as received. Deionized water (DW) was obtained from the laboratory. N-ethoxyl-3′,3′-dimethylspiro (2H-5-nitro-1-benzopyran-2,2′-indoline) (SPOH) was synthesized according to previously reported protocol.34 Spiropyran acrylic monomer (SPMA) was synthesized by modification of SPOH using acryloyl chloride, with corresponding characterizations provided in the Supporting Information (see Figures S1, S2). All other reagents used were analytical grade and applied without further purification. Synthesis of Spiropyran-containing Fluorinated Polyacrylate (F-PA-SP) Latex: The F-PASP latex was synthesized in two steps (Scheme 1). First, sodium hydrogen carbonate (0.06 g), which was used as the buffer, the ionic surfactant SDS (0.2 g), the nonionic surfactant OP-10 (0.4 g), and different monomers, such as MMA (11 g), BA (8.8 g), and AA (0.2 g), were completely dissolved in DW (40 g). The mixture was transferred to a flask equipped with a condenser under a N2 atmosphere and mechanically stirred. After heating to 75 °C, the initiator KPS (0.22 g) was added dropwise into the mixture. Next, polymerization was continued at 80 °C until the emulsion showed blue fluorescence; the final emulsion was considered as the seed emulsion. In the second stage, OP-10 (0.8 g), SDS (0.4 g), MMA (22 g), BA (17.6 g), AA (0.4 g), PFM (4.75 g), and SPMA with different contents (mass fraction relative to the total quantity of MMA and BA, 0.25~1.5 wt.%) were added to DW (20 g) for pre-emulsification at room temperature for 30 min. KPS (0.14 g) was also dissolved in DW (60 g). The pre-emulsion and KPS aqueous solution were simultaneously added dropwise into the seed emulsion within 2.5 h at 80 °C and were allowed to react for another 1 h at 85 °C. After cooling to 45 °C, the pH of the mixture was adjusted to 7–8 using aqueous ammonia. Finally, the reacted solution was filtered


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through a 100-mesh nylon filter to obtain a photochromic fluorinated acrylic latex called F-PASPx, where x represents the added SPMA contents.

Scheme 1 Synthetic route of F-PA-SP latex Synthesis of Blending Fluorinated Polyacrylate Latex with SPOH (F-PA/SPOH): The FPA/SPOH latex was directly prepared by mechanically blending fluorinated polyacrylate latex (F-PA, Supporting Information) with different amounts of SPOH (0.25~1.5 wt.%) at a speed of 1000 r/min using DISPERBYK-2015 (0.1 wt.%) as a dispersant. Preparation of Latex Coatings: Latex coatings were prepared by using a 100 µm applicator roll (RDS #44, DeManyi Instrument Co. Ltd, China) and casting directly onto a glass substrate (CAT. No.7101, SAIL BRAND, China). The coatings were obtained after drying in an oven at 80 °C for 12 h. Preparation of Photochromic Hydrophobic Cellulosic Paper: Cellulosic paper (Whatman○R No. GB/T1914-2007) was immersed in F-PA-SP1.25 latex under ultrasonic vibration (KQ-2200ES, ShuMei Ultrasonic Instrument Co. Ltd, China) for 5 min and then was dried at 60 °C for 12 h to


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prepare photochromic hydrophobic cellulosic paper. Changes in the color and hydrophobicity on the cellulosic paper under irradiation were recorded. Characterization: Fourier-transform infrared (FT-IR) spectra were measured between 4000 and 500 cm−1 over 32 scans at 4 cm−1 resolution with KBr pellets using a Nicolet iS50 spectrophotometer. Proton nuclear magnetic resonance (1H NMR) spectra were recorded on a Bruker spectrometer (400 MHz) using CDCl3 as a solvent at 25 °C and tetramethylsilane (TMS) as the internal standard. Dynamic light scattering (DLS) measurement using a Brookhaven Zeta PALS particle size analyzer was applied to monitor changes in particle size. Transmission electron microscope (TEM) images were obtained from a JEOL JEM-2100 TEM with an accelerating voltage of 200.0 kV. X-ray photoelectron spectroscopy (XPS) measurements were performed on a Kratos ESCA spectrometer (Axis Ultra DLD) with an Al KαX source (150 W, 15 kV) at a take-off angle of 45° from the normal surface. The surface roughness of the coating was analyzed by atomic force microscopy (AFM) using a Bruker-FastScan atomic force microscope in FastScan-B mode, and water contact angle (WCA) was measured by the static drop method using a JY-PHB contact angle analyzer (China). Photochromic Properties: The UV-Vis absorption spectra of diluted F-PA-SP latex and the corresponding coatings were recorded by a Shimadzu UV-450 spectrophotometer. All measurements were carried out at ambient temperature. The fatigue resistance of the corresponding coatings was investigated base on the intensity changes of UV/Vis absorbance at 555 nm. The samples were under irradiation in a photo-reactor equipped with a UV-LED light source (365 nm, LEO Photoelectric Co. Ltd, China) for predetermined length of time and immediately characterized by UV-Vis spectroscopy. Subsequently, the samples were irradiated by a fluorescent lamp for certain amount of time and


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their UV/Vis absorption spectra were recorded again. The alternating UV/Vis irradiation cycle was repeated 10 times. The colors of the coatings were detected by placing a photomask onto the solid coating and irradiating it under a UV-LED light for 5 min. The spot area measured was approximately 4×4 cm2. RESULTS AND DISCUSSION We designed a photochromic fluorinated acrylic latex via emulsion polymerization with several acrylate monomers. MMA, BA, and AA were used to regulate the properties of film formation, while the functional monomers (PFM and SPMA) played important roles on the hydrophobic performance and photochromic behavior of the resulting latex. In this section, the effect of PFM was first discussed. The statistical data and AFM results of the F-PA latex were summarized in Supporting Information (see Table S2, S3 and Figure S3). When the PFM content was 8 wt.%, the latex demonstrates remarkable stability, and the corresponding coating shows excellent hydrophobicity with contact angle larger than 90°. At fixed 8 wt.% PFM feed ratio, the effect of SPMA contents on the performance of the FPA-SP latex was then considered. The results show that all of the F-PA-SP latex samples present remarkable stability and uniform particle sizes despite the variation of SPMA amount from 0.25 wt.% to 1.5 wt.% (see Table S4). Taking the F-PA-SP1.25 latex as an example, the particle size and distribution determined by DLS (Figure 1a) are approximately 200 nm and 0.029, respectively. TEM images (Figure 1b–1c) reveal that the latex particles have been spherical with a uniform size that agree well with the DLS results.


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Figure 1 (a) DLS result and (b-c) TEM images of F-PA-SP1.25 latex The chemical structures of the F-PA-SP1.25 coating were characterized by FT-IR and 1HNMR. In Figure 2a, absorption bands at 1239 and 700 cm−1 could be respectively assigned to C−F stretching and bending vibrations. A strong absorption peak at 1731 cm−1 is assigned to C=O stretching vibrations. The 1H NMR spectrum of F-PA-SP1.25 indicates signals at 4.2~4.4 and 2.4~2.6 ppm, which could be assigned to −CF2CH2− protons. Characteristic FT-IR absorption bands and aromatic proton NMR signals ascribed to SP molecules are not detected in Figure 2, possibly due to the relative small amount of incorporated SPMA species in these samples.

Figure 2 (a) FT-IR and (b) 1H NMR spectra of the F-PA-SP1.25 coating XPS spectroscopy was used to further determine the surface compositions of the F-PASP1.25 coating. In Figure 3a, the signals of C, O, F, and N can be clearly verified in the wide-scan spectrum, thereby indicating that PFM and SPMA have been involved in the copolymerization reaction. The elements S and Na also appear because of the emulsifier SDS in the polymerization system. The C1s regions of the narrow-scan XPS spectrum were investigated, and the results are


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shown in Figure 3b to analyze qualitatively the surface element compositions of the F-PA-SP1.25 coating. The characteristic spectrum of C exhibits a multimodal distribution. Five main peak components with binding energy of 283.6, 284.9, 287.4, 291.2 and 293.6 eV and respectively belonging to C−C/C−H, C−O, C=O, C−F2 and C−F3 were curve-fitted.

Figure 3 XPS spectra of the F-PA-SP1.25 coating: (a) survey spectrum (b) C1s core-level XPS spectrum peak fitting curves Considering that surface roughness is a factor affecting hydrophobicity, the surface morphology of the coatings was analyzed by AFM. Three-dimensional AFM images (Figure 4a) show that the pure PA coating is relatively smooth with a root mean square roughness (Rq) of 0.614 nm. When 8 wt.% PFM was added to the latex, a number of small peaks were observed on the F-PA coating surface (Figure 4b), and the Rq was remarkably improved to 2.61 nm. This finding can be explained as follows: The fluorine-containing segment easily migrates to the surface of the coating and occupies the outermost layer, where it is oriented outwards toward the air (see Figure S4, Table S5), thereby decreasing the surface free energy of the coating (see Table S3), increasing the surface roughness of the coating (see Figure S3) and enhancing coating’s hydrophobicity.35 When 1.25 wt.% SPMA was added to the latex, the surface roughness of the F-PA-SP1.25 coating is similar to that of the F-PA coating and the Rq of the former is 2.42 nm (Figure 4c). In addition, the WCA of the F-PA-SP1.25 coating is over 90°, which is close to that of the F-PA coating but higher than that of PA-SP1.25 (Figure 4d-4f). This result indicates that the surface hydrophobicity of the coating is greatly enhanced with the


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presence of PFM, and no discernible effect on hydrophobicity due to the addition of SPMA is observed.

Figure 4 AFM and WCA images of corresponding coatings: (a, d) PA-SP1.25; (b, e) F-PA and (c, f) F-PA-SP1.25 Photochromic Properties: The photochromic properties of F-PA-SP latex samples with different SPMA contents were investigated by UV-Vis spectroscopy. Before UV irradiation, all samples were diluted to 0.4 wt.%. No obvious absorbance of the F-PA-SP latex in the range of 450~700 nm is observed because most of the SP structures in the copolymer chains present as the closed forms of SP. After exposure to UV-LED light (365 nm), a distinct absorption peak appears at 555 nm due to the transformation of SP to the MC form; the observed absorption intensity increases markedly with the exposure time (see Figure S5). The absorbance also increases with SPMA contents (Figure 5a). Low absorbance by the F-PA-SP0.25 latex is anticipated due to the low concentration of SPMA in the diluted sample. When the SPMA content was 1.25 wt.%, the absorbance reaches 0.87, which stabilizes at this level despite further increases of SPMA.


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The photo-switching ability of the F-PA-SP1.25 latex was examined. The solid line in Figure 5b illustrates the absorbance curves of the samples upon exposure to UV irradiation for 0 and 60 s. The latex turned violet after exposure to UV irradiation. When the F-PA-SP1.25 latex was immediately irradiated with fluorescent lamp, the absorption peak at 555 nm (dashed line in Figure 5b) clearly decreases with the irradiation time and the latex color fades. It can be seen that the absorption peak almost completely restores to its value before UV irradiation upon exposure to visible irradiation for 90 s.

Figure 5 (a) Absorbance curves of F-PA-SPx latex with different SPMA contents after UV irradiation; (b) Absorbance changes with exposure time under UV/Vis irradiation The photochromic properties of the F-PA-SP films were investigated. Here, F-PA/SPOH latex was also prepared by physically blending equal amounts of SPOH with F-PA for control experiments. The absorbance of samples F-PA-SP1.25 and F-PA/SPOH1.25 appears at 555 nm under UV irradiation and reaches maximum level in 80 s (see Figure S6). This peak then gradually decreases to its original state upon exposure to visible irradiation (Figure 6a-6b). When the amount of the SP component in the F-PA/SPOH1.25 coating was same, the absorbance of the physically mixed F-PA/SPOH1.25 coating is far weaker than that of the chemically bonded F-PASP1.25 coating. This is because, on the one hand, lack of chemical bonding between photosensitive compounds and polymeric matrix results in undesired aggregation, and reduction of the photostability and lifetime of SP compounds, which dramatically hampers their photochromic properties.15, 36 On the other hand, the compatibility of SPOH with F-PA latex is


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poor and the SPOH cannot be completely dissolved. These two reasons may explain why the absorbance at 555 nm and color changes of the F-PA/SPOH coatings are weaker than those of the F-PA-SP coatings after exposure to UV irradiation (Figure 6c). Furthermore, the F-PA-SP1.25 coating shows better fatigue resistance after 10 exposure cycles alternating UV/Vis irradiation than the F-PA/SPOH1.25 coating (Figure 6d); specifically, the absorbance of the former at 555 nm is higher than that of the latter and only slightly decreases after 10 exposure cycles. It is well known that the fatigue behavior of SP molecule is mainly caused by photo-degradation, which takes place primarily via photo-oxidation process.3739

Besides that, the aggregated MC species are difficult to convert back to SP structures

immediately, and are thus more susceptible to the photo-oxidation process with extended decoloration time.40 Since conjugation of SP molecules to the copolymer backbone greatly reduces the probability of aggregation of the MC molecules, the degradation rate of the MC forms is thereby decreased.4,13,15 Thus, the fatigue resistance of the F-PA-SP1.25 coating is greatly improved compared with that of the F-PA/SPOH1.25 coating.

Figure 6 Photochromic properties of corresponding coatings under exposure to UV/Vis irradiation: (a) absorbance changes with exposure time for F-PA-SP1.25 and (b) absorbance changes with exposure time for F-PA/SPOH1.25; (c) appearance changes; (d) fatigue resistance


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Figure 7 shows changes in the WCAs of the coatings under alternating UV/Vis irradiation. The WCAs of F-PA-SP1.25 are slightly lower than those of F-PA but greater than those of PASP1.25. Moreover, the WCAs of F-PA-SP1.25 decrease after UV irradiation due to the formation of the hydrophilic MC forms of SP. The WCAs of F-PA-SP1.25 notably remain at approximately 90° with only a slight reduction after UV treatment, which indicates that introduction of PFM exerts a protective effect on the coating’s hydrophobicity in different light environments. Comparatively, it can be seen from the changes of WCAs in F-PA/SPOH1.25 that the WCAs are slightly larger than that of F-PA-SP1.25 under UV/Vis alternating irradiation. The WCAs of FPA/SPOH1.25 under UV irradiation increase slowly with cycle times. These results verify indirectly the poor compatibility of SPOH with F-PA latex and the weakened fatigue resistance of F-PA/SPOH1.25 under alternating UV/Vis irradiation.

Figure 7 Changes of WCAs under UV/Vis alternating irradiation Cellulosic Paper with Photochromic Properties: Comparing the surface morphologies of cellulosic paper before (Figure 8a-8c) and after (Figure 8d-8f)) immersing with F-PA-SP1.25 latex by SEM images, the impregnation of polymer chains into the cellulosic paper is confirmed. The smoother fiber surface of modified cellulosic paper demonstrates the existence of F-PASP1.25 film coating. The uniformity of the wetting paper reveals excellent compatibility and diffusion between F-PA-SP1.25 latex and cellulosic paper. This could be attributed to the


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establishment of hydrogen bonding between carboxyl units (AA) in F-PA-SP1.25 latex and hydroxyl groups in cellulose. No crack is observed in the modified cellulosic paper thanks to the low Tg (see Figure S7) of F-PA-SP1.25 latex.

Figure 8 SEM images of cellulosic paper before (a-c)) and after (d-f)) immersing with F-PA-SP1.25 latex Figure 9 showcases the interesting photo coloration and hydrophobicity of the cellulosic paper. The color of the cellulosic paper changes from essentially colorless to purple under UV irradiation. In addition, water droplets notably stand on the paper surface instead of wetting it under UV/Vis irradiation, thereby proving that the photochromic cellulosic paper features hydrophobicity at different light environments.

Figure 9 Photochromic coloration and hydrophobicity of cellulosic paper with F-PA-SP1.25 latex under UV irradiation


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CONCLUSION Combining the advantages of fluorine and SP-based acrylate monomers, F-PA-SP was synthesized by emulsion polymerization. FT-IR and 1H-NMR spectra demonstrate the successful preparation of an F-PA-SP copolymer, and DLS and TEM results indicate its uniform size and narrow particle distribution. AFM, XPS, and WCAs verify that the fluorine-containing chain segments in the polymer chain migrate to the air interface during film formation, which benefits the construction of a hydrophobic coating. The photochromic behaviors of the F-PA-SP emulsion and its corresponding coating were investigated in detail. When 1.25 wt.% SPMA was added to the reaction system, the obtained F-PA-SP1.25 coating reveals excellent rapid photoreversibility under alternating UV/Vis light irradiation, and its fatigue resistance is better than that of the physically blended F-PA/SPOH1.25 latex. Moreover, the WCAs of the F-PA-SP1.25 coating only reduce slightly and remain at approximately 90° under UV/Vis light irradiation for 10 exposure cycles. Thus, incorporation of SPMA and PFM into the polymer matrix via chemical bonding is suitable to enhance the photo-responsiveness and hydrophobicity of the functionalized polyacrylate coating. Finally, a photochromic cellulosic paper sample was fabricated from F-PA-SP1.25 latex, presenting intensive coloration and excellent hydrophobicity. ASSOCIATED CONTENT Supporting Information Experimental section including materials, the preparation of photochromic spiropyran acrylic monomer and fluorinated acrylic latex, and measurements are listed in Supporting Information. This material is available free of charge


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AUTHOR INFORMATION Correspondence Authors * E-mail: [email protected] ** E-mail: [email protected] Notes The authors declare no competing financial interest. ACKNOWLEDGEMENTS This research was ﬁnancially supported by the Natural Science Foundation of China (Grant No. 21604014, 51641302 and 51873043), and the China Postdoctoral Science Foundation (CPSF2018M633006), and Science and Technology Planning Project of Guangdong Province, China (2017A010103020). REFERENCES (1) Yildiz, I.; Deniz, E.; Raymo, F. M. Fluorescence modulation with photochromic switches in nanostructured constructs. Chem. Soc. Rev. 2009, 38, 1859-1867. (2) Irie, M. Diarylethenes for memories and switches. Chem. Rev. 2000, 100, 1685-1716. (3) Zacharias, P.; Gather, M. C.; Köhnen, A.; Rehmann, N.; Meerholz, K. Photoprogrammable Organic Light-Emitting Diodes. Angew. Chem. Int. Ed. 2009, 48, 4038-4041. (4) Abdollahi, A.; Mahdavian, A. R.; Salehi-Mobarakeh, H. Preparation of stimuli-responsive functionalized latex nanoparticles: the effect of spiropyran concentration on size and photochromic properties. Langmuir 2015, 31, 10672-10682. (5) Tian, W.; Tian, J. Synergy of different fluorescent enhancement effects on spiropyran appended onto cellulose. Langmuir 2014, 30, 3223-3227. (6) Zhang, T.; Fu, L.; Chen, Z.; Cui, Y.; Liu, X. Photochromic properties of spiropyran in epoxy resin as anti-counterfeiting coating on flexible materials. Prog. Org. Coat. 2016, 100, 100-104. (7) Tian, H. Data processing on a unimolecular platform. Angew. Chem., Int. Ed. 2010, 49, 47104712. (8) Inouye, M.; Ueno, M.; Kitao, T.; Tsuchiya, K. Alkali metal recognition induced isomerization of spiropyrans. J. Am. Chem. Soc. 1990, 112, 8977-8979. (9) Zhang, H.; Kou, X.X.; Zhang, Q.; Qu, D.H.; Tian, H., Altering intercomponent interactions in a photochromic multi-state [2] rotaxane. Org. Biomol. Chem. 2011, 9, 4051-4056. (10) Raymo, F. M.; Alvarado, R. J.; Giordani, S.; Cejas, M. A. Memory effects based on


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Preparation and photochromic behavior of spiropyran-containing

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