Photoinduced Dual-Mode Luminescent Patterns in Dicyanostilbene

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Photoinduced Dual-Mode Luminescent Patterns in DicyanostilbeneBased Liquid Crystal Polymer Films for Anticounterfeiting Application Yanrong He, Juntao Li, Jie Li, Chao Zhu, and Jinbao guo ACS Appl. Polym. Mater., Just Accepted Manuscript • DOI: 10.1021/acsapm.8b00276 • Publication Date (Web): 08 Mar 2019 Downloaded from http://pubs.acs.org on March 17, 2019

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ACS Applied Polymer Materials

Photoinduced Dual-Mode Luminescent Patterns in DicyanostilbeneBased Liquid Crystal Polymer Films for Anticounterfeiting Application

Yanrong He,a Juntao Li,a Jie Li,a Chao Zhu,a Jinbao Guo* a a

Key Laboratory of Carbon Fibers and Functional Polymers, Ministry of Education; Beijing

Engineering Research Center for the Synthesis and Applications of Waterborne Polymers and College of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing, 100029, China.

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ACS Paragon Plus Environment

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Abstract: Tunable photoluminescence is highly favored for its unique in light emitting displays, bioimaging and optoelectronic devices fields. Here a photoinduced dual-mode luminescent pattern in dicyanostilbene monomer (DCN-M)-based liquid crystal polymer (LCP) films is first proposed by combining photoinduced alignment with photoisomerization reaction. The high polarized emission patterns at microscopic and macroscopic scale are firstly achieved by employing sulfonic azo dye (SD1) as an alignment agent to control the local orientation of highly emissive DCN-M in LCP matrix. Furthermore, by taking advantage of Z/E photoisomerization of dicyanostilbene moiety in the DCNM-doping LCP film, the photoluminescence intensity of the LCP film could be tuned upon nonpolarized ultraviolet light irradiation, thus enabling alternating light and dark regions in the LCP film. Finally, we proposed a proof-of-concept demonstration of a dual-mode emission pattern in a single LCP film for anti-counterfeiting application with modulation of both polarization and photoluminescence intensity. This work paves a new way for the fabrication of complex patterned fluorescent polymers for photonic applications.

KEYWORDS: Dicyanostilbene-based liquid crystal polymer film, photoalignment, Z/E photoisomerization, dual-mode luminescent patterns, anticounterfeit

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INTRODUCTION Controlling the photoluminescent properties of luminescent materials have been paid attention due

to their potential applications in liquid crystal displays (LCDs), polarized light emitting displays and other optoelectronic devices.1-8 Among them, controllable polarized luminescence is of great importance in backlighting LCDs and polarized luminescent devices.9-11 Until now, a large variety of organic and inorganic luminescent materials, including monomeric and polymeric conjugated materials and inorganic luminescence nanoparticles, have been extensively studied for achieving polarized luminescence emission.12-19 To realize the polarized luminescence, it is generally required to induce luminescent materials into an ordered bulk media. It is well known that the properties such as long-range orientational order with relatively free movement and optical/electrical anisotropy make LC materials highly suitable as a bulk media for the tuning of luminescent materials and other optical devices.20-22 Correspondingly, high-quality orientation of LCs is an important requirement for achieving favorable switching effect. In comparison with traditional alignment methods including controlling of mechanical stretching, buffed films of polyimide, electrospinning, electric or magnetic field, photoalignment technology with no pollution and no static provides high and accurate orientation for LC molecules at micro and macro scale.23-33 For example, photoalignment approach was employed to induce the alignment of inorganic semiconductor nanocrystals with anisotropic absorption and emission into a LC polymer (LCP) matrix, hence forming polarized luminescence patterns.34 However, it is still challenging to disperse high concentrations of semiconductor nanoparticles in LCs due to the existing aggregation problem. Therefore, linear conjugated organic luminophores may be a good choice due to their similar structure

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with bulk materials. Owing to tunable luminescence emission and aggregate-induced enhanced emission (AIEE) properties, ɑ-cyanodistyrylbenzene-based luminophores have attracted great interest in many applications, such as photonic devices, sensors, photo-switches, bioimaging and stimuli-responsive photonic materials.3,4 Furthermore, cyanodistyrylbenzene unit can also undergo Z/E photoisomerization upon ultraviolet (UV) or visible light irradiation.35-40 These features make the ɑ-cyanodistyrylbenzene-based derivatives suitable for the construction of the polarized emission system.12,13 In this study, we demonstrate the first experimental demonstration of a photoinduced dual-mode (polarization-dependent/polarization-independent) luminescent micropattern in a thin LCP film

doped with polymerizable dicyanostilbene monomer (DCN-M). Compared with the systems using non-polymerizable dicyanostilbene molecules, DCN-M with two acrylate groups is able to participate in cross-linking reaction, thus the LCP film with more stable fluorescent patterns can be easily obtained. First, a photoalignment technology is used to control the local orientation of DCN-M which is dispersed in LC monomers mixture and driven by the orientation of LC molecules, further enabling a polarized emission pattern upon polarized UV light irradiation under a photomask. Second, due to the photoluminescence intensity modulation of DCN-M via an irreversible Z/E photoisomerization process, another emission pattern could be fabricated with a photomask with irradiation of nonpolarized UV light. Eventually, we demonstrate a dual-mode luminescent pattern in a LCP film through combining polarization and photoluminescence intensity modulation. This work provides a new facile and reliable method to develop a fluorescence LC film for anticounterfeiting application.

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EXPERIMENTAL SECTION

2.1 Materials 4


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Most of the chemicals and solvents were obtained from commercial sources. Polymerizable liquid crystals, LC242 were purchased from Bayi Space LCD. The dicyanostyrylbenzene-based monomer (DCN-M) was synthesized in three consecutive steps in our lab, the details of synthesized process and characterizations were provided in Supporting Information. Photoinitiator Darocur 784 was purchased from J&K Scientific Ltd. Photoalignment agent, sulfonic azo dye (SD1) was purchased from Nanjing Murun company.

2.2 Fabrication of Dual- Mode Luminescent Patterns in the LCP Films A glass substrate (2.5×1.8 cm2) was washed in ultrasonic bath with deionized water and isopropyl alcohol, then dried in the oven at 80 oC for 20 minutes. After that, the surface of the glass substrate was treated for 6 minutes in Oxygen Plasma Cleaning Machine. Then the glass substrate was spincoated with photoalignment agent (SD1) dissolved in N, N- dimethylformamide (DMF) at a concentration of 0.5 wt%. After baking at 100 °C for 10 minutes, SD1 layer was horizontally aligned in-plane by illumination with linearly polarized UV light (here denoted as θ = 0°, λ = 365 nm) for 5 minutes. Subsequent irradiating under the photomask with polarized light of different polarization azimuth (here θ = 90°) was carried out using the same way as above. Consequently, the SD1 layer recorded the pattern of the photomask with the orthogonal exposure. The polymerizable LC242 and the synthesized dicyanodistyrylbenzene-based monomer (DCN-M) with the weight ratio of 97:3 were dissolved in toluene, in which photoinitiator 784 at a concentration of 0.3 wt% was added in the LC mixture. The LC solution was spin-coated onto the patterned SD1 layer at 2500 rpm for 60 seconds. Afterwards, the obtained LC film was dried at 45 °C with nitrogen for 25 minutes to completely evaporate the solvent. In order to keep the pattern permanently, the polymerization was conducted under visible light at 80 °C for 30 minutes. In this way, the pattern of

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SD1 layer was replicated onto the LCP layer. The resulting LCP film with polarized luminescent pattern was further irradiated under a photomask with non-polarized UV light (about 60 mW/cm2) for 30 minutes, and then the LCP film with dual-mode luminescent patterns could be obtained.

2.3 Measurements 1

H-NMR spectra were measured by a Bruker AVANCE III (400 MHz 1H) spectrometer. Mass

spectra were obtained with XEVO-G2QTOF (ESI) (Waters, USA) in positive ion mode. The photoluminescence intensity was examined by fluorescence spectrum photometer (Hitachi, F-4500) and ultraviolet absorption spectrum were measured by UV/visible spectrophotometer (G91/G9PC). The mesomorphic properties of DCN-M and microscopic patterns of the LCP film were observed using a polarizing optical microscope (POM, Leica, DM2500P) equipped with a hot stage calibrated with an accuracy of ±0.1°C (Linkam, THMS-600) under transmission mode. The thermodynamic properties of DCN-M were measured by a differential scanning calorimeter (DSC, Pyris Diamond) with a heating and cooling rate of 10 °C/min under a dry nitrogen purge. The thickness of the LCP layer was measured by a Bruker Dektak XT. The elemental analysis of DCN-M was measured by vario El CUBE.

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RESULTS AND DISCUSSION

3.1 Polarized Luminescent Patterns in Doping-DCN-M LCP Films Based on Photoalignment Technology To fabricate a polarized fluorescence LC polymer pattern with a high polarized ratio and high resolution, accurate regulating LC orientation is a critical step in the whole process. As shown in Figure 1a, here we choose sulfonic azo dye (SD1) as a photoalignment agent for the orientation of 6


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LC molecules. Compared with conventional orientation methods such as mechanical friction, SD1 molecule as a superior photoalignment agent almost successfully overcomes previous shortcomings and exhibits predominant characteristics via a non-contact method at room temperature.24 Meanwhile, the LC monomer, LC 242 and newly synthesized fluorescent monomer, DCN-M were used in this study. Figure 1b presents schematic of the photoalignment patterning and the fabrication of LC polymer film. Here, we employ sequential exposure of linearly polarized UV light with orthogonal polarization direction to obtain a two-dimensional (2D) pattern of planar alignment. As shown in Figure 1b, the first exposure with linearly polarized UV (LPUV) light may align all molecules in the same direction. It should be noted that SD1 molecules which have their absorption oscillators parallel to UV light polarization may acquire more energy to re-orientate from the initial position, hence yielding that SD1 molecules tend to align with their long axes perpendicular to the UV light polarization (Figure 1b). While subsequent irradiation with polarized light of crossed polarization azimuth (relative to the first exposure) realigns SD1 molecules in-plane in exposure areas. Hence, the SD1 layer was locally aligned to form a predesigned pattern after two-time exposure with linearly polarized UV light. Furthermore, the configured LC mixture deposited on the alignment layer was polymerized upon visible light, hence replicating the pattern of alignment layer beneath due to the strong anchoring energy of SD1 for LC molecules. The description of the specific steps and experimental conditions was available in the experimental section. As mentioned above, the novel monomer, DCN-M was used as photoactive emitting dopant shown in Figure 1a. Here, we added 3.0 wt% of DCN-M into the LC monomers mixture. A detailed description of the preparation procedure and the structure characterizations of the monomer were provided in Supporting Information (Scheme S1, Figure S1, Figure S2, and Figure S3 of Supporting Information). It is seen from UV spectrum in Figure 1c that a strong absorption peak at 399 nm of DCN-M gradually weakened and the peak at 7



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249 nm enhanced slowly upon 365 nm UV light illumination. Meanwhile, the fluorescence intensity of DCN-M gradually weakened with the increase of irradiation time upon 365 nm UV light shown in Figure 1d. Furthermore, the DCN-M solutions was further irradiated by UV light at 254 nm for 2 min or heated at 50 °C for 2 min after irradiation with UV light at 365 nm, the results from UV spectra reveal that the Z/E photoisomerization process was irreversible shown in Figure S4. The photochemical process was also explained from 1H-NMR spectroscopy measurements, wherein the intensity of some signals decreased or even disappeared and some new peaks obviously appeared (Figure S5, Supporting Information). Additionally, according to the data of differential scanning calorimetry (DSC) and POM measurement, DCN-M processed nematic phase interval as shown in Figure S6 from Supporting Information.

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Figure 1. (a) Chemical structure of SD1, dicyanodistyrylbenzene-based monomer (DCN-M) and LC242. (b) Schematic diagram of the photoalignment and photo-curing process of the LCP film. (c) and (d) Absorbance and fluorescence spectra of DCN-M dissolved in chloroform solution with different irradiation times (365 nm, 15 mW/cm2), the inset of (d) shows DCN-M in the excited state. As shown in Figure 2a, the optical grating patterns i and ii which were magnified about 10× and excited by linearly non-polarized UV light (about 2.5 mW/cm2) were observed under the microscope with a single polarizer. Due to that the absorption and emission intensities of DCN-M simultaneously

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possess intense polarization angle dependence, it shows the greatest contrast to form alternate dark and bright stripes when the alignment of DCN-M molecules in adjacent regions were perpendicular to each other. Here, θ represents the angle between long axis direction of DCN-M and polarizer. Therefore, at θ = 0°, the absorption and emission intensity of DCN-M, whose long axis was parallel or perpendicular to the direction of polarized light respectively, reached the maximum value to appear the brightest state or minimum value to show the darkest state. When rotating the polarization azimuth to θ=90°, the opposite phenomenon could be observed. Following the same principle, grid photomask

Figure 2. Patterning of LCP film. (a) Polarized images of LCP films with the patterns of optical grating and square excited by 365 nm UV light. Under the polarizer, the picture (a)i and (a)iii are at θ=0 °, the picture (a)ii and (a)iv are at θ=90 °. (b) The photo of LCP film on glass substrate in ambient light. (c) Schematic view of the experimental setup for polarized photoluminescence measurements. (d) The polarized fluorescence spectra of the LCP film, excitation at λ=365 nm.

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was employed to fabricate the patterns iii and iv, in which the sizes of the repeating unit were magnified approximately 5 times. Herein, white arrows represent the orientation of the molecules in the adjacent regions. Here, we note that the thickness of the LCP layer is around 239 nm, and its relative average deviation is about 2.0 %. A transparent LCP film on the glass substrate is demonstrated in Figure 2b. In this study, we reduce the thickness of the LCP film as much as possible to obtain desired LC orientations induced by photoalignment technology. Just as demonstrated above, DCN-M was dissolved uniformly in LC matrix, which was driven by LC molecules to reach consistent alignment due to the synergistic effect. To further explore the polarized fluorescence emission of the photoactive DCN-M, the polarized fluorescence spectra of the LCP film with a uniform orientation was investigated. A schematic diagram of the experimental setup for the polarized photoluminescence measurement is shown in Figure 2c, here the polarization angle could be modulated by accurately controlling the rotations of the polarizer. As shown in Figure 2d, comparing with no polarizer, there was a distinct decrease of the fluorescence intensity with a polarizer on account of limited transmittance of polarizer. When θ = 0°, the alignment of DCN-M was consistent with the direction of polarized UV light, which resulted in a strong fluorescence emission. After that, with the increase of θ value, the fluorescence intensity gradually decreased and was up to the minimum value at θ =90°. Both the polarization ratio (PR) and the degree of polarization (DOP) were calculated from the spectra data on the basis of following Equations (1) and (2), respectively. PR=Imax / Imin

(1)

DOP= (Imax- I min) / (I max + I min)

(2)

Here I max and I min represent the luminescent intensities when the polarizer-axes are parallel and perpendicular to the orientation of DCN-M, respectively. The measured PR and DOP for the aligned DCN-M are 3.1:1 and 0.51, respectively. 11



S= (Imax- I min) / (I max +2 I min)

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(3)

Apart from the obtained parameters above, the order parameter is 0.41 which is calculated according to the Equations (3). All of these results confirm the high-quality alignment of DCN-M in the LC mixtures enabled by the photoalignment method. Compared with luminescent CdSe/CdS core−shell NRs, PR, DOP and order parameter are generally lower.34 First, there is stronger intermolecular force between the modified nanorod and the liquid crystal molecule, so it may lead to the relatively higher synergy. Second, visible light and non-polarized UV light may disturb the orientation of the LCP film and DCN-M slightly. As a result, the effect of polarized fluorescence was influenced to some extent by the photopolymerization and photoisomerization processes.

3.2

Luminescent

Patterns

in

Doping-DCN-M

LCP

Films

Based

on

Photoisomerization reaction In addition to the polarized emission property, the photoluminescence intensity of the LCP film derived from Z/E photoisomerization of DCN-M was also investigated. First of all, a consistent oriented LCP film was fabricated, which was irradiated by normal UV light（about 55 mW/cm2） with

exposure time changing from

1 min to

30 min as

shown in

Figure 3a.

Figure 3. Photoisomerization of the LCP Film. (a) Fluorescence spectra of the LCP film upon the exposure of non-polarized UV light at different times. (b) and (c) Comparison diagram between exposure region and non-exposure region of the patterned LCP film. Here, (b)i and (c)i: the initial 12


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state; (b)ii and (c)ii: the comparison between the photoisomerization and non-photoisomerization of LCP films.

Apparently, there is a gradual and slow decrease of the fluorescence intensity caused by the irreversible isomerization of DCN-M. Compared with the dicyanostilbene monomer in solvent, we find here more energy was needed to make carbon-carbon double bond twist. This may be the reason that DCN-M dispersed in host LCs was greatly influenced by the steric hindrance from the adjacent LC molecules. It is shown that the decreasing trend of the fluorescence intensity stopped until the irradiation time reached at 30 min. Based on this observation, the LCP film with polarized emission patterns is further switched by an unpolarized UV light as shown in Figure 3b and 3c, wherein the dark area was irradiated for 30 min and the another part was covered by a black mask. Thus, the photoisomerization of DCN-M resulted in decrease in fluorescence intensity, hence yielding the second tuning for the LCP patterns.

3.3 Photoinduced Dual-Mode Luminescent Patterns in LCP Films In order to realize dual-mode patterns in a same LCP film, we design an experiment by combining photoalignment technology with photoisomerization method. Firstly, the first patterning of LC mixtures was based on photoalignment technology using the same route described above. As we all know, the orientation of photosensitive SD1 molecules were easy to be influenced by the linearly polarized and non-polarized UV light. Thus, we choose visible light source to induce photopolymerization of the LCP precursor and correspondingly to fix the first pattern of LCP film which was induced by SD1. The second pattern which was based on photoisomerization of DCN-M was further fabricated under an another photomask with the irradiation of non-polarized UV light for about 30 min, as shown in Figure 4a. The resulting fluorescence images of the LCP films are observed 13



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under an excited non-polarized UV light. As shown in Figure 4b, the optical grating with micro scale was induced by photoisomerization process, and the letters “BUCT” at macro scale was caused by the photoalignment agent. When there is no polarizer, only the optical grating could be observed. However, when observing with a polarizer (θ =0°), the dark “BUCT” appears clearly and other areas are bright due to differentiated orientation of the LCs molecules. Rotating the direction of the polarizer from 0° to 90°, the color of “BUCT” changes to be brighter and background is correspondingly darkened. At θ=45°, the equal intensity absorption and emission of DCN-M with different orientations in different areas led to disappearance of BUCT. Furthermore, another dualmode fluorescent image was fabricated as shown in Figure 4c, wherein the macroscopic flower pattern and the microscopic grid pattern were united into one film. The insets images in Figure 4c were enlarged screenshots from the same area, which showed the greatest contrast and distinct alternating patterns. Similarly, other dual-mode fluorescent images were also shown in Figure S7. All these results reveal that the photoinduced dual-mode patterns with high resolution and definition could be achieved by integrating photoalignment technology with photoisomerization method.

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Figure 4. Fluorescence images of the LCP films excited by non-polarized and polarized UV light.( a) The sketch map of photo-isomerized patterning. (b) The letters “BUCT” is based on photoalignment technology, optical grating is caused by the photoisomerization. (c) Grid is based on photoalignment method, the rose is caused by the photoisomerization. Herein, (b)i and (c)i show patterns with no polarizer, others are at different angles of the polarizer. (b)ii and (c)ii are at θ=0 °, (b)iii and (c)iii are at θ=45 °, (b)iv and (c)iv are at θ=90 °. The inset of (c)ii and (c)iv are the areas that are circled by black frames and have been enlarged.

3.4 LCP Films with Dual- Mode Luminescent Patterns for Anticounterfeiting Application As we know that anti-counterfeiting technique is one of important way to protect copyrights in our daily life. Although many studies have been reported a wide variety of anti-counterfeiting materials and presented a multiple ingenious way to read information,41-46 the way to safeguard the security of important information remains a major challenge. Inspired by the early work of our team, 47 we designed a new kind of QR code that was only fully displayed in dual mode to achieve the purpose of advanced anti-counterfeiting. The specific production process is shown in Figure 5a. First of all, the glass substrate spin-coated with SD1 was irradiated by linear polarized UV light to form a predesigned pattern under a photomask with the QR code, whose left half was covered by an opaque mask. Then, the polymerized LC film with half of the QR code pattern which induced by SD1 was illuminated by normal UV light under above photomask whose another half was covered. Ultimately, a whole QR code pattern was obtained based on photoalignment technology and photo-isomerization shown in Figure 5b. Here the left half of the QR code in the LCP film always appears as long as it is excited by 365 nm UV light (Figure 5b. i). However, applying a polarizer under the same condition as above, it is observed that the right half of the QR code appeared, vanished and changed colors

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when rotating the polarizer to different angles. The right half of the pattern was dark and reached the highest resolution in the dark state that matched the color of the left side exactly at θ=0° (Figure 5b. ii-iii), smartphones were capable of recognizing the QR code successfully in the picture. Because the resolution of right pattern decreased gradually from 0° or 90° to 45°, the QR code was read out when θ was between 0° and 10°. Although the bright right half of the fluorescence pattern was also reached the highest resolution at θ=90°, the chromatic aberration between the patterns in double modes was too big to recognize (Figure 5b. iv). The method of reading information twice with the help of a polarizer provides a powerful guarantee for the information security. To be convenient to implement the LCP film into the field of practical application, there are numerous limitations for the rigid glass substrate. Finding a kind of suitable flexible substrate is an urgent problem to be solved. Therefore, inspired from flexible display materials and related literatures,48 a kind of PET substrate with surface treatment was chosen to fabricate the LCP films with double patterns as shown in Figure 5c and 5d. It is shown that the LCP film on the flexible substrate also exhibited excellent optical properties and remarkable resolution, which further demonstrates its potential application value in anticounterfeiting field.

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Figure 5. The fabrication of anti-counterfeiting film in double modes. (a) Schematic diagram of preparation process of anti-counterfeit film with double patterns in the glass substrate. (b) The LCP film displays different patterns excited by 365nm UV light without polarizer and with a polarizer. (c) Diagrammatic drawing of preparation process and reading information of a flexible LCP film. (d) Fluorescence images of the flexible LCP film excited by non-polarized and polarized UV light. Herein, (b)i and (d)i show patterns with no polarizer, others are at different angles of the polarizer. (b)ii and (d)ii are at θ=0 °, (b)iii and (d)iii are at θ=45 °, (b)iv and (d)iv are at θ=90 °.

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CONCLUSIONS In summary, we have developed the first photoinduced dual-mode fluorescent micropatterns in 17



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the liquid crystal polymer (LCP) films doped with dicyanostilbene-based monomer (DCN-M) based on photoalignment and photoisomerization. The photoalignment method using sulfonic azo dye (SD1) as the alignment agent was employed to control the LC orientation of the LCP film, thus leading to polarized emission patterns with high degree of polarization. Meanwhile, tunable photoluminescence intensity derived from Z/E photoisomerization of dicyanostilbene moiety allowed to pattern the LCP with alternating light and dark fluorescent regions. Finally, dual-mode fluorescence patterns were constructed in a same LCP film by combining the photoalignment technology and photoisomerization process. This work provides a facile and reliable method for the fabrication of multi-functional fluorescent patterns, further possessing potential value in anti-counterfeiting application.

ASSOCIATED CONTENT *Supporting Information The Supporting Information is available free of charge via the Internet at http://pubs.acs.org Preparation details and characterization of DCN-M and other dual-mode fluorescent images (PDF)

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] (J. B. Guo).

ACKNOWLEDGMENTS This research was supported by National Natural Science Foundation of China (Grant Nos. 51773009 and 51373013).

REFERENCES (1) Mei, J.; Leung, N. L.; Kwok, R.T.; Lam, J. W.; Tang, B. Z. Aggregation-Induced Emission: 18


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Together We Shine, United We Soar. Chem. Rev. 2015, 115, 11718-11940. (2) O’Neill, M.; Kelly, S. M. Liquid Crystals for Charge Transport, Luminescence, and Photonics. Adv. Mater. 2003, 15, 1135-1146. (3) Martínez-Abadía, M.; Giménez, R.; Ros, M. B. Self-Assembled α-Cyanostilbenes for Advanced Functional Materials. Adv. Mater. 2018, 30, 1704161. (4) An, B. K.; Gierschner, J.; Park, S. Y. π-Conjugated Cyanostilbene Derivatives: A Unique SelfAssembly Motif for Molecular Nanostructures with Enhanced Emission and Transport. Acc. Chem. Res. 2012, 45, 544-554. (5) Li, J. T.; Zhang, Z. W.; Tian, J. J.; Li, G. Q.; Wei, J.; Guo, J. B. Dicyanodistyrylbenzene-Based Chiral Fluorescence Photoswitches: An Emerging Class of Multifunctional Switches for Dual-Mode Phototunable Liquid Crystals. Adv. Opt. Mater. 2017, 5, 1700014. (6) Li, J. T.; Bisoyi, H. K.; Tian, J. J.; Guo, J, B.; Li, Q. Optically Rewritable Transparent Liquid Crystal Displays Enabled by Light-Driven Chiral Fluorescent Molecular Switches. Adv. Mater. 2019, 31, 1807751. (7) Wang, L.; Li, Q. Photochromism into Nanosystems: Towards Lighting up the Future Nanoworld. Chem. Soc. Rev. 2018, 47, 1044-1097. (8) Wang, L.; Chen, D.; Gutierrez-Cuevas, K. G.; Bisoyi, H. K.; Fan, Jing.; Zola, R. S.; Li, G. Q.; Urbas, A. M.; Bunning, T. J.; Weitzb, D. A.; Li, Q. Optically Reconfigurable Chiral Microspheres of Self-Organized Helical Superstructures with Handedness Inversion. Mater. Horiz. 2017, 4, 1190-1195. (9) Wang, Y.; Shi, J.; Chen, J.; Zhu, W.; Baranoff, E. Recent Progress in Luminescent Liquid Crystal Materials: Design, Properties and Application for Linearly Polarised Emission. J. Mater. Chem. C 2015, 3, 7993-8005. (10) Srivastava, A. K.; Zhang, W.; Schneider, J.; Rogach, A. L.; Chigrinov, V. G.; Kwok, H. S. Photoaligned Nanorod Enhancement Films with Polarized Emission for Liquid-Crystal-Display Applications. Adv. Mater. 2017, 29, 1701091. (11) Mohammadimasoudi, M.; Beeckman, J.; Hens, Z.; Neyts, K. Hybrid Fluorescent Layer Emitting 19



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Polarized Light. APL Mater. 2017, 5, 2060-2063. (12) Lu, H.; Wu, S.; Zhang, C.; Qiu, L.; Wang, X.; Zhang, G.; Hu, J.; Yang, J. Photoluminescence Intensity and Polarization Modulation of a Light Emitting Liquid Crystal via Reversible Isomerization of an α-Cyanostilbenic Derivative. Dyes Pigm. 2016, 128, 289-295. (13) Sha, J.; Lu, H.; Zhou, M.; Xia, G.; Fang, Y.; Zhang, G.; Qiu, L.; Yang, J.; Ding, Y. Highly Polarized Luminescence from an AIEE-Active Luminescent Liquid Crystalline Film. Org. Electron. 2017, 50, 177-183. (14) Kawatsuki, N.; Ando, R.; Ishida, R.; Kondo, M.; Minami, Y. Photoluminescent Color and Polarized Light Emission Tuning of Fluorene Derivatives Using a Photoreactive H-Bonded Liquid Crystalline Polymer. Macromol. Chem. Phys. 2010, 211, 1741-1749. (15) Rosenhauer, R.; Stumpe, J.; Gimenez, R.; Piñol, M.; Serrano, J. L.; Viñuales, A. All-in-one Layer: Anisotropic Emission due to Light-Induced Orientation of a Multifunctional Polymer. Macromol. Rapid Commun. 2007, 28, 932-936. (16) Cunningham, P. D.; Jr, J. B. S.; Fedin, I.; She, C.; Lee, B.; Talapin, D. V. Assessment of Anisotropic Semiconductor Nanorod and Nanoplatelet Heterostructures with Polarized Emission for Liquid Crystal Display Technology. ACS Nano 2016, 10, 5769-278. (17) Du, T.; Schneider, J.; Srivastava, A. K.; Susha, A. S.; Chigrinov, V. G.; Kwok, H. S.; Rogach, A. L. Combination of Photoinduced Alignment and Self-Assembly to Realize Polarized Emission from Ordered Semiconductor Nanorods. ACS Nano 2015, 9, 11049-11055. (18) Zhang, W.; Schneider, J.; Chigrinov, V. G.; Kwok, H. S.; Rogach, A. L.; Srivastava, A. K. Optically Addressable Photoaligned Semiconductor Nanorods in Thin Liquid Crystal Films for Display Applications. Adv. Opt. Mater. 2018, 6, 1800250. (19) Aubert, T.; Palangetic, L.; Mohammadimasoudi, M.; Neyts, K.; Beeckman, J.; Clasen, C.; Hens, Z. Large-Scale and Electroswitchable Polarized Emission from Semiconductor Nanorods Aligned in Polymeric Nanofibers. ACS Photonics. 2015, 2, 583-588. (20) Wang, L.; Urbas, A.M.; Li, Q. Nature-Inspired Emerging Chiral Liquid Crystal Nanostructures: 20


Page 21 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


From Molecular Self-Assembly to DNA Mesophase and Nanocolloids. Adv. Mater. 2018, 30, 1801335. (21) Wang, L.; Li, Q. Liquid-Crystal Nanostructures: Stimuli-Directing Self-Organized 3D LiquidCrystalline Nanostructures: From Materials Design to Photonic Applications. Adv. Funct. Mater. 2016, 26, 10-28. (22) Wang, L. Self-Activating Liquid Crystal Devices for Smart Laser Protection. Liq. Cryst. 2016, 43, 2062-2078. (23) Ichimura, K. Photoalignment of Liquid-Crystal Systems. Chem. Rev. 2000, 100, 1847-1874. (24) Chigrinov, V. G.; Kozenkov, V. M.; Kwok, H. S. Photoalignment of Liquid Crystalline Materials: Physics and Applications, John Wiley & Sons, Chichester 2008, 69-96. (25) Li, Q. Liquid Crystals Beyond Displays: Chemistry, Physics, and Applications, John Wiley & Sons, Hoboken, NJ 2012, 213-250. (26) Bisoyi, H. K.; Li, Q. Light-Driven Liquid Crystalline Materials: From Photo-Induced Phase Transitions and Property Modulations to Applications. Chem. Rev. 2016, 116, 15089–15166. (27) Nersisyan, S. R.; Tabiryan, N. V.; Steeves, D. M.; Kimball, B. R.; Chigrinov, V. G.; Kwok, H. S. Study of Azo Dye Surface Command Photoalignment Material for Photonics Applications. Appl. Opt. 2010, 49, 1720-1727. (28) Yaroshchuk, O.; Reznikov, Y. Photoalignment of Liquid Crystals: Basics and Current Trends. J. Mater. Chem. 2012, 22, 286-300. (29) Seki, T.; Nagano, S.; Hara, M. Versatility of Photoalignment Techniques: From Nematics to a Wide Range of Functional Materials. Polymer 2013, 54, 6053-6072. (30) Wei, B.; Hu, W.; Ming, Y.; Xu, F.; Rubin, S.; Wang, J.; Chigrinov, V.; Lu, Y. Generating Switchable and Reconfigurable Optical Vortices via Photopatterning of Liquid Crystals. Adv. Mater. 2014, 26, 1590-1595. (31) Ma, L.; Tang, M.; Hu, W.; Cui, Z.; Ge, S.; Chen, P.; Chen, L.; Qian, H.; Chi, L.; Lu, Y. Smectic Layer Origami via Preprogrammed Photoalignment. Adv. Mater. 2017, 29, 1606671. 21



Page 22 of 24

(32) Zheng, Z.; Yuan, C.; Hu, W.; Bisoyi, H. K.; Tang, M.; Liu, Z.; Sun, P.; Yang, W.; Wang, X.; Shen, D.; Li, Y.; Ye, F.; Lu, Y.; Li, G.; Li, Q. Light-Patterned Crystallographic Direction of a Self‐Organized 3D Soft Photonic Crystal. Adv. Mater. 2017, 29, 1703165. (33) Liu, Q.; Zhan, Y. Y.; Wei, J.; Ji, W.; Hu, W.; Yu, Y. L. Dual-Responsive Deformation of a Crosslinked Liquid Crystal Polymer Film with Complex Molecular Alignment. Soft Matter 2017, 13, 6145-6151. (34) Schneider, J.; Zhang, W.; Srivastava, A. K.; Chigrinov, V. G.; Kwok, H. S.; Rogach, A. L. Photoinduced Micropattern Alignment of Semiconductor Nanorods with Polarized Emission in a Liquid Crystal Polymer Matrix. Nano Lett. 2017, 17, 3133-3138. (35) Martínez-Abadía, M.; Robles-Hernández, B.; de la Fuente, M. R.; Giménez, R.; Ros, M. B. Photoresponsive Cyanostilbene Bent-Core Liquid Crystals as New Materials with Light-Driven Modulated Polarization. Adv. Mater. 2016, 28, 6586-6591. (36) Martínez-Abadía, M.; Varghese, S.; Romero, P.; Gierschner, J.; Giménez, R.; Ros, M. B. Highly Light-Sensitive Luminescent Cyanostilbene Flexible Dimers. Adv. Opt. Mater. 2017, 5, 1600860. (37) Martínez-Abadía, M.; Varghese, S.; Giménez, R.; Ros, M. B. Multiresponsive Luminescent Dicyanodistyrylbenzenes and Their Photochemistry in Solution and in Bulk. J. Mater. Chem. C 2016, 4, 2886-2893. (38) Tian, J. J.; He, Y. R.; Li, J. T.; Wei, J.; Li, G. Q.; Guo, J. B. Fast, Real-Time, In Situ Monitoring of Solar Ultraviolet Radiation Using Sunlight-Driven Photoresponsive Liquid Crystals Adv. Opt. Mater. 2018, 6, 1701337. (39) Zhang, Z. W.; Li, J.T.; Wei, W. Y.; Wei, J.; Guo, J. B. A Luminescent Dicyanodistyrylbenzenebased Liquid Crystal Polymer Network for Photochemically Patterned Photonic Composite Film. Chinese J. Poly. Sci. 2018, 36, 1-7. (40) Wei, P.; Zhang, J. X.; Zhao, Z.; Chen, Y.; He, X.; Chen, M.; Gong, J.; Sung, H. H.; Williams, I. D.; Lam, J. W. Y.; Tang, B. Z. Multiple yet Controllable Photoswitching in a Single AIEgen System. J. Am. Chem. Soc. 2018, 140, 1966-1975. 22


Page 23 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(41) Kumar, P.; Singh, S.; Gupta, B. K. Future Prospects of Luminescent Nanomaterial Based Security Inks: From Synthesis to Anti-Counterfeiting Applications. Nanoscale 2016, 8, 14297-340. (42) Blumenthal, T.; Meruga, J.; May, P. S.; Kellar, J.; Cross, W.; Ankireddy, K.; Vunnam, S.; Luu, Q. N. Patterned Direct-Write and Screen-Printing of NIR-to-Visible Upconverting Inks for Security Applications. Nanotechnology 2012, 23, 185305. (43) You, M.; Zhong, J.; Hong, Y.; Duan, Z.; Lin, M.; Xu, F. Inkjet Printing of Upconversion Nanoparticles for Anti-Counterfeit Applications. Nanoscale 2015, 7, 4423-4431. (44) Moirangthem, M.; Scheers, A. F.; Schenning, A. P. H. J. A Full Color Photonic Polymer, Rewritable with a Liquid Crystal Ink. Chem. Commun. 2018, 54, 4425-4428. (45) Kumar, P.; Nagpal, K.; Gupta, B. K. Unclonable Security Codes Designed from Multicolor Luminescent Lanthanide-Doped Y2O3 Nanorods for Anticounterfeiting. ACS Appl. Mater. Interfaces. 2017, 9, 14301-14308. (46) Hagstrom, A. L.; Lee, H. L.; Lee, M. S.; Choe, H. S.; Jung, J.; Park, B. G.; Han, W. S.; Ko, J. S.; Kim, J. H.; Kim. J. H. Flexible and Micropatternable Triplet-Triplet Annihilation Upconversion Thin Films for Photonic Device Integration and Anti-Counterfeiting Applications. ACS Appl. Mater. Interfaces. 2018, 10, 8985-8992. (47) Ye, S. M.; Teng, Y. X.; Juan, A.; Wei, J.; Wang, L. Y.; Guo. J. B. Modulated Visible Light Upconversion for Luminescence Patterns in Liquid Crystal Polymer Networks Loaded with Upconverting Nanoparticles. Adv. Opt. Mater. 2017, 5, 1600956. (48) Zhang, Y. H.; Sun, J. T.; Liu, Y.; Shang, J. H.; Liu, H.; Liu, H. S.; Gong, X. H.; Chigrinov, V. G.; Kowk, H. S. A Flexible Optically Re-writable Color Liquid Crystal Display. Appl. Phys. Lett. 2018, 112, 131902.

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Photoinduced Dual-Mode Luminescent Patterns in Dicyanostilbene

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