Photodynamic Pattern Memory Surfaces with Responsive Wrinkled and Fluorescent Patterns

Abstract Reversible pattern systems, namely pattern memory surfaces, possessing tunable morphology play an important role in the development of smart materials; however, the construction of these surfaces is still extensively challenging because of complicated methodologies or chemical reactions. Herein, a functionalized basement is strategically integrated with a multi‐responsive supramolecular network based on hydrogen bonding between aggregation‐induced emission luminogens (AIEgens) and copolymers containing amidogen (poly(St‐co‐Dm) to establish a bilayer system for near‐infrared (NIR)‐driven memory dual‐pattern, where both the fluorescence emission and wrinkled structures can be concurrently regulated by a noninvasive NIR input. The motion of the AIEgens and photo‐to‐thermal expansion of the modified base allow temporal erasing of the fluorescent wrinkling patterns. Meanwhile, when exposed to 365 nm UV radiation, the fluorescent patterns can be independently regulated through photocyclization. The fluorescent wrinkling pattern presented herein is successfully demonstrated to promote the level of information security and capacity. This strategy provides a brand‐new approach for the development of smart memory interfaces.

Carbon nanotube (CNT) and 2-(dimethylamino)ethyl methacrylate (Dm) were provided by Macklin Chemical (Shanghai, China). And all other chemicals were obtained from Hitachi Chemical (Shanghai, China).

Characterizations:
The 1 H nuclear magnetic resonance ( 1 H NMR) spectra were recorded with Bruker Avance III HD spectrometer (500 MHz, Bruker, Germany), 298K. Average molecular weights of copolymers were determined by means of gel permeation chromatography (GPC, LC-20A, Shimadzu, Japan), using tetrahydrofuran as an eluent at a flow rate of 1.0 mL min -1 with a combination of two columns (Shodex, KF-802 and 804, 300 × 8 mm) and equipped with a RID-10A differential refractive index detector. The atomic force microscopy (AFM) images were observed by utilizing a scanning probe microscope (Nanoscope III, Digital Instruments), which operated in tapping mode with silicon cantilevers (with a force constant of 40 Nm -1 ). All the fluorescence spectra were recorded using a steadystate & time-resolved fluorescence spectrofluorometer (QM/TM/IM, USA PTI Industry) equipped with a temperature control system. And glass transition temperature (T g ) was measured by modulated differential scanning calorimety (DSC, TA-Q2000, USA) at a scanning rate of 5 o C/min. Super resolution multiphoton confocal microscopy (STED) was conducted on Keyence VK-X150. Wrinkling patterning surfaces were recorded by profile measurement microscope (VF-7510, KEYNCE, Japan) and laser scanning confocal microscopy (LSCM, LEXT VK-X1000, Keyence, Japan).

Synthesis of Tetrakis(4-(hydroxy)phenyl)ethylene (TPEOH) and Tetraphenylethene (TPE)
The synthetic procedure of the aggregation induced emissive (AIE) molecule TPEOH is presented in Scheme S1. Briefly, zinc dust (3.92 g, 60 mmol) was suspended in a 250 mL three-necked flask with dry THF (60 mL). Then, TiCl 4 (3.32 ml, 30 mmol) was dropwise added to the above zinc suspension within ice-salt baths, followed by room temperature stirring for 30 min and refluxing for 2 h, cool-down to 0 °C and being supplemented with anhydrous pyridine (1.2 mL). Subsequently, 4,4'-dihydroxybenzophenone (4.28 g, 20 mmol) in anhydrous THF (40 mL) was added to the aforementioned solution. After reflux reaction overnight, the yielding crude product was purified according to the following procedures: washing with 10% K 2 CO 3 solution, extraction with DCM and dehydration with Na 2 SO 4 . After evaporation of solvent, the product was purified by silica gel column chromatography (ethyl acetate: petroleum ether = 1:3) to give TPEOH as the purple solid product powder (3.5 g, 89%).
Following the similar procedure described for TPEOH afforded a pure solid product in a yield of 93%. The chemical structure was verified by 1 H NMR ( Figure S1). Scheme S1. Synthetic scheme for preparation of AIE molecules. Figure S1. 1 H-NMR spectra of the synthesized a) TPE and b) TPEOH in DMSO-d 6 solution.

Synthesis of Copolymers.
The synthetic procedure of copolymer was depicted in Scheme S2. In detail, n-butyl acrylate (1.28 g, 1 mmol), styrene (2.08 g, 2 mmol) and AIBN (1 wt.% total monomer weight) were successively added into 15 mL of dry 1,4-dioxane under the protection of nitrogen atomosphere and stirred at 70 o C for 12 h. After cooling to room temperature, the mixture was precipitated in cold n-hexane. The filtered powder was dried in vacuum condition at 50 o C for 24 h to result in copolymer poly(Ba-co-St) as white solid product (yields: 89 %). The respective constituent ratio of the copolymer is confirmed by integrals in 1 H NMR spectra.

Synthesis of the functional Europium complex
General procedure: According to scheme S3, about 1.0 mmol of EuCl 3 dissolved in 10 mL of methanol was added to a solution of thenoyltrifluoroacetone (4.0 mmol, TTA) in methanol (20 mL) while stirring. The clear solution became turbid after its pH value was tuned to 9.0 by adding NH 3 ·H 2 O. This mixture solution was stirred at reflux for 4 h, during which time the white precipitates generated. Finally, the crude product was purified by filtration, washed with cold petrol ether, and dried in vacuum to obtain the title complex as a white solid (yield: 83%).
Scheme S3. Schematic diagram of the preparation of the EuTTA complex.

Preparation of Polydimethylsiloxane (PDMS) Substrate and CNT-containing PDMS
Silicone elastomer (Sylgard 184, Dow Corning) was used to fabricate elastomeric PDMS sheets. Detailedly, the base and crosslinking agent were thoroughly mixed in petri dished at a determined weight ratio (15:1), followed by being degassed at room temperature for 2 h.
Subsequently, the mixture was heated to 70 o C for 4 h to result in a cross-linked PDMS elastomer substrate and then divided into square pieces with 1 cm length of side.
Moreover, CNT was deftly introduced into base agent to give NIR-responsive PDMS sheets. In detail, single-walled CNTs at varying weight (1.5 mg, 7.5 mg and 15 mg), 15 g of PDMS and 10 mL of normal hexane were added into a beaker. After sonication for 24 h, the well-dispersed mixture was dried in a vacuum oven at 70 o C overnight to remove the residual solvent. The obtained CNT-doped PDMS base was moved to a petri dish and then mixed with 1 g of curing agent. Finally, the CNT-PDMS substrates were obtained by solidifying the degassed solution at 70 o C for another 4 h.

Fabrication of dynamic wrinkled pattern
To obtain AIEgens-mediated dynamic wrinkle pattern, 5.12 mg of TPEOH was firstly dissolved in 1 g of anhydrous THF. Then 80 mg of poly(St-co-Dm) dissolved in toluene (1 g) was added to the mixture. After directly complexing for 5 min, the filtered solution of poly(St-co-Dm)@TPEOH was spin-coated onto the CNT-PDMS sheet to give in a bilayer system. The samples were subjected to thermal treatment for 3 min and cooled down to room temperature to result in multifunctional wrinkling pattern with fluorescence.

Preparation of tunable fluorescent wrinkle pattern
The toluene/THF mixed solution of poly(St-co-Dm)@TPEOH or poly(St-co-Dm)@TPEOH@Eu was spin-coated on the PDMS sheet. Upon heating for 3 min and cooling down, wrinkled surfaces with disorder topological structures occurs. To obtain patterned fluorescence wrinkle, the samples were then irradiated by 365 nm UV (15 mW/cm 2 ) at 70 o C for 30 s through figurate photomasks, respectively.
Statistical Analysis. Significant differences in fluorescent ratio of the top layer obtained by super-resolution multiphoton confocal microscopy (STED) between any two groups were evaluated using Student's t test.             Scale bar: 2 mm.

Movies
Movie S1. Video of the reversible disappearance/formation behavior of the random wrinkles during the on/off irradiation by infrared light.
Movie S2. Video of the fluorescent pattern's disappearance/formation behavior under NIR irradiation.