A Flexible Circularly Polarized Luminescence Switching Device Based on Proton‐Coupled Electron Transfer

Abstract Flexible circularly polarized luminescence (CPL) switching devices have been long‐awaited due to their promising potential application in wearable optoelectronic devices. However, on account of the few materials and complicated design of manufacturing systems, how to fabricate a flexible electric‐field‐driven CPL‐switching device is still a serious challenge. Herein, a flexible device with multiple optical switching properties (CPL, circular dichroism (CD), fluorescence, color) is designed and prepared efficiently based on proton‐coupled electron transfer (PCET) mechanism by optimizing the chiral structure of switching molecule. More importantly, this device can maintain the switching performance even after 300 bending‐unbending cycles. It has a remarkable comprehensive performance containing bistable property, low open voltage, and good cycling stability. Then, prototype devices with designed patterns have been fabricated, which opens a new application pattern of CPL‐switching materials.


Characterizations
UV-Vis absorption spectra and kinetic data of absorption intensity were measured using a Shimadzu UV-2550 PC double-beam spectrophotometer. Electrochemical data were measured by a Bio-logic electrochemical work station. Fluorescence emission spectra and kinetic data of fluorescence intensity were measured by a Shimadzu spectrofluorimeter RF-5301PC. Circular dichroism (CD) spectra and the corresponding extinction spectra were collected on a Chiralscan Plus V100 circular dichroism spectrometer (Applied Photophysics Ltd.). 1 H, 13
2.40 g (5.00 mmol) Rhodamine B was dissolved in 40 mL 1,2-dichloroethane, then 3.75 mL (40.00 mmol) phosphorus oxychloride was slowly added into the solution. The mixture was heated to reflux for 3 hours. Then, the solvent of the reaction mixture was distilled off to obtain violet oil.
The system was stirred for 3 hours at room temperature. After the reaction finished, solvent was evaporated under vacuum. The crude product was obtained after dissolving in dichloromethane (CH2Cl2), washing with the deionized water, drying with anhydrous sodium sulfate (Na2SO4) and evaporated. Then, the crude product was purified on a silica gel column eluting with methanol (CH3OH):dichloromethane (CH2Cl2)=1:50 to obtain final pink red product Rh-M2. The yield was 50%. The characterization was shown below ( Figure S20).

Preparation of the acid-responsive films
Herein, PMMA was used as the film-forming material and R-Rhodol-A was used as the acid responsive molecule. And, the doping content of R-Rhodol-A in PMMA was optimized after considering the PL intensity ( Figure S4), which was 2 mg R-Rhodol-A doped in 100 mg PMMA.
Thus, the detailed film-forming process could be described as below: (1)

Electrochemistry
Cyclic voltammetry (CV) analysis was measured using a three-electrode system in acetonitrile  After the preparation of functional solutions, the detailed fabrication process of devices was shown in Scheme S6. Chirality switching layer was formed by drop casting (thickness: 23 μm) on an ITO glass as the working electrode. And, ion storage layer was formed by drop casting on another ITO glass as the counter electrode. Then, ion conductive layer was coated above the ion 9 storage layer by drop casting. Finally, two electrodes with functional layers were connected tightly and the device was assembled successfully.