Large-Scale Nanofiber Manufacturing| Double-Sided Bifunctional Blue-Green Light PhotodetectorBased on Liquid Crystalline Polymer for Light Positioning andHealth Monitoring

Professor Chen Aihua from Beihang University in AFM: Multifunctional All-Flexible Blue-Green Light Photodetector Based on Pseudostilbene Azobenzene Liquid Crystal Elastomer Composite Fabric

Blue-green light holds significant application potential and development prospects in underwater wireless communication and real-time health monitoring. To enhance the portability and integration of electronic devices, developing multifunctional wearable flexible blue-green light detectors is particularly crucial. However, traditional semiconductor materials generally suffer from rigidity, brittleness, and complex processing issues. Meanwhile, the elastic modulus mismatch between photosensitive elements and polymer matrices often causes interlayer separation during dynamic operation, limiting blue-green light applications in wearable fields.

Crosslinked liquid crystal polymers (CLCP) or liquid crystal elastomers containing photosensitive units combine polymer advantages like lightweight and flexibility with environmentally responsive capabilities. By integrating multiple electrical property materials and utilizing the "light-mechanical stress-electrical signal" continuous conversion sensing pathway, they become ideal materials for constructing intrinsically flexible wearable electronic devices.

Recently, Professor Chen Aihua's team at Beihang University published their latest research titled "Double-Sided Bifunctional Blue-Green Light Photodetector Based on Liquid Crystalline Polymer for Light Positioning and Health Monitoring" in Advanced Functional Materials. The researchers synthesized pseudostilbene azobenzene liquid crystal polymer (P2NAzo) by substituting electron-donating amino groups and electron-withdrawing carboxyl groups at the para positions of azobenzene molecules, red-shifting the response range to blue-green light bands. Through electrospinning co-assembly with piezoelectric P(VDF-TrFE) and post-crosslinking, the obtained NAzo-CLCP elastomer composite fabric undergoes microscopic axial fiber contraction under blue/green light irradiation, generating stress that directly activates piezoelectric effects to produce voltage/current output.

Figure 1: Schematic of pseudostilbene azobenzene LCE blue-green light detector based on "light-mechanical-electric" sensing mechanism.

The device exhibits 50-300 mW cm-2 illuminance detection range, with 5-second open-circuit voltage response time and 100-millisecond short-circuit current response time. Benefiting from excellent compatibility between P2NAzo and P(VDF-TrFE), the device maintains stable performance after 1000 irradiation cycles. Due to NAzo-CLCP's intrinsic flexibility, it withstands 180° folding, bending up to 500 m-1 curvature, and dynamic stretching within 10% strain, meeting daily human motion requirements. P(VDF-TrFE)'s hydrophobicity also provides excellent resistance to humidity/temperature fluctuations, establishing a solid foundation for wearable applications.

Figure 2: Basic photodetection performance of the device.

Based on these properties, the device has been applied as detector arrays for underwater light positioning systems (blue light) and wearable bandages for photoplethysmography (PPG) heart rate monitoring (green light). The NAzo-CLCP composite fabric's flexibility and tailorability enable remarkable performance advantages - effective light-receiving area reaches 100× that of semiconductor materials (customizable), achieving 45° wide reception angle without additional lenses. This provides unprecedented convenience and accuracy for light detection tasks in extreme conditions like underwater environments or moving transceiver ends, greatly expanding optical communication applications.Currently, an 8-detector array can precisely determine incident light direction and distance. 

Figure 3: Blue light-based underwater light positioning detector array.

NAzo-CLCP fabric also demonstrates unique advantages in wearables. Integrated with bandages and worn tightly on wrists near green LEDs, it captures PPG signals reflecting arterial vasoconstriction/dilation for real-time heart rate monitoring during various activities and quantitative cardiovascular health analysis. The bandage's superior fit and larger receiving area provide higher fault tolerance and lower operational difficulty, especially beneficial for elderly users without professional guidance, offering 24/7 multi-point unobtrusive health monitoring.

Figure 4: Green light-based PPG real-time heart rate monitoring and quantitative cardiovascular health analysis.

Multifunctional integration is fundamental for comprehensive detection and a key focus for future smart scenarios. Leveraging NAzo-CLCP's material and performance consistency, the team ingeniously integrated two critical functions - blue light ASCII code communication and green light PPG monitoring - onto opposite sides of a single detector, creating a dual-functional device. This integration significantly reduces circuit design complexity, enabling lighter, more comfortable wearable devices.

Figure 5: Application scenarios and performance testing of multifunctional dual-sided integrated device.