A Highly Sensitive Humidity Sensor Based on AIE luminogen-appended　Hygroscopic Polymer Microresonator

摘要

Whispering gallery mode (WGM) optical resonators confine light via total internal reflection at theoutermost surface of the resonator. This efficient light confinement strongly enhances light–matterinteraction especially at the periphery of the resonator. Therefore, their unique spectral feature whichstrongly dependent on the size, geometry and refractive index of the resonator can be applied to highlysensitive chemical and physical sensing. Humidity is one of the major targets in the field of sensorsbecause water molecules often affect the high precision manufacturing processes or chemicalsynthesis/purification processes. High precision and active configuration of the WGM optical humiditysensors are particularly advantageous for this purpose. However, existing active WGM humidity sensorsoften suffer from poor luminescence intensity and poor chemical robustness toward moisture uptake. Toovercome these problems, here we newly design a hygroscopic polymer appended withaggregation-induced emission (AIE) luminogen and prove its excellent performance as a WGM humiditysensor. The newly synthesized polymer (PAA-TPE) is composed of poly(acrylic acid) and AIEluminescent branches. PAA-TPE microspheres, formed by sluggish self-assembly in solution, work asWGM resonators and exhibit peak shift when increasing or decreasing the surrounding humidity with asensitivity as high as 255 pm/%RH, which is the highest value among the reported active optical sensors.The sensitivity toward humidity is kept intact even after several cycles of absorption and desorption ofwater vapor.