Reversible and Broad-Range Oxygen Sensing Based on Purely Organic Long-Lived Photoemitters

Abstract

The detection of oxygen (O2) by optical sensors is of growing importance, for example, in biology, life science, environmental science, and aerodynamics, where the composition of gases is crucial for many applications. Purely organic optical O2 sensors are very attractive for monitoring food deterioration, biosensing, and biomonitoring, as they can provide continuous, reversible, and nondestructive O2 sensing. However, purely organic optical reversible O2 sensors that can work with a broad O2 concentration range and that have robust reversibility are yet to be realized. We hereby developed a purely organic optical O2 sensor by embedding polyimide-based photoemitters within a poly(vinyl alcohol) (PVA) matrix. The photoemitters are synthesized through one-pot hydrothermal reactions. They have a lifetime of room temperature phosphorescence (RTP) of up to a few microseconds (μs) when they are embedded into the polymer matrix. Our results demonstrate that the photoemitters have higher sensitivity and broader sensing range to O2 if they are synthesized with longer reaction times because they possess a more rigid polyimide structure. The O2 sensor with such optimized photoemitters embedded in the polymer matrix exhibits continuous and broad-range O2 sensing in the range of 0-16% O2. The Stern-Volmer quenching constant (Ksv) was calculated to be 0.2351 kPa-1 for the linear response range of 0-4% O2. Moreover, the O2 sensor can be repetitively used at least 10 times in the linear range (0-4% O2) or beyond the linear range (up to 21% O2). The metal-free, purely organic sensors that enable the continuous and repetitive detection of O2 within a relevant O2 sensing range are appealing especially for monitoring packaged food, biomonitoring, and biosensing.