An oxygen sensing system based on the phosphorescence quenching of metalloporphyrin thin film on alumina plates

Abstract

Optical oxygen sensors based on the phosphorescence quenching of tetrakis(4-carboxyphenyl)porphyrin (TCPP) metal complex (platinum, palladium and metal-free complexes) chemisorption films onto alumina plates were developed. The phosphorescence intensity of TCPP metal complex films decreased with increasing oxygen concentration, indicating that the films can be used as an optical oxygen sensing device based on phosphorescence quenching by oxygen. The ratio I₀/I₁₀₀, where I₀ and I₁₀₀ represent the detected phosphorescence intensities from a film exposed to 100% argon and 100% oxygen, respectively, as a sensitivity of the sensing films are estimated to be 16.5 for PtTCPP, 17.7 for PdTCPP and 2.58 for H₂TCPP, showing that the PtTCPP and PdTCPP films are highly sensitive devices for oxygen concentration. These films obeyed Stern–Volmer plots with multi-site models and possessed good operational stability. Response times were 8.6 s for PtTCPP, 36 s for PdTCPP and 3.4 s for H₂TCPP for argon saturated to oxygen saturated conditions and 50.0 s for PtTCPP, 148 s for PdTCPP and 15 s for H₂TCPP for the reverse conditions. These sensing films are stable against irradiation and exhibit minimal decrease (ca. 7%) in initial intensity after continuous irradiation for 24 h.