Optical oxygen sensing based on the luminescence change of metalloporphyrins immobilized in styrene–pentafluorostyrene copolymer film

Abstract

A series of new fluoropolymers, poly(styrene-co-pentafluorostyrene) (poly-Sty_n-co-PFS_m) with different ratios of Sty and PFS units, were synthesized and applied as an optical oxygen sensing matrix using phosphorescence quenching of metalloporphyrins, platinum and palladium octaethylporphyrin (PtOEP and PdOEP), by oxygen. The phosphorescence intensity of PtOEP of PdOEP in poly-Sty_n-co-PFS_m films decreased with increase in oxygen concentration. The ratio I₀/I₁₀₀ was used to express the sensitivity of the sensing film, where I₀ and I₁₀₀ represent the detected phosphorescence intensities from a film exposed to 100% argon and 100% oxygen, respectively. For PtOEP in poly-Sty_n-co-PFS_m films, the I₀/I₁₀₀ values were >24.0 and large Stern–Volmer constants of >0.23%⁻¹ were obtained compared with PtOEP in PS films. For PdOEP in poly-Sty_n-co-PFS_m films, on the other hand, large I₀/I₁₀₀ values of >92.0 are obtained. However, the Stern–Volmer plots of PdOEP in poly-Sty_n-co-PFS_m films exhibit considerable linearity at lower oxygen concentrations between 0 and 20%. These results indicates that PtOEP and PdOEP films are useful optical oxygen sensors for oxygen concentrations between 0 and 100% and between 0 and 20%, respectively. No effect of the ratio of Sty to PFS units in poly-Sty_n-co-PFS_m and on the oxygen sensing properties of PtOEP and PdOEP were observed. The response times of PtOEP and PdOEP immobilized in poly-Sty₁-co-PFS_0.21 films were 5.6 and 3.0 s on going from argon to oxygen and 30.0 and 90.1 s on going from oxygen to argon, respectively. This result indicates that PtOEP and PdOEP immobilized in poly-Sty_n-co-PFS_m films represent a highly sensitive device for oxygen.