Novel optical CO₂ sensing material: pH indicator immobilized in fluorine-containing poly(aryl ether ketone) films

A series of new fluorine-containing poly(aryl ether ketone)s (8F-PEKEK(Ar); Ar: 2-2-bis(4-hydroxyphenyl) -1,1,1,3,3,3-hexafluoropropane (6FBA), 2,2-bis(4-hydroxyphenyl)propane (BA), 2-(4-hydroxyphenyl)-2-(3- hydroxyphenyl)propane (3,4′-BA) or 9,9′-bis(4-hydroxyphenyl)fluorine (HF)) are synthesized and applied to the matrix of optical CO₂ sensor based on the overlay of the CO₂ induced absorbance change of pH indicator dye α-naphtholphthalein with the fluorescence of tetraphenylporphyrin (TPP) was developed. The observed luminescence intensity from TPP at 655 nm increased with increasing the CO₂ concentration. The ratio/₁₀₀//₀ values of the sensing films consisting of α-naphtholphthalein in 8F-PEKEKs layer and TPP in polystyrene layer, where/₀ and /₁₀₀ represent the detected luminescence intensities from a layer exposed to 100% argon and 100% CO₂, respectively, that the sensitivity of the sensor, are more than 3.6. The response and recovery times of the sensing films consisting of α-naphtholphthalein in 8F-PEKEKs layer and TPP in polystyrene layer were less than 8.6 s for switching from argon to CO₂, and for switching from CO₂ to argon. The signal changes were fully reversible and no hysterisis was observed during the measurements. The highly sensitive and fast responsible optical CO₂ sensor based on fluorescence intensity changes of TPP due to the absorption change of a-naphtholphthalein in 8F-PEKEKs layer with CO₂ was achieved.