Oxygen-sensing properties of 5,10,15,20-tetraphenylporphinato platinum(II) and palladium(II) covalently bound on poly(isobutyl-co-2,2,2-trifluoroethyl methacrylate)

A novel methacrylate monomer bearing 5,10,15,20-tetraphenylporphyrinato palladium(II) (PdTPP) (monomer 1a) was synthesized and copolymerized with isobutyl methacrylate (IBM) and 2,2,2-trifluoroethyl methacrylate (TFEM) to give poly (IBM-co-TFEM) bearing PdTPP (copolymer 2a) as a dye-conjugated oxygen-permeable polymer for pressure-sensitive paint applications. The introduction of PdTPP into copolymer 2a was confirmed by UV-vis spectroscopy and extended X-ray absorption fine structure analysis. The Stern-Volmer plots of the copolymer 2a and a mixture of PdTPP and poly(IBM-co-TFEM) both showed downward curvature, unlike that of the platinum complex analogue (copolymer 2b) previously reported. The plots were successfully fitted with a two-site model to give two distinct Stern-Volmer constants (KSV ₁ and KSV ₂) and the partition ratio f₁. Interestingly, the f₁ values for the copolymer 2a were almost constant at about 0.98, whereas those of the mixture of PdTPP and poly(IBM-co-TFEM) increased from 0.889 to 0.967 as the temperature was increased. This finding suggests that there are two distinct microheterogeneities, one temperature-dependent and the other temperature-independent, in the mixture of PdTPP and poly(IBM-co-TFEM). The dye-conjugation approach effectively eliminates the temperature-dependent, but not the temperature-independent microheterogeneity. The luminescence decays of copolymers 2a and 2b and the corresponding mixtures in the absence of oxygen indicated that the temperature-dependent microheterogeneity involves an oxygen diffusion process, whereas the temperature-independent one appears to be inherent nature in PdTPP.