Temperature-Independent Pressure-Sensitive Paint Based on a Bichromophoric Luminophore

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Abstract
A spectroscopic study is presented of a pressure-sensitive paint (PSP) formulation that consists of the bichromophoric luminophore, Ru-pyrene, dispersed in an acrylate co-polymer matrix (MPP, a 1:1 co-polymer of poly(ethylene glycol)ethyl ether methacrylate and tri(propylene glycol) diacrylate). The Ru-pyrene molecule contains Ru(bpy)32+ and pyrene chromophores covalently linked together. The luminophore features a very long-lived emission (τ ⋍ 50 μs) that makes it ideal for incorporation into luminescent oxygen sensor coatings. Stern–Volmer calibrations were carried out on the Ru-pyrene/MPP PSP as a function of temperature over the range from 25 to 55 °C. The calibrations indicate that the Stern–Volmer constant ( Ksv) for the Ru-pyrene/MPP PSP is temperature independent ( Ksv 4.5 atm(air)−1). By contrast, a PSP consisting of meso-tetra-kis-(pentafluorophenyl)porphyrin platinum(II) in MPP exhibits strongly temperature dependent Ksv, demonstrating that the unique temperature dependence of the Ru-pyrene/MPP PSP arises from the combined properties of the Ru-pyrene luminophore and the MPP matrix; i.e., it is not a special property of the MPP matrix alone. Analysis of luminescence decay lifetime data indicates that the temperature-independent Ksv in the Ru-pyrene/MPP PSP arises because the nonradiative decay rate of the Ru-pyrene chromophore varies moderately with temperature. The temperature-dependent nonradiative decay rate is believed to arise due to a thermally activated intramolecular energy transfer process in Ru-pyrene.