Temperature-independent pressure-sensitive paint based on a bichromophoric luminophore

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)(3)(2+) and pyrene chromophores covalently linked together. The luminophore features a very long-lived emission (tau similar or equal to 50 mu s) 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 degrees C. The calibrations indicate that the Stern-Volmer constant (K-sv) for the Ru-pyrene/MPP PSP is temperature independent (K-sv similar or equal to 4.5 atm(air)(-1)). By contrast, a PSP consisting of meso-tetrakis-(pentafluorophenyl)porphyrin platinum(II) in MPP exhibits strongly temperature dependent K-sv, 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 K-sv 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.