Development of Photostable Two-Color Pressure-Sensitive Paints With Organic Luminophores for Unsteady Pressure Measurements

In pressure-sensitive paint (PSP) measurements, variations in temperature and non-uniform excitation light intensity during measurement are the primary sources of measurement error. To correct these errors, two-color PSPs (2C-PSPs) have been developed that can simultaneously measure pressure and either temperature or excitation light intensity. However, photophysical interactions between luminophores have long led to degradation in PSP performance. In particular, fast-responding 2C-PSPs with low polymer content exhibit high photodegradation rates of the luminophore. In this study, we developed fast-responding 2C-PSPs with improved photostability by using organic luminophores, Bis(8-quinolinolato) zinc(II) (ZnHq) or 2,5-Bis(5-tert-butyl-2-benzoxazolyl)thiophene (BBOT), as blue-green-emitting temperature-sensitive dyes, combined with the red-emitting pressure-sensitive dye PtTFPP. The results demonstrate that highly photostable 2C-PSPs can be obtained by reducing the PtTFPP concentration to 0.25 mg/mL. For the combination of PtTFPP and ZnHq, photodegradation rates of −1.8%/h for PtTFPP and −1.7%/h for ZnHq were achieved after one hour of continuous excitation light exposure, values comparable to the photodegradation rate of −1.4%/h for PtTFPP alone. Furthermore, when PtTFPP was combined with BBOT, although the photodegradation rate was high at −12 to −15%/h, efficient energy transfer from BBOT to PtTFPP was observed, resulting in a 1.3 to 2.3-fold increase in the luminescence intensity of PtTFPP.