Development of bright NIR-emitting pressure-sensitive paints using benzoporphyrin luminophores

Pressure-sensitive paints (PSPs) are an optical surface pressure sensor for aerodynamic measurements that operates through the oxygen dependent luminescence of a luminophore molecule. The luminophore has remained relatively consistent over the past 20 years, with platinum(ii)/palladium(ii)-5,10,15,20-tetrakis-(2,3,4,5,6-pentafluorphenyl)-porphyrin (Pt/PdTFPP) being popular choices due to their well-known photostability. In this work, NIR-emitting Pt(ii) and Pd(ii) complexes of tetraphenyl tetrabenzoporphyrins and new para CF₃ substituted tetraphenyl tetrabenzoporphyrins have been investigated as improved luminophores in PSP formulations for the first time. The red shifted NIR emission spectra of the benzoporphyrins offer a wider and more conveniently placed spectral window than Pt/PdTFPP, creating more of a spectral gap for a secondary temperature-sensitive luminophore to be used in future binary PSPs. The para CF₃ substituted Pt(ii) and Pd(ii) benzoporphyrins exhibited substantially increased luminescent brightness over PtTFPP and PdTFPP (5× higher), resulting in signficantly brighter PSP formulations. The benzoporphyrins greatly improved the performance of polystyrene based-PSPs, increasing pressure sensitivity by 20% and decreasing temperature sensitivity by 50%, compared to the current gold standard PtTFPP and PdTFPP.