Pressure-sensitive paint (PSP): concentration quenching of platinum and magnesium porphyrin dyes in polymeric films

We report the effect of dye concentration on luminescence quenching and decay lifetime for metallo-porphyrin dye molecules in polymeric film. In particular we report on films containing platinum tetra(pentafluorophenyl)porphine (PtTFPP), platinum octaethylporphine (PtOEP), and magnesium tetra(pentafluorophenyl)porphine (MgTFPP) in three polymers, two non-fluorinated (MAX and polycarbonate) and one fluorinated (FIB). We found: (i) the emission intensity for PtTFPP, PtOEP, and MgTFPP decreased at higher film concentrations, an effect much more pronounced for PtOEP than for PtTFPP; (ii) the absorption, emission, and excitation spectra for PtTFPP films were relatively unchanged with concentration, while with increased concentration MgTFPP films demonstrated clear absorption, emission, and excitation spectral changes; (iii) Stern–Volmer plots (Iatm/I versus P/Patm) for PtTFPP and PtOEP at different film concentrations overlap at dilute concentrations but separate at higher concentrations; (iv) temperature coefficient values (intensity versus temperature plots) for MgTFPP films range from 0.15%/C to 0.08%/C, whereas for PtTFPP films they range from 1.81%/C to 1.25%/C from the lowest to highest film concentrations studied; (v) lifetimes for PtTFPP, PtOEP, and MgTFPP decrease at higher film concentrations; (vi) the singlet luminescence decay of MgTFPP fits a mono-exponential at all concentrations examined at 1 atm; (vii) the triplet luminescence decay of PtTFPP and PtOEP films is mono-exponential only at dilute dye concentration and in vacuum; (viii) response times for oxygen diffusion into PtTFPP films are faster at higher concentrations of PtTFPP. Concentration effects on spectra and lifetimes are clearly observed at concentration greater than 1.0 g of porphyrin per 60 g of polymer.