Oxygen effects on tetrapropylporphycene near-infrared luminescence kinetics

Tetra-propyl-porphycene (TPrPo) in solution has been studied by means of time-and spectral-resolved near-infrared (NIR) luminescence spectroscopy. The NIR luminescence kinetics exhibits surprising dependence on oxygen concentration. There is a clearly visible long-lived (microsecond range) rise-section in biexponential kinetics at broad NIR spectral range of 800-1100 nm for lowered oxygen concentrations. The rise-section is not present in nitrogen-saturated samples and it also disappears after addition of singlet oxygen (¹O₂) physical quencher DABCO, which means that the effect is ¹O₂-mediated. Kinetics of TPrPo delayed fluorescence detected around 650 nm possess a similar rise-decay character in microsecond range. Simultaneous measurements of ¹O₂ phosphorescence kinetics, triplet-triplet transient absorption, and delayed fluorescence have provided additional information about the phenomenon. It is proposed that TPrPo shows a singlet oxygen-sensitized delayed fluorescence which extends to near-infrared where it is strong enough to override the phosphorescence emission.