Figure 6.

Photoexcitation of oxidised DHE (OxDHE) with a 5 ns laser pulse results in oxygen-dependent infrared emission at 1270 nm decaying with the characteristic for singlet oxygen lifetime and relatively high quantum yields. Representative kinetics of formation and decay of near-infrared emission after photoexcitation of OxDHE with a 355 nm (A) and 425 nm (B) 5 ns laser pulse. OxDHE was solubilised in benzene saturated with either air, oxygen, or argon. All-trans-retinal (AtRal) and tetraphenylporphyrin (TPP) were used as standards of known quantum yields of singlet oxygen generation in benzene. To ensure the same number of absorbed photons by samples containing OxDHE and standards, the samples were diluted to have their absorbances adjusted to the same value at the excitation wavelength. The decays of singlet oxygen phosphorescence were fitted with exponential decay functions to obtain, as fitted parameters, the initial intensities of singlet oxygen phosphorescence. (C,D) The initial intensities, I₀ plotted as a function of laser energy. Straight lines were fitted to datapoints within the linear range of I₀ increase with laser energy. The ratio of the quantum yields of singlet oxygen generation by OxDHE and a standard is the same as the ratio of their corresponding slopes of the fitted straight lines, which allows the calculation of the quantum yield of singlet oxygen generation by OxDHE.