Figure 2.
(A) The line shape of action spectrum for triplet formation (and singlet oxygen generation) for trans-urocanic acid in a deoxygenated pH 7.2 solution (solid line). The line-shape was determined by fitting a Gaussian line-shape function to the photoacoustic data collected from 320 to 360 nm (data points). Each irradiation wavelength was generated by using a home-built temperature-tuned optical parametric amplifier pumped by a home-built Nd:YLF (1 kHz, 1.054 μ) regenerative amplifier. The 10−3 M t-UA samples had an optical density of between 0.05 and 0.1, and, at each irradiation wavelength, the t-UA optical density was matched to within 3% of the optical density of the standard bromocresol purple. (B) The measured in vivo action spectrum for the photosagging of mouse skin taken from the results of Bissett and coworkers (reprinted with permission from ref. 40). The in vivo action spectrum mimics the action spectrum shown in A.