. High-performance liquid chromatograms and absorption spectra of the primary photoproducts of 5mCyd (left) and Cyd (right) before and after low-intensity laser irradiation at 267 nm in ultrapure water, pH 5.6. Samples were freshly prepared the day of each experiment in ultrapure water (pH 5.6) to have an absorbance of 1.0 at the excitation wavelength of 267 nm.