Fluorescence of matrix isolated guanine and 7-methylguanine

We have prepared argon and nitrogen matrices containing guanine and 7-methylguanine, and measured their absorption, fluorescence excitation and fluorescence emission spectra. The fluorescence excitation spectrum of guanine shows four well-resolved bands in the range from 170 to 290 nm; excitation at the wavelengths of each of these bands results in a fluorescence emission with maximum intensity near 350 nm and a single-exponential decay with a lifetime of about 10 ns. There are significant differences between the fluorescent excitation and emission spectra of guanine and of 7-methylguanine, suggesting that the fluorescence observed from the guanine sample does not arise from a minority tautomer.