Excited State Dynamics of 6‑Thioguanine

Here we present the excited state dynamics of jet-cooled 6-thioguanine (6-TG), using resonance-enhanced multiphoton ionization (REMPI), IR–UV double resonance spectroscopy, and pump–probe spectroscopy in the nanosecond and picosecond time domains. We report data on two thiol tautomers, which appear to have different excited state dynamics. These decay to a dark state, possibly a triplet state, with rates depending on tautomer form and on excitation wavelength, with the fastest rate on the order of 10¹⁰ s^–1. We also compare 6-TG with 9-enolguanine, for which we observed decay to a dark state with a 2 orders of magnitude smaller rate. At increased excitation energy (∼+500 cm^–1) an additional pathway appears for the predominant thiol tautomer. Moreover, the excited state dynamics for 6-TG thiols is different from that recently predicted for thiones.