2,6-Diaminopurine (2,6-dAP) is an alternative nucleobase that potentially played a role in prebiotic chemistry. We studied its excited state dynamics in the gas phase by REMPI, IR-UV hole burning, and ps pump-probe spectroscopy and performed quantum chemical calculations at the SCS-ADC(2) level of theory to interpret the experimental results. We found the 9H tautomer to have a small barrier to ultrafast relaxation via puckering of its 6-membered ring. The 7H tautomer has a larger barrier to reach a conical intersection and also has a sizable triplet yield. These results are discussed relative to other purines, for which 9H tautomerization appears to be more photostable than 7H and homosubstituted purines appear to be less photostable than heterosubstituted or singly substituted purines.

Department of Chemistry and Biochemistry University of California Santa Barbara California USA

Institute of Advanced Materials Faculty of Chemistry Wrocław University of Science and Technology Wrocław Poland

Institute of Biophysics of the Czech Academy of Sciences Brno Czech Republic

Regional Centre of Advanced Technologies and Materials Czech Advanced Technology and Research Institute Palacky University Olomouc Olomouc Holice Czech Republic

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