?Excited State Dynamics of Cold Protonated Cytosine Tautomers: Characterization of Charge Transfer, Inter System Crossing and Internal Conversion Processes?

M. BROQUIER; S. SOORKIA; G. A. PINO; C. DEDONDER-LARDEUX; C. JOUVET; G. GRÉGOIRE

JOURNAL OF PHYSICAL CHEMISTRY A

AMER CHEMICAL SOC

Lugar: Washington; Año: 2017 vol. 121 p. 6429 - 6439

1089-5639

Charge transfer reactions are ubiquitous in chemical reactivity and often viewed as ultrafast processes. For DNA, femtochemistry has undeniably revealed the primary stage of the deactivation dynamics of the locally excited state following electronic excitation. We here demonstrate that the full time scale excited state dynamics can be followed up to millisecondsthrough an original pump−probe photodissociation scheme applied to cryogenic ion spectroscopy. Protonated cytosine is chosen as a benchmark system in which the locally excited 1ππ* state decays in the femtosecond range toward long-lived charge transfer and triplet states with lifetimes ranging from microseconds to milliseconds, respectively. A three-step mechanism (1ππ* → 1CT → 3ππ*) is proposed where internal conversion from each state can occur leading ultimately to fragmentation in the ground electronic state.