Excited state dynamics of protonated keto uracil: intersystem crossing pathways in competition

The relaxation dynamics of protonated keto uracil has been investigated through cryogenic UV photodissociation spectroscopy. Steady-state spectroscopy and time-resolved photochemistry, including pump-probe photodissociation and kinetics of appearance of photofragments, are monitored over 10 orders of magnitude as a function of excess energy imparted in the bright 1* state. Although photofragments are produced in the ground electronic state after internal conversion, the non-radiative decay mechanism abruptly changes with a slight increase of excess energy in the 1 pi pi* state. At the band origin, a three-step decay involving electronic couplings to the charge transfer 1no pi* state and the triplet 3 pi pi* state with lifetimes in the range of 10

Automated summary

Cryogenic UV photodissociation spectroscopy was used to investigate the relaxation dynamics of protonated keto uracil. The non-radiative decay mechanism abruptly changes when a slight increase in excess energy occurs in the 1 pi pi* state, involving electronic couplings to the charge transfer 1no pi* state and the triplet 3 pi pi* state with lifetimes in the range of 10.