Ultrafast electronic deactivation dynamics of the rare natural nucleobase hypoxanthine

The electronic deactivation of the 6-oxopurine derivative hypoxanthine, its nucleoside inosine and the nucleotide inosine monophosphate have been studied by femtosecond time-resolved spectroscopy after ππ∗ photoexcitation at λ = 260 nm. The development of a highly sensitive parallel broadband (near-UV/VIS) and single-color (deep-UV) transient absorption setup enabled us to monitor the excited-state decay and the ground-state recovery dynamics in one and the same experiment. The measurements revealed similar relaxation behavior, with time constants of τ1 ≲ 0.1 ps, τ2 ≈ 0.21 ± 0.08 ps and τ3 ≈ 1.8 ± 0.4 ps, for all three investigated molecules. The observed dynamics are assumed to take place through a conical intersection involving an out-of-plane puckering mode of the six-membered ring similar to guanine.