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 pi pi* photoexcitation at lambda = 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 tau(1) less than or similar to 0.1 ps, tau(2) approximate to 0.21 +/- 0.08 ps and tau(3) approximate to 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. (C) 2012 Elsevier B. V. All rights reserved.