Abstract
Gas-phase ultrafast excited-state dynamics of cytosine(Cy)-(H2O)n=4-6, Cy-(MeOH)n=1-3, and Cy-(THF)1 micro-solvated clusters were investigated in molecular beams using femtosecond pump-probe photoionization spectroscopy at about 266 nm excitation to identify the effect of protic and aprotic solvents to the cytosine intrinsic dynamics. The results suggest that the presence of protic solvent molecules allows an extensive relaxation of Cy-(H2O)n=1-6, and Cy-(MeOH)n=1-3 to the lowest-energy tautomer isomers, but aprotic solvent molecules do not exhibit such behaviors. Excited-state lifetimes of Cy-(H2O)n=1-6 and Cy-(MeOH)n=1-3 measured here are 0.2-0.5 ps. On the other hand, there are two components in the Cy-(THF)1 transient: one with an excited-state lifetime of 0.48 ps, and the other ~ 10 ps. The shorter component is ascribed to the keto form of Cy-THF, whereas the longer component is attributed to the enol form of Cy-THF. Comparisons of the Cy-(THF)1 and cytosine monomer transients suggest that THF has a stronger effect on enol-cytosine than keto-cytosine.