Excited-state deactivation of 5-vinyluracil: Effects of π-π conjugation and intramolecular hydrogen bond CH⋯OC

•The 5-substituents induce red shift of the absorption and fluorescence spectra with respect to that of U.•The effects of vinyl substitutent are discussed, including π-π conjugation effect and intramolecular hydrogen bond.•The excited-state lifetime of 5VUA is very long for the cleavage of intramolecular hydrogen bond CH⋯OC in excited state induces a very high barrier along the decay path.

The excited-state decay mechanisms of 5-vinyluracil (5VU) are explored by using a combination of experimental and theoretical methods. The effects of vinyl substitutent, including the π-π conjugation effect and intramolecular hydrogen bond, are discussed. 5VU comprises the conformers 5VUA and 5VUB at ground state, with and without an intramolecular hydrogen bond CH⋯OC, respectively. The steady-state absorption and fluorescence spectra of 5VU are significantly red-shifted with respect to that of uracil. The time-resolved experimental results show that the excited-state decays of 5VU can be described by using three time constants: 2.26 ps, 13.45 ps and 4.66 ns. The decay pathways of 5VU obtained with the linearly interpolated internal coordinate method, predict that the two shorter lifetimes of 2.26 ps and 13.45 ps are attributed to 5VUB, and that the longest lifetime of 4.66 ns is attributed to 5VUA.

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