Excited-state dynamics of oxazole: A combined electronic structure calculations and dynamic simulations study

In the present work, the combined electronic structure calculations and surface hopping simulations have been performed to investigate the excited-state decay of the parent oxazole in the gas phase. Our calculations show that the S-2 state decay of oxazole is an ultrafast process characterized by the ring-opening and ring-closure of the five-membered oxazole ring, in which the triplet contribution is minor. The ring-opening involves the O-C bond cleavage affording the nitrile ylide and airine intermediates, while the ring-closure gives rise to a bicyclic species through a 2-5 bond formation. The azirine and bicyclic intermediates in the S-0 state are very likely involved in the phototranspositions of oxazoles. This is different from the previous mechanism in which these intermediates in the T-1 state have been proposed for these phototranspositions. (C) 2016 Elsevier B.V. All rights reserved.