Photoisomerization and thermal reversion of 5-arylmethylene-2-thioxoimidazolidin-4-one

PEPINO, A. J. ; BURGOS, M.; PELÁEZ, W. J. ; ARGÜELLO, G. A.

Santiago de Chile, Chile

Congreso; 10th Congress of the World Association of Theoretical and Computational Chemists WATOC 2014; 2014

Facultad de Química, Pontificia Universidad Católica de Chile, Santiago, Chile.

Photoinduced isomerization Z/E (cis/trans) is an elementary chemical reaction of fundamental importance in natural biological photoreceptors. This process is the mechanism of choice to trigger large amplitude motion in molecular photo-switches and used to photo-induce peptide folding, control ion complexation or gate the transport properties of ion channels. 1 Thus, looking for new molecules with the possibility of photoisomerization and understanding each detail of the reaction mechanism has become of great importance. To the best of our knowledge, there is no study on the Z/E isomerization mechanism of 5-arylmethylene-2-thioxoimidazolidin-4-ones (1). The pharmaceutically active compounds as antimycobacterials, immunomodulators, anticonvulsivants and antifungal 2 that present the 5-arylmethylene-2-thioxoimidazolidin-4-one nucleus have been a motivating factor for developing improved methods for their synthesis and examination of their reactivity. It is known that they can exist in their Z and E forms, where Z is the preferred, but there are no studies devoted to explain that stability and the mechanism of conversion. In this work, we studied the photochemical isomerization Z→E and the thermal reversion of 1 (figure 1) supporting our experimental results with ab initio calculations at the CASSCF level. The reaction coordinate was simulated in the ground and excited states (S0, S1, S2 and T1). The results lead us to purpose a first excitation to S2 state of π← π* character, followed by a conical intersection to the S1 (n←π* character) where the izomerization through a new conical intersection S0/S1 occurs. For thermal reversion three different mechanisms were proposed concluding that it involves a birradical formation explained by an intersystem crossing (IRC) between S0 and T1 states.