Theoretical study of 2-selenoformyl-3-thioxo-propionaldehyde (STP) in the exited states

Subject Areas :

ramin rafat ^{1 *} , alireza nowroozi ²

1 - Department of Chemistry, Faculty of Science, University of Sistan and Baluchestan (USB), P.O.Box 98135-674, Zahedan, Iran
2 - Department of Chemistry, Faculty of Science, University of Sistan and Baluchestan (USB), P.O.Box 98135-674, Zahedan, Iran

Received: 2019-04-27 Accepted : 2019-07-04 Published : 2019-05-22

Keywords: tautomeric equilibriums, &pi, -electron delocalization, Intramolecular hydrogen bond, excited states,

Abstract :

In the present study, tatomerism process, hydrogen bond strength and π-electron delocalization of 2-selenoformyl-3-thioxo-propionaldehyde (STP) in the singlet and triplet excites states were investigated. First, all of the H-bonded structures in exited states were optimized by CIS and TD-DFT methods. Relative energies indicate that the thiol and enol conformers are the most stable and unstable, respectively: HB Thiol < HB Selenol < HB Enol. Moreover, the electronic energies show that all of the H-bonded structures are more stable in the triplet excited state than the singlet excited state. To justify this order, the affective factors on this stability such as tautomerism, hydrogen bonding and π-electron delocalization were comprehensively investigated. Tautomeric energies express that the thiol tautomer is more stable than the others in terms of thermodynamics. Also, the activation barriers indicate that the thio⇋thiol is more prefer than the other equilibriums, from kinetic point of view. Description of different hydrogen bonds by energetic, geometrical, topological and molecular orbitals emphasize on the presence of a stronger intramolecular hydrogen bond (IMHB) in the enol forms. Furthermore, evaluation of π-electron delocalization (π-ED) represents approximate superiority of enol conformers. The achieved results by HB and π-ED analyzes are in contrast with the mentioned stability order. Ultimately, investigation of above factors indicates that the tautomerism phenomenon plays a dominant role in determining of the structures stability in the excited states.