Towards the understanding of the photochemical ring opening and closing mechanisms for spiropyrans using 2H-pyran and the maximum overlap method
Department of Chemistry, University of Ruhuna, Matara, Sri Lanka
Received in final form: 9 May 2013
Published online: 19 August 2013
A first principle study on 2H-pyran has been carried out to elucidate the photochemical ring opening and closing mechanism of spiropyrans. A systematic study on relative energies using Hartree-Fock, density functional and post-Hartree-Fock methods was carried out to determine an appropriate level of theory for these systems. Second order Møller–Plesset perturbation theory (MP2) shows good agreement with the CCSD calculations, converges at the 6-31 + G(2df,p) basis set level and predicts the closed ring structure as the most stable. The maximum overlap method (MOM) was used to calculate the excited states of both 2H-pyan and the open ring structure 2,4-pentadienal. Excitation of the planar form of 2H-pyran at 189 nm leads to direct photochemical ring opening. Excitation of the open-ring structure at 283 nm causes the reverse process, ring closing, to occur. Our excited state calculations indicate that thermal conversion of the more stable puckered structure of 2H pyran into the planer form needs to take place before the photochemical ring opening can occur.
Key words: Molecular Physics and Chemical Physics
© EDP Sciences, Società Italiana di Fisica and Springer-Verlag 2013