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Comparative Study of the Gas-phase Cyclodimer Formations of Uracil and 6-azauracil in Excited State and Through Conical Intersections S0/S1

Pavlina Bogomilova Kancheva, Vassil Borissov Delchev

Abstract


The photocyclodimerization mechanisms of two oxo tautomers of uracil and 6-azauracil were studied at the CC2 level of theory and cc-pVDZ basis functions. Uracil was explored in three orientations of the monomers - cis-anti, trans-syn and trans-anti, while 6-azauracil - in all four orientations. Conical intersections S0/S1 were found at the CASSCF(2,2)/6-31G* theoretical level. The study propose a photophysical mechanisms of photoformation and photodestruction of cyclodimers (CDs), which occur through the 1ππ* electron excited states (spectroscopically bright states). The photophysical relaxations (internal conversions) to the ground states are mediated by conical intersections S0/S1, which we found and discussed in the current paper.


Keywords


Ab initio calculations; CASSCF optimizations; conical intersections S0/S1; pyrimidine cyclodimers; uracil; 6-azauracil

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DOI: http://dx.doi.org/10.17344/acsi.2017.4040

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