The One S 1 /S 0 MECP is obtained for Ds which is non-planar with a ring-puckered structure. This is comparable with the MECP observed in the case of one of the natural DNA bases Adenine. The MECP of Ds is ∼ 10 kcal/mol lower in energy than the FC region. The MEP-PES of Ds has been constructed to estimate the energy barrier required for accessing S 1 /S 0 MECP. A barrier-less flat PES is obtained.