Protonation effect on the electronic properties of 2-pyridone monomer, dimer and its water clusters: A theoretical study

The CC2 (second order approximate coupled cluster method) has been applied to investigate protonation effect on electronic transition energies of 2-pyridone (2PY), 2-pyridone dimer, and micro-solvated 2-pyridone (0-2 water molecules). The PE profiles of protonated 2-pyridone (2PYH(+)) as well as monohydrated 2PYH(broken vertical bar) at the different electronic states have been investigated. The (1)pi sigma* state in protonated species (2PYH(broken vertical bar)) is a barrier free and dissociative state along the O-H stretching coordinate. In this reaction coordinate, the lowest lying (1)pi sigma* predissociates the bound S-1((1)pi pi*) state, connecting the latter to a conical intersection with the S-0 state. These conical intersections lead the (1)pi pi* state to proceed as predissociative state and finally direct the excited system to the ground state. Furthermore, in presence of water molecule, the (1)pi sigma* state still remains dissociative but the conical intersection between (1)pi sigma* and ground state disappears. In addition, according to the CC2 calculation results, it has been predicted that protonation significantly blue shifts the S-1-S-0 electronic transition of monomer, dimer, and microhydrated 2-pyridone. (c) 2014 AIP Publishing LLC.