Tautomerism in substituted cyanopyridone: Ultrafast dynamics and TDDFT studies in water

Tautomerism of cyanopyridone (CPy) has been studied in both the ground (S0) and first singlet excited (S1) electronic states by means of steady-state and time resolved optical spectroscopy as well as time-dependent density functional theory (TDDFT) calculations. The enol (E)-to-keto (K) tautomerization reactions occur in both the ground and excited states of the neutral structures in water. Gas-phase calculations for the K and E tautomers support that both have similar energies in the ground state. Calculations of the S1 states of each tautomer suggest the energy difference between the tautomers is increased in the excited state, favoring the K tautomer.