A DFT/TDDFT study on the excited-state hydrogen bonding dynamics of 6-aminocoumarin in water solution

► Hydrogen bonding dynamics of 6-aminocoumarin in the water was investigated. ► DFT/TDDFT method has been performed to study the ground and excited states. ► Hydrogen bonds are strengthened in some excited states while weakened in others. ► Photo-induced charge transfer accounts for the weakening of hydrogen bond in the S1 state.