Femtosecond dynamics of a cardiotonic medicine (milrinone) in neutral water

Milrinone is a medicine used to attenuate heart attack disease. Understanding its interaction with water is of importance for the knowledge of its stability and related phenomena. This intimate information requires the unraveling of the dynamics under the physiological conditions. Here we report the first study of ultrafast processes of this medicine. We show that S2 relaxation of the keto structure (K) occurs in ∼150 fs and the intramolecular-charge transfer reaction in less than 100 fs to produce a relaxed CT-K state. An observed ∼10 ps decay is assigned to vibrational relaxation/cooling and twisting in the formed CT-K.