Theoretical modeling of the hydrated serotonin in solution: Insight into intermolecular hydrogen bonding dynamics and spectral shift in the electronic excited states

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In this work, the intermolecular hydrogen bonding interaction in both the ground state and electronic excited states of the hydrogen bonded compounds Serotonin–(H2O)nn = 1,2 were investigated by the density functional theory (DFT) and the time-dependent density functional theory (TDDFT) method. By monitoring the structures in different electronic states, it has been demonstrated that the hydrogen bonds in Serotonin–(H2O)nn = 1, 2 are strengthened upon excitation. And the hydrogen bond site of 5-OH of the ring is always strengthened, more significantly. The simulated infrared (IR) spectrum demonstrated that the red-shifts of the stretching vibration frequencies of hydrogen bonded OH groups were consistent with the change trend of hydrogen bonds. Furthermore, the interaction among the hydrogen bonds caused by the bridged-water structure should be considered while making analysis of the calculated results such as the structure information and the IR spectrum.