DFT calculation of geometrical structure and electronic absorption spectra for neutral, mono-, and diprotonated forms of Risperidone (Risperdal)

Vertical electronic transitions to singlet valence states of an antipsychotic drug, Risperidone (Risperdal), in its neutral, mono-, and diprotonated forms have been calculated within the time-dependent density functional theory using the PBE0 hybrid functional with the 6–31+G* basis set. The results of the computations show that the lowest-energy allowed π–π* electronic excitation is affected by protonation effects, the spectral shifts of this transition being potentially useful to individuate the different forms of risperidone