Structure and electronic spectra of neutral and protonated forms of anticonvulsant drug lamotrigine

In this work, the geometry, acid-base properties, pKa, electronic spectra, and fluorescence spectrum of anticonvulsant drug lamotrigine (LTG) are investigated with the DFT/TD-DFT method and PCM solvent model. Calculated transition with the B3LYP functional at 295 nm corresponds to experimental absorption transition at 306 nm in water. In acidic conditions, the computed maximum transition occurs at 249 nm, comparing with experimental one at 270 nm. The dependence of calculated transitions on density functional used and different solvents in PCM model was studied. The computed transition of fluorescence is at 435 nm, while experimental occurs at 370 nm. Maps of electrostatic potential (MEPs) for S0 and S1 reveal that the ground state of LTG is more polar than the first excited state. Structurally, in the excited state of LTG, the triazine ring is noticeably distorted.