Theoretical study of the ground and excited states of 1-methylamideanthraquinone and its complex with fluoride anion

We have performed a series of calculations using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) for 1-methylamideanthraquinone (MAAQ). In the S-0 state of MAAQ, amide group is coplanar with anthraquinone, and an intramolecular hydrogen bond C = O center dot center dot center dot H-N is formed. The S-0 -> S-1 transition has an intramolecular charge transfer character. Two stable structures (planar nMAAQ and twisted tMAAQ) have been obtained in the S-1 state of MAAQ. Thereinto, nMAAQ is lower by 0.105eV than tMAAQ in energy, so nMAAQ is the dominant conformation in the S-1 state of MAAQ and the emission spectra of tMAAQ cannot be observed in the solution of MAAQ. Excited state intramolecular proton transfer (ESIPT) between C = O and N-H was not observed in the S-1 state of MAAQ. Upon addition of fluoride anion, only twisted conformations were obtained in both S-0 and S-1 states of MAAQ-F-. An intermolecular hydrogen bond F center dot center dot center dot H-N is formed in the S-0 state, and intermolecular proton transfer happens in the S1 state for MAAQ-F-.