The revelation of ESIPT behavior and fluoride response mechanism for (E)-2-(((1H-benzo[d]imidazol-2-yl)-imino)methyl)-5-(dimethylamino)-phenol

摘要

Given the tremendous potential of fluorescence sensors in recent years, in this work, as a kind of novel and few studied sensor containing both NH and OH binding sites, (E)-2-(((1H-benzo[d]imidazol-2-yl)-imino)methyl)-5-(dimethylamino)-phenol (bip) has been investigated on the excited state intramolecular proton transfer (ESIPT) based on time-dependent density functional theory (TDDFT) method. Our simulated absorption and fluorescence spectra based on the TDDFT method are in agreement with the experimental results. Two kinds of bip structures could found in the S-1 state, which could be attributed to the ESIPT reaction. Hydrogen bond strengthening has been testified in the S-1 state based on comparing staple bond lengths and bond angles involved in hydrogen bond between S-0 and S-1 states. The calculated infrared (IR) vibrational spectra at the O-H stretching vibrational region and theoretical hydrogen bonding energy also declare the phenomenon of hydrogen bond strengthening. The frontier molecular orbitals (MOs) analysis and Natural bond orbital (NBO) manifest the intramolecular charge transfer (ICT) characteristic for bip chromophore, which reveals the tendency of proton transfer. The potential energy curvess of the S-0 and S-1 states are constructed to explain the mechanism of the proton transfer in excited state in detail. Further, given fluorescence sensing mechanism, we present the addition of fluoride anion can spontaneously capture the hydrogen proton of hydroxyl forming intermolecular hydrogen bond O-H center dot center dot center dot F, which results in the formation of anion product with response fluoride anion.