Fluoride Anion Sensing Mechanism Of 2-(Quinolin-2-Yl)-3-Hydroxy-4h-Chromen-4-One Chemosensor Based On Inhibition Of Excited State Intramolecular Ultrafast Proton Transfer

The excited state hydrogen bonding interactions and intramolecular proton transfer (ESIPT) process for 2-(quinolin-2-yl)-3-hydroxy-4H-chromen-4-one (Qu3HC) system has been theoretically studied via density functional theory (DFT) and time-dependent DFT (TDDFT) methods. We confirmed that the reversible tuning of intramolecular hydrogen bonding direction is impossible for Qu3HC system. Then, we have studied the S-0-state and S-1-state hydrogen bonding dynamical behaviors of Qu3HC structure and confirmed that the strengthening of intramolecular hydrogen bond in the S(1)state could facilitate ESIPT reaction. Given photo-induced excitation, we find that the charge redistribution around hydroxyl moiety plays important roles in providing driving force for ESIPT. Our constructed potential energy curves further verify that the ESIPT process of Qu3HC should be ultrafast due to low potential barrier. With the addition of fluoride anions, the exothermal deprotonation process occurs spontaneously along with the intermolecular hydrogen bond O-H center dot center dot center dot F, which reveals the uniqueness of detecting fluoride anion using Qu3HC molecule. As a whole, the fluoride anion inhibits the initial ESIPT process of Qu3HC, which results in different fluorescence behaviors.