The sensing mechanism of a reported fluorescent sensor based on Si-O bond for fluoride was studied by (TD)DFT calculations. The reaction energy of fluoride is calculated to be the lowest among various anions, indicating the high selectivity of this sensor. The structures were confirmed by geometry optimizations and scanning potential-energy curves. This sensor could emit strong fluorescence by its local S-1-S-0 transition. The phenolate anion would change its structure at the S-1 state, decreasing its energy and emitting weak fluorescence, which is resulted by a photoinduced electron transfer process. (C) 2014 Published by Elsevier B.V.