Optical properties of newly synthesized molecular two-photon fluorescent probes containing diketopyrrolopyrrole are investigated using density functional theory. Drastic changes in photoabsorption and photoemission of the probes are demonstrated when the probes react with fluoride anion. Responsive mechanism of the probes is analyzed by comparing milliken population of the molecules in the absence and presence of fluoride anion, which is attributed to intramolecular charge transfer. In addition, terminal group is found to be crucial to the sensing performance of the probes. Our results can elucidate the available experimental measurements. Additionally, valuable knowledge for designing efficient fluorescent chemosensors is proposed. (C) 2016 Elsevier B.V. All rights reserved.