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The interaction of 1-Phenyl-3-(pyren-1-yl) urea (LH) and fluoride anion (F - ) with a unique ON 1 -OFF-ON 2 fluorescent response has been investigated by the density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations. The hydrogen-bonding dynamics and photophysical properties of the complex LH-F, as well as its isolated receptor LH and anion form L-H 1 , have been studied in detail. We demonstrate that the intermolecular hydrogen bond (N-H…F) of the complex LH-F is greatly enhanced in the electronically excited state. The nonradiative deactivation via electron transfer and internal conversion rather than excited-state intramolecular proton transfer (ESIPT) can be facilitated by the excited state hydrogen bond strengthening. The results have been cross-validated by molecular structure, electronic spectra, frontier molecular orbitals, and infrared spectra as well as hydrogen bond binding energy. These results indicate that the current calculations completely reproduce the experimental results and provide compelling evidence for the sensing mechanism of LH for F - ., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Colorimetric and fluorescent detection of F - have attracted enormous interest owing to their simplicity, low-cost and high selectivity. However, traditional colorimetric and fluorescent sensors mainly based on the insoluble and toxic organic molecules, which is not favorable for sensing F - in water media and living cells. In this work, we designed fluorescent carbon dots (CDs) with excellent water solubility and good biocompatibility as a colorimetric and fluorescent dual-model probe for the detection of F - . The CDs were prepared by a green, one-step hydrothermal strategy from wheat straw without any additives and surface passivation. The obtained CDs exhibited a bright blue fluorescence, special response to F - and low cytotoxicity. More interestingly, a significant color change from light yellow to red can be observed by the naked eye upon addition of F - ions to the CDs solution probably due to the formation of hydrogen bonding between CDs and F - . Besides, the fluorescence of CDs also can be selectively quenched by F - with the detection limit of about 49 μM. Additionally, the CDs are also applied to intracellular imaging and sensing of F - in living cells. This strategy may provide a new method for the detection of F - in water media and biological systems., Competing Interests: Declaration of competing interest We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work., (Copyright © 2020 Elsevier B.V. All rights reserved.)

A density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations have been used to study the sensing mechanism of an ON 1 -OFF-ON 2 type fluoride anion fluorescent chemosensor (Bis[[7-(diethylamino)-2-oxo-2H-chromene]methyl-ene]‑carbonothioic dihydrazide (CTC). The current theoretical calculation presents a different sensing mechanism from the experimentally proposed one (Sensor and Actuators B 2016, 222, 823-828). Instead of the combination of CTC deprotonation and poorly emissive excited state tautomer or ICT mechanism, the theoretical results predict the sensing mechanism based on dissociation reaction and excited-state proton transfer (ESPT). The calculated vertical excitation energies both in the ground states and first excited states of different forms of CTC, as well as the potential-energy curves, have completely reproduced the experimental results, providing powerful evidence for our proposed CTC sensing mechanism for fluoride anion., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

A highly selective and sensitive colorimetric sensor based on aggregation-induced color change of 4-mercaptophenylboronic modified gold nanoparticles was designed for the determination of fluoride anion. The 4-mercaptophenylboronic modified gold nanoparticles were synthesized by a simple one-pot reaction. The aggregation process occurred when interaction between fluoride anion and 4-mercaptophenylboronic on the surface of gold nanoparticles took place; as a result, fluoroborate anions were formed coupled with changes in the electronic properties of the AuNPs. The change can be measured by UV-Vis absorption spectra. The sensor shows good selectivity and sensitivity for fluoride anion. The linear range is 10.0-30.0 μM for fluoride and the detection limit of fluoride is 3.45 × 10 -7  M according to IUPAC criteria (3σ rule). Furthermore, the sensor has been used for the detection of fluoride anion in tap water, ground water and human serum samples, the recovery can achieve 94.0%-103.3%, 94.7%-101.0% and 89.8-100.9%, respectively. The excellent performance of colorimetric sensor in the detection of the fluoride anion demonstrated the potential application in the detecting fluoride anion present in the complex environmental and biological samples., (Copyright © 2019. Published by Elsevier B.V.)

A series of colorimetric and reversible receptors for fluoride anions based on diketopyrrolopyrrole (DPP) were designed and synthesized successfully. The position of nitro substituent on the phenylhydrazide affected the alteration of photophysical properties to varying degrees. While the photoluminescence intensity of receptor 1 was weaker than that of receptor 2 and receptor 3 on account of the formation of intramolecular hydrogen bond deriving from oxygen atom of nitro substituent and hydrogen atom of hydrazide. The receptor 2 was a preferable chemosensor for responding fluoride anions. The fluorescence was quenched in the presence of fluoride anion resulted from the photo-induced electron transfer (PET) effect from the amide. The formation of deprotonation species, which produced by hydrazide NH moiety and F - was answerable for the spectral changes. Especially, the spectral and color responses of receptors could be switched back and forth successively by adding F - and HSO 4 anions in DMSO solution. These receptors could response fluoride anion sensitively, visually and selectively in a manner of reversible with a low determination.- anions in DMSO solution. These receptors could response fluoride anion sensitively, visually and selectively in a manner of reversible with a low determination., (Copyright © 2018 Elsevier B.V. All rights reserved.)

A novel silicon-oxygen aurone derivative TBDPSA was synthesized and used for the detection of fluoride anions in aqueous solution based on a specifically F - -triggered silicon-oxygen cleavage. Even though the compound has shown high selectivity, obvious absorption and fluorescence response for fluoride anions in aqueous solution, but it also is suffered from many limits, such as low detection sensitivity and long response time. Here the compound was successfully assembled on the graphene oxide (GO) surface by π-π stacking. GO improves recognition sensitivity and shortens response time of TBDPSA for fluoride anions by taking advantage of the nanocarrier GO. Compared with TBDPSA, the response time of GO/TBDPSA is shortened greatly from 1h to <5s and the detection limit is lowered about four times with fluorescence as detected signal. Generally speaking, GO is an excellent promoter for accelerate recognition., (Copyright © 2017 Elsevier B.V. All rights reserved.)