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For TNP chemosensor 2-(4,5-Bis(4-Chlorophenyl)-1H-Imidazol-2-yl)-4-Chlorolphenol (HPICI), previous thought with no theoretical basis was that excited-state intramolecular proton transfer (ESIPT) process and the ground-state HPICI-TNP complex are mainly responsible for its fluorescence emission and the detection of TNP. However, this interpretation has been proved to be wrong by the present theoretical DFT/TDDFT explorations. Actually, the strong fluorescence of HPICI is mainly induced by the local excitation of the enol form HPICI(E) without ESIPT, and the fluorescence quenching by TNP is due to the photo-induced electron transfer (PET) process together with the cooperative effect of hydrogen-bonding interaction and π-π stacking interaction coexisting in the HPICI-TNP complex. The strengthened excited-state hydrogen bond promotes the PET process, thus facilitates the fluorescence quenching. This mechanism is proposed on the basis of the theoretical analyses on molecule geometry, binding energy, Gibbs free energy, electronic transitions, and frontier molecular orbitals (FMOs).

In this work, the fluorescence turn-on mechanism of glutathione probe azido-substituted 2-(2′-hydroxyphenyl)benzoxazole derivative (AHBO) has been thoroughly studied based on the density functional theory and time-dependent density functional theory methods. The constructed potential energy curves demonstrate that the proton transfer (PT) processes of the probe AHBO and the final product AHBOG after the glutathione-azide reaction are more likely to occur in the first excited state than in the ground state. Results of frontier molecular orbital analyses show that the S1 state of AHBO is a complete charge-separation state, and the non-radiative acceptor-excited photoinduced electron transfer (a-PET, fluorophore as the electron acceptor) from the excited azide group to the 2-(2′-hydroxyphenyl)benzoxazole (HBO) would take place upon photoexcitation, which is responsible for the fluorescence quenching of the probe AHBO. Whereas, without the electron-rich azide group, the product AHBOG undergoes the excited state intramolecular proton transfer (ESIPT) in conjunction with the weak intramolecular charge transfer (ICT) process in the S1 state. The absence of the a-PET and the two processes mentioned above provide explanations for the fluorescent enhancement observed with the product AHBOG.

Proton-coupled electron transfer (PCET) reactions play important roles in solar energy conversion processes. Designing efficient artificial photosystems with PCET mechanisms is a promising solution for the growing demands of energy resources. Compared to ground states, inducing the PCET reactions directly from electronically excited states, named excited-state PCET (ES-PCET) reactions, is a more direct and efficient avenue to the formation of solar fuels. Here, based on benzimidazole phenolic derivatives, we have designed and studied some molecular structures that can undergo the electron-driven double-proton transfer (EDDPT) reactions within the ES-PCET framework. According to our DFT/TDDFT calculation results, the two protons transfer in a stepwise manner in the EDDPT process, and compared to the common way of electron-driven single-proton transfer (EDSPT) reactions, the proton transfer in the EDDPT process not only has a smaller energy barrier but also experiences a longer transferring distance, which has beneficial effects on producing solar fuels. The study of ES-PCET reactions under the mechanism of EDDPT may cast light on the regulation of proton transfer at defined distances and time scales, which is important in energy conversion processes.

We performed DFT/TDDFT investigation on the sensing mechanism of the D–π–A type fluorescence probes 4-(5-R-thiophen-2-yl)-2-isobutyl-2H-[1,2,3]triazolo[4,5-e][1,2,4] triazolo[1,5-a]pyrimidines (ITTP1, ITTP2, ITTP3), which are designed for detecting 2,4,6-trinitrophenol (TNP) explosive. Theoretical calculations reveal that the fluorescence sensing mechanism was induced by the combination of the π–π stacking interaction and photo-induced electron transfer. The blueshift in the UV–Vis spectrum of the ITTP sensors was correlated with the decrease in electron-donating ability of the molecule probes and was further evidenced by the calculated 1H NMR spectra and DCT index. The roles of the weak interactions: π–π stacking and hydrogen-bonding interaction for the probes fluorescence sensing process were analyzed, and the π–π stacking interaction was verified to be the dominant for the fluorescence sensing. The present finding should be useful for the future design of explosive fluorescent probes and the interpretation of the sensing mechanisms.

The excited-state proton transfer (ESPT) mechanism of 3,7-dihydroxy-2-phenyl-6-acetyl-4H-chromen-4-one (DPACO) fluorophore was studied by the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) with CAM-B3LYP functional and 6–31 +G(d,p) basis set. The computation levels are reliable as evidenced by the accordance between theory and experiment. In the ground state of DPACO, two intramolecular hydrogen bonds were formed. After photo-excitation, the electron density redistributions provide the driving force for hydrogen-bonding strengthening and ESPT. The constructed potential energy surfaces (PESs) along proton transfer (PT) coordinates indicate that two PT channels exist in the excited state. Among various PT tautomers, T4*is theoretically assigned as the main fluorescence emitter, while the low fluorescence quantum yield possibly correlate with the accelerated internal conversion pathway in the PT tautomer T6*.

To investigate the dynamics mechanism of the Br + HgBr → Br2 + Hg reaction, the quasi-classical trajectory calculations are performed on Balabanov’s potential energy surface (PES) of ground electronic state. Both the scalar and vector properties are investigated to recognize the dynamics of the title reaction. Reaction probability for the total angular momentum quantum number J = 0 is determined at the collision energies (denoted as Ec) in a range of 1–25 kcal/mol, and the product vibrational distributions are given and compared between Ec = 20 and 40 kcal/mol. Other calculation values characterizing product polarizations including polarization-dependent differential cross sections (PDDCSs), distributions of P(θr), P([Formula: see text]), and P(θr, [Formula: see text]), are all discussed and compared between the two different collision energies in detail to analyze the alignment and orientation characteristics. It is revealed that the products prefer forward scattering and the PDDCSs are anisotropic in the whole range of the scattering angle. The product rotational angular momentum j′ shows a tendency to align perpendicular to the reagent relative velocity k. In fact, the product polarization of the title reaction is weak at both collision energies. In terms of horizontal comparison, the alignment is slightly stronger but the orientation is even less remarkable at higher collision energy.

Based on the density functional theory and time-dependent density functional theory, we have investigated the zwitterionic structure of the excited 4-([2,2′-bipyridine]-4-yl) phenol (bpy-phenol) photoacid molecules. The zwitterion can be formed stepwisely via a proton-coupled electron transfer (PCET) reaction in a H-bonded bpy-phenol…F− complex and an intermolecular excited state proton transfer (ESPT) reaction between HF molecules and excited deprotonated anions of bpy-phenol. Supported by the results of Hirshfeld population analysis and electrostatic potential, a basic site was generated in the bpy residue due to the PCET process. With a proper F− ions concentration, the ESPT reaction can be occurred with little barrier between the HF molecules and the bpy-phenol anions, leading to the generation of zwitterions. Moreover, the zwitterion fluoresces at 550 nm, which is longer than that of bpy-phenol anions at 490 nm. Our finding not only discovers the zwitterionic process of photoacid molecules, but also pioneers a frontier field of activity study after PCET reactions.

The sensing mechanism of a fluoride-anion probe BODIPY-amidothiourea (1c) has been elucidated through the density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations. The theoretical study indicates that in the DMSO/water mixtures the fluorescent sensing has been regulated by the fluoride complex that formed between the probe 1c/two water molecules and the fluoride anion, and the excited-state intermolecular hydrogen bond (H-B) plays an important role in the fluoride sensing mechanism. In the first excited state, the H-Bs of the fluoride complex 1cFH2 are overall strengthened, which induces the weak fluorescence emission. In addition, molecular orbital analysis demonstrates that 1cFH2 has more obvious intramolecular charge transfer (ICT) character in the S1 state than 1cH2 formed between the probe 1c and two water molecules, which also gives reason to the weaker fluorescence intensity of 1cFH2 . Further, our calculated UV-vis absorbance and fluorescence spectra are in accordance with the experimental measurements. © 2018 Wiley Periodicals, Inc.

In this paper, the synthesis and spectral properties of a fluorescent probe Nph-An for TNP detection has been introduced and its sensing mechanism has been studied with density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. For TNP detection in aqueous solution the probe shows high sensitivity, selectivity and efficiency. The theoretical results demonstrate that the excited-state intermolecular hydrogen bonding (H B) plays an important role for the TNP detection. In the excited state, the intermolecular H B between Nph-An and TNP is strengthened, and thus strongly facilitates the nonirradiative PET process to induce the fluorescence quenching. Whereas, the probe Nph-An emits strong fluorescence because of the intramolecular charge transfer (ICT) properties, which is confirmed by the solvatochromism effect. The calculated absorption spectra of Nph-An and Nph-An + TNP agree well with the experimental values and theoretical analysis provides a detailed and clear explanation of the sensing mechanism.

In order to address an all-inorganic halide lead-free perovskite for potential photovoltaic applications, we carried out first-principles calculations of bandgaps of 260 all-inorganic halide perovskites belonging to the class ABX3, with A = Li, Na, K, Rb, Cs, B = Pb, Sn, and Ge, and X = F, Cl, Br, I. Three most common crystal symmetries were chosen, including cubic, tetragonal, and two orthorhombic phases. The bandgap exhibited increase with the decreasing of the anions radius (I, Br, Cl, F) and lowering the symmetry of the structures. With consideration of multiple factors forming perovskites, we reported three all-inorganic lead-free halides perovskites including cubic-KSnCl3, cubic-RbSnCl3, and trigonal-NaGeBr3 as candidates with desirable bandgap (1.24–1.44 eV) for photovoltaic applications.

Density functional calculations have been performed to investigate the acidities for the carboxylated single-wall carbon nanotubes and graphene. The pKa values for different COOH-functionalized models with varying lengths, diameters and chirality of nanotubes and with different edges of graphene were predicted using the SMD/M05-2X/6-31G* method combined with two universal thermodynamic cycles. The effects of following factors, such as, the functionalized position of carboxyl group, the Stone-Wales and single vacancy defects, on the acidity of the functionalized nanotube and graphene have also been evaluated. The deprotonated species have undergone decarboxylation when the hybridization mode of the carbon atom at the functionalization site changed from sp2 to sp3 both for the tube and graphene. The knowledge of the pKa values of the carboxylated nanotube and graphene could be of great help for the understanding of the nanocarbon materials in many diverse areas, including environmental protection, catalysis, electrochemistry and biochemistry.

In this article, the sensing mechanism of cyanide anion chemosensor 2-((2-phenyl-2H-1,2,3-triazol-4-yl)methylene)malononitrile ( M1 ) has been investigated through the density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. The theoretical results demonstrate that the reaction barrier of 13.02 kcal/mol means a favorable response speed of the chemosensor M1 for cyanide anion. Cyanide anion attacks C=C double bond and hinders the ICT process from the malononitrile moiety to the fluorophore phenyl ring. The high viscosity of DMSO restrains the twisting of the group, inhibits the formation of the ICT state in the first excited state. Due to weak ICT character, the nucleophilic addition product shows the dramatic “off–on” fluorescence enhancement. Meanwhile, intramolecular charge transfer (ICT) mechanism accounts for how different solvents influence the fluorescence spectra. That is, more obvious ICT character of product in EtOH causes fluorescence quenching. The “reaction-based” recognition mode and large bond energy between M1 and cyanide anion minimize the interference by other anions, such as F − , AcO − . Thus, the chemosensor M1 has a high selectivity for cyanide.

The ion pairing state of the ionic liquids greatly depends on the cosolvent which subsequently affects the properties and the functionalities. Density functional calculations have been performed to study the ion pairing formation process of protic ionic liquids (PILs) ([Et3NH][CH3SO3]/TEAMS or [Et3NH][CF3SO3]/TEATF) dissolved in different solvents. The clusters involving the cation, anion, and different number of solvent molecules have been used to simulate the contact ion pairs (CIPs) and the solvent-separated ion pairs (SIPs) in the mixtures with varying solvent concentrations. The geometric, energetic data, and the natural bond orbital analysis suggest the smallest number of the water molecules required to break the TEAMS CIPs is four, while it is three for TEATF. This is consistent with the experimental prediction that if the mixture of TEAMS and water was replaced by TEATF and water, the transition process began at a lower water concentration. Furthermore, the calculated results also confirm that the weakly polar organic solvents favor the CIP form at all solvent concentrations, while the high polarity solvents promote dissociation of the CIP to generate the SIP form for particular PILs. The different separation nature of the given solvents can be interpreted in terms of their distinct hydrogen bond donor and acceptor abilities.

The interaction between hydrogen donor and acceptor molecules, known well as hydrogen bonding, forms a ubiquitous network in the natural and synthesis world. The hydrogen bonding role has thus been the subject of intensive work in the past. In this article, we discuss and show how the new mechanisms have been established in terms of the hydrogen bonding changes by reviewing some of the combined experimental and theoretical studies that have recently shed light on the intricate role of both triplet and singlet excited-state hydrogen bondings in photoinduced liquid dynamics and phenomena.

The simultaneous biothiols-differentiating fluorescence detecting feature of a boron dipyrromethene (BODIPY) derivative (Probe1) has been investigated through DFT/TDDFT calculations. Two decay pathways are revealed for the fluorescence sensing process, and the probe's ability to simultaneously and fluorescently differentiate cysteine (Cys), homocysteine (Hcy), sulfureted hydrogen (H2S), glutathione (GSH) is associated with the different excited-state properties of Probe1 and the biothiols-induced reaction products: the S1 state of Probe1 and the GSH/H2S-induced reaction product NBD-S-GSH/NBD-S is non-emissive, with complete/obvious charge separation; whereas, the S1 state of Cys/Hcy-induced reaction product NBD-S-Cys/NBD-S-Hcy as well as a common product P1 from all biothiols-induced reactions is a bright emissive state. The energetic and charge features of the excited states suggest a donor photoinduced electron transfer mechanism for the fluorescence quenching. It is also found that the intramolecular charge separation character of S1 state accounts for some of spectral behaviors, such as the signal intensity changes and the spectral shift, which can also be utilized in the simultaneously differentiating sensing of biothiols.

Density functional calculations have been performed to revisit the reversal of the product enantioselectivity in proline-catalyzed amination between propanal and diethylazodicarboxylate under basic conditions. The efficiencies of three stereodetermining transition state models, involving the key intermediates with different nucleophilic natures e.g. enamine carboxylic acid, enamine carboxylate, and prolinate–DBUH+ to mimic the base-free and basic conditions, are examined at the SMD/mPW1K/6-31+G∗∗ computational level. The activation strain analysis has been employed to explain the stereoselectivity associated with different models. The TS model involving the experimentally validated ion pair intermediate of prolinate–DBUH+ as the key nucleophile in the C N bond formation step exhibits good performance in reproducing the observed reversal of enantioselectivity when switching the conditions from base-free to base-present. The computations support the idea that the simple acid/base manipulation can change the active intermediates and subsequently alter the asymmetric induction strategy in the stereodetermining step.

Through the numerical solution of the 3D time-dependent Schrodinger equation, the two-dimensional photoelectron energy spectra (PES) of argon have been calculated, showing good accordance with the experimental measurements. Further analysis on the TDSE calculated data and comparison of PES under linearly and circularly polarized laser pulses demonstrated that the forward rescattering of the recolliding electron is mainly responsible for the appearance of the low energy structure (LES) in the PES. It is further revealed that the LES is correlated with the high angular momenta ( l = 8 – 13 ) of the photoelectron.

In this review article, we discuss and analyze the validities of centrifugal sudden (CS) approximations in chemical reactions, with emphasis on the recent progress in the comparison studies of close-coupling and CS approximations in chemical dynamics both adiabatically and nonadiabatically. All these relevant studies are performed using the time-dependent wave packet approach, focusing on several typical and benchmark chemical reactions, for example, the triatomic adiabatic ion-molecule reactions of Ne + H-2(+), He + HeH-, O- + H-2, O+ + D-2, and O+ + HD, the triatomic nonadiabatic reactions of N+NH and O+N-2, and the tetraatomic and polyatomic adiabatic reactions of H-2 + D-2 and H + CHD3. (C) 2015 Wiley Periodicals, Inc.

Two-electron harmonic emission from the He atom has been investigated by solving the two-electron time-dependent Schrodinger equation (TDSE), which exhibits an extended plateau and many new harmonic cutoffs beyond the classical single-electron harmonic cutoff. Theoretical analyses show that these extended new cutoffs are caused by the sequential double recombination and the nonsequential double recombination of the two electrons, which is a general characteristic for the two-electron harmonic emission and which is revealed through the investigation on laser parameter effects. Moreover, from analyzing the time-dependent wave functions, the motions of the two electrons and the single and double ionization time have been described.

The above-threshold ionization (ATI) process of argon in intensive circularly polarized laser field has been investigated by solving the time-dependent Schrödinger equation in length gauge with emphasis on pulse duration effect. It is shown that the influence of pulse duration is obvious on the transition between multiple-photon and tunneling ionization regimes when the Keldysh parameter is no more than 3.25. That is, photoelectron ionization by shorter pulse occurs in the tunneling regime mainly, and yet the multiple-photon absorption appears more easily with longer pulse. However, such influence disappears when the Keldysh parameter is sufficiently large and the ATI always appears in the multiple-photon ionization regime.

In this work, spectroscopic techniques and quantum chemistry calculations were used to investigate the photophysical properties of 2-ureido-4[1H]-pyrimidinone (UPy) systems in two different solvents of DMSO and DCM. The investigations were carried out on the three UPy systems (AnUP, NaUP and UPNa) with two different choromophores (i.e., anthracene and naphthalene) located at the head and the tail part of the UPy module. In DCM the UPy systems exist as the Keto-2 form that self assembles into a dimer through quadruple H-B arrays AADD–DDAA (solute–solute hydrogen bonds). In DMSO the UPy systems exist in the Keto-1 form which then forms a hydrogen bond complex with the solvent through solute–solvent interaction. The differences in excited state hydrogen bond dynamics and in configuration dynamical processes, account for the measured different fluorescence lifetimes and fluorescence quantum yields (FQY, ΦF) of the UPy systems studied in this work.

By using density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods, the sensing mechanism of a fluorescent probe 2-(2-hydroxyphenyl) benzothiazole (HBT) derivative HBTPP-S for hydrogen sulfide has been thoroughly studied. The thiolysis reaction has a moderate reaction barrier of 18.40 kcal mol–1, which indicates that the hydrogen sulfide sensing process has a favorable response speed. Because of the nonradiative donor-excited photoinduced electron transfer (d-PET, fluorophore as the electron donor) from the excited HBTPP group to the electron-withdrawing 2,4-dinitrophenyl group, as well as the inhibition of the proton transfer (PT) and the excited state intramolecular proton transfer (ESIPT) process by 2,4-dinitrophenyl group, the probe HBTPP-S is essentially nonfluorescent. On the other hand, the added hydrogen sulfide induces the thiolysis of the 2,4-dinitrophenyl ether bond, and then the thiolysis product HBTPP comes into existence. The theoretically simulated potenti...

In this paper, density functional theory (DFT) calculation was employed to study the adsorption of nitric oxide (NO) on the highly reactive anatase TiO 2 (0 0 1) surface. For comparison, the adsorption of NO on the (1 0 1) surface was also considered. Different from the physical adsorption on the (1 0 1) surface, NO molecules are found to chemisorb on the TiO 2 (0 0 1) surface. The twofold coordinate oxygen atoms (O2c) on the anatase (0 0 1) surface are the active sites. Where NO is oxidized into a nitrite species (NO 2 − ) trapping efficiently on the surface, with one of the surface Ti 5c –O 2c bonds adjacent to the adsorption site broken. Our results, therefore, supply a theoretical guidance to remove NO pollutants using highly reactive anatase TiO 2 (0 0 1) facets.

The biothiols sensing mechanism of (E)-7-(diethylamino)-3-(2-nitrovinyl)-2H-chromen-2-one (DCO) has been investigated using the density functional theory (DFT) and time-dependent DFT methods. The theoretical results indicate that the excited-state intermolecular hydrogen bonding (H-B) plays an important role for the biothiols sensing mechanism of the fluorescence sensor DCO. Multiple H-B interaction sites exist in DCO and in its Michael addition product DCOT, which then induce the formation of the H-B complexes with water molecules, DCOH2 and DCOTH4. In the first excited state, the intermolecular H-Bs between water molecule and DCO in DCOH2 are cooperatively and generally strengthened and thus induced the weak fluorescence emission of DCO, while the cooperative H-Bs between water molecule and DCOT in DCOTH4 are overall weakened and thus responsible for the enhanced fluorescence emission of DCOT. Moreover, the theoretical results suggest that the blue shift of the UV-Vis absorption spectrum of DCOT can be attributed to the relatively weak excited-state intramolecular charge transfer in DCOT compared to DCO.

The collision dynamics of deuterium molecule with excited-state nitrogen atom has been investigated at a state-to-state dynamic level by using the real wave packet method. The energy-dependent beha...

The time-dependent density functional theory (TDDFT) method has been applied to investigate the thiazolidinedione (TZD) derivative A and its hydrogen-bonded complexes with dimethylformamide (DMF) (A-DMF and A-2DMF). The calculation results showed that the excited-state hydrogen bondings of O-H⋯O=C and N-H⋯O=C are strengthened and weakened in the hydrogen-bonded trimer A-2DMF, and their cooperation effect caused a blue shift in the electronic spectrum of A-2DMF. This modulation mechanism of the hydrogen-bond strengthening and weakening and its role in influencing the spectroscopy property of the TZD derivative A in DMF have been analyzed and showed in details.

The sensing mechanism of the aqueous fluoride chemosensor N-(3-(benzo[d]thiazol-2-yl)-4-(tert-butyldiphenyl silyloxy)phenyl)-benzamide (BTTPB) has been studied in detail by DFT/TDDFT methods. The desilylation reaction which has a moderate transition barrier of 17.6 kcal mol−1 and the excited state intramolecular proton transfer (ESIPT) of the desilylation reaction product (3-BTHPB) work together for the fluorescent sensing mechanism. The constructed potential energy curves among the optimized 3-BTHPB (enol form) and 3-BTHPB-e (keto form) geometries on the S0 and S1 states, indicated that the ESIPT is a low barrier process (0.1 kcal mol−1), and the energies of the optimized geometries showed that the ESIPT process is exothermic. The calculated vertical excitation energies in the ground state and the first singlet excited state reproduced the experimental UV-Vis absorbance and fluorescence emission spectra well.

Four kinds of guest-driven lanthanide coordination polymers (CPs) have been synthesized. They have similar formula: [Tb(NPA)3CH3CN]n (1, H-NPA = N-phenylanthranilic acid), {[Tb(NPA)3CH3OH]CH3OH}n (2), [Ln(NPA)3DMF]n (Ln = Tb (3a), Gd (3b), Eu (3c)), and [Tb(NPA)3DMSO]n (4). These complexes were characterized by single-crystal diffraction, PXRD, FT-IR, TGA, DTA, EA, UV-vis spectra and luminescence lifetime measurements. They are all highly thermostable, acid and base resistant. The luminescence quantum yields (QY) of Tb3+ complexes: 1, 2, 3a and 4 are 4.0%, 9.0%, 44% and 46% respectively. Interestingly, there is a drastic change from 4.0% to 46% in luminescence QY by exchanging the coordination solvent, the oscillation of small molecule near the Tb3+ causes the drastic change. Furthermore, the octupolar-like structure of 4 has a high two-photon luminescence.

The adsorption of 2-propanol on anatase TiO 2 (101) and (001) surfaces has been investigated by density functional theory (DFT) calculations. Both the influences of faceting and surface coverage were studied. Our results indicated that the adsorption behaviors of 2-propanol on (101) and (001) surfaces are different. 2-Propanol molecularly adsorbs on the (101) surface at both low and high surface coverages. On the (001) surface, the dissociative adsorption of 2-propanol with the cleavage of O H bond was observed at lower coverage. And the molecular adsorption became more energetically preferred with increasing surface coverage.

Through numerical solution of the quasi-three-dimensional time-dependent Schrodinger equation, the harmonic spectra and attosecond-pulse generation have been theoretically investigated when a model He atom is exposed to the modified three-color chirped field (800 nm+1600 nm+1200 nm). It is found that when the chirp parameters are chosen to be (1) = 0.3 (corresponding to the 800-nm field), (2) = 0.6 (corresponding to the 1600-nm field) and (3) = -0.2 (corresponding to the 1200-nm field), the harmonics have an optimal extension resulting in a 491 eV bandwidth. Further, an isolated 32-as pulse is directly achieved with proper harmonic superposition.

The sensing mechanism for fluoride chemosensor based on anthracene structure has been investigated by DFT and TDDFT methods. The results show that the similar geometries in S0 and S1 states in the absence of the fluoride anion induce the local excited (LE) state over the anthracene moiety, which is responsible for the strong fluorescence. The fluorescence quenching phenomenon for F-coordinated complex can be explained by the photoinduced electron transfer (PET) process from benzylic amide to anthracene moiety. Moreover, the strong electronegativity for fluoride anion in the F-complex constructs the intermolecular hydrogen bond of N–H…F in the ground state. In contrast, the upper proton in the urea group close to phenyl group prefers to bind fluoride anion in S1 state of the F-complex, and it presents excited-state proton transfer (ESPT) to form another hydrogen bond like N…H–F, which has been confirmed by natural bond orbital (NBO) analysis and the potential energy curve of S1 state for the function of N–H bond. In this novel and efficient fluoride fluorescent chemosensor based on anthracene, the anthracene moiety is regarded as not only the fluorescent source, but the template for introducing the binding sites for fluoride anion.

We present an efficient method to enhance the attosecond pulse intensity when either a model He+ ion or a neutral He atom is exposed to the combination of a synthesized two-color field (800 and 1600 nm) and a high-order harmonic pulse. The results show that, by properly adding an ultrashort 13th (61.5 nm), 27th (29.6 nm), or 6th (125.2 nm), 13th (62.6 nm) harmonic pulse (corresponding to an 800 nm pulse) to the synthesized two-color field, the harmonic yields from the He+ ion or the He atom are effectively enhanced by two to five or one to two orders of magnitude compared with the original two-color field case. Finally, by properly superposing the harmonic spectrum in the supercontinuum region, we can obtain an intense attosecond pulse as short as 41as (He+) and 46as (He) from our 1-D simulations.

Hydrogen bonding dynamics has received extensive research attention in recent years due to the significant advances in femtolaser spectroscopy experiments and quantum chemistry calculations. Usually, photoexcitation would cause changes in the hydrogen bonding formed through the interaction between hydrogen donor and acceptor molecules on their ground electronic states, and such transient strengthening or weakening of hydrogen bonding could be crucial for the photophysical transformations and the subsequent photochemical reactions that occurred on a time scale from tens of femtosecond to a few nanoseconds. In this article, we review the combined experimental and theoretical studies focusing on the ultrafast electronic and vibrational hydrogen bonding dynamics. Through these studies, new mechanisms and proposals and common rules have been put forward to advance our understanding of the hydrogen bondings dynamics in a variety of important photoinduced phenomena like photosynthesis, dual fluorescence emission, rotational reorientation, excited-state proton transfer and charge transfer processes, chemosensor fluorescence sensing, rearrangements of the hydrogen-bond network including forming and breaking hydrogen bond in water. Graphical Abstract We review the recent advances on exploring the photoinduced hydrogen bonding dynamics in solutions through a joint approach of laser spectroscopy and theoretical calculation. The reviewed studies have put forward a new mechanism, new proposal, and new rule for a variety of photoinduced phenomena such as photosynthesis, dual fluorescence emission, rotational reorientation, excited-state proton transfer and charge transfer, chemosensor fluorescence sensing, and rearrangements of the hydrogen-bond network in water.

Reactive oxygen species (ROS) and changes in their redox cycles have great therapeutic potential for treating serious redox-related human diseases such as acute and chronic inflammation, diabetes, cancer and neurodegenerative disorders. This article presents a survey of the recently (2011-2016) developed NIR small-molecule biosensors for reversibly monitoring oxidation and reduction events in living cells and small animals through in vitro/in vivo fluorescence imaging. Emission and absorption profile, design strategy and fluorescence sensing mechanism, ROS selectivity and sensitivity, reversibility, ability of subcellular location and cytotoxicity are discussed for the NIR small-molecule biosensors capable of quantitatively, continuously and reversibly detecting transient ROS burst and redox changes at cellular level.

The vector correlations between products and reagents of the N (2D) + D 2 reaction are investigated by employing quasi-classical trajectory (QCT) calculation on the accurate DMBE potential energy surface (PES) of the 2A″ state. Stereo-dynamic quantities, including the four generalized polarization-dependent differential cross-sections (PDDCSs), the angular distribution P(θr), the dihedral-angle distribution P(φr), as well as the product rotational angular distribution in the polar form of P(θr, φr), are calculated in the center-of-mass (CM) frame. The results indicate that the product rotational angular momentum j′ not only aligns along the y-axis, but also orients to the negative direction of the y-axis. The isotope effect in the context of chemical stereo-dynamics and influences of different versions of ground-state PESs on vector correlations are shown and discussed.