Theoretical investigation on the fluorescence properties and ESIPT mechanism of the Al3+ ion sensor 1-((2-hydroxynaphthalen-1-yl)methylene)urea(OCN).

A new action mechanism for the fluorescent detection on the Al3+ ion of the sensitive 1-((2-hydroxynaphthalen-1-yl)methylene)urea(OCN) is theoretically studied. The extensive theoretical calculations on the OCN and the isomer structure OCN-T are performed. The emission and absorption spectra consistent with the experiment value. The absorption spectra peaks (362 nm and 326 nm) of OCN and OCN-T molecules are attributed to the experimentally observed absorption spectra at 356 nm and 314 nm, respectively. The calculated fluorescence value of the OCN-AL structure is 460 nm, while the OCN-T-AL structure has no fluorescence. These results better explain that OCN and its isomers OCN-T are involved in the absorption, and the detection spectrum signal is emitted from the OCN-AL complex. The OCN and OCN-T molecules are obvious hydrogen bonding systems. The excited state intramolecular proton transfer photochemical behaviors and detecting Al3+ ion photophysical changes were explained for the first time at the molecular level. As driving force of excited state intramolecular proton transfer (ESIPT) reaction, the bond parameters and vibrational frequencies of intramolecular hydrogen bond were analyzed by optimizing structures and calculating infrared spectra, analysis of frontier molecular orbitals. To further elucidate the proton transfer reactive paths, the scanned the potential energy curves (PECs) of OCN and OCN-T chemosensor in different electronic states are plotted. This work proposes a reasonable explanation for the detection mechanism of the OCN sensor.

The sensing mechanism of a flavone-based ESIPT fluorescent chemodosimeter for selective recognition towards fluoride: a theoretical.

The sensing mechanism of 3-hydroxyflavone-based (3-HF) fluorescent chemodosimeter 3-triisopropylsilylflavone (3-TPSF) for detecting fluoride (F-) has been theoretically investigated. The calculated Laplacian bond order confirms that the Si-O bond of 3-TPSF is the reaction site of F-. The free energy barrier of 18.33 kcal mol-1 indicates that F-triggered desilylation reaction can occur and then form the anionic state of 3-HF (3-HF-) with a fluorescence peak at 545 nm. 3-HF- captures H+ of the mixed aqueous medium to be transformed into 3-HF with an intramolecular hydrogen bond (O1-H⋯O2). The energy barrier of 1.86 kcal mol-1 in the S1 state obtained from the constructed potential energy curves confirms that the excited state intramolecular proton transfer (ESIPT) in 3-HF occurs to form a tautomer structure, which produces a long-wavelength emission of 549 nm. The fluorescence emitted from both 3-HF- and 3-HF agrees with the experimental value of 530 nm appearing after adding F-. Charge transfer analyses indicate that the extent of intramolecular charge transfer in 3-HF- is more intense than that of 3-TPSF, which induces a large Stokes shift of 180 nm. Therefore, the sensing mechanism is attributed to the combination of a large charge transfer feature and ESIPT that are caused by desilylation reaction. The significant fluorescence change makes 3-TPSF a chemodosimeter for detecting F-.

The mechanisms of a bifunctional fluorescent probe for detecting fluoride and sulfite based on excited-state intramolecular proton transfer and intramolecular charge transfer.

The mechanisms of 2-(Benzo[d]thiazol-2-yl)phenol-based bifunctional probe (HBT-FS) for detecting fluoride (F-) and sulfite (SO3 2-) based on excited-state intramolecular proton transfer (ESIPT) and intramolecular charge transfer (ICT) have been theoretically studied. Laplacian bond order of HBT-FS indicates that the F- ion cleaves the Si-O bond and then forms Compound 2 possessing a six-membered ring with a hydrogen bond. Potential energy curves and dynamic simulations confirm that ESIPT in Compound 2 occurs along with this hydrogen bond and forms a keto structure with an emission at 623 nm, which agrees with the observed experimental value (634 nm) after adding F-. Therefore, the fluorescence red-shift (from 498 to 634 nm) of HBT-FS observed in experiment after adding F- is caused by ESIPT. The SO3 2- ion is added to the C5 site of HBT-FS, which is confirmed by orbital-weighted dual descriptor, and then forms Compound 3 with fluorescence located at 404 nm. The experimentally measured fluorescence at 371 nm after adding SO3 2- is assigned to Compound 3. Charge transfer analyses indicate that the ICT extent of Compound 3 is relatively weak compared with that of HBT-FS because of the destruction of the conjugated structure by the addition reaction of SO3 2-, which induces the blue-shift of the fluorescence of HBT-FS from 498 to 371 nm. The different fluorescence responses make HBT-FS a fluorescent probe to discriminatorily detect F- and SO3 2-.

Atomically Precise Copper Cluster with Intensely Near-Infrared Luminescence and Its Mechanism.

In this work, a new Cu(I) cluster is synthesized and structurally characterized: [Cu11(TBBT)9(PPh3)6](SbF6)2 (where TBBT = 4-tert-butylbenzenethiol). This Cu(I) cluster exhibits good stability and a bright-red emission both in solution (685 nm) and in the solid state (675 nm) with a large Stokes shift (∼280 nm) under ambient conditions. Its absolute quantum yield is 0.22 in the solid state. Temperature-dependent emissions and theoretical calculations suggest that the origin of this cluster luminescence mainly results from a mixture of the metal-ligand charge transfer and the cluster-centered triplet excited states. This work not only opens new opportunities for functional applications of copper clusters but also sheds light on the structure-luminescence relationship.

Extensive ab initio study of the electronic states of BSe radical including spin-orbit coupling.

The internally contracted multi-reference configuration interaction method (MRCI) with Davidson modification and the Douglas-Kroll scalar relativistic correction has been used to calculate the BSe molecule at the level of aug-cc-pV5Z basis set. The calculated electronic states, including 9 doublet and 6 quartet Λ-S states, are correlated to the dissociation limit of B((2)P(u))+Se((3)P(g)) and B((2)P(u))+Se((1)D(g)). The Spin-orbit coupling (SOC) interaction is taken into account via the state interaction approach with the full Breit-Pauli Hamiltonian operator, which causes the entire 15 Λ-S states to split into 32Ω states. This is the first time that the spin-orbit coupling calculation has been carried out on BSe. The potential energy curves of the Λ-S and Ω electronic states are depicted with the aid of the avoided crossing rule between electronic states of the same symmetry. The spectroscopic constants of the bound Λ-S and Ω states were determined, which are in good agreement with the experimental data. The transition dipole moments (TDMs) and the Franck-Condon factors (FCs) of the transitions from the low-lying bound Ω states A(2)Π(I)3/2, B(2)Π(I)1/2 and C(2)Δ(I)3/2 to the ground state X(2)Σ(+)1/2 have also been presented. Based on the previous calculations, the radiative lifetimes of the A(2)Π(I)3/2, B(2)Π(I)1/2 and C(2)Δ(I)3/2 were evaluated.

Coriolis coupling effects in O(+)(4S) + H2(X1Σg(+)) → OH (+)(X3Σ(­)) + H(2S) reaction and its isotopic variants: exact time-dependent quantum scattering study.

The time-dependent wave packet quantum method taking into account the Coriolis coupling (CC) has been employed to investigate the dynamics of O(+) + H(2)/D(2)/HD (v(i) = 0, j(i) = 0) reactions based on an accurate potential energy surface [ Martínez et al. J. Chem. Phys. 2004 , 120 , 4705 ]. Through the comparison between the results with and without CC, the pronounced CC effects have been revealed in the title reactions. Moreover, the calculated results with the CC method can well reproduce the data of close-coupling hyperspherical (CCH) exact quantum method. The calculations demonstrate that the CC effects play an important role in the O(+) + H(2) system.

New ab initio potential energy surface and quantum dynamics of the reaction H(2S) + NH(X3Σ-) → N(4S) + H2.

A new global potential energy surface is reported for the ground state ((4)A(")) of the reaction H((2)S) + NH(X(3)Σ(-)) → N((4)S) + H(2) from a set of accurate ab initio data, which were computed using the multi-reference configuration interaction with a basis set of aug-cc-pV5Z. The many-body expansion and neural network methods have been used to construct the new potential energy surface. The topographical features of the new global potential energy surface are presented. The predicted barrier height is lower than previous theoretical estimates and the heat of reaction with zero-point energy is closer to experimental results. The quantum reactive scattering dynamics calculation was carried out over a range of collision energies (0-1.0 eV) on the new potential energy surface. The reaction probabilities, integral cross-section, and rate constants for the title reaction were calculated. The calculated rate constants are in excellent agreement with the available experimental results.

Stereodynamics study of the reaction of O(³P) with CH4(v = 0, j = 0).

A new London-Eyring-Polanyi-Sato (LEPS) potential energy surface (PES) is used in the O + CH(4) --> OH + CH(3) reaction via the quasiclassical trajectory method (QCT). Comparing with the experiments and the former ab initio calculations, the new LEPS PES describes the actual potential energy surface of the O + CH(4) reaction successfully. The four polarization dependent "generalized" differential cross sections (PDDCS) are presented in the center of mass frame. In the meantime, the distribution of dihedral angle [P(phi(r)), the distribution of angle between k and j' (P(theta(r))] and the angular distribution of product rotational vectors in the form of polar plots in theta(r) and phi(r) (P(theta(r), phi(r)) are calculated. The isotope effect for the reactions O + CD(4) is also calculated. These results are in good agreement with the experiments.