The hydrolysis mechanism of americium was calculated using density functional theory, and the detailed microscopic reaction mechanism was obtained. The results show that americium reacts with water along the octet state to produce oxides and H2, and that this reaction is exothermic. The interaction between Am and O atoms gradually changes from initially electrostatic interaction to covalent interaction, and continues to strengthen. During the reaction process, Am atoms always lose electrons, the 5f orbital is obviously involved, and there is df orbital hybridization. This study provides the necessary theoretical data support for the theoretical and experimental study of the actinide system.

A novel and efficient chemosensor 1 for detecting Cu2+ has recently been developed. However, the photophysical properties of chemosensor 1 and its response mechanism to Cu2+ are still unclear. Herein, the density functional theory and the time-dependent density functional theory approaches are implemented to investigate the excited state behavior of chemosensor 1 and its sensing mechanism for Cu2+ is revealed. Through constructing the potential energy curve with the dihedral angle of hydroxide radical as a variable, the irreversibility of the adjustment of the hydrogen proton direction is determined. This feature provides a favorable geometric configuration condition for the formation of intramolecular hydrogen bond. Moreover, the reduced density gradient analysis and topological analysis are performed to visualize the hydrogen bond strength, it is found that the hydrogen bond is enhanced in first singlet excited state (S1) compared with that in ground state (S0). The chemosensor 1 has only a low potential barrier in the S1 state, indicating that it could undergo an ultra-fast excited state intramolecular proton transfer (ESIPT) process. Furthermore, the reaction sites of chemosensor 1 and Cu2+ is theoretically predicted by the electrostatic potential analysis and the coordination mode of 1 + Cu2+-H+ is confirmed. Thus, we verify that the deprotonation inhibits the ESIPT behavior and leads to fluorescence quenching to achieve the recognition of chemosensor 1 to Cu2+. In addition, the binding energy of Cu2+ with chemosensor 1 is greater than that of Mg2+ and Zn2+, the high selectivity of chemosensor 1 to Cu2+ is illustrated. Our investigation clarifies the sensing mechanism of chemosensor 1 to Cu2+ based on inhibiting ultra-fast ESIPT process, which provides a theoretical basis for the development of new metal ion sensors.

This article uses quantum chemical methods and various wave function analysis methods to firstly analyze the optical absorption spectrum and electron migration mechanism of rhodamine 6G molecular complexes on graphene substrates during electron or hole injection. Secondly, since the light absorption properties are very important during photocatalysis, the intermolecular interaction and electronic structure in both cases were calculated and analyzed. Not only the experimental results of the previous photocatalytic devices were explained, but also the physical mechanism was promoted, and the guiding recommendations for the future catalytic device design.

2-(4-(Dimethylamino)phenyl)-3-hydroxy-6,7-dimethoxy-4Hchromen-4-one (HOF) was synthesized in experiment (Wang et al., Sensor. Actuat. B-Chem. 277 (2018) 484), and its photophysical and photochemical properties was reported. However the corresponding full theoretical interpretation of mechanisms is inadequate. In the present research, the intermolecular hydrogen bond structure of HOF-methanol complex (HOF-2M) was found, and mechanism of alcohols monitoring of HOF was deeply studied using the density functional theory (DFT) and time-dependent density functional theory (TDDFT). The enhancing mechanism of the excited state hydrogen bond is verified by analyzing the hydrogen bond parameters, infrared spectra and frontier molecular orbitals. Importantly, the reduced density gradient visual analysis and topological quantificational analysis confirm that the intramolecular hydrogen bond of HOF is broken by strong intermolecular hydrogen bonds of HOF-2M using the Atoms-In-Molecule theory. The obtained absorption and emission spectra are found to agree well with the experimental results and the complete quenched keto-emission in methanol and ethanol solvents provide a suitable sensing mechanism for detecting alcohols. The reaction path of the excited state intramolecular proton transfer for HOF is explained in detail through the constructed potential energy curves.

Excited-state intramolecular proton transfer (ESIPT) reactions occurring in the S1 state for five molecules, which possess five/six-membered ring intramolecular NH···N or OH···N hydrogen bonds bearing quinoline or 2-phenylpyridine moiety, have been described in detail by the time-dependent density functional theory (TD-DFT) approach using the B3LYP hybrid functional. For the five molecules, the constrained potential energy profiles along the ESIPT reactions show that proton transfer is barrierless in molecules possessing six-membered ring intramolecular H-bonds, which is smoother than that with certain barriers in five-membered ring H-bonding systems. For the latter, chemical modification by a more strong acid group can lower the ESIPT barrier significantly, which harnesses the ESIPT reaction from a difficult type to a fast one. The energy barrier of the ESIPT reaction depends on the intensity of the intramolecular H-bond, which can be measured with the topological descriptors by topology analysis of the bond critical point (BCP) of the intramolecular H-bond. It is found that when the value of electron density ρ(r) at BCP is bigger than 0.025a.u., the corresponding molecule might go through an ultrafast and barrierless ESIPT process, which opens a new scenario to explore the ESIPT reactions.