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We investigated the ultrafast photoisomerization of N-(2-methoxybenzylidene)aniline in the gas phase excited into the second singlet (S 2 ) state by nonadiabatic surface-hopping dynamics calculations. Two trans isomers (1E and 1E') were taken into consideration in our dynamics simulation. Three conical intersections (CIs) were characterized in the optimization. The CI between S 2 and the first singlet (S 1 ) states presents a nearly planar structure, while the other two CIs (CI twist -I and CI twist -II) between S 1 and the ground (S 0 ) states show nearly perpendicular geometries. After two trans isomers excited to the S 2 state, the torsion of the C-N bond connected the phenyl group and the stretch of the central bridging bond make the molecule reach CI planar , and the S 2 /S 1 hopping occurs. During the S 1 -state dynamics, the molecule moves to a S 1 /S 0 CI (CI twist -I or CI twist -II) by the rotation of the central bridging bond. The cis isomer is obtained through a barrierless pathway in the S 0 state with the torsion of the three bridging bonds. There is a main channel and an alternative one for the photoisomerization process of both trans isomers. CI twist -I and CI twist -II act as S 1 /S 0 decay funnels in the main isomerization channels of 1E and 1E' isomers, respectively, and the photochemical processes of 1E and 1E' lead to different cis isomers.

The aliphatic Claisen rearrangement of allyl vinyl ether has attracted great interest for its broad applications in chemical synthesis and biosynthesis. Although it is well agreed that this reaction proceeds via a concerted, "chair-like" transition state, certain inconsistencies of kinetic isotope effect (KIE) data between experimental measurements and theoretical simulations or between independent experiments indicate that the nature and mechanism of this important reaction need to be investigated in more detail. In order to verify two independent sets of experimental data, we present theoretical calculations on heavy-atom KIE values of alipahtic Claisen rearrangement, using our recently developed path-integral method with the second-order Kleinert's variational perturbation theory, which goes beyond the traditional method for computing KIE values by employing the Bigeleisen equation. Amazingly, the results demonstrate that both sets of experimental measurements are correct, while the inconsistency originates from the fact that the aliphatic Claisen rearrangement undergoes similar but different mechanisms in gas and solution phases. Different experimental conditions will alter the actual reactant state by tuning the population distribution of reactant conformers. According to the comparison between experimental and theoretical results, a more clear reaction mechanism of aliphatic Claisen rearrangement is revealed.

Nitrogen-containing anthraquinone derivatives are widely applied in vegetable fiber dyes. In this paper, the fluorescence quenching mechanism by an acylamino group twist in the excited state for the 1-(acylamino)anthraquinones (AYAAQs) derivatives in acetonitrile is investigated by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. The calculated Stokes shift is in good agreement with the experimental data. The energy profiles show that each AYAAQs derivative reveals a barrierless twist process, indicating that the involvement of acylamino group rotation in addition to proton transfer becomes as another important coordinate in the excited state relaxation pathway. The effects of electron-substituted group promote twist process compared with 1-aminoanthraquinone (AAQ). Then, the cross points are searched by the constructed linearly interpolated internal coordinate (LIIC) pathways for AYAAQs, demonstrating that the potential energy curves of the S 1 and T 2 states intersect each other and are in accord with the El-Sayed rules. So one can conclude that the acylamino group twist and following intersystem crossing (ISC) processes are important nonradiative inactivation channel for the S 1 state of the AYAAQs derivatives, which is more prone to proton transfer process and can explain the low fluorescence efficiency. In addition, we have measured the phosphorescence spectra of AAQ, and on this basis, it can be predicted that the phosphorescence may occur for the AYAAQs derivatives.

The concerted mechanisms of excited state intramolecular proton transfer (ESIPT) of bis-2,4-(2-benzoxazolyl)-hydroquinone (BBHQ') and its derivatives (BBHQ' - and DHBO') have been investigated using the density functional theory (DFT) and the time-dependent density functional theory (TDDFT). The calculated absorption and emission spectra of BBHQ' and its derivatives are in good agreement with the experimental results. The calculated bond lengths, bond angles, and IR vibrational spectra linked with hydrogen bond of molecular BBHQ' in the S 0 and S 1 states demonstrate that the hydrogen bond is strengthened in the S 1 state. Compared to BBHQ', BBHQ' - has a weak change of hydrogen bond between the S 1 and S 0 states. The calculation results show that there are three stable structures of BBHQ' in the S 1 state. We find that the structure corresponding to the 481 nm fluorescence spectrum corresponds to BBHQ'-A rather than BBHQ' - -K (Tetrahedron Lett., 2016, 57, 3518). The calculated frontier molecular orbitals (MOs) indicate the nature of the charge distribution and the trend of proton transfer of BBHQ'-A. The constructed potential energy surfaces of BBHQ' and DBHO' further elucidate the proposed mechanism that one-proton or two-proton transfer can happen (stepwise or synchronous) in the S 1 states. The proposed ESIPT mechanism can provide a good explanation of the phenomenon of fluorescence quenching of BBHQ' and its derivatives. Finally, the weak interaction types are discriminated through the reduced density gradient (RDG) analyses of BBHQ' and BBHQ' - .

The anharmonic force fields and spectroscopic constants of the electronic ground state (X̃ 1 A') for the HAsO molecule are reported employing the MP2, B3LYP, B3P86, and B3PW91 methods with cc-pVQZ and cc-pV5Z basis sets. The calculated molecular geometries, rotational constants, vibrational frequencies, and anharmonic constants of the HAsO molecule are compared with the experimental data. It is found that the best agreement between the calculated results and experiment data is at the B3LYP/cc-pV5Z theoretical level. The predicted cubic and quartic force fields, vibration-rotation interaction constants, quartic and sextic centrifugal distortion constants, and Coriolis coupling constants of the HAsO molecule at the B3LYP/cc-pV5Z theoretical level are expected to be reliable.

Two-photon-pumped amplified spontaneous emission (ASE) of CH3NH3PbBr3 microdisks (MDs) were investigated by using femtosecond laser system. Low threshold at 2.2 mJ cm(-2) was obtained. Also, emission spectral tunability from 500 to 570 nm was demonstrated by synthesis the mixed halide perovskite MDs. The spatial effect of photoluminescence (PL) properties under one-photon and two-photon excitation were also studied by means of two-photon laser scanning microscope (TPLSM) and time-resolved PL spectroscopy. It was found that the band to band emission of near-surface regions and photocarriers' diffusion from near-surface regions to interior regions is significant for one-photon excitation. By contrast, reabsorption of emission under two-photon excitation plays a major role in the emission properties of the MDs. These results will give a more comprehensive understanding of the nonlinear effect of CH3NH3PbBr3 single crystals.

The reaction of acrylonitrile with the C(001)-2 x 1 surface has been investigated by employing density functional cluster model calculations. The calculations revealed eight possible reaction pathways for acrylonitrile with the surface dimer. Full geometry optimized structures were obtained for all adducts, including intra- and interdimer reaction products. These results were analyzed in terms of both the total energy values and the detailed optimized geometries. We find that the reaction of acrylonitrile with the diamond (001) surface occurs primarily through its nonpolar C=C group and the intradimer [2+2](cc) product is the dominant product. All these results are in good agreement with the experimental work by Schwartz. It is noteworthy that the isomerization process plays an important role in the chemisorption process. Both intradimer [4+2] product and interdimer [2+2](cc) product can isomerize to the intradimer [2+2](cc) product. The present study shows that the isomerization between intradimer [4+2] product and intradimer [2+2](cc) product is slightly favorable over the direct path to formation of the intradimer [2+2](cc) product.