Yunfan Yang

Theoretical Investigation of the Reaction Mechanism of Photodeamination Induced by Excited-State Intramolecular Proton Transfer of Cresol Derivatives

The novel photodeamination process of cresol derivatives 1 and 3 has been reported experimentally ( J. Org. Chem . 2015 , 80 , 10817 ). However, a full theoretical interpretation of the mechanism is still lacking. In the present study, we aim to provide insight into the factors that promote the deamination reaction through density functional theory (DFT) and time-dependent DFT methods. Calculated absorption and emission spectra are in good agreement with the experimental results. Hydrogen-bond strengthening in the excited state has been verified by analyzing relevant bond parameters and vibrational frequencies as well as frontier molecular orbitals (FMOs), implying that hydrogen-bond interaction acts as the important parameter for the excited-state intramolecular proton-transfer (ESIPT) reaction. The proton-transfer and deamination reactions have been qualitatively analyzed through Gibbs free-energy reaction profiles in different electronic states. It can be concluded that the ESIPT and photodeamination reactions occur in the excited state. To further illustrate the photodeamination mechanism, the constructed 2D potential-energy surface indicates that the photodeamination reaction is infeasible without the ESIPT reaction. This work provides the first theoretical rationale for ESIPT-induced photodeamination occurring spontaneously because of protonation of a basic nitrogen atom.

Isotopic Effects on Stereodynamics of the C+ + H-2 -> CH+ + H Reaction

The effects of isotope substitution on stereodynamic properties for the reactions C+ + H-2/HD/HT -> CH+ + H/D/T have been studied applying a quasi classical trajectory method occurring on the new ground state CH2+ potential energy surface [J. Chem. Phys. 142 (2015) 124302]. In the center of mass coordinates applying the quasi classical trajectory method to investigate the orientation and the alignment of the product molecule. Differential cross section and three angle distribution functions P(theta(r)), P(phi(r)), P(theta(r),phi(r)) on the potential energy surface that fixed the collision energy with a value is 40 kcal/mol have been studied. The isotope effect becomes more and more important with the reagent molecules H-2 changing into HD and HT. P(theta(r),phi(r)) as the joint probability density function of both polar angles. r and. r, which can illustrate more detailed dynamics information. The isotope effect is obvious influence on the properties of stereodynamics in the reactions of C+ + H-2/HD/HT -> CH+ + H/D/T.

A detecting Al3+ ion luminophor 2-(Anthracen-1-yliminomethyl)-phenol: Theoretical investigation on the fluorescence properties and ESIPT mechanism

2-(Anthracen-1-yliminomethyl)-phenol (AYP) had been synthesized recently and used as a chemosensor to detect Al3+ ion, while its fluorescent properties and excited-state intramolecular proton transfer (ESIPT) process were not investigated in detail. In this study, the molecular absorption and emission spectra were accurately reproduced by using TDDFT/CAM-B3LYP/6-31 + G(d,p) computational method. The ESIPT- chromophore photochemical behaviors and detecting Al3+ ion photophysical changes were explained for the first time at the molecular level. As driving force of 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 and reduced density gradient isosurfaces. To further elucidate the proton transfer reactive paths, we scanned the potential energy curves of AYP chemosensor in different electronic states. By comparing potential barriers of the S0 and S1 states, the proton transfer is confirmed to occur in the S1 state. In addition, the experimentally unpresented AYP-Enol fluorescence signal was assigned via analyzing molecular fluorescent properties. Moreover, the calculated fluorescence spectra were employed to explain carefully the mechanism of detection of Al3+ ion.

The order of multiple excited state proton transfer in ternary complex of norharmane and acetic acids

Dolores Reyman et al. found the norharmane (9H-pyrido [3,4-b] indole) (NHM) and two acetic acid molecules can form the ternary complex (NHM-2A) in component solvent of dichloromethane and acetic acid via the hydrogen bond chain (J. Lumin. 2014, 148, 64). But the specific reaction details during this process were rarely reported. In this study, we will give an insight into the reasons which promote the occurrence of this reaction as well as its reaction order. The hydrogen bond enhancing behavior in first excited state (S1) is verified through the analysis of geometric configurations, infrared spectra, frontier molecular orbitals and potential energy curves. The absorption and fluorescence spectra we calculated are well coincident with the experimental results. Meanwhile, it is obvious that the hydrogen bond intensity is gradually enhanced from N1H2⋯O3, O4H5⋯O6 to O7H8⋯N9 by analyzing the reduced density gradient (RDG) isosurface. The hydrogen bond strengthening mechanism has been confirmed in which the hydrogen bond interaction acts as driving force for excited state proton transfer (ESPT) reaction. In order to provide a reliable description of the reaction energy profiles, we compare the barrier differences obtained by m062x and B3LYP methods. We might safely draw the conclusion that the multiple ESPT is a gradual process initiated by the proton transfer of O7H8⋯N9. And we further proof the ESPT process can be completed via the NHM-2A → NHM-2AS → NHM-2AD → NHM-2AT in S1 state. Theoretical research of NHM-2A has been carried out by density functional theory (DFT) and time-dependent density functional theory (TDDFT). It is worth noting that we predicted that the fluorescence at 400 nm observed in experiment is more likely to be emitted by NHM-2AS in S1 state.

Reaction Mechanism of Photodeamination Induced by Excited-State Intramolecular Proton Transfer of the Anthrol Molecule

The photodeamination reaction of the anthrol molecule generating the high-activity quinone methide intermediate has been investigated ( J. Org. Chem. 2017 , 82 , 6006 - 6021 ), though lacking careful explanation for its reaction mechanism. In our research, the mechanism of the anthrol molecule photodeamination induced by excited-state intramolecular proton transfer was reported for the first time. Absorption and emission spectra calculated for the work presented here agreed well with experimental results. To propose a molecular-level explanation of the photodeamination reaction, we calculated bond parameters, corresponding infrared vibrational frequencies, Mayer bond orders, and visualized frontier molecular orbitals of different molecules, and the hydrogen bond strengthening behavior in excited states was confirmed, enhancing the excited state intramolecular proton transfer of the anthrol molecule. Moreover, we concluded that photoisomerization weakened the bond strength between nitrogen and carbon atoms, which promoted the photodeamination reaction. Finally, for visually and quantificationally revealing the photodeamination mechanism, we have established the three-dimensional potential energy surfaces for the deamination reaction in different electronic states and calculated the corresponding reaction Gibbs free energies, it can be confirmed that the photodeamination reaction of the anthrol molecule must be induced by a proton transfer reaction in the excited state.

Excited state intramolecular proton transfer mechanism of o-hydroxynaphthyl phenanthroimidazole

By utilizing the density functional theory (DFT) and the time-dependent density functional theory (TDDFT), the excited state intramolecular proton transfer (ESIPT) mechanism of o-hydroxynaphthyl phenanthroimidazole (HNPI) is studied in detail. Upon photo is excited, the intramolecular hydrogen bond is obviously enhanced in the S1 state, which thus promotes the ESIPT process. Hydrogen bond is shown to be strengthened via comparing the molecular structures and the infrared vibration spectra of the S0 and S1 states. Through analyzing the frontier molecular orbitals, we can conclude that the excitation is a type of the intramolecular charge transfer excitation, which also indicates the trend of proton transfer in S1 state. The vertical excitation based on TDDFT calculation can effectively repeat the absorption and fluorescence spectra of the experiment. However, the fluorescence spectrum of normal structure, which is similar to the spectrum of isomer structure is not detected in the experiment. It can be concluded that the fluorescence measured in the experiment is attributed to both structures. In addition, by analyzing the potential energy curves (PECs) calculated by the B3LYP functional method, it can be derived that since the molecule to cross the potential barrier in the S1 state is smaller than in the S0 state and the reverse proton transfer process in the S1 state is more difficult than in the S0 state, the ESIPT occurs in the S1 state.