Potential Energy Surface For Proton Transfer Research Articles

Determinant of ESIPT Mechanism by the Structure Designed for Symmetrical and Unsymmetrical Molecules.

In this work, we present that different structures lead to different excited state properties based on the investigations of the systems with symmetrical and unsymmetrical properties. Our work shows that the symmetrical and unsymmetrical compounds with a modified structure play key roles in regulating the excited state intramolecular proton transfer (PT) (ESIPT) process. For N,N'-bis(salicylidene)-p-phenyle-nediamine (BSP) and N,N'-disalicylidene-1,6-pyrenediamine (BSD), when they are excited, the torsion angels result in the rematch of the spectra. By analyzing the potential energy surfaces (PESs) of the torsion angle and PT process, we conclude that the size of the π stack largely affects the molecular properties in the excited states. For 2'-hydroxychalcone derivatives, which have important applications in biotransformation reactions, investigating the molecules of M1 and M2 could promote innovation in bioengineering. The results of molecular electrostatic potential (MEP) and the real space intramolecular interactions show the state and position of the hydrogen bond (HB) in both S0 and S1 states. The corresponding PT PESs show that the ESIPT reaction is much easier for the M1 system due to the lack of the side chain hydroxyl compared with the M2 system. This work is not only consistent with experimental results and explains its mechanism but also presents that symmetric and nonsymmetric structures modify their own potential regulation and controlling effects for ESIPT behaviors.

Theoretical studies of π-electron delocalization and localization on intramolecular proton transfer in the ground state

Proton transfer processes of 15 benzimidazole compounds are studied by density functional theory methods, and natural orbital energy index (NOEI) is introduced. Here, NOEI and nucleus independent chemical shift (NICS) are applied to estimate the π-electron localization and delocalization, respectively. Proton transfer potential energy surfaces are calculated to explore these processes, and the results show that the changes of the π-electron delocalization of the phenyl (pyridyl) is the main factors for the stability of keto form. There is high correlation between the π-electron delocalization and the proton transfer barrier. When the π-electron localization is considered, the regression increases the correlation coefficient, increasing from 0.9663 to 0.9864. NOEI index is sensitive to π-electron localization; it is a beneficial and useful complement to NICS.

Control of tunneling reactions with an external field in a four-level system: A general Redfield approach

We investigate the possibility of controlling tunneling in a four-level system by the application of an external field. The four level system is defined by a symmetric double well potential energy surface that supports two sets of tunnel doublet states, as is characteristic of some proton transfer potential energy surfaces. The time-dependent external field couples to the dipole moment operator of the tunneling system. In a four-level system, there is the possibility of intrawell transitions via vibrational relaxation and external field induced transition, in addition to the interwell tunneling transitions. We obtain a generalization of Redfield theory that describes the time evolution of the elements of the reduced density matrix for the system in the presence of the external field. The elements of the resulting Redfield tensor are constructed with the use of symbolic algebra. The theory is illustrated with a simple example that shows how the external field can control the rate of population transfer (tunneling) in the presence of the vibrational transitions.

The proton position in amine-HX (X  Br, I) complexes

Proton transfer potential energy surfaces are computed by ab initio methods for complexes of HBr and HI with NH 3 and mono, di, and trimethylamine. The fundamental natures of the SCF and MP n surfaces are distinct in that two separate minima are present in the SCF surfaces, corresponding to a neutral and ion pair, whereas only one minimum is encountered in most of the correlated surfaces. The single minimum in the MP2 surfaces of most of the complexes represents an ion pair. The first exception is BrH⋯NH 3 which exists as a neutral pair. The bridging proton in BrH⋯NH 2CH 3 is located approximately midway between the two molecules in a “shared” arrangement. The last exception is IH⋯NH 3, the surface of which may be best characterized as a long shallow valley for proton motion. The binding energies of these complexes rise as the amine becomes more basic due to progressive methylation.