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

Abstract

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 S 0 and S 1 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 investigation of fluorescence changes caused by methanol bridge based on ESIPT reaction*

“…The pyridine ring is twisted, and the change of structure leads to the different optical properties. [48] This also proves that the addition of MeOH molecule makes the 2a molecule more prone to proton transfer.…”

Harnessing Excited-State Proton Transfer Reaction for 2-(6′-Hydroxy-2′-pyridyl)benzimidazole via Solvents

“…BI is a bifunctional molecule, containing a benzimidazolyl NH group and a hydroxyl OH group. Recently, phototautomerization of different types of molecules by solvent-assisted proton transfer (SAPT) has received extensive attention. − In particular, a series of bifunctional molecules experiencing the SAPT reaction attract intense scientific interest for both theoretical investigations − and potential applications. − Molecules possessing a proton donor (O–H or N–H) or an acceptor (carbonyl oxygen or aromatic nitrogen) may undergo an excited-state proton transfer (ESPT) process upon electronic excitation. − Namely, there exist two possible proton transfer (PT) pathways in BI: (1) Type-A, transfer of the H atom of the benzimidazolyl NH to the pyridyl nitrogen; and (2) Type-B, transfer of the H atom of the hydroxyl OH to the pyridyl nitrogen. Numerous studies on the bifunctional BI molecule are reported to investigate the ESPT process experimentally and theoretically. − The concerted PT reaction by the Type-B pathway in ethanol is reported .…”