Theoretical study the mechanism of ESIPT process for pyridine-hydrazone-substituted naphthalimide receptor 4a-E

Abstract

The mechanism of excited-state intramolecular proton transfer in (E)-N'-(2-butyl-1,3-dioxo-2,3-dihydro-1H-benzo[de]isoquinolin-6-yl)picolinohydrazonoyl cyanide (4a-E) was studied using time-dependent density functional theory. The calculative results promulgate that the proton transfer of the 4a-E molecule in S1 state can realize, producing red fluorescence. The change of intramolecular hydrogen bonds, infrared spectra, and non-covalent interactions upon photoexcited process can influence hydrogen bond interaction of the 4a-E molecule, and then effectively assist proton transfer process in S1 state. The structured potential energy curves were put out by varying N H bond lengths, which show 4a-E molecule can undergo intramolecular proton transfer in the S1 state, overcoming the energy barrier (3.76 kcal/mol). Additionally, 4a-E is required to cross the energy barrier of 2.91 kcal /mol for the reverse proton transfer, helping 4a-E recover to the stable. We hope this study can initiate the synthesis and exploit new-type molecules.