The Experimental And Theoretical Studies On Excited-State Intramolecular And Intermolecular Proton Transfer

Excited-state proton transfer is of fundamental and practical interest in chemistry and biology. They have attracted more and more research attentions and led to thousands of publications on the relevant topics in past years. Various types of the PT reactions have been identified and mainly classified into two categories:Excited-state intramolecular proton transfer and Excited-state intermolecular proton transfer.The system greatly contributes to ESIPT researches should be credited the2-(2-hydroxyphenyl)benzothiazole (HBT) group, they have attracted many attentions because of their applications in chemistry and material fields. In this work, we combined the experimental and theoretical calculation methods to study the photochemical characters of a series of HBT derivatives. It’s indicated that (1) the strong electron-withdrawing trifluoromethyl group (CF3) was introduced into para-position of the hydroxyphenyl ring of the parent indeed decrease the charge density on O atom, which as a result inducing the deprotonation of these compounds.(2) The structure for HBT-1has the D-π-A characters, so that the excited state charge transfer will couple the ESIPT process, in addition, it will give out white-light emission in mixed acetonitrile and ethanol solvent.(3) Polar solvents favor the normal emission while non-polar solvents facilitate ESIPT process and tautomer formation and emission and the protic solutions can facilitate ESIPT process and at the same time promote the deprotonation of these compounds.(4) Electron-withdrawing ability of the substituents will interfere with the ESIPT process.The antioxidant action for4-hydroxybenzoic acid (4-HBA) in living organisms and especially in humans has been amply proved. Hence, its properties are of great biological significance and bio-medical interest. In this wok, we combined the experimental and theoretical calculation method to study the properties of4-HBA. From the fluorescence spectra, the large Stokes Shift for4-4-hydroxybenzoate (4-HB, whenpH=6.74,4-HBA existed as4-HB) implies that the excited state proton transfer process (ESPT) can take place. Further the mechanism of proton transfer dynamics of bridged-complexes of4HB·(H2O)x is investigated using the density functional theory (DFT) and time-dependent density functional theory (TDDFT). These results indicate that:(1) at least three H2O molecules are obviously requested to connect the phenolic group and the acceptor group COO-and the energy barrier for4HB·(H2O)5in which water-wire constructed by five water molecule is smaller than4HB·(H2O)3.(2) The PT process involves-the water bridges in which all protons are transferred simultaneously.