Theoretical Study On The Excited State Hydrogen Bond Of Urea Derivatives With Anions Derivatives With Anions

Fuoride anion plays important roles in biological, industrial,environmental, chemical processes. Therefore, it is important todevelop the chemosensors for fluoride anion in the presence of otheranions. A large amount of anion sensors based on hydrogen bond havebeen designed. Hydrogen bonds in electronic excited states playimportant roles in the many photochemical and photophysicalprocesses. In this paper, we theoretically investigated the hydrogenbond interaction between urea moiety and anions using densityfunctional theory (DFT) and time-dependent density functional theory(TD-DFT). The main results are as follows:1. Theoretical study on a chemosensor for fluoride anion based on aurea derivative.The geometry optimizations of the ground and excited states ofthe N-Phenyl-N’-(3-quinolinyl)urea (PQU) derivatives have beenperformed using DFT and TD-DFT methods. The molecular orbitalsand the electronic spectra of the PQU derivatives and PQU·X-(X=F, Cl,AcO) complexes have also been calculated.(1) In the ground state of PQU, the phenyl and quinolyl groupsremain coplanar with the urea group. The double hydrogen bonds areformed between the PQU and three anions (F-, Cl-, AcO-). The hydrogen bonds cause a slight bathochromic shift of the first absorption peaksof the PQU·X-(X=F, Cl, AcO) complexes. The deprotonation occurs inthe ground state of PQU·F-and induces a significant bathochromicshift.(2) The phenyl and quinolyl groups remain coplanar with the ureagroup in the S1state for PQU and the complex PQU·F-. However, thequinolyl group is twisted along the C2-N3bond of the complexesPQU·Cl-and PQU·AcO-. The hydrogen bonds Ha-X (X=F, Cl, AcO) arestrengthened obviously in the S1states for three complexes ascompared with the S0states. The deprotonation can also occur in theS1state of PQU·F-In conclusion, the high selectivity of PQU for F-is ascribed to theanion-induced deprotonation of the urea group. The deprotonatedanion is formed in the ground state when the chemosensor PQUinteracts with F-.2. A theoretical study on excited state of hydrogen bonds betweendiaryurea and anions.The geometry optimizations of the ground and excited states ofthe1,3-diphenylurea(DPU1), DPU2and DPU3have been performedusing DFT and TD-DFT methods. Conformation preferences of DPU1,DPU2and DPU3on the ground and excited states and the excitedstate hydrogen bonds of the DPU1with anion have been discussed.(1) In the ground state, the intramolecular hydrogen bonds (H1-O6and H10-O6) are strengthened by introducing the electron-withdrawingsubstituent (-NO2). The-NO2group increases the acidity of the N-Hgroup at the adjacent side and, thus, strengthens the interactionbetween the N-H group and anions. In contrary, the electron-donating group (-N(CH3)2) decreases the acidity of the adjacent side, andweakens the hydrogen bonds between the N-H group and anions.Compared with the DPU1and their hydrogen bond complexes, thesubstituent-NO2or-N(CH3)2induced the significant bathochromicshift of the first absorption peaks of DPU2and DPU3and theirhydrogen bond complexes, following the obviously charge transfer ofthe HOMOâ†'LUMO electronic transition.(2) In the first excited singlet state, both DPU1and DPU2havethree different stable geometries, one normal planar structure andtwo twisted structures. DPU3has only one twisted structure. Thetwists of phenyl ring along with the C-N facilite the intramolecularcharge transfer. The hydrogen bond interaction between the DPU1and F-facilitates the excited state proton transfer in PQU·F-complex.However, the double intermolecular hydrogen bonds formed betweenDPU1and AcO-. The deprotonation of PQU·F-occurs in the groundstate, and however, the deprotonation of DPU1·F-occurs in the firstexcited singlet state. This indicates that the substituted aromaticmoiety in diarylureas has a significant effect on the deprotonation incomplexes of the urea derivatives with F-.