No abstract

No abstract

Hydrogen bond dynamics, C–OH bond contracting, O–H bond stretching and O–H⋯O HB strengthening reveal the ESHT in 4MU at the S1state.

Density functional theory (DFT)/time dependent density functional theory (TDDFT) calculations combined with the effective fragment potential (EFP) method have been carried out to study the electronic structure and the excited state properties of 6-aminocoumarin (6AC) with five water molecules (6AC-(H 2 O) 5 complex). Ground-state geometries are optimized using DFT with the B3LYP functional combined with cc-pVDZ basis sets and transition energies are computed with the same basis set and functional. One intermolecular hydrogen bond (HB) NÁ Á ÁH-O (type A) is formed between the amino group of 6AC and one water molecule, two intermolecular HBs CQOÁ Á ÁH-O (type B) are formed between the carbonyl group of 6AC and two water molecules, and two HBs of N-HÁ Á ÁO (type C), via participation of their amino hydrogen atoms, with the oxygen atoms of water molecules. The change in hydrogen bond energy, DE HB of the 6AC-(H 2 O) 5 molecule and DE HB for each HB of the 6AC-(H 2 O) 5 molecule are calculatedseparately. Upon excitation of the 6AC-(H 2 O) 5 complex, the A type HB is weakened with a decrease of 11.03 kJ mol À1 energy, whereas B and C type HBs are strengthened with increases of 5.28 and 18.14 kJ mol À1 energy, respectively. In this theoretical work, DE HB is calculated using the procedure proposed by T. Nagata et al. to calculate solute-solvent interaction energy in J. Chem. Phys., 2011, 134, 034110 and this study also confirmed again that intermolecular hydrogen bonds between the 6AC chromophore and aqueous solvents are strengthened, not cleaved upon electronic excitation, which is in accordance with Zhao's works Wiley Periodicals, Inc. J. Comput. Chem., 2011.

No abstract