Excited-state hydrogen-bonding dynamics of trans-acetanilide in an aqueous environment: a theoretical study

Abstract

In this work, the time-dependent density functional theory (TDDFT) method was carried out to study the hydrogen-bonding dynamics in both singlet and triplet excited states of trans-acetanilide (AA)–(H2O) complexes formed by trans-acetanilide in a water (H2O) solvent. The ground-state geometric structure optimisations were calculated by the density functional theory method, but the electronic excitation energies and corresponding oscillation strengths of the low-lying electronically excited states for isolated AA, H2O monomers and hydrogen-bonded AA(CO)–(H2O)1, AA(NH)–(H2O)1 dimers as well as the dihydrogen-bonded AA–(H2O)2 trimer were calculated by the TDDFT method. In our system, the intermolecular hydrogen bonds C = O…H–O and N–H…O–H can also be formed. From the TDDFT results, we depicted the changes of different hydrogen-bonded complexes in various electronic excited states. According to Zhao's rule on the relationship between the electronic spectral shift and excited-state hydrogen-bonding dynamics, hydrogen bond strengthening can bring the relative electronic spectra redshift, whereas hydrogen bond weakening can make the corresponding electronic spectra shift to blue. In addition, we also discussed the frontier molecular orbitals and the electron density transition.