Time-dependent density functional theory as a tool for isomer assignments of hydrogen-bonded solute.solvent clusters.
ABSTRACT Can isomer structures of hydrogen-bonded solute x solvent clusters be assigned by correlating gas-phase experimental S0 <--> S1 transitions with vertical or adiabatic excitation energies calculated by time-dependent density functional theory (TD-DFT)? We study this question for 7-hydroxyquinoline (7HQ), for which an experimental database of 19 complexes and clusters is available. The main advantage of the adiabatic TD-B3LYP S0 <--> S1 excitations is the small absolute error compared to experiment, while for the calculated vertical excitations, the average offset is +1810 cm(-1). However, the empirically adjusted vertical excitations correlate more closely with the experimental transition energies, with a standard deviation of sigma = 72 cm(-1). For the analogous correlation with calculated adiabatic TD-DFT excitations, the standard deviation is sigma = 157 cm(-1). The vertical and adiabatic TD-DFT correlation methods are applied for the identification of isomers of the 7-hydroxyquinoline.(MeOH) n , n = 1-3 clusters [Matsumoto, Y.; Ebata, T.; Mikami, N. J. Phys. Chem. B 2002, 106, 5591]. These confirm that the vertical TD-DFT/experimental correlation yields more effective isomer assignments.
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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.Molecular Simulation - MOL SIMULAT. 01/2011;