A TD-DFT study on the excited-state hydrogen-bonding interactions in the 2-(2-thienyl)-3-hydroxy-4(1H)-quinolone-(H2O)3 cluster

In the present work, both the intramolecular and intermolecular hydrogen bonding interactions in 2-(2-thienyl)-3-hydroxy-4(1H)-quinolone monomer and the hydrogen-bonded 2-(2-thienyl)-3-hydroxy4(1H)-quinolone-(H2O)(3) cluster in the electronically excited states are theoretically investigated using the time-dependent density functional theory (TD-DFT) method. The calculated bond lengths of the intramolecular hydrogen bond C=O center dot center dot center dot H-1-O-1 in the 2-(2-thienyl)-3-hydroxy-4(1H)-quinolone monomer and the intermolecular hydrogen bonds HB-II, HB-III and HB-IV in the hydrogen-bonded 2-(2-thienyl)-3-hydroxy-4(1H)-quinolone-(H2O)(3) cluster are shorter in the excited state S-1 than those in the ground state S-0. However, the distance between the carbonyl oxygen atom O and the hydroxyl hydrogen atom H-1 is further lengthened in the 2-(2-thienyl)-3-hydroxy-4(1H)-quinolone-(H2O)(3) cluster, and the bond length of the intermolecular hydrogen bond HB-V is slightly lengthened upon electronic excitation to the S-1 state. The calculated stretching vibrational modes of the C=O and O-H of the intramolecular hydrogen bond C=O center dot center dot center dot H-1-O-1 and the intermolecular hydrogen bonds HB-II. HB-III and HB-IV in the excited states are all red-shifted compared with those predicted for the ground state. Therefore, it has been demonstrated that the intramolecular hydrogen bond C=O center dot center dot center dot H-1-O-1 in the 2-(2-thienyl)-3-hydroxy-4(1H)-quinolone monomer and the intermolecular hydrogen bonds HB-II, HB-III and HB-IV in the 2-(2-thienyl)-3-hydroxy-4(1H)-quinolone-(H2O)(3) cluster are all strengthened in the electronically excited state. Moreover, the two emission bands at the short wavelength observed in the experiments have been assigned by our TO-DFT calculations. (c) 2012 Elsevier B.V. All rights reserved.