ISSN 1017-2548(Print)
ISSN 2234-8530(Online)
Volume 55, Number 3
JKCSEZ 55(3)
June 20, 2011 

The time-dependent density functional theory (TDDFT) method has been carried out to investigate the excitedstate hydrogen-bonding dynamics of phenol-(H2O)2 complex. The geometric structures and infrared (IR) spectra in ground state and different electronically excited states (S1 and T1) of the hydrogen-bonded complex have been calculated using the density functional theory (DFT) and TDDFT method. A ring of three hydrogen bonds is formed between phenol and two water molecules. We have demonstrated that the intermolecular hydrogen bond O1-H2···O3-H of the three hydrogen bonds is strengthened in S1 and T1 states. In contrast, the hydrogen bond O5-H6···O1-H is weakened in S1 and T1 states. These results are obtained by theoretically monitoring the changes of the bond lengths of the hydrogen bonds and hydrogen-bonding groups in different electronic states. The hydrogen bond O1-H2···O3-H strengthening in both the S1 and T1 states is confirmed by the calculated stretching vibrational mode of O-H (phenol) being red-shifted upon photoexcitation. The hydrogen bond strengthening and weakening behavior in electronically excited states may exist in other ring structures of phenol-(H2O)n.