Wagging motion of hydrogen-bonded wire in the excited-state multiple proton transfer process of 7-hydroxyquinoline center dot(NH3)(3) cluster

In this work, the dynamics of hydrogen bonds (as well as the hydrogen-bonded wire) in excited-state tautomerization of 7-hydroxyquinoline center dot(NH3)(3) (7HQ center dot(NH3)(3)) cluster has been investigated by using time-dependent density functional theory (TDDFT). It shows that upon an excitation, the hydrogen bond between -OH group in 7-hydroxyquinoline (7HQ) and NH3 moiety would extremely strengthened in S-1 state, which could effectively facilitate the releasing of the proton from the phenolic group of 7HQ moiety to the hydrogen-bonded wire and the forming an Eigen-like cationic wire (NH3 center dot center dot center dot NH4+ center dot center dot center dot NH3) in the cluster. To fulfill the different optimal angles of NH4+ in the wire, a wagging motion of hydrogen-bonded wire would occur in excited state. Moreover, the wagging motion of the hydrogen-bonded wire would effectively promote excited-state proton transfer reaction. As the results, an excited-state multiple proton transfer (ESMPT) mechanism containing two concerted and asymmetrical processes has been proposed for the proton transfer dynamics of 7HQ center dot(NH3)(3) cluster. (c) 2013 Elsevier B.V. All rights reserved