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Issue 21, 2009
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Reconsideration of the excited-state double proton transfer (ESDPT) in 2-aminopyridine/acid systems: role of the intermolecular hydrogen bonding in excited states

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Abstract

In the present work, the excited-state double proton transfer (ESDPT) in 2-aminopyridine (2AP)/acid systems has been reconsidered using the combined experimental and theoretical methods. The steady-state absorption and fluorescence spectra of 2AP in different acids, such as formic acid, acetic acid, propionic acid, etc. have been measured. We demonstrated for the first time that the ESDPT reaction can take place between 2AP and all of these acids due to the formation of the intermolecular double hydrogen bonds. Furthermore, the vitally important role of the intermolecular double hydrogen bonds between 2AP and acids for ESDPT reaction has also been confirmed by the disappearance of ESDPT when we add the polar acetonitrile to the 2AP/acids systems. This may be due to that the respective polar solvation of 2AP and acids by the acetonitrile solvent disrupts the formation of intermolecular double hydrogen bonds between 2AP and acids. Moreover, the intermolecular double hydrogen bonds are demonstrated to be significantly strengthened in the electronic excited state of 2AP/acid systems using the time-dependent density functional theory (TDDFT) method. The ESDPT reaction is facilitated by the electronic excited-state hydrogen bond strengthening. In addition, potential energy curves of the electronic excited state along the proton transfer coordinate are also calculated by the TDDFT method. The stepwise mechanism of the ESDPT reaction in the 2AP/acid systems is theoretically reconfirmed, and the concerted mechanism is theoretically excluded. At the same time, the sequence of the double proton transfers is theoretically clarified for the first time using the potential energy curves calculated by TDDFT method.

Graphical abstract: Reconsideration of the excited-state double proton transfer (ESDPT) in 2-aminopyridine/acid systems: role of the intermolecular hydrogen bonding in excited states

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Publication details

The article was received on 22 Sep 2008, accepted on 12 Feb 2009 and first published on 23 Mar 2009


Article type: Paper
DOI: 10.1039/B816589K
Citation: Phys. Chem. Chem. Phys., 2009,11, 4385-4390
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    Reconsideration of the excited-state double proton transfer (ESDPT) in 2-aminopyridine/acid systems: role of the intermolecular hydrogen bonding in excited states

    S. Chai, G. Zhao, P. Song, S. Yang, J. Liu and K. Han, Phys. Chem. Chem. Phys., 2009, 11, 4385
    DOI: 10.1039/B816589K

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