Excited-State Dynamics Affected by Switching of a Hydrogen-Bond Network in Hydrated Aminopyrazine Clusters

Abstract

The cluster structures of hydrated aminopyrazines, APz−(H 2 O) n=2−4 , in supersonic jets have been investigated measuring the size-selected electronic and vibrational spectra and determined with the aid of quantum chemical calculations. The APz−(H 2 O) 2 structure is assigned as a cyclic N1 type where a homodromic hydrogen-bond chain starts from the amino group and ends at the 1-position nitrogen atom of the pyrazine moiety, corresponding to 2-aminopyridine−(H 2 O) 2 . On the other hand, APz−(H 2 O) n=3,4 has a linear hydrogen-bond network ending at the 4-position one (N4), which resembles 3aminopyridine−(H 2 O) n=3,4 . The hydrogen-bond network switching from the N1 type to the N4 one provides the accompanying red shifts of the S 1 −S 0 electronic transition that are entirely consistent with those of the corresponding 2-aminopyridine and 3aminopyridine clusters and also shows the drastically strengthened fluorescence intensity of origin bands in the electronic spectrum. The significant change in the excited-state dynamics is explored by the fluorescence lifetime measurement and the time-dependent density functional theory (TD-DFT) calculation. It is suggested that the drastic elongation of fluorescence lifetimes is due to the change in the electronic structure of the first excited state from nπ* to ππ*, resulting in the decreasing spin−orbit coupling to T 1 (ππ*).

Computational Evaluation of Intermolecular Interaction in Poly(Styrene-Maleic Acid)-Water Complexes Using Density Functional Theory

“…The bond length in the range of 1.5-1.6 Å and energy stability of >20 kcal/mol made the interaction in O72•••H49 was categorized as a strong hydrogen bonding system [13]. High stabilization energy means that the stronger the hydrogen bonding interaction, the easier the proton transfer [10,[49][50][51].…”

Rearrangement of aniline(H2O)n (n = 0–12) clusters upon photoionization and their excited state properties: Density functional theory and time‐dependent density functional theory study

“…23 Furthermore, in its cationic electronic ground state (D 0 ), aniline ion is planar according to the vibrational spectroscopic analysis. 24 Cationic clusters produced upon photoionization undergo drastic rearrangement in their structures compared to the corresponding neutrals [25][26][27][28][29][30] mainly due to the positive charge produced.…”