Triple hydrogen bonding in a circular arrangement: ab initio, DFT and first-principles MD studies of tris-hydroxyaryl enamines

Agata Martyniak,Jarosław Panek,Aneta Jezierska-Mazzarello,Aleksander Filarowski

doi:10.1007/s10822-012-9597-3

Agata Martyniak, Jarosław Panek + Show 2 more

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https://doi.org/10.1007/s10822-012-9597-3

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Abstract

First-principles Car-Parrinello molecular dynamics, ab initio (MP2) and density functional schemes have been used to explore the tautomeric equilibrium in three tris(amino(R)methylidene)cyclohexane-1,3,5-triones (R = hydrogen, methyl or phenyl group). The dynamic nature of the cyclic hydrogen bonding has been studied by the first-principles MD method. The comparison of the results obtained by aforesaid methods has been accomplished on the basis of calculations of structural and spectroscopic characteristics of the compounds. The conformational analysis of the studied compounds has been carried out at the MP2/6-31+G(d,p) and B3LYP/6-31+G(d,p) levels of theory. The influence of steric and electronic effects on the cyclic hydrogen bonding has been analysed. The extent of the proton delocalization has been modified by the substituents according to the sequence: hydrogen < phenyl < methyl. This fact is verified by the spectroscopic and structural data as well as the energy potential curve. A prevalence of the keto-enamine tautomeric form has been observed in the static ab initio and DFT models, and confirmed by the first-principles MD.Electronic supplementary materialThe online version of this article (doi:10.1007/s10822-012-9597-3) contains supplementary material, which is available to authorized users.

Highlights

The presented tris(amino(R)methylidene)cyclohexane1,3,5-triones belong to the ortho-hydroxyaryl Schiff formation which is an object of wide physicochemical studies [1,2,3]
The potential curves (Fig. 1) calculated by the Density Functional Theory (DFT) and MP2 methods are similar which points out the prevalence of the keto-enamine tautomeric form (the global minimum is observed under the d(NH) % 1 A ; d(OH) % 1.7 A )
Regardless of the tautomeric form optimized at the PBE/ plane-wave level, the gas-phase Car-Parrinello molecular dynamics (CPMD) runs led to instantaneously the protons transfer to the nitrogen atoms, showing the prevalence of the keto-enamine form

Summary

Introduction

The presented tris(amino(R)methylidene)cyclohexane1,3,5-triones belong to the ortho-hydroxyaryl Schiff formation which is an object of wide physicochemical studies [1,2,3]. The latest investigations [10, 11] of two successfully modelled dimensional fluorescence switches are based on the strengthening of p-electronic conjugation in tris-salicylideneamine by the doubled cyclic intramolecular hydrogen bonding. This approach makes it possible to enhance a fluorescent quantum yield of these compounds which refer to the mechanically coupled biconcave systems [11]. The physicochemical characteristics of the aforesaid compounds enable the employment in organic electronics, optoelectronics and photovoltaics, as a molecular logic gate, photochromic crystals and reversible molecular switches [14, 15]

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