How was the proton transfer process in bis-3, 6-(2- benzoxazolyl)-pyrocatechol, single or double proton transfer?

Yongjia Zhang,Mengtao Sun,Yongqing Li

doi:10.1038/srep25568

Yongjia Zhang, Mengtao Sun + Show 1 more

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https://doi.org/10.1038/srep25568

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Abstract

A theoretical analysis of proton transfer process for the symmetric systems with two intramolecular hydrogen bonds, bis-3,6-(2-benzoxazolyl)-pyrocatechol(BBPC) in hexane solvent, has been researched. In this study, we utilized ωB97X-D/ 6-311 + g (d,p) and B3LYP/6-31 + G(d) two procedures calculating the foremost bond length and bond angle, respectively. Our calculations demonstrate the two intramolecular hydrogen bonds were strengthened in S1 state, thus the proton transfer reaction can be facilitated. Furthermore, the calculated IR vibrational spectra confirmed hydrogen bonds were enhanced in S1 state. We found three local minima A B and C from the potential energy surfaces (PESs) on the S1 state, and the energy of B point and C point are identical. A new ESIPT mechanism has been proposed that was not equal to the previous conclusions. The new ESIPT mechanism elucidates that single proton transfer more likely occurs in the symmetric BBPC molecule in comparison with the double proton transfer reaction. And the frontier molecular orbitals(MOs) further illustrate the trend of ESIPT reaction.

Highlights

Owing to the importance of hydrogen bond playing in nature, it has been researched and reported numerous publications on the relevant topics in the past few years
Wortmann et al confirmed the single proton transfer happens in S1 state of BBPC, which was confirmed by the absorption and emission electrooptical spectra[38]
The optimization of geometric structures in S0 and S1 states have been done, vertical excitation energy were calculated, IR vibrational spectra, the frontier molecular orbitals (LUMOs and HOMOs) as well as the potential energy surfaces (PESs) in the S0 and S1 states were calculated in our investigation, we choose both ω B97X-D/ 6-311 + g (d,p) and B3LYP/6-31 + G(d) to calculate the foremost bond length and bond angle, so that ensure the accuracy of the calculation result

Summary

Introduction

Owing to the importance of hydrogen bond playing in nature, it has been researched and reported numerous publications on the relevant topics in the past few years. The best-known examples, bis-3,6-(2-benzoxazolyl)-pyrocatechol (BBPC) and bis-2, 5-(2-benzoxazolyl)-hydroquinon (BBHQ) , are symmetrical system with double intramolecular hydrogen bonds Both of them were published by Mordzinski et al firstly, through the nodal plane model method[34]. Their calculation predict that the BBHQ undergoes single proton transfer process in S1 state, while BBPC do double proton transfer reaction. Wortmann et al confirmed the single proton transfer happens in S1 state of BBPC, which was confirmed by the absorption and emission electrooptical spectra[38] They proposed that the electrooptical measurements and quantum chemical calculations were the reliable tools for studying the mechanism of phototautomer.

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