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Molecules 2018, 23(5), 1231; https://doi.org/10.3390/molecules23051231

Density Functional Theory Applied to Excited State Intramolecular Proton Transfer in Imidazole-, Oxazole-, and Thiazole-Based Systems

Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, Santo André, São Paulo 5001, Brazil
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Received: 16 April 2018 / Revised: 15 May 2018 / Accepted: 17 May 2018 / Published: 21 May 2018
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Abstract

Excited state intramolecular proton transfer (ESIPT) is a photoinduced process strongly associated to hydrogen bonding within a molecular framework. In this manuscript, we computed potential energy data using Time Dependent Density Functional Theory (TDDFT) for triphenyl-substituted heterocycles, which evidenced an energetically favorable proton transfer on the excited state (i.e., ESIPT) but not on the ground state. Moreover, we describe how changes on heterocyclic functionalities, based on imidazole, oxazole, and thiazole systems, affect the ESIPT process that converts an enolic species to a ketonic one through photon-induced proton transfer. Structural and photophysical data were obtained theoretically by means of density functional theory (DFT) calculations and contrasted for the three heterocyclics. Different functionals were used, but B3LYP was the one that adequately predicted absorption data. It was observed that the intramolecular hydrogen bond is strengthened in the excited state, supporting the occurrence of ESIPT. Finally, it was observed that, with the formation of the excited state, there is a decrease in electronic density at the oxygen atom that acts as proton donor, while there is a substantial increase in the corresponding density at the nitrogen atom that serves as proton acceptor, thus, indicating that proton transfer is indeed favored after photon absorption. View Full-Text
Keywords: ESIPT; DFT; hydrogen bonding; imidazole; oxazole; thiazole ESIPT; DFT; hydrogen bonding; imidazole; oxazole; thiazole
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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de Carvalho, F.; Coutinho Neto, M.D.; Bartoloni, F.H.; Homem-de-Mello, P. Density Functional Theory Applied to Excited State Intramolecular Proton Transfer in Imidazole-, Oxazole-, and Thiazole-Based Systems. Molecules 2018, 23, 1231.

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