Investigação mecanística da reação de alquenilação C-H e desenvolvimento de sensores fluorescentes para íons bissulfito: uma abordagem computacional

Abstract

This work describes two computational approaches based on Density Functional Theory (DFT), aimed at investigating the application of quinoidal derivatives in the synthesis of substrates for SuFEx (Sulfur(VI) Fluoride Exchange) click-type reactions and in the development of fluorescent sensors for bisulfite ion detection. The first part addresses the elucidation of the C−H alkenylation mechanism of 1,4-naphthoquinone mono-methylated with the Ethenesulfonyl Fluoride (FES) group, aiming to obtain a suitable substrate for SuFEx reactions. Transition State Theory (TST) based calculations were performed to identify the energy profile and propose a catalytic cycle for this transformation. Furthermore, a benchmark process was conducted to assess the energy profiles obtained using nine density functionals, distributed into seven distinct classes, and compared with results obtained from the reference method, Coupled Cluster (CC). The results indicated that the hybrid GGA PBE0 functional, chosen to describe the proposed mechanism, is suitable for computational studies of catalysis by ruthenium organometallic complexes. The second part describes the photophysical studies based on Time-Dependent Density Functional Theory (TD-DFT), conducted with three imidazole derivatives of β-lapachone, to evaluate possible changes in their fluorescence profiles in response to bisulfite ion detection. Optimized geometries of the ground states (S0) and excited states (S1, T1, and T2), as well as the electronic energy of the investigated compounds, were obtained. Additionally, fluorescence constants, derived from the Einstein coefficient, and intersystem crossing constants were calculated using Fermi’s Golden Rule and Marcus theory. The results suggest that the experimental differences observed in the fluorescence emission profiles of the three compounds after interaction with the analyte cannot be exclusively explained by the unfavorable intramolecular charge transfer (ICT) process. Moreover, for one of the regioisomers, the possibility of radiative deactivation via phosphorescence was identified. The two compounds that exhibited fluorescence changes upon reacting with bisulfite were considered suitable for potential sensor applications. However, the lapimidazole which did not show emission profile changes after interaction with the target ion was not deemed appropriate for the same application.