Síntese, caracterização estrutural e estudo fotofísico de 1,1- diflúor-3-aril-6-aril(heteroaril)-1H-[1,3,4]oxadiazolo[3,2-c] [1,3,5,2]oxadiazaborininos

Abstract

This work presents the results obtained for the synthesis, structural characterization and evaluation of the photophysical properties, in solution and in the solid state, of a series of nine specimens of 1,1-difluoro-3-aryl-6-aryl(heteroaryl)-1H-1λ4 ,8λ4 -[1,3,4]oxadiazolo[3,2- c][1,3,5,2]oxadiazaborinines (6). Aiming to achieve the objectives of this dissertation, initially a series of (E)-2-aryl(heteroaryl)-idenohydrazine-1-carboxyamides (semicarbazones 2) was synthesized, starting from condensation reactions between aryl aldehydes (1) and semicarbazide. In sequence, a series of 2-amino-5-aryl(heteroaryl)-1,3,4-oxadiazoles (3) was obtained, after performing oxidative cyclization reactions of the initial semicarbazones (2) in the presence of elemental bromine (Br2) as an oxidizing agent. Next, the series of 5- aryl(heteroaryl)-2-amino-1,3,4-oxadiazoles (3) was then converted to the respective N-(5- aryl(heteroaryl)-1,3,4-oxadiazol-2-yl)benzamides (5) from N-acylation reactions employing selected acyl chlorides 4. Finally, the benzamides 5 were successfully used in reactions with BF3.OEt2 for the synthesis of a series of difluoro-organoboro derivatives 6, targets of this dissertation, in 37 _ 91% of yield. Structural characterization was performed by means of 1H, 13C, 11B and 19F NMR and infrared spectroscopic analysis, single-crystal X-ray diffraction and high-resolution mass spectrometry (HRMS) and/or elemental analysis (CHN). Subsequently, the oxadiazaborinine 6 series was evaluated for its absorption and emission photophysical properties in solution and in the solid state. Results regarding fluorescence quantum yield, Stokes shift and cyclic voltammetry were obtained and discussed. In addition, time-dependent density functional theory (TD-DFT) calculations were performed for the heterocycles 6, which were obtained synthetically and the results were compared with theoretical data and thermogravimetric analyses complemented the present study by verifying the thermal stability of these new difluor-organoboron derivatives.