Síntese e estudo fotofísico de sistemas Π-Estendidos derivados de Quinoxalinas fusionadas a núcleos Benzotiazínico, Benzooxazínico e Benzodiazínico

Abstract

Fluorescent quinoxaline derivatives constitute a class of compounds of interest for several applications, such as chemical sensors and materials for optoelectronic devices. This work aims to synthesize, structurally characterize, and investigate the photophysical properties of the quinoxaline derivatives 12H-benzooxazino[2,3-b]quinoxaline 12H-benzothiazino[2,3-b]quinoxaline (BOQX), (BTQX), and 5-methyl-5,12-dihydroquinoxalino[2,3-b]quinoxaline (BDQX), evaluating the influence of structural differences on the optical properties of these π-conjugated systems. The compounds were obtained from the reactions of the precursor 2,3-dichloroquinoxaline (DCQX) with 2-aminothiophenol, 2-aminophenol, and N-methyl-o-phenylenediamine, and characterized by infrared spectroscopy, ¹H and 13C nuclear magnetic resonance spectroscopy, and mass spectrometry. The photophysical properties were investigated by UV–Vis absorption and fluorescence spectroscopies, evaluating parameters such as Stokes shift and fluorescence quantum yield (ΦF) in different media and in the solid state. The results showed that the nature of the heteroatom significantly influences the optical properties of the derivatives. BTQX was associated with the most red-shifted bands, BDQX showed the highest emission intensity, and BOQX exhibited the highest fluorescence quantum yields in solution, reaching ΦF = 0.86 in dichloromethane. The photophysical studies revealed positive solvatochromic behavior and evidence of intramolecular charge transfer (ICT), consistent with donor–acceptor (D–A) architectures. In aqueous medium, the three derivatives exhibited aggregation-caused quenching (ACQ), attributed to π–π stacking interactions. In the solid state, the compounds showed low quantum yields when directly deposited on quartz; however, a significant increase in emissive efficiency was observed when they were dispersed in Zeonex® films, reaching ΦF values between 0.405 and 0.495. Additionally, the derivatives demonstrated sensitivity to pH variations, with BDQX standing out due to its more complex spectral response and visible color changes. Overall, the results contribute to the understanding of the relationships between molecular structure and photophysical properties in quinoxaline derivatives, especially for the BDQX core, highlighting the potential of these systems for the development of luminescent materials.