Síntese e avaliação fotofísica de xantonas para sensores luminescentes

Abstract

Organic compounds that have in their structure an abundance of π electrons, rigidity and unsaturation occupy a prominent position in photophysical research. The compound 2-(2'-hydroxyphenyl) benzazole, known as cyclobenzazole, is widely studied in photophysics due to its fluorescence emission by the existence of the ESIPT mechanism. In this way, the luminescence of xanthones has been considered, since they present structural similarity with the cyclobenzazole. By synthesizing functional xanthones, new structures may have wide application, such as for fluorescent sensors. In this study, three 1-hydroxy-9H-xanthen-9-one derivatives (1,3-dihydroxy-9H-xanthen-9-one, 1,3-dihydroxy-4-nitro-9H-xanthen-9-one, one and 4-amino-1,3-dihydroxy-9H-xanthen-9-one) were synthesized and evaluated their photophysical properties, as well as the fluorescence emission mechanism of such compounds. In the photophysical evaluation, solutions with dichloromethane, ethanol and acetonitrile were used, at a concentration of 10-3 M. When measuring the maximum absorption of the compounds in the three types of solvents, it was verified that there was no significant variation, since there was no interaction between them. In the emissions, different interactions of the compounds with the employed solvents suggested the existence of a keto-enol equilibrium and the possible ESIPT mechanism, which would explain the fluorescence emission. The synthesis of the compound 5-hydroxy-2-(2-hydroxyphenyl)-6H-xanthen-[4, 3-d]-oxazol-6-one, derived from xanthone and with the benzazole ring in its structure, was developed, still requiring optimizations in the process. However, it was observed that at basic pH the structure emits a significant amount of fluorescence and can be used as a sensor. Therefore, new studies are suggested for a more in-depth photophysical evaluation and expansion of the chemical applicability of the synthesized structures.