Banca de QUALIFICAÇÃO: ANA PAULA TAVARES PADILHA

Uma banca de QUALIFICAÇÃO de MESTRADO foi cadastrada pelo programa.
STUDENT : ANA PAULA TAVARES PADILHA
DATE: 06/09/2024
TIME: 14:00
LOCAL: videoconferência
TITLE:

ANALYSIS OF THE STRUCTURAL EFFFECTS ON ACIDOCHROMIC PROPERTIES OF 2,4,6-TRIARYLPYRIDINES.

KEY WORDS:

N-Heterocycles; Triarylpyridines; Fluorescence; Acidochromism; Chemosensors

PAGES: 70
BIG AREA: Ciências Exatas e da Terra
AREA: Química
SUBÁREA: Química Orgânica
SPECIALTY: Fotoquímica Orgânica
SUMMARY:

Aromatic N-heterocyclic compounds have proven to be highly relevant in the design of emissive materials with diverse applications, such as in the fields of sensors and organo-electronics. The present work reports the synthesis and study of the acidochromism of derivatives based on the 2,4,6-triarylpyridine (TAP) heterocyclic core. A total of six TAPs were designed, four of which contain 4-dodecyloxyphenyl substituents at the 2 and 6 positions of the pyridine core, in addition to 4-carbazolylphenyl (1a), 4-fluorophenyl (1b), 2-thienyl (1c), and 4-piperidinophenyl (1d) substituents at the 6 position of the heterocyclic core. The other two derivatives, 1e and 1b, lack the alkoxy groups and contain 2-thienyl and 4-fluorophenyl substituents at the 4-position of the pyridine core, respectively. To date, the derivatives 1a, 1b, 1c, 1e, and 1f have been synthesized and characterized by IR and 1H NMR, while compound 1d is still under characterization. The TAPs were obtained with moderate yields (30-54%) through multicomponent reactions involving two equivalents of acetophenones and one equivalent of appropriate aldehydes, in the presence of ammonium acetate and cobalt (II) chloride as a catalyst, and in the absence of solvent. The emissive properties of the TAPs were evaluated in a 70:30 v/v acetone-water solution, and all synthesized compounds exhibited fluorescence, with maximum emission wavelengths ranging from 359 nm to 407 nm. The carbazole derivative 1a showed the highest intensity and the longest wavelength emission. All the compounds evaluated thus far exhibited acidochromism upon the addition of HCl. However, while acid addition led to the suppression of the emission of derivative 1a, all other TAPs were characterized by the suppression of the original emission band, accompanied by the emergence of a new emission band between 402 nm and 476 nm. It was observed that the presence of dodecyloxy groups, which are electron-donating, induced longer wavelength emissions after acid addition, with values reaching 476 nm for both 1b-H+ and 1c-H+. On the other hand, the absence of alkoxy groups induced smaller variations in the emission wavelengths before and after acid addition. The 1H NMR analysis conducted for compound 1b revealed that the alkoxy groups effectively participate in the stabilization of the pyridinium cation formed after the protonation of the TAPs, which likely contributes to the greater differences in emission wavelengths of these derivatives before and after acid addition. The study involving derivative 1d will further elucidate the differentiated acidochromism observed in derivative 1a. As a practical application, compound 1b adsorbed on filter paper was evaluated as a disposable sensor, demonstrating its usefulness for the detection of gaseous HCl.

COMMITTEE MEMBERS:
Presidente - 1803692 - FABRICIO GAVA MENEZES
Externa à Instituição - JANNYELY MOREIRA NERI - UFRN
Interno - 1198847 - JOSE LUIS CARDOZO FONSECA