Banca de DEFESA: ERIVALDO PAULINO DA COSTA

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : ERIVALDO PAULINO DA COSTA
DATE: 31/07/2023
TIME: 14:00
LOCAL: videoconferência
TITLE:

Mesomorphic properties of 4-(quinoxalin-2-yl)phenyl 4-alkoxybenzoates and photophysical investigation of alkoxy-(E)-styrylquinoxalin-2(1H)-one

KEY WORDS:

Heterocycles; Quinoxaline; 3-Styrylquinoxalin-2(1H)-one; Liquid crystals; Photophysical properties

PAGES: 86
BIG AREA: Ciências Exatas e da Terra
AREA: Química
SUBÁREA: Química Orgânica
SPECIALTY: Síntese Orgânica
SUMMARY:

The development of functional organic materials has proved relevant to many fields. Liquid crystals are very relevant to optical electronics industry, as well as fluorescent compounds, which are commonly relevant in the development of sensors. The present thesis is divided into two main parts: the first one is centered in the study of liquid crystal properties of 4-(quinoxalin-2-yl)phenyl 4-alkoxybenzoates (QX1, QX2, DMQX1 e DMQX2). These target-compounds were obtained in good yields from four-step protocols and properly characterized by spectroscopic techniques. All quinoxaline derivatives were verified to present liquid crystalline behavior with mesophases ranging up to 112 oC, which were identified as both nematic and smectic mesophase, except compound DMQX1, which was a nematic liquid crystal. IN general, structural features do not affect considerably the mesomorphic behavior of these compounds, which were properly characterized by polarized optical microscopy based on classical Schieleren (nematic) and fan-shaped (smectic) patterns, among non-conventional textures. Exact phase transition temperatures were verified by differential scanning calorimetry. In the second part of this thesis, photophysical properties of alkoxy-(E)-styrylquinoxalin-2(1H)-one derivatives (SQX1-SQX3) were investigated. The reversible cis-trans isomerism of these compounds was studied in different organic solvents (methanol, acetonitrile, dichloromethane and hexane) and in aqueous medium by UV-Vis and fluorescence spectroscopies. Also, induced aggregation effect was studies by addition of water to solutions of SQX derivatives in polar solvents, including to verify the possibility of [2+2] cycloaddition in solution. Structural features are under discussion, including data obtained from theoretical calculations, in attempt to justify the photophysical properties of these compounds in different conditions.

COMMITTEE MEMBERS:
Externo à Instituição - ANDRÉ ALEXANDRE VIEIRA - UFBA
Externo à Instituição - FABIO DA SILVA MIRANDA - UFF
Presidente - 1803692 - FABRICIO GAVA MENEZES
Interno - 1859346 - MIGUEL ANGELO FONSECA DE SOUZA
Externo à Instituição - RODRIGO CRISTIANO - UFPB