Banca de DEFESA: ABAD ROGER CASTILLO HINOJOSA
Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.STUDENT : ABAD ROGER CASTILLO HINOJOSA
DATE: 14/04/2023
TIME: 14:00
LOCAL: Seminários e Defesas da Pós-Graduação em Química da UFBA
TITLE:
EFFECT OF BENZAZOLIC HETEROCYCLES AND ALCOXY SUBSTITUENTS ON THE PROPERTIES OF FLUORESCENT CALAMITIC LIQUID CRYSTALS
KEY WORDS:
Liquid Crystals, Luminescence, Benzazole
PAGES: 219
BIG AREA: Ciências Exatas e da Terra
AREA: Química
SUBÁREA: Química Orgânica
SPECIALTY: Síntese Orgânica
SUMMARY:
This work describes the synthesis, characterization and study of novel organic molecules with liquid crystals properties. Liquid crystals are substances that preserve both liquid and solid behaviors, whose structures are generally made up of aromatic nuclei and linear aliphatic chains. LCs have technological applications as displays (e.g. LCD - Liquid Crystal Display), organic solar cells, analytical identification, thermometers, smart windows etc. Liquid crystals are important in controlling the passage of light and also show a low energy consumption.
Heterocyclic compounds are important in the elaboration of liquid crystals, because they have polarized and asymmetric aromatic structures, this favors a low melting point. Benzazole LCs (benzene azole cycles) usually produce calamitic (rod-shaped) liquid crystals, due to their elongated geometry. Our research group, the Functional Molecular Materials Synthesis Group, have experience on the preparation and study of liquid crystals based on symmetrical and asymmetric conjugated benzazole structures in order to get scientific highlights and propose new applications.
Asymmetric benzazole derivatives has been synthesized, such as: N-methyl benzotriazoles (BTZ), benzoxadiazoles (BOX), benzothiadiazoles (BTD) and benzoxazoles employing Suziki-Miyaura and Sonogashira cross-coupling reactions. Different linear aliphatic chains of the CnH2n+1 type (n = 6, 8, 10, 12 and 14) were used to favor mesomorphic entropy.
Once the materials were characterized by IR, NMR and mass spectrometry, the thermal properties were studied by POM, DSC and XRD, where it was noticed that the predominance of the SmC / N phases for BOX and BTD, and SmX / SmA for BTZ depends on the heteroatom volume and the aliphatic chain size. TGA analysis determined that the structures are stable up to 360°C.
Photophysical properties were studied by UV-Vis spectrophotometry, it noticed that the BTZ absorption band is maximum at 367 nm and the BOX and BTD bands have 60 nm red shift. The fluorescence intensity (radiative relaxation) it is twice greater in BTZ (blue emission) than BOX and BTD (yellow emission) systems. That explains why the quantum yield is more efficient for BTZ (63%) than the BOX and BTD conjugated systems (44%).
Additionally, the study of benzoxazoles (the B series) with / without terminal alkoxy chain showed comparable luminescence with first series BTZ, but have the ordered SmC phase, which caused the absence of mesophase in B1. By that, the influence of group substitution and linear chain extension size on the liquid crystal properties was understood.
COMMITTEE MEMBERS:
Presidente - 2166886 - ANDRE ALEXANDRE VIEIRA
Interna - 3156252 - LUIZA AMIM MERCANTE
Interno - 1276681 - RONAN BATISTA
Interno - 2285902 - TIAGO VINICIUS ALVES
Interna - 1148522 - ELIANE DE OLIVEIRA SILVA
Externo à Instituição - IVAN HELMUTH BECHTOLD - UFSC
Externo à Instituição - ALOIR ANTONIO MERLO - UFRGS
Externo à Instituição - FABRICIO GAVA MENEZES - UFRN