Banca de DEFESA: ANDRÉ HERCULANO DE OLIVEIRA

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : ANDRÉ HERCULANO DE OLIVEIRA
DATE: 30/01/2023
TIME: 09:00
LOCAL: Anfiteatro do CCET
TITLE:

Synthesis and thermal-optical properties of aromatic N-heterocycle-based soft molecular materials as potential liquid crystals.

KEY WORDS:

Functional organic materials; Liquid crystal; Benzimidazole; Imidazophenanthroline.

PAGES: 95
BIG AREA: Ciências Exatas e da Terra
AREA: Química
SUBÁREA: Química Orgânica
SPECIALTY: Síntese Orgânica
SUMMARY:

In the last decades, functional organic materials have contributed greatly to the advance of electronic devices. In this context, liquid crystals have been broadly employed as screens and displays components in televisions and computers, as sensors, amongst others. At molecular level, liquid crystal are characterized by a rigid nucleus, usually from (hetero)aromatic nature, surrounded by flexible units, usually aliphatic long chains. Such structural features lead to supramolecular organizations able to induce mesophase, the crystal liquid state, characterized by simultaneous solid and liquid properties, such as birefringence and fluidity, respectively. In the search of new N- heterocycle-based mesogens, this work presents the synthesis of three [4-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)]phenol (38) and nine 2-phenyl-1H-benzo[d]imidazole (50) derivatives, which were obtained in good yields and properly characterized by IR, 1H NMR and 13C spectroscopies, and had their thermal properties evaluated by POM and DSC. The effect of aliphatic chains in thermal properties of N,O-dialkylated 38 derivatives indicated that decyl and dodecyl chains, 39b and 39c, respectively, induce to SmX mesophase formation under heating, at 0,67-157 oC e 23-130 oC. On the other hand, compound 39a presented a direct transition from crystal to isotropic liquid phases at 108 oC, which may be due to higher attractive interaction between heteroaromatic cores. The derivatives from 50 molecular system were divided into three groups. Two of them were structurally characterized by the presence of chlorine atom in the benzimidazole moiety besides one or two alkoxy chains (8, 10 and 12 carbon atoms)  in the 2-phenyl ring (48a-48c e 47a-47b, respectively). The third benzimidazolic series (43a-43c) is characterized as esterified 4-(1H-benzo[d]imidazol-2-yl)-2-methoxyphenol obtained from reactions with appropriated 4-alkoxybenzoic acids (8, 10 and 12 carbons atoms). All compounds from the first two series, 48a-48c and 47a-47c, presented SmX mesophases. The mesogens derived from 48 presented liquid crystal behavior, with temperatures ranging from 79-91 oC to 128-151 oC, being higher values obtained for the octyl derivatives. Mesophases for 47a-47c  were found from 47-48 oC to 121-132 oC, and lower temperature transitions compared to compounds derived from 48 are coherent to more alkoxy chains. Lastly, at first, esterified derivatives 43 didi not present liquid crystal property. In summary, nine from twelve final compounds herein reported were found to present liquid crystal behavior, including notable low temperature transition and broad mesophase ranges. While for imidazo-phenanthroline derivatives, intermolecular associations are based on π-stacking and Van der Waals interactions, hydrogen bonding must contribute to the intermolecular association of the benzimidazolic derivatives. These results represent a relevant advance for the development of advanced molecular materials, notably liquid crystals.

COMMITTEE MEMBERS:
Externo à Instituição - FABIO DA SILVA MIRANDA - UFF
Presidente - 1803692 - FABRICIO GAVA MENEZES
Externa ao Programa - 2140775 - LIVIA NUNES CAVALCANTI - UFRNInterno - 1859346 - MIGUEL ANGELO FONSECA DE SOUZA
Externo à Instituição - RODRIGO CRISTIANO - UFPB