Síntese e estudo das propriedades termo-ópticas de materiais moleculares macios derivados de N-heterociclos aromáticos aplicados aos cristais líquidos
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 crys...
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Formato: | doctoralThesis |
Idioma: | pt_BR |
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Universidade Federal do Rio Grande do Norte
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Endereço do item: | https://repositorio.ufrn.br/handle/123456789/52766 |
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Resumo: | 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 (73)
and nine 2-phenyl-1H-benzo[d]imidazole (4) 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 (73) derivatives indicated that decyl and dodecyl chains, 70b and (70c),
respectively, induce to SmX mesophase formation under heating, at 0,67-157 °C e 23-130 °C.
On the other hand, compound (70a) presented a direct transition from crystal to isotropic
liquid phases at 108 °C, 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 (67a-c e 68a-68a, respectively). The third benzimidazolic series (69a-69c) 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). Lastly, at
first, esterified derivatives 69 did not present liquid crystal property. In summary, two from
twelve final compounds herein reported were found to present liquid crystal behavior,
including notable low temperature transition and broad mesophase ranges. While for imidazophenanthroline 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. |
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