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Síntesis y características estructurales de los helicenos cuádruples: sistemas de π altamente distorsionados

Takao Fujikawa¹, Yasutomo Segawa¹, Kenichiro Itami¹

¹Graduate School of Science, ‡JST, ERATO, Itami Molecular Nanocarbon Project, and §Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University , Nagoya 464-8602, Japan.

Journal of the American Chemical Society

|February 27, 2016

Resumen

Se sintetizaron helicenos cuádruples, revelando formas únicas de hélice y silla de montar. Sus geometrías distintas influyen en las propiedades electrónicas y las vías de isomerización, demostrando estados electrónicos dependientes de la geometría.

Área de la Ciencia:

Química orgánica
Química supramolecular
Ciencias de los materiales

Sus antecedentes:

Los helicenos son hidrocarburos aromáticos quirales con estructuras helicoidales únicas.
El control de la helicidad en los hidrocarburos aromáticos policíclicos es crucial para el desarrollo de nuevos materiales.

Objetivo del estudio:

Para sintetizar y caracterizar helicenos cuádruples con dithia[6]heliceno y [5]subestructuras de heliceno.
Investigar la relación entre la geometría molecular, las propiedades fotofísicas y electroquímicas.
Para aclarar las vías de estereoisomerización y la cinética.

Principales métodos:

Reacción controlada de Scholl para la síntesis.
Cristalografía de rayos X para la determinación estructural.
Estudios fotofísicos y electroquímicos (UV-Vis, fluorescencia, voltametría cíclica).
Cálculos de la teoría funcional de la densidad (DFT).
(1) RMN H y dicroísmo circular para estudios cinéticos.

Principales resultados:

Se han sintetizado con éxito helicenos cuádruples con 9 estereoisómeros.
Determinación de estructuras distintas en forma de hélice (QH-A) y en forma de silla de montar (QH-B) mediante cristalografía de rayos X.
QH-B exhibió una torsión extrema (69,5 °) debido a las repulsiones estéricas.
Propiedades electrónicas dependientes de la geometría observadas: brecha HOMO-LUMO ampliada y HOMO inferior en QH-B.
Se han identificado vías de isomerización y factores que influyen en las barreras de inversión.

Conclusiones:

La geometría molecular tiene un impacto significativo en los estados electrónicos de los helicenos cuádruples.
El estudio proporciona información sobre la síntesis, caracterización y comportamiento de sistemas helicoidales complejos.
La comprensión de la estereoisomerización es clave para el diseño de materiales funcionales basados en heliceno.

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