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Síntesis, estructura y resolución de pentacenos excepcionalmente retorcidos
Jun Lu1, Douglas M Ho, Nancy J Vogelaar
1Department of Chemistry, Princeton University, Princeton, NJ 08544, USA.
Journal of the American Chemical Society
|December 21, 2006
Resumen
Se sintetizaron y caracterizaron hidrocarburos aromáticos policíclicos altamente retorcidos, 9,10,11,20,21,22-hexafeniltetrabenzo[a,c,l,n]pentaceno (2) y su derivado dimetilo (2m). Estos compuestos exhiben giros extremos y una alta actividad óptica, con una lenta racemización a temperatura ambiente.
Área de la Ciencia:
- Química orgánica es la química orgánica.
- Ciencia de los materiales Ciencia de los materiales.
- Química supramolecular de las moléculas.
Sus antecedentes:
- Los hidrocarburos aromáticos policíclicos (HAP) son componentes fundamentales en la electrónica orgánica y la ciencia de los materiales.
- Lograr altos grados de torsión molecular en los HAP es desafiante pero crucial para afinar sus propiedades fotofísicas y electrónicas.
- Comprender las relaciones estructura-propiedad en HAP retorcidos puede conducir a nuevos materiales funcionales.
Objetivo del estudio:
- Para sintetizar hidrocarburos aromáticos policíclicos novedosos y altamente retorcidos, específicamente 9,10,11,20,21,22-hexafeniltetrabenzo[a,c,l,n]pentaceno (2) y su derivado dimetilo (2m).
- Para caracterizar las propiedades estructurales, fotofísicas y quirópticas de estos compuestos sintetizados.
- Para investigar la dinámica de racemization y comparar los hallazgos experimentales con predicciones computacionales.
Principales métodos:
- Síntesis a través de la reacción de 1,3-diphenylphenanthro[9,10-c]furan con equivalentes de bisarina, seguido por la desoxigenación.
- Cristalografía de rayos X para la determinación estructural detallada de las arquitecturas moleculares retorcidas.
- Cromatografía quiral para resolución enantiomérica y medición de rotaciones específicas.
- Estudios de racemicidad de temperatura variable y modelado computacional.
Principales resultados:
- Síntesis exitosa de 9,10,11,20,21,22-hexafeniltetrabenzo[a,c,l,n]pentaceno (2) y su derivado dimetilo (2m), que son sólidos de color rojo brillante con fuerte fluorescencia naranja.
- Las estructuras de rayos X revelan estos compuestos como los hidrocarburos aromáticos policíclicos más altamente retorcidos conocidos, con giros de extremo a extremo de hasta 144 grados.
- Los enantiómeros puros exhiben rotaciones específicas extremadamente altas ([alfa]D = 7400 grados para 2, 5600 grados para 2m), pero se someten a una racemicidad lenta a temperatura ambiente (DeltaG++rac = 24 kcal/mol).
- Los datos experimentales se alinean bien con los estudios computacionales con respecto a la geometría y las barreras de racicización.
Conclusiones:
- El estudio presenta una nueva clase de HAP altamente retorcidos con propiedades estructurales y quirópticas significativas.
- La torsión extrema y la alta actividad óptica demuestran una nueva frontera en el diseño de HAP.
- La barrera de racemización observada proporciona información sobre el comportamiento dinámico de estas moléculas complejas.
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