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Isolating Free Carbenes, their Mixed Dimers and Organic Radicals
Published on: April 19, 2019
Influencia del disolvente en las tasas de cruce intersistémico de carbenos
Jin Wang1, Jacek Kubicki, Huolei Peng
1Department of Chemistry, The Ohio State University, 100 West 18th Avenue, Columbus, Ohio 43210, USA.
Journal of the American Chemical Society
|April 25, 2008
Resumen
Los disolventes de coordinación influyen en las tasas de cruce intersistémico (ISC) de carbenos. Las interacciones específicas del disolvente, no solo la polaridad, afectan a la CSI al estabilizar los carbenos individuales, aparentemente violando la regla de oro de las transiciones sin radiación.
Área de la Ciencia:
- Química Física es la química física.
- La fotoquímica es la fotoquímica.
- La cinética química es la cinética química.
Sus antecedentes:
- El cruce intersistémico (ISC) es un proceso fotofísico crucial que implica cambios en el estado de espín de las moléculas.
- Los carbenos son intermedios reactivos con diversas configuraciones electrónicas, que influyen en su comportamiento fotofísico.
- Los efectos del disolvente sobre las velocidades de reacción y las propiedades moleculares son fundamentales en la dinámica química.
Objetivo del estudio:
- Investigar el impacto de los disolventes de coordinación en las tasas de cruce intersistémico (ISC) de carbenos singlet a triplet.
- Aclarar el mecanismo por el cual los disolventes influyen en la CSI, en particular para el difenilcarbeno (DPC) y para-bifeniltrifluorometilcarbeno (BpCCF 3).
- Para conciliar los efectos del disolvente observados con las teorías establecidas de las transiciones sin radiación.
Principales métodos:
- Se empleó espectroscopia de resolución temporal ultra rápida para monitorear la dinámica del carbeno.
- Los estudios se llevaron a cabo utilizando difenilcarbeno (DPC) y para-biphenyltrifluoromethylcarbene (BpCCF 3) en varios disolventes de coordinación.
- Se consideraron las propiedades del disolvente, incluida la polaridad y las capacidades específicas de coordinación.
Principales resultados:
- La capacidad de coordinación del disolvente, en lugar de la polaridad de la masa, afecta significativamente las tasas de ISC para DPC y BpCCF 3.
- Los disolventes halogenados retrasan drásticamente las tasas de CSI para BpCCF 3, lo que sugiere interacciones específicas.
- Las variaciones observadas de la tasa de ISC parecen contradecir la "regla de oro" debido a los efectos específicos de la solvación.
Conclusiones:
- Un mecanismo propuesto implica la coordinación de carbenos individuales con átomos de halógeno del disolvente, formando un complejo pseudoilido.
- La solución específica de carbenos singlet y triplet crea un factor similar a Franck-Condon que influye en las tasas de ISC.
- La estabilización inducida por disolventes de los carbenos singlet conduce a una ISC más lenta, desafiando las predicciones simples de brecha de energía.
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