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Dependencia de distancia exponencial de la transferencia gradual de electrones fotoiniciada en moléculas
Annie Butler Ricks1, Kristen E Brown, Matthias Wenninger
1Department of Chemistry and Argonne-Northwestern Solar Energy Research (ANSER) Center, Northwestern University, Evanston, Illinois 60208-3113, United States.
Journal of the American Chemical Society
|February 17, 2012
Resumen
Los sistemas de donante-puente-aceptor con puentes de fluorenona muestran transferencia de electrones a través de saltos escalonados, no de túnel directo. Esto desafía la suposición de que los gradientes redox cuesta abajo garantizan un comportamiento de alambre en la separación de cargas.
Área de la Ciencia:
- La fotoquímica es la fotoquímica.
- Ciencia de los materiales Ciencia de los materiales.
- Electrónica orgánica y electrónica orgánica.
Sus antecedentes:
- Los sistemas de donante-puente-aceptor (D-B-A) son cruciales para el transporte de cargas.
- Comprender los mecanismos de transferencia de electrones en los cables moleculares es clave para el desarrollo de dispositivos electrónicos orgánicos.
- El mecanismo de superintercambio a menudo se invoca para la transferencia de electrones de largo alcance, pero también pueden funcionar mecanismos escalonados.
Objetivo del estudio:
- Para sintetizar y caracterizar los sistemas D-B-A con puentes de fluorenona de diferentes longitudes.
- Para aclarar el mecanismo de transferencia de electrones y separación de cargas en estos sistemas.
- Para investigar la relación entre la estructura molecular y las propiedades de transporte de carga.
Principales métodos:
- Síntesis de sistemas D-B-A con donante 3,5-dimetil-4-(9-antracenil) julolidina (DMJ-An) y aceptor naftaleno-1,8:4,5-bis(dicarboximida) (NI) unidos por puentes oligoméricos de 2,7-fluorenona (FN(n)) (n=1-3).
- Espectroscopia de absorción transitoria de femtosegundos en regiones visibles e infrarrojas medias para rastrear la dinámica de transferencia de electrones.
- Modelado cinético para analizar la dependencia de distancia e identificar mecanismos de transferencia de carga.
Principales resultados:
- La fotoexcitación selectiva de DMJ-An inició un proceso secuencial de transferencia de electrones: DMJ(+•) -An(-•) -FN(n) -NI → DMJ(+•) -An-FN(n) -NI → DMJ(+•) -An-FN(n) -NI → DMJ(+•) -An-FN(n) -NI-•).
- Se observó que el anión del radical de fluorenona (FN) era un intermediario clave, lo que confirma un mecanismo de salto incoherente.
- La transferencia de electrones exhibió una dependencia de distancia exponencial (β = 0,34 Å−1) atribuida a la inyección inicial de electrones y el posterior salto, influenciado por la atracción electrostática.
Conclusiones:
- La separación de la carga en estos sistemas D-B-A procede a través de un mecanismo de salto incoherente por etapas, no sólo a través de superexcambio.
- La dependencia de distancia observada surge de una combinación de inyección de electrones y salto inter-fluorenona, modulada por fuerzas electrostáticas.
- El diseño de cables moleculares con un gradiente redox gradual y cuesta abajo no garantiza automáticamente un comportamiento similar al de los cables; el mecanismo de salto juega un papel crítico.
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