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Evidencia espectroscópica de que un cambio de espín acompaña la absorción de luz en los complejos polipirídicos de
Andrew B Maurer1, Gerald J Meyer1
1Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States.
Journal of the American Chemical Society
|March 29, 2020
Resumen
Usamos la espectroscopia Stark para estudiar los estados excitados iniciales de los complejos de metal-bipiridina. Los campos eléctricos revelaron distintas transiciones tripletas, incluso para complejos de hierro, impactando aplicaciones como OLED y catálisis.
Área de la Ciencia:
- La fotoquímica
- Espectroscopia
- Química inorgánica
Sus antecedentes:
- El estado excitado de Franck-Condon (FC) es el estado inicial después de la absorción de fotones visibles.
- Los complejos de metal-bipiridina como [M(bpy) 3]2+ son cruciales en varias aplicaciones.
- La comprensión de la dinámica de espín del estado FC es clave para optimizar los procesos fotofísicos.
Objetivo del estudio:
- Para investigar los estados excitados de FC de los complejos (M = Fe, Ru, Os) usando espectroscopias de absorción Stark y visibles.
- Para resolver y caracterizar las transiciones directas de transferencia de carga de metal a ligando (MLCT).
- Para determinar la influencia de los campos eléctricos en las propiedades del estado excitado.
Principales métodos:
- Espectroscopia Stark para sondear los efectos del campo eléctrico en las transiciones electrónicas.
- Espectroscopia de absorción visible para analizar las transiciones MLCT.
- Análisis Liptay de los espectros Stark para determinar los cambios en los momentos dipolo y las distancias de transferencia de carga.
Principales resultados:
- Las transiciones directas de triplet MLCT se resolvieron mal en el campo cero para los complejos de Fe y Ru, pero fueron evidentes para Os.
- En campos eléctricos fuertes (0,4-0,8 MV / cm), aparecieron transiciones bien resueltas para todos los complejos.
- Una característica de electroabsorción a 633 nm confirmó la población directa de un estado excitado de MLCT de alto espín en [Fe(bpy) 3 2+.
- Se observaron cambios significativos de momento dipolo inducidos por la luz (3-9 D), con distancias de transferencia de carga más cortas para las transiciones tripletas.
Conclusiones:
- El espín del estado excitado FC inicialmente poblado puede diferir del estado fundamental, incluso para metales de transición más ligeros.
- Este hallazgo tiene implicaciones para la conversión de energía hacia arriba, la sensibilización de tintes, la espintrónica, la catálisis fotorredóxica y los OLED.
- La espectroscopia Stark es una herramienta poderosa para resolver las transiciones de estado excitado ocultas.
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