Shedding new light on the role of the Rydberg state in the photochemistry of aniline.

Roman Spesyvtsev, Oliver M Kirkby, Morgane Vacher, Helen H Fielding

Department of Chemistry, University College London, 20 Gordon Street, London, UK WC1H 0AJ.

Physical chemistry chemical physics : PCCP 2012 Jul 28

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Efficient electronic relaxation following the absorption of ultraviolet light is crucial for the photostability of biological chromophores, so understanding the microscopic details of the decay pathways is of considerable interest. Here, we employ femtosecond time-resolved photoelectron imaging to investigate the ultrafast intramolecular dynamics of aniline, a prototypical aromatic amine, following excitation just below the second absorption maximum. We find that both the second ππ* state and the Rydberg state are populated during the excitation process. Surprisingly, the dominant non-radiative decay pathway is an ultrafast relaxation mechanism that transfers population straight back to the electronic ground-state. The vibrational energy resolution and photoelectron angular distributions obtained in our experiments reveal an interesting bifurcation of the Rydberg population to two non-radiative decay channels. The existence of these competing non-radiative relaxation channels in aniline illustrates how its photostability arises from a subtle balance between dynamics on different electronically excited states and importantly between Rydberg and valence states.

Citation

Roman Spesyvtsev, Oliver M Kirkby, Morgane Vacher, Helen H Fielding. Shedding new light on the role of the Rydberg state in the photochemistry of aniline. Physical chemistry chemical physics : PCCP. 2012 Jul 28;14(28):9942-7