Seminars Archive

Ultrafast photochemistry of organic photo-switches: The central role of the conical intersection

Abstract
Recent studies of photo-isomerizing molecules, like the retinal protonated Schiff base, or derivatives thereof, in solution challenge the common picture according to which, the faster the photo-reaction, the larger its quantum efficiency: more isomerized species being formed [1]. We'll show two examples, photo-isomerization in the retinal protein ASR [2], and small molecular photoswitches [3] mimicking retinal where exactly the opposite behaviour is observed. These non-intuitive observations are due to the specific character of the conical intersection seam, a region of the electronic potential energy surfaces where ground and excited states are predicted to cross leading to a branching of the forward and backward reactive vibrational wavepackets [4]. While this region is spectroscopically inaccessible with VIS and near-IR laser pulses, non-linear spectroscopy with ultra-short soft X-ray pulses may enable new approaches.

[1] J. Briand, O. Braem, J. Rehault, J. Leonard, A. Cannizzo, M. Chergui, V. Zanirato, M. Olivucci, J. Helbing and S. Haacke, "Coherent ultrafast torsional motion and isomerization of a biomimetic dipolar photoswitch", Phys. Chem. Chem. Phys. 12, 3178-3187 (2010).
[2] R. M. Weiss and A. W. Warshel, "A New View of the Dynamics of Singlet Cis-Trans Photoisomerization ", J. Am. Chem. Soc., 101, 6131-6133 (1979).
[3] "100 fs photo-isomerization with vibrational coherences but low quantum yield in Anabaena Sensory Rhodopsin", A. Cheminal, J. Léonard, S. Y. Kim, K.-H. Jung, H. Kandori, and S. Haacke, PCCP (2015), 17, 25429 – 25439, DOI: 10.1039/c5cp04353k.
[4] D. Polli, O. Weingart, D. Brida, E. Poli, M. Maiuri, K. M. Spillane, A. Bottoni, P. Kukura, R. A. Mathies, G. Cerullo and M. Garavelli, "Wavepacket splitting and two-pathway deactivation in the photoexcited visual pigment isorhodopsin", Angew Chem Int Ed. 53, 2504-7 (2014).