Mechanistic Origin of the Vibrational Coherence Accompanying the Photoreaction of Biomimetic Molecular Switches |
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Authors: | Dr. Julien Briand Dr. Stefania Fusi Dr. Riccardo Rossi Paccani Prof. Massimo Olivucci Prof. Stefan Haacke |
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Affiliation: | 1. Institut de Physique et Chimie des Matériaux de Strasbourg, IPCMS‐DON, CNRS—Université de Strasbourg, 23 rue du Loess, 67034 Strasbourg (France), Fax: (+33)?3‐88‐10‐7245;2. Dipartimento di Chimica, Università degli Studi di Siena via Aldo Moro 2, 53100 Siena (Italy);3. Chemistry Department, Bowling Green State University, Bowling Green, OH 43403 (USA) |
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Abstract: | The coherent photoisomerization of a chromophore in condensed phase is a rare process in which light energy is funneled into specific molecular vibrations during electronic relaxation from the excited to the ground state. In this work, we employed ultrafast spectroscopy and computational methods to investigate the molecular origin of the coherent motion accompanying the photoisomerization of indanylidene–pyrroline (IP) molecular switches. UV/Vis femtosecond transient absorption gave evidence for an excited‐ and ground‐state vibrational wave packet, which appears as a general feature of the IP compounds investigated. In close resemblance to the coherent photoisomerization of rhodopsin, the sudden onset of a far‐red‐detuned and rapidly blue‐shifting photoproduct signature indicated that the population arriving on the electronic ground state after nonadiabatic decay through the conical intersection (CI) is still very focused in the form of a vibrational wave packet. Semiclassical trajectories were employed to investigate the reaction mechanism. Their analysis showed that coupled double‐bond twisting and ring inversions, already populated during the excited‐state reactive motion, induced periodic changes in π‐conjugation that modulate the ground‐state absorption after the non‐adiabatic decay. This prediction further supports that the observed ground‐state oscillation results from the reactive motion, which is in line with a biomimetic, coherent photoisomerization scenario. The IP compounds thus appear as a model system to investigate the mechanism of mode‐selective photomechanical energy transduction. The presented mechanism opens new perspectives for energy transduction at the molecular level, with applications to the design of efficient molecular devices. |
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Keywords: | ab initio calculations conical intersections isomerization molecular dynamics time‐ resolved spectroscopy |
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