LABORATOIRE D’OPTIQUE ET BIOSCIENCES Unité INSERM U1182 - UMR CNRS 7645 - Ecole Polytechnique Ecole Polytechnique, 91128 Palaiseau cedex

Attention jour inhabituel

Lundi 7 décembre 2015 à 11h

Ecole Polytechnique Amphithéâtre Monge

Andreas STEINBACHER

Instut für Physikalische und Theoretische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany

Accumulative and Circular of Chiral

Steady-state circular dichroism (CD) or optical activity (OA) are common techniques to analyze chiral samples. However, the utilized long optical path lengths, high concentrations, and long integration times are not suitable for ultrafast spectroscopy. Hence, only few -sensitive spectroscopic approaches in the liquid phase are known in the literature [1]. In this presentation we introduce our recently developed for CD and OA detection. In the case of OA probing, a sensitive polarimeter was developed via the combination of common-path optical heterodyne interferometry and accumulative femtosecond spectroscopy [2]. With this setup it is possible to detect the change accompanying a chirality-modifying photochemical reaction with femtosecond time resolution [2]. Furthermore, one can achieve all-optical discrimination between racemic and achiral molecular solutions [3]. The second chirality-sensitive detection method we have developed is based on the detection of photoinduced changes of CD signals. Due to the small changes in CD which must be detected, this type of spectroscopy is prone to artifacts. Hence, typically only single- detection is employed [1]. Here, we present broadband time-resolved CD spectroscopy which is based on a setup capable of mirroring an arbitrary state of an ultrashort laser pulse. Hence, by passing a broadband probe pulse through this setup we can switch betweenopposite handedness on a shot-to-shot basis to detect pump-induced CD changes. To demonstrate the capabilities of this approach we investigated the early photochemistry of . By virtue of the flexibility of the setup not only ultrafast pump—probe CD experiments are possible but also ellipsometry or anisotropy spectroscopy can be performed.

References: [1] J. Meyer-Ilse, D. Akimov, and B. Dietzek, Laser Photon. Rev. 7, 495 (2013). [2] A. Steinbacher, J. Buback, P. Nuernberger, and T. Brixner, Opt. Express 20, 11838 (2012). [3] A. Steinbacher, P. Nuernberger, and T. Brixner, Phys. Chem. Chem. Phys. 17, 6340 (2015).

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