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Accumulative Polarimetry and Circular Dichroism Spectroscopy of Chiral Femtochemistry

le 13 mai 2016 à 11 h
Andreas Steinbacher, Institute for Physical and Theoretical Chemistry, University of Würzburg, Germany

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 chirality-sensitive spectroscopic approaches in the liquid phase are known in the literature [1]. In this presentation we introduce our recently developed spectrometers 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 optical rotation 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-wavelength detection is employed [1]. Here, we present broadband time-resolved CD spectroscopy which is based on a setup capable of mirroring an arbitrary polarization state of an ultrashort laser pulse. Hence, by passing a broadband probe pulse through this setup we can switch between opposite 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 hemoglobin. 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).
 


Lieu(x) :         Amphithéatre Monge, Ecole Polytechnique


Contact :       François Hache
                      francois.hache at polytechnique.edu


À télécharger :       Séminaire STEINBACHER.pdf - PDF