Electronic Spectroscopy with Polarized light on Aligned Samples: Synchrotron Linear Dichroism Measurements

Spanget-Larsen, J. (Participant)

    Activity: OtherOther (prizes, external teaching and other activities) - Period visiting other institutions

    Description

    The purpose of this project is measurement of Linear Dichroism (LD) electronic spectra of oriented molecular samples. In Roskilde, partially aligned samples are prepared by using uniaxially stretched polymers as anisotropic solvents; most reasonably rigid molecules are efficiently aligned when imbedded in a stretched polymer matrix (e.g., polyethylene (PE) or polyvinylalcohol (PVA)). In the present project, the main target species are aromatic hydrocarbons, heterocyclics, and other compounds, including dyes and biologically interesting systems. The first series of regular experiments at ASTRID within this project took place in January 2005. The measurements were continued in August 2005, considering in particular a series of intramolecularly H-bonded hydroxyanthraquinones. The results were highly encouraging. Several obvious advantages were observed, relative to standard optical spectrophotometry. Most importantly, a significantly higher signal-to-noise ratio was obtained at ASTRID, a circumstance of vital importance to the project, since it is frequently difficult to prepare polymer samples with sufficient optical density for traditional spectrophotometry (f.inst., polar molecules have a low solubility in non-polar polyethylene). In addition, the wavelength region could be extended towards lower wavelengths (below 210 nm), enabling the observation of high-energy electronic states, many of which have sofar not been assigned. It is the aim of the project to extend the investigation to a range of systems, including compounds with very strong intramolecular H-bonding, e.g., dibenzoylmethane enol and benzoylacetone enol, as well as “simpler” species such as diphenylmethane, diphenylether, and diphenylamine. The latter series of compounds have characteristic transitions below 210 nm which cannot easily be investigated with traditional spectrophotometry.

    Institute for Storage Ring Facilities (ISA) University of Aarhus Ny Munkegade, bygn. 520 DK-8000 Århus C Denmark
    Period19 Apr 2006 - 21 Apr 2006