Wavelength shifts in solid-state circular dichroism spectra: A possible explanation

We have devised an artificial sampling approach generating "absorption flattening" (AF) on the UV-Vis spectrum of a solution of a chiral compound: Tris (ethylendiamine)cobalt(III) chloride (A-Co(en)(3)Cl-3). We have observed a concomitant red shift of the CD maxima. Related CD and absorption spectra have been calculated from spectra recorded on diluted homogeneous solutions, thus monitoring the effect of AF on both types of data. Experimental data are in good agreement with calculated spectra. Simulations with suitable bandshapes show that the red shift of the CD spectrum is due to AF. On the basis of these results, we conclude that AF is an important cause of distortions in CD spectra for inhomogeneous samples. Plans to compensate or at least to take into account this effect are presented. (C) 2007 Wiley-Liss, Inc.