Atom-Specific Identification of Adsorbed Chiral Molecules by Photoemission

Abstract

The study of chiral adsorbed molecules is important for an analysis of enantioselectivity in heterogeneous catalysis. Here we show that such molecules can be identified through circular dichroism in corelevel photoemission arising from the chiral carbon atoms in stereoisomers of 2,3-butanediol molecules adsorbed on Si(100), using circularly polarized x rays. The asymmetry in the carbon 1s intensity excited by right and left circularly polarized light is readily observed, and changes sign with the helicity of the radiation or handedness of the enantiomers; it is absent in the achiral form of the molecule. This observation demonstrates the possibility of determining molecular chirality in the adsorbed phase.

Circular dichroism in molecular frame photoemission

“…Furthermore, although the origin of circular dichroism is different, it would be interesting to explore the circular dichroism for simple chiral systems in the recoil frame of the fragmenting molecule [50], that will differ from the molecular frame for non-linear molecules in general. The relative importance of the PECD induced by the intrinsic chirality of the system, and that of the CDAD due to the spatial geometry discussed here, has been investigated recently for core level PI of chiral molecules adsorbed on surfaces [51,52]. Such investigations would be very interesting to perform for valence-shell PI of simple chiral molecules in the gas phase.…”

A Stable Room‐Temperature Molecular Assembly of Zwitterionic Organic Dipoles Guided by a Si(111)‐7×7 Template Effect

“…Most previous studies regarding chiral structures have been concerned with metal surfaces, [12] and relatively little work has been reported for semiconductor surfaces. [13] However, the chirality induced in these previous studies on semiconductors is due to the formation of at least one stereogenic center after the chemisorption, for example by cycloaddition, of molecules on silicon or germanium atoms. The results reported here show, to the best of our knowledge, the first example of chiral assembly of achiral molecules on Si(111)-7 7.…”

Transfer of chirality from adsorbed chiral molecules to the substrate highlighted by circular dichroism in angle-resolved valence photoelectron spectroscopy

“…34 The average magnitude of A CDAD parameters founded for alaninol adsorbed on Cu(100) is higher than those measured for free alaninol 34 and for molecules adsorbed on surface in the cases of alanine on Cu(110) and 2,3-butanediol on Si(100) for C 1s core level. [20][21][22] We studied the effect of the angular dependence on the dichroic parameters in the scattering plane defined by the [011] surface direction and the surface normal (see inset of Figure 1a).…”

“…[17][18][19] Few published papers used CDAD to investigate the chiral character of the electronic states of 2D molecular chiral systems and they focused on the study of the core level photoelectrons from chiral surfaces, obtained by the adsorption of small chiral molecules (alanine on Cu(110) and 2,3-butanediol on Si(100)). [20][21][22] In this way they succeed to correlate the dichroism of core level photoelectron peaks to the position of the chiral centers in the molecular net of the carbon atoms.…”