Credit: ©2008 ACS

The transmission of chirality in the solid state is still little understood. Non-flat, chiral materials have mainly been prepared in a racemic (or slightly enantiometrically biased) form, in which chirality was then incorporated through the use of templates or surfactants. In the case of organosilicates — in which siloxane units are bridged by organic linkers — templates are often used during the synthesis to create order and porosity, and so chirality has mostly been introduced by attaching chiral groups to siloxane units.

Cathleen Crudden and co-workers from Queen's University, Ontario, have now prepared1 a chiral organosilicate material by polymerization of a silicon-containing biphenyl monomer with a chiral dopant. The dopant prepared was based on a biaryl segment with substituents added in strategic positions to prevent racemization. A two-dimensional, porous organosilicate material that retained the chirality of the dopant was obtained on co-condensation, without the need for any inorganic silica source.

Characterization revealed that the main peak in the UV spectrum of the organosilicate was red-shifted compared with those of the monomers. Modifying the synthesis conditions enabled the researchers to attribute this shift to monomer–dopant interactions, suggesting the formation of new chiral aggregates within the material. This was further supported by theoretical calculations using dimers as models. Crudden and colleagues are hoping to exploit such materials for catalysis and separation purposes.