A Lewis acid-mediated conformational switch.

Molecules that change conformation in response to a stimulus have numerous uses, such as artificial chemoreceptors, novel drug delivery strategies and liquid crystal technology. Here we describe the design, synthesis and conformational behaviour of an isonicotinamide-substituted diphenylacetylene upon recognition of Lewis acids, including metalloporphyrins. Binding of these at a remote site - the pyridyl nitrogen - increases hydrogen-bond donor ability of the proximal amide NH, causing an increased preference for the alkyne rotamer in which this hydrogen bond is maintained.