Nanoscale tripodal 1,3,5,7-tetrasubstituted adamantanes for AFM applications.

The synthesis of four novel nanoscale 1,3,5,7-tetrasubstituted adamantanes 22 and 25-27 designed for atomic force microscopy (AFM) applications is described. Each tetrahedrally shaped molecule incorporates a broad tripodal base made up of three identical legs that terminate with a sulfur-containing moiety, which is either a 4-acetylsulfanylmethylphenyl unit or else a (1,2,5-dithiazepan-1-yl)phenyl unit. The sulfur atoms are intended for eventual binding of the molecule multivalently to the apex of a gold-coated commercial AFM tip through formation of multiple S-Au bonds. In each molecule, the fourth terminus is a para-substituted benzoic acid methyl ester that is designed to scan the sample. We demonstrate that 27 is sufficiently large and rigid to be imaged by a conventional AFM tip. Adamantanes 22 and 25-27 may also find application as chemically well-defined nanoscale objects for calibration of AFM tips.