Scanning tunneling microscopy of indolo[2,1-b]quinazolin-6,12-dione (tryptanthrin) on HOPG: Evidence of adsorption-induced stereoisomerization

Scanning tunneling microscopy was used to observe monolayers of indolo[2,1-b]quinazolin-6,12-dione (tryptanthrin) at the solution-graphite interface. The monolayers were formed via physisorption from a saturated solution in 1-phenyloctane. Sub-molecular resolution was achieved allowing elucidation of the primary electronic features of the molecule. The adsorbed molecules form rows that are differentiable via the apparent heights of portions of each molecule, from row to row. The variation between the rows is attributed to adsorption-induced stereoisomerization of individual molecules, with each row comprised of one stereoisomer.