The formation of two-dimensional supramolecular chiral lamellae by diamide molecules at the solution/graphite interface: A scanning tunneling microscopy study

We report on a scanning tunneling microscopy (STM) study of a self-assembled monolayer at the solution/graphite interface of long-chain molecules functionalized with two amide groups in the middle. The diamide molecules were synthesized by the condensation of acid chloride with the appropriate diamine. Our results have shown that the molecules organize side-by-side into well-ordered two-dimensional (2-D) lamellae through an interchain hydrogen-bonded network. The molecularly resolved STM images indicate that these supramolecular lamellae express chirality due to the constraints of the interchain hydrogen bonding, even though individual molecules are achiral. Supramolecular lamellae with opposite chirality are spontaneously separated into crystalline domains of respective handedness. The structure of these 2-D lamellae is different from the cutoff of their three-dimensional crystals. The stability of the monolayer is very sensitive to the balance of adsorbate/substrate and interchain interactions. The domain boundaries have shown interesting dynamic motion at different stages of the film growth.