Dipolar Control of Monolayer Morphology on Graphite: Self-Assembly of Anthracenes with Odd Length Diether Side Chains

The monolayers self-assembled at the solution-graphite interface by 18 1,5-bis(2,X-dioxaalkyl) anthracene derivatives bearing odd length side chains are studied using scanning tunneling microscopy and molecular mechanics (MM) simulations. 1-D molecular tapes are the key and common building block of the many morphologies self-assembled by these compounds. The dominant monolayer morphology and the extent of monolayer polymorphism depend critically on the position of the X-ether group and side chain length. MM simulations of the compounds' different morphologies are useful tools with which to dissect, explain, and predict morphological variation and polymorphism as a function of side chain structure. The simulations reveal that the dependence on X-ether group position arises from dipolar repulsions between ether groups in adjacent tapes, dipolar attractions between ether and anthracene C-H groups in adjacent tapes, and geometric distortions of the side chains.