Self-Assembled Monolayers of Gemini-Type Amphiphilic Hexabenzocoronenes on Gold : Contribution of Their Triethylene Glycol Side Chains to Self-Assembly Formation

We report two-dimensional (2D) self-assembled structures of amphiphilic hexabenzocoronene (HBC) derivatives bearing hydrophilic oligo(ethylene glycol) (EG) side chains. Two molecules were studied : HBCGemini, with dodecyl and triethylene glycol (TEG) chains on opposite sides of the HBC core, and HBCTNFGemini, which includes a trinitrofluorenone (TNF) unit at the end of one TEG chain. Scanning tunneling microscopy (STM) revealed distinct 2D structures for both molecules on gold substrates under vacuum. HBCGemini exhibited two patterns - rectangular and square like arrangements - formed through interactions among phenyl groups, TEG chains, and alkyl chains. HBCTNFGemini showed three ordered structures, attributed to dimeric cores formed by interdigitated TEG chains. The flexible EG units adapt to the HBC core and contribute significantly to the self-assembly process through electrostatic and van der Waals interactions.