Stability and flexibility of self-assembled monolayers of thiols consisting of a horizontal large π-system and a vertical spacer

Self-assembled monolayers (SAMs) of (4-mercaptophenyl) (10-nitro-9-anthryl) acetylene (MPNAA) on Au(111) are studied with scanning tunneling microscopy (STM). Through careful analysis of the bias-dependent sub-molecular features observed in the high-resolution STM images, important structural details of the MPNAA SAM are disclosed, in addition to its structural character common for the anthracene-based thiol SAMs studied in a recent paper (Dou et al 2006 Langmuir 22 3049). With these experimental results, a new model is proposed for the SAM structure to explain, particularly, the molecule-substrate, molecule-molecule and intramolecular interactions, as well as their competitions and compromises in the formation of the SAM structure. Flexibilities and application potentials of the SAMs of thiols based on a long π-system (like that of anthracene or even pentacene) arranged horizontally and a vertical spacer (like the phenyl-acetylene group) are also discussed.