Stability and flexibility of self-assembled monolayers of thiols consisting of a horizontal large pi-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. (Some figures in this article are in colour only in the electronic version)