Steroid-bridged thiophenes: Synthesis and self-organization at the solid/liquid interface

The synthesis of the oligothiophene 6a as well as the terminally mono- and diformylated oligothiophenes 6b and 6c, in which mono- and bithiophene unit s are bridged by androstene, is described. Starting from epiandrostane the thiophene units were linked in positions 3 and 17 by Grignard reaction. The synthesis was accomplished by introduction of formyl groups. The self-orga nization of compounds 6 on highly oriented pyrolytic graphite at the liquid /solid interface was studied by STM, Derivatives 6a,b,c spontaneously forme d ordered monolayers on graphite, although neither are they planar nor do t hey have alkyl chains. Due to their different energy gaps in all cases the thiophene units were imaged as bright areas and the steroid unit as a dark area representing a novel type of surface structuring. While 6a and 66 are loosely packed, resulting in an area per molecule of 3 nm(2), the dialdehyd e 6c self-assembles to form a closely packed monolayer (area per molecule 2 nm(2)) obviously owing to interactions between the formyl groups.