Amplification of Conformational Effects via tert-Butyl Groups: Hexa-tert-butyl Decacyclene on Cu(100) at Room Temperature

The design of molecular systems as functional elements for use in next-generation electronic sensors and devices often relies on the addition of functional groups acting as spacers to modify adsorbate–substrate interactions. Although advantageous in many regards, these spacer groups have the secondary effect of amplifying internal conformational effects of the parent molecule. Here we investigate one such molecule2,5,8,11,14,17-hexa-tert-butyl-decacyclene (HBDC, C60H66)deposited on Cu(100) at monolayer and submonolayer coverages using an ultra-high vacuum (UHV) scanning tunneling microscope (STM). By combining submolecular resolution imaging with computational methods, we describe a variety of properties related to the effects of adding tert-butyl spacers to a decacyclene core, including the molecular conformation, structure, and chiral separation of the molecular adlayer, strong intermolecular interactions, and a metastable pinned conformation of the molecule brought on by deformation under high-bias conditions that enable an examination of its diffusive 2D molecular gas at room temperature. Collectively, these observations provide direct insight into the effect of adding spacers to a flexible molecular core such as decacyclene as relates to both intermolecular and adsorbate–substrate interfaces.