1 research outputs found
Competing Intermolecular and Molecule鈥揝urface Interactions: Dipole鈥揇ipole-Driven Patterns in Mixed Carborane Self-Assembled Monolayers
Carboranedithiol
isomers adsorbing with opposite orientations of
their dipoles on surfaces are self-assembled together to form mixed
monolayers where both lateral dipole鈥揹ipole and lateral thiol鈥搕hiolate
(S鈥揌路路路S) interactions provide enhanced stability
over single-component monolayers. We demonstrate the first instance
of the ability to map individual isomers in a mixed monolayer using
the model system carboranedithiols on Au{111}. The addition of methyl
groups to one isomer provides both an enhanced dipole moment and extra
apparent height for differentiation via scanning tunneling microscopy
(STM). Associated computational investigations rationalize favorable
interactions of mixed pairs and the associated stability changes that
arise from these interactions. Both STM images and Monte Carlo simulations
yield similarly structured mixed monolayers, where approximately 10%
of the molecules have reversed dipole moment orientations but no direct
chemical attachment to the surface, leading to homogeneous monolayers
with no apparent phase separation. Deprotonating the thiols by depositing
the molecules under basic conditions eliminates the lateral S鈥揌路路路S
interactions while accentuating the dipole鈥揹ipole forces. The
molecular system investigated is composed of isomeric molecules with
opposite orientations of dipoles and identical surface packing, which
enables the mapping of individual molecules within the mixed monolayers
and enables analyses of the contributions of the relatively weak lateral
interactions to the overall stability of the assemblies