Polymorphic Self-Assemblies of 2,7-Bis(decyloxy)-9-fluorenone at the Solid/Gas Interface: Role of C–H···OC Hydrogen Bond
2017-01-25T00:00:00Z (GMT)
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The self-assembly
of 2,7-bis(decyloxy)-9-fluorenone on highly oriented pyrolytic graphite
is investigated at the solid/gas interface by scanning tunneling microscopy,
which allows us to determine the effect of its molecular structure
on the formation of monolayer morphology. By varying the solution
concentration in dichloromethane, seven types of supramolecular assemblies
can be obtained. The concentration-dependent structural polymorphism
is discussed in terms of thermodynamics. In particular, these different
patterns are identified to be bound with weak intermolecular C(sp2)–H···OC
hydrogen bonds. As discerned by its position in the fluorenone moiety,
the C(sp2)–H group with larger chemical shift value and stronger
acidity displays a higher priority when involving in the formation
of a C(sp2)–H···O hydrogen bond. Owing to the
high density of C(sp2)–H donors, various hydrogen-bonding
configurations arise, further leading to the occurrence of structural
polymorphism. Besides, intermolecular van der Waals interactions as
well as the dipole–dipole interactions act as the complementary
roles to stabilize the whole monolayer. The underlying mechanism is
further confirmed by the density functional theory calculations.
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