Using solid-state 15N
NMR spectroscopy, the cis/trans isomerization
in a two-dimensional
(2-D) array of surface-mounted azobenzene-based switches was detected
for the first time. In order to achieve this, a new class of rod-shaped
molecular switches, suitable for formation of 2-D regular arrays on
large facets of tris(o-phenylenedioxy)cyclotriphosphazene
(TPP) nanocrystals, was synthesized. A mechanochemical approach was
used to prepare corresponding host–guest surface inclusions
in a TPP matrix. Comparison of thermal steps in solution and supramolecular
surface inclusions revealed that switching of individual molecules
is not compromised by the close proximity of neighbors.
Mechanochemical synthesis represents a new path towards unique types of cucurbit[n]uril/guest inclusion complexes that are not accessible due to limited solubility of the individual components.
Herein we introduce fully modular synthesis leading to three representative examples of rigid molecular rods that are intended to form sturdy monolayers on various surfaces. These molecules contain two triptycene units that are designed to interlock into a compact “double‐decker” structure. Two of the three final products provided suitable crystals for X‐ray diffraction (analyzed on synchrotron), allowing deeper insight into packing in the 3‐D crystal lattice. The acidity of all three compounds were determined by capillary electrophoresis, and the pKa values ranged between 2.06‐2.53. All three rigid rods easily formed Langmuir‐Blodgett monolayers (LBMs) on the water‐air interfaces, with the area per molecule equal to 55–59 Å2/molecule, suggesting tight intermolecular packing. The thickness of all three films reached ∼19 Å after transfer to a gold (111) surface, meaning that individual molecules are tilted maximally 38° from the axis perpendicular to the surface. The structure of one of these films on a gold (111) surface was visualized by AFM. These geometrically unique molecules represent promising platforms with a wide scope of applicability in the supramolecular architecture.
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